Humidity of the tropical lower stratosphere: Observations and analysis |
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Authors: | S M Khaykin V A Yushkov L I Korshunov A N Luk’yanov J -P Pommereau J Nielsen H Vömel |
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Institution: | (1) Wegener Center for Climate and Global Change (WegCenter) and Institute for Geophysics, Astrophysics, and Meteorology (IGAM), University of Graz, Graz, Austria;(2) GeoForschungsZentrum Potsdam (GFZ), Potsdam, Germany |
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Abstract: | The results of measurements of water-vapor vertical profiles in the upper troposphere and stratosphere on board a meteorological
balloon with a FLASH-B optical fluorescent hygrometer (Russia) are presented. These data were obtained during two international
field campaigns in West Africa (August 2006) and Central America (August 2007). Eleven high-resolution water-vapor vertical
profiles measured in the course of these works make it possible to characterize the processes controlling humidity in the
tropical tropopause region. Layers with increased humidity are detected in the lower stratosphere over West Africa to the
level of the potential temperature 450 K. An analysis of satellite maps of the brightness temperature, balloon ozone measurements,
and aerosol scattering, as well as trajectory modeling, display the relation between the observed layers with increased humidity
and the phenomena of convective overshooting of the tropopause, as a result of which cold and ozone-depleted air penetrates
into the lower stratosphere together with ice particles, which, rapidly sublimating, locally increase the water-vapor concentration.
A comparison of the humidity data obtained in West Africa in 2006 and in Central America in 2007 reveals substantial distinctions
in values and vertical structures of water vapor, both in the tropopause region and in the middle stratosphere. |
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