Todd Robert E.

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Todd

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Robert E.

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0000-0002-6854-7729

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The scientific and societal uses of global measurements of subsurface velocity

(Frontiers Media, 2019-07-24) Szuts, Zoltan B. ; Bower, Amy S. ; Donohue, Kathleen A. ; Girton, James B. ; Hummon, Julia M. ; Katsumata, Katsuro ; Lumpkin, Rick ; Ortner, Peter B. ; Phillips, Helen E. ; Rossby, H. Thomas ; Shay, Lynn Keith ; Sun, Charles ; Todd, Robert E.

Ocean velocity defines ocean circulation, yet the available observations of subsurface velocity are under-utilized by society. The first step to address these concerns is to improve visibility of and access to existing measurements, which include acoustic sampling from ships, subsurface float drifts, and measurements from autonomous vehicles. While multiple programs provide data publicly, the present difficulty in finding, understanding, and using these data hinder broader use by managers, the public, and other scientists. Creating links from centralized national archives to project specific websites is an easy but important way to improve data discoverability and access. A further step is to archive data in centralized databases, which increases usage by providing a common framework for disparate measurements. This requires consistent data standards and processing protocols for all types of velocity measurements. Central dissemination will also simplify the creation of derived products tailored to end user goals. Eventually, this common framework will aid managers and scientists in identifying regions that need more sampling and in identifying methods to fulfill those demands. Existing technologies are capable of improving spatial and temporal sampling, such as using ships of opportunity or from autonomous platforms like gliders, profiling floats, or Lagrangian floats. Future technological advances are needed to fill sampling gaps and increase data coverage.
The equatorial current system west of the Galapagos Islands during the 2014-16 El Niño as observed by underwater gliders

(American Meteorological Society, 2020-12-21) Rudnick, Daniel L. ; Owens, W. Brechner ; Johnston, T. M. Shaun ; Karnauskas, Kristopher B. ; Jakoboski, Julie K. ; Todd, Robert E.

The strong El Niño of 2014–16 was observed west of the Galápagos Islands through sustained deployment of underwater gliders. Three years of observations began in October 2013 and ended in October 2016, with observations at longitudes 93° and 95°W between latitudes 2°N and 2°S. In total, there were over 3000 glider-days of data, covering over 50 000 km with over 12 000 profiles. Coverage was superior closer to the Galápagos on 93°W, where gliders were equipped with sensors to measure velocity as well as temperature, salinity, and pressure. The repeated glider transects are analyzed to produce highly resolved mean sections and maps of observed variables as functions of time, latitude, and depth. The mean sections reveal the structure of the Equatorial Undercurrent (EUC), the South Equatorial Current, and the equatorial front. The mean fields are used to calculate potential vorticity Q and Richardson number Ri. Gradients in the mean are strong enough to make the sign of Q opposite to that of planetary vorticity and to have Ri near unity, suggestive of mixing. Temporal variability is dominated by the 2014–16 El Niño, with the arrival of depressed isopycnals documented in 2014 and 2015. Increases in eastward velocity advect anomalously salty water and are uncorrelated with warm temperatures and deep isopycnals. Thus, vertical advection is important to changes in heat, and horizontal advection is relevant to changes in salt. Implications of this work include possibilities for future research, model assessment and improvement, and sustained observations across the equatorial Pacific.
Autonomous instruments significantly expand ocean observing : an introduction to the special issue on autonomous and Lagrangian platforms and sensors (ALPS).

(Oceanography Society, 2017-06) Lee, Craig M. ; Paluszkiewicz, Theresa ; Rudnick, Daniel L. ; Omand, Melissa M. ; Todd, Robert E.

Oceanography relies heavily on observations to fuel new ideas and drive advances, creating a strong coupling between the science and the technological developments that enable new measurements. Novel observations, such as those that resolve new properties or scales, often lead to advances in understanding. Physical, biological, and chemical processes unfold over a broad range of scales—seconds to decades and millimeters to ocean basins—with critical interactions between scales. Observational studies work within a tradespace that balances spatial and temporal resolution, scope, and resource constraints. New platforms and sensors, along with the novel observational approaches they enable, address this challenge by providing access to an expanding range of temporal and spatial scales.
Thermohaline structure in the California Current System : observations and modeling of spice variance

(American Geophysical Union, 2012-02-03) Todd, Robert E. ; Rudnick, Daniel L. ; Mazloff, Matthew R. ; Cornuelle, Bruce D. ; Davis, Russ E.

