Seasonal Variability of the Observed Barrier Layer in the Arabian Sea

The formation mechanisms of the barrier layer ( BL) and its seasonal variability in the Arabian Sea ( AS) are studied using a comprehensive dataset of temperature and salinity profiles from Argo and other archives for the AS. Relatively thick BL of 20-60 m with large spatial extent is found in the central-southwestern AS ( CSWAS), the convergence zone of the monsoon wind, during the peak summer monsoon ( July-August) and in the southeastern AS ( SEAS) and northeastern AS ( NEAS) during the winter ( January-February). Although the BL in the SEAS has been reported before, the observed thick BL in the central-southwestern AS during the peak summer monsoon and in the northeastern AS during late winter are the new findings of this study. The seasonal variability of BL thickness ( BLT) is closely related to the processes that occur during summer and winter monsoons. During both seasons, the Ekman processes and the distribution of low-salinity waters in the surface layer show a dominant influence on the observed BLT distributions. In addition, Kelvin and Rossby waves also modulate the observed BL thickness in the AS. The relatively low salinity surface water overlying the Arabian Sea high-salinity water ( ASHSW) provides an ideal ground for strong haline stratification in the CSWAS ( during summer monsoon) and in NEAS ( during winter monsoon). During summer, northward advection of equatorial low-salinity water by the Somali Current and the offshore advection of low-salinity water from the upwelling region facilitate the salinity stratification that is necessary to develop the observed BL in the CSWAS. In the SEAS, during winter, the winter monsoon current ( WMC) carries less saline water over relatively high salinity ambient water to form the observed BL there. The winter West India Coastal Current ( WICC) transports the low-salinity water from the SEAS to the NEAS, where it lies over the subducted ASHSW leading to strong haline stratification. Ekman pumping together with the downwelling Kelvin wave in the NEAS deepen the thermocline to cause the observed thick BL in the NEAS

Observed anomalous upwelling in the Lakshadweep Sea during the summer monsoon season of 2005

Repeat near-fortnightly expendable bathythermograph (XBT) transects made along Kochi-Kavaratti (KK) shipping lane in the Lakshadweep Sea (LS) during 2002–2006 are examined to describe the observed year-to-year variability of upwelling during summer monsoon season (SMS). Among all the years, the upwelling characterized by up-sloping of 25°C isotherm is relatively weaker and persisted until November during SMS of 2005 and is stronger during the SMS of 2002. As a result of prolonged upwelling, the sea surface temperature has shown cooling extending into the postmonsoon season. The estimated marine pelagic fish landings along the southwest coast of India (SWCI) have also shown increase until December. The governing mechanisms both in terms of local and remote forcings are examined to explain the observed anomalous upwelling during SMS of 2005. The equatorward alongshore wind stress (WS) along the KK XBT transect persisted in a transient manner beyond September only during SMS of 2005. The westerly wind bursts over the equator during the winter of 2004–2005 are both short-lived and relatively weaker triggering weaker upwelling Kelvin waves that propagated into LS in the following SMS of 2005. The observed distribution of negative sea surface height anomaly in the LS is relatively weaker during the SMS of 2005 and lasted longer. The correlation analysis suggests that the local alongshore WS off the SWCI and the remote forcing from the southern coast of Sri Lanka has greater influence on the observed interannual variability of upwelling in the LS when compared to the remote forcing from the equator

Temperature and depth error in the Mechanical Bathythermograph data from the Indian Ocean

1288-1291For arriving at realistic estimates of warming rate of oceans at regional and global level, it is important to understand persistent biases in observations of ocean temperature. In the present study, collocated MBT and CTD data from the Indian Ocean are used to understand the observed errors in temperature and depth of MBT data. The estimated error from the match up data shows that both temperature and depth measurement of MBT are over estimated, compared to CTD measurements. Estimated thermal bias is 0.14°C during the study period, which is significantly higher compared to earlier reports. The corrected MBT data for thermal bias and depth error shows a significant reduction in the existing error

Temperature error in digital bathythermograph data

234-236Simultaneous Digital Bathythermograph (DBT) and Nansen Cast data collected during two cruises of R.V. Gaveshani (GV-117 and GV-118) and archived in Indian Oceanographic Data Centre (IODC) are used to determine existing temperature errors in DBT. The resulting mean error for DBT data from the GV-117 cruise varies from -0.5 to - 1 oC, while it varied between -0.3 and -0.6 oC for data from cruise GV-118. For both the data sets, the error shows consistently negative bias from surface to 800 m depth, however there is no apparent or measurable systematic dependence of the error on depth. Considering the given temperature accuracy of 0.05 oC, the observed DBT error, varying from -0.3 to -1 oC, is significant and such offsets should be removed from DBT archives. It is found that a corrective measure of +0.5 oC, equivalent to the mean surface offset obtained from two cruises, can considerably reduce the temperature error at all DBT depths

VALIDATION OF ARGO DATA IN THE INDIAN OCEAN

ARGO-salinity data from the Indian Ocean are validated using salinity from float-versus-float match-ups and also using CTD observations from three cruises. Validation data sets are selected in such a way that the float and the match-up data are collocated with tolerable space-time difference. For validation a time difference of less than 10 days and space difference less than 100 Km have been considered. The evaluation is done using salinity data on theta (potential temperature) surfaces from deeper observations. One of the significant observation of float-versus-float validation is the large random error observed in the initial profiles of the float-salinity compared to later profiles. While the float salinity data is found to be largely in good agreement with the ship based CTD observations, there are cases where the salinity error exceeds the desired 0.01 PS

Quality of temperature and salinity data from Argo profiling floats in the Bay of Bengal

1870-1878<span style="font-size:9.0pt;font-family: " times="" new="" roman";mso-fareast-font-family:"times="" roman";mso-bidi-font-family:="" mangal;mso-ansi-language:en-gb;mso-fareast-language:zh-cn;mso-bidi-language:="" hi"="" lang="EN-GB">In the present study, temperature and salinity from APEX -Argo floats with reported SPB (Argo-SPB) and salinity from <i style="mso-bidi-font-style: normal">normal floats without any reported SPB (Argo-N) in the BoB have been subjected to quality check (QC). Method used for QC depends on time-space de-correlation scales (TSD-scales) of temperature and salinity in the BoB at selected potential temperature (θ) surface (10 oC). High quality shipboard CTD observations in the BoB have been used to identify TSD-scales of temperature and salinity. Observed TSD scales for salinity (temperature) at θ surface of 10 oC are 5 days and 60 km (8 days and 80 km). QC has been performed on matchups between Argo and shipboard CTD observations falling within the identified TSD- scales. QC on Argo-SPB could not identify any significant systematic bias/error, except for a single profile (cycle No. 48) of float-4900675. In the case of Argo-N, significant error is found in most of the salinity profiles from the float-2900268.</span