RAYLEIGH LIDAR OBSERVATIONS OF THERMAL STRUCTURE AND GRAVITY-WAVE ACTIVITY IN THE HIGH ARCTIC DURING A STRATOSPHERIC WARMING

During February and March 1993, Rayleigh lidar observations of temperature structure and gravity wave activity were carried out in the high Canadian Arctic at Eureka, Northwest Territories (80 degrees N, 86 degrees W). A sudden warming was observed first in the upper stratosphere during late February and then at lower levels in early March. The warming appeared to be part of a disturbance of the entire middle atmosphere with temperature changes in the mesosphere and lower stratosphere being opposite in sign to those in the upper stratosphere. Shorter time and length scale temperature fluctuations, observed in the upper stratosphere, are interpreted as being a result of atmospheric gravity waves. The wave amplitudes are shown to be capable of inducing convective instability. The rms perturbation and available potential energy density show substantial vertical and day-to-day variability in regions of conservative and dissipative growth rates. Vertical growth of the potential energy spectral density is seen to cease at the broadband convective instability saturated limit. There appeared to be substantially greater dissipation of gravity wave energy within the upper-stratospheric warming in comparison with the preceding and following periods.