The Caspian Sea-Hindu Kush Index (CasHKI): A regulatory factor for dust activity over southwest Asia

Abstract This work investigates the modulation in dust activity over southwest (SW) Asia attributed to changes in the mean sea level pressure (MSLP) between the Caspian Sea (CS) and Hindu Kush (HK) during the summer months (June–July–August–September, JJAS) of the period 2000–2014. The MSLP anomalies obtained via NCEP/NCAR re-analysis are evaluated via a new climatology index, the Caspian Sea – Hindu Kush Index ( CasHKI ), which is defined as CasHKI = MSLP anom.CS  − MSLP anom.HK , over specific domains taken over the CS and HK. The changes in CasHKI intensity are examined against dust activity and rainfall distributions over south Asia. The satellite remote sensing (Meteosat, OMI, MODIS) analyses show that high CasHKI values corresponding to enhanced pressure gradient between the CS and the HK, are associated with intensification of northerly winds, increased dust emissions and transportation over SW Asia and north Arabian Sea. In contrast, variations in CasHKI intensity do not seem to have a significant effect on the Indian summer monsoon. Only a slight decrease of precipitation over the southern Indian peninsula and the neighboring oceanic areas and an increase of precipitation along the Ganges Basin and Himalayan range are found to be related to high CasHKI values. Model (MIROC-SPRINTARS) simulations of dust concentration and dust AOD (Aerosol Optical Depth) over SW Asia are consistent with the satellite observations, highlighting for the first time the modulation of the SW Asian dust activity by CasHKI.