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  • Other Sources  (271)
  • AMS (American Meteorological Society)  (160)
  • GFZ, Helmholtz-Zentrum  (111)
  • 2010-2014  (176)
  • 2000-2004  (82)
  • 1985-1989  (13)
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  • 101
    Publication Date: 2021-03-29
    Description: report
    Keywords: 551
    Language: German
    Type: article , publishedVersion
    Format: 54 S.
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  • 102
    Publication Date: 2021-03-29
    Description: report
    Keywords: 551 ; TVI 000 ; Jahreszeiten als meteorologische Erscheinung
    Language: English
    Type: article , publishedVersion
    Format: 16 S.
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  • 103
    Publication Date: 2021-03-29
    Description: report
    Keywords: 551 ; TVI 000 ; TM 600 ; Jahreszeiten als meteorologische Erscheinung ; Grenzgebiete. Beziehungen. Einflüsse. Wirkungen {Geophysik}
    Language: English
    Type: article , publishedVersion
    Format: 17 S.
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  • 104
    Publication Date: 2021-03-29
    Description: report
    Keywords: 551 ; TOB 100 ; Drehbewegungen {Geophysik: Erde}
    Language: English
    Type: article , publishedVersion
    Format: 43 S.
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  • 105
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    GFZ, Helmholtz-Zentrum | [Bibliothek des Wiss.-Parks Albert Einstein] [Vertrieb], [Potsdam]
    Publication Date: 2021-03-29
    Description: thesis
    Keywords: 551 ; VBJ 000 ; Satellitenbildgeologie
    Language: German
    Type: monograph , publishedVersion
    Format: 113 S.
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  • 106
    Publication Date: 2021-03-29
    Description: thesis
    Keywords: 551 ; VBN 500 ; VAE 811 ; VEB 168 ; VEX 100 ; VEX 500 ; TSX 500 ; TSB 168 ; VKB 270 ; VAE 880 ; Geochronologie einzelner Regionen im allgemeinen ; Alpidische Orogene {Geologie} ; Schweizer Alpen {Geologie} ; Anden {Geologie} ; Chile {Geologie} ; Chile {Geophysik} ; Schweizer Alpen {Geophysik} ; Produkte mechanischer Deformation {Petrologie} ; Passive und aktive Kontinentalränder {Geologie}
    Language: English
    Type: monograph , publishedVersion
    Format: 179 S.
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  • 107
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    GFZ, Helmholtz-Zentrum | [Bibliothek des Wiss.-Parks Albert Einstein] [Vertrieb], [Potsdam]
    Publication Date: 2021-03-29
    Description: report
    Keywords: 551
    Language: German
    Type: article , publishedVersion
    Format: 43 S.
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  • 108
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    GFZ, Helmholtz-Zentrum | [Bibliothek des Wissenschaftsparks Albert Einstein] [Vertrieb], [Potsdam]
    Publication Date: 2021-03-29
    Description: thesis
    Keywords: 551 ; TOD 200 ; TOD 410 ; TSB 000 ; VAE 812 ; VEB 130 ; TOH 100 ; Erdkruste {Geophysik} ; Oberer Erdmantel {Geophysik} ; Mitteleuropa {Geophysik} ; Variszisch-herzynische Orogene {Geologie} ; Böhmische Masse {Geologie} ; Seismometrie {Geophysik}
    Language: English
    Type: monograph , publishedVersion
    Format: 149 S.
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  • 109
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    GFZ, Helmholtz-Zentrum | [Bibliothek des Wissenschaftsparks Albert Einstein] [Vertrieb], [Potsdam]
    Publication Date: 2021-03-29
    Description: report
    Keywords: 551
    Language: English
    Type: article , publishedVersion
    Format: 12 S.
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  • 110
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    GFZ, Helmholtz-Zentrum | [Bibliothek des Wissenschaftsparks Albert Einstein] [Vertrieb], [Potsdam]
    Publication Date: 2021-03-29
    Description: thesis
    Keywords: 551 ; VAE 500 ; VBB 000 ; VAJ 400 ; Geotektonische Entwicklung der Erdkruste {Geologie} ; Experimentelle Geologie ; Abtragung durch Erosion {Geologie}
    Language: English
    Type: monograph , publishedVersion
    Format: 141 S.
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  • 111
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    GFZ, Helmholtz-Zentrum | [Bibliothek des Wissenschaftsparks Albert Einstein] [Vertrieb], [Potsdam]
    Publication Date: 2021-03-29
    Description: report
    Keywords: 551 ; VBT 000 ; Wirtschaftsgeologie
    Language: German
    Type: anthology , publishedVersion
    Format: 77 S.
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  • 112
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    GFZ, Helmholtz-Zentrum | [Bibliothek des Wissenschaftsparks Albert Einstein], Potsdam
    Publication Date: 2021-03-29
    Description: report
    Keywords: 551 ; TOH 530 ; TST 000 ; VET 600 ; Häufigkeit und Verbreitung von Erdbeben {Geophysik} ; Ozeanien {Geophysik} ; Sonstige Inselgruppen {Geologie}
    Language: English
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  • 113
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    GFZ, Helmholtz-Zentrum
    Publication Date: 2021-03-29
    Description: thesis
    Keywords: 551 ; TOG 000 ; VAE 300 ; Isostasie {Geophysik} ; Epirogenese {{Geologie}}
    Language: German
    Type: monograph , publishedVersion
    Format: 221 S.
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  • 114
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    GFZ, Helmholtz-Zentrum | [Bibliothek des Wissenschaftsparks Albert Einstein] [Vertrieb], [Potsdam]
    Publication Date: 2021-03-29
    Description: thesis
    Keywords: 511.8 ; 551 ; TOO 000 ; VAQ 400 ; Geothermik {Geophysik} ; Morphologie, Ausmaß und Dicke, Masse und Energiegleichgewicht {Glaziologie}
    Language: English
    Type: monograph , publishedVersion
    Format: 106 S.
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  • 115
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    GFZ, Helmholtz-Zentrum | [Bibliothek des Wissenschaftsparks Albert Einstein] [Vertrieb], Potsdam
    Publication Date: 2021-03-29
    Description: report
    Keywords: 511.8 ; 551
    Language: English
    Type: article , publishedVersion
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  • 116
    Publication Date: 2021-03-29
    Description: The main objective of this thesis is an investigation and description of the secular variation of the Earth's magnetic field between 1980 and 2000. In particular, in the first part of this study the phenomenon of geomagnetic jerks are investigated by means of a deterministic model, which basically gives a description of the secular variation as a parameterization of typical periodicities of the external field. I argue that the conclusion drawn from this approach is not valid for explaining jerks as caused by external events and not valid to describe the global secular variation. In the second part a time--dependent model of the secular variation between 1980 and 2000 is developed. The endpoints of the time interval were chosen, because of the availability of high quality field models from satellite data for these epochs. The Gauss coefficients are expanded in time as function of cubic B--splines. This model is forced to fit field models from high quality vector measurements from MAGSAT in 1980 and OERSTED in 2000. The methodology is new. The model is a valuable extension of the hitherto existing time--dependent description of the secular variation, the GUFM which was valid until 1990. Unlike GUFM the model is based on observatory monthly means, and the knot spacing of the cubic B--Splines tighter than GUFM. Therefore it reveals a short term secular variation on subdecadal time scale, which was not as yet resolved. The model is also valuable to test the frozen flux hypothesis and to link some of the morphology of the radial field at the core--mantle boundary to the geodynamo. The third part of this thesis deals with the inversion of the time--dependent field and secular variation model for different kinds of core surface flow ...
    Description: thesis
    Keywords: 551 ; TOT 500 ; TOD 500 ; Ursprung und säkulare Änderungen des Erdmagnetfeldes {Geophysik} ; Erdkern {Geophysik}
    Language: English
    Type: monograph , publishedVersion
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  • 117
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    GFZ, Helmholtz-Zentrum
    Publication Date: 2021-03-29
    Description: The Erongo complex is the largest of the Cretaceous igneous complexes in the Damaraland, Southern Etendeka Province, Namibia. Erongo is made up of a series of mainly silicic volcanic and intrusive units, like many of the Damaraland complexes, but it is unique by virtue of its size and well-preserved igneous sequence silicic magmas as well as tholeiitic and alkaline basalts.The goals of this study were to determine the ages and petrogenetic relationships of the silicic and basic units in the Erongo complex, and to contribute to understanding the magmatic evolution of the Damaraland province. As part of this investigation, Os isotope compositions were determined on basic rocks from the complex, and this is the first study of Os isotopes in the Etendeka Province. The Erongo is built up on a sequence of tholeiitic basaltic lavas which are compositionally equivalent to the Southern Etendeka flood basalts (Tafelberg type) and probably represent erosional remnants of these (see below). The felsic volcanic units at Erongo include two types of rhyodacites and one rhyolite. The most voluminous of these is the Ombu rhyodacite, which has a thickness of up to 500 m and makes up most of the topographic expression of the complex. The Ombu rhyodacite rests directly on the basal tholeiites in the southern and eastern part of the complex, but to the north and west, a second rhyodacite occurs below it, the Erongorus rhyodacite ...
    Description: thesis
    Keywords: 551 ; VBN 500 ; VER 300 ; VAC 000 ; VKB 111 ; VKB 124 ; VBO 000 ; VJJ 000 ; Geochronologie einzelner Regionen im allgemeinen ; Botswana {Geologie} ; Magmatismus {Geologie} ; Granitische Gesteine {Petrologie} ; Basaltische Vulkanite {Petrologie} ; Isotopengeologie ; Spezielle Geochemie
    Language: German
    Type: monograph , publishedVersion
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  • 118
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    GFZ, Helmholtz-Zentrum
    Publication Date: 2021-03-29
    Description: report
    Keywords: 551 ; TM 300 ; Methodik. Arbeitsmittel. Abkürzungsverzeichnisse {Geophysik}
    Language: English
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  • 119
    Publication Date: 2021-03-29
    Description: report
    Keywords: 551 ; TOB 000 ; TOT 500 ; Periodische Bewegungen der Erde {Geophysik} ; Ursprung und säkulare Änderungen des Erdmagnetfeldes {Geophysik}
    Language: English
    Type: article , publishedVersion
    Format: 41 S.
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  • 120
    Publication Date: 2021-03-29
    Description: For deep underground excavations, the prediction of locations of small-scale geotechnical hazardous structures such as faults is nearly impossible when exploration is restricted to surface based methods. Therefore, for many base tunnels, exploration ahead of the advancing tunnel face is an essential component of the excavation plan. This PhD thesis aims at improving the technology for geological interpretations of seismic data, collected in underground excavations. For that purpose GeoForschungsZentrum Potsdam carried out a series of seismic measurements along the 2600 m long and up to 1400 m deep Faido access tunnel, an adit to the 57 km long Gotthard base tunnel in Switzerland.
