Investigation of the 'elevated heat pump' hypothesis of the Asian monsoon using satellite observations

摘要

The "elevated heat pump" (EHP) hypothesis has been a topic of intensiveresearch and controversy. It postulates that aerosol-induced anomalous mid-and upper-tropospheric warming in the Himalayan foothills and above theTibetan Plateau leads to an early onset and intensification of Asian monsoonrainfall. This finding is primarily based on results from a NASAfinite-volume general circulation model run with and without radiativeforcing from different types of aerosols. In particular, black carbonemissions from sources in northern India and dust from Western China,Afghanistan, Pakistan, the Thar Desert, and the Arabian Peninsula drive themodeled anomalous heating. Since the initial discussion of the EHP hypothesisin 2006, the aerosol–monsoon relationship has been investigated usingvarious modeling and observational techniques. The current study takes anovel observational approach to detect signatures of the "elevated heatpump" effect on convection, precipitation, and temperature for contrastingaerosol content years during the period of 2000–2012. The analysis benefitsfrom unique high-resolution convection information inferred from Meteosat-5observations as available through 2005. Additional data sources includetemperature data from the NCEP/NCAR Reanalysis and the European Reanalysis(ERA-Interim) precipitation data from the Global Precipitation ClimatologyProject (GPCP), aerosol optical depth from the Multi-angle ImagingSpectroradiometer (MISR) and the Moderate Resolution ImagingSpectroradiometer (MODIS), and aerosol optical properties from the Modern-EraRetrospective Analysis for Research and Applications (MERRA) aerosolreanalysis. Anomalous upper-tropospheric warming and the early onset andintensification of the Indian monsoon were not consistently observed duringthe years with high loads of absorbing aerosols. Possibly, model assumptionsand/or unaccounted semi-direct aerosol effects caused the disagreementbetween observed and hypothesized behavior.