1. |
- Baars, Holger, et al.
(författare)
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An overview of the first decade of Polly(NET) : an emerging network of automated Raman-polarization lidars for continuous aerosol profiling
- 2016
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Ingår i: Atmospheric Chemistry And Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 16:8, s. 5111-5137
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Tidskriftsartikel (refereegranskat)abstract
- A global vertically resolved aerosol data set covering more than 10 years of observations at more than 20 measurement sites distributed from 63 degrees N to 52 degrees S and 72 degrees W to 124 degrees E has been achieved within the Raman and polarization lidar network Polly(NET). This network consists of portable, remote-controlled multiwavelength-polarization-Raman lidars (Polly) for automated and continuous 24/7 observations of clouds and aerosols. Polly(NET) is an independent, voluntary, and scientific network. All Polly lidars feature a standardized instrument design with different capabilities ranging from single wavelength to multiwavelength systems, and now apply unified calibration, quality control, and data analysis. The observations are processed in near-real time without manual intervention, and are presented online at polly.tropos.de. The paper gives an overview of the observations on four continents and two research vessels obtained with eight Polly systems. The specific aerosol types at these locations (mineral dust, smoke, dust-smoke and other dusty mixtures, urban haze, and volcanic ash) are identified by their Angstrom exponent, lidar ratio, and depolarization ratio. The vertical aerosol distribution at the Polly(NET) locations is discussed on the basis of more than 55 000 automatically retrieved 30 min particle backscatter coefficient profiles at 532 nm as this operating wavelength is available for all Polly lidar systems. A seasonal analysis of measurements at selected sites revealed typical and extraordinary aerosol conditions as well as seasonal differences. These studies show the potential of Polly(NET) to support the establishment of a global aerosol climatology that covers the entire troposphere.
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2. |
- Ehard, Benedikt, et al.
(författare)
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Combination of Lidar and Model Data for Studying Deep Gravity Wave Propagation
- 2016
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Ingår i: Monthly Weather Review. - 0027-0644 .- 1520-0493. ; 144:1, s. 77-98
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Tidskriftsartikel (refereegranskat)abstract
- The paper presents a feasible method to complement ground-based middle atmospheric Rayleigh lidar temperature observations with numerical simulations in the lower stratosphere and troposphere to study gravity waves. Validated mesoscale numerical simulations are utilized to complement the temperature below 30-km altitude. For this purpose, high-temporal-resolution output of the numerical results was interpolated on the position of the lidar in the lee of the Scandinavian mountain range. Two wintertime cases of orographically induced gravity waves are analyzed. Wave parameters are derived using a wavelet analysis of the combined dataset throughout the entire altitude range from the troposphere to the mesosphere. Although similar in the tropospheric forcings, both cases differ in vertical propagation. The combined dataset reveals stratospheric wave breaking for one case, whereas the mountain waves in the other case could propagate up to about 40-km altitude. The lidar observations reveal an interaction of the vertically propagating gravity waves with the stratopause, leading to a stratopause descent in both cases.
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3. |
- Sotiropoulou, Georgia, et al.
(författare)
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Atmospheric conditions during the Arctic Clouds in Summer Experiment (ACSE) : Contrasting open-water and sea-ice surfaces during melt and freeze-up seasons
- 2016
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Ingår i: Journal of Climate. - 0894-8755 .- 1520-0442. ; 29:24, s. 8721-8744
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Tidskriftsartikel (refereegranskat)abstract
- The Arctic Clouds in Summer Experiment (ACSE) was conducted during summer and early autumn 2014, providing a detailed view of the seasonal transition from ice melt into freeze-up. Measurements were taken over both ice-free and ice-covered surfaces, near the ice edge, offering insight to the role of the surface state in shaping the atmospheric conditions. The initiation of the autumn freeze-up was related to a change in air mass, rather than to changes in solar radiation alone; the lower atmosphere cooled abruptly leading to a surface heat loss. During melt season, strong surface inversions persisted over the ice, while elevated inversions were more frequent over open water. These differences disappeared during autumn freeze-up, when elevated inversions persisted over both ice-free and ice-covered conditions. These results are in contrast to previous studies that found a well-mixed boundary layer persisting in summer and an increased frequency of surface-based inversions in autumn, suggesting that our knowledge derived from measurements taken within the pan-Arctic area and on the central ice-pack does not necessarily apply closer to the ice-edge. This study offers an insight to the atmospheric processes that occur during a crucial period of the year; understanding and accurately modeling these processes is essential for the improvement of ice-extent predictions and future Arctic climate projections.
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4. |
- Tesche, Matthias, et al.
(författare)
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Aviation effects on already-existing cirrus clouds
- 2016
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 7
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Tidskriftsartikel (refereegranskat)abstract
- Determining the effects of the formation of contrails within natural cirrus clouds has proven to be challenging. Quantifying any such effects is necessary if we are to properly account for the influence of aviation on climate. Here we quantify the effect of aircraft on the optical thickness of already-existing cirrus clouds by matching actual aircraft flight tracks to satellite lidar measurements. We show that there is a systematic, statistically significant increase in normalized cirrus cloud optical thickness inside mid-latitude flight tracks compared with adjacent areas immediately outside the tracks.
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