    Description: thesis
    Keywords: 551 ; TQC 500 ; VBP 400 ; VBP 100 ; Untertageseismik {Geophysik} ; Felsmechanik, Gebirgsmechanik, Gebirgsdruck ; Methodik, Untersuchungsverfahren und Instrumente {Ingenieurgeologie}
    Language: English
    Type: monograph , publishedVersion
    Format: 127 S.
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  • 121
    Publication Date: 2021-03-29
    Description: Present-day sea-level change around Greenland is examined by assessing the roleplayed by glacial-isostatic adjustment (GIA). We consider the contributions from: (1) the ongoing GIA due to changes in the extent and thickness of the Greenland Ice Sheet (GIS) following the Last Glacial Maximum (LGM), (2) the equivalent signal associated with the continental ice masses located outside of Greenland, and (3) present-day changes in the GIS. Changes in the GIS arising from the last glacial-interglacial transition generally result in falling sea level today. The contribution from ice-load changes outside of Greenland causes rising sea level, owing to Greenland's location on the collapsing forebulge that surrounds the former North American ice sheets. Combining predictions of these contributions gives results showing rising sea level in the southwest and falling sea level in the north and east. However, this is strongly dependent upon the neoglacial part of the GIS's history. The present-day behaviour of the GIS is predicted to cause falling sea level with rates of several mm yr?1 around areas experiencing the larger ice-load changes. The available tide-gauge data are considered unusable by the standards of many workers. Nevertheless, we compare rates of local sea-level change inferred from this type of data with our predictions. In Southern Greenland, where the tide-gauge stations are located, sea level is predicted to be rising at a rate of 4 to 5 mm yr?1. Our predictions match most of the rates obtained from the tide-gauge time series, with the exception of Qaqortoq where the inferred rates may also reect additional oceanic and meteorological effects. Similarly, our predictions are consistent with GPS observations, with again the exception of Qaqortoq.
    Description: report
    Keywords: 551 ; TOG 000 ; VSY 000 ; Isostasie {Geophysik} ; Polargebiete {Fossile Energieträger}
    Language: English
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  • 122
    Publication Date: 2021-03-29
    Description: Der vorliegende Report fasst die wissenschaftlichen und technischen Arbeiten zur Steigerung der Produktivität von Thermalwasser in der Geothermie-Forschungsbohrung Groß Schönebeck 3/90 zusammen, die von 2002 bis 2004 durchgeführt wurden. Das Ziel des Projektes ist die Erschließung von heißen Wässern in tiefen Speichergesteinen, die sich zur Erzeugung von elektrischem Strom eignen. Dies erfordert die Bereitstellung einer kontinuierlichen Förderung heißer Tiefenwässer mit Temperaturen 〉 150 ʿC und Fließraten 〉 50 mđ/h. In Tiefen mit Mindesttemperaturen um 150 ʿC ist die natürliche Permeabilität (Durchlässigkeit) der Gesteine jedoch nicht ausreichend. Die Gesteine müssen stimuliert werden, d. h. zu vorhandenen Rissen werden zusätzliche künstlich erzeugt, damit das Wasser ungehindert zirkulieren kann. Bereits vorliegende Erkenntnisse zur Erschließung und Charakterisierung der in weiten Regionen des Norddeutschen Sedimentbeckens in Tiefen von etwa 4000 bis 5000 Metern verbreiteten Speichertypen basieren größtenteils auf Erfahrungen der Erdöl- und Erdgasindustrie. Für die geothermische Nutzung sind diese jedoch nur eingeschränkt anwendbar, da bei der Erschließung von Kohlenwasserstoffen schon kleine Fließraten genügen. Daher liegt der Schlüssel zum Durchbruch der Geothermie in der Entwicklung effektiver Stimulationstechniken zur gezielten Produktivitätssteigerung geothermischer Reservoire. Die Geothermiebohrung Groß Schönebeck schließt geothermisch relevante Horizonte des Norddeutschen Beckens zwischen 3900 m und 4300 m in einem Temperaturniveau von etwa 150 ʿC auf. Diese Bohrung bietet derzeit die einzigartige Möglichkeit, die geothermische Nutzbarkeit unterschiedlicher Gesteinsformationen des Rotliegenden vertiefend zu untersuchen: die Vulkanite an der Basis und den darüber liegenden Sandstein. Experimente zur Erhöhung der Zuflussrate von heißen Wässern aus Sandsteinformationen durch hydraulische Stimulation konnten bereits erfolgreich durchgeführt werden (siehe Berichte zu den Projekten BEO 0327063 und ZIP 0327063C). Die erzielten Fließraten reichten jedoch für eine wirtschaftliche Elektrizitätserzeugung noch nicht aus ...
    Description: report
    Keywords: 551
    Language: German
    Type: anthology , publishedVersion
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  • 123
    Publication Date: 2021-03-29
    Description: We review the historical, geological, tide-gauge, GPS and gravimetric evidence advanced in favour of or against continuing land uplift around Hudson Bay, Canada. After this, we reanalyse the tide-gauge and GPS data for Churchill using longer time series than those available to previous investigators. The dependence of the mean rate of relative sea-level change obtained on the length and mid-epoch of the observation interval considered is investigated by means of the newly developed linear-trend analysis diagram. For studying the shorter-period variability of the tide-gauge record, the continuous-wavelet transform is used. The mean rate of land uplift obtained from GPS is based on a new analysis using IGS solutions of GFZ. Furthermore, sea-level indicators from the Churchill region representing the relative sea-level history during the past 8000 a are included. Finally, the four types of observable are jointly inverted in terms of mantle viscosity. The optimum values are 3×10^20 Pa s and 1.6 × 10^22 Pa s for the upper- and lower-mantle viscosities, respectively.
    Description: report
    Keywords: 551
    Language: English
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  • 124
    Publication Date: 2021-03-29
    Description: Recently released global gravity field models generated solely from CHAMP and GRACE satellite observations allow with an unprecedented accuracy and resolution the recovery of the mean sea surface topography from the difference between an altimetry-based mean sea surface height model and the gravity model's derived geoid. Here the CHAMP EIGEN-2 gravity field model, and the first GFZ GRACE gravity model, EIGEN-GRACE01S, are used. The mean sea surface height model has been compiled from four years'; worth of TOPEX altimeter data. To evaluate the accuracy and resolution limits of the CHAMP and GRACE geoids for the envisaged application, a low pass filter in the spatial domain with different cut-off wavelengths has been applied to the geoid and sea surface data before subtraction. The minimum wavelength, where noisy and erroneous features in the recovered sea surface topography are minimised, can be interpreted as an indicator for the best suited common spatial resolution. The EIGEN-2 model's geoid has been tested to have a resolution of 1800 km, which corresponds to a truncation degree of l = 22 in terms of spherical harmonics. Using the EIGEN-GRACE01S model, the resolution could be extended to 1000 km (l = 40). These boundaries can be attributed to the geoid's error, exceeding 2 cm in case of the CHAMP model, and in case of the GRACE model to spurious systematic signals increasing with increasing spherical harmonic degree. The calculated sea surface topography models have been used to derive absolute geostrophic sea surface velocities. An error propagation shows that the requirement of 1 cm/s for geoid induced velocity errors is fulfilled at the given resolutions for all latitudes excluding a narrow equatorial band. Maximum geostrophic velocities are derived in the 1000 km-resolution model for the Kuroshio region with 40 cm/s, and for the Gulf Stream east off Cape Hatteras with 25 cm/s.
    Description: report
    Keywords: 551 ; TQI 000 ; Geophysikalische Satellitenfernerkundung
    Language: English
    Type: article , publishedVersion
    Format: 22 S.
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  • 125
    Publication Date: 2021-03-29
    Description: Mit der vorliegenden Arbeit werden voneinander unabhängige Experimente zur Untersuchung der elektrischen Leitfähigkeit im Untergrund miteinander verknüpft, mit dem Ziel, das Potenzial der Methode Magnetotellurik für das Abbilden aktiver und fossiler tektonischer Systeme aufzuzeigen. Die Magnetotellurik hat sich in den letzten zehn bis fünfzehn Jahren zunehmend zu einem zuverlässigen und aussagekräftigen Tiefensondierungsverfahren entwickelt. Dieser positive Entwicklungsprozess wird auch durch meine Forschungsergebnisse dokumentiert, die in verschiedenen Projekten während meiner Zeit am GeoForschungsZentrum entstanden sind. Eine Übersicht über die verwendeten Arbeiten befindet sich in Tabelle 1.1. Große geophysikalische Feldexperimente, wie die hier beschriebenen Magnetotellurikprojekte, lassen sich nur im Team durchführen. Im akademischen Bereich bedeutet dies die Integration von Studenten und Doktoranden bei den Feldmessungen und der anschließenden Bearbeitung der Daten. Entsprechend gehen einige der in Tabelle 1.1 aufgeführten Arbeiten auf Diplomarbeiten oder Promotionsschriften zurück, die von mir mitbetreut wurden. Bei anschließender Veröffentlichung der Arbeiten habe ich als Co-Autor mitgewirkt. Die beiliegenden Veröffentlichungen enthalten eine Einführung in die Methode der Magnetotellurik und gegebenenfalls die Beschreibung neu entwickelter Methoden. Eine allgemeine Darstellung der theoretischen Grundlagen der Magnetotellurik findet man z.B. in (Kaufman & Keller, 1981; Nabighian, 1987; Weaver, 1994). Am Ende der Arbeit befindet sich ein Glossar, in dem einige Begriffe und Abkürzungen erklärt werden.
    Description: thesis
    Keywords: 551 ; TQD 000 ; VAE 120 ; Elektrische Verfahren {Geophysik} ; Methodik {Strukturgeologie}
    Language: German
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  • 126
    Publication Date: 2021-03-29
    Description: The objective of this research is the quantification of modal composition of magmatic rocks using infraredspectra and based on spectral analysis of individual minerals. For that purpose a new, model-based spectralunmixing method was developed. This method is based on thermal infrared reflection spectroscopy at a wave-lenght between 8 - 14 æm since silicates and magmatic rocks show their strongest spectral features(Reststrahlen bands) in this range of the electromagnetic spectrum. Rock samples from the precambrian igne-ous complex Mt. Timna in Southern Israel were analyzed. The samples include different granitoid rocks andone ultrabasic rock unit. This research was part of preparatory investigations to develop new approaches ofdata analysis for a new thermal hyperspectral sensor (ARES) which is scheduled for operation in 2005 by GFZand DLR. Before the modal composition of the magmatic rock samples was quantified, extensive spectral analysis wasperformed to identify and study the spectral behavior of silicates within their original rock context. The mostimportant rock-forming minerals were measured for the first time in thin sections using a microscope and bidi-rectional reflection spectroscopy methods in the thermal infrared. For quantitative mineral analysis a methodwas developed that calculates the correlation of automatically extracted spectral features and chemical com-position or solid solution of different minerals and selects the best suited results ...
