Ashley Jones

Intercomparisons of trace gases profiles from the Odin/SMR and Aura/MLS limb sounders

This paper presents the intercomparison of O(3), HNO(3), ClO, N(2)O and CO profiles measured by the two spaceborne microwave instruments MLS ( Microwave Limb Sounder) and SMR ( Submillimetre Radiometer) on board the Aura and Odin satellites, respectively. We compared version 1.5 level 2 data from MLS with level 2 data produced by the French data processor version 222 and 225 and by the Swedish data processor version 2.0 for several days in September 2004 and in March 2005. For the five gases studied, an overall good agreement is found between both instruments. Most of the observed discrepancies between SMR and MLS are consistent with results from other intercomparison studies involving MLS or SMR. O(3) profiles retrieved from the SMR 501.8 GHz band are noisier than MLS profiles but mean biases between both instruments do not exceed 10%. SMR HNO(3) profiles are biased low relative to MLSs by similar to 30% above the profile peak. In the lower stratosphere, MLS ClO profiles are biased low by up to 0.3 ppbv relative to coincident SMR profiles, except in the Southern Hemisphere polar vortex in the presence of chlorine activation. N(2)O profiles from both instruments are in very good agreement with mean biases not exceeding 15%. Finally, the intercomparison between SMR and MLS CO profiles has shown a good agreement from the middle stratosphere to the middle mesosphere in spite of strong oscillations in the MLS profiles. In the upper mesosphere, MLS CO concentrations are biased high relative to SMR while negative values in the MLS retrievals are responsible for a negative bias in the tropics around 30 hPa.

Internal consistency in the Odin stratospheric ozone products

The two independent instruments on the Odin satellite, the Optical Spectrograph and Infrared Imaging System (OSIRIS) and the Sub-Millimetre Radiometer (SMR) produce atmospheric profiles of various atmospheric species including stratospheric ozone. Comparisons are made between OSIRIS version 3.0 and SMR version 2.1 ozone data to evaluate the consistency of the Odin ozone data sets. Results show good agreement between OSIRIS and SMR in the range 25-40 km, where systematic differences are less than 15% for all latitudes and seasons. Larger systematic differences are seen below 25 km, which can be explained by the increase of various error sources and lower signals. The random differences are between 20-30% in the middle stratosphere. Differences between Odin up-scans and down-scans or AM and PM are insignificant in the middle stratosphere. Furthermore, there is little variation from year to year, but a slight positive trend in the differences (OSIRIS minus SMR) of 0.045 ppmv/year at 30 km over validation period (2002-2006). The fact that the two fundamentally different measurement techniques, (absorption spectroscopy of scattering sunlight and emission measurements in the sub-millimetre region) agree so well, provides confidence in the robustness of both techniques.

Analyzing the applications of an assimilation model as a method for validation of satellite data

An analysis was performed to illustrate that data assimilation is an appropriate method for validation of satellite measurements when very few coincidences are available between satellite measurements and balloon sondes. Results showed that the mean differences between the Isentropic Assimilation model for StratospheriC Ozone (IASCO) model ozone profiles and co-located ozone sondes shared systematic differences similar to those obtained from co-located MIPAS and ozone sonde coincidences. The spatial and temporal constraints of 12 hours and 800 km produced the optimal number of MIPAS/sonde matches for a statistical analysis. The largest residual between the IASCO/sonde mean difference and MIPAS/sonde mean difference, using these constraints, was less than 0.25 ppmv, between potential temperature levels of 425-975 K. By using the assimilation model coincidences, we also conclude that the maximum time/distance constraint sizes that can be used when obtaining matches between satellite measurements and in-situ measurements should be no more than 24 hours and a maximum of 1500-2000 km. However, local conditions such as the presence of a dynamical feature, for example the edge of the polar vortex, may of course greatly restrict these limits.

Report on Recent Validation Results from the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS)

This paper will describe current validation results for the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS) focusing on version 3.0 of the data set.