Understanding and Predicting the Gulf of Mexico Loop Current Critical Gaps and Recommendations (2018) / Chapter Skim
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3 Critical Gaps and Recommendations
3 Critical Gaps and Recommendations
Pages 37-62
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From page 37... ...
Because such observational gaps exist, understanding is limited, comprehensive data (other than SSH, SST, and episodic surface drifter data) are not assimilated, and numerical models may not include the necessary physical expressions of inflow/outflow, bathymetric effects, deep and upper ocean coupled dynamics, or air–sea boundary information.
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From page 38... ...
inflow/outflow study areas. expressions that reflect new understanding gained by an improved observational program in the full water column at the inflow/outflow points and as bathymetry affects LCS variability.
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From page 39... ...
. The LCS's Layered System Within the LCS active area -- an area roughly defined by the 200-meter isobaths on the Campeche Bank, West Florida Shelf and North Gulf Coast, 91° West, and Gulf areas west of the Texas/Mexico coast when an LCE is propagating westward, and by the areas of inflow and outflow (see Figure 3.1a)
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From page 40... ...
• Inflow/outflow forcing: role of flow through the Yucatan Channel and the Florida Straits • Interactions with bathymetry: internal interactions between the mesoscale circulation with bathymetry, including the continental shelves as well as new theory. Specific gaps and recommendations within this region, from atmosphere to seafloor, follow.
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From page 41... ...
While surface drifters can carry SST, air temperature, wind, and air pressure sensors, they typically give the position only and are not deployed widely or at regular time intervals. Recommendation 1: Additional instrumented surface drifters should be deployed when the LCS becomes active and throughout the LCS area to collect data on surface currents, SST, wind speed, air temperature, and air pressure at the air– sea interface.
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From page 42... ...
A recommendation in the Inflow/Outflow Recommendations section will be made to, in the near term, procure and/or install and operate HF radars to observe surface flows in the inflow/outflow areas (Yucatan Channel and Florida Straits)
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From page 43... ...
This is a critical gap, because forecasting the evolution of the baroclinic structure of the LC and related instability leading to eddy shedding relative to observations will be an important metric for success. Continual subsurface vertical profile data are missing, but especially required, in "pinch points" where the extended LC narrows before creating and shedding an eddy or reattaching an eddy; in the cooler water transported from the West Florida Shelf when eddies do separate; in areas where the anticyclonic LCEs interact with the cyclonic eddies; and as the LC front moves north into the Gulf, potentially interacting with bathymetry.
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From page 44... ...
It was not possible during those studies for a widely deployed and highly populated field of deep water instruments to report observations in near real time in an affordable manner. The recovered data were used by scientists to better understand the role of the deep ocean in LCS behaviors, and, as stressed above, the interaction between the deep barotropic layer with the baroclinic region above it; however, longer time series are clearly required to sample the variety of processes that affect different events.
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From page 45... ...
to provide lower- and upper-layer observations of currents, temperatures, salinity, and air–sea surface interface data in real time for data assimilation, and to serve as a calibration reference for other deep instrument installations and vehicles/profilers working in the upper layer. Inflow/Outflow Gulf of Mexico regional-scale ocean forecast models are required to have boundary conditions for inflow and outflow supplied from a larger scale global- or basin-scale model.
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From page 46... ...
Recommendation 9: The GRP should work closely with the appropriate Mexican institutions, in the near term, to keep the Yucatan Channel and Florida Straits mooring arrays operating beyond 2018 (for the next decade) with appropriate 1 At the time of report release, the data are publicly available at the following site: https://www.dropbox.
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From page 47... ...
data sharing; the Yucatan Channel array should take priority over the Florida Straits array. Recommendation 10: HF radars should be procured and operated to provide new real-time data, in the near term, for model assimilation and validation and to better understand complex and variable surface outflow regions.
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From page 48... ...
There is increasing interest in the role that bathymetry plays in triggering LC extension and its role in generating TRWs that then interact with the LCS's vertical structure. During the 2009–2011 BOEM-supported field study, in cooperation with Mexican colleagues, two mooring arrays were positioned across the Campeche Bank (moorings "N" and "E" in Figure 2.5)
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From page 49... ...
