Spaceborne Scattcrometer in Studies of Atmospheric and oceanic Phenomena from Synoptic to I

SpaceborneW. Timothyof TechnologyPasadena, CA 91109, U.S.A.1. IntroductionWind is driven by the differential heating of the atmosphere. Atmospheric water and latent heat arein both atmosphere andin moderating the world’s climate. Without wind, the Earth would be a hostile and less suitable habitat.The ocean and the atmosphere are turbulent fluids with non-linear interaction; processes at one scale affectspatial scales.The ocean surface wind. Becausemicrowave penetrates clouds, themeasures bothis given in Section 2.TheThe repeated climateSouthern Oscillation.in studying these atmospheric and oceanic phenomena are given in Section 3-6.A state-of-ml instrument, the NASA will be launched inAugust 1996 and its specifications are described in Section 7. The potential of synergistic application of NSCAT data with otherA few decades ago, marine radar noise on their radar screenswhich(reflection) of the radar pulses from the ocean surface by the rippling waves on the ocean’s surface. The idea of remote sensing of ocean surface windswinds. In the last two decades, empirical relations have been developed between the radaret al., 19S4] and andhave be-en discussed by Stewart[1985],send microwave pukes to the ocean surface and measure theremained. The retrieval of surface wind vectors from observations by spacebornemodelfunction essentially expresses theas a function of the equivalent wind speed at a referencethe polarization of the microwave, and a number of secondary non-wind factors, suchthe effect of) with maxima at upwind and downwind and minima near crosswind. ondensity stratification, in addition to surface roughness, the equivalent neutral wind is used with the intention to remove the effect of atmosphericThe secondary factors on the the relation between wind andet al. [1988], and others. The normalizedat [ 1981 ] andA single anddirection. For the orientedantennae, up to four solutions measurements [e.g., Longand ambiguity in wind direction can theoretically, bypractice, however, the model function inversion usually results in multiple solutions having nearly the same speed but differing widely in direction, because of noisy additional processing is stillrequired to select a unique wind direction, the capability of presentazimuth angles reduces the task ofmade by merchant ships; ship reportsbut does not reveal the surface intensity. Spacebornepotential ofwhen numerical prognoses of major weather centers missed the intensification. Surface pressure which would help to gauge the intensity and to locate the center of the storm can also be derived from and Liu, 1982] assuming1986]. Hsu and Liu [1996] extended such technique to study typhoon (tropical cyclone) by adding a gradient wind balance in deriving pressure field usingwinds.The detailed structure of the wind-field within theThe overlaid ofwater dramatically visualizes not only the structure of the typhoon, but the relation between the dynamics and the hydrologic balance in theM o n s o o nMonsoon is the seasonal change of winds which is forced byMonsoon affects a large area of the world [Ram age, 1971]. It is periodic only in the sense that it comes every andintensity, and retreat varygreatly, and the variation has strong economic impact and may cause severe human suffering. While the economic impact ofin planetary waves, and the effects mayand upwelling [e.g., Liu et al. 1992]. Over landbut the breedingmonitored. Spacebornespatial resolution is conducive to monitoring and understanding monsoon.The differences between the monsoon in the South China Sea and the Bay of Bengal are obvious in Fig. 2. in theflow changing from southeast to southwest direction. Atarea, leaving the atmosphere over the the humid air returns to the .ocean again.oriented inmonsoonChina Sea. TheIn the fall, stronger off-shore windsCurrentOver small scale and near the equator, the effect of the earth’s rotation is small. The relation wind just drags the water along,large scale, wind and current is not in the same direction, A century ago, the Norwegian explorer,driftersThe track of the drifters deployed in 1992 at 15m depth to withinwere first interpolated to the time and position of the drifter. Then a coherence