European Environmental Satellite Research Articles

Stratospheric N2O5 in the austral spring 2002 as retrieved from limb emission spectra recorded by the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS)

N2O5 was retrieved from infrared limb emission spectral radiances made by the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) on board the European environmental satellite (ENVISAT). The measurements were taken during the period covering the Antarctic polar vortex split between 20 September and 13 October 2002. The retrieval of N2O5 is aggravated by its continuum‐like emission feature covering a wide spectral region, which is hardly distinguishable from background continuum emission. The method of constraining the background continuum in the N2O5 analysis spectral region to its value in a N2O5‐free spectral region was found to be appropriate to solve this problem. Retrieved volume mixing ratios (VMR) of N2O5 exhibit features consistent with the dynamics prevalent at the time in the Antarctic and known N2O5 chemistry governing diurnal variability. The observations of low N2O5 inside vortex air mass and rich N2O5 exvortex air mass are strongly in support of the chemistry that governs its partitioning within the NOy family. The enhanced nighttime high geographic latitude N2O5 VMR with a peak of 4.4 ppbv in the altitude range of 32–37 km during the last week of September 2002 is consistent with air mass transport from lower to high latitudes and temperature‐sensitive N2O5 formation chemistry. N2O5 enhancement up to 6 ppbv was also observed by the Cryogenic Limb Array Etalon Spectrometer(CLAES) and Improved Stratospheric and Mesospheric Sounder (ISAMS) experiments on Upper Atmospheric Research Satellite (UARS) during Northern Hemisphere January 1992 stratospheric warming which was a factor of 3 larger than any measurements of N2O5 prior to UARS. In contrast, a maximum of 4.4 ppbv N2O5 VMR observed by MIPAS at 32–37 km is only a factor of 2 larger than its prewarming values.

Spaceborne ClO observations by the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) before and during the Antarctic major warming in September/October 2002

The first ClO profiles retrieved from limb emission spectra recorded by the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) Fourier transform spectrometer on board the European research satellite ENVISAT (Environmental Satellite) are presented. These measurements were taken between 8 September and 13 October 2002. They cover the Antarctic major warming around 25 September, an event which had never been observed before. Since ClO has only weak signatures in the midinfrared, more than a dozen of the strongest lines, all situated in the central P branch and Q branch region of the 1‐0 band, were used for profile retrievals, which were based on constrained nonlinear least squares fitting. During the period of investigation, MIPAS measured typical ClO volume mixing ratios (vmrs) between 1 ± 0.4 and 2 ± 0.6 ppbv from 8 September until 23 September in contiguous parts of the dayside lower Antarctic stratosphere (400–625 K levels of potential temperature, Θ), i.e., before and at the beginning of the major warming. After 23 September no significant amounts of ClO were detected anymore, apart from some remains on 26 September. Daily averages of inside vortex daytime ClO showed a slight increase until about 17 September and a subsequent rapid ClO decrease. Further, a positive response of inside vortex nighttime ClO to increasing temperatures due to enhanced Cl2O2 dissociation was detected. Comparison with measurements of the Microwave Limb Sounder (MLS) on the Upper Atmospheric Research Satellite (UARS) from the years 1992–1997 generally showed a similar temporal development. Thus the warming event obviously happened too late to lead to a premature chlorine deactivation significantly different from previous Antarctic winters.

Retrieval of trace gas vertical columns from SCIAMACHY/ENVISAT near-infrared nadir spectra: first preliminary results

