The Great Tsunami of 26 December 2004 in the Indian Ocean is described using data from tide gauge... more The Great Tsunami of 26 December 2004 in the Indian Ocean is described using data from tide gauges along the coast of India. The tsunami struck the Indian east coast around 0330 UTC. The amplitude was 2.0 m above the tide at Chennai and Paradip, 1.5 m at Visakhapatnam and less than a metre at Tuticorin. The tsunami propagated into the Arabian Sea from the south and Kochi was hit at 0541 UTC. The maximum amplitude had decayed to about 80 cm at Kochi and it was less than 10 cm at Okha in Gujarat. All these tide gauges are to the west of the earthquake zone and the detided sea levels show first a rise in sea level with the arrival of the tsunami, and then a sharp decrease. Spectral and wavelet analysis of the residuals shows that the maximum amplitude was at a period of 35-45 min, with another maximum around 20 min. Along the Indian east coast, however, there is another broad peak between 1-2 hours within the first few hours after the first tsunami wave. Numerical simulation of this ev...
Proceedings of SPIE - The International Society for Optical Engineering
The seasonal cycles of surface chlorophyll (SCHL) in the Indian Ocean (IO) are regionally describ... more The seasonal cycles of surface chlorophyll (SCHL) in the Indian Ocean (IO) are regionally described by means of 6 parameters: the timing of the bloom onset and of the bloom peak, and the integrated SCHL value in between these two extrema for both winter and summer blooms. This description, based on a climatology constructed from 7 years of SeaWiFS data, provides a regional image of the influence of the two monsoons on phytoplankton blooms. Over a large part of the basin, the seasonal cycle is characterized by two distinct growth periods, one in summer during the South West Monsoon (SWM), the other in winter during the North East Monsoon (NEM). However, in some specific areas such as the southwestern coast of India, there is no maxima during the NEM. The bloom areas during the SWM and the NEM show totally different regional patterns. Important lags in the timing of the blooms are identified, and are also associated with distinct regional patterns. The next step in the understanding o...
Cold and dry winds of the northeast monsoon cool the northern Arabian Sea during November-January... more Cold and dry winds of the northeast monsoon cool the northern Arabian Sea during November-January. The intensity of cooling is highest in the proximity of the peninsula of Saurashtra, India. Using hydrographic data, we propose that the cooling in this region, particularly during cold outbreaks, increases the density of shelf waters sufficiently to form a water mass which sinks and spreads at a depth of about 150 m and is characterizEd. by a weak salinity minimum with sigma-theta in the range of 25.5-26.6 gm/cm super(3). It appears that the advection of lower salinity water into the basin by the northeast monsoon coastal current and subsequent evaporation in the mixed-layer also plays a role in recharge of the salinity minimum
The near-surface Bay of Bengal remains significantly warmer than the Arabian Sea during summer mo... more The near-surface Bay of Bengal remains significantly warmer than the Arabian Sea during summer monsoon (June-September). Analysis of the heat budgets of the near-surface Arabian Sea and Bay of Bengal shows significant differences between them during the summer monsoon. In the Arabian Sea, the winds associated with the summer monsoon are stronger and favour the transfer of heat to deeper layers owing to overturning and turbulent mixing. In contrast, the weaker winds over the bay force a relatively sluggish oceanic circulation that is unable to overturn, forcing a heat-budget balance between the surface fluxes and diffusion and the rate of change of heat in the near-surface layer.
Satellite Infrared observations, from Advanced Very High Resolution Radiometer (AVHRR), during No... more Satellite Infrared observations, from Advanced Very High Resolution Radiometer (AVHRR), during November 1987-February 1988 and hydrographic data from the eastern Arabian Sea are used to describe the poleward flowing coastal current in the eastern Arabian Sea during the northeast monsoon. The current, identifiEd. by a band of warm water, forms in November in the south, and is best developed during December-January when it can be traced along the entire coast of the eastern Arabian Sea. Off the southwest coast of India (10 degrees N) the current was approximately 400 km wide. At about 22 degrees N, the flow was restricted mainly to the vicinity of the continental slope and the current was a narrow jet of about 150 km width. Further north the core of the current narrowed down to about 50 km and turned west following the shelf off Pakistan. The current carried warmer waters (greater than 29 degrees C) of southern origin to the North Arabian Sea. In the northern half of the coastline (no...
