Scientists Derive First Bottom-Up Determination of Air-Sea Momentum Transfer Under a Major Hurricane
March 29, 2007
The eye of Hurricane Ivan passed directly over an array of 14 ocean moorings containing acoustic Doppler current profilers and wave/tide gauges on the outer continental shelf and upper slope in the northeastern Gulf of Mexico. Black dots indicate the mooring locations, spaced about 10 to 20 km apart. Here, the wind stress field (color background) and wind direction arrows are shown as Hurricane Ivan passed over the array. Wind stress ranged from zero in the eye (dark blue circle) to about 10 Pascal in the red-shaded region northeast of the eye. All moorings survived the direct hit of the storm. Wind fields were provided by the National Oceanic & Atmospheric Administration's Hurricane Research Division, Atlantic Oceanographic and Meteorological Laboratory. Source: NRL
Scientists at the Naval Research Laboratory - Stennis Space Center (NRL-SSC) have directly derived the air-sea momentum exchange at the ocean interface using observed ocean currents under Hurricane Ivan and determined that it decreases when winds exceed 32 meters per second.
This is the first time that momentum exchange at the air-sea interface has been directly calculated from ocean current observations under extreme winds generated by a major tropical cyclone. The complete findings of this study titled "Bottom-up Determination of Air-Sea Momentum Exchange Under a Major Tropical Cyclone," are published in the March 23, 2007 issue of Science.
Proper evaluation of the air-sea exchange under extreme winds is of great importance for modeling and forecasting used in hurricane studies, such as in forecasting of storm track and intensity, surges, waves, and currents, particularly since our coasts have become so heavily populated. These results should be of widespread interest to the public, oceanographers, atmospheric scientists, numerical modelers, oil and gas concerns, commerce, and government agencies, explains William Teague of NRL. This research has a direct impact on storm surge modeling. Many models have been estimating the air-sea momentum exchange by assuming that it increases as the wind speed increases. But the NRL research definitely shows that this is not the case. This research will lead to a better estimation of the air-sea momentum exchange which will improve both ocean circulation and storm surge models.
During NRL's Slope to Shelf Energetics and Exchange Dynamics (SEED) field experiment, six current profiler moorings were deployed on the continental shelf at water depths ranging between 60 and 90 meters just west of the DeSoto Canyon, about 100 miles south of Mobile Bay, Alabama. Eight moorings were also deployed down the slope, but not used in this study. Fortuitously, early on September 16, the eye of Hurricane Ivan passed directly over the array of moorings. Historically, instruments moored in the ocean do not even survive such powerful storms, much less direct hits. Fortunately, all of the SEED moorings survived this powerful storm, and provided the best ocean measurements of currents and waves ever obtained directly under a major hurricane.
Past studies have attempted to determine the air-sea momentum exchange from the atmospheric side of the air-sea interface ("top-down determination") using limited, difficult to interpret meteorological observations and/or models developed for the atmospheric boundary layer. For instance, drop sondes launched from airplanes during hurricanes have been used to measure wind profiles and to estimate air-sea momentum transfer. These wind analyses suggest that the air-sea momentum transfer decreases at high wind speeds, not increases as previously thought.
No attempt has been made to determine this momentum transfer independently based on ocean observations until now. The initial forced oceanic response to Hurricane Ivan on the continental shelf consisted of a strong barotropic flow and a much weaker baroclinic component. This response was governed to the first order by the linear time-dependent depth-integrated momentum balance. Such behavior of the currents allowed a direct estimation of air-sea momentum exchange for winds greater than 20 meters per second.
NRL's direct derivation of the air-sea momentum exchange using unique ocean current profiles measured directly under Hurricane Ivan confirms the trend suggested by studies based on meteorological measurements and models developed for the atmospheric boundary layer. NRL researchers found that the exchange decreases when hurricane winds exceed 32 meters per second. These findings are compared with the atmospheric-based work using the drag coefficient. The wind stress at the sea surface, which was directly calculated from current measurements, is related to the square of the wind speed times the drag coefficient. NRL researchers were able to determine good estimates of the drag coefficient with error bounds for high winds up to 48 meters per second.
