scholarly journals Ice crystal number concentration from lidar, cloud radar and radar wind profiler measurements

2019 ◽  
Vol 12 (12) ◽  
pp. 6601-6617 ◽  
Author(s):  
Johannes Bühl ◽  
Patric Seifert ◽  
Martin Radenz ◽  
Holger Baars ◽  
Albert Ansmann
Keyword(s):  
Number Concentration ◽  
Lookup Table ◽  
Wind Profiler ◽  
Ice Crystal ◽  
Fall Velocity ◽  
Magnitude Comparison ◽  
Cloud Radar ◽  
Order Of Magnitude ◽  
The One ◽  
First Time

Abstract. A new method for the retrieval of ice crystal number concentration (ICNC) from combined active remote-sensing measurements of Raman lidar, cloud radar and radar wind profiler is presented. We exploit – for the first time – measurements of terminal fall velocity together with the radar reflectivity factor and/or the lidar-derived particle extinction coefficient in clouds for retrieving the number concentration of pristine ice particles with presumed particle shapes. A lookup table approach for the retrieval of the properties of the particle size distribution from observed parameters is presented. Analysis of methodological uncertainties and error propagation is performed, which shows that a retrieval of ice particle number concentration based on terminal fall velocity is possible within 1 order of magnitude. Comparison between a retrieval of the number concentration based on terminal fall velocity on the one hand and lidar and cloud radar on the other shows agreement within the uncertainties of the retrieval.

scholarly journals Ice crystal number concentration from measurements of lidar, cloud radar and radar wind profiler

2019 ◽  
Author(s):  
Johannes Bühl ◽  
Patric Seifert ◽  
Martin Radenz ◽  
Holger Baars ◽  
Albert Ansmann
Keyword(s):  
Particle Number ◽  
Number Concentration ◽  
Lookup Table ◽  
Wind Profiler ◽  
Ice Crystal ◽  
Fall Velocity ◽  
Magnitude Comparison ◽  
Cloud Radar ◽  
Order Of Magnitude ◽  
The One

Abstract. A new method for the retrieval of ice particle number concentrations from combined active remote-sensing measurements of Raman lidar, cloud radar and radar wind profiler is presented. We exploit – for the first time – measurements of terminal fall velocity together with radar reflectivity factor and/or lidar-derived particle extinction coefficient in clouds for retrieving the number concentration of pristine ice particles with presumed particle shapes. A lookup table approach for the retrieval of the properties of the particle size distribution from observed parameters is presented. Analysis of methodological uncertainties and error propagation are performed, which shows that a retrieval of ice particle number concentration is possible within the order of magnitude. Comparison between a retrieval of number concentration based on terminal fall velocity on the one hand and lidar and cloud radar on the other shows agreement within the uncertainties of the retrieval.

scholarly journals Impurity-controlled densification: a new model for stratified polar firn

2013 ◽  
Vol 59 (218) ◽  
pp. 1163-1169 ◽  
Author(s):  
Johannes Freitag ◽  
Sepp Kipfstuhl ◽  
Thomas Laepple ◽  
Frank Wilhelms
Keyword(s):  
Ice Cores ◽  
Ion Concentration ◽  
Impurity Effect ◽  
Air Entrapment ◽  
Density Profiles ◽  
Climate Conditions ◽  
Order Of Magnitude ◽  
Effect Of Impurities ◽  
The One ◽  
First Time

AbstractA new densification model, which simulates the effect of impurities on the densification of polar firn, is presented. The classical densification models of Herron and Langway (1980) and Pimienta and Barnola (Barnola and others, 1991) are modified by assuming that the activation energy for deformation is reduced by the impurities. Motivated by recent observations, the impurity effect is formulated on an empirical basis using the seasonally varying Ca2+ ion concentration. Excellent agreement between simulated and measured high-resolution density profiles confirms the new approach. The same parameterization applies for Greenland and Antarctica despite the one order of magnitude difference in impurity concentration. The new models allow us, for the first time, to simulate the density layering in firn down to the firn–ice transition. Our results emphasize the importance of impurities and density layering for the air entrapment and for dating gas records of deep ice cores, in particular for glacial climate conditions where the impurity concentrations are 10–100-fold higher than in modern firn.

