5 results
Search Results
Now showing 1 - 5 of 5
- ItemInfluence 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.
- ItemLong-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.
- ItemSeasonal 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.
- ItemValidation of the Atmospheric Chemistry Experiment (ACE) version 2.2 temperature using ground-based and space-borne measurements(München : European Geopyhsical Union, 2008) Sica, R.J.; Izawa, M.R.M.; Walker, K.A.; Boone, C.; Petelina, S.V.; Argall, P.S.; Bernath, P.; Burns, G.B.; Catoire, V.; Collins, R.L.; Daffer, W.H.; De Clercq, C.; Fan, Z.Y.; Firanski, B.J.; French, W.J.R.; Gerard, P.; Gerding, M.; Granville, J.; Innis, J.L.; Keckhut, P.; Kerzenmacher, T.; Klekociuk, A.R.; Kyrö, E.; Lambert, J.C.; Llewellyn, E.J.; Manney, G.L.; McDermid, I.S.; Mizutani, K.; Murayama, Y.; Piccolo, C.; Raspollini, P.; Ridolfi, M.; Robert, C.; Steinbrecht, W.; Strawbridge, K.B.; Strong, K.; Stübi, R.; Thurairajah, B.An ensemble of space-borne and ground-based instruments has been used to evaluate the quality of the version 2.2 temperature retrievals from the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS). The agreement of ACE-FTS temperatures with other sensors is typically better than 2 K in the stratosphere and upper troposphere and 5 K in the lower mesosphere. There is evidence of a systematic high bias (roughly 3–6 K) in the ACE-FTS temperatures in the mesosphere, and a possible systematic low bias (roughly 2 K) in ACE-FTS temperatures near 23 km. Some ACE-FTS temperature profiles exhibit unphysical oscillations, a problem fixed in preliminary comparisons with temperatures derived using the next version of the ACE-FTS retrieval software. Though these relatively large oscillations in temperature can be on the order of 10 K in the mesosphere, retrieved volume mixing ratio profiles typically vary by less than a percent or so. Statistical comparisons suggest these oscillations occur in about 10% of the retrieved profiles. Analysis from a set of coincident lidar measurements suggests that the random error in ACE-FTS version 2.2 temperatures has a lower limit of about ±2 K.
- ItemComparison of NLC particle sizes derived from SCIAMACHY/Envisat observations with ground-based LIDAR measurements at ALOMAR (69° N)(München : European Geopyhsical Union, 2009) von Savigny, C.; Robert, C.E.; Baumgarten, G.; Bovensmann, H.; Burrows, J.P.SCIAMACHY, the Scanning Imaging Absorption spectroMeter for Atmospheric CHartographY has provided measurements of limb-scattered solar radiation in the 220 nm to 2380 nm wavelength range since summer of 2002. Measurements in the UV spectral range are well suited for the retrieval of particle sizes of noctilucent clouds (NLCs) and have been used to compile the largest existing satellite data base of NLC particle sizes. This paper presents a comparison of SCIAMACHY NLC size retrievals with the extensive NLC particle size data set based on ground-based LIDAR measurements at the Arctic LIDAR Observatory for Middle Atmosphere Research (ALOMAR, 69° N, 16° E) for the Northern Hemisphere NLC seasons 2003 to 2007. Most of the presented SCIAMACHY NLC particle size retrievals are based on cylindrical particles and a Gaussian particle size distribution with a fixed width of 24 nm. If the differences in spatial as well as vertical resolution between SCIAMACHY and the ALOMAR LIDAR are taken into account, very good agreement is found. The mean particle size derived from SCIAMACHY limb observations for the ALOMAR overpasses in 2003 to 2007 is 56.2 nm with a standard deviation of 12.5 nm, and the LIDAR observations yield a value of 54.2 nm with a standard deviation of 17.4 nm.