Ocean Buoy Data Research Articles

Comparison of TOPEX/POSEIDON altimeter derived wave period with ocean buoy data in the East China Sea and South China Sea

Altimeter wave period data obtained from continental shelf seas are analyzed in this paper. Empirical models are introduced for zero up-crossing and peak wave period calculation with TOPEX/POSEIDON data. Their performances are assessed using independent validation dataset in four sites in the open ocean of China. To provide more accurate wave period estimation, new coefficients are applied to reliablein situ data. Comparison of our estimated the wave periods with new linear calibrations based on independent data of Seapac 2100 deployed in the East China Sea and South China Sea showed that the accuracy was improved over estimates determined from earlier empirical models. Regional analysis indicated that the wave period model works better under wind sea condition.

Diurnal cycle of tropical precipitation in Tropical Rainfall Measuring Mission (TRMM) satellite and ocean buoy rain gauge data

The climatological diurnal cycle of precipitation in the tropics is analyzed using data from rain gauges on ocean buoys and satellite measurements by the Tropical Rainfall Measuring Mission (TRMM) satellite. The ocean buoy data are from the NOAA/Pacific Marine Environmental Laboratory Tropical Atmosphere‐Ocean/Triangle Trans‐Ocean buoy Network in the tropical Pacific Ocean. TRMM data are from the precipitation radar (PR) and the TRMM microwave imager (TMI). Climatological hourly mean precipitation rates are analyzed in terms of the diurnal and semidiurnal harmonics. Both data sets confirm an early morning peak in precipitation over ocean regions. The amplitude of the diurnal harmonic over the oceans is typically less than 25% of the mean precipitation rate. Over tropical land masses the rainfall peaks in the afternoon and evening hours. The relative amplitude of the diurnal harmonic over land is larger than over the ocean, often exceeding 50% of the mean rain rate. Previously noted differences between the TMI and PR rainfall retrievals persist in the diurnal cycle. On average the TMI measures more rainfall than the PR and has a larger diurnal variation. Phase differences between the two instruments do not show a consistent bias.

Pulse of an Ocean: Sonification of Ocean Buoy Data

The author presents his work in sonifying ocean buoy data for scientific, pedagogical and compositional purposes. Mapping the spectral buoy data to audible frequencies creates interesting and illuminating sonifications of ocean wave dynamics. Several phenomena can be heard, including both those visible and those invisible in graphical representations of the data. The author has worked extensively with this data to compose music and to produce Music from the Ocean, a multi-media CD-ROM demonstrating the data, the phenomena and the sonification. After a brief introduction to physical oceanography, many examples are presented and a composition and installation created from the sonifications are discussed.

Surface winds in The Arabian Sea from MSMR — an Empirical approach

Multi-channel Scanning Microwave Radiometer (MSMR) onboard 1RS P4 (Oceansat I) measured Brightness Temperature data of the different bands are found sensitive to the surface and the overlying atmosphere to different degrees. A judicious combination of multi-channel data can provide such oceanic/atmospheric parameters as surface wind speed, sea surface temperature, water vapour in the marine atmosphere, etc. This paper highlights results obtained in relation to surface wind speed. Co-location and concurrence of several ocean data buoys in the Arabian Sea with MSMR observations allowed empirical construction of D-matrix coefficients for surface wind speed. With both MSMR and the Arabian Sea buoys functioning for the period of one and a half year (June, 1999 to December, 2000) without interruptions provided a large database. All channels are found to exhibit moderate sensitivity to surface wind speed. MSMR data in the immediate vicinity (within 150 km) of the buoy locations and within a time window of one hour were used. A multi-channel linear equation for surface wind speed was subsequently derived. The equation was subjected to tests with independent data set for the period January - June 2001 over the Arabian Sea and found to be moderately accurate. The empirical equation is expected to be useful for regional applications over the Arabian Sea and over regions closer to west coasts, which might have been flagged out in the operational geophysical data stream. An interesting subset of data revealed the wind signatures of the May 2001 cyclone in the Arabian Sea.

