The Caspian Sea – Hindu Kush Index (CasHKI): definition, meteorological influences and Dust activities over southwest Asia

This work introduces for the first time a new meteorology/climatology Index over Asia, the so-called “Caspian Sea – Hindu Kush Index (CasHKI)”, which consists of changes in the mean sea level pressure (MSLP) gradient between two geographical domains over the Caspian Sea (40-50oN, 50-55oE) and Hindu Kush (35-40oN, 70-75oE). CasHKI is defined as the difference in MSLP anomalies between the Caspian Sea and Hindu Kush (MSLPanom.Casp – MSLPanom.HK) and is examined during the summer months (June- September) of 2000-2014 in view of modulating the atmospheric and climate dynamics and dust activity over southwest (SW) Asia. The CasHKI intensity and long-term trends are mostly modulated by the evolution in MSLP anomalies over the Caspian Sea, while the respective changes in Hindu Kush contribute to the CasHKI trends. A neutral-to-slight increasing trend (not statistically significant) in CasHKI is shown in all months during 2000-2014. The intensity in CasHKI enhances the MSLP over central Asia and deepens the Indo-Pakistan thermal low associated with the Indian summer monsoon. Larger wind speeds associated with a decrease in visibility, increase in dust emissions and slightly lower temperatures over Zabol are observed for the high CasHKI values. In synopsis, the high CasHKI modes enhance the near-surface and mid-troposphere northerlies over SW Asia, thus increasing the activation of the dust-sources and enhance the Asian continental outflow over the Arabian Sea.