William J. Teague

The Modular Ocean Data Assimilation System (MODAS)

The Modular Ocean Data Assimilation System (MODAS) is used by the U.S. Navy for depiction of three- dimensional fields of temperature and salinity over the global ocean. MODAS includes both a static climatology and a dynamic climatology. While the static climatology represents the historical averages, the dynamic cli- matology assimilates near-real-time observations of sea surface height and sea surface temperature and provides improved temperature and salinity fields. The methodology for the construction of the MODAS climatology is described here. MODAS is compared with Levitus and Generalized Digital Environmental Model climatologies and with temperature and salinity profiles measured by SeaSoar in the Japan/East Sea to illustrate MODAS capabilities. MODAS with assimilated remotely sensed data is able to portray time-varying dynamical features that cannot be represented by static climatologies.

Bottom-Up Determination of Air-Sea Momentum Exchange Under a Major Tropical Cyclone

As a result of increasing frequency and intensity of tropical cyclones, an accurate forecasting of cyclone evolution and ocean response is becoming even more important to reduce threats to lives and property in coastal regions. To improve predictions, accurate evaluation of the air-sea momentum exchange is required. Using current observations recorded during a major tropical cyclone, we have estimated this momentum transfer from the ocean side of the air-sea interface, and we discuss it in terms of the drag coefficient. For winds between 20 and 48 meters per second, this coefficient initially increases and peaks at winds of about 32 meters per second before decreasing.

A statistical comparison of wind speed, wave height, and wave period derived from satellite altimeters and ocean buoys in the Gulf of Mexico region

The capability of spaceborne altimeters to provide precise measurement of significant wave height and wind speed has been demonstrated repeatedly. It is shown in this paper that in addition to the significant wave height and wind speed, the wave period can be calculated from the semiempirical functions established from earlier wave research. The calculated characteristic wave period using the altimeter-derived wind speed and wave height are found to be in excellent agreement with the peak wave period and average wave period from the ocean buoy measurements in the Gulf of Mexico. Also, with the long time series of collocated data set, it is possible to compare altimeter output of wind and wave parameters with ocean buoy measurements taking into consideration the spatial lags between the buoy locations and the altimeter footprints, and the temporal lags between the two sensor systems. It is found that when the spatial lags are less than 10 km, the RMS difference of the significant wave height is approximately 0.1 m, which is the digitization resolution of the output from both altimeter and ocean buoy. For the wind speed, the RMS difference approaches 1.2 m/s in the Gulf of Mexico using the empirical algorithms. The wind speed agreement is significantly improved to 0.8 m/s when the tilting effect on the altimeter cross section is accounted for. In contrast to the spatial lags, temporal lags of up to 1 hour do not appear to produce significant difference in the statistics of comparison based on this study.

Low-Frequency Current Observations in the Korea/Tsushima Strait*

Abstract High resolution, continuous current measurements made in the Korea/Tsushima Strait between May 1999 and March 2000 are used to examine current variations having time periods longer than 2 days. Twelve bottom-mounted acoustic Doppler current profilers provide velocity profiles along two sections: one section at the strait entrance southwest of Tsushima Island and the second section at the strait exit northeast of Tsushima Island. Additional measurements are provided by single moorings located between Korea and Tsushima Island and just north of Cheju Island in Cheju Strait. The two sections contain markedly different mean flow regimes. A high velocity current core exists at the southwestern section along the western slope of the strait for the entire recording period. The flow directly downstream of Tsushima Island contains large variability, and the flow is disrupted to such an extent by the island that a countercurrent commonly exists in the lee of the island. The northeastern section is marked b...

Connectivity of the Taiwan, Cheju and Korea Straits

Insight into the circulation of the East China Sea and origin of the Tsushima Current are investigated through direct, concurrent measurements of velocities through the Taiwan, Cheju, and Korea Straits. Current data are obtained from six bottom-mounted acoustic Doppler current profilers (ADCPs) arrayed along a section spanning the Korea Strait, a single bottom-moored ADCP in the Cheju Strait, and four bottom-moored ADCPs along a section spanning the Taiwan Strait. Mass transports are computed for the October–December, 1999 time period. In addition, temperature and salt transports are examined in conjunction with climatological values of temperature and salinity. Average volume transport is 0.14 Sverdrups (Sv) through the Taiwan Strait, 0:59 Sv for the Cheju Strait, and 3:17 Sv for the Korea Strait. Salt and temperature transport through the Korea Strait and into the Japan/East Sea are 110:48 � 10 6 kg=s and 0:24 � 10 15 watts (W), respectively. Heat loss in the East China Sea is approximately 200 W=m 2 : Winds affect the transports in each of the straits. Most noticeable wind effects are observed in the Taiwan Strait where strong north wind events force flow into the South China Sea. The main source for the Tsushima Current and its flow into the Japan/East Sea is clearly the Kuroshio for fall, 1999. Published by Elsevier Science Ltd.