Levitus (1982) climatology has been used to identify four extrema, three maxima and one minimum, ... more Levitus (1982) climatology has been used to identify four extrema, three maxima and one minimum, in the vertical salinity profiles in the Arabian Sea. Their geographical distribution, depths, theta-S characteristics, and seasonal variability are described. Two of the maxima arise from the influence of Red Sea and the Persian Gulf Water. The third, which lies at the bottom of the Equatorial Surface Water, forms due to freshening at the surface of high salinity Arabian Sea near-surface waters. The dominant factors leading to the dormation of the little known subsurface salinity minimum appear to be, (1) transport of the low salinity water by the northeast monsoon coastal current along the west coast of India and subsequent increase in the surface salinity of this water due to evaporation in the North Arabian Sea, (2) poleward coastal undercurrent along the west coast of India during the southwest monsoon. The theta-S characteristics of the four salinity extrema are used to put into pe...
In the present study the pentad Global Precipitation Climatology Project (GPCP) estimate have bee... more In the present study the pentad Global Precipitation Climatology Project (GPCP) estimate have been used, which is a blended product of microwave, infrared and in-situ gauge data for the region bounded by 8 degrees - 13 degrees N; 70 degrees - 95 degrees E, from 1st March to 31 May for the years 1979 to 2001. The monsoon onset dates over Kerala, as declared by India Meteorological Department has been used in the present study. For each year, the midday of the pentad with the rainfall peak was looked for in the period from 1st April to 10th May and identified as the Pre Monsoon Rainfall Peak (PMRP). The analysis showed that PMRP exists about seven pentads prior to the onset of the monsoon over Kerala coast. The correlation between PMRP date and the monsoon onset date over Kerala was found to be 0.72, which was statistically significant. Thus, as is felt that the pre monsoon rainfall estimate from the satellite data can be used for predicting the monsoon onset over Kerala coast. The re...
Tsunamis are one of the most destructive natural hazards that affect the coastal areas. Tsunami w... more Tsunamis are one of the most destructive natural hazards that affect the coastal areas. Tsunami waves that impact the coast with enormous energy are capable of destroying the objects on the coast and re-shaping the coastal geography, geomorphology and ecosystem. These waves can also cause extensive damage and disruption to human lives, their livelihood, infrastructure and economic activities. The 26 December 2004 Sumatra-Andaman earthquake, one of the largest recorded and deadliest tremor, created an unparalleled catastrophic tsunami wiping out thousands of human lives and throwing millions homeless. This event attracted the interest of several geoscientists in India and stimulated extensive scientific research. This article summarizes the tsunami related research work carried out in India during the past four years.
ABSTRACT Satellite-tracked surface drifters were used to analyze the characteristics of inertial ... more ABSTRACT Satellite-tracked surface drifters were used to analyze the characteristics of inertial currents in the tropical Indian Ocean. The drifters were drogued at 15 m depth and had wind-produced slips less than 0.1% of the wind speed. The rotary spectra of surface velocity components indicated the significance of intertial currents. They are circular (rotary coefficient greater than 0.5), highly intermittent and contribute up to 46% to the total kinetic energy of the surface flow field. Events of intertial activity, either triggered by the passage of atmospheric disturbances or by the local fluctuations in the atmospheric pressure (winds), did not last for more than 4 to 5 intertial cycles. The observed intertial frequency exhibited a shift towards the red end of the spectrum by 12%. Cyclonic storm induced inertial events even at a location 300 km away from it
The reliability of the operational Ocean State Forecast system at the Indian National Centre for ... more The reliability of the operational Ocean State Forecast system at the Indian National Centre for Ocean Information Services (INCOIS) during tropical cyclones that affect the coastline of India is described in this article. The performance of this system during cyclone Thane that severely affected the southeast coast of India during the last week of December 2011 is reported here. Spec-tral wave model is used for forecasting the wave fields generated by the tropical cyclone and vali-dation of the same is done using real-time automated observation systems. The validation results indicate that the forecasted wave parameters agree well with the measurements. The feedback from the user community indicates that the forecast was reliable and highly useful. Alerts based on this operational ocean state forecast system are thus useful for protecting the property and lives of the coastal communities along the coastline of India. INCOIS is extending this service for the benefit of the other cou...
