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J. Fiedler - One of the best experts on this subject based on the ideXlab platform.
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Small-scale structures in Noctilucent Clouds observed by lidar
Journal of Atmospheric and Solar-Terrestrial Physics, 2020Co-Authors: Britta Schäfer, Gerd Baumgarten, J. FiedlerAbstract:Abstract Noctilucent Clouds (NLC) are mesospheric ice Clouds occurring in the summer hemisphere at high latitudes and an altitude of about 83km. This region is the coldest of the earth’s atmosphere and is characterized by the presence of wave interaction and dissipation. The processes involved here lead to a variety of structures and instabilities that become visible in Noctilucent Clouds and are observed by different instruments. In this work high-resolution lidar measurements are used to give a wide overview of the structures at small scales below the Brunt–Vaisala period of ∼ 5min. For the first time a large amount of NLC profiles from lidar with a temporal resolution of 1s is analyzed in detail, covering about 1400h during the summer from 2011 to 2018. A new categorization focusing on small-scale structures is introduced, and occurrence statistics for these categories in the season of 2014 are performed. Both wave structures with periods below 10min and thin layers of 100m thickness are commonly found. When taking simultaneous wind measurements into account, we find that structures often are advected by the wind.
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on microphysical processes of Noctilucent Clouds nlc observations and modeling of mean and width of the particle size distribution
Atmospheric Chemistry and Physics, 2010Co-Authors: Gerd Baumgarten, J. Fiedler, Markus RappAbstract:Abstract. Noctilucent Clouds (NLC) in the polar summer mesopause region have been observed in Norway (69° N, 16° E) between 1998 and 2009 by 3-color lidar technique. Assuming a mono-modal Gaussian size distribution we deduce mean and width of the particle sizes throughout the Clouds. We observe a quasi linear relationship between distribution width and mean of the particle size at the top of the Clouds and a deviation from this behavior for particle sizes larger than 40 nm, most often in the lower part of the layer. The vertically integrated particle properties show that 65% of the data follows the linear relationship with a slope of 0.42±0.02 for mean particle sizes up to 40 nm. For the vertically resolved particle properties (Δz = 0.15 km) the slope is comparable and about 0.39±0.03. For particles larger than 40 nm the distribution width becomes nearly independent of particle size and even decreases in the lower part of the layer. We compare our observations to microphysical modeling of Noctilucent Clouds and find that the distribution width depends on turbulence, the time that turbulence can act (cloud age), and the sampling volume/time (atmospheric variability). The model results nicely reproduce the measurements and show that the observed slope can be explained by eddy diffusion profiles as observed from rocket measurements.
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Vertical structure of particle properties and water content in Noctilucent Clouds
Geophysical Research Letters, 2008Co-Authors: G. Baumgarten, J. FiedlerAbstract:[1] Noctilucent Clouds (NLC) have been observed by lidar in Norway (69N, 16E) between 1998 and 2005 to study the vertical variation of particle properties inside the Clouds. We find that the maximum size of the particles is reached below the altitude of maximum backscattering. The mean radius of the particle ensemble increases from 38.1 ± 1.1 nm 0.9 km above the peak to 58.5 ± 2.5 nm, 0.6 km below the peak of the layer. At the peak the particle size is 47.7 nm. The distribution width increases from 14.0 nm to 17.7 nm and the number density decreases from 133/cm3 to 29/cm3 from top to bottom of the layer. The unexpected observation that the largest particles are not found at the peak of the layer indicates that the supersaturated region extends below the brightness peak of the layer. We observe that the distribution width is an indicator for the cloud age.
