Intercomparison of Odin–SMR ozone profiles with ground-based millimetre-wave observations in the Arctic, the mid-latitudes, and the tropics

Abstract

The sub-millimetre radiometer (SMR) on board the Odin satellite measures signatures of ozone in two bands centred at 501.8 and 544.6 GHz. From the measurements, ozone volume mixing ratio profiles in the stratosphere and lower mesosphere are retrieved using the Optimal Estimation Method. In this paper, the ozone profiles measured by Odin–SMR (level-2 data ver. 2.1 and 2.0, respectively) are compared to measurements taken by ground-based millimetre wave radiometers in the Arctic; at Kiruna, Sweden; in the mid-latitudes on the Zugspitze, Germany; and in the tropics at Mérida, Venezuela. The Kiruna Microwave Radiometer (KIMRA) covers the frequency range 195–224 GHz, and the Millimeter Wave Radiometer MIRA 2, which was operated on the Zugspitze and at Mérida, measures in the frequency band 268–281 GHz. From the measurements, ozone profiles in the vertical range between approximately 15–65 km were retrieved using the Optimal Estimation Method. Since the ground-based measurements have a lower vertical resolution than those of Odin the latter were degraded using the averaging kernels of the ground-based retrievals. The comparison of the resulting profiles to the ground-based data enables the identification of biases in the Odin measurements and their possible latitudinal variation. In general, a good agreement between satellite and ground-based measurements for the 501.8 GHz band was found in the stratosphere except for a negative bias in the Odin data of about 10–15% in the tropical measurements. The Odin measurements taken at 544.9 GHz yielded systematically 20–30% lower ozone mixing ratios in the middle stratosphere than the ground-based measurements at all sites. PACS No.: 92.60.hd