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- ItemLarge mesospheric ice particles at exceptionally high altitudes(München : European Geopyhsical Union, 2009) Megner, L.; Khaplanov, M.; Baumgarten, G.; Gumbel, J.; Stegman, J.; Strelnikov, B.; Robertson, S.We here report on the characteristics of exceptionally high Noctilucent clouds (NLC) that were detected with rocket photometers during the ECOMA/MASS campaign at Andøya, Norway 2007. The results from three separate flights are shown and discussed in connection to lidar measurements. Both the lidar measurements and the large difference between various rocket passages through the NLC show that the cloud layer was inhomogeneous on large scales. Two passages showed a particularly high, bright and vertically extended cloud, reaching to approximately 88 km. Long time series of lidar measurements show that NLC this high are very rare, only one NLC measurement out of thousand reaches above 87 km. The NLC is found to consist of three distinct layers. All three were bright enough to allow for particle size retrieval by phase function analysis, even though the lowest layer proved too horizontally inhomogeneous to obtain a trustworthy result. Large particles, corresponding to an effective radius of 50 nm, were observed both in the middle and top of the NLC. The present cloud does not comply with the conventional picture that NLC ice particles nucleate near the temperature minimum and grow to larger sizes as they sediment to lower altitudes. Strong up-welling, likely caused by gravity wave activity, is required to explain its characteristics.
- ItemThe atmospheric background situation in northern Scandinavia during January/February 2003 in the context of the MaCWAVE campaign(München : European Geopyhsical Union, 2006) Blum, U.; Baumgarten, G.; Schöch, A.; Kirkwood, S.; Naujokat, B.; Fricke, K.H.The atmosphere background wind field controls the propagation of gravity waves from the troposphere through the stratosphere into the mesosphere. During January 2003 the MaCWAVE campaign took place at Esrange, with the purpose of observing vertically ascending waves induced by orography. Temperature data from the U. Bonn lidar at Esrange (68° N/21° E) and the ALOMAR RMR lidar (69° N/16° E), wind data from Esrange MST radar ESRAD, as well as wind data from the ECMWF T106 model, are used to analyse the atmospheric background situation and its effect on mountain wave propagation during January/February 2003. Critical levels lead to dissipation of vertically ascending waves, thus mountain waves are not observable above those levels. In the first half of January a minor as well as a major stratospheric warming dominated the meteorological background situation. These warmings led to a wind reversal, thus to critical level filtering and consequently prevented gravity waves from propagating to high altitudes. While the troposphere was not transparent for stationary gravity waves most of the time, there was a period of eight days following the major warming with a transparent stratosphere, with conditions allowing gravity waves generated in the lower troposphere to penetrate the stratosphere up to the stratopause and sometimes even into the lower mesosphere. In the middle of February a minor stratospheric warming occurred, which again led to critical levels such that gravity waves were not able to ascend above the middle stratosphere. Due to the unfavourable troposphere and lower stratosphere conditions for gravity wave excitation and propagation, the source of the observed waves in the middle atmosphere is probably different from orography.
- ItemFirst in situ measurement of the vertical distribution of ice volume in a mesospheric ice cloud during the ECOMA/MASS rocket-campaign(München : European Geopyhsical Union, 2009) Rapp, M.; Strelnikova, I.; Strelnikov, B.; Latteck, R.; Baumgarten, G.; Li, Q.; Megner, L.; Gumbel, J.; Friedrich, M.; Hoppe, U.-P.; Robertson, S.We present in situ observations of mesospheric ice particles with a new particle detector which combines a classical Faraday cup with the active photoionization of particles and subsequent detection of photoelectrons. Our observations of charged particles and free electrons within a decaying PMSE-layer reveal that the presence of charged particles is a necessary but not sufficient condition for the presence of PMSE. That is, additional requirements like a sufficiently large electron density – which we here estimate to be on the order of ~100 cm−3 – and the presence of small scale structures (commonly assumed to be caused by turbulence) need to be satisfied. Our photoelectron measurements reveal a very strong horizontal structuring of the investigated ice layer, i.e., a very broad layer (82–88 km) seen on the upleg is replaced by a narrow layer from 84.5–86 km only 50 km apart on the downleg of the rocket flight. Importantly, the qualitative structure of these photoelectron profiles is in remarkable qualitative agreement with photometer measurements on the same rocket thus demonstrating the reliability of this new technique. We then show that the photoelectron currents are a unique function of the ice particle volume density (and hence ice mass) within an uncertainty of only 15% and we derive corresponding altitude profiles of ice volume densities. Derived values are in the range ~2–8×10−14 cm3/cm3 (corresponding to mass densities of ~20–80 ng/m3, and water vapor mixing ratios of 3–12 ppm) and are the first such estimates with the unique spatial resolution of an in situ measurement.