Asymmetry and Non-linearity in Upper Tropospheric Humidity Variability
Abstract
Changes in upper tropospheric humidity (UTH) are important in understanding the climatic response to increased anthropogenic forcing. This paper explores the asymmetry and non-linearity in the response of subtropical UTH to tropical intraseasonal forcing. HIRS (High Resolution Infrared Sounder) UTH data with pentad time resolution, spanning the period January 1979 to December 1998, were used and compared with ERA-40 (European Centre for Medium-Range Weather Forecasts 40 year Reanalysis) UTH and dynamical fields. During northern winter, subtropical UTH anomalies, varying on intraseasonal timescales, propagate eastwards from northern Africa to the central Pacific. These anomalies are associated with the Rossby response to tropical intraseasonal heating in a baroclinic atmosphere. There is a discontinuity in the propagation of moist anomalies over the Tibetan Plateau, whilst dry anomalies show reduced propagation in the lee. This is consistent with the expected evolution of cyclones and anticyclones incident on high topography. Correlations of five-day mean UTH show no significant linear correlation between moist anomalies over Indonesia and subtropical anomalies to the north. This appears to be explained by the limitation of dry anomalies in the region of low ambient vorticity south of the East Asian Jet Stream.
- Publication:
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AGU Spring Meeting Abstracts
- Pub Date:
- May 2004
- Bibcode:
- 2004AGUSM.A33A..02K
- Keywords:
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- 0365 Troposphere: composition and chemistry;
- 3309 Climatology (1620)