Effect of seasonal and cyclonic winds on internal tides over the Bay of Bengal

The influence of seasonal and cyclonic winds is studied on the characteristics of internal waves (IWs) over the western Bay of Bengal (BoB) by using MITgcm model. As the BoB experiences reversal of seasonal winds and also tropical cyclones during pre-monsoon and post-monsoon months, its effect is seen through the computation of spectral estimates of the IWs. It is seen that the peak estimate is associated with the semidiurnal frequency at all the depths and is found higher in May compared to November. This is attributed to the presence of shallow mixed layer depth and deep thermocline due to the upwelling favorable winds. The computation of isopycnal displacement infers that the internal tides are present from 40 to 120 m depth in case of upwelling favorable winds of May, whereas, the presence of internal tides is restricted between 90 and 120 m for the downwelling favorable winds of November. During May, the available potential energy is also seen in a narrow coastal stretch, whilst it is absent in November. During the Hudhud cyclone period of October 7–14, 2014, it is noticed from the spectral estimates that the IWs of tidal frequency are replaced by inertial frequency with a periodicity of about 2 days as a consequence of strong cyclonic winds. The progressive vector diagram shows the mean current is initially westward up to October 17, 2014 and then northeastward with well-defined clockwise circulation. The maximum radius of inertial oscillation of 15 km is observed. After the cyclone ceases, the estimate associated with inertial frequency slowly diminishes and enhances the estimates related to internal tides. The simulations also suggest that the internal tides are absent for about 6 weeks as a response of the cyclonic winds.

     

An observational perspective on tropical cyclone activity over Indian seas in a warming environment

The genesis of tropical cyclones (TCs) over Indian seas comprising of Bay of Bengal (BoB) and Arabian Sea (AS) is highly seasonal with primary maximum in postmonsoon season (mid-September to December) and secondary maximum during premonsoon season (April and May). The present study is focused to demonstrate changes in genesis and intensity of TCs over Indian seas in warming environment. For this purpose, observational data of TCs, obtained from the India Meteorological Department (IMD), are analyzed. The sea surface temperature (SST), surface wind speed, and potential evaporation factor (PEF), obtained from the International Comprehensive Ocean Atmosphere Data Set (ICOADS), are also analyzed to examine the possible linkage with variations in TC activities over Indian seas. The study period has been divided into two epochs: past cooling period (PCP, period up to 1950) and current warming period (CWP, period after 1950) based on SST anomaly (became positive from 1950) over the BoB and AS. The study reveals that the number of severe cyclones (SCS) increases significantly (statistically significant at 99% confidence level) by about 41% during CWP though no such significant change is observed in cyclonic disturbances (CDs) and cyclones (CS) over Indian seas. It is also observed that the rate of dissipation of CS and SCS over Indian seas has been decreasing considerably by about 63 and 71%, respectively, during CWP. The analysis shows that the BoB contributes about 75% in each category of TCs and remaining 25% by the AS towards total of Indian seas. A detailed examination on genesis and intensity of TC over both the basins and the seasons illustrates that significant enhancement of SCS by about 65% during CWP is confined to the postmonsoon season of the BoB. Further, the BoB is sub-divided into northern, central, and southern sectors and the AS into western and eastern sectors based on genesis of TCs and SST gradient. Results show that in postmonsoon season during CWP, the number of SCS increases significantly by about 71% in southern BoB and 300% over western AS.     

