Monitoring the Antarctic mesopause region for signatures of climate change

Abstract

The polar mesopause region (80-100 km) is the coldest region of the Earth's atmosphere and is expected to be sensitive to global change. Reported increases in observations of polar mesospheric clouds over the last 100 years have been postulated to be related to decreased temperatures (associated with tropospheric warming) and increased water vapour at mesospheric altitudes (a result of increased methane concentrations in the troposphere). The temperature of this region can be monitored by spectroscopic techniques utilising hydroxyl (OH) emissions which originate near 87 km. The Australian Antarctic Division, Atmospheric and Space Physics group has been analyzing OH (6-2) band spectra recorded with a Czerny—Turner scanning spectrometer at Davis Station, Antarctica (68.6° S, 78.0° E) to optimise temperature determinations for climate change studies. A number of difficulties were encountered, some of which have been overcome and all of which can be overcome. The mid-winter average temperature of the OH layer for May-July 1990 has been measured as 224 ±2 K. The equivalent value for 1996 is 215±2 K. Possible reasons for the difference are discussed.