The three‐dimensional, regional and large‐scale atmospheric circulation during the “Dust Bowl” is analyzed based on newly available historical upper‐air data and reconstructed upper‐level fields. The Great Plains Low Level Jet, transporting moisture into the region, was weakened on its eastern side, shallower, and penetrated less far north than during wet years. Nocturnal convection was likely suppressed by increased stability. Strong mid‐tropospheric ridging was found over the Great Plains, and upper‐tropospheric flow anomalies extended from the North Pacific across North America to the Atlantic. These findings provide a dynamical view of the “Dust Bowl” droughts, some aspects of which are distinct from other droughts. It is demonstrated that this is important for assessing predictive capabilities of current modeling systems.
T o improve our understanding of global weather and climate variability and its change under the inf luence of global warming, it is vital to extend our knowledge about the atmospheric state and variability in the past. Current reanalysis datasets [the National Centers for Environmental Prediction (NCEP)-National Center for Atmospheric Research (NCAR) 50-Year Reanalysis (Kistler et al. 2001) and the 40-yr European Centre for MediumRange Weather Forecasts (ECMWF) Re-Analysis (ERA-40; Uppala et al. 2005)] provide detailed information on the atmosphere during the past 60 years. The first half of the twentieth century, however-which features some very prominent climate fluctuations such as A systematic compilation of global upperair data from the first half of the twentieth century has weather and climate applications and may be useful in reanalyses.Two men launching a meteorological kite (a so-called "umbrella kite"). This type of kite amongst others was used during the first half of the twentieth century (e.g., at the observatory of Lindenberg, Germany), to obtain vertical profiles of atmospheric variables like temperature, pressure and humidity. The umbrella kite was also used during field expeditions, for launches on board ships, and as an observational platform for military air weather service and artillery during World War I. A still valid world record is connected to the umbrella kite: a maximum altitude of 9,740 m a.s.l. was reached during an ascent on August 1st 1919 by a combination of several such kites. (Photo courtesy of www.wetterdrachen.de.)
The European Arctic experienced a pronounced warming around 1920 and a sustained warm period in the 1920s and 1930s. The causes of this climatic event are not fully known. However, understanding this event is considered important for assessing current and future climate change in the Arctic. Here we investigate the role of atmospheric circulation variability based on newly available historical upper-air data and statistical reconstructions of atmospheric circulation. The strongest warming at the ground from the 1910s to the 1920s and 1930s was found in wintertime. Historical upper-air data in this region from the 1930s show warm temperatures also in the lower troposphere. Reconstructed geopotential height f elds suggest stronger than normal meridional transport of warm air into the European Arctic during the warm period compared to the preceding cold period. We propose that the 1920-1940 warm period can be subdivided into two periods with distinct circulation regimes: During the 1920s, warm, relatively clean air masses from the North Atlantic lead to a warming, while during the 1930s warm, rather polluted air masses from Western Europe played an important role. This is ref ected in a sudden increase in sulphate concentrations in an ice core from Svalbard around 1930. The aerosols might have amplif ed the warming via changing cloud long wave emissivity, but this mechanism remains to be further studied. The circulation anomalies in the North Atlantic region during the early 20 th century warm period that are shown in this paper form an observation-based counterpart against which model studies can be compared. Zusammenfassung Der skandinavisch-europäische Sektor der Arktis erfuhr um 1920 eine ausgeprägte Erwärmung, die von einer anhaltend warmen Periode in den 20er und 30er Jahren gefolgt wurde. Die Ursachen für dieses Klimaereignis sind bis jetzt nicht vollständig bekannt, sein Verständnis erscheint jedoch wichtig, um die aktuellen und für die Zukunft vorhergesagten Veränderungen im arktischen Klimasystem korrekt zu beurteilen. Hier untersuchen wir die Rolle der Variabilität der atmosphärischen Zirkulation auf der Grundlage neu verfügbarer, historischer Messdaten aus der freien Atmosphäre und statistischer Rekonstruktionen der atmosphärischen Zirkulation. Die stärkste, bodennahe Erwärmung wurde von 1910 bis in die 30er Jahre im Winter registriert. Die historischen Messdaten aus der Region zeigen, dass die Erwärmung sich zumindest in den 30er Jahren auch auf die untere Troposphäre erstreckte. Rekonstruierte Felder der geopotentiellen Höhe legen einen uberdurchschnittlich ausgeprägten Meridionaltransport von Luftmassen aus südlichen Richtungen in die europäische Arktis während der warmen Periode im Vergleich zur vorhergehenden kalten Periode nahe. Aus der Analyse der Felder treten zwei signif kant unterschiedliche Zirkulationsregime während der Periode 1920-1940 hervor: Während der 20er Jahre führten warme, aber relativ saubere Luftmassen vom Nordatlantik zur beobachteten Erwärmung, wohingegen während der 30er Jahre ...
This work presents statistically reconstructed global monthly mean fields of temperature and geopotential height (GPH) up to 100 hPa for the period . For the statistical model several thousand predictors were used, comprising a large amount of historical upper-air data as well as data from the earth's surface. In the calibration period , the statistical models were fit using the 40-yr European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-40) as the predictand. After the weighting of the predictors, principal component (PC) analyses were performed on both the predictand and predictor dataset. Multiple linear regression models relate each principal component time series from the predictand with an optimal subset of principal component time series from the predictor. To assess the quality of the reconstructions, statistical split-sample validation (SSV) experiments were performed within the calibration period. Furthermore, the reconstructions were compared with independent historical upper-air and total ozone data. Based on the SSV experiment, this study obtained good reconstructions for temperature and GPH in the Northern Hemisphere; however, the skill in the tropics and the Southern Hemisphere was much lower. The reconstruction skill shows a clear annual cycle with the highest values in January. The lower levels were better reconstructed except in the tropics where the highest levels showed the best skill. With the inclusion of a considerable amount of upper-air data after 1939 the skill increased substantially. The fields were analyzed for selected months in the 1920s and 1930s to demonstrate the usefulness of the reconstructions. It is shown that the reconstructions are able to capture regional-to-global dynamical features.
A multi-data set comparison of the vertical structure of temperature variability and change over the Arctic during the past 100 yearsBrönnimann, S; Grant, A N; Compo, G P; Ewen, T; Griesser, T; Fischer, A M; Schraner, M; Stickler, A Abstract: We compare the daily, interannual, and decadal variability and trends in the thermal structure of the Arctic troposphere using eight observation-based, vertically resolved data sets, four of which have data prior to 1948. Comparisons on the daily scale between historical reanalysis data and historical upper-air observations were performed for Svalbard for the cold winters 1911/1912 and 1988/1989, the warm winters 1944/1945, and the International Geophysical Year 1957/1958. Excellent agreement is found at mid-tropospheric levels. Near the ground and at the tropopause level, however, systematic differences are identified. On the interannual time scale, the correlations between all data sets are high, but there are systematic biases in terms of absolute values as well as discrepancies in the magnitude of the variability. The causes of these differences are discussed. While none of the data sets individually may be suitable for trend analysis, consistent features can be identified from analyzing all data sets together. To illustrate this, we examine trends and 20-year averages for those regions and seasons that exhibit large sea-ice changes and have enough data for comparison. In the summertime Pacific Arctic and the autumn eastern Canadian Arctic, the lower tropospheric temperature anomalies for the recent two decades are higher than in any previous 20-year period. AbstractWe compare the variability and trends in the thermal structure of the Arctic troposphere in eight observation-based, vertically resolved data sets, four of which have data prior to 1948.
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