Upper ocean thermohaline structure in the California Current System is investigated using sustained observations from autonomous underwater gliders and a numerical state estimate. Both observations and the state estimate show layers distinguished by the temperature and salinity variability along isopycnals (i.e., spice variance). Mesoscale and submesoscale spice variance is largest in the remnant mixed layer, decreases to a minimum below the pycnocline near 26.3 kg m−3, and then increases again near 26.6 kg m−3. Layers of high (low) meso- and submesoscale spice variance are found on isopycnals where large-scale spice gradients are large (small), consistent with stirring of large-scale gradients to produce smaller scale thermohaline structure. Passive tracer adjoint calculations in the state estimate are used to investigate possible mechanisms for the formation of the layers of spice variance. Layers of high spice variance are found to have distinct origins and to be associated with named water masses; high spice variance water in the remnant mixed layer has northerly origin and is identified as Pacific Subarctic water, while the water in the deeper high spice variance layer has southerly origin and is identified as Equatorial Pacific water. The layer of low spice variance near 26.3 kg m−3 lies between the named water masses and does not have a clear origin. Both effective horizontal diffusivity, κh, and effective diapycnal diffusivity, κv, are elevated relative to the diffusion coefficients set in the numerical simulation, but changes in κh and κv with depth are not sufficient to explain the observed layering of thermohaline structure.
Horizontal scales of variability over the Middle Atlantic Bight shelf break and continental rise from finescale observations

(American Meteorological Society, 2013-01) Todd, Robert E. ; Gawarkiewicz, Glen G. ; Owens, W. Brechner

Observations with fine horizontal resolution are used to identify the horizontal scales of variability over the Middle Atlantic Bight (MAB) shelf break and continental rise. Spray gliders collected observations along two alongshelf transects over the continental rise in March–April 2006 and along 16 cross-shelf transects over the shelf break and continental rise during July–October 2007. Horizontal resolution varied from 1 km or finer over the shelf to 6 km in deep water. These observations allow horizontal thermohaline variability offshore of the MAB shelf break to be examined for the first time. Structure functions of temperature and salinity, the mean square difference between observations separated by specified distances, reveal the horizontal spatial scales in the region. Exponential (e-folding) scales of temperature and salinity increase from 8–13 km near the shelf break to about 30 km over the continental rise. Just offshore of the shelf break, alongshelf structure functions exhibit periodicity with a 40–50-km wavelength that matches the wavelength of shelfbreak frontal meanders. Farther offshore, alongshelf structure functions suggest a dominant wavelength of 175–250 km, but these scales are only marginally resolved by the available observations. Examination of structure functions of along-isopycnal salinity (i.e., spice) suggests that interleaving of shelf and slope water masses contributes most of the horizontal variability near the MAB shelf break, but heaving of isopycnals is the primary source of horizontal variability over the continental rise.
More than 50 years of successful continuous temperature section measurements by the global expendable bathythermograph network, its integrability, societal benefits, and future

(Frontiers Media, 2019-07-24) Goni, Gustavo J. ; Sprintall, Janet ; Bringas, Francis ; Cheng, Lijing ; Cirano, Mauro ; Dong, Shenfu ; Domingues, Ricardo ; Goes, Marlos Pereira ; Lopez, Hosmay ; Morrow, Rosemary ; Rivero, Ulises ; Rossby, H. Thomas ; Todd, Robert E. ; Trinanes, Joaquin ; Zilberman, Nathalie ; Baringer, Molly O. ; Boyer, Tim ; Cowley, Rebecca ; Domingues, Catia M. ; Hutchinson, Katherine ; Kramp, Martin ; Mata, Mauricio M. ; Reseghetti, Franco ; Sun, Charles ; Udaya Bhaskar, T. V. S. ; Volkov, Denis L.

