29 research outputs found
Combined vertical-velocity observations with Doppler lidar, cloud radar and wind profiler
Case studies of combined vertical-velocity measurements of Doppler lidar, cloud radar and wind profiler are presented. The measurements were taken at the Meteorological Observatory, Lindenberg, Germany. Synergistic products are presented that are derived from the vertical-velocity measurements of the three instruments: a comprehensive classification mask of vertically moving atmospheric targets and the terminal fall velocity of water droplets and ice crystals corrected for vertical air motion. It is shown that this combination of instruments can up-value the measurement values of each single instrument and may allow the simultaneous sensing of atmospheric targets and the motion of clear air
Combining cloud radar and radar wind profiler for a value added estimate of vertical air motion and particle terminal velocity within clouds
Vertical-stare observations from a 482âMHz radar wind profiler and a
35âGHz cloud radar are combined on the level of individual Doppler
spectra to measure vertical air motions in clear air, clouds and
precipitation. For this purpose, a separation algorithm is proposed to remove
the influence of falling particles from the wind profiler Doppler spectra and
to calculate the terminal fall velocity of hydrometeors. The remaining error
of both vertical air motion and terminal fall velocity is estimated to be
better than 0.1âmâsâ1 using numerical simulations. This
combination of instruments allows direct measurements of in-cloud vertical
air velocity and particle terminal fall velocity by means of ground-based
remote sensing. The possibility of providing a profile every 10âs
with a height resolution of â<â100âm allows further insight into the
process scale of in-cloud dynamics. The results of the separation algorithm
are illustrated by two case studies, the first covering a deep frontal cloud
and the second featuring a shallow mixed-phase cloud.</p
Ship-borne aerosol profiling with lidar over the Atlantic Ocean: from pure marine conditions to complex dustâsmoke mixtures
The multi-wavelength Raman lidar PollyXT has been
regularly operated aboard the research vessel Polarstern on
expeditions across the Atlantic Ocean from north to south and vice versa. The
lidar measurements of the RV Polarstern cruises PS95 from
Bremerhaven, Germany, to Cape Town, Republic of South Africa (November 2015),
and PS98 from Punta Arenas, Chile, to Bremerhaven, Germany (April/May 2016),
are presented and analysed in detail. The latest set-up of
PollyXT allows improved coverage of the marine boundary
layer (MBL) due to an additional near-range receiver.Three case studies provide an overview of the aerosol detected over the
Atlantic Ocean. In the first case, marine conditions were observed near South
Africa on the autumn cruise PS95. Values of optical properties
(depolarisation ratios close to zero, lidar ratios of 23âŻsr at 355 and
532âŻnm) within the MBL indicate pure marine aerosol. A layer of dried marine
aerosol, indicated by an increase of the particle depolarisation ratio to
about 10âŻ% at 355âŻnm (9âŻ% at 532âŻnm) and thus confirming the
non-sphericity of these particles, could be detected on top of the MBL. On
the same cruise, an almost pure Saharan dust plume was observed near the
Canary Islands, presented in the second case. The third case deals with
several layers of Saharan dust partly mixed with biomass-burning smoke
measured on PS98 near the Cabo Verde islands. While the MBL was partly mixed
with dust in the pure Saharan dust case, an almost marine MBL was observed in
the third case.A statistical analysis showed latitudinal differences in the optical
properties within the MBL, caused by the down-mixing of dust in the tropics
and anthropogenic influences in the northern latitudes, whereas the optical
properties of the MBL in the Southern Hemisphere correlate with typical
marine values. The particle depolarisation ratio of dried marine layers
ranged between 4 and 9âŻ% at 532âŻnm.Night measurements from PS95 and PS98 were used to illustrate the potential
of aerosol classification using lidar ratio, particle depolarisation ratio at
355 and 532âŻnm, and Ă
ngström exponent. Lidar ratio and particle
depolarisation ratio have been found to be the main indicator for particle
type, whereas the Ă
ngström exponent is rather variable.</p
The DACAPO-PESO campaign: Dynamics, Aerosol, Cloud and Precipitation Observations in the Pristine Environment of the Southern Ocean: An overview
This article gives an overview of the DACAPO-PESO field experiment,
which has taken place in Punta Arenas, Chile, from November 2018 to November 2021,
and showcases first exciting research results that have already emerged from it.In diesem Artikel wird ein Ăberblick ĂŒber das DACAPO-PESO
Experiment gegeben, welches von November 2018 bis November 2021 in Punta Arenas,
Chile, stattgefunden hat. AuĂerdem werden erste spannende Forschungsergebnisse
vorgestellt, die bereits daraus gewonnen wurden
Long-term validation of Aeolus L2B wind products at Punta Arenas, Chile, and Leipzig, Germany
Ground-based observations of horizontal winds have been performed at Leipzig (51.35ââN, 12.43ââE), Germany, and at Punta Arenas (53.15ââS, 70.91ââW), Chile, in the framework of the German initiative EVAA (Experimental Validation and Assimilation of Aeolus observations) with respect to the validation of the Mie and Rayleigh wind products of Aeolus (L2B data).
