TURBULENCE EDDY DISSIPATION RATES FROM RADAR OBSERVATIONS AT 5-20 KM AT WHITE-SANDS MISSILE RANGE, NEW-MEXICO

A climatology of the eddy dissipation rate is presented based on the w idths of the Doppler radar spectra observed by the 50-MHz, clear-air p rofiler located at White Sands Missile Range, New Mexico. The observat ions are from radar beams 15 degrees off zenith and extend from about 5 to 20 km altitude. The data are nearly continuous over the 5-year pe riod 1991-1995. Mean corrections to the observed spectral widths are m uch larger for beam-broadening effects than for vertical shear of the wind or gravity-wave effects. The mean eddy dissipation rate falls bet ween about 10(-35) and 10(-25) m(2) s(-3) altitudes and all seasons. T he hourly means at a given height have an approximately lognormal freq uency distribution. The hourly values have larger standard deviations in the troposphere than in the stratosphere. The maximum eddy dissipat ion rate is found at the lowest altitude observed, and the minimum val ue is found about 2-3 km below the tropopause, depending upon season. At about 6-10 km altitude the summer values of eddy dissipation rate a re several decibels larger than those during other seasons. When the o bservations are sorted according to distance from the tropopause, ther e is very little difference among the seasonal values. The summer trop ospheric values show very large interannual changes; the large values of eddy dissipation rate correlate with high surface temperatures and with large mean hourly standard deviations of vertical velocity (an in dicator of convective activity in the troposphere). The diurnal change s of eddy dissipation rate and of hourly vertical velocity standard de viations also have similar patterns; that is, largest values occur in the afternoon, and smallest values occur during the night. The largest diurnal range of eddy dissipation rates is found during the summer in the troposphere. The correlation of hourly values of eddy dissipation rate with hourly values of wind speed and vertical wind shear is rela tively low, which suggests that the eddy dissipation rate is strongly controlled by the small-scale flow and is not well predicted from feat ures of the large-scale flow.