    Description: thesis
    Keywords: 551 ; VJA 240 ; VJB 311 ; VKA 110 ; VKB 100 ; VEI 400 ; VGB 700 ; VBE 000 ; Spektroskopische Verfahren {Geochemie} ; Geochemie der Magmatite ; Gesteinsbestimmung ; Petrologie der Magmatite ; Israel, Palästina {Geologie} ; Spektroskopische Methoden {Mineralogie} ; Modellierung von Prozessen in der Geosphäre
    Language: German
    Type: monograph , publishedVersion
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  • 127
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    GFZ, Helmholtz-Zentrum
    Publication Date: 2021-03-29
    Description: report
    Keywords: 551 ; QFC 240 ; VBS 900 ; VEB 210 ; V 200 ; Hazards {Angewandte Geographie} ; Umweltgeologie einzelner Regionen ; Deutschland {Geologie} ; Wissenschaftsorganisation und -Pflege {Geologische Wissenschaften}
    Language: German
    Type: monograph , publishedVersion
    Format: 339 S.
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  • 128
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    GFZ, Helmholtz-Zentrum
    Publication Date: 2021-03-29
    Description: Obwohl der Wasserdampf eines der wichtigsten Treibhausgase ist, Energie durch die Atmosphäre transportiert, und das Strahlungsbudget durch Wolkenbildung beeinflusst, ist seine sehr variable zeitliche und räumliche Verteilung bis heute unzureichend erfasst, insbesondere unter Wolken und während Niederschlagsereignissen, wo seine Kenntnis am wichtigsten wäre. Die GPS-Technik bietet sich als wetterunabhängiges Verfahren an, diese Lücke zu schließen. Im Rahmen des Projektes sollte in Deutschland eine Infrastruktur (Empfängernetz, Kommunikation, Auswertesoftware) zur Nutzung der bodengebundenen und satellitengestützten GPS-Technik aufgebaut werden. Insbesondere sollte eine operationelle, flächendeckende Erfassung des atmosphärischen Wasserdampfes in einem dichten, deutschlandweiten Netz von GPS-Bodenstationen demonstriert werden, und der Einfluss dieser neuen Messwerte auf die Wettervorhersage und die Klimaforschung untersucht werden. Im zweiten Projektschwerpunkt sollte die innovative GPS-Radiookkultationstechnik, als Fernerkundungsmethode zur globalen Sondierung der Atmosphäre/Ionosphäre mit vielfältigen Anwendungen in der Wettervorhersage, Klima-, Atmosphären- und Ionosphärenforschung in Deutschland etabliert werden. Hierzu gehört die Installierung einer entsprechenden operationellen Infrastruktur für die Datenanalyse zur Bereitstellung der atmosphärischen Information in Near-Real-Time (Polarempfangsstation, globales unterstützendes GPS-Bodennetz ...
    Description: report
    Keywords: 551
    Language: German
    Type: article , publishedVersion
    Format: 52 S.
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  • 129
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    GFZ, Helmholtz-Zentrum
    Publication Date: 2021-03-29
    Description: report
    Keywords: 551 ; TOF 000 ; Schwerkraft {Geophysik}
    Language: English
    Type: article , publishedVersion
    Format: 17 S.
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  • 130
    Publication Date: 2021-03-29
    Description: report
    Keywords: 551
    Language: English
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  • 131
    Publication Date: 2021-03-29
    Description: Der glazio-isostatische Ausgleich in Island als Folge des Abschmelzens der größten europäischen Eiskappe, dem Vatnajökull, verursacht zeitliche Änderungen der Schwere und Landhebung. Nach Auswertung der Schweredaten zeigt sich ein charakteristisches Verhalten. Die Schwereänderungsrate beträgt ca. -4 mikroGal/a am Eisrand (50 km Entfernung vom Eiszentrum)und ca. 1 mikroGal/a in Höfn (75 km Entfernung vom Eiszentrum). In größeren Entfernungen vom Eiszentrum (150 bis 250 km) werden die Raten kleiner als 1 mikroGal/a und nähern sich schließlich Null. Vorwärtsmodellierung liefert eine Lithosphärenmächtigkeit von 10 bis 15 km. Die Asthenosphärenviskosität ist 3 x 1017 bis 1 x 1018 Pa s. Diese Werte bestätigen frühere Resultate aus GPS-, seismischen und theoretischen Untersuchungen. Eine deutlich bessere Anpassung an die Meßdaten ergibt sich für erhöhte Asthenosphäremächtigkeit (165 bis 170km). Vermutlich reflektiert dies die spezielle Lage Islands oberhalb eines Plumes.
    Description: report
    Keywords: 551
    Language: German
    Type: monograph , publishedVersion
    Format: 69 S.
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  • 132
    Publication Date: 2021-03-29
    Description: thesis
    Keywords: 551 ; VAE 820 ; TSB 000 ; Sedimentationsbecken als Erdkrustentypen {Geologie} ; Mitteleuropa {Geophysik}
    Language: German
    Type: monograph , publishedVersion
    Format: VI, 101 S.
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  • 133
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    GFZ, Helmholtz-Zentrum
    Publication Date: 2021-03-29
    Description: This report describes the set-up, logistics and results of the CHICAGO (Chilean Coastal AeroGeophysical Observations) survey. It gives a short overview about the scientific intentions, detailed documentation of all technical aspects starting from the survey equipment via the aircraft installation to the GPS stations set-up and the experiences in flight. All processing results for the individual profiles are discussed in detail. Finally, the data is compared and combined with available recent marine gravity data and altimetry derived solutions.
    Description: report
    Keywords: 551 ; TQH 000 ; TSX 500 ; Aerogeophysik ; Chile {Geophysik}
    Language: English
    Type: article , publishedVersion
    Format: 100 S.
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  • 134
    Publication Date: 2021-03-29
    Description: report
    Keywords: 551 ; TOB 300 ; Polbewegungen {Geophysik: Erde}
    Language: English
    Type: article , publishedVersion
    Format: 33 S.
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  • 135
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    GFZ, Helmholtz-Zentrum
    Publication Date: 2021-03-29
    Description: thesis
    Keywords: 551 ; VKB 128 ; VAD 600 ; VBN 500 ; VEF 200 ; Pyroklastika {Petrologie} ; Paläovulkanismus {Geologie} ; Geochronologie einzelner Regionen im allgemeinen ; Italien {Geologie}
    Language: German
    Type: monograph , publishedVersion
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  • 136
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    GFZ, Helmholtz-Zentrum
    Publication Date: 2021-03-29
    Description: The objective of this study was to reconstruct the palaeolimnological history of Lake Holzmaar, Germany in order to infer palaeoclimatological changes and to track anthropogenic activity during the time-span investigated (ca. 6340 - 1470 cal yr BP). Fossil diatom assemblages, geochemical parameters and varve substructure were used as basic tools for further reconstructions. The combined consideration of all proxy gathered information allowed to infer causally determined changes in diatom assemblage composition, annual algae succession and productivity. For example, it was deduced that changes in lake circulation patterns, precipitation rates and/or erosion rates which are ultimately controlled by climate, caused shifts in nutrient ratios and/or concentrations (e.g., silica and phosphorus) and subsequently in fossil algae composition. Major lacustrine changes which occurred ca. 5800, 5100, 4500, 3660 and 2660 cal yr BP correspond to glacier movements or to lake level changes observed at different locations in western Europe which may reflect large-scale Holocene variability over western Europe. In how far decreasing solar activity as it is proposed for the time around 2660 cal yr BP led to major changes within the lake and in the lake's catchment is difficult to disentangle from anthropogenic activity which increased sharply with the beginning of the Iron Age as evidenced by palynology and archaeology. A satisfying discrimination of anthropogenic and climate influence upon the lake is one of the future goals. A further aim is to look for possible periodicities inherent in the varve formation investigated. Answering those questions will help to better understand natural climatic processes and will allow to make suggestions upon future climate variability.
    Description: thesis
    Keywords: 551
    Language: German
    Type: monograph , publishedVersion
    Format: 181 S.
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  • 137
    Publication Date: 2021-03-29
    Description: report
    Keywords: 551 ; TOB 300 ; VBF 000 ; Polbewegungen {Geophysik: Erde} ; Elektronische Datenverarbeitung in der Geologie
    Language: English
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  • 138
    Publication Date: 2021-03-29
    Description: thesis
    Keywords: 551 ; VAE 400 ; VEX 500 ; UNF 000 ; Tektogenese {Geologie} ; Chile {Geologie} ; Satellitengeodäsie
    Language: English
    Type: monograph , publishedVersion
    Format: 127 S.
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  • 139
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    GFZ, Helmholtz-Zentrum
    Publication Date: 2021-03-29
    Description: The LaCoste & Romberg gravity meter S124b and its associated system environment were installed and tested in conjunction with a strap-down gravity meter system (SAGS) of the Bayerische Akademie der Wissenschaften in Munich on a Cessna Grand Caravan of the DLR in Oberpfaffenhofen. This report describes the design and instrumentation of the aerogravimetry system, it documents the installation on the aircraft and it discusses some of the results of the test flights performed within AGFA (Airborne Gravity Flight Approach). Beyond the documentation of the system this report gives a short introduction to the basics of the instruments including a short theory of their operation and data processing. The intention is to give readers from disciplines other than aero-gravimetry and aero-altimetry a technical insight into how the system works and what it is capable of. This should help the reader to evaluate the systems usefulness in other geo-scientific projects. The experiences from the test flights are briefly summarized and an update of the current status and future plans for the individual instruments is given. The aerogravimetry system consists of two major instrument blocks: the gravimetry sensing system and the positioning system. The gravimetry sensors are the LaCoste & Romberg S124b and the SAGS-2.2 systems. The navigation block holds GPS receivers, an inertial navigation system and a laser altimeter. The aircraft used for the primary tests was a Cessna Grand Caravan of the DLR in Oberpfaffenhofen. It offers superb conditions for scientific installations and is widely used in geophysical exploration all over the world. The test flights were flown from Oberpfaffenhofen airport. One profile covers the Bavarian Alps to map short wavelength, topography induced gravity disturbances, and another flight crosses the Rhine Graben to map long wavelength structures of the deeper crust. The software for data processing for navigation, gravimetry and geoid calculations is briefly summarized.
    Description: report
    Keywords: 551 ; TQH 000 ; Aerogeophysik
    Language: English
    Type: article , publishedVersion
    Format: 74 S.
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  • 140
    Publication Date: 2021-03-29
    Description: report
    Keywords: 551
    Language: English
    Type: article , publishedVersion
    Format: 143 S.
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  • 141
    Publication Date: 2021-03-29
    Description: thesis
    Keywords: 551 ; VKB 250 ; VJB 312 ; VEB 128 ; Metasedimente {Petrologie} ; Geochemie der Metamorphite ; Saxothuringikum {Geologie}
    Language: German
    Type: monograph , publishedVersion
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  • 142
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    GFZ, Helmholtz-Zentrum
    Publication Date: 2021-03-29
    Description: thesis
    Keywords: 551 ; TM 300 ; VBD 000 ; Methodik. Arbeitsmittel. Abkürzungsverzeichnisse {Geophysik} ; Mathematische und Statistische Geologie
    Language: German
    Type: monograph , publishedVersion
    Format: 98 S.
