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- ItemOn 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, AndreasGround-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.
- ItemDiurnal variation of the potassium layer in the upper atmosphere(Hoboken, NJ : Wiley, 2015) Feng W.; Höffner J.; Marsh D.R.; Chipperfield M.P.; Dawkins E.C.M.; Viehl T.P.; Plane J.M.C.Measurements of the diurnal cycle of potassium (K) atoms between 80 and 110 km have been made during October (for the years 2004–2011) using a Doppler lidar at Kühlungsborn, Germany (54.1°N, 11.7°E). A pronounced diurnal variation is observed in the K number density, which is explored by using a detailed description of the neutral and ionized chemistry of K in a three-dimensional chemistry climate model. The model captures both the amplitude and phase of the diurnal and semidiurnal variability of the layer, although the peak diurnal amplitude around 90 km is overestimated. The model shows that the total potassium density (≈ K + K+ + KHCO3) exhibits little diurnal variation at each altitude, and the diurnal variations are largely driven by photochemical conversion between these reservoir species. In contrast, tidally driven vertical transport has a small effect at this midlatitude location, and diurnal fluctuations in temperature are of little significance because they are small and the chemistry of K is relatively temperature independent.
- ItemCalifornian Wildfire Smoke Over Europe: A First Example of the Aerosol Observing Capabilities of Aeolus Compared to Ground‐Based Lidar(Hoboken, NJ : Wiley, 2021) Baars, Holger; Radenz, Martin; Floutsi, Athena Augusta; Engelmann, Ronny; Althausen, Dietrich; Heese, Birgit; Ansmann, Albert; Flament, Thomas; Dabas, Alain; Trapon, Dimitri; Reitebuch, Oliver; Bley, Sebastian; Wandinger, UllaIn September 2020, extremely strong wildfires in the western United States of America (i.e., mainly in California) produced large amounts of smoke, which was lifted into the free troposphere. These biomass-burning-aerosol (BBA) layers were transported from the US west coast toward central Europe within 3–4 days turning the sky milky and receiving high media attention. The present study characterizes this pronounced smoke plume above Leipzig, Germany, using a ground-based multiwavelength-Raman-polarization lidar and the aerosol/cloud product of ESA’s wind lidar mission Aeolus. An exceptional high smoke-AOT >0.4 was measured, yielding to a mean mass concentration of 8 μg m−3. The 355 nm lidar ratio was moderate at around 40–50 sr. The Aeolus-derived backscatter, extinction and lidar ratio profiles agree well with the observations of the ground-based lidar PollyXT considering the fact that Aeolus’ aerosol and cloud products are still preliminary and subject to ongoing algorithm improvements.
- 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.
- 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.
- ItemStudy of the tidal variations in mesospheric temperature at low and mid latitudes from WINDII and potassium lidar observations(Göttingen : Copernicus GmbH, 2004) Shepherd, M.; Fricke-Begemann, C.Zonal mean daytime temperatures from the Wind Imaging Interferometer (WINDII) on the Upper Atmosphere Research Satellite (UARS) and nightly temperatures from a potassium (K) lidar are employed in the study of the tidal variations in mesospheric temperature at low and mid latitudes in the Northern Hemisphere. The analysis is applied to observations at 89 km height for winter solstice, December to February (DJF), at 55° N, and for May and November at 28° N. The WINDII results are based on observations from 1991 to 1997. The K-lidar observations for DJF at Kühlungsborn (54° N) were from 1996-1999, while those for May and November at Tenerife 28° N were from 1999. To avoid possible effects from year-to-year variability in the temperatures observed, as well as differences due to instrument calibration and observation periods, the mean temperature field is removed from the respective data sets, assuming that only tidal and planetary scale perturbations remain in the temperature residuals. The latter are then binned in 0.5 h periods and the individual data sets are fitted in a least-mean square sense to 12-h and 8-h harmonics, to infer semidiurnal and terdiurnal tidal parameters. Both the K-lidar and WINDII independently observed a strong semidiurnal tide in November, with amplitudes of 13 K and 7.4 K, respectively. Good agreement was also found in the tidal parameters derived from the two data sets for DJF and May. It was recognized that insufficient local time coverage of the two separate data sets could lead to an overestimation of the semidiurnal tidal amplitude. A combined ground-based/satellite data set with full diurnal local time coverage was created which was fitted to 24 h+ 12 h+8 h harmonics and a novel method applied to account for possible differences between the daytime and nighttime means. The results still yielded a strong semidiurnal tide in November at 28° N with an amplitude of 8.8 K which is twice the SD amplitude in May and DJF. The diurnal tidal parameters were practically the same at 28° N and 55° N, in November and DJF, respectively, with an amplitude of 6.5 K and peaking at ∼9h. The diurnal and semidiurnal amplitudes in May were about the same, 4 K, and 4.6 K, while the terdiurnal tide had the same amplitudes and phases in May and November at 28° N. Good agreement is found with other experimental data while models tend to underestimate the amplitudes.