Impact of Oceansat-I MSMR data on analyzed oceanic winds and wave predictions

The present study makes an assessment of the impact of satellite data on ocean surface wind analysis and predicted wave heights. The surface wind analysis data utilized in this study were generated by assimilation of satellite data in numerical weather prediction models. The impact of these winds on the wave heights predicted by a third generation ocean wave model (WAM) was also studied. Results of several numerical experiments involving analysis products generated with a multi-frequency scanning microwave radiometer (MSMR) on board the Oceansat-I satellite and their comparison with those generated by the SSM/I radiometer onboard the DMSP satellites, as well as without these satellite products, have been presented. Extensive comparison results of MSMR ingested surface wind analyses (and corresponding model predicted wave heights) with ocean buoy data and co-located and concurrent measurements of the Topex/Poseidon altimeter over the Indian Ocean are presented in this work. The impact of satellite derived winds was also seen through time series analysis. The results of the experiments carried out show that ingestion of MSMR data produces significant improvement in the surface wind analysis and predicted wave heights for the corresponding winds compared to those generated without ingestion of satellite winds. The experiments also show that the surface wind analysis with MSMR ingested surface wind speed is almost as good as that obtained with SSM/I.

Evaluation of Wind Vectors Observed by QuikSCAT/SeaWinds Using Ocean Buoy Data

Wind vectors observed by the QuikSCAT/SeaWinds satellite mission are validated by comparing with wind and wave data from ocean buoys. Effects of oceanographic and atmospheric environment on scatterometer measurements are also assessed using the buoy data. Three versions of QuikSCAT/SeaWinds wind data were collocated with buoy observations operated by the National Data Buoy Center (NDBC), Tropical Atmosphere Ocean (TAO), and Pilot Research Moored Array in the Tropical Atlantic (PIRATA) projects, and the Japan Meteorological Agency (JMA). Only buoys located offshore and in deep water were analyzed. The temporal and spatial differences between the QuikSCAT/SeaWinds and buoy observations were limited to less than 30 min and 25 km. The buoy wind speeds were converted to equivalent neutral winds at a height of 10 m above the sea surface. The comparisons show that the wind speeds and directions observed by QuikSCAT/SeaWinds agree well with the buoy data. The root-mean-squared differences of the wind speed and direction for the standard wind data products are 1.01 m s - 1 and 23°, respectively, while no significant dependencies on the wind speed or cross-track cell location are discernible. Inaddition, the dependencies of wind speed residuals on oceanographic and atmospheric parameters observed by buoys are examined using the collocated data. A weak positive correlation of the wind speed residuals with the significant wave height is found, while dependencies on the sea surface temperature or atmospheric stability are not physically significant.

Comparison of TOPEX/POSEIDON Altimeter Derived Wind Speed and Wave Parameters with Ocean Buoy Data in the North Indian Ocean

Results of comparison exercises carried out between the state-of-the-art TOPEX/POSEIDON altimeter-derived ocean surface wind speed and ocean wave parameters (significant wave height and wave period) and those measured by a set of ocean data buoys in the North Indian Ocean are presented in this article. Altimeter-derived significant wave height values exhibited rms deviation as small as - 0.3 m, and surface wind speed of - 1.6 m/s. These results are found consistent with those found for the Pacific Ocean. For estimation of ocean wave period, the spectral moments-based semiempirical approach, earlier applied on GEOSAT data, was extended to TOPEX/POSEIDON. For this purpose, distributions of first four years of TOPEX/POSEIDON altimeter data and climatology over the North Indian Ocean were analyzed and a new set of coefficients generated for estimation of wave period. It is shown that wave periods thus estimated from TOPEX/POSEIDON data (for the subsequent two years), when compared with independent data set of ocean data buoys deployed in the North Indian Ocean, exhibit improved accuracy (rms ~ - 1.4 nos) over those determined earlier with GEOSAT data.

