Mesospheric radar echoes at Poker Flat, Alaska: Evidence for seasonally dependent generation mechanisms


  • B. B. Balsley,

  • W. L. Ecklund,

  • D. C. Fritts


The long-term character of VHF mesospheric echoes obtained by using the Poker Flat MST radar in Alaska show the following characteristics: (1) The winter time echoes are relatively weak and are only present in the height range 55–80 km, while (2) the summertime echoes are much stronger, with the maximum echo intensity centered at 86 km. The evidence currently available indicates that the winter time echoes arise, from the nonlinear breakup of tropospherically generated gravity waves. The stronger summertime echoes, on the other hand, appear to arise in situ as a result of the combined effects of the steep summertime vertical temperature gradient that exists at these latitudes and the horizontal wind shears.