The European environmental satellite ENVISAT was successfully launched on 1st of March 2002. The UV/visible/near-infrared grating spectrometer SCIAMACHY is part of ENVISAT's atmospheric science payload. SCIAMACHY observes the atmosphere in nadir, limb, and solar and lunar occultation viewing geometries with moderate spectral resolution (0.2–1.5 nm). At the University of Bremen a modified DOAS algorithm (WFM-DOAS) is being developed primarily for the retrieval of CH 4 , CO, CO 2 , H 2 O, N 2 O, and O 2 total column amounts from ratios of SCIAMACHY nadir radiance and solar irradiance spectra in the near-infrared and visible spectral regions. First preliminary results concerning this activity are presented. SCIAMACHY is currently (September 2002) in its commissioning phase and only preliminary, i.e., not yet fully calibrated, Level 1 data products are available, generated mainly for initial Level 0 to 1 processing verification purposes. A method aimed at improving the retrieval in case of systematic artifacts resulting from, e.g., residual calibration errors, is presented. This study focuses on methane vertical column retrieval using channel 8 (2260–2385 nm). One of the major scientific objectives of the SCIAMACHY methane measurements is to derive information on methane (surface) sources and sinks. Such an application requires a relative radiometric accuracy close to the signal-to-noise performance of the instrument (S/N ∼50–100 in channel 8 for albedo 0.1 and solar zenith angle 60°) and an accurate and fast retrieval algorithm. This study presents first steps undertaken to reach this ambitious goal, focusing on the retrieval algorithm.

First retrieval of global water vapour column amounts from SCIAMACHY measurements

Abstract. Global water vapour column amounts have been derived for the first time from measurements of the SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY (SCIAMACHY) on the European environmental satellite ENVISAT. For this purpose, two different existing retrieval algorithms have been adapted, namely the Air Mass Corrected Differential Absorption Spectroscopy (AMC-DOAS) which was originally designed for GOME and the Weighting Function Modified Differential Absorption Spectroscopy (WFM-DOAS) which was mainly designed for the retrieval of CH4, CO2 and CO from SCIAMACHY near-infrared spectra. Here, both methods have been applied to SCIAMACHY's nadir measurements in the near-visible spectral region around 700 nm. Taking into account a systematic offset of 10%, the results of these two methods agree within a scatter of about ±0.5 g/cm2 with corresponding SSM/I and ECMWF water vapour data. This deviation includes contributions from the temporal and spatial variability of water vapour. In fact, the mean deviation between the SCIAMACHY and the correlative data sets is much smaller: the SCIAMACHY total water vapour columns are typically about 0.15 g/cm2 lower than the SSM/I values and less than 0.1 g/cm2 lower than corresponding ECMWF data. The SCIAMACHY water vapour results agree well with correlative data not only over ocean but also over land, thus showing the capability of SCIAMACHY to derive water vapour concentrations on the global scale.

Retrieval of trace gas vertical columns from SCIAMACHY/ENVISAT near-infrared nadir spectra: first preliminary results

The European environmental satellite ENVISAT was successfully launched on 1st of March 2002. The UV/visible/near-infrared grating spectrometer SCIAMACHY is part of ENVISAT's atmospheric science payload. SCIAMACHY observes the atmosphere in nadir, limb, and solar and lunar occultation viewing geometries with moderate spectral resolution (0.2–1.5 nm). At the University of Bremen a modified DOAS algorithm (WFM-DOAS) is being developed primarily for the retrieval of CH 4, CO, CO 2, H 2O, N 2O, and O 2 total column amounts from ratios of SCIAMACHY nadir radiance and solar irradiance spectra in the near-infrared and visible spectral regions. First preliminary results concerning this activity are presented. SCIAMACHY is currently (September 2002) in its commissioning phase and only preliminary, i.e., not yet fully calibrated, Level 1 data products are available, generated mainly for initial Level 0 to 1 processing verification purposes. A method aimed at improving the retrieval in case of systematic artifacts resulting from, e.g., residual calibration errors, is presented. This study focuses on methane vertical column retrieval using channel 8 (2260–2385 nm). One of the major scientific objectives of the SCIAMACHY methane measurements is to derive information on methane (surface) sources and sinks. Such an application requires a relative radiometric accuracy close to the signal-to-noise performance of the instrument (S/N ∼50–100 in channel 8 for albedo 0.1 and solar zenith angle 60°) and an accurate and fast retrieval algorithm. This study presents first steps undertaken to reach this ambitious goal, focusing on the retrieval algorithm.