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  • 143
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    GFZ, Helmholtz-Zentrum
    Publication Date: 2021-03-29
    Description: thesis
    Keywords: 551 ; ZHB 380 ; Geothermische Energie {Energietechnik}
    Language: German
    Type: monograph , publishedVersion
    Format: 184 S.
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  • 144
    Publication Date: 2021-03-29
    Description: thesis
    Keywords: 551 ; VAE 830 ; VBL 500 ; TQC 220 ; TQG 000 ; VEB 110 ; TSB 110 ; Bruchschollenstrukturen {Geologie} ; Geologische Bohrungen in einzelnen Regionen ; Reflexionsseismik {Geophysik} ; Geophysikalische Bohrlochmessungen ; Norddeutsche Senke {Geologie} ; Norddeutsche Senke {Geophysik}
    Language: English
    Type: monograph , publishedVersion
    Format: 144 S.
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  • 145
    Publication Date: 2021-03-29
    Description: thesis
    Keywords: 551 ; VAE 850 ; TQC 220 ; TSI 000 ; TQI 000 ; VBJ 000 ; VEI 400 ; Festländische Lineamente {Geologie} ; Reflexionsseismik {Geophysik} ; Vorderasien {Geophysik} ; Geophysikalische Satellitenfernerkundung ; Satellitenbildgeologie ; Israel, Palästina {Geologie}
    Language: English
    Type: monograph , publishedVersion
    Format: 98 S.
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  • 146
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    GFZ, Helmholtz-Zentrum
    Publication Date: 2021-03-29
    Description: This report presents the results of a wavelet analysis of Ocean Angular Momentum (OAM) time series, that were generated by the OMCT-Model (Ocean Model for Circulation and Tides). The findings from this analysis were then compared with the same time series that had been projected in the fre-quency domain, using the Fast Fourier Transformation. The oscillations we studied are located in the period window between 14 days to 20 years. From the wavelet transformation, we find that the strictly periodic oscillations (e.g. fortnightly, semiannual, annual) of the tide-driven OAM are modulated by the moon cycle (18.6 years). In addition to the dominant annual oscillation in the mass term of the atmospheric-driven part, we find also non-strictly periodic signals with periods up to one year. The cycle durations of the powerful quasiperiodic oscillations are between 4 and 12 years. A quasiperiodic oscillation in the axial mass term of the atmospheric-driven part can also been correlated with the eleven-years solar cycle. Furthermore, the atmospheric-driven part of the OAM time series shows some aperiodic oscillation be-tween one and three years.
    Description: report
    Keywords: 551 ; TVF 000 ; TUA 500 ; TOB 000 ; Allgemeine Zirkulation der Atmosphäre {Meteorologie} ; Meteorologische Modelle ; Periodische Bewegungen der Erde {Geophysik}
    Language: German
    Type: monograph , publishedVersion
    Format: 85 S.
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  • 147
    Publication Date: 2021-03-29
    Description: thesis
    Keywords: 551 ; VJC 400 ; VEG 111 ; Fluid-Gestein-Wechselwirkungen {Geochemie} ; Baltischer Schild {Geologie}
    Language: German
    Type: monograph , publishedVersion
    Format: 113 S.
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  • 148
    Publication Date: 2021-03-29
    Description: report
    Keywords: 551 ; TOB 100 ; Drehbewegungen {Geophysik: Erde}
    Language: English
    Type: article , publishedVersion
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  • 149
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    GFZ, Helmholtz-Zentrum | [Bibliothek des Wiss.-Parks Albert Einstein] [Vertrieb], [Potsdam]
    Publication Date: 2021-03-29
    Description: thesis
    Keywords: 551 ; VAE 880 ; VAE 140 ; Passive und aktive Kontinentalränder {Geologie} ; Gesteinsdeformation {Strukturgeologie}
    Language: German
    Type: monograph , publishedVersion
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  • 150
    Publication Date: 2021-03-29
    Description: The GRACE dual satellite mission (launched in March, 2002) offers the possibility of computing monthly highly accurate mean gravity fields over an expected lifetime of five years. Unfortunately, the quality of these monthly gravity field products does not yet reach the pre-launch expectations. Possible error sources might be insufficient instrument data processing and parameterization or modeling of short-term atmospheric and oceanic mass variations. Another candidate is the ocean tide model. Especially, incomplete subtraction (de-aliasing) of short period tides may be partially aliased into the monthly gravity field solutions. Therefore, we analyzed the difference of two ocean tide models (FES2004 and CSR 4.0) which are used at the GRACE Science Data System level-2 processing centers at GFZ Potsdam and CSR (Center for Space Research, Austin), respectively, and which may serve as a measure of the ocean tide model error. We have computed: a) straightforward monthly means of tidal elevation differences and b) simulations of tidal elevation differences at footpoints of GRACE A. The results of a) represent the differences of the monthly means of both tide models with respect to an uniform sampling (grid). The results of b) include the influence of spatially uneven sampling distribution (only along the orbit) and show that for the S2 and K2 tidal constituents, aliasing causes effects which cannot be neglected with respect to the presently achievable GRACE measurement accuracy for degrees n.le.7 (S2) and n.le.8 (K2).
    Description: report
    Keywords: 551
    Language: English
    Type: article , publishedVersion
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  • 151
    Publication Date: 2021-03-29
    Description: thesis
    Keywords: 551 ; TSB 000 ; VAE 700 ; TOH 530 ; Mitteleuropa {Geophysik} ; Bau der Erdkruste großer Regionen der Erde {Geologie} ; Häufigkeit und Verbreitung von Erdbeben {Geophysik}
    Language: English
    Type: monograph , publishedVersion
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  • 152
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    GFZ, Helmholtz-Zentrum
    Publication Date: 2021-03-29
    Description: This report describes the set-up, logistics and results of the MEXAGE (Mexican Aero-Geophysical Survey) survey. It gives a short overview about the scientific intentions, detailed documentation of all technical aspects starting from the survey equipment via the aircraft installation to the GPS stations set-up to the experiences in flight. The processing results for the individual profiles are briefly discussed.
    Description: report
    Keywords: 551 ; TQH 000 ; TSV 300 ; Aerogeophysik ; Mexiko {Geophysik}
    Language: English
    Type: article , publishedVersion
    Format: 94 S.
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  • 153
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    GFZ, Helmholtz-Zentrum
    Publication Date: 2021-03-29
    Description: This study is concerned with the forward modelling of the present-day glacial-isostatic adjustment (GIA) of the earth to present and past changes of the Antarctic ice sheet (AIS). We predict temporal variations in the geoid height and topographic height within the context of the Gravity Recovery and Climate Experiment (GRACE) satellite mission and terrestrial Global Positioning System (GPS) stations in Antarctica. We first adopt an elastic-compressible earth model and calculate the earth's response to seasonal (〈 1 a) and secular (~ 100 a) ice-mass changes. Then, we consider a viscoelastic-incompressible earth model and determine the earth's response to the melting of the AIS since the last glacial maximum (LGM), i.e. the post-glacial rebound (PGR). Both models are radially symmetric and self gravitating. A range of viscosity values account for the uncertainty in the viscosity stratification and the lateral heterogeneity of the mantle beneath Antarctica. We employ six load models simulating the most important temporal aspects of the AIS's evolution. Finally, we predict the geoid-height change and the land uplift and compare them with recent GRACE observations and determinations of the uplift rate for the permanent GPS stations along the Antarctic coast.
    Description: report
    Keywords: 551
    Language: English
    Type: article , publishedVersion
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  • 154
    Publication Date: 2021-03-29
    Description: report
    Keywords: 551
    Language: English
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  • 155
    Publication Date: 2021-03-29
    Description: Hawaii gehört zu den bekanntesten Beispielen für Hotspot-Vulkanismus weltweit. Die von weiteren tektonischen Einflüssen isolierte Position inmitten des Pazifischen Ozeans macht Hawaii zu einem interessanten Untersuchungsobjekt auf dem Gebiet der Mantelplumes. Weder die Entstehungstiefe noch die genaue Lage des Plumeschlauches im Erdmantel sind bislang genau bekannt - Fragen, deren Beantwortung auch neue Erkenntnisse bezüglich der dynamischen Prozesse des Mantels, wie etwa der Konvektion, liefern könnte. In dieser Arbeit wurde die Methode der Receiver Functions angewendet, um die Strukturen bis in den obersten Teil des unteren Mantels unter Hawaii zu untersuchen. Zur Auswertung standen Daten von elf temporären Breitbandstationen auf den vier größten Hawaii-Inseln zur Verfügung, welche im Zeitraum von Juni bzw. November 1999 bis Mai 2001 kontinuierlich registrierten, sowie zusätzliche Daten permanenter Breitbandstationen. Die Untersuchung ergab eine Reihe von neuen Ergebnissen der seismischen Struktur in verschiedenen Tiefenbereichen. In Übereinstimmung mit früheren Studien konnte die Moho in Tiefen zwischen 12 - 17 km beobachtet werden. Im jüngeren Teil der Inselkette, von Big Island bis etwa Oahu, tritt zusätzlich eine sehr starke Konvertierte auf ..
    Description: thesis
    Keywords: 551 ; TQC 210 ; TOD 410 ; TSZ 300 ; VAC 100 ; VAD 700 ; TOH 130 ; Praktische Handhabung der seismischen Verfahren {Geophysik} ; Oberer Erdmantel {Geophysik} ; Pazifischer Ozean {Geophysik} ; Magmatismus im allgemeinen {Geologie} ; Regionaler Vulkanismus {Geologie} ; Signalanalyse {Geophysik}
    Language: German
    Type: monograph , publishedVersion
    Format: 129 S.
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  • 156
    Publication Date: 2020-10-05
    Description: The Altiplano represents a key region of the Central Andes, where the interplay between faults and syn-tectonic sediments allow the reconstruction of the kinematic evolution of the Central Andean high plateau. This study aims, by the use of incrementally-balanced crosssections, interpretation of reflection-seismic profiles, 3D strain analysis, gravity data interpretation, isotopic-age dating, and surface observations, to reconstruct the geological and tectonic history of the Southern Altiplano at 21o S between the Eastern and the Western Cordillera. The Southern Altiplano is a complex intramontane basin with 6-8km Cenozoic fill. It can be structurally divided in three domains; the Eastern, Central, and Western Altiplano. 2D balanced cross-sections based on seismic-reflector analysis and field observations show that the Eastern Altiplano is the buried, thin-skinned deformation front of the western part of the Eastern Cordillera's bivergent thrust system. The 20-40ʿ dipping, blind faults merge into a shallow, eastward-dipping detachment at 7-9km depth that continues into the Eastern Cordillera. The Central Altiplano forms a bivergent system with 30-90ʿ dipping, basement-involving thrusts in the east, and fault-propagation folds in the west. The shallow, westward-dipping detachment lies at 9-10km depth and possibly continues into the Western Altiplano, which forms a separate bivergent thrust-system.The computer-aided (GeoSec and 2DMove), incremental restoration of the balanced crosssections of the Eastern and Central Altiplano, and preliminary line-length balancing of the Western Altiplano, yields 38km shortening due to folding and thrusting ...
