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  • 11
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    Towards a better representation of the solar cycle in general circulation models (2007)
    Copernicus Publ.
    In:  Atmospheric Chemistry and Physics, 7 (20). pp. 5391-5400.
    Details
    Publication Date: 2020-04-09
    Description: We introduce the improved Freie Universität Berlin (FUB) high-resolution radiation scheme FUBRad and compare it to the 4-band standard ECHAM5 SW radiation scheme of Fouquart and Bonnel (FB). Both schemes are validated against the detailed radiative transfer model libRadtran. FUBRad produces realistic heating rate variations during the solar cycle. The SW heating rate response with the FB scheme is about 20 times smaller than with FUBRad and cannot produce the observed temperature signal. A reduction of the spectral resolution to 6 bands for solar irradiance and ozone absorption cross sections leads to a degradation (reduction) of the solar SW heating rate signal by about 20%. The simulated temperature response agrees qualitatively well with observations in the summer upper stratosphere and mesosphere where irradiance variations dominate the signal. Comparison of the total short-wave heating rates under solar minimum conditions shows good agreement between FUBRad, FB and libRadtran up to the middle mesosphere (60–70 km) indicating that both parameterizations are well suited for climate integrations that do not take solar variability into account. The FUBRad scheme has been implemented as a sub-submodel of the Modular Earth Submodel System (MESSy).
    Type: Article , PeerReviewed
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  • 12
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    The climate during the Maunder Minimum: a simulation with the Freie Universität Berlin Climate Middle Atmosphere Model (FUB-CMAM) (2005)
    Elsevier
    In:  Journal of Atmospheric and Solar-Terrestrial Physics, 67 (1-2). pp. 55-69.
    Details
    Publication Date: 2016-11-24
    Description: A model simulation of the climate during Maunder Minimum (MM) (1645–1715) was performed using the Freie Universität Berlin Climate Middle Atmosphere Model (FUB-CMAM). A multi-year equilibrium integration with prescribed solar insolation, atmospheric composition and sea surface temperatures (SSTs) for MM conditions was compared with a present-day (PD) simulation. We find that during MM the stratosphere was significantly warmer (up to 3 K) than during PD, and dynamically more disturbed in winter. The warming is due to the dominant effect of the lower atmospheric CO2 concentration during MM, which leads to a reduced emission of long-wave radiation, and compensates the cooling due to the reduced solar irradiance. The troposphere was about 1–1.5 K cooler in the annual mean during MM. The global mean surface air temperature decreased by 0.86 K. Northern hemisphere winters were on average characterized by cooler and drier weather over the northern parts of the continents, with an increase in precipitation in the southern parts. These climate anomalies are shown to be related to a shift in the North Atlantic Oscillation (NAO) towards a predominantly low phase during MM. The simulated climate anomalies are in very good agreement with reconstructions from proxy-data. Changes in the dynamical coupling between the troposphere and stratosphere were found in the MM simulation, indicating the importance of the stratosphere for climate change.
    Type: Article , PeerReviewed
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  • 13
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    Decadal-scale periodicities in the stratosphere associated with the solar cycle and the QBO (2008)
    AGU
    In:  Journal of Geophysical Research: Atmospheres, 113 (D5).
    Details
    Publication Date: 2020-07-24
    Description: An interactive two-dimensional model is used to analyze the response of the stratosphere to the 11-year solar cycle in the presence of a quasi-biennial oscillation (QBO). The purpose of the paper is to demonstrate how the solar cycle response of stratospheric ozone and temperature diagnosed from model simulations depends on the QBO. The analyses show that (1) the simulated response to the solar flux when no QBO is imposed is very similar in different periods, despite differences in the magnitude and variability of the solar forcing; (2) the apparent solar response of temperature and ozone is modified by the presence of an imposed QBO; and (3) the impact of the QBO on the derived solar response is greatly reduced when the observed QBO forcing is replaced by an idealized sinusoidal forcing. The impact of the QBO on the solar cycle analysis is larger when only two solar cycles are analyzed but is not negligible even for analysis of four solar cycles. Differences in the QBO contribution account for most of the differences in analyses of separate 22-year periods. The statistical significance is not always a reliable indicator that the QBO effect has been separated.
    Type: Article , PeerReviewed
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  • 14
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    Transfer of the solar signal from the stratosphere to the troposphere: Northern winter (2006)
    AGU (American Geophysical Union)
    In:  Journal of Geophysical Research: Atmospheres, 111 (D6).