Chemical characteristics of aerosols in MABL of Bay of Bengal and Arabian Sea during spring inter-monsoon: A comparative study

The chemical composition of aerosols in the Marine Atmospheric Boundary Layer (MABL) of Bay of Bengal (BoB) and Arabian Sea (AS) has been studied during the spring and inter-monsoon (March-May 2006) based on the analysis of water soluble constituents (Na⁺, NH ₄ ⁺ , K⁺, Mg²⁺, Ca²⁺, Cl^?, NO ₃ ^? and SO ₄ ^2? ), crustal elements (Al, Fe, and Ca) and carbonaceous species (EC, OC). The total suspended particulates (TSP) ranged from 5.2 to 46.6 μg m^?3 and 8.2 to 46.9 μg m^?3 during the sampling transects in the BoB and AS respectively. The water-soluble species, on average, accounted for 44% and 33% of TSP over BoB and AS respectively, with dominant contribution of SO ₄ ^2? over both the oceanic regions. However, distinct differences with respect to elevated abundances of NH ₄ ⁺ in the MABL of BoB and that of Na⁺ and Ca²⁺ in AS are clearly evident. The non-sea-salt component of SO ₄ ^2? ranging from 82 to 98% over BoB and 35 to 98% over AS; together with nss-Ca²⁺/nss-SO ₄ ^2? equivalent ratios 0.12 to 0.5 and 0.2 to 1.16, respectively, provide evidence for the predominance of anthropogenic constituents and chemical transformation processes occurring within MABL. The concentrations of OC and EC average around 1.9 and 0.4 μg m^?3 in BoB and exhibit a decreasing trend from north to south; however, abundance of these carbonaceous species are not significantly pronounced over AS. The abundance of Al, used as a proxy for mineral aerosols, varied from 0.2 to 1.9 μg m^?3 over BoB and AS, with a distinctly different spatial pattern — decreasing north to south in BoB in contrast to an increasing pattern in the Arabian Sea.     

Influence of circulation parameters on the AOD variations over the Bay of Bengal during ICARB

MODIS (Moderate Resolution Imaging Spectroradiometer) level-3 aerosol data, NCEP (National Centers for Environmental Prediction) reanalysis winds and QuikSCAT ocean surface winds were made use of to examine the role of atmospheric circulation in governing aerosol variations over the Bay of Bengal (BoB) during the first phase of the ICARB (Integrated Campaign for Aerosols, gases and Radiation Budget) campaign (March 18–April 12, 2006). An inter-comparison between MODIS level-3 aerosol optical depth (AOD) data and ship-borne MICROTOPS measurements showed good agreement with correlation 0.92 (p < 0.0001) and a mean MODIS underestimation by 0.01. During the study period, the AOD over BoB showed high values in the northern/north western regions, which reduced towards the central and southern BoB. The wind patterns in lower atmospheric layers (> 850 hPa) indicated that direct transport of aerosols from central India was inhibited by the presence of a high pressure and a divergence over BoB in the lower altitudes. On the other hand, in the upper atmospheric levels, winds from central and northern India stretched south eastwards and converged over BoB with a negative vorticity indicative of a downdraft. These wind patterns pointed to the possibility of aerosol transport from central India to BoB by upper level winds. This mechanism was further confirmed by the significant correlations that AOD variations over BoB showed with aerosol flux convergence and flux vorticity at upper atmospheric levels (600–500 hPa). AOD in central and southern BoB away from continental influences displayed an exponential dependence on the QuikSCAT measured ocean surface wind speed. This study shows that particles transported from central and northern India by upper atmospheric circulations as well as the marine aerosols generated by ocean surface winds contributed to the AOD over the BoB during the first phase of ICARB.     

A coupled physical-biological-chemical model for the Indian Ocean

A coupled physical-biological-chemical model has been developed at C-MMACS. for studying the time-variation of primary productivity and air-sea carbon-dioxide exchange in the Indian Ocean. The physical model is based on the Modular Ocean Model, Version 2 (MOM2) and the biological model describes the nonlinear dynamics of a 7-component marine ecosystem. The chemical model includes dynamical equation for the evolution of dissolved inorganic carbon and total alkalinity. The interaction between the biological and chemical model is through the Redfield ratio. The partial pressure of carbon dioxide (pCO₂) of the surface layer is obtained from the chemical equilibrium equations of Penget al 1987. Transfer coefficients for air-sea exchange of CO₂ are computed dynamically based on the wind speeds. The coupled model reproduces the high productivity observed in the Arabian Sea off the Somali and Omani coasts during the Southwest (SW) monsoon. The entire Arabian Sea is an outgassing region for CO₂ in spite of high productivity with transfer rates as high as 80 m-mol C/m² /day during SW monsoon near the Somali Coast on account of strong winds.     

