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End date: 2020 × Start date: 2020 × Start date: 1990 × DDC: 550 × Type: Article × Subject: lidar × Subject: mesosphere ×

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Now showing 1 - 3 of 3
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    Influence of tides and gravity waves on layering processes in the polar summer mesopause region
    (Göttingen : Copernicus, 2008) Hoffmann, P.; Rapp, M.; Fiedler, J.; Latteck, R.
    Polar Mesosphere Summer Echoes (PMSE) have been studied at Andenes (69° N, 16° E), Norway, using VHF radar observations since 1994. One remarkable feature of these observations is the fact that {during 50% of the time,} the radar echoes occur in the form of two or more distinct layers. In the case of multiple PMSE layers, statistical analysis shows that the lower layer occurs at a mean height of ∼83.4 km, which is almost identical to the mean height of noctilucent clouds (NLC) derived from observation with the ALOMAR Rayleigh/Mie/Raman lidar at the same site. To investigate the layering processes microphysical model simulations under the influence of tidal and gravity waves were performed. In the presence of long period gravity waves, these model investigations predict an enhanced formation of multiple PMSE layer structures, where the lower layer is a consequence of the occurrence of the largest particles at the bottom of the ice cloud. This explains the coincidence of the lowermost PMSE layers and NLC. During periods with enhanced amplitudes of the semidiurnal tide, the observed NLC and PMSE show pronounced tidal structures comparable to the results of corresponding microphysical simulations. At periods with short period gravity waves there is a tendency for a decreasing occurrence of NLC and for variable weak PMSE structures.
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    Mesospheric anomalous diffusion during noctilucent cloud scenarios
    (Göttingen : Copernicus GmbH, 2019) Laskar, F.I.; Stober, G.; Fiedler, J.; Oppenheim, M.M.; Chau, J.L.; Pallamraju, D.; Pedatella, N.M.; Tsutsumi, M.; Renkwitz, T.
    The Andenes specular meteor radar shows meteor trail diffusion rates increasing on average by about 10% at times and locations where a lidar observes noctilucent clouds (NLCs). This high-latitude effect has been attributed to the presence of charged NLC after exploring possible contributions from thermal tides. To make this claim, the current study evaluates data from three stations at high, middle, and low latitudes for the years 2012 to 2016 to show that NLC influence on the meteor trail diffusion is independent of thermal tides. The observations also show that the meteor trail diffusion enhancement during NLC cover exists only at high latitudes and near the peaks of NLC layers. This paper discusses a number of possible explanations for changes in the regions with NLCs and leans towards the hypothesis that the relative abundance of background electron density plays the leading role. A more accurate model of the meteor trail diffusion around NLC particles would help researchers determine mesospheric temperature and neutral density profiles from meteor radars at high latitudes. © 2019 Author(s).
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    First global observations of the mesospheric potassium layer
    (Hoboken, NJ : Wiley-Blackwell Publishing Ltd, 2014) Dawkins, E.C.M.; Plane, J.M.C.; Chipperfield, M.P.; Feng, W.; Gumbel, J.; Hedin, J.; Höffner, J.; Friedman, J.S.
    Metal species, produced by meteoric ablation, act as useful tracers of upper atmosphere dynamics and chemistry. Of these meteoric metals, K is an enigma: at extratropical latitudes, limited available lidar data show that the K layer displays a semiannual seasonal variability, rather than the annual pattern seen in other metals such as Na and Fe. Here we present the first near-global K retrieval, where K atom number density profiles are derived from dayglow measurements made by the Optical Spectrograph and Infrared Imager System spectrometer on board the Odin satellite. This robust retrieval produces density profiles with typical layer peak errors of ±15% and a 2km vertical grid resolution. We demonstrate that these retrieved profiles compare well with available lidar data and show for the first time that the unusual semiannual behavior is near-global in extent. This new data set has wider applications for improving understanding of the K chemistry and of related upper atmosphere processes. Key Points First quantitative retrieval of the terrestrial K layer from space The unusual semiannual behavior of K is near global in extent.