Selected   Results

The "Elevated Heat Pump" Hypothesis

It has been postulated that aerosol-induced anomalous mid-and upper-tropospheric warming above the Tibetan Plateau leads to an early onset and intensification of monsoon rainfall. This so-called "Elevated Heat Pump" effect is based on results from the NASA finite-volume general circulation model with and without radiative forcing from different types of aerosols (Lau et al., 2006)*.
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An observational approach to detect signatures of the "Elevated Heat Pump" effect in the cloud cover and cloud type distributions as derived from Meteosat-5 data over the Asian Monsoon region, has been undertaken (Wonsick et al., 2009). The satellite data are supplemented with surface temperature data from the NCEP/NCAR Reanalysis and precipitation data from the Global Precipitation Climatology Project. Clouds, convection, precipitation, and surface temperature features for the highest-aerosol year of the current decade (2004) are compared with lower-aerosol content years during the period 2000 - 2005. Selected findings are illustrated here:

Evaluation of the EHP hypothesis: Selected findings

• Anomalous warming over the Tibetan Plateau was observed but appears too far north to be associated with the absorbing aerosols in the Indo-Gangetic Basin

Figure 1. Difference in NCEP/NCAR Reanalysis 400 mb Temperature Anomaly (°C)
April 2004 - April 2001

• Enhanced convection in the foothills of the Himalayas and northward shift in precipitation in May was not observed

Figure 2. Difference in frequency of occurrence of convection for May of a) 2004-2000, b) 2004-2001, c) 2004-2002, d) 2004-2003, e) 2004-2005

* Lau K-M, Kim MK, Kim KM (2006). Asian summer monsoon anomalies induced by aerosol direct forcing: the role of the Tibetan Plateau. Clim Dyn 26:855-864