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Beschreibung: A unique automated planetary boundary layer (PBL) retrieval algorithm is proposed as a common cross-platform method for use with commercially available ceilometers for implementation under the redesigned U.S. Environmental Protection Agency Photochemical Assessment Monitoring Stations program. This algorithm addresses instrument signal quality and screens for precipitation and cloud layers before the implementation of the retrieval methodology using the Haar wavelet covariance transform method. Layer attribution for the PBL height is supported with the use of continuation and time-tracking parameters, and uncertainties are calculated for individual PBL height retrievals. Commercial ceilometer retrievals are tested against radiosonde PBL height and cloud-base height during morning and late afternoon transition times, critical to air quality model prediction and when retrieval algorithms struggle to identify PBL heights. A total of 58 radiosonde profiles were used and retrievals for nocturnal stable layers, residual layers and mixing layers were assessed. Overall good agreement was found for all comparisons with one system showing limitations for the cases of nighttime surface stable layers and daytime mixing layer. It is recommended that nighttime shallow stable layer retrievals be performed with a recommended minimum height or with additional verification. Retrievals of residual layer heights and mixing layer comparisons revealed overall good correlations to radiosonde heights (correlation coefficients, r2, ranging from 0.89 – 0.96 and bias ranging from ~ -131 to +63 m, and r2 from 0.88 – 0.97 and bias from -119 to +101 m, respectively).

Print ISSN: 0739-0572

Digitale ISSN: 1520-0426

Thema: Geographie , Geologie und Paläontologie , Physik

Publiziert von American Meteorological Society

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Dynamical Diagnosis: A Comparison of Quasigeostrophy and Ertel Potential Vorticity (2008)

Nielsen-Gammon, John W. ; Gold, David A.

American Meteorological Society

In: Meteorological Monographs. 2008; 55: 183-202. Published 2008 Nov 01. doi: 10.1175/0065-9401-33.55.183.

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Publikationsdatum: 2008-11-01

Beschreibung: Advances in computer power, new forecasting challenges, and new diagnostic techniques have brought about changes in the way atmospheric development and vertical motion are diagnosed in an operational setting. Many of these changes, such as improved model skill, model resolution, and ensemble forecasting, have arguably been detrimental to the ability of forecasters to understand and respond to the evolving atmosphere. The use of nondivergent wind in place of geostrophic wind would be a step in the right direction, but the advantages of potential vorticity suggest that its widespread adoption as a diagnostic tool on the west side of the Atlantic is overdue. Ertel potential vorticity (PV), when scaled to be compatible with pseudopotential vorticity, is generally similar to pseudopotential vorticity, so forecasters accustomed to quasigeostrophic reasoning through the height tendency equation can transfer some of their intuition into the Ertel-PV framework. Indeed, many of the differences between pseudopotential vorticity and Ertel potential vorticity are consequences of the choice of definition of quasigeostrophic PV and are not fundamental to the quasigeostrophic system. Thus, at its core, PV thinking is consistent with commonly used quasigeostrophic diagnostic techniques.

Print ISSN: 0065-9401

Digitale ISSN: 1943-3646

Thema: Geographie , Geologie und Paläontologie , Physik

Publiziert von American Meteorological Society

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Ensemble Synoptic Analysis (2008)

Hakim, Gregory J. ; Torn, Ryan D.

American Meteorological Society

In: Meteorological Monographs. 2008; 55: 147-162. Published 2008 Nov 01. doi: 10.1175/0065-9401-33.55.147.

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Publikationsdatum: 2008-11-01

Beschreibung: Synoptic and mesoscale meteorology underwent a revolution in the 1940s and 1950s with the widespread deployment of novel weather observations, such as the radiosonde network and the advent of weather radar. These observations provoked a rapid increase in our understanding of the structure and dynamics of the atmosphere by pioneering analysts such as Fred Sanders. The authors argue that we may be approaching an analogous revolution in our ability to study the structure and dynamics of atmospheric phenomena with the advent of probabilistic objective analyses. These probabilistic analyses provide not only best estimates of the state of the atmosphere (e.g., the expected value) and the uncertainty about this state (e.g., the variance), but also the relationships between all locations and all variables at that instant in time. Up until now, these relationships have been determined by sampling in time by, for example, case studies, composites, and time-series analysis. Here the authors propose a new approach, ensemble synoptic analysis, which exploits the information contained in probabilistic samples of analyses at one or more instants in time. One source of probabilistic analyses is ensemble-based state-estimation methods, such as ensemble-based Kalman filters. Analyses from such a filter may be used to study atmospheric phenomena and the relationships between fields and locations at one or more instants in time. After a brief overview of a research-based ensemble Kalman filter, illustrative examples of ensemble synoptic analysis are given for an extratropical cyclone, including relationships between the cyclone minimum sea level pressure and other synoptic features, statistically determined operators for potential-vorticity inversion, and ensemble-based sensitivity analysis.