Seasonal controls on surface pCO2 in the central and eastern Arabian Sea

The variability in partial pressure of carbon dioxide (pCO₂) and its control by biological and physical processes in the mixed layer (ML) of the central and eastern Arabian Sea during inter-monsoon, northeast monsoon, and southwest monsoon seasons were studied. The ML varied from 80–120 m during NE monsoon, 60–80 m and 20–30 m during SW- and inter-monsoon seasons, respectively, and the variability resulted from different physical processes. Significant seasonal variability was found in pCO₂ levels. During SW monsoon, coastal waters contain two contrasting regimes; (a) pCO₂ levels of 520–685 μatm were observed in the SW coast of India, the highest found so far from this region, driven by intense upwelling and (b) low levels of pCO₂ (266 μatm) were found associated with monsoonal fresh water influx. It varied in ranges of 416–527 μatm and 375–446 μatm during inter- and NE monsoon, respectively, in coastal waters with higher values occurring in the north. The central Arabian Sea pCO₂ levels were 351–433, 379–475 and 385–432 μatm during NE-inter and SW monsoon seasons, respectively. The mixed layer pCO₂ relations with temperature, oxygen, chlorophylla and primary production revealed that the former is largely regulated by physical processes during SW- and NE monsoon whereas both physical and biological processes are important in inter-monsoon. Application of Louanchiet al (1996) model revealed that the mixing effect is the dominant during monsoons, however, the biological effect is equally significant during SW monsoon whereas thermodynamics and fluxes influence during inter-monsoons.     

Fluxes of material in the Arabian Sea and Bay of Bengal — Sediment trap studies

In order to investigate how monsoons influence biogeochemical fluxes in the ocean, twelve time-series sediment traps were deployed at six locations in the northern Indian Ocean. In this paper we present particle flux data collected during May 1986 to November 1991 and November 1987 to November 1992 in the Arabian Sea and Bay of Bengal respectively. Particle fluxes were high during both the SW and NE monsoons in the Arabian Sea as well as in the Bay of Bengal. The mechanisms of particle production and transport, however, differ in both the regions. In the Arabian Sea, average annual fluxes are over 50gm^-2y^-1 in the western Arabian Sea and less than 27gm^-2 y^-1 in the central part. Biogenic matter is dominant at sites located near upwelling centers, and is less degraded during peak flux periods. High particle fluxes in the offshore areas of the Arabian Sea are caused by injection of nutrients into the euphotic zone due to wind-induced mixed layer deepening. In the Bay of Bengal, average annual fluxes are highest in the central Bay of Bengal (over 50gm^-2y^-1) and are least in the southern part of the Bay (37gm^-2y^-1). Particle flux patterns coincide with freshwater discharge patterns of the Ganges-Brahmaputra river system. Opal/carbonate and organic carbon/carbonate carbon ratios increase during the SW monsoon due to variations in salinity and productivity patterns in the surface waters as a result of increased freshwater and nutrient input from rivers. Comparison of S years data show that fluxes of biogenic and lithogenic particulate matter are higher in the Bay of Bengal even though the Arabian Sea is considered to be more productive. Our results indicate that in the northern Indian Ocean interannual variability in organic carbon flux is directly related to the strength and intensity of the SW monsoon while its transfer from the upper layers to the deep sea is partly controlled by input of lithogenic matter from adjacent continents.     