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Lidar observations of temperatures, waves, and Noctilucent Clouds at 69° N
Remote Sensing of Clouds and the Atmosphere IX, 2004Co-Authors: J. Fiedler, Gerd Baumgarten, Gotz Von Cossart, Armin SchochAbstract:The ALOMAR Rayleigh/Mie/Raman (RMR) lidar is an active remote sensing instrument for the investigation of the Arctic middle atmosphere during day and night. It is located in Northern Norway and operated on a routine basis to measure relative density profiles and aerosol properties in the stratosphere and mesosphere since 1995. Temperature profiles derived from the density measurements assuming hydrostatic equilibrium are used to investigate the mean temperature structure as well as gravity waves in the polar middle atmosphere. During the last two years, temperature data were acquired for approximately 2100 hours. A subset of this data basis was used to determine the potential energy density to characterize the gravity wave activity above the station. Noctilucent Clouds (NLC) are the highest Clouds of the Earth's atmosphere and a visible sign of extreme atmospheric conditions with temperatures far below radiative equilibrium. During the last 7 years a continuous data set with 1880 measurement hours was acquired during the summer seasons, of which 640 hours contain NLC signatures. This actually most extensive lidar acquired NLC archive was analyzed regarding brightness, altitude, vertical extent, as well as occurrence frequency of Noctilucent Clouds above ALOMAR.
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lidar observations of temperatures waves and Noctilucent Clouds at 69 n
Remote Sensing, 2004Co-Authors: J. Fiedler, Gerd Baumgarten, Gotz Von Cossart, Armin SchochAbstract:The ALOMAR Rayleigh/Mie/Raman (RMR) lidar is an active remote sensing instrument for the investigation of the Arctic middle atmosphere during day and night. It is located in Northern Norway and operated on a routine basis to measure relative density profiles and aerosol properties in the stratosphere and mesosphere since 1995. Temperature profiles derived from the density measurements assuming hydrostatic equilibrium are used to investigate the mean temperature structure as well as gravity waves in the polar middle atmosphere. During the last two years, temperature data were acquired for approximately 2100 hours. A subset of this data basis was used to determine the potential energy density to characterize the gravity wave activity above the station. Noctilucent Clouds (NLC) are the highest Clouds of the Earth's atmosphere and a visible sign of extreme atmospheric conditions with temperatures far below radiative equilibrium. During the last 7 years a continuous data set with 1880 measurement hours was acquired during the summer seasons, of which 640 hours contain NLC signatures. This actually most extensive lidar acquired NLC archive was analyzed regarding brightness, altitude, vertical extent, as well as occurrence frequency of Noctilucent Clouds above ALOMAR.
W. Schröder - One of the best experts on this subject based on the ideXlab platform.
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Simultaneous appearance of aurora and Noctilucent Clouds
Acta Geodaetica et Geophysica Hungarica, 2006Co-Authors: W. SchröderAbstract:The present paper deals with the simultaneous appearance of aurora and Noctilucent Clouds during end of July 1963. The simultaneous appearance of aurora and Noctilucent Clouds was observed at Lerwick, Shetland Islands and at Rönnebeck, Germany. As, independently of these phenomena, rockets were launched at Kronogard, Sweden, on July 30, 1963, due to the appearance of the Noctilucent Clouds, therefore data are available about the average parameters of the mesopause in this time interval. Data about some additional events from the end of July 1963 yielded supplementary information to this main event.
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comment on are Noctilucent Clouds truly a miner s canary for global change
Eos Transactions American Geophysical Union, 2003Co-Authors: W. SchröderAbstract:I noted with interest the article, “Are Noctilucent Clouds Truly a ‘Miner's Canary” for Global Change?” by von Zahn [2003]. I am in agreement with the argument of this article; namely, that the frequency of Noctilucent Clouds is well controlled by temperature and water vapor in the mesospheric layers. Von Zahn used short-term data for 1960–2001 (see his Figure l), but the long-term observations from Russia [Astapovic, 1961] and Germany [Schroder, 1966, 1975, 1996, 1999] are also of interest. These observations for the years 1885–1996 show no long-term variability in frequency, but indicate variability in brightness and partial duration of Noctilucent Clouds (NLC) for different years.
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Comment on “Are Noctilucent Clouds truly a “Miner's Canary” for Global Change?”
