News from the environmental physics group

von Savigny, C., Ernst, F., Rozanov, A., Hommel, R., Eichmann, K.-U., Rozanov, V., Burrows, J. P., and Thomason, L. W.: Improved stratospheric aerosol extinction profiles from SCIAMACHY: validation and sample results, Atmos. Meas. Tech., 8, 5223 - 5235, 2015.

Summary:
Stratospheric aerosol extinction profiles have been retrieved from SCIAMACHY/Envisat measurements of limb-scattered solar radiation. The retrieval is an improved version of an algorithm presented earlier. The retrieved aerosol extinction profiles are compared to co-located aerosol profile measurements from the SAGE II solar occultation instrument at a wavelength of 525 nm. Comparisons were carried out with two versions of the SAGE II data set (version 6.2 and the new version 7.0). In a global average sense the SCIAMACHY and the SAGE II version 7.0 extinction profiles agree to within about 10 % for altitudes above 15 km. Larger relative differences (up to 40 %) are observed at specific latitudes and altitudes. We also find differences between the two SAGE II data versions of up to 40 % for specific latitudes and altitudes, consistent with earlier reports. Sample results on the latitudinal and temporal variability of stratospheric aerosol extinction and optical depth during the SCIAMACHY mission period are presented. The results confirm earlier reports that a series of volcanic eruptions is responsible for the increase in stratospheric aerosol optical depth from 2002 to 2012. Above about an altitude of 28 km, volcanic eruptions are found to have negligible impact in the period 2002–2012.

In collaboration with the Institute of Atmospheric Physics (IAP) at Kühlungsborn, the Institute of Physics operates a cloud camera on the roof of the Physics Building. The main purpose of the camera is to study Noctilucent Clouds (clouds), i.e. optically thin ice clouds that occur during the summer months at mid and high latitudes at altitudes of about 82 km. However, the camera also operates during the day and outside the NLC season and the pictures on this webpage are updated every few minutes.

Link to cloud camera pictures

• Cloud camera page

Langowski, M., Sinnhuber, M., Aikin, A. C., von Savigny, C., and Burrows, J. P.: Retrieval algorithm for densities of mesospheric and lower thermospheric metal atom and ion species from satellite-borne limb emission signals, Atmos. Meas. Tech., 7, 29-48, doi:10.5194/amt-7-29-2014, 2014.

Summary:
Meteoroids bombard Earth's atmosphere during its orbit around the Sun, depositing a highly varying and significant amount of matter into the thermosphere and mesosphere. The strength of the material source needs to be characterized and its impact on atmospheric chemistry assessed. In this study an algorithm for the retrieval of metal atom and ion number densities for a two-dimensional (latitude, altitude) grid is described and explained. Dayglow emission spectra of the mesosphere and lower thermosphere are used, which are obtained by passive satellite remote sensing with the SCIAMACHY (SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY) instrument on board Envisat. The limb scans cover the tangent altitude range from 50 to 150 km. Metal atoms and ions are strong emitters in this region and form sharply peaked layers with a FWHM (full width at half maximum) of several 10 km in the mesosphere and lower thermosphere measuring peak altitudes between 90 to 110 km. The emission signal is first separated from the background signal, arising from Rayleigh and Raman scattering of solar radiation by air molecules. A forward radiative transfer model calculating the slant column density (SCD) from a given vertical distribution was developed. This nonlinear model is inverted in an iterative procedure to yield the vertical profiles for the emitting species. Several constraints are applied to the solution for numerical stability reasons and to get physically reasonable solutions. The algorithm is applied to SCIAMACHY limb-emission observations for the retrieval of Mg and Mg⁺ using emission signatures at 285.2 and 279.6/280.4 nm, respectively. Results are presented for these three lines as well as error estimations and sensitivity tests on different constraint strength and different separation approaches for the background signal.

Link to AMT website<link typo3 www.atmos-meas-tech.net _blank external-link>
www.atmos-meas-tech.net

Sonkaew, T., von Savigny, C., Eichmann, K.-U., Weber, M., Rozanov, A., Bovensmann, H., Burrows, J. P., and Grooß, J.-U.: Chemical ozone losses in Arctic and Antarctic polar winter/spring season derived from SCIAMACHY limb measurements 2002–2009, Atmos. Chem. Phys., 13, 1809-1835, doi:10.5194/acp-13-1809-2013, 2013.

