Monthly mean vertical profiles of pressure, temperature and water vapour volume mixing ratio in the polar stratosphere and low mesosphere from a multi-year set of MIPAS-ENVISAT limb-scanning measurements

Abstract

Measurements performed at polar latitudes by the MIPAS limb-scanning Fourier Transform spectrometer aboard ENVISAT, from July 2002 to March 2004 (FR mission) and January 2005 to April 2010 (OR mission) were analysed with the 2-D tomographic Geofit Multi-Target Retrieval (GMTR) procedure (Dinelli et al., 2010. The MIPAS2D database of MIPAS/ENVISAT measurements retrieved with a multi-target 2-dimensional tomographic approachAtmos. Meas. Techn. Discuss. (AMTD) 2, 2639–2688.) to obtain the MIPAS2D database, and extract more than 386,000 vertical profiles of pressure p, temperature T and water vapour volume mixing ratio Q. They were subdivided into 12 latitudinal classes selected in steps of 5° from 65°N to 90°N and 65°S to 90°S, each vertical profile consisting of values measured at 14 altitude levels from 12 to 60 km. Each latitudinal set was subdivided into 12 monthly sets to determine the multi-year monthly mean vertical profiles of the three parameters: those of p (monthly average standard deviations (SD) 5–15%) provide evidence of marked seasonal variations above 30 km; those of T (SD values of a few percent) show large seasonal variations, with summer maxima at all stratospheric levels; and those of Q (SD lower than 20% from 20 to 50 km) present values ranging in general between 2 and 6 ppmv at the 12–25 km levels and 4 and 7 ppmv at higher altitudes. To verify the reliability of the MIPAS results, the pressure profiles are compared with those obtained from radiosounding data-sets taken at Arctic and Antarctic sites from 2000 to 2003; those of T with both radiosounding measurements and MLS/Aura satellite data from 2005 to 2010; and those of Q with the MLS/Aura satellite data, finding a substantial agreement in all cases. Comparison of MIPAS pressure and temperature profiles with pre ozone-hole CIRA models at 70° and 80° latitudes highlights the variations occurring in the polar atmosphere over the last 3 decades, with relative pressure decreases of 5–10% on average, and overall average decreases in temperature of 0.4 and 2.0 K in the Arctic and Antarctica, respectively. Using the MIPAS profiles of p, T and Q, the monthly mean vertical profiles of absolute humidity were also calculated, from which the monthly values of stratospheric water vapour content from 12 to 50 km were determined, varying between 0.0047 and 0.0070 mm at Arctic latitudes and between 0.0026 and 0.0055 mm at Antarctic latitudes.