A Simplified Model for the Baroclinic and Barotropic Ocean Response to Moving Tropical Cyclones: 1. Satellite Observations
Abstract
Changes of sea surface temperature and height, derived from 20-day passive microwave and altimeter measurements for three tropical cyclones (TCs), Jimena, Ignacio and Kilo, during the 2015 Pacific hurricane season, sampling different stages of intensification, wind speeds, radii, Coriolis parameter, translation velocities, and ocean stratification conditions, are reported and analyzed. As triggered along the path of moving TCs, very large interior ocean displacements can occur to leave prominent sea surface height (SSH) anomalies in the TC wake. Resulting surface depressions can reach 0.3-0.5 m, depending upon size, translation speed, and ocean stratification conditions. These signatures can be quite persistent, that is, more than few weeks, to possibly be intercepted with satellite altimeters. To interpret sea surface temperature (SST) and SSH anomalies, a semiempirical framework is adopted, based on the heat and momentum conservations laws for the upper wind driven mixed layer. As interpreted, SSH anomalies provide direct estimates to evaluate the upwelling impact, that is, the upwelling amplification on the SST wake. For the reported cases, the influence of the upwelling is found rather moderate, of order 10-40%. More promising, the proposed bottom-up approach can help document the resulting wind forcing and practical drag coefficient under extreme TC conditions. As found for these three TCs, a marked drag reduction for wind speed higher than 35 m/s is inferred to ensure consistency with the measured SSH and SST anomalies.
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