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search.filters.applied.f.access: openAccess × End date: 2009 × Start date: 2000 × DDC: 550 × Has files: Yes × Version: publishedVersion × WGL Institute: IAP ×

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Now showing 1 - 10 of 32
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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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    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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    Long-term lidar observations of polar stratospheric clouds at Esrange in northern Sweden
    (Milton Park : Taylor & Francis, 2005) Blum, U.; Fricke, K.H.; Müller, K.P.; Siebert, J.; Baumgarten, G.
    Polar stratospheric clouds (PSCs) play a key role in the depletion of polar ozone. The type of cloud and the length of time for which it exists are crucial for the amount of chlorine activation during the polar night. The Bonn University backscatter lidar at Esrange in northern Sweden (68◦N, 21◦E) is well equipped for long-term observation and classification of these clouds. Nearly continuous measurements through several winters are rare, in particular in wave-active regions like Esrange. Lidar measurements have been performed each winter since 1997—a total of more than 2000 h of observation time has been accumulated, including more than 300 h with PSCs. Analysis of this unique data set leads to a classification scheme with four different scattering characteristics which can be associated with four different cloud types: (1) supercooled ternary solution (STS), (2) nitric acid trihydrate (NAT), (3) ice and (4) mixtures of solid and liquid particles. The analysis of observations over seven winters gives an overview of the frequency of appearance of the individual PSC types. Most of the clouds contain layers of different PSC types. The analysis of these layers shows STS and mixed clouds to occur most frequently, with more than 39% and 37% of all PSC observations, respectively, whereas NAT (15%) and ice clouds (9%) are seen only rarely. The lidar is located close to the Scandinavian mountain ridge, which is a major source of orographically induced gravity waves that can rapidly cool the atmosphere below cloud formation temperatures. Comparing the individual existence temperature of the observed cloud type with the synoptic-scale temperature provided by the European Centre for Medium-range Weather Forecasts (ECMWF) gives information on the frequency of synoptically and wave-induced PSCs. Further, the analysis of ECMWF temperature and wind data gives an estimate of the transparency of the atmosphere to stationary gravity waves. During more than 80% of all PSC observations in synoptic-scale temperatures which were too warm the atmosphere was transparent for stationary gravity waves. Our measurements show that dynamically induced cooling is crucial for the existence of PSCs above Esrange. In particular ice PSCs are observed only in situations where there are gravity waves.
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    Charging of mesospheric aerosol particles: The role of photodetachment and photoionization from meteoric smoke and ice particles
    (Göttingen : Copernicus, 2009) Rapp, M.
    Time constants for photodetachment, photoemission, and electron capture are considered for two classes of mesospheric aerosol particles, i.e., meteor smoke particles (MSPs) and pure water ice particles. Assuming that MSPs consist of metal oxides like Fe2O3 or SiO, we find that during daytime conditions photodetachment by solar photons is up to 4 orders of magnitude faster than electron attachment such that MSPs cannot be negatively charged in the presence of sunlight. Rather, even photoemission can compete with electron capture unless the electron density becomes very large (≫1000 cm-3) such that MSPs should either be positively charged or neutral in the case of large electron densities. For pure water ice particles, however, both photodetachment and photoemission are negligible due to the wavelength characteristics of its absorption cross section and because the flux of solar photons has already dropped significantly at such short wavelengths. This means that water ice particles should normally be negatively charged. Hence, our results can readily explain the repeated observation of the coexistence of positive and negative aerosol particles in the polar summer mesopause, i.e., small MSPs should be positively charged and ice particles should be negatively charged. These results have further important implications for our understanding of the nucleation of mesospheric ice particles as well as for the interpretation of incoherent scatter radar observations of MSPs. © 2009 Author(s).
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    ROMA - Rocketborne observations in the middle atmosphere : Abschlussbericht zum Vorhaben
    (Hannover : Technische Informationsbibliothek (TIB), 2008) Lübken, Franz-Josef; Rapp, Markus
    [no abstract available]
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    Upper stratospheric ozone decrease events due to a positive feedback between ozone and the ozone dissociation rate
    (Göttingen : Copernicus, 2009) Sonnemann, G.R.; Hartogh, P.
