Investigation of the mesopheric OH-Layer via FT spectroscopy and mesospheric models, OHTEMP II
Final Report Abstract
Mesopause temperatures above Ny-Ålesund: The comparison between a new cooled InGaAs detector with the former uncooled InGaAs detector revealed that despite the increased thermal noise, the performance of the uncooled detector is superior for the OH(3-1),OH(4-2), and OH(8-5) emission bands due to its narrow band sensitivity. It was therefore decided to proceed the measurements with the uncooled detector. A time series of rotational temperatures from the OH* emission above Ny-Ålesund was created for 3 polar winter seasons between 2010 and 2014 in the frame of the second part of this project. Further refinements in the automated operation of the FTIR measurements and the change from a zenith to a low elevation LOS led to an improvement of the number of non-discarded spectra versus operational time by more than a factor of three compared to the precedent 2008-10 winter seasons. The analysis of this project included rotational temperature estimates from the OH(3-1), OH(4-2), and OH(8-5) emission bands, the three most intense emission features in the recorded spectra. Systematic differences between these rotational temperatures could be identified. The most common features are: • very few OH(8 - 5) temperatures remain after spectral filtering, • OH(8 - 5) temperatures are exceptionally low, i.e. up to 92 K lower compared to OH(4 - 2) temperatures, • most of the OH(4 - 2) temperatures are higher than the OH(3 - 1) temperatures, i.e. differences range between a few Kelvin up to 30 K. In addition to the intercomparison of OH(3 - 1), OH(4 - 2), and OH(8 - 5) temperatures, the comparison with MLS temperatures shows that: • MLS temperatures are often higher than OH(3 - 1) temperatures, but in the range of OH(4 - 2) temperatures, • day-to-day variability is more pronounced in ground-based temperatures estimates. Evidence of mesospheric temperature anomalies was found in the rotational temperatures during two minor SSW events in 2011 and 2012. Finally, the investigation of the OH* emission at hourly scales revealed harmonic signatures in the rotational temperatures as well as emission line intensities. The coherency between temperature and brightness changes at these time scales suggest the response of the OH* emission to the passage of vertically propagating tidal waves as well as large scale gravity waves. Model study: The study of the relationship between odd oxygen and OH* temperature in search of an explanation of the differences in retrieved mesospheric temperatures of different transitions in the deexcitation of OH and th differences to mesospheric temperatures derived from satellite measurements led to a publication. It has been found that both Quenching with both O and O2 should be taken into account when studying the variability in OH* temperatures but also tides play an important role in explaining the temperature variability.
Publications
- Observation of the OH rotational emission with high resolution Fourier Transform Spectroscopy: First results from measurements above Ny-Ålesund, Spitsbergen. 4th NDMC Meeting 2011 at DLR Oberpfaffenhofen, Germany
S. Kowalewski, M. Palm, and J. Notholt
- The Mesospheric OH layer above Spitsbergen: Observation of the OH rotational emission with high resolution Fourier Transform Spectroscopy. EGU General Assembly 2011, Vienna, Austria
S. Kowalewski, M. Palm, C. Weinzierl, and J. Notholt
- Investigation of polar mesospheric dynamics and temperature trends by means of groundbased OH* airglow measurements and model studies above Spitsbergen. EGU General Assembly 2012, Vienna, Austria
S. Kowalewski, M. Palm, C. Weinzierl, and J. Notholt
- OH*-airglow measurements at Ny-Ålesund, Spitsbergen via Fourier Transform Spectroscopy: An update on the establishment of OH*-airglow observations and current model studies. 5th NDMC Meeting 2012 at DLR Oberpfaffenhofen, Germany
S. Kowalewski, M. Palm, C. Weinzierl, and J. Notholt
- Investigation of polar mesospheric dynamics and temperature changes by means of ground-based OH* airglow spectroscopy and model studies above Spitsbergen. NSERC CREATE Summer School in Arctic Atmospheric Science 2013, Alliston, Ontario, Canada
S. Kowalewski, C. von Savigny, M. Palm, C. Weinzierl, and J. Notholt
- A sensitivity study on the quenching process of OH* by O and O2 based on SD-WACCM4. 6th NDMC Meeting 2014, Grainau, Germany
S. Kowalewski, C. von Savigny, M. Palm, I.C. McDade, and J. Notholt
- On the impact of the temporal variability of the collisional quenching process on the mesospheric OH emission layer: a study based on SD–WACCM4 and SABER. Atmos. Chem. Phys., 14(18):10193–10210
S. Kowalewski, C. von Savigny, M. Palm, I.C. McDade, and J. Notholt
(See online at https://doi.org/10.5194/acp-14-10193-2014)