Eos Transactions American Geophysical Union, 2003Co-Authors: W. SchröderAbstract:I noted with interest the article, “Are Noctilucent Clouds Truly a ‘Miner's Canary” for Global Change?” by von Zahn [2003]. I am in agreement with the argument of this article; namely, that the frequency of Noctilucent Clouds is well controlled by temperature and water vapor in the mesospheric layers. Von Zahn used short-term data for 1960–2001 (see his Figure l), but the long-term observations from Russia [Astapovic, 1961] and Germany [Schroder, 1966, 1975, 1996, 1999] are also of interest. These observations for the years 1885–1996 show no long-term variability in frequency, but indicate variability in brightness and partial duration of Noctilucent Clouds (NLC) for different years.
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Widespread Occurrence of Noctilucent Clouds
Acta Geodaetica et Geophysica Hungarica, 2000Co-Authors: W. SchröderAbstract:The widespread, partially simultaneous occurrence of Noctilucent Clouds is discussed with respect to the frequency of occurrence of Noctilucent Clouds being a function of the meteorological conditions at the mesopause.
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Aurora and Noctilucent Clouds
Acta Geodaetica et Geophysica Hungarica, 2000Co-Authors: W. SchröderAbstract:The problem of coupling of auroras with Noctilucent Clouds (abbreviated NLC) at mid-latitudes is discussed. Two cases of the simultaneous occurrence of auroras and NLC (July 1964) are described. No unusual changes were observed in NLC after onset of aurora.
C. Von Savigny - One of the best experts on this subject based on the ideXlab platform.
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Impacts of the January 2005 solar particle event on Noctilucent Clouds and water at the polar summer mesopause
Atmospheric Chemistry and Physics, 2012Co-Authors: H. Winkler, C. Von Savigny, J. P. Burrows, J. M. Wissing, M. J. Schwartz, A. Lambert, M. García-comasAbstract:Abstract. The response of Noctilucent Clouds to the solar particle event in January 2005 is investigated by means of icy particle and ion chemistry simulations. It is shown that the decreasing occurrence rate of Noctilucent Clouds derived from measurements of the SCIAMACHY/Envisat instrument can be reproduced by one-dimensional model simulations if temperature data from the MLS/Aura instrument are used. The model calculations indicate that the sublimation of Noctilucent Clouds leads to significant changes of the water distribution in the mesopause region. These model results are compared with H2O measurements from the MLS and the MIPAS/Envisat satellite instruments. The pronounced modelled water enhancement below the icy particle layer and its decrease during the SPE are not observed by the satellite instruments. At altitudes >85 km the satellite measurements show an increase of H2O during the SPE in qualitative agreement with the model predictions. The discrepancies between model H2O and observations at lower altitudes might be attributed to the one-dimensional model approach which in particular neglects inhomogeneities and horizontal transport processes. Additionally, it is revealed that the water depletion due to reactions of proton hydrates during the considered solar particle event has only a minor impact on the icy particles.
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Impacts of the January 2005 solar particle event on Noctilucent Clouds and water at the polar summer mesopause
2012Co-Authors: H. Winkler, C. Von Savigny, J. P. Burrows, J. M. Wissing, M. J. Schwartz, A. Lambert, M. García-comasAbstract:Abstract. The response of Noctilucent Clouds to the solar particle event in January 2005 is investigated by means of icy particle and ion chemistry simulations. It is shown that the decreasing occurrence rate of Noctilucent Clouds derived from measurements of the SCIAMACHY/Envisat instrument can be reproduced by one-dimensional model simulations if temperature data from the MLS/Aura instrument are used. The sublimation of Noctilucent Clouds leads to significant changes of the water distribution in the mesopause region. The model predictions are in general agreement with H2O measurements from the MLS and the MIPAS/Envisat satellite instruments, although the modelled effect of water redistribution is stronger than the observed one. Additionally, it is revealed that the water depletion due to reactions of proton hydrates during the considered solar particle event has only a minor impact on the icy particles.
