S. Kellmann

Mixing Processes during the Antarctic Vortex Split in September–October 2002 as Inferred from Source Gas and Ozone Distributions from ENVISAT–MIPAS

Abstract In late September 2002, an Antarctic major stratospheric warming occurred, which led to a strong distortion of the southern polar vortex and to a split of its mid- and upper-stratospheric parts. Such an event had never before been observed since the beginning of regular Antarctic stratospheric temperature observations in the 1950s. The split is studied by means of nonoperational level-2 CH4, N2O, CFC-11, and O3 data, retrieved at the Institute for Meteorology and Climate Research Karlsruhe (IMK) from high-resolution atmospheric limb emission spectra from the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) on board the European research satellite, Environmental Satellite (ENVISAT). Retrieved horizontal and vertical distributions of CH4 and N2O show good consistency with potential vorticity fields of the European Centre for Medium-Range Weather Forecasts (ECMWF) analysis for the entire period under investigation, even for fine structures such as vortex filaments. Tracer correlatio...

An enhanced HNO3 second maximum in the Antarctic midwinter upper stratosphere 2003

Vertical profiles of stratospheric HNO 3 were retrieved from limb emission spectra recorded by the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) aboard the Envisat research satellite during the Antarctic winter 2003. A high second maximum of HNO 3 was found around 34 km altitude with abundances up to 14 ppbv HNO 3 during July. Similar high abundances have not been reported in the literature for previous winters, but for the subsequent Arctic winter 2003/2004, after severe perturbations due to solar proton events. The second HNO 3 maximum in the Antarctic stratosphere started to develop in early June 2003, reached peak values during July 2003, and decreased to about 7 ppbv at the end of August while being continuously transported downward before finally forming a single HNO 3 layer over all latitudes in the lower stratosphere together with the out-of-vortex primary HNO 3 maximum. The HNO 3 decrease in August 2003 was correlated with photochemical buildup of other NO v species as ClONO 2 and NO x . From the time scales observed, it can be ruled out that the 2003 long-term HNO 3 enhancements were caused by local gas phase reactions immediately after the solar proton event on 29 May 2003. Instead, HNO 3 was produced by ion cluster chemistry reactions and/or heterogeneous reactions on sulfate aerosols via N 2 O 5 from high amounts of NOy being continuously transported downward from the lower thermosphere during May to August.

Remote sensing of the middle atmosphere with MIPAS

On 1 March 2002 the Envisat research satellite has been launched successfully into its sun-synchronous orbit. One of its instruments for atmospheric composition sounding is the Michelson Interferometer for Passive Atmospheric Sounding, a limb-scanning mid-infrared Fourier transform spectrometer. Different scientific objectives of data users require different approaches to data analysis, which are discussed. A strategy on how to validate the involved algorithms and relevant strategies is presented.

Early IMK/IAA MIPAS/ENVISAT results

On March 1, 2002 the space-borne limb viewing mid-infrared high-resolution Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) has been brought on board the ENVISAT satellite into a polar sun-synchroneous orbit. Although the level-1 testing and validation phase has not been finished, ESA has made available datasets of 4 early orbits to several groups involved in MIPAS calibration/validation; the groups have been given the opportunity for functionality tests of their analysis codes. We here present some example results of the IMK/IAA MIPAS level-2 processor the concept of which is presented in a companion paper. Temperatures retrieved along the orbits are compared to ECMWF data. Processing parameters as chosen in pre-launch studies, such as cloud identification thresholds, microwindow selection, or instrument characteristics, are discussed. Preliminary retrievals for various atmospheric conditions are shown.

Comparisons of MIPAS-observed temperature profiles with other satellite measurements

MIPAS on ENVISAT measures vertical profiles of atmospheric temperature, ozone, and other species with nearly global coverage and high accuracy/precision. The standard observation mode covers the altitude region between 6 and 68 km. The atmospheric state parameters retrieved from MIPAS measurements using the IMK data analysis processor are compared with a number of other satellite observations. Our comparisons in this paper will focus on temperatures measured by MIPAS, HALOE, SABER, and UKMO Stratospheric Assimilated Data. Both individual profiles and zonal means measured by MIPAS and other instruments at different seasons and geolocations show reasonable agreement, though some differences exist due to characteristics of the individual instruments and observation scenarios. The MIPAS measurements during the stratospheric major sudden warming during the southern hemisphere winter of 2002 are also presented to show the features of this unusual event. The analysis indicates the reliability of MIPAS-IMK data products and their capability for providing valuable scientific information.

Comparison of GPS/SAC-C and MIPAS/ENVISAT Temperature Profiles and Its Possible Implementation for EOS MLS Observations

This analysis presents comparisons of the atmospheric temperatures retrieved from GPS/SAC-C radio occultation observations using the JPL retrieval software, and from MIPAS/ENVISAT infrared spectrum measurements using the IMK data processor. Both individual profiles and zonal means of the atmospheric temperature at different seasons and geo-locations show reasonable agreement. For the temperatures at altitudes between 8–30 km, the mean differences between the correlative measurements are estimated at less than 2 K with rms deviations less than 5 K. A similar cross comparison technique can be used to help validate the observed temperatures from the new EOS MLS instrument, to be launched in 2004.

Comparisons of MIPAS/ENVISAT and GPS-RO/CHAMP Temperatures

The temperatures retrieved from MIPAS/ENVISAT limb mid-infrared emission and CHAMP GPS radio occultation measurements are compared at altitudes between 8 – 30 km during the stratospheric major sudden warming in the southern hemisphere winter of 2002. The mean differences between the correlative measurements of the two instruments are less than ∼1 K with rms deviations of ∼3–5 K. The MIPAS temperatures are slightly higher than those of GPS-RO around 30 km. Possible explanation is discussed.

Retrievability of Upper Tropospheric Species and Parameters from MIPAS/ENVISAT Data

ENVISAT with MIPAS (Michelson Interferometer for Passive Atmospheric Sounding) (Fischer and Oelhaf, 1996) on board was successfully launched on 1st March, 2002. Since 24th March 2002, MIPAS has been measuring high-quality mid-infrared limb emission spectra with 0.035 cm-1 spectral resolution. The non-operational scientific level-2 data analysis of MIPAS/ENVISAT data to be performed at IMK has been developed further. The work of this project was focussed on various retrieval aspects in the upper troposphere region. On the basis of synthetic spectra, the information content of the spectra was analysed with respect to about 45 trace species, temperature and microphysical properties of cirrus clouds. The retrieval strategy for more than 30 trace species was set up, verified, and fine-tuned within test retrievals. Up to 20 species in the upper troposphere region can be detected with total accuracy (including all relevant systematic error sources) better than ±100 %, many of them better than ±10 %. Among these species are constituents which are of utmost interest for the understanding of the global and regional ozone budget in the upper troposphere, like acetone, NMHCs, PAN, or HO2. For the first time the impact of scattering of mid-infrared tropospheric radiation into the line-of-sight by cirrus particles was modelled with high spectral resolution. Spectrally high resolved signatures from tropospheric radiation scattered into the line-of-sight allow an improvement in the retrievability of microphysical parameters of cirrus clouds. The observation and retrieval scenarios to be applied for the derivation of tropical water vapour volume mixing ratio (VMR) close to the tropical tropopause was optimised with respect to accuracy versus vertical resolution. The achievable accuracy and vertical resolution is high enough to contribute to questions referring to processes in the tropical tropopause layer. First available MIPAS spectra were inspected in order to verify the predictions achieved on the basis of simulated measurements.