Model simulation of tide-induced currents in Gauthami-Godavari estuary

Predictive spatial distribution of flow field has been simulated from the time series data on currents and tides during dry season (11-19, February, 2009) in the Gauthami-Godavari Estuary utilizing TIDAL model. A 2D-Tidal Estuarine model has been considered (instead of 3D model) due to well-mixed type system and its circulation is dominated by tides during the observational period. The model forcing functions consist of wind and tidal elevations along the open boundaries and no fresh water inflow from the main stream and no land flood in river system. The bathymetry data of the river basin has been collected and supplemented to the model as one of the rigid boundary conditions to evaluate integration. The bottom roughness length (K) was adjusted to achieve model calibration and verification in model simulations of flow field. The model simulation results are in qualitative agreement with the observational data with calibrated bottom roughness length which is about 0.085 m. Model results reveal that the majority of flow was found to be along the channel axis (i.e. high iso-bath contour). During flood time, flow is south-west direction and it is changed to northeast direction during ebb period which is indicating that the model results resemble flow in the real eastern system

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

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

Role of the Indian Ocean on the southern oscillation, atmospheric circulation indices and monsoon rainfall over India

The relationship between the sea surface temperature (SST) in a small region (0-5 N; 80-85 E) in the Eastern Equatorial Indian Ocean and Indian monsoon rainfall and monsoon Indices (M1, U200) has been examined. The role of SSTA in the Southern Oscillation and ENSO is also examined. Indian monsoon rainfall is strongly and positively correlated with the SST of November month (0.77; statistically significant at 99% level) of the preceding calendar year. Monsoon indices (M1, U200) are strongly correlated (0.70 and -0.76) with the February SST of the previous year. Summer OLR anomaly field over south Indian Ocean is negatively and strongly (-0.68) correlated with January SST of the previous calendar year. OLR anomalies over south Asian and North African sectors are strongly correlated with the November SST of the previous year. The influence of SST anomalies in the study area on SOI is seen at a lag of 25 months. A sharp fall in SST from September to December in the Eastern Equatorial Indian Ocean is noticed several months before the mature phase of ENSO. The study indicates that the remote forcing from the SST in the eastern equatorial Indian Ocean is playing an important role in the ocean-atmosphere coupling over Pacific and north Australia Indonesia regions, through the eastward propagating low frequency convective systems and the Walker circulation in the zonal wind fiel

Estimation of tropical cyclone heat potential in the Bay of Bengal and its role in the genesis and intensification of storms

132-138In the present study, cyclone heat potential (CHP) in the Bay of Bengal has been estimated for different seasons using Levitus climatology. A good association was noticed between CHP and the efficiency of intensification (i.e the ratio between severe storms to total number of storms (in 5º × 5º grid), for the period, 1877-1977. CHP has been estimated using CTD data collected along the transects 88° E (4º -20º N) and 11.5º N (81º -92º E) during 1993-96 under pre-, during and post- SW monsoon seasons. These estimates are compared with those obtained from TOPEX/Poseidon sea surface height anomalies (SSHA) and TMI (Tropical Rainfall Measuring Mission Microwave Imager) SST using a two layer gravity model. The above estimates are also compared in the Andaman Sea for the 1996 post– SW monsoon season. It appears that the later method underestimates the CHP in the regions of anti cyclonic gyre (ACG). A relation between CHP and SSHA is proposed for the Bay of Bengal which shows a high correlation of 0.79 (N= 67; significant at > 99% level) using the CTD data

Drifting and Meandering of Olive Ridley Sea Turtles in the Bay of Bengal: Role of Oceanic Rossby Waves

Olive Ridley turtles in the Bay of Bengal are previously thought to migrate southward from their nesting ground, along the east coast of India (Orissa coast), towards Sri Lanka. Surprisingly, three of the four Platform Transmitter Terminal (PTT) attached turtles in April-June 2001 meandered off the east coast of India for about two months. It is found that these turtles meandered at the peripherals of cold core cyclonic eddy surrounded by warm core eddies on either side. Concentrations of prey for the turtles in those frontal regions are known to be abundant. Only one of the four PTT attached turtles migrated to the south along the frontal regions in the direction of geostrophic currents. It is found that the locations of these thermal fronts in the Bay of Bengal are primarily determined by the Oceanic Rossby waves and local Ekman pumping

Alongshore wind stress and heat flux divergence off Visakhapatnam, east coast of India

18-21Annual variation of heat flux divergence (Qv) was computed for the coastal waters of Visakhapatnam. The mean values of net heat exchange (Qn) and heat flux divergence (Qv) were found to be 114 and 115 W.m-2 respectively on annual scale. The net heat storage in the water column is almost negligible. The winds and currents in the study area are favourable for upwelling during premonsoon and SW monsoon seasons. This resulted in large divergence of heat from the region

Variability of Mixed Layer Depth in the Northern Indian Ocean during 1977 and 1979 Summer Monsoon Seasons

258-264Influences of wind stress (tau) and wind stress curl (Grad Gamma) on the short term variability of the mixed layer depth at different locations in the northern Indian Ocean during different phases of summer monsoon activity were examined quantitatively making use of time-series data collected during MONSOON-77 and MONEX-79 programmes. After the onset of monsoon (June/July 1977) over the central Arabian Sea, wind stress together with possible sinking processes on account of negative wind stress curl and convective turnover seemed to play an important role in the development of mixed layer while in the southern Arabian Sea region, the mixed layer mainly responded to the wind stress forcing, whose magnitude though was one order less during May/June 1979. In the northern Bay of Bengal the correlation between wind stress and mixed layer was weak indicating influence of stratification caused by the fresh water discharges from Hooghly and Brahmaputra rivers