The first eXpendable BathyThermographs (XBTs) were deployed in the 1960s in the North Atlantic Ocean. In 1967 XBTs were deployed in operational mode to provide a continuous record of temperature profile data along repeated transects, now known as the Global XBT Network. The current network is designed to monitor ocean circulation and boundary current variability, basin-wide and trans-basin ocean heat transport, and global and regional heat content. The ability of the XBT Network to systematically map the upper ocean thermal field in multiple basins with repeated trans-basin sections at eddy-resolving scales remains unmatched today and cannot be reproduced at present by any other observing platform. Some repeated XBT transects have now been continuously occupied for more than 30 years, providing an unprecedented long-term climate record of temperature, and geostrophic velocity profiles that are used to understand variability in ocean heat content (OHC), sea level change, and meridional ocean heat transport. Here, we present key scientific advances in understanding the changing ocean and climate system supported by XBT observations. Improvement in XBT data quality and its impact on computations, particularly of OHC, are presented. Technology development for probes, launchers, and transmission techniques are also discussed. Finally, we offer new perspectives for the future of the Global XBT Network.
Autonomous and Lagrangian ocean observations for Atlantic tropical cyclone studies and forecasts

(Oceanography Society, 2017-06) Goni, Gustavo J. ; Todd, Robert E. ; Jayne, Steven R. ; Halliwell, George R. ; Glenn, Scott ; Dong, Jili ; Curry, Ruth G. ; Domingues, Ricardo ; Bringas, Francis ; Centurioni, Luca R. ; DiMarco, Steven F. ; Miles, Travis ; Morell, Julio M. ; Pomales, Luis ; Kim, Hyun-Sook ; Robbins, Pelle E. ; Gawarkiewicz, Glen G. ; Wilkin, John L. ; Heiderich, Joleen ; Baltes, Rebecca ; Cione, Joseph J. ; Seroka, Greg ; Knee, Kelly ; Sanabia, Elizabeth

The tropical Atlantic basin is one of seven global regions where tropical cyclones (TCs) commonly originate, intensify, and affect highly populated coastal areas. Under appropriate atmospheric conditions, TC intensification can be linked to upper-ocean properties. Errors in Atlantic TC intensification forecasts have not been significantly reduced during the last 25 years. The combined use of in situ and satellite observations, particularly of temperature and salinity ahead of TCs, has the potential to improve the representation of the ocean, more accurately initialize hurricane intensity forecast models, and identify areas where TCs may intensify. However, a sustained in situ ocean observing system in the tropical North Atlantic Ocean and Caribbean Sea dedicated to measuring subsurface temperature, salinity, and density fields in support of TC intensity studies and forecasts has yet to be designed and implemented. Autonomous and Lagrangian platforms and sensors offer cost-effective opportunities to accomplish this objective. Here, we highlight recent efforts to use autonomous platforms and sensors, including surface drifters, profiling floats, underwater gliders, and dropsondes, to better understand air-sea processes during high-wind events, particularly those geared toward improving hurricane intensity forecasts. Real-time data availability is key for assimilation into numerical weather forecast models.
A shelf water cascading event near Cape Hatteras

(American Meteorological Society, 2021-06-01) Han, Lu ; Seim, Harvey E. ; Bane, John M. ; Todd, Robert E. ; Muglia, Michael

Carbon-rich Middle Atlantic Bight (MAB) and South Atlantic Bight (SAB) shelf waters typically converge on the continental shelf near Cape Hatteras. Both are often exported to the adjacent open ocean in this region. During a survey of the region in mid-January 2018, there was no sign of shelf water export at the surface. Instead, a subsurface layer of shelf water with high chlorophyll and dissolved oxygen was observed at the edge of the Gulf Stream east of Cape Hatteras. Strong cooling over the MAB and SAB shelves in early January led to shelf waters being denser than offshore surface waters. Driven by the density gradient, the denser shelf waters cascaded beneath the Gulf Stream and were subsequently entrained into the Gulf Stream, as they were advected northeastward. Underwater glider observations 80 km downstream of the export location captured 0.44 Sv (1 Sv ≡ 106 m3 s−1) of shelf waters transported along the edge of the Gulf Stream in January 2018. In total, as much as 7 × 106 kg of carbon was exported from the continental shelf to a greater depth in the open ocean during this 5-day-long cascading event. Earlier observations of near-bottom temperature and salinity at a depth of 230 m captured several multiday episodes of shelf water at a location that was otherwise dominated by Gulf Stream water, indicating that the January 2018 cascading event was not unique. Cascading is an important, yet little-studied pathway of carbon export and sequestration at Cape Hatteras.
The changing nature of shelf-break exchange revealed by the OOI Pioneer Array