scholarly journals Combining cloud radar and radar wind profiler for a value added estimate of vertical air motion and particle terminal velocity within clouds

2018 ◽  
Author(s):  
Martin Radenz ◽  
Johannes Bühl ◽  
Volker Lehmann ◽  
Ulrich Görsdorf ◽  
Ronny Leinweber
Keyword(s):  
Value Added ◽  
Terminal Velocity ◽  
Wind Profiler ◽  
Air Velocity ◽  
Fall Velocity ◽  
Cloud Radar ◽  
A Value ◽  
Direct Measurements ◽  
Air Motion ◽  
Better Than

Abstract. Vertical-stare observations from a 482 MHz radar wind profiler and a 35 GHz 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 0.1 m s−1 using numerical simulations. This combination of both 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 10 s with a height resolution of

scholarly journals Combined vertical-velocity observations with Doppler lidar, cloud radar and wind profiler

2015 ◽  
Vol 8 (8) ◽  
pp. 3527-3536 ◽  
Author(s):  
J. Bühl ◽  
R. Leinweber ◽  
U. Görsdorf ◽  
M. Radenz ◽  
A. Ansmann ◽  
...  
Keyword(s):  
Vertical Velocity ◽  
Wind Profiler ◽  
Doppler Lidar ◽  
Velocity Measurements ◽  
Fall Velocity ◽  
Cloud Radar ◽  
Meteorological Observatory ◽  
Comprehensive Classification ◽  
Single Instrument ◽  
Simultaneous Sensing

Abstract. 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.

scholarly journals Combined vertical-velocity observations with Doppler lidar, cloud radar and wind profiler

2015 ◽  
Vol 8 (1) ◽  
pp. 353-373
Author(s):  
J. Bühl ◽  
R. Leinweber ◽  
U. Görsdorf ◽  
M. Radenz ◽  
A. Ansmann ◽  
...  
Keyword(s):  
Vertical Velocity ◽  
Ice Crystals ◽  
Wind Profiler ◽  
Doppler Lidar ◽  
Velocity Measurements ◽  
Fall Velocity ◽  
Cloud Radar ◽  
Meteorological Observatory ◽  
Abstract Case ◽  
Comprehensive Classification

Abstract. 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 the measurements of the Doppler lidar can extent the view of the cloud radar and the wind profiler, especially when observing clouds.

Soluble meso-tetrakis(arylethynyl)porphyrins — synthesis and optical properties

2014 ◽  
Vol 18 (10n11) ◽  
pp. 998-1013 ◽  
Author(s):  
Agnieszka Nowak-Król ◽  
Łukasz G. Łukasiewicz ◽  
Joy E. Haley ◽  
Mikhail Drobizhev ◽  
Aleksander Rebane ◽  
...  
Keyword(s):  
Optical Properties ◽  
Red Light ◽  
Photon Absorption ◽  
Two Photon Absorption ◽  
Two Photon ◽  
Resonance Enhancement ◽  
Order Of Magnitude ◽  
Homo And Lumo ◽  
The One ◽  
First Time

