SPATIAL AND TEMPORAL VARIABILITY OF CLONO2, HNO3, AND O-3 IN THE ARCTIC WINTER OF 1992/1993 AS OBTAINED BY AIRBORNE INFRARED-EMISSION SPECTROSCOPY

In the winter of 1992/1993 the airborne Michelson interferometer for passive atmospheric sounding (MIPAS-FT) was operated on board a German research aircraft (Transall C-160) to record infrared emission spectra of the atmosphere inside and outside the Arctic vortex. Measurements were made during four campaigns between December 4, 1992, and March 29, 1993, in the European Arctic as well as over central and southern Europe (82 degrees N - 37.5 degrees N). We present the retrieved zenith column amounts of the stratospheric trace gases ClONO2, HNO3, and O-3 of this period. Inside the polar vortex, the column amounts of ClONO2 and HNO3 were considerably enhanced already in early December, up to 3.1 x 10(15) cm(-2) and 2.7 x 10(16) cm(-2), respectively. Around the end of January, low ClONO2 (1 x 10(15) cm(-2)) and high HNO3 column amounts (up to 3.7 x 10(16) cm(-2)) were observed inside the vortex; whereas a highly variable ''collar'' of ClONO2 had developed at the vortex edge. During March, after temperatures had been above the threshold for polar stratospheric clouds (PSCs) for several weeks, we measured lower HNO3 (below 2.5 x 10(16) cm(-2)) and very high ClONO2 column amounts (up to 6 x 10(15) cm(-2)) inside the vortex. Thus a major part of the reactive chlorine had been converted into ClONO2, and the potential for rapid ozone depletion was reduced markedly in the region observed. On March 10, when the polar vortex extended southward to the Mediterranean, ClONO2 column amounts as high as 4.6 x 10(15) cm(-2) were observed at 40 degrees N. At the end of March, considerable amounts of ClONO2 (up to 3.4 x 10(15) cm(-2)) were measured also far outside the vortex.