Michael Gerding

Aerosol layers from the 2008 eruptions of Mount Okmok and Mount Kasatochi: In situ upper troposphere and lower stratosphere measurements of sulfate and organics over Europe

In 2008 Mt. Okmok and Mt. Kasatochi started erupting on 12 July and 7 August, respectively, in the Aleutians, depositing emissions of trace gases and aerosols as high as 15.2 km into the atmosphere. During an aircraft campaign, conducted over Europe in October/November 2008, the volcanic aerosol was measured by an Aerodyne Aerosol Mass Spectrometer (AMS), capable of particle chemical composition measurements covering a size diameter range between 40 nm and 1 µm. In the volcanic aerosol layer enhanced submicron particulate sulfate concentrations of up to 2.0 µg m-3 standard temperature and pressure (STP) were observed between 8 and 12 km altitude while background values did not exceed 0.5 µg m-3 (STP). 21 % of the volcanic aerosol consisted of carbonaceous material that increased by a factor of 1.9 in mass compared to the free troposphere. Enhanced gaseous sulfur dioxide concentrations measured by an ion trap chemical ionization mass spectrometer (IT-CIMS) of up to 1.3 µg m-3 were encountered. An onboard radiation measurement system simultaneously detected an enhanced aerosol signal. Furthermore, two German lidar stations identified an aerosol layer before and after the campaign. Data analysis shows that the aerosol layer was observed mainly in the lowermost stratosphere. Correlation of particulate sulfate concentration and sulfur dioxide mixing ratios indicate that after 3 month residence time in the stratosphere not all sulfur dioxide has been converted into sulfate aerosol. The significant fraction of organic material might have implications on heterogeneous chemistry in the stratosphere which need to be explored more thoroughly

Multiwavelength lidar observation of a strange noctilucent cloud at Kühlungsborn, Germany (54°N)

On July 6/7, 1997, we observed a noctilucent cloud (NLC) by lidar at Kuhlungsborn, Germany (54°N, 12°E) using four laser wavelengths (393, 423, 532, and 770 nm). While at the near-ultraviolet and visible wavelengths clear backscatter signals were detected, the NLC did not produce significant backscattering at the near-infrared wavelength 770 nm. The latter signature can not be explained by backscattering on any size distribution of homogeneous water ice spheres. In this work we discuss the spectral backscatter signatures of particles with various shapes and compositions. We found three different particle types matching the experimental results, but there are physical arguments excluding these candidates as well. Our lidar observations of this strange NLC event appear to contradict the common understanding of NLC particle formation and sublimation. We emphasize the importance of multiwavelength observations for an in-depth interpretation of noctilucent cloud lidar backscatter data, including also the infrared part of the spectrum.

Observations of noctilucent clouds and temperature structure from 1-105 km by co-located lidars at 54°N

At the mid-latitude location of Kuehlungsborn (54°N, 12°E) a resonance lidar and a Rayleigh-Mie-Raman (RMR) lidar are operated to observe e.g. the occurrence and particle properties of Noctilucent Clouds (NLC) and to measure continuous temperature profiles from the troposphere to the lower thermosphere. For the temperature profiles the two lidars (RMR lidar and potassium lidar) and three different measurement methods (rotational Raman, Rayleigh/vib. Raman, Doppler resonance) are combined. The profiles are obtained continuously between 1 and 105 km with a temporal and vertical resolution of at least 15 min and 1 km, respectively. Temperature fluctuations due to gravity waves and tides with amplitudes of up to ±20 K are observed. In summer during the cold phases of waves the temperature above 80 km drops occasionally below the frostpoint temperature. However, the mean temperature below 83 km is a few Kelvin above the frost point and only for about two weeks in summer the air becomes continuously supersaturated between 85 and 90 km. Therefore, the existence of NLC ice particles above our site is only allowed in the cold phases of waves. We will present lidar-observations of NLC and temperatures below and above the NLC layer showing the coupling of the NLC to supersaturated air in the mesopause region.

Temperature and aerosol soundings in the middle atmosphere at different mid and high-latitude lidar stations during day and night

Lidars provide an important tool to measure temperature and minor constituents in the atmosphere up to ~110 km altitude with high accuracy and temporal resolution. The Leibniz-Institute of Atmospheric Physics operates various lidars for the whole range between troposphere and lower thermosphere. The lidars are installed at Kühlungsborn, Germany (54°N, 12°E), at the ALOMAR site, Norway (69°N, 16°E), or in a mobile 20-foot container. Summertime soundings in polar regions as well as coverage of tides and gravity waves require measurements during full daylight. With a standard lidar the daylight background is several magnitudes larger than the signal in the mesosphere. Narrowband spectral filtering by etalons as well as spatial filtering by small fields of view (~50 μrad) are realized instead. At this low FOV turbulence and jitter of the beam pointing affects the signal and have to be compensated. We describe the techniques applied at our lidars. Additionally we will discuss the influence of the etalon filter technique on calculated temperature profiles. The etalon transmission of the Doppler-broadened backscatter signal is temperature dependent and has to be taken into account to avoid systematic errors. Overall, narrow-band lidars provide temperature profiles in the whole range up to the lower thermosphere. We will present observations of temperatures profiles of the lower and middle atmosphere as well as noctilucent clouds (NLC). These quantities provide important insights into the dynamics of the middle atmosphere. Time-resolved and averaged profiles of observations at the different locations will be shown and the results from different latitudes compared.