(The Oceanography Society, 2018-02-09) Gawarkiewicz, Glen G. ; Todd, Robert E. ; Zhang, Weifeng G. ; Partida, Jacob ; Gangopadhyay, Avijit ; Monim, Mahmud-Ul-Hasan ; Fratantoni, Paula S. ; Mercer, Anna Malek ; Dent, Margaret

Although the continental shelf and slope south of New England have been the subject of recent studies that address decadal-scale warming and interannual variability of water mass properties, it is not well understood how these changes affect shelf-break exchange processes. In recent years, observations of anomalous shelf and slope conditions obtained from the Ocean Observatories Initiative Pioneer Array and other regional observing programs suggest that onshore intrusions of warm, salty waters are becoming more prevalent. Mean cross-shelf transects constructed from Pioneer Array glider observations collected from April 2014 through December 2016 indicate that slope waters have been warmer and saltier. We examine shelf-break exchange events and anomalous onshore intrusions of warm, salty water associated with warm core rings located near the shelf break in spring 2014 and winter 2017 using observations from the Pioneer Array and other sources. We also describe an additional cross-shelf intrusion of ring water in September 2014 to demonstrate that the occurrence of high-salinity waters extending across the continental shelf is rare. Observations from the Pioneer Array and other sources show warm core ring and Gulf Stream water masses intrude onto the continental shelf more frequently and penetrate further onshore than in previous decades.
Overview of the Processes driving Exchange At Cape Hatteras Program

(Oceanography Society, 2022-05-12) Seim, Harvey E. ; Savidge, Dana ; Andres, Magdalena ; Bane, John M. ; Edwards, Catherine ; Gawarkiewicz, Glen G. ; He, Ruoying ; Todd, Robert E. ; Muglia, Michael ; Zambon, Joseph B. ; Han, Lu ; Mao, Shun

The Processes driving Exchange At Cape Hatteras (PEACH) program seeks to better understand seawater exchanges between the continental shelf and the open ocean near Cape Hatteras, North Carolina. This location is where the Gulf Stream transitions from a boundary-trapped current to a free jet, and where robust along-shelf convergence brings cool, relatively fresh Middle Atlantic Bight and warm, salty South Atlantic Bight shelf waters together, forming an important and dynamic biogeographic boundary. The magnitude of this convergence implies large export of shelf water to the open ocean here. Background on the oceanography of the region provides motivation for the study and gives context for the measurements that were made. Science questions focus on the roles that wind forcing, Gulf Stream forcing, and lateral density gradients play in driving exchange. PEACH observational efforts include a variety of fixed and mobile observing platforms, and PEACH modeling included two different resolutions and data assimilation schemes. Findings to date on mean circulation, the nature of export from the southern Middle Atlantic Bight shelf, Gulf Stream variability, and position variability of the Hatteras Front are summarized, together with a look ahead to forthcoming analyses.
Along-stream evolution of Gulf Stream volume transport

(American Meteorological Society, 2020-07-30) Heiderich, Joleen ; Todd, Robert E.

The Gulf Stream affects global climate by transporting water and heat poleward. The current’s volume transport increases markedly along the U.S. East Coast. An extensive observing program using autonomous underwater gliders provides finescale, subsurface observations of hydrography and velocity spanning more than 15° of latitude along the path of the Gulf Stream, thereby filling a 1500-km-long gap between long-term transport measurements in the Florida Strait and downstream of Cape Hatteras. Here, the glider-based observations are combined with shipboard measurements along Line W near 68°W to provide a detailed picture of the along-stream transport increase. To account for the influences of Gulf Stream curvature and adjacent circulation (e.g., corotating eddies) on transport estimates, upper- and lower-bound transports are constructed for each cross–Gulf Stream transect. The upper-bound estimate for time-averaged volume transport above 1000 m is 32.9 ± 1.2 Sv (1 Sv ≡ 106 m3 s−1) in the Florida Strait, 57.3 ± 1.9 Sv at Cape Hatteras, and 75.6 ± 4.7 Sv at Line W. Corresponding lower-bound estimates are 32.3 ± 1.1 Sv in the Florida Strait, 54.5 ± 1.7 Sv at Cape Hatteras, and 69.9 ± 4.2 Sv at Line W. Using the temperature and salinity observations from gliders and Line W, waters are divided into seven classes to investigate the properties of waters that are transported by and entrained into the Gulf Stream. Most of the increase in overall Gulf Stream volume transport above 1000 m stems from the entrainment of subthermocline waters, including upper Labrador Sea Water and Eighteen Degree Water.
Ocean observations in support of studies and forecasts of tropical and extratropical cyclones