    Description: thesis
    Keywords: 551 ; VAE 811 ; TQC 220 ; VEX 300 ; VEX 100 ; Alpidische Orogene {Geologie} ; Reflexionsseismik {Geophysik} ; Bolivien und Paraguay {Geologie} ; Anden {Geologie}
    Language: English
    Type: monograph , publishedVersion
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  • 157
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    GFZ, Helmholtz-Zentrum
    Publication Date: 2021-03-29
    Description: report
    Keywords: 551
    Language: German
    Type: anthology , publishedVersion
    Format: 210 S.
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  • 158
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    GFZ, Helmholtz-Zentrum
    Publication Date: 2021-03-29
    Description: Die Arbeit beschäftigt sich mit den Deformationen des Erdkörpers, die durch die Auflasten der eiszeitlichen Eisschilde hervorgerufen werden. Die Kräfte, die der Erdkörper dabei den Auflasten entgegensetzt, sind die Auftriebskraft des Erdmantels und die Gegenkraft durch die elastische Verbiegung der Lithosphäre. Für den hinsichtlich geologischer Zeitskalen recht kurzfristigen eiszeitlichen Belastungsprozess von wenigen hunderttausend Jahren muss zusätzlich noch das viskoelastische Verhalten des Erkörpers berücksichtigt werden, das zu einer verzögerten Antwort des Erdkörpers führt, und noch heute, ca. 8000 Jahre nach Ende der letzten Vereisung, in einer nacheiszeitlichen Hebung der vormals vereisten Gebiete beobachtet wird. Um den Auftrieb durch den Erdmantel zu modellieren, wird dieser häufig durch eine viskose inkompressible Flüssigkeit homogener Dichte beschrieben. Neuere Arbeiten berücksichtigen auch die Kompressibilität des Mantelmaterials, behalten jedoch die homogene Dichte bei, wodurch sich das Kontinuum in keinem konsisten Anfangszustand befindet, da die Eigenkompression durch den lithostatischen Druck vernachlässigt wird. Diese Modelle werden in der Arbeit diskutiert, und die Probleme aufgezeigt, die sich bei der Lösung der viskoelastischen Bewegungsgleichung für eine Halbraumgeometrie ergeben. Die Gegenkraft aus der elastischen Verbiegung der Lithosphäre wird durch ihre Biegesteifigkeit bestimmt. Nehmen wir viskoelastische Schichten innerhalb der Lithosphäre an, so setzen diese die Biegesteifigkeit herab. Somit ist die Mächtigkeit einer viskoelastisch geschichteten Lithosphäre weitaus größer als die sich allein aus einer elastischen Schicht ableitbaren effektiven elastischen Dicke...
    Description: thesis
    Keywords: 551 ; TOE 000 ; TOG 000 ; VAE 200 ; VAE 130 ; Physikalisches Verhalten der Erde {Geophysik} ; Isostasie {Geophysik} ; Geodynamik der Lithosphäre {Geologie} ; Geomechanik
    Language: German
    Type: monograph , publishedVersion
    Format: 150 S.
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  • 159
    Publication Date: 2021-03-29
    Description: thesis
    Keywords: 551 ; VAJ 400 ; V 300 ; VEX 500 ; VAE 880 ; VBB 000 ; Abtragung durch Erosion {Geologie} ; Methodik. Arbeitsmittel. Abkürzungsverzeichnisse {Geologische Wissenschaften} ; Chile {Geologie} ; Passive und aktive Kontinentalränder {Geologie} ; Experimentelle Geologie
    Language: English
    Type: monograph , publishedVersion
    Format: 233 S.
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  • 160
    Publication Date: 2021-03-29
    Description: report
    Keywords: 551 ; TOB 000 ; TOF 000 ; Periodische Bewegungen der Erde {Geophysik} ; Schwerkraft {Geophysik}
    Language: German
    Type: article , publishedVersion
    Format: 94 S.
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  • 161
    Publication Date: 2021-03-29
    Description: report
    Keywords: 551
    Language: English
    Type: article , publishedVersion
    Format: 18 S.
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  • 162
    Publication Date: 2021-03-29
    Description: thesis
    Keywords: 551 ; TSX 100 ; TOH 100 ; VAE 880 ; Anden {Geophysik} ; Seismometrie {Geophysik} ; Passive und aktive Kontinentalränder {Geologie}
    Language: English
    Type: monograph , publishedVersion
    Format: 125 S.
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  • 163
    Publication Date: 2021-03-29
    Description: report
    Keywords: 551
    Language: German
    Type: article , publishedVersion
    Format: 43 S.
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  • 164
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    Publication Date: 2021-03-29
    Description: thesis
    Keywords: 551 ; TOG 000 ; VAQ 400 ; VAE 300 ; Isostasie {Geophysik} ; Morphologie, Ausmaß und Dicke, Masse und Energiegleichgewicht {Glaziologie} ; Epirogenese {{Geologie}}
    Language: English
    Type: monograph , publishedVersion
    Format: 162 S.
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  • 165
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    Publication Date: 2021-03-29
    Description: thesis
    Keywords: 551 ; VAE 885 ; VAE 400 ; VEG 190 ; Inselbögen {Geologie} ; Tektogenese {Geologie} ; Koriakia-Kamtchatkasystem {Geologie}
    Language: German
    Type: monograph , publishedVersion
    Format: 127 S.
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  • 166
    Publication Date: 2021-03-29
    Description: thesis
    Keywords: 551 ; TSR 000 ; VAE 880 ; VER 200 ; Südafrika {Geophysik} ; Passive und aktive Kontinentalränder {Geologie} ; Namibia {Geologie}
    Language: German
    Type: monograph , publishedVersion
    Format: I125 S.
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  • 167
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    Publication Date: 2021-03-29
    Description: report
    Keywords: 551
    Language: English
    Type: article , publishedVersion
    Format: 23 S.
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  • 168
    Publication Date: 2021-03-29
    Description: Polar motion data is available from the mid-19th century to the present. Based on time series with a variety of sampling intervals (monthly, 0.05-year, 5-day and daily), we have separated the low-frequency terms by low-pass filtering and the Chandler and annual terms by recursive band-pass filtering of the pole coordinates. Using a simple unweighted least-squares fit to the filtered low-frequency terms, the linear trends of the rotation pole were estimated. Assessing the estimates based on intercomparisons, the most reliable trend estimate was found. Using a Fast Fourier Transform, we have computed the prograde, retrograde and total amplitude spectra of the low-frequency part of polar motion in order to reveal the long-periodic signals. The characteristics and time evolution of the Chandler and annual wobbles are described by changes in their parameters (radii, directions and period lengths) over one century.
    Description: report
    Keywords: 551 ; TOB 000 ; Periodische Bewegungen der Erde {Geophysik}
    Language: English
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  • 169
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    GFZ, Helmholtz-Zentrum
    Publication Date: 2021-03-29
    Description: report
    Keywords: 551 ; TOB 300 ; VBF 000 ; Polbewegungen {Geophysik: Erde} ; Elektronische Datenverarbeitung in der Geologie
    Language: English
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  • 170
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    AMS (American Meteorological Society)
    In:  Journal of Atmospheric and Oceanic Technology, 27 (9). pp. 1533-1546.
    Publication Date: 2018-07-04
    Description: The eddy correlation technique is rapidly becoming an established method for resolving dissolved oxygen fluxes in natural aquatic systems. This direct and noninvasive determination of oxygen fluxes close to the sediment by simultaneously measuring the velocity and the dissolved oxygen fluctuations has considerable advantages compared to traditional methods. This paper describes the measurement principle and analyzes the spatial and temporal scales of those fluctuations as a function of turbulence levels. The magnitudes and spectral structure of the expected fluctuations provide the required sensor specifications and define practical boundary conditions for the eddy correlation instrumentation and its deployment. In addition, data analysis and spectral corrections are proposed for the usual nonideal conditions, such as the time shift between the sensor pair and the limited frequency response of the oxygen sensor. The consistency of the eddy correlation measurements in a riverine reservoir has been confirmed—observing a night–day transition from oxygen respiration to net oxygen production, ranging from −20 to +5 mmol m−2 day−1—by comparing two physically independent, eddy correlation instruments deployed side by side. The natural variability of the fluctuations calls for at least ∼1 h of flux data record to achieve a relative accuracy of better than ∼20%. Although various aspects still need improvement, eddy correlation is seen as a promising and soon-to-be widely applied method in natural waters.
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  • 171
    Publication Date: 2020-08-04
    Description: Some studies of ocean climate model experiments suggest that regional changes in dynamic sea level could provide a valuable indicator of trends in the strength of the Atlantic meridional overturning circulation (MOC). This paper describes the use of a sequence of global ocean–ice model experiments to show that the diagnosed patterns of sea surface height (SSH) anomalies associated with changes in the MOC in the North Atlantic (NA) depend critically on the time scales of interest. Model hindcast simulations for 1958–2004 reproduce the observed pattern of SSH variability with extrema occurring along the Gulf Stream (GS) and in the subpolar gyre (SPG), but they also show that the pattern is primarily related to the wind-driven variability of MOC and gyre circulation on interannual time scales; it is reflected also in the leading EOF of SSH variability over the NA Ocean, as described in previous studies. The pattern, however, is not useful as a “fingerprint” of longer-term changes in the MOC: as shown with a companion experiment, a multidecadal, gradual decline in the MOC [of 5 Sv (1 Sv ≡ 106 m3 s−1) over 5 decades] induces a much broader, basin-scale SSH rise over the mid-to-high-latitude NA, with amplitudes of 20 cm. The detectability of such a trend is low along the GS since low-frequency SSH changes are effectively masked here by strong variability on shorter time scales. More favorable signal-to-noise ratios are found in the SPG and the eastern NA, where a MOC trend of 0.1 Sv yr−1 would leave a significant imprint in SSH already after about 20 years.
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  • 172
    Publication Date: 2020-08-04
    Description: Changes in the ventilation of the oxygen minimum zone (OMZ) of the tropical North Atlantic are studied using oceanographic data from 18 research cruises carried out between 28.5° and 23°W during 1999–2008 as well as historical data referring to the period 1972–85. In the core of the OMZ at about 400-m depth, a highly significant oxygen decrease of about 15 μmol kg−1 is found between the two periods. During the same time interval, the salinity at the oxygen minimum increased by about 0.1. Above the core of the OMZ, within the central water layer, oxygen decreased too, but salinity changed only slightly or even decreased. The scatter in the local oxygen–salinity relations decreased from the earlier to the later period suggesting a reduced filamentation due to mesoscale eddies and/or zonal jets acting on the background gradients. Here it is suggested that latitudinally alternating zonal jets with observed amplitudes of a few centimeters per second in the depth range of the OMZ contribute to the ventilation of the OMZ. A conceptual model of the ventilation of the OMZ is used to corroborate the hypothesis that changes in the strength of zonal jets affect mean oxygen levels in the OMZ. According to the model, a weakening of zonal jets, which is in general agreement with observed hydrographic evidences, is associated with a reduction of the mean oxygen levels that could significantly contribute to the observed deoxygenation of the North Atlantic OMZ.
