Abstract
Abstract. Spatial and temporal variability of the Marine Atmospheric Boundary Layer (MABL) height for the Indian Ocean Experiment (INDOEX) study period are examined using the data collected through Cross-chained LORAN (Long-Range Aid to Navigation) Atmospheric Sounding System (CLASS) launchings during the Northern Hemispheric winter monsoon period. This paper reports the results of the analyses of the data collected during the pre-INDOEX (1997) and the INDOEX-First Field Phase (FFP; 1998) in the latitude range 14°N to 20°S over the Arabian Sea and the Indian Ocean. Mixed layer heights are derived from thermodynamic profiles and they indicated the variability of heights ranging from 400m to 1100m during daytime depending upon the location. Mixed layer heights over the Indian Ocean are slightly higher during the INDOEX-FFP than the pre-INDOEX due to anomalous conditions prevailing during the INDOEX-FFP. The trade wind inversion height varied from 2.3km to 4.5km during the pre-INDOEX and from 0.4km to 2.5km during the INDOEX-FFP. Elevated plumes of polluted air (lofted aerosol plumes) above the marine boundary layer are observed from thermodynamic profiles of the lower troposphere during the INDOEX-FFP. These elevated plumes are examined using 5-day back trajectory analysis and show that one group of air mass travelled a long way from Saudi Arabia and Iran/Iraq through India before reaching the location of measurement, while the other air mass originates from India and the Bay of Bengal.
Highlights
Mixed layer heights over the Indian Ocean are slightly higher during the INDian Ocean EXperiment (INDOEX)-First Field Phase (FFP) than the preINDOEX due to anomalous conditions prevailing during the INDOEX-FFP
Ciated with high moisture content in the mixed layer, as well as a weak transition layer, mostly cloudy skies, all of which could have enabled the increase in the height of the conditionally unstable layer, due to which the trade wind inversion height is forced to greater altitudes of around
Though a considerable amount of work has gone into studying the structure and characteristics of Marine Atmospheric Boundary Layer (MABL) over the Pacific Ocean and the Atlantic Ocean, the Indian Ocean remained one of the least explored regions
Summary
INDian Ocean EXperiment (INDOEX) is an international field campaign research programme aimed at understanding the interaction between aerosols and radiation, the transport and dispersion of trace species and pollutants of continental origin over the Indian Ocean during the north-east Asian winter monsoon period (Ramanathan et al, 1995; Mitra, 1999). In the frame of the INDOEX, extensive dynamical and thermodynamical measurements were made over the Arabian Sea and Indian Ocean during the winter (dry) season (Ramana et al, 2004). The present study is based on tropospheric soundings made from the ship platform of ORV-SagarKanya during the preINDOEX (27 December 1996–31 January 1997) in the During the Northern Hemispheric winter the meridional latitude range 15◦ N to 14◦ S and the INDOEX-FFP (18 circulation over the Arabian Sea and the Indian Ocean is February 1998–31 March 1998) in the latitude range 15◦ N often idealized as an equatorward flow capped by the trade to 20◦ S. Tal variability of the Sea Surface Temperature (SST) and air Potential temperature (θ ), virtual potential temperature masses due to meridional advection during the pre-INDOEX (θv ), mixing ratio (q), saturated mixing ratio (qs ), equivalent and the INDOEX-FFP through ship-borne in-situ measurepotential temperature (θe ) and saturated equivalent potential ments
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