Summary:
The chemical ozone loss in the Arctic and Antarctic polar vortices during winter-spring is retrieved for the years 2002 - 2009 from SCIAMACHY limb measurements of stratospheric ozone profiles employing a vortex average technique. In the Antarctic polar vortex little interannual variability in the derived lower stratospheric chemical ozone losses is observed, as expected. In the northern hemisphere, the derived ozone losses vary significantly from year to year, with large ozone losses in the cold Arctic winters 2005, 2007 and 2008 and essentially no ozone losses in the warm winters 2004 and 2006.

Link to ACP website
www.atmos-chem-phys.net

von Savigny, C., K.-U. Eichmann, C. E. Robert, J. P. Burrows, and M. Weber (2012), Sensitivity of equatorial mesopause temperatures to the 27-day solar cycle, Geophys. Res. Lett., 39, L21804, doi:10.1029/2012GL053563.

Summary:
Night-time observations of OH(3-1) rotational temperatures with SCIAMACHY on Envisat are used to study the sensitivity of equatorial mesopause temperatures to the 27-day solar forcing. Fourier and cross-correlation analysis are first used to demonstrate the presence of a solar-driven 27-day cycle in OH rotational temperatures. The temperature sensitivity to solar forcing is quantitatively evaluated based on a superposed epoch analysisl. The most remarkable result is that the temperature sensitivity to solar forcing in terms of the 27-day solar cycle agrees within uncertainties with the majority of published sensitivity values in terms of the 11-year solar cycle. This implies that the same underlying physical mechanism drives the mesopause temperature response to solar variability at both the 27-day and the 11-year time scale.

Link to GRL website
www.agu.org

von Savigny, C., McDade, I. C., Eichmann, K.-U., and Burrows, J. P.: On the dependence of the OH* Meinel emission altitude on vibrational level: SCIAMACHY observations and model simulations, Atmos. Chem. Phys., 12, 8813-8828, doi:10.5194/acp-12-8813-2012, 2012.

Summary:
This study deals with airglow emissions of the OH radical occurring near the mesopause at altitudes around 87 km. Vibrational levels of up to v' = 9 are excited through the exothermic reaction H + O3, leading to vibrational-rotational transitions from levels up to v' = 9. This study provides evidence - based on satellite observations with the SCIAMACHY instrument on Envisat - that OH emissions originating from different vibrational levels occur at different altitudes. The emission peak altitude difference between adjacent vibrational levels is about 0.5 km. The SCIAMACHY measurements are shown to be well reproduced by model simulations.

Link to von Savigny et al. (2012)
www.atmos-chem-phys.net

von Savigny, C., C. Robert, N. Rahpoe, H. Winkler, E. Becker, H. Bovensmann, J. P. Burrows, and M. T. DeLand, Impact of short term solar variability on the polar summer mesopause and noctilucent clouds, In: Climate and Weather of the Sun-Earth System (CAWSES): Highlights from a priority programme, Springer, September 30, 2012.

Link to Springer CAWSES book
www.springer.com

Winkler, H., von Savigny, C., Burrows, J. P., Wissing, J. M., Schwartz, M. J., Lambert, A., and García-Comas, M.: Impacts of the January 2005 solar particle event on noctilucent clouds and water at the polar summer mesopause, Atmos. Chem. Phys., 12, 5633-5646, doi:10.5194/acp-12-5633-2012, 2012.

Summary:
This publication provides model results estimating the effect the January 2005 solar proton event on the amount of water vapour near the polar summer mesopause, and subsequent potential effects on noctilucent clouds (NLCs). The main conclusion is that the proton-induced ion-chemical removal of H2O only has a minor influence on the NLC particles. The dramatic depletion of NLCs during the solar proton event is mainly caused by the significant temperature increase most likely related to a complicated physico-chemical chain of events as described in Becker and von Savigny (2010).

Link to Winkler et al. (2012)
www.atmos-chem-phys.net