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  • 173
    Publication Date: 2020-08-04
    Description: The Atlantic meridional overturning circulation (AMOC) makes the strongest oceanic contribution to the meridional redistribution of heat. Here, an observation-based, forty-eight-month-long time series of the vertical structure and strength of the AMOC at 26.5°N is presented. From April 2004 to April 2008 the AMOC had a mean strength of 18.7 ±2.1 Sv with fluctuations of 4.8 Sv rms. The best guess of the peak-to-peak amplitude of the AMOC seasonal cycle is 6.7 Sv, with a maximum strength in autumn and a minimum in spring. While seasonality in the AMOC was commonly thought to be dominated by the northward Ekman transport, this study reveals that fluctuations of the geostrophic mid-ocean and Gulf Stream transports of 2.2 Sv and 1.7 Sv rms, respectively, are substantially larger than those of the Ekman component (1.2 Sv rms). A simple model based on linear dynamics suggests that the seasonal cycle is dominated by wind stress curl forcing at the eastern boundary of the Atlantic. Seasonal geostrophic AMOC anomalies might represent an important and previously underestimated component of meridional transport and storage of heat in the subtropical North Atlantic. There is evidence that the seasonal cycle observed here is representative of much longer intervals. Previously, hydrographic snapshot estimates between 1957 and 2004 had suggested a long-term decline of the AMOC by 8 Sv. This study suggests that aliasing of seasonal AMOC anomalies might have accounted for a large part of the inferred slowdown.
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  • 174
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    AMS (American Meteorological Society)
    In:  Bulletin of the American Meteorological Society, 91 (7, S). pp. 66-69.
    Publication Date: 2020-08-13
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  • 175
    Publication Date: 2018-04-12
    Description: Analysis of modern and historical observations demonstrates that the temperature of the intermediate-depth (150–900 m) Atlantic water (AW) of the Arctic Ocean has increased in recent decades. The AW warming has been uneven in time; a local 1°C maximum was observed in the mid-1990s, followed by an intervening minimum and an additional warming that culminated in 2007 with temperatures higher than in the 1990s by 0.24°C. Relative to climatology from all data prior to 1999, the most extreme 2007 temperature anomalies of up to 1°C and higher were observed in the Eurasian and Makarov Basins. The AW warming was associated with a substantial (up to 75–90 m) shoaling of the upper AW boundary in the central Arctic Ocean and weakening of the Eurasian Basin upper-ocean stratification. Taken together, these observations suggest that the changes in the Eurasian Basin facilitated greater upward transfer of AW heat to the ocean surface layer. Available limited observations and results from a 1D ocean column model support this surmised upward spread of AW heat through the Eurasian Basin halocline. Experiments with a 3D coupled ice–ocean model in turn suggest a loss of 28–35 cm of ice thickness after 50 yr in response to the 0.5 W m−2 increase in AW ocean heat flux suggested by the 1D model. This amount of thinning is comparable to the 29 cm of ice thickness loss due to local atmospheric thermodynamic forcing estimated from observations of fast-ice thickness decline. The implication is that AW warming helped precondition the polar ice cap for the extreme ice loss observed in recent years.
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  • 176
    Publication Date: 2020-08-04
    Description: The 20th century Northern Hemisphere surface climate exhibits a long-term warming trend, largely caused by anthropogenic forcing, and natural decadal climate variability superimposed on it. This study addresses the possible origin and strength of internal decadal climate variability in the Northern Hemisphere during the recent decades. We present results from a set of climate model simulations that suggest natural internal multidecadal climate variability in the North Atlantic-Arctic Sector could have considerably contributed to the Northern Hemisphere surface warming since 1980. Although covering only a few percent of the earth’s surface, the Arctic may have provided the largest share in this. It is hypothesized that a stronger Meridional Overturning Circulation in the Atlantic and the associated increase in northward heat transport enhanced the heat loss from the ocean to the atmosphere in the North Atlantic region, and especially in the North Atlantic portion of the Arctic due to anomalously strong sea ice melt. The model results stress the potential importance of natural internal multidecadal variability originating in the North Atlantic-Arctic Sector in generating inter-decadal climate changes not only on a regional, but possibly also on a hemispheric and even global scale.
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  • 177
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    AMS (American Meteorological Society)
    In:  Journal of Climate, 17 (19). pp. 3761-3774.
    Publication Date: 2017-08-23
    Description: The decadal-scale variability in the tropical Pacific has been analyzed herein by means of observations and numerical model simulations. The two leading modes of the sea surface temperature (SST) variability in the central western Pacific are a decadal mode with a period of about 10 yr and the ENSO mode with a dominant period of about 4 yr. The SST anomaly pattern of the decadal mode is ENSO like. The decadal mode, however, explains most variance in the western equatorial Pacific and off the equator. A simulation with an ocean general circulation model (OGCM) forced by reanalysis data is used to explore the origin of the decadal mode. It is found that the variability of the shallow subtropical–tropical overturning cells is an important factor in driving the decadal mode. This is supported by results from a multicentury integration with a coupled ocean–atmosphere general circulation model (CGCM) that realistically simulates tropical Pacific decadal variability. Finally, the sensitivity of the shallow subtropical–tropical overturning cells to greenhouse warming is discussed by analyzing the results of a scenario integration with the same CGCM.
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  • 178
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    AMS (American Meteorological Society)
    In:  Journal of Physical Oceanography, 34 . pp. 817-843.
    Publication Date: 2020-08-04
    Description: The current system east of the Grand Banks was intensely observed by World Ocean Circulation Experiment (WOCE) array ACM-6 during 1993–95 with eight moorings, reaching about 500 km out from the shelf edge and covering the water column from about 400-m depth to the bottom. More recently, a reduced array by the Institut für Meerskunde (IfM) at Kiel, Germany, of four moorings was deployed during 1999–2001, focusing on the deep-water flow near the western continental slope. Both sets of moored time series, each about 22 months long, are combined here for a mean current boundary section, and both arrays are analyzed for the variability of currents and transports. A mean hydrographic section is derived from seven ship surveys and is used for geostrophic upper-layer extrapolation and isopycnal subdivision of the mean transports into deep-water classes. The offshore part of the combined section is dominated by the deep-reaching North Atlantic Current (NAC) with currents still at 10 cm s−1 near the bottom and a total northward transport of about 140 Sv (Sv ≡ 106 m3 s−1), with the details depending on the method of surface extrapolation used. The mean flow along the western boundary was southward with the section-mean North Atlantic Deep Water outflow determined to be 12 Sv below the σθ = 27.74 kg m−3 isopycnal. However, east of the deep western boundary current (DWBC), the deep NAC carries a transport of 51 Sv northward below σθ = 27.74 kg m−3, resulting in a large net northward flow in the western part of the basin. From watermass signatures it is concluded that the deep NAC is not a direct recirculation of DWBC water masses. Transport time series for the DWBC variability are derived for both arrays. The variance is concentrated in the period range from 2 weeks to 2 months, but there are also variations at interannual and longer periods, with much of the DWBC variability being related to fluctuations and meandering of the NAC. A significant annual cycle is not recognizable in the combined current and transport time series of both arrays. The moored array results are compared with other evidence on deep outflow and recirculation, including recent models of different types and complexity.
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  • 179
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    AMS (American Meteorological Society)
    In:  Journal of Climate, 17 (22). pp. 4301-4315.
    Publication Date: 2020-08-04
    Description: Simulations and seasonal forecasts of tropical Pacific SST and subsurface fields that are based on the global Consortium for Estimating the Circulation and Climate of the Ocean (ECCO) ocean-state estimation procedure are investigated. As compared to similar results from a traditional ENSO simulation and forecast procedure, the hindcast of the constrained ocean state is significantly closer to observed surface and subsurface conditions. The skill of the 12-month lead SST forecast in the equatorial Pacific is comparable in both approaches. The optimization appears to have better skill in the SST anomaly correlations, suggesting that the initial ocean conditions and forcing corrections calculated by the ocean-state estimation do have a positive impact on the predictive skill. However, the optimized forecast skill is currently limited by the low quality of the statistical atmosphere. Progress is expected from optimizing a coupled model over a longer time interval with the coupling statistics being part of the control vector.
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  • 180
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    AMS (American Meteorological Society)
    In:  Journal of Physical Oceanography, 34 (11). pp. 2398-2412.
    Publication Date: 2020-08-04
    Description: In the eastern South Pacific Ocean, at a depth of about 200 m, a salinity minimum is found. This minimum is associated with a particular water mass, the “Shallow Salinity Minimum Water” (SSMW). SSMW outcrops in a fresh tongue (Smin) centered at about 45°S. The Smin appears to emanate from the eastern boundary, against the mean flow. The watermass transformation that creates SSMW and Smin is investigated here. The Smin and SSMW are transformed from saltier and warmer waters originating from the western South Pacific. The freshening and cooling occur when the water is advected eastward at the poleward side of the subtropical gyre. Sources of freshening and cooling are air–sea exchange and advection of water from south of the subtropical gyre. A freshwater and heat budget for the mixed layer reveals that both sources equally contribute to the watermass transformation in the mixed layer. The freshened and cooled mixed layer water is subducted into the gyre interior along the southern rim of the subtropical gyre. Subduction into the zonal flow restricts the transformation of interior properties to diffusion only. A simple advection/diffusion balance reveals diffusion coefficients of order 2000 m2 s−1. The tongue shape of the Smin is explained from a dynamical viewpoint because no relation to a positive precipitation–evaporation balance was found. Freshest Smin values are found to coincide with slowest eastward mixed layer flow that accumulates the largest amounts of freshwater in the mixed layer and creates the fresh tongue at the sea surface. Although the SSMW is the densest and freshest mode of water subducted along the South American coast, the freshening and cooling in the South Pacific affect a whole range of densities (25.0–26.8 kg m−3). The transformed water turns northward with the gyre circulation and contributes to the hydrographic structure of the gyre farther north. Because the South Pacific provides most of the source waters that upwell along the equatorial Pacific, variability in South Pacific hydrography may influence equatorial Pacific hydrography. Because one-half of the transformation is found to be controlled through Ekman transport, variability in wind forcing at the southern rim of the subtropical gyre may be a source for variability of the equatorial Pacific.
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  • 181
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    AMS (American Meteorological Society)
    In:  Journal of Physical Oceanography, 34 (1). pp. 293-305.
    Publication Date: 2018-04-11
    Description: An analytical model is developed to study the tidally induced mean circulation in the frontal zone. Four distinct forcing mechanisms are identified, which result in the generation of the counterclockwise Bernoulli cell, the clockwise Ekman cell, the clockwise frontal cell, and the Stokes drift (facing in the direction with the shallow water to the left). The decomposition of the cross-frontal circulation provides a dynamical framework for interpreting and understanding its complex structure. To illustrate the underlying physics, three model configurations are considered pertaining to a homogenous ocean and winter and summer fronts. For a homogeneous ocean, the circulation is dominated by three cells; for the winter front, the offshore Bernoulli cell is strengthened; and for the summer front, two counterrotating cells are found in the vertical direction, associated with the two branches of the front. The dependence of the cell structure on the Ekman, Burger, and other dimensionless numbers is examined.