Revised ocean backscatter models at C and Ku band under high‐wind conditions

A series of airborne scatterometer experiments designed to collect C and Ku band ocean backscatter data in regions of high ocean surface winds has recently been completed. More than 100 hours of data were collected using the University of Massachusetts C and Ku band scatterometers, CSCAT and KUSCAT. These instruments measure the full azimuthal normalized radar cross section (NRCS) of a common surface area of the ocean simultaneously at four incidence angles. Our results demonstrate limitations of the current empirical models, C band geophysical model function 4 (CMOD4), SeaSat scatterometer 2 (SASS 2), and NASA scatterometer 1 (NSCAT) 1, that relate ocean backscatter to the near‐surface wind at high wind speeds. The discussion focuses on winds in excess of 15 m s−1 in clear atmospheric conditions. The scatterometer data are collocated with measurements from ocean data buoys and Global Positioning System dropsondes, and a Fourier analysis is performed as a function of wind regime. A three‐term Fourier series is fit to the backscatter data, and a revised set of coefficients is tabulated. These revised models, CMOD4HW and KUSCAT 1, are the basis for a discussion of the NRCS at high wind speeds. Our scatterometer data show a clear overprediction of the derived NRCS response to high winds based on the CMOD4, SASS 2, and NSCAT 1 models. Furthermore, saturation of the NRCS response begins to occur above 15 m s−1. Sensitivity of the upwind and crosswind response is discussed with implications toward high wind speed retrieval.

Ocean Surface Winds off the West Coast of New Zealand: A Comparison of Ocean Buoy, ECMWF Model, and Land-Based Data

Abstract Wind data for the period July–October 1994 from an ocean buoy moored off the west coast of New Zealand have been compared with model wind data from the European Centre for Medium-Range Weather Forecasts (ECMWF) and data from the nearest land-based station. The buoy and ECMWF winds were highly coherent and strongly polarized in the alongshore direction, suggesting that the ECMWF model correctly accounts for the orographic effect of the mountainous New Zealand landmass on the prevailing synoptic weather systems. At low frequencies, the ECMWF data can be used as a substitute for in situ wind data in oceanographic applications in the New Zealand region. This is a similar result to that reported in some Northern Hemisphere studies. In contrast, winds at the land-based site were much weaker and less strongly aligned alongshore than winds recorded offshore.

Validation of wind speeds and significant wave heights observed by the TOPEX altimeter around Japan

The wind speeds and significant wave heights observed by the TOPEX altimeter during the first 30 repeat cycles (for about 10 months) are validated by comparing with the data obtained at Japanese Ocean Data Buoy stations. The values of Kuband σ0 observed by the altimeter show good agreement with those estimated from the buoy wind speed using the modified Chelton-Wentz algorithm. The wind speeds derived from the Ku-band σ0 using the algorithm agree well with the buoy data with an rms difference of 1.99 ms−1. The significant wave heights observed by the altimeter have a systematic bias of 0.3 m.

A statistical method to get surface level air-temperature from satellite observations of precipitable water

Ten-day mean surface level air-temperature from SSMI precipitable water (SSMI-T a ) has been derived and compared with the temperature from two ocean data buoys (Buoy-T a ) of Japan Meteorological Agency (JMA) for a period of six months (July–December, 1988). Statistical relations between air-temperature and mixing ratio, using data from ocean data buoys are used to derive air-temperature from mixing ratio, obtained from SSMI precipitable water. For getting the mixing ratio from precipitable water, regional mixing ratio-precipitable water relations have been used, instead of global relation proposed by Liu (1986). The rms errors (standard deviation of the difference between SSMI-T a and Buoy-T a ) for two buoy locations are found to be 1.15 and 1.12°C, respectively. Surface level temperature for the two buoy locations are also derived using direct regression relation between Buoy-T a and precipitable water. The rms errors of the SSMI-T a , in this case are found to be reduced to 1.0°C.

