Climate response of the south Asian monsoon system to West Asia, Tibetan Plateau and local dust emissions

The equilibrium climate response of the south Asian monsoon (SAM) system to West Asia (WA), Tibetan Plateau (TP) and local dust emissions is investigated through a series of systematically designed idealized numerical experiments using CESM1-SOM, an atmospheric general circulation model coupled with a slab ocean model. Our results show that while an increased (decreased) dust emissions from the WA region produces a significant positive impact in the range of 0.20-0.40 mm/day (negative impact similar to 0.40-0.60 mm/day) on the summer monsoon precipitation over south Asia particularly over the Indian subcontinent, a perpetual perturbation ranging from complete suppression to nearly doubling of dust emissions from the TP region or locally within south Asia yield relatively weaker and largely insignificant responses in the seasonal mean monsoon climate over south Asia. Distinctly opposite responses of the SAM system are noted to the suppression and enhancement of dust emissions from the WA region. A perpetual enhancement (suppression) of dust emissions from the WA region results in atmospheric circulation changes and alters the atmospheric temperature distribution over the south Asian region by warming (cooling) the free troposphere in such a way that it strengthens (weakens) the crucial north-south meridional mid-to-upper tropospheric temperature gradient as well as the magnitude of the vertical shear of zonal winds during the beginning of the summer monsoon season which further results in atmospheric circulation by favoring (opposing) the prevailing low level south-westerly winds and upper level northerly winds, leading to a strengthening (weakening) of the climatological summertime local Hadley cell circulation and leading to an increase (a decrease) in seasonal mean precipitation across most parts of South Asia and most significantly during the month of June.