Oceanic Response to Tropical Cyclone Gonu (2007) in the Gulf of Oman and the Northern Arabian Sea: Estimating Depth of the Mixed Layer Using Satellite SST and Climatological Data

Abstract

The category 5-equivalent tropical Cyclone Gonu (2007) was the strongest cyclone to enter the northern Arabian Sea and Gulf of Oman. The impact of this cyclone on the sea surface temperature (SST) cooling and deepening of the mixed layer was investigated herein using an optimally interpolated (OI) cloud-free sea surface temperature (SST) dataset, climatological profiles of water temperature, and data from Argo profilers. SST data showed a maximum cooling of 1.7–6.5 °C during 1–7 June 2007 over the study area, which is similar to that of slow- to medium-moving cyclones in previous studies. The oceanic heat budget equation with the assumptions of the dominant turbulent mixing effect was used to establish relationships between SST and mixed layer depth (MLD) for regions that were directly affected by cyclone-induced turbulent mixing. The relationships were applied to the SST maps from satellite to obtain maps of MLD for 1–7 June, when Gonu was over the study area. Comparing with the measured MLD from Argo data showed that this approach estimated the MLDs with an average error of 15%, which is an acceptable amount considering the convenience of this approach in estimating MLD and the simplifications applied in the heat budget equation. Some inconsistencies in calculating MLD were attributed to use of climatological temperature profiles that may not have appropriately represented the pre-cyclone conditions due to pre-existing cold/warm core eddies. Estimation of the diapycnal diffusion that quantified the turbulent mixing across the water column showed consistent temporal and spatial variations with the calculated MLDs.

Analysis of Internal Solitary Waves in the Gulf of Oman and Sources Responsible for Their Generation

“…Despite the important role of ISWs in water mixing in this region, only a few studies have been carried out thus far on this issue. In the meantime, the GoO is rarely affected by extreme events such as cyclones which can drastically change the stratification [25,31] and, therefore, a distinct seasonally stratification exists in this basin. Nevertheless, there are some factors that may regionally modify the depth of the thermocline, solely or by their interactions, including mesoscale and submesoscale eddies, upwelling, and intrusion of PG water.…”

“…Additionally, Sandven and Johannessen, and Johannessen et al presented a SAR image showing a small eddy with the characteristic scale of 5 km where IWs with wavelengths of a few hundred meters up to 1000 m were radiating out of the center of the eddy [22,23]. This mechanism can be substantially important in the GoO owing to the well-documented persistent existence of mesoscale and sub-mesoscale eddies in this basin [24,25].…”