National Aeronautics and Space Administration

Wallops Flight Facility

Coastal Air-Sea Interaction Studies

Overview:

This work involves applying ocean surface and subsurface satellite remote sensing to study the exchange of energy and/or mass between the air and sea. One of NASA’s roles in these studies is the development of measurement techniques that ultimately serve to help answer questions about short or long-term climate conditions and their variation. The spatial and temporal resolution of satellite sensors is presently not well matched to fully determine the episodic ocean-atmosphere characteristics of a coastal region, but there is much work that can be done to exploit sensor data sets that have traditionally been developed for ‘open-ocean’ work. These sensors include the satellite scatterometer, synethic aperture radar (SAR) and altimeter. These systems resolve various aspects of the ocean surface roughness (i.e. waves) state and the process studies discussed below are designed to discover better uses for such data within coastal observation programs. Much of this works relies upon data collected using a small versatile air-sea flux research aircraft (NOAA N3R) instrumented to directly measure km-scale spatial variations in the ocean-atmosphere system.

Present Activities:

Coastal wave development and air-sea flux during cold air outbreaks

The continental east coast at mid-to-high latitude represents a unique boundary where cold polar continental air bursts eastward across the coastal ocean during strong post-frontal conditions in winter. These conditions occur annually and the strong air-to-sea thermal differences combine with strong turbulence to drive a large flux of energy between the ocean and atmosphere. This flux is by nature episodic but strongly impacts seasonal and annual means. These coastal situations are also unique because the surface wave energy builds seaward from the coast, i.e. starting from a near zero wave energy level at the beach. This idealized fetch-limited case is the subject of most theoretical ocean wave developments but is seldom observed in open-ocean satellite datasets where an energetic background field is usually present. The estimated flux of heat and momentum are modified by the wave roughness in the cold-air outbreak case but the level of impact is not well resolved, nor is the wave field definition itself.

Present research makes use of long-term NDBC buoy records for the Great Lakes and the U.S. east coast, along with satellite altimeter and scatterometer data for tracks that pass from land to sea, to look at the issue of how waves grow and dissipate during these strong air flow situations. Initial results merge buoy and altimeter data to show that the wave-induced turbulence is generally overestimated. We also show that the wave field models presently used do not match the measurements. A key implication is that the total flux for the episodes is likely overestimated and will have a strong cross-shore gradient that can be defined with help from an altimeter.

Small-scale spatial variations in CO2 flux – measurement and interpretation

Budgets for the air-sea exchange of carbon dioxide remain uncertain at both global and regional scales. This work addresses two aspects of CO2 exchange that require further investigation. The first is application of ocean remote sensing products to global CO2 flux measurement and monitoring. Second is the need for in situ CO2 flux characterization within coastal margins over time and space scales that cannot be obtained using buoy or ship-based programs. Field work targets aspects of both problems by a unique and timely combination of aircraft and surface-based observations, biogeochemical modeling and satellite data.

A field program is taking place in Aug. 2002 and 2003 to: 1) measure, catalogue, and analyze near-surface CO2 flux observations over a well-documented coastal region at < 10 km spatial resolution and over a one month time period, 2) use aircraft, buoy, ship, and satellite data to evaluate issues surrounding the nominal bulk air-sea mass flux equation, its global and/or local application, and effective input from ocean remote sensors. At heart is a unique eddy correlation CO2 flux data set to be collected by the NOAA LongEZ. Supporting surface data and modeling anticipate physical, chemical and biological modification of the ocean surface layer carbon dioxide system and resulting gas flux. Use of SeaWIFS, MODIS, and AVHRR imagery is central to both objectives.

Educational Outreach

Open opportunity to foster collaboration with the Earth, Ocean and Space Institute at the University of New Hampshire where a joint research center has been established with NASA/GSFC. An undergraduate student earth science recruitment program was established in 2002 to develop joint NASA/UNH mentoring for candidates with a long-term look towards developing career-long interests in earth system observation.

Future/Planned Directions:

Coastal wave development and air-sea flux during cold air outbreaks

Future work involves development of a altimeter-based coastal cold-air outbreak model that uses a catalogue of all observed events to depict the role that wave-induced fluxes play here. This study would be well-supported by an operational CODAR system set up on an U.S. east coast site to measure the wave field development for all such events.

Small-scale spatial variations in CO2 flux: measurement and interpretation

Preparations are underway for 2002 measurements off of Cape Cod as part of CBLAST. We are implementing a new surface reflectance capability based on the MicroPac hyperspectral radiometer and also adding a novel new Ku-band radar scatterometer built under a grant with the Univ. of Michigan. Results from the initial study should help to define a more rigorous use of branch tools and expertise within coastal CO2 flux studies and satellite inversions over this dynamic target.

Educational Outreach

A new Coastal Ocean Observation and Analysis (COOA) program, established between NOAA and UNH in 2002 offers another opportunity to interact with undergraduate and graduate students involved in related coastal studies.

Collaborators:

Lead Investigator: Douglas Vandemark