12th Conference on Middle Atmosphere

Wednesday, 6 November 2002
A gravity wave induced ice-cloud over Greenland: model validation and investigation of dynamical mechanisms
S. Buss, Institute for Atmospheric and Climate Science, Zurich, Switzerland; and H. Wernli and H. Davies
On the 14th of January 2000, the backscattar ratios from the lidar mounted on the NASA DC-8 revealed the presence of a mesoscale (about 25 km in the direction of the flight) ice cloud at an altitude of 24 km. In fact, this was the only ice-cloud over Greenland that has been observed during the intensive observation campaign SOLVE-THESEO 2000.

Here we present results of mesoscale simulations for this event which encompass the entire island. The model is hydrostatic, has a horizontal resolution of 0.125 degree and 60 vertical levels up to 2 hPa. Simulations for such a large domain (800 x 3000 km) are challenging and the lidar observations provide a unique opportunity to validate the numerical experiments. These deliver clear evidence that the low temperatures below the frost point that lead to the formation of the ice-cloud can only be explained in terms of a vertically propagating gravity wave.

The mesoscale model produces a pronounced temperature minimum at the exact location of the observed cloud. In contrast, ECMWF analyses (which do not capture the gravity wave) show 6 degrees warmer temperatures. The dynamical mechanisms that produce the wave are investigated in detail.

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