ODIN/SMR LIMB OBSERVATIONS OF TRACE GASES IN THE POLAR LOWER STRATOSPHERE DURING 2004-2005 ´ Dupuy c,2 , J. de La No¨e c , P. Eriksson a , J. Urban a,∗ , D. Murtagh a , N. Lauti´e a,1 , B. Barret b , E. d a ´ b e U. Frisk , A. Jones , E. Le Flochmo¨en , M. Olberg , C. Piccolo f , P. Ricaud b , and J. R¨osevall a a
Department of Radio and Space Science, Chalmers University of Technology, 412 96 G¨ oteborg, Sweden Observatoire de Midi-Pyr´en´ees, Laboratoire d’A´erologie, 31400 Toulouse, France c Observatoire Aquitain des Sciences de l’Univers, L3AB, 33270 Floirac, France d Swedish Space Corporation, 171 04 Solna, Sweden b
e f
Onsala Space Observatory, Chalmers University of Technology, 439 92 Onsala, Sweden Department of Physics, University of Oxford, Oxford OX1 3PU, UK
ABSTRACT Profile measurements of key constituents relevant to stratospheric chemistry and dynamics such as ozone (O3 ), nitrous oxide (N2 O), chlorine monoxide (ClO), and nitric acid (HNO 3 ), taken by the Odin Sub-Millimetre Radiometer (SMR), are presented and the characteristics of the Chalmers-v2.0 level-2 data are described. A comparison with correlative measurements of the Envisat/MIPAS instrument for this version results in a very good agreement for N 2 O, whilst Odin/SMR HNO3 mixing ratios are systematically larger than MIPAS data by up to 1.7 ppbv. Observations taken in the polar winter stratosphere of both hemispheres during the period 2004-2005 are also presented. The Odin/SMR measurements of nitrous oxide, chlorine monoxide, nitric acid, and ozone allow to study the chemical and dynamical evolution of the Arctic and Antarctic vortices by providing information on subsidence of vortex air, chlorine activation, denitrification, and on ozone loss.
1
INTRODUCTION
The Sub-Millimetre Radiometer (SMR) on board the Odin satellite, launched on 20 February 2001 in a polar sun-synchronous orbit at ∼600 km altitude, employs four tunable singlesideband Schottky-diode heterodyne receivers in the 486-581 GHz spectral range and a 1.1 m telescope for passive observations of thermal emissions originating from the Earth’s limb. Spectra are recorded using two high resolution auto-correlator spectrometers. Atmospheric measurements are performed in a time sharing mode with astronomical observations [1; 2]. In aeronomy mode, various target bands are dedicated to observations of trace constituents relevant to stratospheric and mesospheric chemistry and dynamics such as O3 , ClO, N2 O, HNO3 , H2 O, NO, CO, and isotopes of H2 O and O3 [3]. Vertical profiles (level-2 data) are retrieved from the calibrated spectral measurements of the limb scans (level-1b data) by inverting the radiative transfer equation for a non-scattering atmosphere [4; 5]. Measurements of stratospheric ozone (O3 ), nitrous oxide (N2 O), chlorine monoxide (ClO), and nitric acid (HNO3 ), are performed roughly every third day using two 700 MHz wide bands centred at 501.8 and 544.6 GHz [6]. The characteristics of the reprocessed Odin/SMR stratospheric mode level-2 data (version 2.0) are discussed in Section 2. We then present in Section 3 an update of the validation analysis for N2 O and HNO3 by comparison with correlative measurements obtained from the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) on the Envisat satellite [7]. Scientific results with respect to chemical and dynamical processes in the Antarctic and Arctic winter vortices during 2004 and 2005 are shown in Section 4. ∗ Corresponding author. Email address:
[email protected] (J. Urban). 1 now at Noveltis, 31520 Ramonville Saint Agne, France 2 now at Institute of Space and Atmospheric Studies, University of Saskatchewan, Saskatoon SK S7N 5E2, Canada
Proc. Atmospheric Science Conference, 8-12 May 2006, Frascati, Italy
2
ODIN/SMR CAPABILITIES: STRATOSPHERIC MODE
Optimised non-linear retrieval schemes for level-2 processing have been developed in parallel in Sweden and in France. The operational and systematical production of the level-2 data is performed at the Chalmers University of Technology in G¨oteborg (Sweden), whilst a reference version is produced for validation purposes using the so-called Chaˆıne de Traitement Scientifique Odin (CTSO), developed at the Observatoire Aquitain des Sciences de l’Univers, Floirac (France). In this paper we focus on profile data from the latest Chalmers-v2.0 retrieval scheme, available since the end of 2005. Diagnostical information on the retrieval results is calculated during the processing and can be extracted from the retrieval error covariance and averaging kernel matrices. Typical characteristics of the Odin/SMR Chalmers-v2.0 data for the main target gases ClO, N2 O, HNO3 , and O3 are summarised in Table 1 for a polar scenario. Estimates of the total systematic error, derived from known instrumental and spectroscopic uncertainties, are also provided (see [6] for details). Table 1 Single-scan retrieval capabilities of Odin/SMR for stratospheric mode target species retrieved with the operational Chalmers version 2.0 level-2 processor. Indicated are target line frequencies, single-scan precisions, estimated systematic errors (from error analysis [6]), and altitude resolutions (full widths at half maximum of the averaging kernel functions) in the lower stratosphere, as well as approximate altitude ranges for a polar scenario.
species
frequency [GHz]
Odin/SMR Stratospheric Mode – Chalmers-v2.0 precision (1-σ) systematic error
O3 ClO N2 O O3 HNO3
501.5 501.3 502.3 544.9 544.4
≤ 1.5 ppmv (∼ 20 %) ≤ 0.15 ppbv ≤ 30 ppbv (10-15 %
