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) data corresponding to five hurricanes that traversed across the Gulf of Mexico (GOM) and Caribbean Sea were analyzed for evaluating the response of upper-ocean parameters to passing hurricanes. Data on SST, rainfall, wind speed, and MLD (from HYCOM) were compared from pre- and post-storm conditions. Daily data from the satellites were extracted from TMI data archives (http://www.remss.com/missions/tmi/) and further averaged during the time of hurricanes traversing across the GOM. Pre-storm conditions were generated by averaging data from the immediate days before hurricanes entering the GOM. Fast-moving Hurricane Charley cooled the West Florida Shelf by merely ~ 0.5°C, while Hurricane Ivan came through the following month as a much larger and slow-moving storm and a cooling impact up to 2°C. SST cooling from Hurricane Ivan extended over a wider region covering most of eastern GOM. The following year, Hurricanes Dennis, Katrina, Rita, and Wilma caused substantial ocean surface cooling with an observed maximum of 3.8°C. Precipitation from the hurricanes also exceeded 2.5-3.0 mm/hr, particularly along the right side of the hurricane path. Wind speed distribution showed significant spatial variability with maximum winds observed along the eastern side of the tracks. MLD data extracted from HYCOM model archives also responded dynamically to the passing hurricanes with the cooling extended to more than 100 m water depth after a major hurricane.
As the Gulf of Mexico has experienced major environmental hazards in the recent past, e.g. the BP oil spill in 2010, landfall of major hurricanes, and the frequent outbreak of red tide (Karenia brevis), it is required to evaluate possible alterations in the water quality and biogeochemical balance of this partially enclosed waterbody. Chlorophyll concentrations (Chl-a) and sea surface temperature (SST) Level-2 data from five satellites during the period from 2009 to 2013 were analyzed for their spatial, temporal, and inter-annual variability. Based on the evaluation of data from 24 transects from the West Florida Shelf (WFS), highest Chl-a was observed for the sector from St. Petersburg to Sanibel Island. Additionally, high Chl-a was observed for the Big Bend region, particularly during the spring and early summer. SST distribution also closely followed Chl-a distribution, even though occasional uptick in SST values were noticed from the inner continental shelf even during high primary productivity. Furthermore, between 2010 and 2011, monthly Chl-a and SST varied across the shelf significantly and can be due to the incursion of the Loop Current towards the WFS, as suggested by Weisberg et al. (2014).
Ocean Colour (OC) sensors have been primarily used in biological studies. More recently, OC information has been attracting the attention of oceanographers, as a potential method for revealing physical structures in the ocean. In this study, OC data obtained from SeaWiFS imagery is used, for the first time, to detect the weak Azores Current (AzC) and the associated Azores Front (AzF). Previous studies show that the frontal interface is well seen on SST imagery only during the cold season, while it is disguised during the warm season through the formation of a strong seasonal thermocline. With SeaWiFS imagery, the frontal interface is well identified around 34° N as an asymmetric zonally stretched band of higher near-surface chlorophyll a (CHL a) values north of the AzF, accompanied by a sharp decrease to the south. Quasi-stationary meanders, previously derived from SST fields for the same region, are also well observed in OC imagery. Monthly-averaged Chl a along a meridional cross-section shows that, from spring to autumn, the front is clearly visible. In winter, differences across the front are less pronounced, and the front is more easily identified on SST fields. OC gradients weaken to the east, corresponding to the general weakening of the AzC. In situ CTD data reveal a sharp and meandering thermohaline and dissolved oxygen front ocated at 33-34.5° N and 31° W. This study suggests that OC imagery, combined with other sensors, provide an important tool to investigate ocean dynamic variability, by helping to detect frontal zones with great precision.
Using 1.1 km resolution imagery from NOAA-12, -14, -16, and -17 recorded from April 2001 to May 2003 by "HAZO" HRTP mid-Atlantic satellite receiving station, 8-day average image are calculated to investigate AVHRR-derived SST distributions and associated dominant space and time scales around the Azores archipelago (34° to 42° N, 33° to 23° W). Eight-day average images together with zonal and meridional averages show a distinct seasonal cycle and typical gradi-ents, which emphasise the dual influence of the Gulf Stream and the Azores Current in this region. In late spring, iso-therms start moving to the north and retreat in early autumn. Low horizontal gradients are found during summertime, with warmer waters located to the south and west. Orientation of SST patterns changes with time from SW-NE (e.g. July 2001) to NNW-SSE (e.g. July 2002, August 2001 and 2002). The later orientation involves the sudden warming of the waters surrounding the northwestern group of islands of the Azores archipelago. This warming persists during 3 to 6 weeks with mean temperature differences of the order of 0.8° C. At a more local scale (2° x 2° in size) SST variability is also observed. In some cases, it is found that wind-driven coastal upwelling, a few km wide, occurs to the south of the islands during spring and summer months. Field data demonstrate that upwelling events increase local biomass. This result highlights the relevance of SST data to improve stock assessment and fishery management studies.