Observation of temperature and velocity from a surface buoy moored in the Shikoku Basin (OMLET-88) —An oceanic response to a Typhoon

A surface buoy was moored from 20 April to 2 November 1988 at 28°48′ N and 135°01′ E where the water depth was 4900 m to measure temperature and velocity in the upper 150 m. The Typhoon 8824 passed at 0300 (JST) on 8 October about 50 km north to the mooring station with a maximum wind speed of 43.5 m s−1. The buoy was shifted about 30 km to southwest, and the instruments were damaged. The records of temperature at 0.5 m and velocity at 50 m were obtained. The inertial oscillation caused by the typhoon is described using the current record. The oscillation endured for about 20 days. Deep mixing and vertical, heart transport by the typhoon are discussed based on the data from the Ocean Data Buoy of the Japan Meteorological Agency moored at 29°N and 135°E.

Estimation of sea surface temperatures around Japan using the advanced very high resolution radiometer (AVHRR)/NOAA-11

The accuracy of sea surface temperatures (SSTs) derived from the Advanced Very High Resolution Radiometer (AVHRR)/NOAA-11 is examined by comparison with sea-truth SSTs obtained from ocean data buoys durings November 1988 through December 1989. We made a 122 point data set of buoy SSTs from the oceans around Japan and the corresponding brightness temperatures of channels 4 and 5 during cloud free periods. The satellite temperatures are corrected for atmospheric effects using the NOAA Multi-Channel SST (MCSST) and Cross Product SST (CPSST) algorithms. The two algorithms give similar results for our data set and result in biases of about −0.1°C with rms errors of about 0.6°C relative to buoy SSTs. It is found that MCSSTs and CPSSTs tend to be higher than SSTs from the buoy in the Japan Sea in summer. New coefficients for the MCSST equations suitable for our data set are determined and the resultant rms error is 0.49°C. If we eliminate the cluster of anomalous summer data in the Japan Sea, the rms error becomes 0.43°C.

Wave propagation in the marginal ice zone: Model predictions and comparisons with buoy and synthetic aperture radar data

In this paper the ocean wave dispersion relation and viscous attenuation by a sea ice cover are studied for waves propagating into the marginal ice zone (MIZ). The derivation of the dispersion relation and the viscous attenuation by an ice sheet are discussed for waves under flexure and pack compression. In the MIZ, the flexure effect is important for short waves. For a fixed wave period the changes in wavelength and group velocity as a function of ice thickness are significant. In turn, the exponential wave attenuation rate shows a rollover at short wave periods, whereby the rapid increase in wave attenuation rate with decreasing wave period slows down or even turns into a decrease. The Labrador Ice Margin Experiment (LIMEX), conducted on the MIZ off the east coast of Newfoundland, Canada, in March 1987, provides us with aircraft synthetic aperture radar (SAR) imagery, wave buoy, and ice property data. On the basis of the wave number spectrum from the SAR data and the concurrent wave frequency spectrum from the ocean buoy data and accelerometer data on the ice during LIMEX '87, the dispersion relation has been estimated and compared with a model. Wave energy attenuation rates are estimated from SAR data and the ice motion package data which were deployed at the ice edge and into the ice pack, and compared with the model. The model‐data comparisons are reasonably good for the ice conditions observed during LIMEX '87. Some previously reported data of wave attenuation in the MIZ are revisited for model comparison.

A comparison between geostrophic and observed winds at a Japan Meteorological Agency Buoy in the East China Sea

Geostrophic winds (vg) calculated over the East China Sea from surface pressure maps are compared to observed winds (vo) from a Japan Meteorological Agency Ocean Data Buoy for the period of January-April 1986. For mean winds, the average counterclockwise veering angle fromvg tov0 is 32° and there is no difference in speed. For fluctuating winds, the Ekman veering and speed reduction fromvg tov0 are respectively 16° and 2%. Co-spectral analysis of the two time series indicates very high coherency and a slight lead in phase by the buoy observations. The phase difference is consistent with the general movement of fronts from west to east and the fact that the geostrophic winds are calculated for a point 155 km to the southeast of the buoy.

