The Bay of Bengal upper‐ocean response to tropical cyclone forcing during 1999

Abstract

[1] The regional upper-ocean dynamical and thermodynamical responses to two consecutive, strong tropical cyclones (TCs)-04B (15-19 October) and 05B (25 October to 3 November) in 1999 (hereafter, TC1 and TC2) in the Bay of Bengal (BoB) and the associated oceanic processes are investigated using an eddy-permitting Hybrid Coordinate Ocean Model. The TC winds induce positive sea surface height anomalies (SSHA) along the northern BoB coastline and Andaman Sea due to onshore convergence, and negative SSHA along the TC tracks due to Ekman divergence, which in turn induce geostrophic flow. The TC-associated radiation and precipitation have negligible effects on the northwestern BoB top 30 m averaged temperature (T 0-30 m ), while the strong TC winds significantly enhance turbulent heat flux causing T 0-30 m decrease. Due to the existence of the barrier layer and subsurface warm advection in the northwestern BoB, vertical mixing may induce near-surface warming by entraining warm water from below. As a result, the proportion of the T 0-30 m cooling caused by turbulent heat flux is likely elevated in the 6 3 6 footprints of the TCs. Both TC wind-induced vertical mixing and upwelling significantly cool T 0-30 m in TC1's wake, while upwelling dominates the maximum cooling region in TC2's wake, likely due to the preceding deepening of the mixed layer by TC1. The near-surface cooling for both TCs has rightward bias because of the higher winds and the resonant response on the right, and Ekman divergence extends the cooling areas outward. TC1 and TC2's sizes and prestorm oceanic conditions are found to be the most influential factors for near-surface cooling.

Development of tropical cyclone wind field for simulation of storm surge/sea surface height using numerical ocean model

“…the western parts of BoB, the positive SSH at 00UTC, 06UTC and 12UTC is observed, in spite being in the left side of storm track. This could be attributed to the current driven coastal convergence of water masses and the counter-clockwise propagating sea-level signal around the perimeter of the BoB that increased the SSH along the western BoB boundary (Wang et al 2012;Wang and Han 2014). At 18UTC the higher SSH band is not extended to southernmost part of the coast, whereas, at 12UTC the higher SSH band along the western coastal waters is more pronounced and extended to further southern parts of coastal region.…”

“…Cubic spline interpolation technique is used to bring the superimposed wind fields to match the resolution of ocean model. Wang and Han (2014) superimposed the reconstructed winds with the Cross-Calibrated Multiplatform (CCMP) satellite ocean surface wind field in forcing the ocean model in their studies.…”

“…Along the west coast, the PMSS varies from *2 m near Thiruvananthapuram to *5 m near the Gulf of Khambat in the Saurashtra region of Gujarat (CRRI 2013). The impact of the storm in generating the surface currents, modulating the SSH and giving rise to the storm surge is well investigated (Wang et al 2012;Wang and Han 2014). Strom induced SSH changes and their anomalies (positive and negative) have the strong bearing in dynamic and thermodynamic characteristics of the ocean and in modulating the air-sea interaction processes in different seasons and scales.…”

“…Since, quantitatively, neither the satellite-retrieved nor numerical model/reanalysis winds able to represent realistically the observed magnitude of TC's, although the general circulation patterns are captured (Wang and Han 2014). So, a TC wind field model based on the formulation of Carr and Elsberry (1997) is adopted for developing cyclonic winds.…”

Modulation of June Rainfall in India by Winter Salinity Barrier Layer in the Bay of Bengal

“…Thus, any process that affects SST may play a role in ISM activity. Previous studies mainly focused on the effects of BL on concurrent SST variability 32,[38][39][40]43,49,50 , but the persistent effect of the prior winter (December-February) BL on air-sea interaction in the following seasons and its mechanisms remain unclear. Here we show evidence that an anomalously thick BL in the BoB in the prior winter may advance the ISM onset date and enhance precipitation in June over the South Asian subcontinent.…”