The Caspian – Hindu Kush Index (CasHKI): a regulatory factor for dust activity over southwest Asia

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Kaskaoutis D.G., Houssos E.E., Rashki A., Francois P., Legrand M., Goto D., Bartzokas A., Kambezidis H.D., Takemura T. (2016)
Global and Planetary Change, 137, 10-23

Abstract

This work investigates the modulation in dust activity over southwest (SW) Asia attributed to changes in the mean sea level pressure (MSLP) between Caspian Sea and Hindu Kush during the summer months (JJAS) of the period 2000-2014. The MSLP anomalies obtained via NCEP/NCAR re-analysis are evaluated via a new climatology index, the Caspian – Hindu Kush Index (CasHKI), which is defined as CasHKI = MSLPanom.Caspia – MSLPanom.HK, over specific domains taken over Caspian Sea and Hindu Kush range. The changes in intensity of CasHKI are examined against dust activity and rainfall distributions over south Asia. The results show that increase in CasHKI intensity enhances the pressure gradient and the blow of northern wind, which leads to dust mobilization along the eastern Iran borders and enhanced continental outflow over the north Arabian Sea. Stronger near-surface winds associated with high CasHKI values activate the dust source regions over SW Asia, thus leading to significantly larger dust emissions and export, which are clearly detected by satellite remote sensing, i.e. Metoosat, OMI, MODIS. On the other hand, variations in CasHKI intensity have a much lesser effect on the Indian summer monsoon, consisting in 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. Model (MIROC-SPRINTARS) simulations of dust concentration and dust AOD over SW Asia are consistent with the satellite observations, highlighting for the first time, the modulation of the SW Asian dust activity by CasHKI.