Arctic Data Buoy Program

The Arctic Data Buoy Program described in this article is designed to provide certain fundamental data from an inaccessible region, using automatic devices rather than costly manned stations. The first effort in that direction was the Soviet Drifting Automatic Radiometeorological Stations (DARMS) programme of the 1950s and 1960s (Olenicoff, 1968). These buoys reflected the then state of technology which involved the use of heavy storage batteries and a method of location by high frequency (HF) radio wave triangulation (Figs 1,2; Table 1). Restrictions of that system—high cost, weight, and limited range and accuracy of HF radio wave triangulation— apparently caused the Soviet Union to terminate the programme. At about the same time satellite navigation and data transmission technology, developed in the United States, created a new generation of data buoys. These buoys can accommodate a wide range of sensors, data compression and pre-processing devices and hull designs, for stationary use on land, as moored or drifting ocean data buoys, or on sea ice; they can be installed on land, in the ocean from ships, or by parachute drops from aircraft.

NOAA deploys two new buoys

A deep ocean data buoy has been deployed recently in the Gulf of Mexico, by the National Oceanic and Atmospheric Administration (NOAA) with the assistance of the U.S. Coast Guard, to provide additional meteorological data for forecasting the drift of oil from the Campeche oil spill.The NOAA buoy will be anchored 65 miles off the Texas coast, in 4800 feet of water at 26.5°N, 96°W, in front of the expected drift of oil.

Experimental Evaluation of Ground-Based Microwave Radiometric Sensing of Atmospheric Temperature and Water Vapor Profiles

Profiles of atmospheric temperature and water vapor derived from ground-based microwave radiometric measurements are compared with concurrent rawinsonde profiles including both clear and cloudy cases. Accuracies of the temperature profiles including the cloudy cases are quite close to predicted accuracies. Mean virtual temperatures between commonly used pressure levels are also compared and resulting rms accuracies are 1.1, 1.6, 2.0 and 2.8/sup 0/C for the 1000--850, 850--700, 700--500 and 500--300 mb layers, respectively. The microwave technique is potentially useful in applications requiring high time resolution or in data-sparse regions of the oceans that might be covered by an ocean data buoy system.

Effective Cloudiness Derived from Ocean Buoy Data

Abstract There is a need in the study of the dynamic aspects of radiation balance at the sea surface for cloud cover information on a finer scale than is presently available, especially for analyses of historic data. Although cloud cover is difficult to obtain without a human observer, or more recently without a satellite, insolation can be readily measured and recorded by an untended instrument. Cloud cover can then be estimated by using well-known formulas usually intended for calculating insolation from known cloud cover. An example of such a computation on a daily basis is presented here using insolation data from deep-moored instrument stations in the North Pacific Ocean. The effective cloudiness thus obtained is used to calculate the radiation balance at the sea surface.

Electronics in meteorological instrumentation

The review traces the development of electronics as applied to meteorological instrumentation. A brief introduction and history is followed by a short survey of meteorological communications, illustrating the need for the rapid availability of accurate current data in forecasting work. The development of the use of electronics in instrumental methods is then traced with reference to the work done within the British Meteorological Office. A Section on upper-air instrumentation commences with the general design principles of radiosondes, and includes examples of the techniques given. A survey of methods used for upper-wind finding follows, and the Section ends with an account of techniques employed in measuring atmospheric ozone. In a Section on ground instrumentation, the methods used for measuring the basic parameters of cloud height, visibility, surface wind and sunshine are surveyed, and examples of the various techniques for the automatic acquisition and recording of data follow next. The role of electronics in the instrumentation of ocean-data buoys used for obtaining meteorological data is then treated, with examples of systems in use. The various satellite systems developed for meteorological purposes are then surveyed. In the conclusion, an attempt is made to forecast the part to be played by electronics in meteorological instrumentation during the next decade or so.