Abstract
Hurricanes are tropical weather systems that play a significant role in the exchange of energy (heat) between the atmosphere and ocean. Sea surface temperature (SST) variability and mixed layer depth (MLD) modulates the intensity of tropical cyclones. TRMM Microwave Imager (TMI), GPM Microwave Imager (GMI), and HYbrid Coordinate Ocean Model (HYCOM) data corresponding to eight hurricanes that traversed across the Gulf of Mexico (GOM) and Western Caribbean Sea (WCS) were analyzed to evaluate the response of upper-ocean parameters to passing hurricanes. Data on SST, precipitation, wind speed (WS), and MLD were compared between pre- and post-storm conditions. Daily satellite data were extracted from TMI and GMI data archives and further averaged during the traverse time of hurricanes across the GOM and WCS. Pre-storm conditions were generated by averaging data from the immediate days before hurricanes entered the study site. HYCOM model outputs were analyzed for MLD parameters and SST cross-validation. Visible and infrared remote sensing data from six satellite missions were analyzed for cross-validation of SST and chlorophyll-a (Chl-a) dynamics associated with hurricane-induced ocean surface cooling and upwelling. HURDAT2 data archives from the National Hurricane Center (NHC) were analyzed for delineating the periphery of 50 knots wind at the NW and NE hurricane track quadrants to determine the spatial variability in hurricane oceanic interactions on both sides of the storm. WS distribution showed significant spatial variability with maximum winds observed along the eastern (right) side of most tracks. MLD data extracted from HYCOM archives also responded positively to the passing hurricanes even though the GOM and WCS showed differences in the MLD response; deeper MLDs were observed in the WCS, an almost completely land-locked body of water. Cooling corresponding to the deepening MLD extended more than 100 m after major hurricane passage. Cross-validation of SST from numerical models and active and passive remote sensing provided similar cooling patterns particular to each storm; Chl-a was observed as having a positive effect in the areas of cooler ocean temperatures following hurricane passage and along the coastlines where hurricanes made landfall. In addition, it was noticed that hurricanes entering the GOM via the Florida Straits had minimal effect on WCS, especially on MLD, while forward translational speed (FTS) had a profound effect on the SST cooling and MLD. Hurricane Charley, which made landfall in August 2004, did not make any significant effect on MLD nor did it largely cool the ocean along its track. On the contrary, Hurricane Ivan, which came just one month later, caused significant cooling of the ocean surface as well as substantially deepening the MLD substantially in the WCS and GOM. Increased Chl-a along the path of major hurricanes was observed for all storms that traversed across the GOM. This ephemeral primary productivity can be attributed to hurricane-induced deep-ocean upwelling as well as upper-ocean cooling from intense heat exchange from the MLD to the atmosphere/hurricane. Looking at the long-term guidance in hurricane intensification in the GOM and WCS, an increasing trend was observed in the intensity of hurricanes and the amount of precipitation produced by these tropical weather systems. Hurricane Michael, which spawned in the WCS, exploded as a category 5 hurricane while crossing the Loop Current (LC) and became one of the most destructive hurricanes in the present decade. SST cooling along its wake and the Chl-a patch that was observed after its landfall demonstrated the intensity of the hurricane and the extent of its interaction with the eastern GOM.