- ItemObservations of Reduced Turbulence and Wave Activity in the Arctic Middle Atmosphere Following the January 2015 Sudden Stratospheric Warming(Hoboken, NJ : Wiley, 2018-12-11) Triplett, Colin C.; Li, Jintai; Collins, Richard L.; Lehmacher, Gerald A.; Barjatya, Aroh; Fritts, David C.; Strelnikov, Boris; Lübken, Franz‐Josef; Thurairajah, Brentha; Harvey, V. Lynn; Hampton, Donald L.; Varney, Roger H.Measurements of turbulence and waves were made as part of the Mesosphere-Lower Thermosphere Turbulence Experiment (MTeX) on the night of 25–26 January 2015 at Poker Flat Research Range, Chatanika, Alaska (65°N, 147°W). Rocket-borne ionization gauge measurements revealed turbulence in the 70- to 88-km altitude region with energy dissipation rates between 0.1 and 24 mW/kg with an average value of 2.6 mW/kg. The eddy diffusion coefficient varied between 0.3 and 134 m2/s with an average value of 10 m2/s. Turbulence was detected around mesospheric inversion layers (MILs) in both the topside and bottomside of the MILs. These low levels of turbulence were measured after a minor sudden stratospheric warming when the circulation continued to be disturbed by planetary waves and winds remained weak in the stratosphere and mesosphere. Ground-based lidar measurements characterized the ensemble of inertia-gravity waves and monochromatic gravity waves. The ensemble of inertia-gravity waves had a specific potential energy of 0.8 J/kg over the 40- to 50-km altitude region, one of the lowest values recorded at Chatanika. The turbulence measurements coincided with the overturning of a 2.5-hr monochromatic gravity wave in a depth of 3 km at 85 km. The energy dissipation rates were estimated to be 3 mW/kg for the ensemble of waves and 18 mW/kg for the monochromatic wave. The MTeX observations reveal low levels of turbulence associated with low levels of gravity wave activity. In the light of other Arctic observations and model studies, these observations suggest that there may be reduced turbulence during disturbed winters.
- ItemFirst 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.
- 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.
- ItemYear-round stratospheric aerosol backscatter ratios calculated from lidar measurements above northern Norway(Göttingen : Copernicus GmbH, 2019) Langenbach, A.; Baumgarten, G.; Fiedler, J.; Lübken, F.-J.; Von Savigny, C.; Zalach, J.We present a new method for calculating backscatter ratios of the stratospheric sulfate aerosol (SSA) layer from daytime and nighttime lidar measurements. Using this new method we show a first year-round dataset of stratospheric aerosol backscatter ratios at high latitudes. The SSA layer is located at altitudes between the tropopause and about 30 km. It is of fundamental importance for the radiative balance of the atmosphere. We use a state-of-the-art Rayleigh-Mie-Raman lidar at the Arctic Lidar Observatory for Middle Atmosphere Research (ALOMAR) station located in northern Norway (69N, 16E; 380ma.s.l.). For nighttime measurements the aerosol backscatter ratios are derived using elastic and inelastic backscatter of the emitted laser wavelengths 355, 532 and 1064nm. The setup of the lidar allows measurements with a resolution of about 5 min in time and 150 m in altitude to be performed in high quality, which enables the identification of multiple sub-layers in the stratospheric aerosol layer of less than 1 km vertical thickness. We introduce a method to extend the dataset throughout the summer when measurements need to be performed under permanent daytime conditions. For that purpose we approximate the backscatter ratios from color ratios of elastic scattering and apply a correction function. We calculate the correction function using the average backscatter ratio profile at 355nm from about 1700 h of nighttime measurements from the years 2000 to 2018. Using the new method we finally present a year-round dataset based on about 4100 h of measurements during the years 2014 to 2017. © Author(s) 2019.
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