Wave fields, both measured and forecast during the very severe cyclone Phailin, are discussed in ... more Wave fields, both measured and forecast during the very severe cyclone Phailin, are discussed in this communication. Waves having maximum height of 13.54 m were recorded at Gopalpur, the landfall point of the cyclone. The forecast and observed significant wave heights matched well at Gopalpur with correlation coefficient of 0.98, RMS error of 0.35 m and scatter index of 14%. Forecasts were also validated in the open ocean and found to be reliable (scatter index < 15%). The study also revealed the presence of Southern Ocean swells with a peak period of 20-22 sec hitting Gopalpur coast along with the cyclone-generated waves.
Deep Sea Research Part A. Oceanographic Research Papers, 1991
... Press plc Observed low-frequency currents in the deep mid-Arabian Sea SR SHETYE,* SC SHENOI* ... more ... Press plc Observed low-frequency currents in the deep mid-Arabian Sea SR SHETYE,* SC SHENOI* and D. SUNDAR* (Received 12 ... NAIR RR, V. ITrEKKOT, SJ MANGININI, V. RAMASWAMY, B. HAAKE, ET DEGENS, BN DESAI and S. Homo (1989) Increased particle flux ...
The dynamics and thermodynamics of the surface layer of the Arabian Sea, north of about 10N, are ... more The dynamics and thermodynamics of the surface layer of the Arabian Sea, north of about 10N, are dominated by the monsoon-related annual cycle of air-sea fluxes of momentum and heat. The currents in open-sea regime of this layer can be largely accounted for by Ekman drift and the thermal field is dominated by local heat fluxes. The geostrophic currents in open-sea subsurface regime also show a seasonal cycle and there is some evidence that signatures of this cycle appear as deep as 1000 m. The forcing due to Ekman suction is an important mechanism for the geostrophic currents in the central and western parts of the Sea. Recent studies suggest that the eastern part is strongly influenced by the Rossby waves radiated by the Kelvin waves propagating along the west coast of India. The circulation in the coastal region off Oman is driven mainly by local winds and there is no remotely driven western boundary current. Local wind-driving is also important to the coastal circulation off west...
The Great Tsunami of 26 December 2004 in the Indian Ocean is described using data from tide gauge... more The Great Tsunami of 26 December 2004 in the Indian Ocean is described using data from tide gauges along the coast of India. The tsunami struck the Indian east coast around 0330 UTC. The amplitude was 2.0 m above the tide at Chennai and Paradip, 1.5 m at Visakhapatnam and less than a metre at Tuticorin. The tsunami propagated into the Arabian Sea from the south and Kochi was hit at 0541 UTC. The maximum amplitude had decayed to about 80 cm at Kochi and it was less than 10 cm at Okha in Gujarat. All these tide gauges are to the west of the earthquake zone and the detided sea levels show first a rise in sea level with the arrival of the tsunami, and then a sharp decrease. Spectral and wavelet analysis of the residuals shows that the maximum amplitude was at a period of 35-45 min, with another maximum around 20 min. Along the Indian east coast, however, there is another broad peak between 1-2 hours within the first few hours after the first tsunami wave. Numerical simulation of this ev...
Proceedings of SPIE - The International Society for Optical Engineering
The seasonal cycles of surface chlorophyll (SCHL) in the Indian Ocean (IO) are regionally describ... more The seasonal cycles of surface chlorophyll (SCHL) in the Indian Ocean (IO) are regionally described by means of 6 parameters: the timing of the bloom onset and of the bloom peak, and the integrated SCHL value in between these two extrema for both winter and summer blooms. This description, based on a climatology constructed from 7 years of SeaWiFS data, provides a regional image of the influence of the two monsoons on phytoplankton blooms. Over a large part of the basin, the seasonal cycle is characterized by two distinct growth periods, one in summer during the South West Monsoon (SWM), the other in winter during the North East Monsoon (NEM). However, in some specific areas such as the southwestern coast of India, there is no maxima during the NEM. The bloom areas during the SWM and the NEM show totally different regional patterns. Important lags in the timing of the blooms are identified, and are also associated with distinct regional patterns. The next step in the understanding o...
