Aerological observations in the Tropics in the Early Twentieth Century

Abstract

In the first decades of the 20 th century, aerological observations were for the first time performed in tropical regions. One of the most prominent endeavours in this respect was ARTHUR BERSON's aerological expedition to East Africa. Although the main target was the East African monsoon circulation, the expedition provided also other insights that profoundly changed meteorology and climatology. BERSON observed that the tropical tropopause was much higher and colder than that over midlatitudes. Moreover, westerly winds were observed in the lower stratosphere, apparently contradicting the high-altitude equatorial easterly winds that were known since the Krakatoa eruption (''Krakatoa easterlies''). The puzzle was only resolved five decades later with the discovery of the Quasi-Biennial Oscillation (QBO). In this paper we briefly summarize the expedition of BERSON and review the results in a historical context and in the light of the current research. In the second part of the paper we re-visit BERSON's early aerological observations, which we have digitized. We compare the observed wind profiles with corresponding profiles extracted from the ''Twentieth Century Reanalysis'', which provides global three-dimensional weather information back to 1871 based on an assimilation of sea-level and surface pressure data. The comparison shows a good agreement at the coast but less good agreement further inland, at the shore of Lake Victoria, where the circulation is more complex. These results demonstrate that BERSON's observations are still valuable today as input to current reanalysis systems or for their validation.

ERA-CLIM: Historical Surface and Upper-Air Data for Future Reanalyses

“…The assimilation of these data into ERA-20C and other reanalyses will produce valuable feedback information to the observations community; such information might be used to produce a "corrected" version of the ERA-CLIM and CHUAN datasets. The ERA-CLIM upper-air data provide an independent reference for the validation of other products such as 20CR (e.g., Brönnimann and Stickler 2013). Also, observation errors can be estimated directly from the observations (Wartenburger et al 2013).…”

Description of the ERA-CLIM historical upper-air data

“…The inventoried expedition reports cover amongst others the German East Africa Expedition 1908 (Berson, 1910;Süring, 2013;Brönnimann and Stickler, 2013a), the 20 Swiss Greenland Expedition 1912/13 (de Quervain et al, 1913, the Norwegian North Polar Expedition with the Maud 1918-25 (Sverdrup, 1933a, the German Atlantic Expedition with the research vessel Meteor 1925-27 (Kuhlbrodt andReger, 1933;Stickler and Brönnimann, 2013b), the Greenland Expedition of the University of Michigan ESSDD 6,2013 Description of the ERA-CLIM historical upper-air data 1926-31 (Hobbs andFergusson, 1931), the German Greenland Expedition 1930/31 (Holzapfel et al, 1939, the Byrd Antarctic Expeditions 1928-30 and 1930-35 (Grimminger and Haines, 1939, and the Canadian Polar Year Expeditions 1932/33 (Meteorological Services of Canada, 1940. The data from the expeditions to the polar regions are also discussed in Brönnimann and Stickler (2013b).…”

“…Also some early East Asian upper-air data sources, for China during the first half of the 1930s (National Research Institute of Meteorology 1930Meteorology , 1931Meteorology , 1932Meteorology , 1933Meteorology , 1934Meteorology , 1935Haude, 1940), and for Korea and China from Japanese, formerly classified military WWII observations (Central Meteorological Observatory, 1950a-g), were discovered (see also Stickler and Brönnimann, 2013a).…”

“…for analysing past weather extremes, can be 10 found in Stickler et al (2013a), see also their Figs. 2), the imaging and digitisation process (Sect.…”

Multidecadal variations of the effects of the Quasi-Biennial Oscillation on the climate system

“…In the meantime, we have digitized a large amount of additional historical upper-air data (Stickler et al, 2014a), which partly cover the equatorial stratosphere. Among the new data are Berson's 1908 observations in East Africa (Brönnimann and Stickler, 2013), 1910-1911wind profiles from Batavia, 1925-1927 profiles from cruises of the research vessel Meteor (Stickler et al, 2015), as well as several other measurements.…”