In Leipzig, at the Leibniz Institute for Tropospheric Research (TROPOS), radiosondes have been launched for the Aeolus overpasses on each Friday (ascending orbit) since the middle of May 2019.
In Punta Arenas, scanning Doppler cloud radar observations have been performed in the framework of the DACAPO-PESO campaign (dacapo.tropos.de) for more than 3Â years from the end of 2018 until the end of 2021 and could be used to validate Aeolus measurements on its ascending and descending orbits. We present two case studies and longâterm statistics of the horizontal winds derived with the ground-based reference instruments compared to Aeolus horizontal line-of-sight (HLOS) winds. The wind products of Aeolus considered are the Mie cloudy and Rayleigh clear products. It was found that the deviation of the Aeolus HLOS winds from the ground reference is usually of Gaussian shape, which allowed the use of the median bias and the scaled median absolute deviation (MAD) for the determination of the systematic and random errors of Aeolus wind products, respectively. The case study from August 2020 with impressive atmospheric conditions at Punta Arenas shows that Aeolus is able to capture strong wind speeds of up to more than 100âmâsâ1.
The long-term validation was performed in Punta Arenas covering the period from December 2018 to November 2021 and in Leipzig from May 2019 until September 2022.
This analysis showed that the systematic error of the Aeolus wind products could be significantly lowered during the mission lifetime with the changes introduced into the processing chain (different versions are called baselines). While in the early mission phase, systematic errors of more than 2âmâsâ1 (absolute values) were observed for both wind types (Mie and Rayleigh), these biases could be reduced with the algorithm improvements, such as the introduction of the correction for temperature fluctuations at the main telescope of Aeolus (M1 temperature correction) with Baseline 09.
Hence, since Baseline 10, a significant improvement in the Aeolus data was found, leading to a low systematic error (close to 0âmâsâ1) and similar values for the midlatitudinal sites in both hemispheres. The random errors for both wind products were first decreasing with an increasing baseline but later increasing again due to performance losses of the Aeolus lidar instrument. Nevertheless, no significant increase in the systematic error in the Aeolus wind products was found. Thus, one can conclude that the uncertainty introduced by the reduced atmospheric return signal received by Aeolus mostly affects the random error.
Even when considering all the challenges during the mission, we can confirm the general validity of Aeolus observations during its lifetime. Therefore, this space explorer mission could demonstrate that it is possible to perform active wind observations from space with the applied technique.</p
Annual cycle of aerosol properties over the central Arctic during MOSAiC 2019â2020 â light-extinction, CCN, and INP levels from the boundary layer to the tropopause
The MOSAiC (Multidisciplinary drifting Observatory for the Study of Arctic Climate) expedition was the largest Arctic field campaign ever conducted. MOSAiC offered the unique opportunity to monitor and characterize aerosols and clouds with high vertical resolution up to 30âkm height at latitudes from 80 to 90ââN over an entire year (October 2019 to September 2020). Without a clear knowledge of the complex aerosol layering, vertical structures, and dominant aerosol types and their impact on cloud formation, a full understanding of the meteorological processes in the Arctic, and thus advanced climate change research, is impossible. Widespread ground-based in situ observations in the Arctic are insufficient to provide these required aerosol and cloud data.