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  • 182
    Publication Date: 2016-09-07
    Description: A multi-model ensemble-based system for seasonal-to-interannual prediction has been developed in a joint European project known as DEMETER (Development of a European Multimodel Ensemble Prediction System for Seasonal to Interannual Prediction). The DEMETER system comprises seven global atmosphere–ocean coupled models, each running from an ensemble of initial conditions. Comprehensive hindcast evaluation demonstrates the enhanced reliability and skill of the multimodel ensemble over a more conventional single-model ensemble approach. In addition, innovative examples of the application of seasonal ensemble forecasts in malaria and crop yield prediction are discussed. The strategy followed in DEMETER deals with important problems such as communication across disciplines, downscaling of climate simulations, and use of probabilistic forecast information in the applications sector, illustrating the economic value of seasonal-to-interannual prediction for society as a whole.
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  • 183
    Publication Date: 2020-08-04
    Description: This study focuses on an important aspect of air–sea interaction in models, namely, large-scale, spurious heat fluxes due to false pathways of the Gulf Stream and North Atlantic Current (NAC) in the “storm formation region” south and east of Newfoundland. Although high-resolution eddy-resolving models show some improvement in this respect, results are sensitive to poorly understood, subgrid-scale processes for which there is currently no complete, physically based parameterization. A simple method to correct an ocean general circulation model (OGCM), acting as a practical substitute for a physically based parameterization, is explored: the recently proposed “semiprognostic method,” a technique for adiabatically adjusting flow properties of a hydrostatic OGCM. The authors show that application of the method to an eddy-permitting model of the North Atlantic Ocean yields more realistic flow patterns and watermass characteristics in the Gulf Stream and NAC regions; in particular, spurious surface heat fluxes are reduced. Four simple modifications to the method are proposed, and their benefits are demonstrated. The modifications successfully account for three drawbacks of the original method: reduced geostrophic wave speeds, damped mesoscale eddy activity, and spurious interaction with topography. It is argued that use of a corrected (eddy permitting) OGCM in a coupled modeling system for simulating present climate (as now becomes possible because of increasing computer power) should lead to a more realistic simulation in regions of strong air–sea interaction as compared with that obtained with an uncorrected model. The method is also well suited for the simulation of the uptake and transport of passive tracers, such as anthropogenic carbon dioxide or components of ecosystem models.
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  • 184
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    AMS (American Meteorological Society)
    In:  Journal of Physical Oceanography, 34 (3). pp. 566-581.
    Publication Date: 2020-08-04
    Description: Two major water masses dominate the deep layers in the Mariana and Caroline Basins: the Lower Circumpolar Water (LCPW), arriving from the Southern Ocean along the slopes north of the Marshall Islands, and the North Pacific Deep Water (NPDW) reaching the region from the northeastern Pacific Ocean. Hydrographic and moored observations and multibeam echosounding were performed in the East Mariana and the East Caroline Basins to detail watermass distributions and flow paths in the area. The LCPW enters the East Mariana Basin from the east. At about 13°N, however, in the southern part of the basin, a part of this water mass arrives in a southward western boundary flow along the Izu–Ogasawara–Mariana Ridge. Both hydrographic observations and moored current measurements lead to the conclusion that this water not only continues westward to the West Mariana Basin as suggested before, but also provides bottom water to the East Caroline Basin. The critical throughflow regions were identified by multibeam echosounding at the Yap Mariana Junction between the East and West Mariana Basins and at the Caroline Ridge between the East Mariana and East Caroline Basins. The throughflow is steady between the East and West Mariana Basins, whereas more variability is found at the Caroline Ridge. At both locations, throughflow fluctuations are correlated with watermass property variations suggesting layer-thickness changes. The total transport to the two neighboring basins is only about 1 Sverdrup (1Sv ≡ 106 m3 s−1) but has considerable impact on the watermass structure in these basins. Estimates are given for the diapycnal mixing that is required to balance the inflow into the East Caroline Basin. Farther above in the water column, the high-silica tongue of NPDW extends from the east to the far southwestern corner of the East Mariana Basin, with transports being mostly southward across the basin.
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  • 185
    Publication Date: 2020-08-04
    Description: Sea surface temperature (SST) observations in the North Atlantic indicate the existence of strong multidecadal variability with a unique spatial structure. It is shown by means of a new global climate model, which does not employ flux adjustments, that the multidecadal SST variability is closely related to variations in the North Atlantic thermohaline circulation (THC). The close correspondence between the North Atlantic SST and THC variabilities allows, in conjunction with the dynamical inertia of the THC, for the prediction of the slowly varying component of the North Atlantic climate system. It is shown additionally that past variations of the North Atlantic THC can be reconstructed from a simple North Atlantic SST index and that future, anthropogenically forced changes in the THC can be easily monitored by observing SSTs. The latter is confirmed by another state-of-the-art global climate model. Finally, the strong multidecadal variability may mask an anthropogenic signal in the North Atlantic for some decades.
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  • 186
    Publication Date: 2017-08-18
    Description: A systematic modular approach to investigate the respective roles of the ocean and atmosphere in setting El Niño characteristics in coupled general circulation models is presented. Several state-of-the-art coupled models sharing either the same atmosphere or the same ocean are compared. Major results include 1) the dominant role of the atmosphere model in setting El Niño characteristics (periodicity and base amplitude) and errors (regularity) and 2) the considerable improvement of simulated El Niño power spectratoward lower frequencywhen the atmosphere resolution is significantly increased. Likely reasons for such behavior are briefly discussed. It is argued that this new modular strategy represents a generic approach to identifying the source of both coupled mechanisms and model error and will provide a methodology for guiding model improvement.
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  • 187
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    AMS (American Meteorological Society)
    In:  Journal of Physical Oceanography, 34 . pp. 772-792.
    Publication Date: 2018-04-11
    Description: The Indonesian Throughflow (ITF) spreading pathways and time scales in the Indian Ocean are investigated using both observational data and two numerical tracer experiments, one being a three-dimensional Lagrangian trajectory experiment and the other a transit-time probability density function (PDF) tracer experiment, in an ocean general circulation model. The model climatology is in agreement with observations and other model results except that speeds of boundary currents are lower. Upon reaching the western boundary within the South Equatorial Current (SEC), the trajectories of the ITF tracers within the thermocline exhibit bifurcation. The Lagrangian trajectory experiment shows that at the western boundary about 38%±5% thermocline ITF water flows southward to join the Agulhas Current, consequently exiting the Indian Ocean, and the rest, about 62%±5%, flows northward to the north of SEC. In boreal summer, ITF water penetrates into the Northern Hemisphere within the Somali Current. The primary spreading pathway of the thermocline ITF water north of SEC is upwelling to the surface layer with subsequent advection southward within the surface Ekman layer toward the southern Indian Ocean subtropics. There it is subducted and advected northward in the upper thermocline to rejoin the SEC. Both the observations and the trajectory experiment suggest that the upwelling occurs mainly along the coast of Somalia during boreal summer and in the open ocean within a cyclonic gyre in the Tropics south of the equator throughout the year. All the ITF water eventually exits the Indian Ocean along the western boundary within the Mozambique Channel and the east coast of Madagascar and, farther south, the Agulhas Current region. The advective spreading time scales, represented by the elapsed time corresponding to the maximum of transit- time PDF, show that in the upper thermocline the ITF crosses the Indian Ocean, from the Makassar Strait to the east coast of the African continent, on a time scale of about 10 yr and reaches the Arabian Sea on a time scale of over 20 yr.
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  • 188
    Publication Date: 2020-08-04
    Description: Aspects of the sea level changes in the western Mediterranean Sea are investigated using a numerical tidal model of the Strait of Gibraltar. As a prerequisite, the performance of this model, that is, a two-dimensional, nonlinear, two-layer, boundary-fitted coordinate numerical model based on the hydrostatic approximation on an f plane, is assessed in the simulation of mean and tidal circulation of the Strait of Gibraltar. The model is forced by imposing mean interface and surface displacements as well as M2, S2, O1, and K1 tidal components along the Atlantic and Mediterranean model open boundaries. Model results are compared with observations and with results obtained from a tidal inverse model for the eastern entrance of the Strait of Gibraltar. In general, good agreement is found. A sensitivity study performed by varying different model parameters shows that the model behaves reasonably well in the simulation of the averaged circulation. The model is then used to investigate the climatological sensitivity of the simulated dynamics in the Strait of Gibraltar to changes in the density difference between Atlantic and Mediterranean waters. For this purpose, given a certain density difference between Atlantic and Mediterranean waters, the authors iteratively searched for that sea level drop between the Atlantic and the Mediterranean that fulfills the mass balance of the Mediterranean. It is found that an increase of the density difference leads to an increase of the exchange flow and to an increase of the sea level drop between the two basins. A trend in the sea level drop of O(1 cm yr−1), such as the one observed between 1994 and 1997, is explained by the model as the result of a trend of O(10−4 yr−1) in the relative density difference between the Mediterranean and Atlantic waters. The observed north–south asymmetry in this trend is also captured by the model, and it is found to arise from changes in the along-strait velocity. Results suggest that the dynamics within the Strait of Gibraltar cannot be neglected when sea level changes in the western Mediterranean basin are investigated.
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  • 189
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    AMS (American Meteorological Society)
    In:  Journal of Physical Oceanography, 34 (12). pp. 2756-2760.
    Publication Date: 2020-08-04
    Description: The bifurcation behavior of a conceptual heat–salt oscillator model is analyzed by means of numerical continuation methods. A global (homoclinic) bifurcation acts as an organizing center for the dynamics of the simplified convective model. It originates from a codimension-2 bifurcation in an extended parameter space. Comparison with earlier work by Cessi shows that the intriguing stochastic thermohaline excitability can be understood from the bifurcation structure of the model. It is argued that global bifurcations may play a crucial role in determining long-term variability of the thermohaline circulation.
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  • 190
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    AMS (American Meteorological Society)
    In:  Journal of Climate, 17 . pp. 2157-2169.
    Publication Date: 2019-07-02
    Description: A method is presented to reconstruct decadal variations of the North Atlantic Oscillation (NAO). The spectral characteristics of the NAO on time scales of decades and longer are of particular interest for the understanding of North Atlantic ocean–atmosphere interactions. The reconstruction is based on a transfer model calibration that uses bandpass-filtered time series. The maximum overlap discrete wavelet transform (MODWT) is applied for decomposing the time series variance into different time scales. A total of 43 proxies, including Greenland ice cores and European tree-ring chronologies, are selected and regionally grouped providing four independent reconstructions for the period 1700–1978. The mean reconstruction agrees well with two recently published reconstructions during most of the time period. However, there are considerable differences in the earliest part before 1750. Running correlations between the reconstructions indicate that time-dependent relations exist among the different NAO reconstructions. The results suggest that the geographical distribution of proxies strongly affects the reconstruction and could explain some of the apparent discrepancies among the reconstructions recently published in literature. In the early eighteenth century, external forcing (solar, volcanic) seems to mask the NAO signature within the proxies
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  • 191
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    AMS (American Meteorological Society)
    In:  Journal of Physical Oceanography, 34 . pp. 1548-1570.