SPH-based simulation of flow process of a landslide at Hongao landfill in China

The cyclones over Bay of Bengal (BoB) have varied socio-economic impacts and meteorological importance. There are considerable uncertainties in predicting the track and intensity of cyclonic systems in the BoB. The present study examines the cyclogenesis characteristics over the BoB and addresses the regional impacts and their importance in terms of intensification of cyclones. An analysis of cyclone track data from 1971–2013 reveals that the cyclones generated in Andaman Sea (a regional sea of BoB) and propagating through central BoB sustain maximum life time. Furthermore, within the BoB, the cyclones originated from Andaman Sea are the most intensified and characterized by highest cyclogenesis potential index. Interestingly, we have found that higher value of mid-tropospheric relative humidity over Andaman Sea during the cyclone period is enhancing the cyclone’s intensity. Climatologically also the Andaman Sea is dominated by higher values of mid-tropospheric relative humidity compared to other regions of BoB. There is no significant distinction between Andaman Sea and rest of the BoB for other meteorological and oceanic parameters that supports cyclogenesis. Climatologically dominant east–west asymmetry in mid-tropospheric relative humidity is enhancing the intensity of cyclones from Andaman Sea. The results will be helpful in understanding the processes of cyclone intensification and useful in the statistical and dynamical prediction of cyclones.     

Meso-scale atmospheric events promote phytoplankton blooms in the coastal Bay of Bengal

The Bay of Bengal is considered to be a low productive region compared to the Arabian Sea based on conventional seasonal observations. Such seasonal observations are not representative of a calendar year since the conventional approach might miss episodic high productive events associated with extreme atmospheric processes. We examined here the influence of extreme atmospheric events, such as heavy rainfall and cyclone Sidr, on phytoplankton biomass in the western Bay of Bengal using both in situ time-series observations and satellite derived Chlorophyll a (Chl a) and sea surface temperature (SST). Supply of nutrients through the runoff driven by episodic heavy rainfall (234 mm) on 4–5 October 2007 caused an increase in Chl a concentration by four times than the previous in the coastal Bay was observed within two weeks. Similar increase in Chl a, by 3 to 10 times, was observed on the right side of the cyclone Sidr track in the central Bay of Bengal after the cyclone Sidr. These two episodic events caused phytoplankton blooms in the western Bay of Bengal which enhanced ~40% of fishery production during October–December 2007 compared to that in the same period in 2006.     

南海海-气通量交换研究进展

1998年的"南海季风试验(SCSMEX)"已经过去10年了,SCSMEX启动的南海海-气通量试验研究也有10个年头.在SCSMEX和国家自然科学基金面上项目"南海季风爆发期近海面层通量观测和湍流结构的观测研究"支持下,10年来在西沙实施了3次(1998年、2000年、2002年)海-气通量观测试验,开展了试验资料分析研究,重点是西南季风爆发前后海-气通量交换过程研究,辐射通量、感热通量、潜热通量、动量通量随天气条件的变化研究,海-气通量日变化,通量交换系数以及通量变化对低层大气、上层海洋的影响研究.对10年来南海通量研究作一回顾,对未来的通量观测研究计划特别是2008"亚洲季风年"西沙通量观测提出一些建议.     

Deciphering the Origin of Abiotic Organic Compounds on Earth: Review and Future Prospects

The geologic production of abiotic organic compounds has been the subject of increasing scientific attention due to their use in the global carbon flux balance, by chemosynthetic biological communities, and for energy resources. Extensive analysis of methane(CH₄) and other organics in diverse geologic settings, combined with thermodynamic modelings and laboratory simulations, have yielded insights into the distribution of specific abiotic organic molecules on Earth and the favorable c...     