    Ozone measurements taken with a ground based microwave instrument at Lindau (51.66° N, 10.13° E) over some years showed strong ozone decrease events within the stratopause region, particularly during the winter half-year. These events are characterized by a marked drop of the ozone mixing ratio from two to three ppmv to less than half a ppmv in extreme cases. Simultaneous water vapor measurements at the same place, also carried out by a microwave instrument, showed a strong increase of its mixing ratio and the temperature was also enhanced during these episodes. The theoretical analysis brought evidence that these events result from a positive feedback in the complex radiatively-chemical system between the ozone column density and the ozone dissociation rate.
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    Seasonal variation of nocturnal temperatures between 1 and 105 km altitude at 54° N observed by lidar
    (München : European Geopyhsical Union, 2008) Gerding, M.; Höffner, J.; Lautenbach, J.; Rauthe, M.; Lübken, F.-J.
    Temperature soundings are performed by lidar at the mid-latitude station of Kühlungsborn (Germany, 54° N, 12° E). The profiles cover the complete range from the lower troposphere (~1 km) to the lower thermosphere (~105 km) by simultaneous and co-located operation of a Rayleigh-Mie-Raman lidar and a potassium resonance lidar. Observations have been done during 266 nights between June 2002 and July 2007, each of 3–15 h length. This large and unique data set provides comprehensive information on the altitudinal and seasonal variation of temperatures from the troposphere to the lower thermosphere. The remaining day-to-day-variability is strongly reduced by harmonic fits at constant altitude levels and a representative data set is achieved. This data set reveals a two-level mesopause structure with an altitude of about 86–87 km (~144 K) in summer and ~102 km (~170 K) during the rest of the year. The average stratopause altitude is ~48 km throughout the whole year, with temperatures varying between 258 and 276 K. From the fit parameters amplitudes and phases of annual, semi-annual, and quarter-annual variations are derived. The amplitude of the annual component is largest with amplitudes of up to 30 K in 85 km, while the quarter-annual variation is smallest and less than 3 K at all altitudes. The lidar data set is compared with ECMWF temperatures below about 70 km altitude and reference data from the NRLMSISE-00 model above. Apart from the temperature soundings the aerosol backscatter ratio is measured between 20 and 35 km. The seasonal variation of these values is presented here for the first time.
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    Long-term behavior of the concentration of the minor constituents in the mesosphere-a model study
    (Göttingen : Copernicus, 2009) Grygalashvyly, M.; Sonnemann, G.R.; Hartogh, P.
    We investigate the influence the rising concentrations of methane, nitrous oxide and carbon dioxide which have occurred since the pre-industrial era, have had on the chemistry of the mesosphere. For this investigation we use our global 3-D-model COMMA-IAP which was designed for the exploration of the MLT-region and in particular the extended mesopause region. Assumptions and approximations for the trends in the Lyman-flux (needed for the water vapor dissociation rate), methane and the water vapor mixing ratio at the hygropause are necessary to accomplish this study. To approximate the solar Lyman-α flux back to the pre-industrial time, we derived a quadratic fit using the sunspot number record which extends back to 1749 and is the only solar proxy available for the Lyman-α flux prior to 1947. We assume that methane increases with a constant growth rate from the pre-industrial era to the present. An unsolved problem for the model calculations consists of how the water vapor mixing ratio at the hygropause should be specified during this period. We assume that the hygropause was dryer during pre-industrial times than the present. As a consequence of methane oxidation, the model simulation indicates that the middle atmosphere has become more humid as a result of the rising methane concentration, but with some dependence on height and with a small time delay of few years. The solar influence on the water vapor mixing ratio is insignificant below about 80 km in summer high latitudes, but becomes increasingly more important above this altitude. The enhanced water vapor concentration increasesthe hydrogen radical concentration and reduces the mesospheric ozone. A second region of stronger ozone decrease is located in the vicinity of the stratopause. Increases in CO2 concentration enhance slightly the concentration of CO in the mesosphere. However, its influence upon the chemistry is small and its main effect is connected with a cooling of the upper atmosphere. The long-term behavior of water vapor is discussed in particular with respect to its impact on the NLC region.