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End date: 2019 × Start date: 2019 × Type: Text × WGL Institute: IAP ×

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Now showing 1 - 10 of 108
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    Model studies of short-term variations induced in trace gases by particle precipitation in the mesosphere and lower thermosphere
    (Hoboken, NJ : Wiley, 2016) Fytterer, T.; Bender, S.; Berger, U.; Nieder, H.; Sinnhuber, M.; Wissing, J.M.
    The 3-D global chemistry and transport model (3dCTM) was used to investigate NO, OH, and O3 from January 2002 to May 2010 between 60 km and 133 km. Their daytime and nighttime mean zonal means (55°–75° geomagnetic latitude) were analyzed with respect to short-term variations associated with particle precipitation. The corresponding ionization rates were derived from the 3-D atmospheric ionization module Osnabrück (AIMOS), which is based on particle flux measurements. The trace gas variations with respect to their background were investigated by using a superposed epoch analysis. The 27 day signature associated with particle precipitation is found in NO, while it is only indicated in OH and O3 during winter. A varying solar spectrum associated with the 11 year solar cycle causes modifications of this signal up to 10%, while the main patterns are conserved. Published observations show a clear 27 day signal, qualitatively agreeing with the model results at altitudes >70 km except for O3 in Northern Hemisphere winter. Further differences occur with respect to the magnitude of the trace gas variations, primarily attributed to the different trace gas background and dynamical variations of the background atmosphere. Absolute OH variations are overestimated by the 3dCTM during winter, while the opposite is true for O3. These differences might originate from an unknown offset in AIMOS, incorrect chemical reaction rates, a different background of H2O and O3, and the model dynamics. However, their nonlinear relationship and their altitude of largest response are qualitatively captured in Southern Hemisphere winter.
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    On the upper tropospheric formation and occurrence of high and thin cirrus clouds during anticyclonic poleward Rossby wave breaking events
    (Milton Park : Taylor & Francis, 2010) Eixmann, Ronald; Peters, Dieter H.W.; Zülicke, Christoph; Gerding, Michael; Dörnbrack, Andreas
    Ground-based lidar measurements and balloon soundings were employed to examine the dynamical link between anticyclonic Rossby wave breaking and cirrus clouds from 13 to 15 February 2006. For this event, an air mass with low Ertel’s potential vorticity appeared over Central Europe. In the tropopause region, this air mass was accompanied with both an area of extreme cold temperatures placed northeastward, and an area of high specific humidity, located southwestward. ECMWF analyses reveal a strong adiabatic northeastward and upward transport of water vapour within the warm conveyor belt on the western side of the ridge over Mecklenburg, Northern Germany. The backscatter lidar at K¨uhlungsborn (54.1◦N, 11.8◦E) clearly identified cirrus clouds at between 9 and 11.4 km height. In the tropopause region high-vertical resolution radiosoundings showed layers of subsaturated water vapour over ice but with a relative humidity over ice >80%. Over Northern Germany radiosondes indicated anticyclonically rotating winds in agreement with backward trajectories of ECMWF analyses in the upper troposphere, which were accompanied by a relatively strong increase of the tropopause height on 14 February. Based on ECMWF data the strong link between the large-scale structure, updraft and ice water content was shown.
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    ECOMA - Existence and charge state of meteoric dust particles in the middle atmosphere : Abschlussbericht zum Vorhaben
    (Hannover : Technische Informationsbibliothek (TIB), 2009) Rapp, Markus
    [no abstract available]
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    Verbundprojekt im Rahmen von "Wirtschaft trifft Wissenschaft": Technologietransfer Leibniz-Nordost : Schlussbericht
    (Hannover : Technische Informationsbibliothek (TIB), 2011) Eixmann, Ronald; Hoffmann, Peter
    [no abstract available]
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    Physik der kleinskaligen Schichten in der oberen Mososphäre: OPOSSUM : Schlussbericht zum Forschungsvorhaben
    (Hannover : Technische Informationsbibliothek (TIB), 2005) Lübken, Franz-Josef
    [no abstract available]
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    Very low ozone episodes due to polar vortex displacement
    (Milton Park : Taylor & Francis, 2000) James, P.M.; Peters, D.; Waugh, D.W.
    The large-scale ozone distribution over the northern hemisphere undergoes strong fluctuationseach winter on timescales of up to a few weeks. This is closely linked to changes in the stratosphericpolar vortex, whose shape, intensity and location vary with time. Elliptical diagnosticparameters provide an empirical description of the daily character of the polar vortex. Theseparameters are used as an objective measure to define two characteristic wintertime vortexdisplacements, towards northern Europe and Canada, respectively. The large-scale structuresin both the stratosphere and troposphere and the 3D ozone structures are determined for bothvortex displacement scenarios. A linear ozone transport model shows that the contribution ofhorizontal ozone advection dominates locally in the middle stratosphere. Nevertheless, thelargest contribution is due to vertical advection around the ozone layer maximum. The findingsare in agreement with an EOF analysis which reveals significant general modes of ozone variabilitylinked to polar vortex displacement and to phase-shifted large-scale tropospheric waves.When baroclinic waves travel through the regions of vortex-related ozone reduction, the combinedeffect is to produce transient synoptic-scale areas of exceptionally low ozone; namelydynamically induced strong ozone mini-holes.
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    Trägheitsschwerewellen und ihre Verbindung zu brechenden Rossbywellen : Schlussbericht
    (Hannover : Technische Informationsbibliothek (TIB), 2005) Peters, Dieter H.W.; Gerding, Michael; Hoffmann, Peter; Zülicke, Christoph; Serafimovich, Andrei
    [no abstract available]
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    Resolving the strange behavior of extraterrestrial potassium in the upper atmosphere
    (Hoboken, NJ : Wiley, 2014) Plane, J.M.C.; Feng, W.; Dawkins, E.; Chipperfield, M.P.; Höffner, J.; Janches, D.; Marsh, D.R.
    It has been known since the 1960s that the layers of Na and K atoms, which occur between 80 and 105 km in the Earth's atmosphere as a result of meteoric ablation, exhibit completely different seasonal behavior. In the extratropics Na varies annually, with a pronounced wintertime maximum and summertime minimum. However, K varies semiannually with a small summertime maximum and minima at the equinoxes. This contrasting behavior has never been satisfactorily explained. Here we use a combination of electronic structure and chemical kinetic rate theory to determine two key differences in the chemistries of K and Na. First, the neutralization of K+ ions is only favored at low temperatures during summer. Second, cycling between K and its major neutral reservoir KHCO3 is essentially temperature independent. A whole atmosphere model incorporating this new chemistry, together with a meteor input function, now correctly predicts the seasonal behavior of the K layer.
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    ECOMA - Existence and charge state of meteoric dust particles in the middle atmosphere - Teil 2 : Abschlussbericht zum Vorhaben
    (Hannover : Technische Informationsbibliothek (TIB), 2011) Rapp, Markus
    [no abstract available]