In this article, a summary of our MOSAiC observations of tropospheric aerosol profiles with a state-of-the-art multiwavelength polarization Raman lidar aboard the icebreaker Polarstern is presented. Particle optical properties, i.e., light-extinction profiles and aerosol optical thickness (AOT), and estimates of cloud-relevant aerosol properties such as the number concentration of cloud condensation nuclei (CCN) and ice-nucleating particles (INPs) are discussed, separately for the lowest part of the troposphere (atmospheric boundary layer, ABL), within the lower free troposphere (around 2000âm height), and at the cirrus level close to the tropopause. In situ observations of the particle number concentration and INPs aboard Polarstern are included in the study. A strong decrease in the aerosol amount with height in winter and moderate vertical variations in summer were observed in terms of the particle extinction coefficient. The 532ânm light-extinction values dropped from >50âMmâ1 close to the surface to <5âMmâ1 at 4â6âkm height in the winter months. Lofted, aged wildfire smoke layers caused a re-increase in the aerosol concentration towards the tropopause. In summer (June to August 2020), much lower particle extinction coefficients, frequently as low as 1â5âMmâ1, were observed in the ABL. Aerosol removal, controlled by in-cloud and below-cloud scavenging processes (widely suppressed in winter and very efficient in summer) in the lowermost 1â2âkm of the atmosphere, seems to be the main reason for the strong differences between winter and summer aerosol conditions. A complete annual cycle of the AOT in the central Arctic could be measured. This is a valuable addition to the summertime observations with the sun photometers of the Arctic Aerosol Robotic Network (AERONET).
In line with the pronounced annual cycle in the aerosol optical properties, typical CCN number concentrations (0.2â% supersaturation level) ranged from 50â500âcmâ3 in winter to 10â100âcmâ3 in summer in the ABL. In the lower free troposphere (at 2000âm), however, the CCN level was roughly constant throughout the year, with values mostly from 30 to 100âcmâ3.
A strong contrast between winter and summer was also given in terms of ABL INPs which control ice production in low-level clouds. While soil dust (from surrounding continents) is probably the main INP type during the autumn, winter, and spring months, local sea spray aerosol (with a biogenic aerosol component) seems to dominate the ice nucleation in the ABL during the summer months (JuneâAugust). The strong winter vs. summer contrast in the INP number concentration by roughly 2â3 orders of magnitude in the lower troposphere is, however, mainly caused by the strong cloud temperature contrast. A unique event of the MOSAiC expedition was the occurrence of a long-lasting wildfire smoke layer in the upper troposphere and lower stratosphere. Our observations suggest that the smoke particles frequently triggered cirrus formation close to the tropopause from October 2019 to May 2020.</p
Tropospheric and stratospheric smoke over Europe as observed within EARLINET/ACTRIS in summer 2017
For several weeks in summer 2017, strong smoke layers were observed over Europe at numerous EARLINET
stations. EARLINET is the European research lidar network and part of ACTRIS and comprises more than 30
ground-based lidars.
The smoke layers were observed in the troposphere as well as in the stratosphere up to 25 km from Northern
Scandinavia over whole western and central Europe to the Mediterranean regions.
Backward trajectory analysis among other tools revealed that these smoke layers originated from strong wild fires
in western Canada in combination with pyrocumulus convection. An extraordinary fire event in the mid of August
caused intense smoke layers that were observed across Europe for several weeks starting on 18 August 2017.
Maximum aerosol optical depths up to 1.0 at 532 nm were observed at Leipzig, Germany, on 22 August 2017
during the peak of this event.
The stratospheric smoke layers reached extinction coefficient values of more than 600 Mmâ1 at 532 nm, a factor
of 10 higher than observed for volcanic ash after the Pinatubo eruption in the 1990s. First analyses of the intensive
optical properties revealed low particle depolarization values at 532 nm for the tropospheric smoke (spherical
particles) and rather high values (up to 20%) in the stratosphere. However, a strong wavelength dependence of
the depolarization ratio was measured for the stratospheric smoke. This indicates irregularly shaped stratospheric
smoke particles in the size range of the accumulation mode. This unique depolarization feature makes it possible
to distinguish clearly smoke aerosol from cirrus clouds or other aerosol types by polarization lidar measurements.