Monthly Variations of Water Masses in the Yellow and East China Seas, November 6, 1998

The monthly water mass variations in the Yellow Sea and the East China Sea are investigated using over 40 years of historical temperature and salinity observations via a cluster analysis that incorporates geographical distance and depth separation in addition to the temperature and salinity. Results delineate monthly variations in the major water masses and provide some insight into formation mechanisms and intermixing. The major water masses include the Kuroshio-East China Sea water (KE), the Yellow Sea surface water (YSS) and bottom cold water (YSB), mixed water (MW), and coastal water (CW). The distribution of the KE water mass reveals the intrusion pattern into the area west of Cheju. A separate mixed water type appears between the KE water mass and the Yellow Sea water masses during winter. The formation mechanism of the YSB appears to be the surface cooling and active mixing in winter. In the East China Sea, during summer, surface water is differentiated from the subsurface water while there is no differentiation during winter. In the Yellow Sea, a three layer system exists in the summer and fall (May–November) while a two layer system exists during the rest of the year. A fresh water mass generated by Yangtze River discharge (YD) is present over the northern East China Sea and the southern Yellow Sea during summer.

Observed Oceanic Response over the Upper Continental Slope and Outer Shelf during Hurricane Ivan

Abstract Hurricane Ivan passed directly over an array of 14 acoustic Doppler current profilers deployed along the outer continental shelf and upper slope in the northeastern Gulf of Mexico. Currents in excess of 200 cm s−1 were generated during this hurricane. Shelf currents followed Ekman dynamics with overlapping surface and bottom layers during Ivan’s approach and transitioned to a dominant surface boundary layer as the wind stress peaked. Slope currents at the onset of Ivan were wind driven near the surface, but deeper in the water column they were dominated during and after the passage of Ivan by subinertial waves with a period of 2–5 days that had several characteristics of topographic Rossby waves. Currents on the slope at 50 m and greater depths commonly exceeded 50 cm s−1. Surprisingly, the strongest currents were present to the left of the storm track on the shelf while more energetic currents were to the right of the hurricane path on the slope during the forced stage. Near-inertial motion last...

Monthly Variations of Water Masses in the Yellow and East China Seas

The monthly water mass variations in the Yellow Sea and the East China Sea are investigated using over 40 years of historical temperature and salinity observations via a cluster analysis that incorporates geographical distance and depth separation in addition to the temperature and salinity. Results delineate monthly variations in the major water masses and provide some insight into formation mechanisms and intermixing. The major water masses include the Kuroshio-East China Sea water (KE), the Yellow Sea surface water (YSS) and bottom cold water (YSB), mixed water (MW), and coastal water (CW). The distribution of the KE water mass reveals the intrusion pattern into the area west of Cheju. A separate mixed water type appears between the KE water mass and the Yellow Sea water masses during winter. The formation mechanism of the YSB appears to be the surface cooling and active mixing in winter. In the East China Sea, during summer, surface water is differentiated from the subsurface water while there is no differentiation during winter. In the Yellow Sea, a three layer system exists in the summer and fall (May– November) while a two layer system exists during the rest of the year. A fresh water mass generated by Yangtze River discharge (YD) is present over the northern East China Sea and the southern Yellow Sea during summer.

Current and tide observations in the southern Yellow Sea

Determination of mean currents and tides are particularly difficult in coastal regions. Flows are often nongeostrophic and short lived. Bathymetry is frequently not adequately known and can greatly influence coastal dynamics. To better quantify tides and currents in the southern Yellow Sea, three pressure gauges and three acoustic Doppler current profilers (ADCPs) were bottom moored for 4–6 month intervals at depths ranging from 77 to 89 m. Tidal range is over 2 m, and maximum current velocities are between 50 and 80 cm/s at the mooring locations. The present data are analyzed for 13 significant tidal constituents which are found to account for ∼85% of the sea surface height variability. M2 is the dominant constituent, followed by S2 and K1. Flow is dominated by the tides. Mean currents are relatively small, ranging from ∼1.5 cm/s at the northern mooring to ∼4 cm/s at the southern mooring. Delineations of barotropic and depth-dependent currents are made from the ADCP measurements in terms of mean and eddy kinetic energy. Currents are found to be most depth dependent in the near-surface layers. Approximately 85–90% of the eddy kinetic energy is depth independent.

Evaluation and Sensitivity Analysis of an Ocean Model Response to Hurricane Ivan

Abstract An ocean model response to Hurricane Ivan (2004) over the northwest Caribbean Sea and Gulf of Mexico is evaluated to guide strategies for improving performance during strong forcing events in a region with energetic ocean features with the ultimate goal of improving coupled tropical cyclone forecasts. Based on prior experience, a control experiment is performed using quasi-optimal choices of initial ocean fields, atmospheric forcing fields, air–sea flux parameterizations, vertical mixing parameterizations, and both horizontal and vertical resolutions. Alternate experiments are conducted by altering one single model attribute and comparing the results to SST analyses and moored ADCP current measurements to quantify the sensitivity to that attribute and identify where to concentrate model improvement efforts. Atmospheric forcing that does not resolve the eye and eyewall of the storm (scales >10 km) substantially degrades the ocean response. Ordering other model attributes from greatest to least sen...