Francis Bringas

Loop Current excursions and ring detachments during 1993–2009

Linkages between the variability of Loop Current (LC) surface dynamics, LC ring detachments, and the mean sea height anomaly in the Gulf of Mexico (GOM) are explored using a new methodology that locates the LC fronts and detects the shedding of LC rings. Based on satellite altimetry observations and dynamic height gradient, this methodology allows the determination of the dynamic structure in the region from 1993 to 2009. Northward penetration of the LC was found to be seasonal, with a tendency to increase during the spring and peaking in summer. Whereas northward oscillations exhibit ranges of 4 degrees of latitude, the range of westward oscillations is 6 degrees of longitude. Using the newly developed methodology, 28 LC rings are identified and described during 1993–2009. Starting in 2003, the LC is located more to the north on average, and the average number of LC rings formed per year increases. Since 2003, a significant increase in sea height residuals in the GOM has been observed, exhibiting a linear trend of 2.78 ± 0.26 cm/decade for the period 1993–2009. It is hypothesized here that the increase observed in sea height residuals is linked to the increase in mesoscale activity (LC northward intrusions and number of rings shed) obtained from satellite altimetry observations. Results shown here complement previous observational studies in the region, cover a longer time span, and define objectively the locations of the LC front and the shedding of the rings.

Temporal variability of the South Atlantic Meridional Overturning Circulation between 20°S and 35°S

Altimetry-derived synthetic temperature and salinity profiles between 20°S and 34.5°S are used to estimate the Meridional Overturning Circulation (MOC) and meridional heat transport (MHT), which are assessed against estimates obtained from expendable bathythermograph (XBT) measurements. Consistent with studies from XBTs and Argo data, both the geostrophic and Ekman contributions to the MOC exhibit annual cycles and play an equal role in the MOC seasonal variations. The strongest variations on seasonal and interannual time scales in our study region are found at 34.5°S. The dominance of the geostrophic and Ekman components on the interannual variations in the MOC and MHT varies with time and latitude, with the geostrophic component being dominant during 1993–2006 and the Ekman component dominant between 2006 and 2011 at 34.5°S.

Upper ocean response to Hurricane Gonzalo (2014): Salinity effects revealed by targeted and sustained underwater glider observations

During October 2014, Hurricane Gonzalo traveled within 85 km from the location of an underwater glider situated north of Puerto Rico. Observations collected before, during, and after the passage of this hurricane were analyzed to improve our understanding of the upper ocean response to hurricane winds. The main finding in this study is that salinity potentially played an important role on changes observed in the upper ocean; a near-surface barrier layer likely suppressed the hurricane-induced upper ocean cooling, leading to smaller than expected temperature changes. Poststorm observations also revealed a partial recovery of the ocean to prestorm conditions 11 days after the hurricane. Comparison with a coupled ocean-atmosphere hurricane model indicates that model-observations discrepancies are largely linked to salinity effects described. Results presented in this study emphasize the value of underwater glider observations for improving our knowledge of how the ocean responds to tropical cyclone winds and for tropical cyclone intensification studies and forecasts.

Early Dynamics of Deep Blue XBT Probes

AbstractExpendable bathythermographs (XBTs) are probes widely used to monitor global ocean heat content, variability of ocean currents, and meridional heat transports. In the XBT temperature profile, the depth is estimated from the time of descent in the water using a fall-rate equation. There are two main errors in these profiles: temperature and depth errors. The reduction of error in the estimates of the depth allows a corresponding reduction in the errors in the computations in which XBTs are used. Two experiments were carried out to study the effect of the deployment height on the depth estimates of Deep Blue XBT probes. During these experiments, XBTs were deployed from different heights. The motion of the probes after entering the water was analyzed to determine the position and the velocity of the probes as a function of time, which was compared to that obtained using the Hanawa et al. fall-rate equation. Results showed a difference or offset between the experimentally observed depths and those der...

Impact of Assimilating Underwater Glider Data on Hurricane Gonzalo (2014) Forecasts

AbstractThe initialization of ocean conditions is essential to coupled tropical cyclone (TC) forecasts. This study investigates the impact of ocean observation assimilation, particularly underwater glider data, on high-resolution coupled TC forecasts. Using the coupled Hurricane Weather Research and Forecasting (HWRF) Model–Hybrid Coordinate Ocean Model (HYCOM) system, numerical experiments are performed by assimilating underwater glider observations alone and with other standard ocean observations for the forecast of Hurricane Gonzalo (2014). The glider observations are able to provide valuable information on subsurface ocean thermal and saline structure, even with their limited spatial coverage along the storm track and the relatively small amount of data assimilated. Through the assimilation of underwater glider observations, the prestorm thermal and saline structures of initial upper-ocean conditions are significantly improved near the location of glider observations, though the impact is localized be...