Research Topics

Research in my group focuses on boundary, coastal, and equatorial current systems. We primarily use autonomous underwater gliders (http://gliders.whoi.edu) to collect long-duration, high-resolution observations that are then analyzed to understand upper ocean dynamics in these regions. We work in a variety of temperate and tropical locations around the world.

Gulf Stream

The Gulf Stream is the mid-latitude western boundary current of the North Atlantic and plays a key role in the Earth’s climate system as it transports heat from the tropics to mid-latitudes. Despite its proximity to the US East Coast, the Gulf Stream has been chronically under sampled. We are using Spray gliders to collect high-resolution transects across the Gulf Stream as it flows along the US East Coast between Florida and New England, filling a critical gap in long-duration, subsurface observations of this important current. This work has been funded by NSF, ONR, NOAA, Eastman Chemical, and WHOI. For more on our Gulf Stream work, please go here.

Cape Hatteras (PEACH)

Offshore of Cape Hatteras, NC, coastal waters from the Middle Atlantic Bight and South Atlantic Bight converge in close proximity to the Gulf Stream as it separates from the continental margin. The NSF-funded ‘Processes driving Exchange At Cape Hatteras (PEACH)’ program aims to understand the dynamics controlling exchange between the continental shelf and deep ocean in this highly variable area. Observations from a variety of observation platforms, including Spray gliders operated by our group, are being combined with numerical models to understand the drivers of exchange. Information on the entire PEACH program is available here. Details of our work in support of PEACH are here.

Equatorial Indian Ocean (NASCar and MISO-BOB)

Circulation in the equatorial and tropical Indian ocean is strongly influenced by the Asian monsoon, which has large-scale winds switching directions twice per year. As part of two ONR-funded DRIs, ‘Northern Arabian Sea Circulation–autonomous research (NASCar)’ and ‘Oceanic Control of Monsoon Intra-seasonal Oscillations in the Tropical Indian Ocean and the Bay of Bengal (MISO-BOB)’, we are conducting Spray and Slocum glider surveys in the western equatorial Indian Ocean and the Bay of Bengal. For more information on our Indian Ocean work, please go here.

Middle Atlantic Bight (TEMPESTS and Pioneer)

The continental shelf circulation over the Middle Atlantic Bight is strongly influenced by both offshore forcing (e.g., Gulf Stream rings) and passing weather systems (e.g., Nor’easters and Tropical Storms/Hurricanes). As part of a NOAA-funded program entitled `The Experiment to Measure and Predict East coast STorm Strength (TEMPESTS)’, we deployed a Slocum glider over the Middle Atlantic Bight shelf ahead of Hurricane Arthur (2014) and Hurricane Hermine (2016), as well as during springtime storms. The hurricane related work is documented in Goni et al. (2017, Oceanography). The Middle Atlantic Bight shelf break is also home to the Ocean Observatories Initiative’s Pioneer Array, which consists of moorings and gliders deployed for several years to measure shelf-ocean exchange processes. Prior to construction of the Pioneer Array, a Spray glider surveyed the region, and our analysis of those glider observations identified the key horizontal scales that the Pioneer Array needed to resolve (Todd et al., 2013, J. Phys. Oceanogr.). More recently, we have begun analysis of the large volume of observations collected by Pioneer Array Slocum glider; initial results from that examination suggest that shelfbreak processes and regional water properties have been heavily influenced by Gulf Stream Warm Core Rings in recent years (Gawarkiewicz et al., 2018, Oceanography).

California Current System (CUGN)

Along the West Coast of the US, the California Current System consists of a cool, fresh, equatorward flow near the surface (the California Current) and a warmer, saltier, poleward flow along the continental margin (the California Undercurrent). For more than a decade, Spray gliders have routinely surveyed along three cross-shore lines off central and southern California. Todd’s Ph.D. thesis work at the Scripps Institution of Oceanography relied on these observations. More on the results from the California Underwater Glider Network are available from the CUGN page at Scripps.

Equatorial Pacific Ocean (ROGER)

The Galápagos Archipelago is situated on the equator in the eastern Pacific, so it presents a barrier to the eastward flow of the Pacific Equatorial Undercurrent. The NSF-funded ‘Repeat Observations by Gliders in the Equatorial Region (ROGER)’ program used Spray gliders from our group at WHOI and from our collaborators at Scripps to survey the Equatorial Undercurrent and Equatorial Front to the west of the Galápagos for multiple years.

Doppler Current Profilers on Autonomous Underwater Gliders

With colleagues in the Instrument Development Group at Scripps, we have led efforts to use small acoustic Doppler current profilers (ADCPs) to estimate absolute horizontal velocities from gliders. Unlike geostrophic current estimates that are routinely made using glider observations of temperature, salinity, and depth averaged currents, ADCP-derived current estimates are available for each glider dive and in both horizontal directions. In equatorial regions, ADCPs on gliders allow us to measure the vertical structure of currents where the geostrophic estimates cannot be used due to the vanishing of the Coriolis parameter. We have also shown that ADCP measurements can be used to correct for the effects of biofouling-induced drag on glider-based estimates of depth averaged currents. Results from this work have been published in Todd et al. (2011, J. Geophys. Res.; 2017, J. Atmos. Oceanic Technol.).


 

Research in our group has been generously supported by the Office of Naval Research (ONR), National Science Foundation (NSF), National Oceanic and Atmospheric Administration (NOAA), Eastman Chemical Co., and WHOI.