RADAR OBSERVATIONS OF GRAVITY-WAVE MOMENTUM FLUXES IN THE TROPOSPHERE AND LOWER STRATOSPHERE

The vertical flux of horizontal momentum in the troposphere and lower stratosphere has been measured with a 46.5 MHz radar system at Aberystwyth (52.4 degrees N, 4.1 degrees W) operating with two pairs of beams directed symmetrically about the vertical direction. The results refer to mean values for a total of 23 days, with distinctions being drawn between wave periods less and greater than 6 h and between days of low and high activity, as indicated by the wind values at 10 km altitude. It is found that for tropospheric heights the momentum fluxes deduced for the shorter periods are greater than for longer periods, for both zonal and meridional components. At lower stratospheric heights the short-period values are larger for the zonal component but not for the meridional. The momentum fluxes for long periods show little change with activity whereas the values for short periods are enhanced substantially during active periods. It is suggested that the relative momentum fluxes for short and long periods is influenced by the different directional dependence of the two sets of waves and that long-period motions are relatively more important in the troposphere and lower stratosphere than previously considered.