• Y Sadhuram

      Articles written in Journal of Earth System Science

    • Variability in the surface wind direction at a coastal site of complex terrain

      Y Sadhuram

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      Variability in the standard deviation of surface wind direction (σθ), under different Pasquill stability regimes on diurnal, seasonal and interannual scales has been investigated making use of a 10-year data set collected at Visakhapatnam (17°42′ N., 82° 18′ E) during January, April, August and October for winter, pre-monsoon, monsoon and post-monsoon seasons respectively. The diurnal scale variability in σθ is more pronounced during day time than in night. The seasonal variability in σθ is only moderate around noon while relatively large fluctuations are noticed on inter-annual scale only during day time in January and August. The seasonal dispersion in σθ decreased from most unstable regime to most stable regime.

    • Latent and sensible heat fluxes under active and weak phases of the summer monsoon of 1986

      P N Vinayachandran Y Sadhuram V Ramesh Babu

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      An analysis of the meteorological data collected by the research vessel ORV Sagarkanya for the mean latent and sensible heat fluxes over the Arabian Sea has indicated appreciable changes between active and weak phases of the southwest monsoon of 1986. We suggest that: (a) the presence of a core of low level winds associated with the Somali jet and its southward shift during the season, along with (b) a ridge in surface pressure over the central Arabian Sea could be responsible for the deficit in monsoon rainfall along the west coast of India in 1986.

    • The value ofCefor the Arabian Sea during summer monsoon

      A Suryachandra Rao Y Sadhuram V V Gopala Krishna

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      We estimate, from the moisture budget the bulk aerodynamic coefficient for latent heat flux (Ce) during the monsoon season over the central Arabian Sea. The average value ofCeunder active monsoon conditions was found to be 2.25 × 10−3 which is nearly 60% higher than those previously used.

    • Seasonal variability of physico-chemical characteristics of the Haldia channel of Hooghly estuary, India

      Y Sadhuram V V Sarma T V Ramana Murthy B Prabhakara Rao

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      Physical and chemical characteristics of the Hooghly estuary during winter (December 1997–January 1998), summer (May 1998) and post-monsoon (November 1998) seasons have been studied. Salinity varied spatially and temporally and seasonally during ebb and flood tide conditions. Water temperature showed a difference of 10‡C in winter to summer. Temperature did not vary much vertically as it is a well-mixed estuary. Strong currents exceeding 100 cm S-1 were observed during peak ebb and flood tide conditions irrespective of the season. Longitudinal eddy diffusion coefficient (Kx) was estimated as 757m S-1 and 811m2 S-1 during summer and post-monsoon seasons, respectively. The vertical eddy diffusion coefficient (εv) was estimated as 0.0337 m2 S-1 during post-monsoon season. The salinity and current observations are compared with those obtained from models reported earlier. Values of pH, Dissolved Oxygen and Biological Oxygen Demand are within the threshold limits of the estuarine environment. Nutrients show seasonal variation in the estuarine environment. High values (160-2686 mg l-1) of total suspended matter were noticed both at surface and bottom in the study region showing the impact of fresh water and sediment transportation.

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

      K Maneesha V V S S Sarma N P C Reddy Y Sadhuram T V Ramana Murty V V Sarma M Dileep Kumar

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      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.

    • Variability in stratification and flushing times of the Gautami–Godavari estuary, India

      B Sridevi V V S S Sarma T V R Murty Y Sadhuram N P C Reddy K Vijayakumar N S N Raju Ch Jawahar Kumar Y S N Raju R Luis M D Kumar K V S R Prasad

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      In order to examine the influence of forcing (river flow and tides) and anthropogenic activities (dredging and dam regulation) on stratification, a study was conducted over a period of 19 months (June 2008–December 2009) in the Gautami–Godavari estuary (G–GE) during spring and neap tide periods covering entire spectrum of discharge over a distance of 36 km from the mouth. The bathymetry of the estuary was recently changed due to dredging of ∼20 km of the estuary from the mouth for transportation of barges. This significantly changed the mean depth and salinity of the estuary from its earlier state. The variations in the distribution of salinity in the Godavari estuary are driven by river discharge during wet period (June–November) and tides during dry period (December–May). The weak stratification was observed during high discharge (July–August) and no discharge (January–June) periods associated with dominant fresh water and marine water respectively. The strong stratification was developed associated with decrease in discharge during moderate discharge period (October–December). Relatively stronger stratification was noticed during neap than spring tides. The 15 psu isohaline was observed to have migrated ∼2–3 km more towards upper estuary during spring than neap tide suggesting more salt enters during former than latter period. Total salt content was inversely correlated with river discharge and higher salt of about 400×106 m3 psu was observed during spring than neap tide. Flushing times varied between less than a day and more than a month during peak and no discharge periods respectively with lower times during spring than neap tide. The flushing times are controlled by river discharge during high discharge period, tides during dry period and both (river discharge and tides) under moderate discharge period. This study suggests that modification of discharge, either natural due to weak monsoon, or artificial such as dam constructions and re-routing the river flow, may have significant impact on the stratification and biogeochemistry of the Godavari estuary.

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