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satellite observations of the quasi 5 day wave in Noctilucent Clouds and mesopause temperatures
Geophysical Research Letters, 2007Co-Authors: C. Von Savigny, J P Burrows, Charles Robert, Heinrich Bovensmann, M J SchwartzAbstract:[1] We report on simultaneous measurements of the westward propagating quasi 5-day wave in the occurrence rate of Noctilucent Clouds (NLCs) and the temperature field at NLC altitude during the 2005 NLC season in the northern hemisphere. NLCs are detected using SCIAMACHY/Envisat limb scattering measurements, and the temperature profiles are measured with MLS/Aura. Quasi 5-day wave signatures are clearly identified in both physical and wavelet space. We find good general agreement in the quasi 5-day wave activity of NLC occurrence rates and the mesopause temperature field, indicating that planetary wave signatures in the temperature field are the main driver of corresponding signatures in NLCs.
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uv limb scatter spectra of Noctilucent Clouds consistent with mono modal particle size distribution
Geophysical Research Letters, 2007Co-Authors: C. Von Savigny, J P Burrows, Markus RappAbstract:[1] Limb-backscatter spectra of Noctilucent Clouds (NLCs) are retrieved from limb measurements made with the Scanning Imaging Absorption spectroMeter for Atmospheric CartograpHY (SCIAMACHY) on the Envisat satellite. The spectral dependence of many hundred sun-normalized NLC spectra measured during the 2005 NLC season in the northern hemisphere can be well approximated with a power-law in the 240–300 nm spectral range. In particular, no spectral signatures indicative of the presence of a second particle mode at radii exceeding 200 nm are found, in contradiction to recent studies. The results presented are consistent with a mono-modal NLC particle size distribution.
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on the disappearance of Noctilucent Clouds during the january 2005 solar proton events
Geophysical Research Letters, 2007Co-Authors: C. Von Savigny, J P Burrows, Heinrich Bovensmann, Miriam Sinnhuber, M B Kallenrode, M J SchwartzAbstract:[1] A possible connection between the January 2005 solar proton events (SPEs) and the partial disappearance of Noctilucent Clouds (NLCs) in the southern polar mesopause region is studied. Space-borne measurements of the NLC occurrence rate made with SCIAMACHY on Envisat as well as temperature measurements with MLS on Aura are employed. Immediately after the onset of the enhanced solar particle precipitation on January 16, 2005, we observe a severe decrease in the NLC occurrence rate. Between 70°S–80°S the NLC occurrence rate drops from about 80% to less than 20% within the period of enhanced solar proton fluxes. Throughout this period an anti-correlation between NLC occurrence rate and temperatures at NLC altitude is found, and the disappearance of NLCs is apparently caused by increasing temperatures. Potential mechanisms leading to the warming are discussed.
M J Schwartz - One of the best experts on this subject based on the ideXlab platform.
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first identification of lunar tides in satellite observations of Noctilucent Clouds
Journal of Atmospheric and Solar-Terrestrial Physics, 2017Co-Authors: Christian Von Savigny, Matthew T Deland, M J SchwartzAbstract:Abstract Noctilucent Clouds (NLCs) are optically thin ice Clouds occurring near the polar summer mesopause. NLCs are a highly variable phenomenon subject to different sources of variability. Here we report on a poorly understood mechanism affecting NLCs, i.e., the lunar gravitational tide. We extract remarkably clear and statistically highly significant lunar semidiurnal tidal signatures in NLC occurrence frequency, NLC albedo and NLC ice water content from observations with the Solar Backscatter Ultraviolet (SBUV) satellite instruments using the superposed epoch analysis method applied to a data set covering more than 3 decades. The lunar semidiurnal tide is identified in NLC measurements in both hemispheres. In addition, lunar semidiurnal tidal signatures in polar summer mesopause temperature were extracted from space borne observations with the Microwave Limb Sounder (MLS) and the phases of the lunar tidal signatures in NLC parameters and temperature are demonstrated to be consistent. To our best knowledge these results constitute the first identification of the lunar tide in non-visual NLC observations.