Source: Naval Research Laboratory
-
Report: Electronic health records still need work
Jan 27, 2012 |
not rated yet |
0
-
Global health funding slows as deadline for Millennium Development Goals nears
Dec 14, 2011 |
not rated yet |
0
-
India's Satyam posts strong profit growth
Nov 10, 2011 |
not rated yet |
0
-
India's Wipro positive despite global uncertainty
Oct 31, 2011 |
not rated yet |
0
-
Spin lasers in the fast lane: New concept for ultrafast lasers developed
Oct 28, 2011 |
5 / 5 (5) |
0
-
Engineers build first sub-10-nm carbon nanotube transistor
Feb 01, 2012 |
4.9 / 5 (31) |
30
-
Something old, something new: Evolution and the structural divergence of duplicate genes
Jan 31, 2012 |
4.6 / 5 (7) |
1
-
The hidden nanoworld of ice crystals: Revealing the dynamic behavior of quasi-liquid layers
Jan 30, 2012 |
5 / 5 (3) |
1
-
Stock market network reveals investor clustering
Jan 27, 2012 |
3.9 / 5 (23) |
8
-
Of microchemistry and molecules: Electronic microfluidic device synthesizes biocompatible probes
Jan 26, 2012 |
5 / 5 (1) |
0
-
Do some geologists actually act a lot like Randy Marsh?
17 hours ago
-
Discrepancy between oxygen and carbon-dioxide levels
Feb 09, 2012
-
where gems are found in the world
Feb 09, 2012
-
Wind Waves in Reservoir ~ Wind run-up and Wind set-up
Feb 08, 2012
-
Balance of oxygen in the atmosphere
Feb 01, 2012
-
The case for a methanol-based economy
Jan 30, 2012
- More from Physics Forums - Earth
More news stories
Europe stakes billion-dollar bet on new rocket
A pencil-slim rocket is scheduled to lift into space from South America on Monday, carrying a billion-dollar bet that Europe can grab a juicy slice of the market to place satellites in low orbit.
Space & Earth / Space Exploration
16 hours ago |
3.5 / 5 (2) |
0
Political leaders play key role in how worried Americans are by climate change: study
More than extreme weather events and the work of scientists, it is national political leaders who influence how much Americans worry about the threat of climate change, new research finds.
Feb 06, 2012 |
5 / 5 (6) |
72
NASA budget will axe Mars deal with Europe: scientists
US President Barack Obama's budget proposal to be submitted next week for 2013 will cut NASA's budget by 20 percent and eliminate a major partnership with Europe on Mars exploration, scientists said Thursday.
Space & Earth / Space Exploration
Feb 10, 2012 |
5 / 5 (3) |
48
Humans may have helped the decline of African rainforests 3000 years ago
(PhysOrg.com) -- Large areas of rainforests in Central Africa mysteriously disappeared over three thousand years ago, to be replaced by savannas. The prevailing theory has been that the cause was a change ...
Could Venus be shifting gear?
(PhysOrg.com) -- ESAs Venus Express spacecraft has discovered that our cloud-covered neighbour spins a little slower than previously measured. Peering through the dense atmosphere in the infrared, the ...
Space & Earth / Space Exploration
Feb 10, 2012 |
5 / 5 (8) |
10
|
Walney offshore wind farm is world's biggest (for now)
(PhysOrg.com) -- The Walney wind farm on the Irish Sea--characterized by high tides, waves and windy weather--officially opened this week. The farm is treated in the press as a very big deal as the Walney ...
GPS court ruling leaves US phone tracking unclear
A US Supreme Court decision requiring a warrant to place a GPS device on the car of a criminal suspect leaves unresolved the bigger issue of police tracking using mobile phones, legal experts say.
Europeans protest controversial Internet pact
Tens of thousands of people marched in protests in more than a dozen European cities Saturday against a controversial anti-online piracy pact that critics say could curtail Internet freedom.
Study finds that anti-diabetic medication can prevent the long-term effects of maternal obesity
In a study to be presented today at the Society for Maternal-Fetal Medicine's annual meeting, The Pregnancy Meeting, in Dallas, Texas, researchers will report findings that show that short therapy with the anti-diabetic medication ...
Netflix settlement trims 14 pct off 4Q earnings
(AP) -- Netflix pressed the rewind button on its fourth-quarter earnings after settling allegations that the video subscription service violated a consumer-privacy law.
Navy to begin tests on electromagnetic railgun prototype launcher
The Office of Naval Research (ONR)'s Electromagnetic (EM) Railgun program will take an important step forward in the coming weeks when the first industry railgun prototype launcher is tested at a facility ...