(Frontiers Media, 2019-07-29) Domingues, Ricardo ; Kuwano-Yoshida, Akira ; Chardon-Maldonado, Patricia ; Todd, Robert E. ; Halliwell, George R. ; Kim, Hyun-Sook ; Lin, I.-I. ; Sato, Katsufumi ; Narazaki, Tomoko ; Shay, Lynn Keith ; Miles, Travis ; Glenn, Scott ; Zhang, Jun A. ; Jayne, Steven R. ; Centurioni, Luca R. ; Le Hénaff, Matthieu ; Foltz, Gregory R. ; Bringas, Francis ; Ali, M. M. ; DiMarco, Steven F. ; Hosoda, Shigeki ; Fukuoka, Takuya ; LaCour, Benjamin ; Mehra, Avichal ; Sanabia, Elizabeth ; Gyakum, John R. ; Dong, Jili ; Knaff, John A. ; Goni, Gustavo J.

Over the past decade, measurements from the climate-oriented ocean observing system have been key to advancing the understanding of extreme weather events that originate and intensify over the ocean, such as tropical cyclones (TCs) and extratropical bomb cyclones (ECs). In order to foster further advancements to predict and better understand these extreme weather events, a need for a dedicated observing system component specifically to support studies and forecasts of TCs and ECs has been identified, but such a system has not yet been implemented. New technologies, pilot networks, targeted deployments of instruments, and state-of-the art coupled numerical models have enabled advances in research and forecast capabilities and illustrate a potential framework for future development. Here, applications and key results made possible by the different ocean observing efforts in support of studies and forecasts of TCs and ECs, as well as recent advances in observing technologies and strategies are reviewed. Then a vision and specific recommendations for the next decade are discussed.
Bifurcation and upwelling of the equatorial undercurrent west of the Galapagos Archipelago

(American Meteorological Society, 2020-03-19) Jakoboski, Julie K. ; Todd, Robert E. ; Owens, W. Brechner ; Karnauskas, Kristopher B. ; Rudnick, Daniel L.

The Equatorial Undercurrent (EUC) encounters the Galápagos Archipelago on the equator as it flows eastward across the Pacific. The impact of the Galápagos Archipelago on the EUC in the eastern equatorial Pacific remains largely unknown. In this study, the path of the EUC as it reaches the Galápagos Archipelago is measured directly using high-resolution observations obtained by autonomous underwater gliders. Gliders were deployed along three lines that define a closed region with the Galápagos Archipelago as the eastern boundary and 93°W from 2°S to 2°N as the western boundary. Twelve transects were simultaneously occupied along the three lines during 52 days in April–May 2016. Analysis of individual glider transects and average sections along each line show that the EUC splits around the Galápagos Archipelago. Velocity normal to the transects is used to estimate net horizontal volume transport into the volume. Downward integration of the net horizontal transport profile provides an estimate of the time- and areal-averaged vertical velocity profile over the 52-day time period. Local maxima in vertical velocity occur at depths of 25 and 280 m with magnitudes of (1.7 ± 0.6) × 10−5 m s−1 and (8.0 ± 1.6) × 10−5 m s−1, respectively. Volume transport as a function of salinity indicates that water crossing 93°W south (north) of 0.4°S tends to flow around the south (north) side of the Galápagos Archipelago. Comparisons are made between previous observational and modeling studies with differences attributed to effects of the strong 2015/16 El Niño event, the annual cycle of local winds, and varying longitudes between studies of the equatorial Pacific.
The Pacific Equatorial Undercurrent in three generations of global climate models and glider observations

(American Geophysical Union, 2020-10-22) Karnauskas, Kristopher B. ; Jakoboski, Julie K. ; Johnston, T. M. Shaun ; Owens, W. Brechner ; Rudnick, Daniel L. ; Todd, Robert E.

