Katabatic wind intensity and direction over Antarctica derived from scatterometer data

Abstract

Although satellite radar scatterometers are initially designed to measure ocean surface wind speed and direction, they also provide important observations over continental ice sheets. Data from the Seasat scatterometer analysed over a sector of Antarctica show that the signal is strongly dependent on the incidence angle of observation, but that it also depends on azimuth [Ledroit et al., 1992]. The minimum values of the backscatter coefficient (the ratio of backscattered versus incident power) are always observed in the direction of katabatic winds. A theoretical analysis shows that the backscatter coefficient must be very sensitive to the sastrugi slopes and orientations, which are streamlined features formed on the snow surface in the wind direction [Parish and Bromwich, 1987]. Satellite scatterometers can thus map the characteristics of sastrugis, of importance for the interpretation of microwave measurements above ice sheets; this indirectly provides the intensity and direction of these very persistent and strong winds, which play a important role in the behaviour of the atmosphere and ocean in high southern latitudes.