Pearn P. Niiler

Air–Sea Exchange in Hurricanes: Synthesis of Observations from the Coupled Boundary Layer Air–Sea Transfer Experiment

The Coupled Boundary Layer Air–Sea Transfer (CBLAST) field program, conducted from 2002 to 2004, has provided a wealth of new air–sea interaction observations in hurricanes. The wind speed range for which turbulent momentum and moisture exchange coefficients have been derived based upon direct flux measurements has been extended by 30% and 60%, respectively, from airborne observations in Hurricanes Fabian and Isabel in 2003. The drag coefficient (CD) values derived from CBLAST momentum flux measurements show CD becoming invariant with wind speed near a 23 m s−1 threshold rather than a hurricane-force threshold near 33 m s−1 . Values above 23 m s−1 are lower than previous open-ocean measurements. The Dalton number estimates (CE) derived from CBLAST moisture flux measurements are shown to be invariant with wind speeds up to 30 m s −1 which is in approximate agreement with previous measurements at lower winds. These observations imply a CE/CD ratio of approximately 0.7, suggesting that additional energy sour...

Ocean mixed layer depth: A subsurface proxy of ocean‐atmosphere variability

A new criterion, based on the shallowest extreme curvature of near surface layer density or temperature profiles, is established for demarking the mixed layer depth, h mix. Using historical global hydrographic profile data, including conductivity-temperature-depth and expendable bathythermograph data obtained during World Ocean Circulation Experiment, its seasonal variability and monthly to interannual anomalies are computed. Unlike the more commonly used Δ criterion, the new criterion is able to deal with both different vertical resolutions of the data set and a large variety of observed stratification profiles. For about two thirds of the profiles our algorithm produces an h mix/c that is more reliable than the one of the Δ criterion. The uncertainty for h mix/c is ±5 m for high- (<5 m) and ±8 m for low- (<20 m) resolution profiles. A quality index, QImix, which compares the variance of a profile above h mix to the variance to a depth of 1.5 × h mix, shows that for the 70% of the profile data for which a clearly recognizable well-mixed zone exists near the surface, our criterion identifies the depth of the well-mixed zone in all cases. The standard deviation of anomalous monthly h mix/c is typically 20–70% of the long-term mean h mix/c . In the tropical Pacific the monthly mean anomalies of h mix/c are not well correlated with anomalies of sea surface temperature, which indicate that a variety of turbulent processes, other than surface heat fluxes, are important in the upper ocean there. Comparisons between observed h mix/c and Massachusetts Institute of Techonology/ocean general circulation model/Estimating the Circulation and Climate of the Ocean model simulated mixed layer depth indicate that the KPP algorithm captures in general a 30% smaller mixed layer depth than observed.

Surface currents in the Bransfield and Gerlache Straits, Antarctica

We used 39 tracks of mixed layer drifters deployed during the period from November 1988 to January 1990 to study the surface flow characteristics in the Bransfield and Gerlache Straits, Antarctica. The results revealed both the Gerlache Strait Current and the Bransfield Strait Current, which flows along the deep channel of the Gerlache Strait, northeastward to the southern continental margin of the South Shetland Islands following the 750 m isobath. The observed strongest sustained daily mean current reached approximately 40 cm s � 1 in the Bransfield Strait and was confined to the shelf break south of the South Shetland Islands. The computed acceleration of drifters in the Bransfield Strait Current indicates the southward transversal component limits drifters from approaching isobaths shallower than 750 m. The southern side of the Current is rich in cyclonic eddies. Drifters spun off and circulated in cyclonic eddies over deep basins. The residence time of a water parcel in the current is approximately 10–20 days. Anticyclonic circulations were observed around Tower, Hoseason and Liege Islands, and long residence times were found for drifters in shallows and bays of up to 70 days. Results also indicate the Gerlache Strait water can extend along the shelf of the Antarctic peninsula to Tower Island, where it meets the southewestward Weddell Sea water. Most of the Gerlache Strait water exits northward and enters the Bransfield Strait Current. It Spins off and mixes with other waters in the Bransfield Strait. Several long tracks indicated the existence of a cyclonic large circulation gyre in the Bransfield Strait during the ice-free condition. The circulation patterns in both Bransfield and Gerlache Straits change seasonally. The analysis of force balance indicates that currents and eddies are geostrophic though the ageostrophic components are important to maintain currents and form eddies. This composition of eddies and currents provides ideal physical settings for zooplankton growth in eddies and bays and zooplankton dispersion in currents. r 2002 Elsevier Science Ltd. All rights reserved.

Cold‐core eddy detected in South China Sea

A large, cyclonic, cold-core eddy was present in the South China Sea in January 1994. The eddy was first indicated in altimetric data from TOPEX/Poseidon; measurements of sea-surface height revealed levels characteristic of eddy activity. The surface topography of the 500-km-wide eddy was then charted by surface-drifting buoy data and sea surface temperature acquired by satellite. The use of TOPEX/Poseidon data to study surface current variability is common, but the confirmation of transient sea level anomalies and their associated geostrophic velocities by several types of measurements is rare.

The Labrador Sea Deep Convection Experiment data collection

Between 1996 and 1998, a concerted effort was made to study the deep open ocean convection in the Labrador Sea. Both in situ observations and numerical models were employed with close collaboration between the researchers in the fields of physical oceanography, boundary layer meteorology, and climate. A multitude of different methods were used to observe the state of ocean and atmosphere and determine the exchange between them over the experiments period. The Labrador Sea Deep Convection Experiment data collection aims to assemble the observational data sets in order to facilitate the exchange and collaboration between the various projects and new projects for an overall synthesis. A common file format and a browsable inventory have been used so as to simplify the access to the data.

Coastal meteorology and oceanography: Report of the third prospectus development team of the U. S. Weather Research Program to NOAA and NSF

U.S. Weather Research Program (USWRP) prospectus development teams (PDTs) are small groups of scientists that are convened by the USWRP lead scientist on a one-time basis to discuss critical issues...