Seasonal forecasting of tropical cyclogenesis over the North Indian Ocean

Over the North Indian Ocean (NIO) and particularly over the Bay of Bengal (BoB), the post-monsoon season from October to December (OND) are known to produce tropical cyclones, which cause damage to life and property over India and many neighbouring countries. The variability of frequency of cyclonic disturbances (CDs) during OND season is found to be associated with variability of previous large-scale features during monsoon season from June to September, which is used to develop seasonal forecast model of CDs frequency over the BoB and NIO based on principal component regression (PCR). Six dynamical/thermodynamical parameters during previous June–August, viz., (i) sea surface temperature (SST) over the equatorial central Pacific, (ii) sea level pressure (SLP) over the southeastern equatorial Indian Ocean, (iii) meridional wind over the eastern equatorial Indian Ocean at 850 hPa, (iv) strength of upper level easterly, (v) strength of monsoon westerly over North Indian Ocean at 850 hPa, and (vi) SST over the northwest Pacific having significant and stable relationship with CDs over BoB in subsequent OND season are used in PCR model for a training period of 40 years (1971–2010) and the latest four years (2011–2014) are used for validation. The PCR model indicates highly significant correlation coefficient of 0.77 (0.76) between forecast and observed frequency of CD over the BoB (NIO) for the whole period of 44 years and is associated with the root mean square error and mean absolute error ≤ 1 CD. With respect to the category forecast of CD frequency over BoB and NIO, the Hit score is found to be about 63% and the Relative Operating Curves (ROC) for above and below normal forecast is found to be having much better forecast skill than the climatology. The PCR model performs very well, particularly for the above and below normal CD year over the BoB and the NIO, during the test period from 2011 to 2014.     

Dynamics of sea-ice biogeochemistry in the coastal Antarctica during transition from summer to winter

The seasonality of carbon dioxide partial pressure(pCO_2).air-sea CO_2 fluxes and associated environmental parameters were investigated in the Antarctic coastal waters.The in-situ survey was carried out from the austral summer till the onset of winter[January 2012,February 2010 and March 2009) in the Enderby Basin.Rapid decrease in pCO_2 was evident under the sea-ice cover in January,when both water column and sea-ice algal activity resulted in the removal of nutrients and dissolved inorganic carbon(DIC) and increase in pH.The major highlight of this study is the shift in the dominant biogeochemical factors from summer to early winter.Nutrient limitation(low Si/N),sea-ice cover,low photosynthetically active radiation(PAR),deep mixed layer and high upwelling velocity contributed towards higher pCO_2during March(early winter).CO_2 fluxes suggest that the Enderby Basin acts as a strong CO_2 sink during January(-81 mmol m~2 d~(-1)),however it acts as a weak sink of CO_2 with-2.4 and-1.7 mmol m~(-2) d~(-1)during February and March,respectively.The present work,concludes that sea ice plays a dual role towards climate change,by decreasing sea surface PCO_2 in summer and enhancing in early winter.Our observations emphasize the need to address seasonal sea-ice driven CO_2 flux dynamics in assessing Antarctic contributions to the global oceanic CO_2 budget.     

Nutrient biogeochemistry in an upwelling-influenced estuary of the Pacific northwest (Tillamook Bay,Oregon, USA)

Tillamook Bay, Oregon, is a drowned river estuary that receives freshwater input from 5 rivers and exchanges ocean water through a single channel. Similar to other western United States estuaries, the bay exhibits a strong seasonal change in river discharge in which there is a pronounced winter maximum and summer minimum in precipitation and runoff. The behavior of major inorganic nutrients (phosphorus, nitrogen, and silica) within the watershed is examined over seasonal cycles and under a range of river discharge conditions for October 1997–December 1999. Monthly and seasonal sampling stations include transects extending from the mouth of each river to the mouth of the estuary as well as 6–10 sites upstream along each of the 5 major rivers. Few studies have examined nutrient cycling in Pacific Northwest estuaries. This study evaluates the distributions of inorganic nutrients to understand the net processes occurring within this estuary. Based upon this approach, we hypothesize that nutrient behavior in the Tillamook Bay estuary can be explained by two dominant factors: freshwater flushing time and biological uptake and regeneration. Superimposed on these two processes is seasonal variability in nutrient concentrations of coastal waters via upwelling. Freshwater flushing time determines the amount of time for the uptake of nutrients by phytoplankton, for exchange with suspended particles, and for interaction with the sediments. Seasonal coastal upwelling controls the timing and extent of oceanic delivery of nutrients to the estuary. We suggest that benthic regeneration of nutrients is also an important process within the estuary occurring seasonally according to the flushing characteristics of the estuary. Silicic acid, nitrate, and NH₄ ⁺ supply to the bay appears to be dominated by riverine input. PO₄ ⁻³ supply is dominated by river input during periods of high river flow (winter months) with oceanic input via upwelling and tidal exchange important during other times (spring, summer, and fall months). Departures from conservative mixing indicate that internal estuarine sources of dissolved inorganic phosphorus and nitrogen are also significant over an annual cycle.     