The Equatorial Undercurrent (EUC) is a vital component of the coupled ocean‐atmosphere system in the tropical Pacific. The details of its termination near the Galápagos Islands in the eastern Pacific have an outsized importance to regional circulation and ecosystems. Subject to diverse physical processes, the EUC is also a rigorous benchmark for global climate models (GCMs). Simulations of the EUC in three generations of GCMs are evaluated relative to recent underwater glider observations along 93°W. Simulations of the EUC have improved, but a slow bias of ~36% remains in the eastern Pacific, along with a dependence on resolution. Additionally, the westward surface current is too slow, and stratification is too strong (weak) by ~50% above (within) the EUC. These biases have implications for mixing in the equatorial cold tongue. Downstream lies the Galápagos, now resolved to varying degrees by GCMs. Properly representing the Galápagos is necessary to avoid new biases as the EUC improves.
Equatorial circulation in the western Indian Ocean during onset of the 2018 summer monsoon and links to the Bay of Bengal

(American Geophysical Union, 2020-02-29) Todd, Robert E.

Cross‐equator transects occupied by an underwater glider and a research vessel in the western Indian Ocean captured the evolution of equatorial circulation during onset of the boreal summer monsoon in 2018. At the end of the winter monsoon in March, surface currents were westward, while the equatorial undercurrent carried salty Arabian Sea High‐Salinity Water eastward. As winds transitioned from westward to eastward during April, an eastward near‐surface Wyrtki Jet developed, while the equatorial undercurrent weakened, vanishing by May. A first‐mode baroclinic Kelvin wave propagated through the survey region after westward winds relaxed. However, the vertical structure of the evolving circulation was inconsistent with the first baroclinic mode, suggesting the influence of higher modes in setting observed vertical structure. The strong equatorial undercurrent at the end of the winter monsoon allowed high‐salinity waters from the western equatorial Indian Ocean to reach the southern Bay of Bengal in summer 2018.
High-frequency internal waves and thick bottom mixed layers observed by gliders in the Gulf Stream

(John Wiley & Sons, 2017-06-26) Todd, Robert E.

Autonomous underwater gliders are conducting high-resolution surveys within the Gulf Stream along the U.S. East Coast. Glider surveys reveal two mechanisms by which energy is extracted from the Gulf Stream as it flows over the Blake Plateau, a portion of the outer continental shelf between Florida and North Carolina where bottom depths are less than 1000 m. Internal waves with vertical velocities exceeding 0.1 m s−1 and frequencies just below the local buoyancy frequency are routinely found over the Blake Plateau, particularly near the Charleston Bump, a prominent topographic feature. These waves are likely internal lee waves generated by the subinertial Gulf Stream flow over the irregular bathymetry of the outer continental shelf. Bottom mixed layers with O(100) m thickness are also frequently encountered; these thick bottom mixed layers likely form in the lee of topography due to enhanced turbulence generated by O(1) m s−1 near-bottom flows.
Export of middle Atlantic Bight Shelf waters near Cape Hatteras from two years of underwater glider observations

(American Geophysical Union, 2020-03-17) Todd, Robert E.

Equatorward flow of Middle Atlantic Bight (MAB) shelf waters meets poleward flowing South Atlantic Bight shelf waters over the continental shelf near Cape Hatteras, NC, leading to net export of shelf waters into the deep ocean. This export occurs in close proximity to the Gulf Stream, which separates from the continental margin near Cape Hatteras. Observations from sustained underwater glider surveys of the outer continental shelf and slope north of Cape Hatteras from spring 2017 to spring 2019 are used to examine the mean and variability of MAB shelf water export in the region. The 0.3 Sv (1 Sv = 106 m3 s−1) time‐mean export of MAB shelf water south of 37°N was dominated by discrete export events; 50% of export occurred during the 17% of the time during which transport was more than 1 standard deviation above the mean. These events typically occurred in late spring and summer of both years when equatorward flow into the region peaked. Export of MAB shelf water was correlated with equatorward flow into the region, which was itself correlated with the density gradient across the continental shelf break. Observations during specific time periods that capture extrema in MAB shelf water export are examined to highlight the variability in shelf‐deep ocean exchange scenarios in the Hatteras region. These include near‐surface export driven by hurricanes, subsurface export below the northern edge of the Gulf Stream, and a multi‐month near‐cessation of export.
Ocean observations to improve our understanding, modeling, and forecasting of subseasonal-to-seasonal variability

