Gravity Waves and Polar Stratospheric Clouds

 Simultaneous observations from UARS MLS and CLAES/ISAMS enable joint statistical analyses on GW and PSC activities. Such study provides a unique opportunity to assess GW contribution to PSC formation in the polar regions. The following figures show (a) GW activities at ~28km during July-October 1992, (b) PSC occurrence at 32 hPa during the same period, and (c) statistices of the cloud occurrence as a function of temperature under enhanced and depressed GW situations at latitudes of 50S-80S. MLS channel 1 variances (~28km) are used for GW detections, and the threshold used for GW events is 0.004 K², three times of the noise level. The cloud distributions are obtained from CLAES 780cm^-1 extinction measurements where the center of high PSC occurrence leans toward the Drake Passage region as seen similarly in MLS GW variances.  One approach to quantify GW contributions to the cloud formation is to compare cloud occurrence frequencies under GW-active and GW-depressed conditions. Strikingly, the frequency of PSC occurrence is significantly higher by 10-20% at 32 hPa in GW activitive regions at temperatures between 175K-190K. CLAES temperature is used in this analysis.
 
 

(a) MLS Ch1 GW Variance

(b) CLAES PSC

(c) GW-PSC Statistics