analysis on the two vector quantities - wind and current, was performed, The phase of the coherence which represents the average angle between the two vectors clearly showswind in southern hemisphere. The angle roughly falls between 145/16/17/18/19/110/120N15N5s10s Iof surface wind (black arrows temperature (upper) and in horizontal axis represents vertical axis run from the n the to the Bangladesh at microwave1, and then interpolatedseven-day maps through iteration,1--’”----”-10.8—-- —--o100200300-50.0 -40.0-30.0-20.0 -10.0drifters deployed in colors represent magnitude(upper) and phase (lower) of fromand ocean current velocity at 15 m Thewind velocity is interpolated to drifter locationvaries with latitudeare found in the equatorialsubtropicalfrom thewind-driven ocean circulation, Such and thecomponent removed driftervelocity) has been developed by Ralph andOn the basis of temporally averaged observations [Rasmussen andhas been traditionallyeastward-propagating disturbances in theby thenumerical models. The intensity of episodic wind anomalies an ElNine) event, as shown by data taken at island stations and at mood buoys [e.g., Luther et al., changes in surface temperature is on forcing and response is notcomprehensive enough to answer this question.Recently, the evolution of an El Nino warming event in the eastern tropical Pacific at the second half of 1994spacecraft [Space News, Vol. 6, No. 5, page 13, 1995]. in Fig, 4, four spaceborneareshown and these deviations are, hereafter, referred to as anomalies. In the equatorial eastern Pacific, the Trades Winds generally blow from the west to the east and theirpropagating,altimeter. Corresponding to the passage of Kelvin waves are surface-warming episodes observed byepisodes. Unlikemore frequent, last for shorter periods, and are less intense. Whether the 1994 warming can be classified as an El Nino is being debated. The coincident observations infer clearly that the westerly wind anomalies are precursor of Elunderstanding, and prediction of7Noss.160M7165E160W125W90W“c-10121,5right); sea surface temperature7. NASAsun-synchronous orbit on the Japanese Advanced in August 1996 on an H-IIwill sendTheantennas will scan two separated by a330measures the provide surface wind vectorat 50on ERS 1 which scans only one 475Data ActiveArchive Center at the Jet Propulsion Laboratoryobserved over ocean with quality flags, in wind vein the ground tracks organized bywith the selected wind Level 3products are time and space averaged daily maps of wind vectors over gl by 0.5 longitude grid. A near real time fast data product will(NOAA) and will be availablefrom NOAA and productand the forSeaWinds, onvariability is beingand complementary data for monitoring, understanding, and predicting global climate and environmental is the providedirect (wind) and derived (current) dynamiccycles. Thus, it is complementary to otherspaceborne sensors which measure hydrologic parameters, e.g., the operational SpecialSensor Microwave on theColor and Temperature SensorThe continuous acquisition ofsampling requirements equal or superior to the requirements for SeaWinds, is highlydesirable to assure sufficient observations in the understanding ofAcknowledgmentsThis study is performed at the Jet Propulsion Laboratory, California Institute ofTechnology, under contract with the National Aeronautics and Space AdministrationNASA and EarthObserving Systemdrifter data andBrown, R. A., and G. Levy, 1986:J.M.H., and 1993: A preliminary C-bandFirst79-84.Fu, The Sea, Volume 9, Ocean Engineering andandR. E., and J.Rev.,T.N., 1985: Summer monsoon experiment - a review. Mon. Wea. Rev.,Psi,1979: Bulk parametrization of air-sea exchanges of heat and water vapor including themolecularJ. 36, 1722.-1735.Liu, W. T., andtemperature and atmosphericstability in the estimation of average. wind speed bymeasurements. IEEE Trans. Sensing. 29, 268-276.Lukas, R., S. Hayes, and K.Carpenter,Nine, Mon. Wea. Rev. 110, 354.sock and TRISTAR drifters. Deep-SeaJ.10735-10749.Ralph, E. A., and P. measurement of the mean wind-drivencurrents in the tropical Pacific. InternationalC. S., 1971: Monsoon Meteorology. Academic Press, New York, 296 pp.Stewart, Univ. ofD.E.. ILL. Davidson,relationships and stress:Ii’cS., 99, 10087-10108. A model function forJ.。