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satellite observations of the quasi 5 day wave in Noctilucent Clouds and mesopause temperatures
Geophysical Research Letters, 2007Co-Authors: C. Von Savigny, J P Burrows, Charles Robert, Heinrich Bovensmann, M J SchwartzAbstract:[1] We report on simultaneous measurements of the westward propagating quasi 5-day wave in the occurrence rate of Noctilucent Clouds (NLCs) and the temperature field at NLC altitude during the 2005 NLC season in the northern hemisphere. NLCs are detected using SCIAMACHY/Envisat limb scattering measurements, and the temperature profiles are measured with MLS/Aura. Quasi 5-day wave signatures are clearly identified in both physical and wavelet space. We find good general agreement in the quasi 5-day wave activity of NLC occurrence rates and the mesopause temperature field, indicating that planetary wave signatures in the temperature field are the main driver of corresponding signatures in NLCs.
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on the disappearance of Noctilucent Clouds during the january 2005 solar proton events
Geophysical Research Letters, 2007Co-Authors: C. Von Savigny, J P Burrows, Heinrich Bovensmann, Miriam Sinnhuber, M B Kallenrode, M J SchwartzAbstract:[1] A possible connection between the January 2005 solar proton events (SPEs) and the partial disappearance of Noctilucent Clouds (NLCs) in the southern polar mesopause region is studied. Space-borne measurements of the NLC occurrence rate made with SCIAMACHY on Envisat as well as temperature measurements with MLS on Aura are employed. Immediately after the onset of the enhanced solar particle precipitation on January 16, 2005, we observe a severe decrease in the NLC occurrence rate. Between 70°S–80°S the NLC occurrence rate drops from about 80% to less than 20% within the period of enhanced solar proton fluxes. Throughout this period an anti-correlation between NLC occurrence rate and temperatures at NLC altitude is found, and the disappearance of NLCs is apparently caused by increasing temperatures. Potential mechanisms leading to the warming are discussed.
Gerd Baumgarten - One of the best experts on this subject based on the ideXlab platform.
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Small-scale structures in Noctilucent Clouds observed by lidar
Journal of Atmospheric and Solar-Terrestrial Physics, 2020Co-Authors: Britta Schäfer, Gerd Baumgarten, J. FiedlerAbstract:Abstract Noctilucent Clouds (NLC) are mesospheric ice Clouds occurring in the summer hemisphere at high latitudes and an altitude of about 83km. This region is the coldest of the earth’s atmosphere and is characterized by the presence of wave interaction and dissipation. The processes involved here lead to a variety of structures and instabilities that become visible in Noctilucent Clouds and are observed by different instruments. In this work high-resolution lidar measurements are used to give a wide overview of the structures at small scales below the Brunt–Vaisala period of ∼ 5min. For the first time a large amount of NLC profiles from lidar with a temporal resolution of 1s is analyzed in detail, covering about 1400h during the summer from 2011 to 2018. A new categorization focusing on small-scale structures is introduced, and occurrence statistics for these categories in the season of 2014 are performed. Both wave structures with periods below 10min and thin layers of 100m thickness are commonly found. When taking simultaneous wind measurements into account, we find that structures often are advected by the wind.
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Noctilucent Clouds general properties and remote sensing
2020Co-Authors: Christian Von Savigny, Gerd Baumgarten, Franzjosef LubkenAbstract:Noctilucent Clouds (NLC) – also known as polar mesospheric Clouds (PMC) – occur at mid and high latitudes during the summer months in each hemisphere and are with altitudes of about 83 km the highest Clouds in the terrestrial atmosphere. NLC are an optically thin phenomenon. They are known to consist of H2O ice particles with radii of less than about 100 nm. The first reported sightings of NLC occurred in 1885, two years after the eruption of the volcano Krakatoa in 1883. They exhibit spatial and temporal variability over a large range of scales and react very sensitively to variations in ambient conditions. This high sensitivity makes them highly relevant observables for the investigation of a wide variety of different atmospheric processes including dynamical effects, solar-terrestrial interactions and long-term changes of the Earth’s middle atmosphere. The role of NLC as indicators of long-term changes in the mesopause region in particular has been a topic of intensive debate.