Trans- A 2 B 2-tetrakis(arylethynyl)porphyrins with suitable solubility in CH 2 Cl 2, CHCl 3, EtOAc , acetone and toluene have been obtained for the first time. Among two possible strategies the one comprising the synthesis of 5,15-dibromo-10,20-bis[(isopropylsilyl)ethynyl]porphyrin proved to be more efficient. The pathway towards densely substituted arylacetylenes has been optimized. The use of previously identified 3,4,5-trialkoxyaryl substituent was crucial for achieving the reasonable solubility. The optical properties of meso-substituted tetrakis(arylethynyl)porphyrins were studied showing that strong polarization imparted by direct conjugation of all four substituents with porphyrin core resulted not only in strong absorption of red light but also in a relatively long triplet lifetime. Meso-tetrakis(arylethynyl)porphyrins have a significantly longer lifetime of T1 state than bis(arylethynyl)porphyrins and in their case all the states are mixtures of transitions between the HOMO-1, HOMO and LUMO, LUMO+1 MOs. We show that the presence of two additional arylethynyl substituents at meso-positions enhance the maximum two-photon absorption cross-section of trans- A 2 B 2-tetrakis(arylethynyl)porphyrins by more than one order of magnitude. Maximum values as high as σ2 = 500 GM at 950 nm result from realization of suitable conditions for effective resonance enhancement along with a lowering of the energy and intensification of the two-photon allowed transitions in the Soret region.

scholarly journals Combining cloud radar and radar wind profiler for a value added estimate of vertical air motion and particle terminal velocity within clouds

2018 ◽  
Vol 11 (10) ◽  
pp. 5925-5940 ◽  
Author(s):  
Martin Radenz ◽  
Johannes Bühl ◽  
Volker Lehmann ◽  
Ulrich Görsdorf ◽  
Ronny Leinweber
Keyword(s):  
Value Added ◽  
Terminal Velocity ◽  
Wind Profiler ◽  
Separation Algorithm ◽  
Fall Velocity ◽  
Cloud Radar ◽  
A Value ◽  
Cloud Dynamics ◽  
Direct Measurements ◽  
Air Motion

Abstract. Vertical-stare observations from a 482 MHz radar wind profiler and a 35 GHz 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 0.1 m s−1 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 10 s with a height resolution of <100 m 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.

scholarly journals Continuous secondary-ice production initiated by updrafts through the melting layer in mountainous regions

2021 ◽  
Vol 21 (5) ◽  
pp. 3855-3870
Author(s):  
Annika Lauber ◽  
Jan Henneberger ◽  
Claudia Mignani ◽  
Fabiola Ramelli ◽  
Julie T. Pasquier ◽  
...  
Keyword(s):  
Number Concentration ◽  
Ice Crystals ◽  
Radiation Budget ◽  
Ice Crystal ◽  
High Concentration ◽  
Melting Layer ◽  
Mountainous Regions ◽  
Order Of Magnitude ◽  
Ice Production ◽  
Droplet Fragmentation

Abstract. An accurate prediction of the ice crystal number concentration in clouds is important to determine the radiation budget, the lifetime, and the precipitation formation of clouds. Secondary-ice production is thought to be responsible for the observed discrepancies between the ice crystal number concentration and the ice-nucleating particle concentration in clouds. The Hallett–Mossop process is active between −3 and −8 ∘C and has been implemented into several models, while all other secondary-ice processes are poorly constrained and lack a well-founded quantification. During 2 h of measurements taken on a mountain slope just above the melting layer at temperatures warmer than −3 ∘C, a continuously high concentration of small plates identified as secondary ice was observed. The presence of drizzle drops suggests droplet fragmentation upon freezing as the responsible secondary-ice mechanism. The constant supply of drizzle drops can be explained by a recirculation theory, suggesting that melted snowflakes, which sedimented through the melting layer, were reintroduced into the cloud as drizzle drops by orographically forced updrafts. Here we introduce a parametrization of droplet fragmentation at slightly sub-zero temperatures, where primary-ice nucleation is basically absent, and the first ice is initiated by the collision of drizzle drops with aged ice crystals sedimenting from higher altitudes. Based on previous measurements, we estimate that a droplet of 200 µm in diameter produces 18 secondary-ice crystals when it fragments upon freezing. The application of the parametrization to our measurements suggests that the actual number of splinters produced by a fragmenting droplet may be up to an order of magnitude higher.

scholarly journals Establishment and preliminary application of forward modeling method for Doppler spectral density of ice particles