    Details
    Publication Date: 2017-12-12
    Description: The atmospheric response to the solar cycle has been previously investigated with the Freie Universität Berlin Climate Middle Atmosphere Model (FUB-CMAM) using prescribed spectral solar UV and ozone changes as well as prescribed equatorial, QBO-like winds. The solar signal is transferred from the upper to the lower stratosphere through a modulation of the polar night jet and the Brewer-Dobson circulation. These model experiments are further investigated here to show the transfer of the solar signal from the lower stratosphere to the troposphere and down to the surface during Northern Hemisphere winter. Analysis focuses on the transition from significant stratospheric effects in October and November to significant tropospheric effects in December and January. The results highlight the importance of stratospheric circulation changes for the troposphere. Together with the poleward-downward movement of zonal wind anomalies and enhanced equatorward planetary wave propagation, an AO-like pattern develops in the troposphere in December and January during solar maximum. In the middle of November, one third of eddy-forced tropospheric mean meridional circulation and surface pressure tendency changes can be attributed to the stratosphere, whereas most of the polar surface pressure tendency changes from the end of November through the middle of December are related to tropospheric mechanical forcing changes. The weakening of the Brewer-Dobson circulation during solar maximum leads to dynamical heating in the tropical lower stratosphere, inducing circulation changes in the tropical troposphere and down to the surface that are strongest in January. The simulated tropospheric effects are identified as indirect effects from the stratosphere because the sea surface temperatures are identical in the solar maximum and minimum experiment. These results confirm those from other simplified model studies as well as results from observations.
    Type: Article , PeerReviewed
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  • 15
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    Modeling the whole atmosphere response to solar cycle changes in radiative and geomagnetic forcing (2007)
    AGU
    In:  Journal of Geophysical Research: Atmospheres, 112 (D23).
    Details
    Publication Date: 2020-07-23
    Description: The NCAR Whole Atmosphere Community Climate Model, version 3 (WACCM3), is used to study the atmospheric response from the surface to the lower thermosphere to changes in solar and geomagnetic forcing over the 11-year solar cycle. WACCM3 is a general circulation model that incorporates interactive chemistry that solves for both neutral and ion species. Energy inputs include solar radiation and energetic particles, which vary significantly over the solar cycle. This paper presents a comparison of simulations for solar cycle maximum and solar cycle minimum conditions. Changes in composition and dynamical variables are clearly seen in the middle and upper atmosphere, and these in turn affect terms in the energy budget. Generally good agreement is found between the model response and that derived from satellite observations, although significant differences remain. A small but statistically significant response is predicted in tropospheric winds and temperatures which is consistent with signals observed in reanalysis data sets.
    Type: Article , PeerReviewed
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  • 16
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    Dynamics of the middle atmosphere as simulated by the Whole Atmosphere Community Climate Model, version 3 (WACCM3) (2008)
    AGU
    In:  Journal of Geophysical Research: Atmospheres, 113 (D8).
    Details
    Publication Date: 2020-07-24
    Description: The Whole Atmosphere Community Climate Model, version 3 (WACCM3) is a state-of-the-art climate model extending from the Earth's surface to the lower thermosphere. In this paper we present a detailed climatology of the dynamics of the middle atmosphere as represented by WACCM3 at various horizontal resolutions and compare them to observations. In addition to the mean climatological fields, we examine in detail the middle atmospheric momentum budget as well as several lower and upper atmosphere coupling phenomena including stratospheric sudden warmings, the 2-day wave, and the migrating diurnal tide. We find that in large part, differences between WACCM3 and observations and the mean state of the model at various horizontal resolutions are related to gravity wave drag, which is parameterized in WACCM3 (and similar models). All three lower and upper atmosphere coupling processes examined show high sensitivity to the model's resolution.
    Type: Article , PeerReviewed
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  • 17
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    Climate-Ozone Connections (2007)
    WMO
    In:  In: Report of the 2006 Assessment of the Scientific Assessment Panel : SCIENTIFIC ASSESSMENT OF OZONE DEPLETION: 2006 - Pursuant to Article 6 of the Montreal Protocol on Substances that Deplete the Ozone Layer. World Meteorological Organization Global Ozone Research and Monitoring Project, 50 . WMO, pp. 1-53.
    Details
    Publication Date: 2012-09-07
    Type: Book chapter , NonPeerReviewed
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  • 18
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    Amplifying the Pacific Climate System Response to a Small 11-Year Solar Cycle Forcing (2009)
    American Association for the Advancement of Science (AAAS)
    In:  Science, 325 (5944). pp. 1114-1118.
    Details
    Publication Date: 2017-10-24
    Description: One of the mysteries regarding Earth’s climate system response to variations in solar output is how the relatively small fluctuations of the 11-year solar cycle can produce the magnitude of the observed climate signals in the tropical Pacific associated with such solar variability. Two mechanisms, the top-down stratospheric response of ozone to fluctuations of shortwave solar forcing and the bottom-up coupled ocean-atmosphere surface response, are included in versions of three global climate models, with either mechanism acting alone or both acting together. We show that the two mechanisms act together to enhance the climatological off-equatorial tropical precipitation maxima in the Pacific, lower the eastern equatorial Pacific sea surface temperatures during peaks in the 11-year solar cycle, and reduce low-latitude clouds to amplify the solar forcing at the surface.
    Type: Article , PeerReviewed
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  • 19
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    Amplifying the Pacific Climate System Response to a Small 11-Year Solar Cycle Forcing (2009)
    American Association for the Advancement of Science
    Details
    Publication Date: 2009-08-28
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science
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