Airborne Submillimeter Measurements of Arctic Middle Atmospheric Trace Gases: Evidence for Denitrification in the Arctic Polar Stratosphere

Abstract

Denitrification inside the Arctic vortex in winter 1999/2000 was studied based on measurements of HNO:sub:3:/sub: and N:sub:2:/sub:O by the airborne submillimeter radiometer ASUR for the first time. Vortexwide denitrification was found in mid-March 2000 compared to early-December 1999 shown by a vortex averaged NO:sub:y:/sub: deficit between 1.2±0.9 ppb at ~16 km and 5.3±2.7 ppb at ~20.5 km altitude. A trend of stronger denitrification with increasing equivalent latitude was evident. The observations were compared with runs of the SLIMCAT model applying different denitrification schemes based on ice, large NAT particles in equilibrium, and non-equilibrium NAT particles (DLAPSE). The DLAPSE scheme showed the best agreement with the observed denitrification in winter 1999/2000. Denitrification was also studied in winter 2002/2003. Calculations applying the DLAPSE scheme were able to reproduce the observed HNO:sub:3:/sub: levels north of 75° on 19/1/2003 reasonably well. During the major stratospheric warming in mid-January 2003 unusually high mixing ratios of ozone and N:sub:2:/sub:O were observed by ASUR in the middle stratosphere on 23/1/2003 around 69°N. The observed similarities above a potential temperature of ~800 K with profiles measured around 20°N on 1/3/2003 lead to the conclusion that the airmasses must have been transported from the tropics to the Arctic by rapid isentropic transport in ~3-7 days. To extend the altitude range of ASUR´s measurement capabilities into the mesosphere a high resolution chirp-transform spectrometer has been integrated in the ASUR. A scheme for the retrieval of mesospheric ozone has been developed using measurements from September 2002. Retrievals with total integration times of ~180-720 seconds show reasonable results up to 64-68 km altitude with a total error of ~25%. Measurements of the diurnal variation of mesospheric ozone were in reasonable agreement with the results calculated by a mesospheric chemistry model.