SYNOPTIC VIEW OF OCEAN SURFACE WIND BY NASA SCATTEROMETER

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[From Liu, W.T., and W. Tang, 1997: Spaceborne scattterometer in studies of atmospheric and oceanic phenomena from synoptic to interannual time scales. In Space Remotre Sensing of Subtropical Ocean., C.T. Liu (ed.), Elsevier Press, Amsterdam.]

This image shows ocean surface wind speeds and directions over the Pacific Ocean on 21 September 1996, 12 UTC, derived from observations by the NASA Scatterometer (NSCAT) onboard Japan's Advanced Earth Observing Satellite (ADEOS). The background color indicates wind speed and the white arrows show the direction of the wind. The basin-wide wind field is typical of near-Equinox atmospheric circulation. The strong (red color)Trade Winds blow steadily from the cooler subtropical ocean to the warm water of the Intertropical Convergence Zone (ITCZ) located just north the Equator. Instead of blowing in the north-south direction, the winds are deflected westward by the Corriolis Force due to the Earth's rotation. The air rises over the warm water of ITCZ and sinks in the subtropics at the Horse Latitudes, forming the Hadley Circulation. Both the convergence area at the ITCZ and the divergence area at the Horse Latitudes are indicated by low wind speed of blue color. In the mid-latitudes, the high vorticity due to strong Corriolis Force generates cyclones (yellow spirals) moving in the eastward direction. Two typhoons are observed in the western Pacific. Typhoon Violet is just south of Japan. After these data were taken, Typhoon Violet struck the East Coast of Japan causing damage and deaths. Typhoon Tom is located further east and did not land.

The image is based on preliminary processing of the first set of NSCAT observations, using prelaunch model function and calibration. The NSCAT data is objectively interpolated into 12 hourly and 1 degree longitude by 1 degree latitude grids, using the methodology described by Tang and Liu [JPL Publication 96-19, 1996], but with no other data used for initialization. This preliminary analysis clearly demonstrates that the high spatial resolution of NSCAT and its observing capability under cloudy conditions improve the monitoring of sever storms, such as typhoon, whose location and intensity are usually not well-defined by conventional methods. It also shows that the repeated global coverage provides a better description of atmospheric circulation over ocean, which has not been adequately sampled in the past.