Role of Lee Waves in the Formation of Solid Polar Stratospheric Clouds: Case Studies from February 1997
LABORATOIRE DE PHYSIQUE ET CHIMIE DE L'ENVIRONNEMENT ORLEANS (FRANCE)
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Recently theories of solid polar stratospheric clouds PSCs formation have shown that particles could remain liquid down to 3 K or 4 K below the ice frost point. Such temperatures are rarely reached in the Arctic stratosphere at synoptic scale, but nevertheless, solid PSCs are frequently observed. Mesoscale processes such as mountain-induced gravity waves could be responsible for their formation. In this paper, a microphysical-chemical Lagrangian model MiPLaSMO and a mountain wave model NRLMWFM are used to interpret balloon-borne measurements made by an optical particle counter OPC and by the Absorption par Minoritaires Ozone et NOx AMON instrument above Kiruna on February 25 and 26, 1997, respectively. The model results show good agreement with the particle size distributions obtained by the OPC in a layer of large particles, and allow us to interpret this layer as an evaporating mesoscale type Ia PSC nitric acid trihydrate mixed with liquid particles. The detection of a layer of solid particles by AMON is also qualitatively reproduced by the model and is interpreted to be frozen sulfate acid aerosols SAT. In this situation, the impact of mountain waves on chlorine activation is studied. It appears that mesoscale perturbations amplify significantly the amount of computed CIO, as compared to synoptic runs. Moreover, MiPLaSMO chemical results concerning HNO3 and HCl agree with measurements made by the Limb Profile Monitor of the Atmosphere LPMA instrument on February 26 at a very close location to AMON, and explain part of the differences between LPMA measurement and Reactive Processes Ruling the Ozone Budget in the Stratosphere REPROBUS model outputs.