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  • Author or Editor: Stéphanie Vénel x
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Philippe Drobinski
,
Fatima Karbou
,
Peter Bauer
,
Philippe Cocquerez
,
Christophe Lavaysse
,
Terry Hock
,
David Parsons
,
Florence Rabier
,
Jean-Luc Redelsperger
, and
Stéphanie Vénel

Abstract

During the international African Monsoon Multidisciplinary Analysis (AMMA) project, stratospheric balloons carrying gondolas called driftsondes capable of dropping meteorological sondes were deployed over West Africa and the tropical Atlantic Ocean. The goals of the deployment were to test the technology and to study the African easterly waves, which are often the forerunners of hurricanes. Between 29 August and 22 September 2006, 124 sondes were dropped over the seven easterly waves that moved across Africa into the Atlantic between about 10° and 20°N, where almost no in situ vertical information exists. Conditions included waves that developed into Tropical Storm Florence and Hurricanes Gordon and Helene. In this study, a selection of numerical weather prediction model outputs has been compared with the dropsondes to assess the effect of some developments in data assimilation on the quality of analyses and forecasts. By comparing two different versions of the Action de Recherche Petite Echelle Grande Echelle (ARPEGE) model of Météo-France with the dropsondes, first the benefits of the last data assimilation updates are quantified. Then comparisons are carried out using the ARPEGE model and the Integrated Forecast System (IFS) model of the European Centre for Medium-Range Weather Forecasts. It is shown that the two models represent very well the vertical structure of temperature and humidity over both land and sea, and particularly within the Saharan air layer, which displays humidity below 5%–10%. Conversely, the models are less able to represent the vertical structure of the meridional wind. This problem seems to be common to ARPEGE and IFS, and its understanding still requires further investigations.

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Stephen A. Cohn
,
Terry Hock
,
Philippe Cocquerez
,
Junhong Wang
,
Florence Rabier
,
David Parsons
,
Patrick Harr
,
Chun-Chieh Wu
,
Philippe Drobinski
,
Fatima Karbou
,
Stéphanie Vénel
,
André Vargas
,
Nadia Fourrié
,
Nathalie Saint-Ramond
,
Vincent Guidard
,
Alexis Doerenbecher
,
Huang-Hsiung Hsu
,
Po-Hsiung Lin
,
Ming-Dah Chou
,
Jean-Luc Redelsperger
,
Charlie Martin
,
Jack Fox
,
Nick Potts
,
Kathryn Young
, and
Hal Cole

Constellations of driftsonde systems— gondolas floating in the stratosphere and able to release dropsondes upon command— have so far been used in three major field experiments from 2006 through 2010. With them, high-quality, high-resolution, in situ atmospheric profiles were made over extended periods in regions that are otherwise very difficult to observe. The measurements have unique value for verifying and evaluating numerical weather prediction models and global data assimilation systems; they can be a valuable resource to validate data from remote sensing instruments, especially on satellites, but also airborne or ground-based remote sensors. These applications for models and remote sensors result in a powerful combination for improving data assimilation systems. Driftsondes also can support process studies in otherwise difficult locations—for example, to study factors that control the development or decay of a tropical disturbance, or to investigate the lower boundary layer over the interior Antarctic continent. The driftsonde system is now a mature and robust observing system that can be combined with flight-level data to conduct multidisciplinary research at heights well above that reached by current research aircraft. In this article we describe the development and capabilities of the driftsonde system, the exemplary science resulting from its use to date, and some future applications.

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