Transient Response of the Gulf Stream to Multiple Hurricanes in 2017

Abstract

Autonomous underwater glider observations collected during and after 2017 Hurricanes Irma, Jose, and Maria show two types of transient response within the Gulf Stream. First, anomalously fresh water observed near the surface and within the core of the Gulf Stream offshore of the Carolinas likely resulted from Irma's rainfall being entrained into the Loop Current-Gulf Stream system. Second, Gulf Stream volume transport was reduced by as much as 40% for about 2 weeks following Jose and Maria. The transport reduction had both barotropic and depth-dependent characteristics. Correlations between transport through the Florida Straits and reanalysis winds suggest that both local winds in the Florida Straits and winds over the Gulf Stream farther downstream may have contributed to the transport reduction. To clarify the underlying dynamics, additional analyses using numerical models that capture the Gulf Stream's transient response to multiple tropical cyclones passing nearby in a short period are needed.

Ocean Observations in Support of Studies and Forecasts of Tropical and Extratropical Cyclones

“…By the end of September, positive SST anomalies recorded before the passage of these hurricanes had dissipated due to the intense mixing caused by these major storms, and SSTs closer to neutral conditions were observed (Figure 7A). Farther north, Todd et al (2018) used glider observations and volume transport measurements in the Florida Straits to show that the Gulf Stream exhibited a large freshwater anomaly that was attributable to rains from Irma and also a transient reduction in volume transport that was attributable to wind forcing associated with the passing storm; further studies with numerical simulations are needed to better understand the dynamics of the storm impacts on the western boundary current.…”

“…Glider observations are, for example, frequently assimilated into oceanatmosphere coupled models and used for hurricane intensity forecasts. Sustained glider deployments monitor upper ocean conditions in areas frequently impacted by TCs (e.g., Domingues et al, 2015;Miles et al, 2015;Todd et al, 2018) and are part of the NOAA Hurricane Field Program 4 . Gliders also have particular utility measuring ocean processes on continental shelves before and during landfall of TCs, where alternative ocean observations are scarce (e.g., Glenn et al, 2016;Miles et al, 2017).…”

“…Since gliders move slowly (about 25 km/day) compared to most atmospheric cyclones O (300 km/day), actively piloting them into the paths of storms is generally not feasible due to the short lead times of forecasts. Thus, sustained deployment of gliders at locations prone to TCs or ECs (e.g., Domingues et al, 2015;Glenn et al, 2016;Perry et al, 2017) or along oceanic boundaries as part of boundary current observing systems (Todd et al, 2018(Todd et al, , 2019Testor et al, 2019) is preferable. Compared to rapid response deployments (e.g., Miles et al, 2015;Goni et al, 2017), sustained glider surveillance has the distinct advantage of providing critical high-resolution observations in the open ocean and over the continental shelf prior to storm arrival; these observations have been shown to improve the representation of the ocean in operational coupled forecast models of hurricane intensity (e.g., Dong et al, 2017).…”

Export of Middle Atlantic Bight Shelf Waters Near Cape Hatteras From Two Years of Underwater Glider Observations

“…Spray gliders for PEACH were typically deployed and recovered just beyond the shelf break near 35°50'N, 74°50'W using small vessels based in Wanchese, NC, except for the first glider deployed in April 2017, which was deployed from R/V Neil Armstrong just offshore of the shelf break near 38°22'N. Spray gliders tasked with surveying the Gulf Stream (Figure b, gray tracks; Todd, ; Todd & Locke‐Wynne, ; Todd et al, ) provided additional occupations of the slope transect before and during PEACH.…”

Advection by the North Equatorial Current of a Cold Wake due to Multiple Typhoons in the Western Pacific: Measurements From a Profiling Float Array

“…Many other oceanic measurements represent only chance encounters of a few days or statistical analyses of global data sets. Such data will become more common with intentional and fortuitous placement of moorings, air‐launched probes, surface drifters, gliders, and profiling floats (e.g., Baranowski et al, ; Black et al, ; Chang et al, ; Domingues et al, ; Jayne & Bogue, ; Lin et al, ; Mitarai & McWilliams, ; Mitchell et al, ; Mrvaljevic et al, ; Pallàs‐Sanz et al, ; Park et al, ; Price, ; Todd et al, ). Such data communicated in real time will increasingly contribute to forecasts (Chen, Cummings, et al, ; Domingues et al, ; Goni et al, ; Zhang & Emanuel, ).…”