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impact of particle shape on the morphology of Noctilucent Clouds
Atmospheric Chemistry and Physics, 2015Co-Authors: Gerd Baumgarten, Franzjosef Lubken, Johannes Kiliani, U BergerAbstract:Abstract. Noctilucent Clouds (NLCs) occur during summer in the polar region at altitudes around 83 km. They consist of ice particles with a typical size around 50 nm. The shape of NLC particles is less well known but is important both for interpreting optical measurements and modeling ice cloud characteristics. In this paper, NLC modeling of microphysics and optics is adapted to use cylindrical instead of spherical particle shape. The optical properties of the resulting ice Clouds are compared directly to NLC three-color measurements by the Arctic Lidar Observatory for Middle Atmosphere Research (ALOMAR) Rayleigh/Mie/Raman (RMR) lidar between 1998 and 2014. Shape distributions including both needle- and disc-shaped particles are consistent with lidar measurements. The best agreement occurs if disc shapes are 60 % more common than needles, with a mean axis ratio of 2.8. Cylindrical particles cause stronger ice Clouds on average than spherical shapes with an increase of backscatter at 532 nm by a 30 % and about 20 % in ice mass density. This difference is less pronounced for bright than for weak ice Clouds. Cylindrical shapes also cause NLCs to have larger but a smaller number of ice particles than for spherical shapes.
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on microphysical processes of Noctilucent Clouds nlc observations and modeling of mean and width of the particle size distribution
Atmospheric Chemistry and Physics, 2010Co-Authors: Gerd Baumgarten, J. Fiedler, Markus RappAbstract:Abstract. Noctilucent Clouds (NLC) in the polar summer mesopause region have been observed in Norway (69° N, 16° E) between 1998 and 2009 by 3-color lidar technique. Assuming a mono-modal Gaussian size distribution we deduce mean and width of the particle sizes throughout the Clouds. We observe a quasi linear relationship between distribution width and mean of the particle size at the top of the Clouds and a deviation from this behavior for particle sizes larger than 40 nm, most often in the lower part of the layer. The vertically integrated particle properties show that 65% of the data follows the linear relationship with a slope of 0.42±0.02 for mean particle sizes up to 40 nm. For the vertically resolved particle properties (Δz = 0.15 km) the slope is comparable and about 0.39±0.03. For particles larger than 40 nm the distribution width becomes nearly independent of particle size and even decreases in the lower part of the layer. We compare our observations to microphysical modeling of Noctilucent Clouds and find that the distribution width depends on turbulence, the time that turbulence can act (cloud age), and the sampling volume/time (atmospheric variability). The model results nicely reproduce the measurements and show that the observed slope can be explained by eddy diffusion profiles as observed from rocket measurements.
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Lidar observations of temperatures, waves, and Noctilucent Clouds at 69° N
Remote Sensing of Clouds and the Atmosphere IX, 2004Co-Authors: J. Fiedler, Gerd Baumgarten, Gotz Von Cossart, Armin SchochAbstract:The ALOMAR Rayleigh/Mie/Raman (RMR) lidar is an active remote sensing instrument for the investigation of the Arctic middle atmosphere during day and night. It is located in Northern Norway and operated on a routine basis to measure relative density profiles and aerosol properties in the stratosphere and mesosphere since 1995. Temperature profiles derived from the density measurements assuming hydrostatic equilibrium are used to investigate the mean temperature structure as well as gravity waves in the polar middle atmosphere. During the last two years, temperature data were acquired for approximately 2100 hours. A subset of this data basis was used to determine the potential energy density to characterize the gravity wave activity above the station. Noctilucent Clouds (NLC) are the highest Clouds of the Earth's atmosphere and a visible sign of extreme atmospheric conditions with temperatures far below radiative equilibrium. During the last 7 years a continuous data set with 1880 measurement hours was acquired during the summer seasons, of which 640 hours contain NLC signatures. This actually most extensive lidar acquired NLC archive was analyzed regarding brightness, altitude, vertical extent, as well as occurrence frequency of Noctilucent Clouds above ALOMAR.