Particle extinction-to-backscatter ratios were rather low in the order of 40 to 50 sr at 355 nm, while values between
70-90 sr were measured at higher wavelengths.
In the western and central Mediterranean, stratospheric smoke layers were most prominent in the end of August
at heights between 16 and 20 km. In contrast, stratospheric smoke started to occur in the eastern Mediterranean
(Cyprus and Israel) in the beginning of September between 18 and 23 km. Stratospheric smoke was still visible in
the beginning of October at certain locations (e.g. Evora, Portugal), while tropospheric smoke was mainly observed
until the end of August within Europe.
An overview of the smoke layers measured at several EARLINET sites will be given. The temporal development
of these layers as well as their geometrical and optical properties will be presented
Overview of the MOSAiC expeditionâAtmosphere
With the Arctic rapidly changing, the needs to observe, understand, and model the changes are essential. To support these needs, an annual cycle of observations of atmospheric properties, processes, and interactions were made while drifting with the sea ice across the central Arctic during the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition from October 2019 to September 2020. An international team designed and implemented the comprehensive program to document and characterize all aspects of the Arctic atmospheric system in unprecedented detail, using a variety of approaches, and across multiple scales. These measurements were coordinated with other observational teams to explore cross-cutting and coupled interactions with the Arctic Ocean, sea ice, and ecosystem through a variety of physical and biogeochemical processes. This overview outlines the breadth and complexity of the atmospheric research program, which was organized into 4 subgroups: atmospheric state, clouds and precipitation, gases and aerosols, and energy budgets. Atmospheric variability over the annual cycle revealed important influences from a persistent large-scale winter circulation pattern, leading to some storms with pressure and winds that were outside the interquartile range of past conditions suggested by long-term reanalysis. Similarly, the MOSAiC location was warmer and wetter in summer than the reanalysis climatology, in part due to its close proximity to the sea ice edge. The comprehensiveness of the observational program for characterizing and analyzing atmospheric phenomena is demonstrated via a winter case study examining air mass transitions and a summer case study examining vertical atmospheric evolution. Overall, the MOSAiC atmospheric program successfully met its objectives and was the most comprehensive atmospheric measurement program to date conducted over the Arctic sea ice. The obtained data will support a broad range of coupled-system scientific research and provide an important foundation for advancing multiscale modeling capabilities in the Arctic
Overview of the MOSAiC expedition - Atmosphere
With the Arctic rapidly changing, the needs to observe, understand, and model the changes are essential. To support these needs, an annual cycle of observations of atmospheric properties, processes, and interactions were made while drifting with the sea ice across the central Arctic during the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition from October 2019 to September 2020. An international team designed and implemented the comprehensive program to document and characterize all aspects of the Arctic atmospheric system in unprecedented detail, using a variety of approaches, and across multiple scales. These measurements were coordinated with other observational teams to explore cross-cutting and coupled interactions with the Arctic Ocean, sea ice, and ecosystem through a variety of physical and biogeochemical processes. This overview outlines the breadth and complexity of the atmospheric research program, which was organized into 4 subgroups: atmospheric state, clouds and precipitation, gases and aerosols, and energy budgets. Atmospheric variability over the annual cycle revealed important influences from a persistent large-scale winter circulation pattern, leading to some storms with pressure and winds that were outside the interquartile range of past conditions suggested by long-term reanalysis. Similarly, the MOSAiC location was warmer and wetter in summer than the reanalysis climatology, in part due to its close proximity to the sea ice edge. The comprehensiveness of the observational program for characterizing and analyzing atmospheric phenomena is demonstrated via a winter case study examining air mass transitions and a summer case study examining vertical atmospheric evolution. Overall, the MOSAiC atmospheric program successfully met its objectives and was the most comprehensive atmospheric measurement program to date conducted over the Arctic sea ice. The obtained data will support a broad range of coupled-system scientific research and provide an important foundation for advancing multiscale modeling capabilities in the Arctic