Chemical characteristics of PM<Subscript>10</Subscript> aerosols and airmass trajectories over Bay of Bengal and Arabian Sea during ICARB

For the first time, chemical characterization of PM₁₀ aerosols was attempted over the Bay of Bengal (BoB) and Arabian Sea (AS) during the ICARB campaign. Dominance of SO ₄ ^2? , NH ₄ ⁺ and NO ₃ ^? was noticed over both the regions which indicated the presence of ammonium sulphate and ammonium nitrate as major water soluble particles playing a very important role in the radiation budget. It was observed that all the chemical constituents had higher concentrations over Bay of Bengal as compared to Arabian Sea. Higher concentrations were observed near the Indian coast showing influence of landmass indicating that gaseous pollutants like SO₂, NH₃ and NO _x are transported over to the sea regions which consequently contribute to higher SO ₄ ^2? , NH ₄ ⁺ and NO ₃ ^? aerosols respectively. The most polluted region over BoB was 13°?19°N and 70°?90°E while it was near 11°N and 75°E over AS. Although the concentrations were higher over Bay of Bengal for all the chemical constituents of PM₁₀ aerosols, per cent non-sea salt (nss) fraction (with respect to Na) was higher over Arabian Sea. Very low Ca2+ concentration was observed at Arabian Sea which led to higher atmospheric acidity as compared to BoB. Nss SO ₄ ^2? alone contributed 48% of total water soluble fraction over BoB as well as AS. Ratios SO ₄ ^2? /NO _? ³ over both the regions (7.8 and 9 over BoB and AS respectively) were very high as compared to reported values at land sites like Allahabad (0.63) and Kanpur (0.66) which may be due to very low NO.3 over sea regions as compared to land sites. Air trajectory analysis showed four classes: (i) airmass passing through Indian land, (ii) from oceanic region, (iii) northern Arabian Sea and Middle East and (iv) African continent. The highest nss SO ₄ ^2? was observed during airmasses coming from the Indian land side while lowest concentrations were observed when the air was coming from oceanic regions. Moderate concentrations of nss SO2. 4 were observed when air was seen moving from the Middle East and African continent. The pH of rainwater was observed to be in the range of 5.9–6.5 which is lower than the values reported over land sites. Similar feature was reported over the Indian Ocean during INDOEX indicating that marine atmosphere had more free acidity than land atmosphere.     

Geochemistry of sterols in sediments from Black Sea and the southwest African shelf and slope

Surface sediment samples from the shelf and continental slope off southwest Africa and sediment cores from the deepest part of the Black Sea were analyzed for sterols. Because the organic matter in these anoxic sediments is relatively well-preserved, the input from source organisms in the water column is important in controlling sterol distribution patterns. The sterol distribution on the Namibian shelf is complex, probably because of the great spatial and temporal variability of biological productivity caused by seasonal upwelling and changes in oxygen concentration. The Black Sea, perhaps because of greater physical stability of the water column, has sterol distributions which can be explained by microbial activity or chemical processes acting on a constant input of organic carbon from surface production.     