Cold and dry winds of the northeast monsoon cool the northern Arabian Sea during November-January... more Cold and dry winds of the northeast monsoon cool the northern Arabian Sea during November-January. The intensity of cooling is highest in the proximity of the peninsula of Saurashtra, India. Using hydrographic data, we propose that the cooling in this region, particularly during cold outbreaks, increases the density of shelf waters sufficiently to form a water mass which sinks and spreads at a depth of about 150 m and is characterizEd. by a weak salinity minimum with sigma-theta in the range of 25.5-26.6 gm/cm super(3). It appears that the advection of lower salinity water into the basin by the northeast monsoon coastal current and subsequent evaporation in the mixed-layer also plays a role in recharge of the salinity minimum
The near-surface Bay of Bengal remains significantly warmer than the Arabian Sea during summer mo... more The near-surface Bay of Bengal remains significantly warmer than the Arabian Sea during summer monsoon (June-September). Analysis of the heat budgets of the near-surface Arabian Sea and Bay of Bengal shows significant differences between them during the summer monsoon. In the Arabian Sea, the winds associated with the summer monsoon are stronger and favour the transfer of heat to deeper layers owing to overturning and turbulent mixing. In contrast, the weaker winds over the bay force a relatively sluggish oceanic circulation that is unable to overturn, forcing a heat-budget balance between the surface fluxes and diffusion and the rate of change of heat in the near-surface layer.
Satellite Infrared observations, from Advanced Very High Resolution Radiometer (AVHRR), during No... more Satellite Infrared observations, from Advanced Very High Resolution Radiometer (AVHRR), during November 1987-February 1988 and hydrographic data from the eastern Arabian Sea are used to describe the poleward flowing coastal current in the eastern Arabian Sea during the northeast monsoon. The current, identifiEd. by a band of warm water, forms in November in the south, and is best developed during December-January when it can be traced along the entire coast of the eastern Arabian Sea. Off the southwest coast of India (10 degrees N) the current was approximately 400 km wide. At about 22 degrees N, the flow was restricted mainly to the vicinity of the continental slope and the current was a narrow jet of about 150 km width. Further north the core of the current narrowed down to about 50 km and turned west following the shelf off Pakistan. The current carried warmer waters (greater than 29 degrees C) of southern origin to the North Arabian Sea. In the northern half of the coastline (no...
Levitus (1982) climatology has been used to identify four extrema, three maxima and one minimum, ... more Levitus (1982) climatology has been used to identify four extrema, three maxima and one minimum, in the vertical salinity profiles in the Arabian Sea. Their geographical distribution, depths, theta-S characteristics, and seasonal variability are described. Two of the maxima arise from the influence of Red Sea and the Persian Gulf Water. The third, which lies at the bottom of the Equatorial Surface Water, forms due to freshening at the surface of high salinity Arabian Sea near-surface waters. The dominant factors leading to the dormation of the little known subsurface salinity minimum appear to be, (1) transport of the low salinity water by the northeast monsoon coastal current along the west coast of India and subsequent increase in the surface salinity of this water due to evaporation in the North Arabian Sea, (2) poleward coastal undercurrent along the west coast of India during the southwest monsoon. The theta-S characteristics of the four salinity extrema are used to put into pe...
In the present study the pentad Global Precipitation Climatology Project (GPCP) estimate have bee... more In the present study the pentad Global Precipitation Climatology Project (GPCP) estimate have been used, which is a blended product of microwave, infrared and in-situ gauge data for the region bounded by 8 degrees - 13 degrees N; 70 degrees - 95 degrees E, from 1st March to 31 May for the years 1979 to 2001. The monsoon onset dates over Kerala, as declared by India Meteorological Department has been used in the present study. For each year, the midday of the pentad with the rainfall peak was looked for in the period from 1st April to 10th May and identified as the Pre Monsoon Rainfall Peak (PMRP). The analysis showed that PMRP exists about seven pentads prior to the onset of the monsoon over Kerala coast. The correlation between PMRP date and the monsoon onset date over Kerala was found to be 0.72, which was statistically significant. Thus, as is felt that the pre monsoon rainfall estimate from the satellite data can be used for predicting the monsoon onset over Kerala coast. The re...
