† The contribution of R. J. Allan was written in the course of his employment at the Met Office, UK, and is published with the permission of the Controller of HMSO and the Queen's Printer for Scotland. ‡ The contributions of these authors were prepared as part of their official duties as US Federal Government employees.The Twentieth Century Reanalysis (20CR) project is an international effort to produce a comprehensive global atmospheric circulation dataset spanning the twentieth century, assimilating only surface pressure reports and using observed monthly sea-surface temperature and sea-ice distributions as boundary conditions. is similar to that of current three-day operational NWP forecasts. Intercomparisons over the second half-century of these surface-based reanalyses with other reanalyses that also make use of upper-air and satellite data are equally encouraging.It is anticipated that the 20CR dataset will be a valuable resource to the climate research community for both model validations and diagnostic studies. Some surprising results are already evident. For instance, the long-term trends of indices representing the North Atlantic Oscillation, the tropical Pacific Walker Circulation, and the Pacific-North American pattern are weak or non-existent over the full period of record. The long-term trends of zonally averaged precipitation minus evaporation also differ in character from those in climate model simulations of the twentieth century.

The International Surface Pressure Databank (ISPD) is the world's largest collection of global surface and sea-level pressure observations. It was developed by extracting observations from established international archives, through international cooperation with data recovery facilitated by the Atmospheric Circulation Reconstructions over the Earth (ACRE) initiative, and directly by contributing universities, organizations, and countries. The dataset period is currently 1768-2012 and consists of three data components: observations from land stations, marine observing systems, and tropical cyclone best track pressure reports. Version 2 of the ISPD (ISPDv2) was created to be observational input for the Twentieth Century Reanalysis Project (20CR) and contains the quality control and assimilation feedback metadata from the 20CR. Since then, it has been used for various general climate and weather studies, and an updated version 3 (ISPDv3) has been used in the ERA-20C reanalysis in connection with the European Reanalysis of Global Climate Observations project (ERA-CLIM). The focus of this paper is on the ISPDv2 and the inclusion of the 20CR feedback metadata. The Research Data Archive at the National Center for Atmospheric Research provides data collection and access for the ISPDv2, and will provide access to future versions.

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.)