海气CO2通量与涡动相关法应用研究进展

海气CO2交换速率及通量的测定、估算是碳循环研究的重要内容。测定、估算海气CO2交换速率及通量有多种方法,但都有其局限性,准确定量海气碳通量的大小仍是碳循环研究的热点问题。当前应用最广泛的海气界面分压差法需要通过间接手段测定海气交换速率,交换速率和风速的关系基于经验公式,不确定性较大;而涡动相关法（eddy covariance / eddy correlation）是一种直接测量方法,理论上不需要任何经验参数,在近年来取得较大进展。综述了近年来国内外CO2海气交换速率及通量的测定、估算方法的研究进展,并对各种方法的原理、应用、优缺点进行了分析,着重介绍了涡动相关法测量CO2通量的原理、国内外研究现状、相对传统方法的优缺点以及发展前景等,对未来海气CO2交换速率及通量研究发展趋势和研究方法作了展望。     

Temporal Variability in Ecological Stoichiometry and Material Exchange in a Tidally Dominated Estuary (North Inlet,South Carolina) and the Impact on Community Nutrient Status

Across the coastal zone, rates of carbon and nutrient exchange are defined by the spatiotemporal heterogeneity of individual estuarine systems. Elemental stoichiometry provides a mechanism for simplifying overlapping physical, chemical, and biological drivers into proxies that can be used to compare and monitor estuarine biogeochemistry. To this end, the seasonal and tidal variability of estuarine stoichiometry was examined over an annual cycle in North Inlet (NI), South Carolina. Surface samples for dissolved and particulate carbon (C), nitrogen (N), and phosphorus (P) were collected every 20 days (August 2014 to August 2015) over a semi-diurnal tidal cycle. Dissolved nutrient flux estimates of an individual tidal creek were also made. Overall, the results demonstrated the dominance of seasonal versus tidal forcing on water column C:N:P stoichiometry. This seasonal behavior mediated the relative exchange of N and P into and out of the tidal creek and influenced the nutrient status index (NSI) of NI plankton communities. These communities were largely N deficient with the magnitude of this deficiency impacted by assumptions of inorganic versus organic plankton P demand and nutrient supply. Persistent N deficiency appeared to help drive the net import of N, while temporary P surplus likely drives its seasonal export. Combined, these results indicate that material delivery must be considered on seasonal time frames, as net annual fluxes do not reflect the short-term deliveries of C and nutrients into nearshore ecosystems.     

Hydrography and circulation in the northwestern Bay of Bengal during the retreat of southwest monsoon

The distribution of temperature and salinity in the upper 500 m of the northwestern Bay of Bengal, adjoining the east coast of India, during the retreat of southwest monsoon (September) of 1983 is presented. This study reveals coastal upwelling (limited to the upper 40 m) induced by the local winds. Waters of higher surface salinity near the coast characterize the upwelling. The freshwater influx near the head of the Bay diluted the surface salinity to as low as 26.0 × 10⁻³. The surface circulation was weak and led to a net transport of 2.0 × 10⁶m³.s⁻¹ directed towards northeast.     

Inertial-Dissipation flux measurements over south Bay of Bengal during BOBMEX-Pilot experiment

This paper describes measurement of air-sea parameters and estimation of sensible and latent heat fluxes by the “Inertial-Dissipation” technique over south Bay of Bengal. The data were collected on ORV Sagar Kanya during BOBMEX-Pilot cruise during the period 23rd October 1998 to 12th November 1998 over south Bay of Bengal. The fluxes are estimated using the data collected through fast response sensors namely Gill anemometer, Sonic anemometer and IR Hygrometer. In this paper the analyses carried out for two days, one relatively cloud free day on November 3rd and the other cloudy with rain on November 1st, are presented. Sea surface and air temperatures are higher on November 3rd than on November 1st. Sensible heat flux for both the days does not show any significant variation over the period of estimation, whereas latent heat flux is more for November 3rd than November 1st. An attempt is made to explain the variation of latent heat flux with a parameter called thermal stability on the vapor transfer from the water surface, which depends on wind speed and air to sea surface temperature difference.