Validation of multi-channel scanning microwave radiometer on-board Oceansat-I

Sea surface temperature (SST), sea surface wind speed (WS) and columnar water vapour (WV) derived from Multi-frequency Scanning Microwave Radiometer (MSMR) sensor on-board IRS-P4 (Oceansat-I) were validated against the in situ measurements from ship, moored buoy (MB), drifting buoy (DB) and autonomous weather station (AWS). About 1400 satellite in situ match-ups were used for the validation of SST and WS, while only 60 match-ups were available for the validation of WV. Therefore specific humidity, Q a was used as a proxy for validating WV. The drifting buoy SSTs showed good correlation with the satellite values (r = 0.84). The correlation of MB SSTs was better during night when the WS varied between 0 and 10 m/s. During the day, correlation peaked for higher wind speeds (> 10 m/s). MB (r > 0.80) was relatively better than AWS (r � 0.70) and ship (r < 0.50) for validating satellite-derived WS. Daytime winds exhibited better correlation with satellite values when measured from ocean platforms (MB and ship), but the winds measured from land-based platforms (AWS) were closer to satellite values during night-time. Q a values consistently showed higher correlation with satellite values during night-time. The low root mean square deviation (RMSD) of DB SST (1.17°C) and MB WS (1.52 m s -1) is within the achievable accuracy of the microwave sensor when validated with data collected over the tropical Indian Ocean. The RMSD of Q a (1.81 g kg -1), however, falls much beyond the attainable accuracy of the microwave sensor

Does sea level pressure modulate the dynamic and thermodynamic forcing in the tropical Indian Ocean?

Three areas, the north Indian Ocean (NIO), the equatorial Indian Ocean (EIO) and the south Indian Ocean (SIO), were chosen over the tropical Indian Ocean to investigate the dependency of sea surface temperature (SST), wind speed (WS) and sea level pressure (SLP) on latent heat flux (LHF). The dynamic and thermodynamic behaviour of the tropical Indian Ocean was studied from the trends of the scatter represented by the mean and standard deviation of LHF, WS and humidity gradient, q s - q a, D q, binned in 1°C SST interval plotted against SST. The direct linear relationship of LHF with SST reverses at some point to display an inverse relationship when the atmosphere is coupled with the ocean. The point at which the reversal takes place marks the threshold SST which appears to have an inherent relationship with the SLP, especially when the ocean-atmosphere system is coupled. North of 5° S, the LHF peaks at the threshold SST of 27.5°C and decreases gradually on either side. The resemblance of the SST-LHF curve of SIO and EIO to that of the equatorial Pacific Ocean can be attributed to the fact that both regimes fell under the same pressure band that covers the equatorial Pacific. Shifting of LHF maxima to a lower SST regime as SLP increases is noticed at southern and northern latitudes, while such a regime shift is not noticed at the equator. This phenomenon can be attributed to relatively weaker air-sea coupling and subsequent lower LHF production at the EIO

Thermodynamic structure of the Atmospheric Boundary Layer over the Arabian Sea and the Indian Ocean during pre-INDOEX and INDOEX-FFP campaigns

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

Environmental set-up and tidal propagation in a tropical estuary with dual connection to the sea (SW Coast of India)

The Kochi Backwater (KB) is the second largest wetland system in India. It is connected to the sea at Fort Kochi and Munambam (Pallipuram) (30 km north of Kochi). As the tide is forced through two openings, its propagation in the backwater system is very complicated, particularly in the northern arm of the estuary. Using synchronous water level (WL) and current measurements in the KB from a network of stations during 2007-2008, it was convenient to demarcate the northern KB into two distinct regions according to the tidal forcing from the north (Pallipuram) and south (Vallarpadam). This demarcation is useful for computing the propagation speeds of the dominant tidal constituents in the northern branch of the KB with dual opening for opposing tides. WL variations indicated that M 2 tide (Principal lunar semidiurnal constituent) dominated in the sea level variance, followed by the K 1 constituent (Luni-solar declinational diurnal constituent). The M 2 tidal influence was the strongest near the mouth and decayed in the upstream direction. The propagation speed of the M 2 tide in the southern estuary was ~3.14 m/s. The ratio of the total annual runoff to the estuarine volume is ~42 that indicates the estuary will be flushed 42 times in a year. KB can be classified as a monsoonal estuary where the river discharge exhibits large seasonal variation