    Publication Date: 2020-08-04
    Description: The deep circulation and related transports of the southern Labrador Sea are determined from direct current observations from ship surveys and a moored current-meter array. The measurements covered a time span from summer 1997 to 1999 and show a well-defined deep boundary current extending approximately out to the 3300-m depth contour and weak reverse currents farther offshore. The flow has a strong barotropic component, and significant baroclinic flow is only found in the shallow Labrador Current at the shelf break and associated with a deep core of Denmark Strait Overflow Water. The total deep-water transport below σΘ = 27.74 kg m−3 was 26 ± 5 Sv (Sv ≡ 106 m3 s−1) comprising Labrador Sea Water (LSW), Gibbs Fracture Zone Water (GFZW), and Denmark Strait Overflow Water (DSOW). Intraseasonal variability of the flow and transport was high, ranging from 15 to 35 Sv, and the annual means differed by 17%. A seasonal cycle is confined to the shallow Labrador Current; in its deeper part, where the mean flow is still strong, no obvious seasonality could be detected. The transport of the interior anticyclonic recirculation was estimated from lowered acoustic Doppler current profiler stations and geostrophy, yielding about 9 Sv. Thus, the net deep-water outflow from the Labrador Sea was about 17 Sv. The baroclinic transport of GFZW and DSOW referenced to the depth of the isopycnal σΘ = 27.80 kg m−3 is only about one-third of the total transport in these layers. Longer-term variations of the total transports are not represented well by the baroclinic contribution.
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  • 192
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    AMS (American Meteorological Society)
    In:  Journal of Climate, 17 (22). pp. 4463-4472.
    Publication Date: 2017-08-23
    Description: On seasonal time scales, ENSO prediction has become feasible in an operational framework in recent years. On decadal to multidecadal time scales, the variability of the oceanic circulation is assumed to provide a potential for climate prediction. To investigate the decadal predictability of the coupled atmosphere–ocean general circulation model (AOGCM) European Centre-Hamburg model version 5/Max Planck Institute Ocean Model (ECHAM5/MPI-OM), a 500-yr-long control integration and “perfect model” predictability experiments are analyzed. The results show that the sea surface temperatures (SSTs) of the North Atlantic, Nordic Seas, and Southern Ocean exhibit predictability on multidecadal time scales. Over the ocean, the predictability of surface air temperature (SAT) is very similar to that of SST. Over land, there is little evidence of decadal predictability of SAT except for some small maritime-influenced regions of Europe. The AOGCM produces predictable signals in lower-tropospheric temperature and precipitation over the North Atlantic, but not in sea level pressure.
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  • 193
    Publication Date: 2022-03-07
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  • 194
    Publication Date: 2022-03-10
    Description: The huge warming of the Arctic that started in the early 1920s and lasted for almost two decades is one of the most spectacular climate events of the twentieth century. During the peak period 1930–40, the annually averaged temperature anomaly for the area 60°–90°N amounted to some 1.7°C. Whether this event is an example of an internal climate mode or is externally forced, such as by enhanced solar effects, is presently under debate. This study suggests that natural variability is a likely cause, with reduced sea ice cover being crucial for the warming. A robust sea ice–air temperature relationship was demonstrated by a set of four simulations with the atmospheric ECHAM model forced with observed SST and sea ice concentrations. An analysis of the spatial characteristics of the observed early twentieth-century surface air temperature anomaly revealed that it was associated with similar sea ice variations. Further investigation of the variability of Arctic surface temperature and sea ice cover was performed by analyzing data from a coupled ocean–atmosphere model. By analyzing climate anomalies in the model that are similar to those that occurred in the early twentieth century, it was found that the simulated temperature increase in the Arctic was related to enhanced wind-driven oceanic inflow into the Barents Sea with an associated sea ice retreat. The magnitude of the inflow is linked to the strength of westerlies into the Barents Sea. This study proposes a mechanism sustaining the enhanced westerly winds by a cyclonic atmospheric circulation in the Barents Sea region created by a strong surface heat flux over the ice-free areas. Observational data suggest a similar series of events during the early twentieth-century Arctic warming, including increasing westerly winds between Spitsbergen and Norway, reduced sea ice, and enhanced cyclonic circulation over the Barents Sea. At the same time, the North Atlantic Oscillation was weakening.
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  • 195
    Publication Date: 2016-09-07
    Description: Oceanic ecosystems altered by interdecadal climate variability may provide a feedback to the physical climate by phytoplankton affecting heat fluxes into the upper ocean and dimethylsulfide fluxes into the atmosphere
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  • 196
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    AMS (American Meteorological Society)
    In:  Journal of Physical Oceanography, 33 . pp. 1990-1999.
    Publication Date: 2018-04-10
    Description: Intrinsic oscillations of stable geophysical surface frontal currents of the unsteady, nonlinear, reduced-gravity shallow-water equations on an f plane are investigated analytically and numerically. For frictional (Rayleigh) currents characterized by linear horizontal velocity components and parabolic cross sections, the primitive equations are reduced to a set of coupled nonlinear ordinary differential equations. In the inviscid case, two periodic analytical solutions of the nonlinear problem describing 1) the inertially reversing horizontal displacement of a surface frontal current having a fixed parabolic cross section and 2) the cross-front pulsation of a coastal current emerging from a motionless surface frontal layer are presented. In a linear and in a weakly nonlinear context, analytical expressions for field oscillations and their frequency shift relative to the inertial frequency are presented. For the fully nonlinear problem, solutions referring to a surface frontal coastal current are obtained analytically and numerically. These solutions show that the currents oscillate always superinertially, the frequency and the amplitude of their oscillations depending on the magnitude of the initial disturbance and on the squared current Rossby number. In a linear framework, it is shown that disturbances superimposed on the surface frontal current are standing waves within the bounded region, the frequencies of which are inertial/superinertial for the first mode/higher modes. In the same frame, a zeroth mode, which could be interpreted as the superposition of an inertial wave on a background vorticity field, would formally yield subinertial frequencies. For surface frontal currents affected by Rayleigh friction, it is shown that the magnitude of the mean current decays according to a power law and that the oscillations decay faster, because this decay follows an exponential law. Implications of the intrinsic oscillations and of their rapid dissipation for the near-inertial motion in an active ambient ocean are discussed.
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  • 197
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    AMS (American Meteorological Society)
    In:  Journal of Physical Oceanography, 33 . pp. 431-435.
    Publication Date: 2018-04-10
    Description: Aspects of the dynamics of warm-core eddies evolving in a deep ocean are investigated using the results of laboratory experiments and numerical simulations. The vortices, produced experimentally in a system brought to solid body rotation by rapidly lifting a bottomless cylinder containing freshwater immersed in a salty ambient fluid, show clearly the presence of inertial oscillations: deepenings and contractions, shoalings and expansions, alternate during an exact inertial period. These pulsations, though predicted analytically and simulated numerically, had never been measured before for surface eddies having aspect ratios, as well as Rossby and Burger numbers, typical of geophysical warm-core eddies. The spatial structure of the vortex radial and tangential velocity components is analyzed using the experimental results and numerical simulations carried out by means of a layered, nonlinear, reduced-gravity frontal model. It is found that, while the dependence of the vortex radial velocity on the vortex radius evolves toward linearity as time elapses, different spatial structures seem to be possible for the vortex tangential velocity dependence. This behavior, which strongly differs from the “pulson” dynamics, is instead consistent with recently found analytical solutions of the nonlinear, reduced-gravity shallow-water equations describing the dynamics of warm-core eddies on an f plane.
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  • 198
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    AMS (American Meteorological Society)
    In:  Journal of Physical Oceanography, 33 (1). pp. 75-87.
    Publication Date: 2018-04-11
    Description: Two large-scale free-drifting isobaric-floats experiments, “SOFARGOS”/Marine Science and Technology Programme, phase 2 (MAST2) and Mass Transfer and Ecosystem Response (MATER)/MAST3, undertaken in 1994–95 in the northwestern Mediterranean Sea and in 1997–98 in the Algerian Basin, respectively, have revealed for the first time that Western Mediterranean Deep Water, newly formed by deep convection in the Gulf of Lion (the so-called Medoc site), can be advected several hundreds of kilometers away from the formation area by anticyclonic submesoscale coherent vortices (SCVs). This behavior implies that SCVs participate actively in the large-scale thermohaline circulation and deep ventilation of the western Mediterranean Sea. These SCVs are characterized by small radius (5 km), very low potential vorticity, high aspect ratio (0.1), and extended lifetime (〉0.5 yr).
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  • 199
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    AMS (American Meteorological Society)
    In:  Journal of Physical Oceanography, 33 (7). pp. 1351-1364.
    Publication Date: 2019-04-29
    Description: Bulk properties of the Denmark Strait overflow (DSO) plume observed in velocity and hydrography surveys undertaken in 1997 and 1998 are described. Despite the presence of considerable short-term variability, it is found that the pathway and evolution of the plume density anomaly are remarkably steady. Bottom stress measurements show that the pathway of the plume core matches well with a rate of descent controlled by friction. The estimated entrainment rate diagnosed from the rate of plume dilution with distance shows a marked increase in entrainment at approximately 125 km from the sill, leading to a net dilution consistent with previous reports of a doubling of overflow transport measured by current meter arrays. The entrainment rate increase is likely related to the increased topographic slopes in the region, compounded by a decrease in interface stratification as the plume is diluted and enters a denser background.
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  • 200
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    AMS (American Meteorological Society)
    In:  Journal of Atmospheric and Oceanic Technology, 20 (5). pp. 742-751.
    Publication Date: 2020-08-04
    Description: A new shipboard current profiler, a 75-kHz ocean surveyor, was operationally used during two research cruises in the tropical Atlantic and the subpolar North Atlantic, respectively. Here, a report is presented on the first experience with this instrument in two very different current regimes, in the Tropics with large vertical shears, and in the subpolar regime with mainly barotropic flow. The ocean surveyor continuously measured currents in the upper ocean from near the surface to about 500–700-m depth. The measurement range showed a dependence on the regional and temporal variations of scattering particles and on the intensity of swell and wind waves. Statistical comparisons are performed with on-station lowered acoustic Doppler current profiler (LADCP) profiles and underway measurements by classic shipboard acoustic Doppler current profiler (ADCP) measurements. Accuracy estimates for hourly averaged ocean surveyor currents result in errors of about 1 cm s–1 for on-station data and of 2–4 cm s–1 for underway measurements, depending on the regional abundance of scatterers and on the weather conditions encountered.
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