Excitation and Evolution of the Quasi 2-Day Wave Observed in UARS/MLS Temperature Measurements

The quasi 2-day wave is known as a strong dynamic perturbation occurring usually after solstice in the middle and upper atmosphere. The excitation mechanism of this transient wave is discussed for years but no clear answe] has been altained. In this paper, propagating characteristics of the 2-day wave are studied based on 8-month temperature measurements from the Microwave Limb Sounde~ (MLS) on the Upper Atmosphere Research Satellite (UARS). The studies are focused on the wave events that happened in January 1993 and in July/August 1993. The data suggest that winter planetary waves could be responsible for triggering the summer 2-day wave through long penetration into the summer stratosphere. A connection is evident in the evolution of the wave amplitude between the summer 2-day wave generation and winter wave penetration. The data also suggest that the enhancement of the wave amplitude is a result mixed with a local unstable wave and a global normtil-mode Rossby wave.