Tsunamis are one of the most destructive natural hazards that affect the coastal areas. Tsunami w... more Tsunamis are one of the most destructive natural hazards that affect the coastal areas. Tsunami waves that impact the coast with enormous energy are capable of destroying the objects on the coast and re-shaping the coastal geography, geomorphology and ecosystem. These waves can also cause extensive damage and disruption to human lives, their livelihood, infrastructure and economic activities. The 26 December 2004 Sumatra-Andaman earthquake, one of the largest recorded and deadliest tremor, created an unparalleled catastrophic tsunami wiping out thousands of human lives and throwing millions homeless. This event attracted the interest of several geoscientists in India and stimulated extensive scientific research. This article summarizes the tsunami related research work carried out in India during the past four years.
ABSTRACT Satellite-tracked surface drifters were used to analyze the characteristics of inertial ... more ABSTRACT Satellite-tracked surface drifters were used to analyze the characteristics of inertial currents in the tropical Indian Ocean. The drifters were drogued at 15 m depth and had wind-produced slips less than 0.1% of the wind speed. The rotary spectra of surface velocity components indicated the significance of intertial currents. They are circular (rotary coefficient greater than 0.5), highly intermittent and contribute up to 46% to the total kinetic energy of the surface flow field. Events of intertial activity, either triggered by the passage of atmospheric disturbances or by the local fluctuations in the atmospheric pressure (winds), did not last for more than 4 to 5 intertial cycles. The observed intertial frequency exhibited a shift towards the red end of the spectrum by 12%. Cyclonic storm induced inertial events even at a location 300 km away from it
The reliability of the operational Ocean State Forecast system at the Indian National Centre for ... more The reliability of the operational Ocean State Forecast system at the Indian National Centre for Ocean Information Services (INCOIS) during tropical cyclones that affect the coastline of India is described in this article. The performance of this system during cyclone Thane that severely affected the southeast coast of India during the last week of December 2011 is reported here. Spec-tral wave model is used for forecasting the wave fields generated by the tropical cyclone and vali-dation of the same is done using real-time automated observation systems. The validation results indicate that the forecasted wave parameters agree well with the measurements. The feedback from the user community indicates that the forecast was reliable and highly useful. Alerts based on this operational ocean state forecast system are thus useful for protecting the property and lives of the coastal communities along the coastline of India. INCOIS is extending this service for the benefit of the other cou...
Wave fields, both measured and forecast during the very severe cyclone Phailin, are discussed in ... more Wave fields, both measured and forecast during the very severe cyclone Phailin, are discussed in this communication. Waves having maximum height of 13.54 m were recorded at Gopalpur, the landfall point of the cyclone. The forecast and observed significant wave heights matched well at Gopalpur with correlation coefficient of 0.98, RMS error of 0.35 m and scatter index of 14%. Forecasts were also validated in the open ocean and found to be reliable (scatter index < 15%). The study also revealed the presence of Southern Ocean swells with a peak period of 20-22 sec hitting Gopalpur coast along with the cyclone-generated waves.
Deep Sea Research Part A. Oceanographic Research Papers, 1991
... Press plc Observed low-frequency currents in the deep mid-Arabian Sea SR SHETYE,* SC SHENOI* ... more ... Press plc Observed low-frequency currents in the deep mid-Arabian Sea SR SHETYE,* SC SHENOI* and D. SUNDAR* (Received 12 ... NAIR RR, V. ITrEKKOT, SJ MANGININI, V. RAMASWAMY, B. HAAKE, ET DEGENS, BN DESAI and S. Homo (1989) Increased particle flux ...
The dynamics and thermodynamics of the surface layer of the Arabian Sea, north of about 10N, are ... more The dynamics and thermodynamics of the surface layer of the Arabian Sea, north of about 10N, are dominated by the monsoon-related annual cycle of air-sea fluxes of momentum and heat. The currents in open-sea regime of this layer can be largely accounted for by Ekman drift and the thermal field is dominated by local heat fluxes. The geostrophic currents in open-sea subsurface regime also show a seasonal cycle and there is some evidence that signatures of this cycle appear as deep as 1000 m. The forcing due to Ekman suction is an important mechanism for the geostrophic currents in the central and western parts of the Sea. Recent studies suggest that the eastern part is strongly influenced by the Rossby waves radiated by the Kelvin waves propagating along the west coast of India. The circulation in the coastal region off Oman is driven mainly by local winds and there is no remotely driven western boundary current. Local wind-driving is also important to the coastal circulation off west...
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