, or at the shelf break region just to the northwest of the Dry Tortugas, to get the long-term observational effort started earlier and to confirm times regarding when the LC is driving the West Florida Shelf circulation, a phenomenon hypothesized to also be controlling the LC itself.
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From page 50... ...
m TECHNOLOGY Chapter 2 describes the state of sensors, moorings, and other underwater emplacements and vehicles that carry sensors commonly used in measuring currents in the Gulf. Generally, existing technologies can now measure the variables that scientists need to better understand LCS behavior.
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From page 51... ...
Later, in Recommendation 22, the committee will discuss the value of a nearterm desktop modeling study, during which deeper data from bottom-mounted PIES instruments, along with glider and float observations -- data not currently assimilated in numerical models -- can inform modelers about the impact of fully assimilated deep data and can therefore inform decisions about investments in near-real-time capture of deeper observations. The committee notes that NOAA's tsunami warning array illustrates that bottom-mounted instruments can transfer data acoustically to a nearby mooring, which then telemeters the data ashore.
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From page 52... ...
can meet many of the recommendations listed in this report and can gather useful data at their specified mobility rates, the committee envisions evolving needs for more capable and bigger vehicles that might carry larger payloads and provide the requisite power for longer operational duration, higher speed, or an ability to maneuver more quickly to capture data during a rapidly changing LCS event. Another potential benefit to future glider operations is on-board path-planning algorithms to better execute desired trajectories in the face of challenging, dynamic conditions.
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From page 53... ...
Finally, the committee recommends that all glider operations in the LCS campaign use the NOAA IOOS-developed "glider DAC" protocols. DATA ASSIMILATION AND NUMERICAL MODELING Due either to the lack of data, or lack of long-term data, the physics involved in LCS behavior is not fully understood; hence, it may not be completely included in models' physical expressions.
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From page 54... ...
As discussed in Recommendations 16 and 17, this desktop study should pay special attention to the assimilation of deep observations, noting their impact on model skill and value if provided in near real time. Furthermore, such analyses can inform decisions on the value of near-real-time deep, but not bottom-mounted, instruments (e.g., deep gliders and Argo 54
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From page 55... ...
2014–2015, when the LCS was hyperactive, in which various LCE sheddings, reattachments, and propagations occurred. Each modeling system will be tasked to use its latest models and data assimilation schemes to assimilate observations (e.g., BOEM deep observations in 2009–2012, along with other publicly available surface observations such as satellite SSH, SST)
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From page 56... ...
Similarly, improved mixing and diffusion parameterizations are needed for lateral and bottom boundary layer dynamics, and for the energy and vorticity cascading across different scales. The assimilation of altimeter data in some LCS models relies on climatology-based synthetic T/S profiles that may deviate significantly from the real state, especially when energetic deep eddies perturb SSH and the LCS is active.
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From page 57... ...
. Such Monte Carlo schemes run an ensemble of simulations with perturbed initial conditions, boundary conditions, and/or stochastic forcing (Lermusiaux, 2006, 2007; Lermusiaux et al., 2006b)
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From page 58... ...
So far, most of the modeling efforts for the LCS use primitive equation ocean models. Recent developments in statistical modeling based on machine learning have shown promising potential in offering credible long-range LC and LCE separation forecasts.
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From page 59... ...
prediction of the LCS. Recommendation 26: Numerical modelers should be consulted in developing the specific observational programs' design, and that "adaptive sampling," based on model results, be continually practiced throughout the campaign, especially for those observational subprograms that have a choice in timing, areas of deployment, and vertical/horizontal spacing.
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From page 60... ...
METRICS OF SUCCESS There are two main parts to the campaign effort: the first is to use new observations to better understand the science, or dynamics, associated with the LCS; the second part and ultimate goal of the campaign is to use both the observations and the new scientific understanding to improve models of the LCS and thus increase predictive skill of LCS activity. The first measure of success hinges on advances in our understanding of the dynamics driving the LCS.
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From page 61... ...
and in areas where the LCEs propagate. The committee recommends a hierarchy of forecast periods, matched to the relevant processes and regions of interest: • Improved predictive skill in forecasting the LC and/or LCE current speed, vertical structure, and duration in the oil/gas operating area out to a fore cast period of days to 1 week • Improved predictive skill in forecasting the extension of the LC (location and duration)
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