2019 ◽  
Author(s):  
Han Ding ◽  
Liping Liu
Keyword(s):  
Particle Size ◽  
Spectral Density ◽  
Cross Section ◽  
Ice Crystals ◽  
Ice Crystal ◽  
Fall Velocity ◽  
Density Data ◽  
Cloud Radar ◽  
Backscattering Cross Section ◽  
Ice Particles

Abstract. Owing to the various shapes of ice particles, the relationships between fall velocity, backscattering cross-section, mass, and particle size are complicated, which affects the application of cloud radar Doppler spectral density data to retrieve the microphysical properties of ice crystals. In this paper, under the assumption of six particle shape types, the relationships between particle mass, fall velocity, backscattering cross-section, and particle size were established based on existing research. Variations of Doppler spectral density with the same particle size distribution (PSD) of different ice particle types are discussed, and the radar-retrieved liquid and ice PSDs, water content, and mean volume-weighted particle diameter are compared with airborne in situ observations in Xingtai, Hebei Province, China, in 2018. The results showed the following: (1) for particles with the same equivalent diameter (De), the fall velocity of aggregates is the largest, followed by hexagonal columns, hexagonal plates, sector plates, and stellar crystals, with ice spheres falling two to three times faster than ice crystals with the same De. Hexagonal columns have the largest backscattering cross-section, followed by stellar crystals and sector plates, and the backscattering cross-sections of hexagonal plates and two kinds of aggregates are very close to those of ice spheres. (2) The width of the simulated radar Doppler spectral density generated by various ice crystal types with the same PSD is mainly affected by particle fall velocity and increased fall velocity rates with increased particle size, as do PSDs retrieved from the same Doppler spectral density data. (3) PSD comparisons showed that each ice crystal type retrieved from the cloud radar corresponded well to aircraft observations within a certain scale range when assuming that only a certain type of ice crystals existed in the cloud, which can fully prove the feasibility of retrieving ice PSDs from reflectivity spectral density.

scholarly journals Establishment and Preliminary Application of the Forward Modeling Method for Doppler Spectral Density of Ice Particles

2020 ◽  
Vol 12 (20) ◽  
pp. 3378
Author(s):  
Han Ding ◽  
Liping Liu
Keyword(s):  
Particle Size ◽  
Spectral Density ◽  
Cross Section ◽  
Ice Crystals ◽  
Doppler Spectrum ◽  
Ice Crystal ◽  
Fall Velocity ◽  
Cloud Radar ◽  
Backscattering Cross Section ◽  
Ice Particles

Owing to the various shapes of ice particles, the relationships between fall velocity, backscattering cross-section, mass, and particle size are complicated. This affects the application of cloud radar Doppler spectral density data in the retrieval of the microphysical properties of ice crystals. In this study, under the assumption of six particle shape types, the relationships between particle mass, fall velocity, backscattering cross-section, and particle size were established based on existing research. Variations of Doppler spectral density with the same particle size distribution (PSD) of different ice particle types are discussed. The radar-retrieved liquid and ice PSDs, water content, and mean volume-weighted particle diameter were compared with airborne in situ observations in the Xingtai, Hebei Province, China, in 2018. The results showed the following. (1) For the particles with the same equivalent diameter (De), the fall velocity of the aggregates was the largest, followed by hexagonal columns, hexagonal plates, sector plates, and stellar crystals, with the ice spheres falling two to three times faster than ice crystals with the same De. Hexagonal columns had the largest backscattering cross-section, followed by stellar crystals and sector plates, and the backscattering cross-sections of hexagonal plates and the two types of aggregates were very close to those of ice spheres. (2) The width of the simulated radar Doppler spectral density generated by various ice crystal types with the same PSD was mainly affected by the particle’s falling velocity, which increased with the particle size. Turbulence had different degrees of influence on the Doppler spectrum of different ice crystals, and it also brought large errors to the PSD retrieval. (3) PSD comparisons showed that each ice crystal type retrieved from the cloud radar corresponded well to aircraft observations within a certain scale range, when assuming that only a certain type of ice crystals existed in the cloud, which could fully prove the feasibility of retrieving ice PSDs from the reflectivity spectral density.

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