(Frontiers Media, 2019-08-08) Subramanian, Aneesh C. ; Balmaseda, Magdalena A. ; Centurioni, Luca R. ; Chattopadhyay, Rajib ; Cornuelle, Bruce D. ; DeMott, Charlotte ; Flatau, Maria ; Fujii, Yosuke ; Giglio, Donata ; Gille, Sarah T. ; Hamill, Thomas M. ; Hendon, Harry ; Hoteit, Ibrahim ; Kumar, Arun ; Lee, Jae-Hak ; Lucas, Andrew J. ; Mahadevan, Amala ; Matsueda, Mio ; Nam, SungHyun ; Paturi, Shastri ; Penny, Stephen G. ; Rydbeck, Adam ; Sun, Rui ; Takaya, Yuhei ; Tandon, Amit ; Todd, Robert E. ; Vitart, Frederic ; Yuan, Dongliang ; Zhang, Chidong

Subseasonal-to-seasonal (S2S) forecasts have the potential to provide advance information about weather and climate events. The high heat capacity of water means that the subsurface ocean stores and re-releases heat (and other properties) and is an important source of information for S2S forecasts. However, the subsurface ocean is challenging to observe, because it cannot be measured by satellite. Subsurface ocean observing systems relevant for understanding, modeling, and forecasting on S2S timescales will continue to evolve with the improvement in technological capabilities. The community must focus on designing and implementing low-cost, high-value surface and subsurface ocean observations, and developing forecasting system capable of extracting their observation potential in forecast applications. S2S forecasts will benefit significantly from higher spatio-temporal resolution data in regions that are sources of predictability on these timescales (coastal, tropical, and polar regions). While ENSO has been a driving force for the design of the current observing system, the subseasonal time scales present new observational requirements. Advanced observation technologies such as autonomous surface and subsurface profiling devices as well as satellites that observe the ocean-atmosphere interface simultaneously can lead to breakthroughs in coupled data assimilation (CDA) and coupled initialization for S2S forecasts. These observational platforms should also be tested and evaluated in ocean observation sensitivity experiments with current and future generation CDA and S2S prediction systems. Investments in the new ocean observations as well as model and DA system developments can lead to substantial returns on cost savings from disaster mitigation as well as socio–economic decisions that use S2S forecast information.
Transient response of the Gulf Stream to multiple hurricanes in 2017

(John Wiley & Sons, 2018-10-04) Todd, Robert E. ; Asher, Taylor G. ; Heiderich, Joleen ; Bane, John M. ; Luettich, Richard A.

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.
Submesoscale coherent vortices in the Gulf Stream.

(American Geophysical Union, 2019-02-27) Gula, Jonathan ; Blacic, Tanya M. ; Todd, Robert E.

Seismic images and glider sections of the Gulf Stream front along the U.S. eastern seaboard capture deep, lens‐shaped submesoscale features. These features have radii of 5–20 km, thicknesses of 150–300 m, and are located at depths greater than 500 m. These are typical signatures of anticyclonic submesoscale coherent vortices. A submesoscale‐resolving realistic simulation, which reproduces submesoscale coherent vortices with the same characteristics, is used to analyze their generation mechanism. Submesoscale coherent vortices are primarily generated where the Gulf Stream meets the Charleston Bump, a deep topographic feature, due to the frictional effects and intense mixing in the wake of the topography. These submesoscale coherent vortices can transport waters from the Charleston Bump's thick bottom mixed layer over long distances and spread them within the subtropical gyre. Their net effect on heat and salt distribution remains to be quantified.

Todd Robert E.

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