Westward propagating twin gyres in the equatorial Indian Ocean

A reduced-gravity (11/2-layer) model forced by daily climatological winds simulates twin, anticyclonic gyres, which propagate westward on either side of the equator. The gyres form at the beginning of both the Southwest Monsoon and the Northeast monsoon in the equatorial eastern Indian Ocean, and subsequently propagate across the basin. Their existence is supported by velocity observations taken during WOCE in 1995 and by TOPEX/Poseidon sea-level observations during 1993. They are also present in the ECCO model/data product. They form at the front of a Rossby-wave packet generated by the reflection of the equatorial jet (EJ) from the eastern boundary of the basin. They are likely either Rossby solitons or result from the nonlinear interaction between the EJ and the Rossby-wave front

Oceanic mixed layer variations during the movement of cyclone along symmetric tracks in the Indian Ocean

The understanding of significant changes in the oceanic mixed layer is important for dynamical prediction of tropical cyclone. Present study aims at examining the variations in the upper ocean parameters during the movement of tropical cyclone in northern and southern Indian Ocean, by applying 11/2 layer wind driven reduced gravity ocean model. Different idealized tracks in the Bay of Bengal and their mirror images in southern hemisphere are considered. The model produced mixed layer depth, temperature and currents are compared for northern and southern hemispheric cyclone cases. Also the effect of latitude for westward moving cyclones in both the hemisphere is investigated. For this, tracks in the Arabian Sea and their counter parts in the southern hemisphere are considered. The maximum cooling found in the wake of cyclone is of the order of 3-4°C, which is comparable with earlier studies and observations. This significant cooling can cause weakening of the storm. This can be useful for prediction especially in the event of a cyclonic storm heading towards land and likely to make land fall. Moreover it is also seen that the mixed layer is cooled more on the right (left) of the storm track in northern (southern) hemisphere. This cooling decreases for the storms translating along higher latitudes implying the sensitivity of the latitudinal location of the storm

Simulation of Ocean Upper Layer Response to Moving Indian Ocean Cyclone Using Reduced Gravity Ocean Model

The sensitivity of the ocean mixed layer response to different parameters such as model horizontal resolution, vertical temperature gradient and eye size is investigated in response to moving Indian Ocean cyclone. For this, a one and one-half layer wind-driven reduced-gravity ocean model is forced with synthetic cyclonic vortex. The sensitivity studies are carried out for a cyclone moving along idealized tracks, initially and then for three observed cyclones (TC 01A), (TC02B) and (TC04A) during 2004. Increasing model resolution resulted in stronger ocean response. The role of initial vertical temperature gradient in modulating the ocean response is found to be important

Variability of mini cold pool off the southern tip of India as revealed from a thermodynamic upper ocean model

A 2.5-layer thermodynamic ocean model has been used to understand the processes associated with the formation of cold pool off southern tip of India. The mean model simulations from the 13 year integration for the period 1992-2004 renders a cold region off southern tip of India during the months of June to September which is recognized as mini cold pool (MCP). The inter-annual and intra-seasonal variability of the MCP for the 5 years from 2000 to 2004 is explored in detail in the present paper. The analysis of model SST shows intense and widespread MCP during the long breaks occurred in the months of July and August of the bad monsoon years 2002 and 2004. The intense cooling is in response to the wind induced upwelling and the resultant entrainment of cold water from the bottom layer. The presence of cyclonic gyre in the model currents also supports the intense MCP which might modulate the monsoon during break phase

Interannual variability in simulated circulation along east coast of India

A two and a half layer reduced gravity model is used to simulate the upper layer circulation along the east coast of India. The model climatology of upper layer circulations obtained from 15 year model simulation (1977-1991) is found to be in good agreement with the observed currents. A cyclonic gyre found in June-July around 10°N in the lower layer (∼60m below surface) has large interannual variability. The gyre is absent in 1982 and 1984 and is very weak in 1987. Transport anomalies computed at four sections along the coast indicate large interannual variability. The upper layer transports along some section have shown a periodicity of 5-6 year

Numerical simulation of North Indian Ocean State prior to the onset of SW monsoon using SSM/I winds

The Sea Surface Temperatures (SST) and currents are simulated over the north Indian Ocean, during the onset phase of southwest monsoon for the three years 1994, 1995, and 1996, using daily Special Sensor Microwave/Imager (SSM/I) winds and National Center for Environmental Prediction (NCEP) heat fluxes as forcings in the 21/2 layer thermodynamic numerical ocean model. The results are discussed for the 30-day period from 16 May to 13 June for all the three years, to determine the ocean state during the onset phase of SW monsoon. The maximum variability in the simulated SST is found along the Somali coast, Indian coasts, and equatorial regions. The maximum SST in the North Arabian Sea is found to be greater than 30°C and minimum SST in the west equatorial region is 25°C during the onset phase of all three years. Model SSTs are in agreement with Reynolds SST. SST gradients in the north-south as well as in the east-west directions, west of 80°E are found to change significantly prior to the onset. It can be inferred from the study that the SST gradient of 2.5°C/2000 km is seen due north and due west of the region 2°-7°S, 60°-65°E, about 8 to 10 days prior to the arrival of SW monsoon near Kerala coast. Upper and lower layer circulation fields do not show prominent interannual variability