Print ISSN: 0065-9401

Digitale ISSN: 1943-3646

Thema: Geographie , Geologie und Paläontologie , Physik

Publiziert von American Meteorological Society

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Closed Anticyclones of the Subtropics and Midlatitudes: A 54-Yr Climatology (1950–2003) and Three Case Studies (2008)

Galarneau, Thomas J. ; Bosart, Lance F. ; Aiyyer, Anantha R.

American Meteorological Society

In: Meteorological Monographs. 2008; 55: 349-392. Published 2008 Nov 01. doi: 10.1175/0065-9401-33.55.349.

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Publikationsdatum: 2008-11-01

Beschreibung: The pioneering large-scale studies of cyclone frequency, location, and intensity conducted by Fred Sanders prompt similar questions about lesser-studied anticyclone development. The results of a climatology of closed anticyclones (CAs) at 200, 500, and 850 hPa, with an emphasis on the subtropics and midlatitudes, is presented to assess the seasonally varying distribution and hemispheric differences of these features. To construct the CA climatology, a counting program was applied to twice-daily 2.5° NCEP–NCAR reanalysis 200-, 500-, and 850-hPa geopotential height fields for the period 1950–2003. Stationary CAs, defined as those CAs that were located at a particular location for consecutive time periods, were counted only once. The climatology results show that 200-hPa CAs occur preferentially during summer over subtropical continental regions, while 500-hPa CAs occur preferentially over subtropical oceans in all seasons and over subtropical continents in summer. Conversely, 850-hPa CAs occur preferentially over oceanic regions beneath upper-level midocean troughs, and are most prominent in the Northern Hemisphere, and over midlatitude continents in winter. Three case studies of objectively identified CAs that produced heal waves over the United States, Europe, and Australia in 1995, 2003, and 2004, respectively, are presented to supplement the climatological results. The case studies, examining the subset of CAs than can produce heat waves, illustrate how climatologically hot continental tropical air masses produced over arid and semiarid regions of the subtropics and lower midlatitudes can become abnormally hot in conjunction with dynamically driven upper-level ridge amplification. Subsequently, these abnormally hot air masses are advected downstream away from their source regions in conjunction with transient disturbances embedded in anomalously strong westerly jets.

Print ISSN: 0065-9401

Digitale ISSN: 1943-3646

Thema: Geographie , Geologie und Paläontologie , Physik

Publiziert von American Meteorological Society

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An Empirical Perspective on Cold Fronts (2008)

Kessler, Edwin

American Meteorological Society

In: Meteorological Monographs. 2008; 55: 97-108. Published 2008 Nov 01. doi: 10.1175/0065-9401-33.55.97.

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Publikationsdatum: 2008-11-01

Beschreibung: Oklahoma Mesonetwork data are used to illustrate important atmospheric features that are not well shown by the usual synoptic data. For example, some shifts of wind from south to north that are shown as cold fronts on synoptic charts are not cold fronts by any plausible definition. As previously discussed by Fred Sanders and others, such errors in analysis can be reduced by knowledge of the wide variety of weather phenomena that actually exists, and by more attention to temperatures at the earth's surface as revealed by conventional synoptic data. Mesoscale data for four cases reinforce previous discussions of the ephemeral nature of fronts and deficiencies in the usual analyses of cold fronts. One type of misanalyzed case involves post-cold-frontal boundary layer air that is warmer than the prefrontal air. A second type is usually nocturnal, with a rise of local temperature during disruption of an inversion and a wind shift with later cooling that accompanies advection of a climatological gradient of temperature.

Print ISSN: 0065-9401

Digitale ISSN: 1943-3646

Thema: Geographie , Geologie und Paläontologie , Physik

Publiziert von American Meteorological Society

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Back to Norway: An Essay (2008)

Emanuel, Kerry

American Meteorological Society

In: Meteorological Monographs. 2008; 55: 87-96. Published 2008 Nov 01. doi: 10.1175/0065-9401-33.55.87.

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Publikationsdatum: 2008-11-01

Beschreibung: The advent of the polar front theory of cyclones in Norway early in the last century held that the development of fronts and air masses is central to understanding midlatitude weather phenomena. While work on fronts continues to this day, the concept of air masses has been largely forgotten, superseded by the idea of a continuum. The Norwegians placed equal emphasis on the thermodynamics of airmass formation and on the dynamical processes that moved air masses around; today, almost all the emphasis is on dynamics, with little published literature on diabatic processes acting on a large scale. In this essay, the author argues that a lack of understanding of large-scale diabatic processes leads to an incomplete picture of the atmosphere and contributes to systematic errors in medium- and long-range weather forecasts. At the same time, modern concepts centered around potential vorticity conservation and inversion lead one to a redefinition of the term "air mass" that may have some utility in conceptualizing atmospheric physics and in weather forecasting.

Print ISSN: 0065-9401

Digitale ISSN: 1943-3646

Thema: Geographie , Geologie und Paläontologie , Physik

Publiziert von American Meteorological Society

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