scholarly journals The TRIple-frequency and Polarimetric radar Experiment for improving process observation of winter precipitation

2018 ◽  
Author(s):  
José Dias Neto ◽  
Stefan Kneifel ◽  
Davide Ori ◽  
Silke Trömel ◽  
Jan Handwerker ◽  
...  
Keyword(s):  
Winter Season ◽  
Winter Precipitation ◽  
Doppler Velocity ◽  
Depolarization Ratio ◽  
Time Duration ◽  
Frequency Space ◽  
Triple Frequency ◽  
Linear Depolarization Ratio ◽  
Process Observation ◽  
Processing Steps

Abstract. This study describes a two-months dataset of ground-based triple-frequency (X, Ka, and W-Band) Doppler cloud radar observations during the winter season obtained at the Jülich ObservatorY for Cloud Evolution core facility (JOYCE-CF), Germany. All relevant post-processing steps, such as re-gridding, offset and attenuation correction as well as quality flagging are described. The dataset contains all information needed to recover data at intermediate processing steps for user-specific applications and corrections (DOI: https://doi.org/10.5281/zenodo.1405539). The rather long time duration of the dataset allowed for a statistical analysis, which we focused on the ice and snow part of the cloud. The reflectivity differences quantified by dual-wavelength ratios revealed temperature regimes, where aggregation seems to be triggered. Overall, the aggregation signatures found in the triple-frequency space agree with and corroborate conclusions from previous studies. Combining the information from reflectivity information with mean Doppler velocity and linear depolarization ratio, enables us to distinguish signatures of rimed particles and melting snowflakes; while the riming signatures agree well with results from previous studies, we find very strong aggregation signatures close to the melting layer, which have not been reported before. Mean Doppler velocity and the linear depolarization ratio have been used to separate the extreme aggregation signature from the triple-frequency characteristics of melting particles.

scholarly journals The TRIple-frequency and Polarimetric radar Experiment for improving process observations of winter precipitation

2019 ◽  
Vol 11 (2) ◽  
pp. 845-863 ◽  
Author(s):  
José Dias Neto ◽  
Stefan Kneifel ◽  
Davide Ori ◽  
Silke Trömel ◽  
Jan Handwerker ◽  
...  
Keyword(s):  
Doppler Radar ◽  
Winter Season ◽  
Winter Precipitation ◽  
Doppler Velocity ◽  
Depolarization Ratio ◽  
Frequency Space ◽  
Triple Frequency ◽  
Temperature Regimes ◽  
Linear Depolarization Ratio ◽  
Processing Steps

Abstract. This paper describes a 2-month dataset of ground-based triple-frequency (X, Ka, and W band) Doppler radar observations during the winter season obtained at the Jülich ObservatorY for Cloud Evolution Core Facility (JOYCE-CF), Germany. All relevant post-processing steps, such as re-gridding and offset and attenuation correction, as well as quality flagging, are described. The dataset contains all necessary information required to recover data at intermediate processing steps for user-specific applications and corrections (https://doi.org/10.5281/zenodo.1341389; Dias Neto et al., 2019). The large number of ice clouds included in the dataset allows for a first statistical analysis of their multifrequency radar signatures. The reflectivity differences quantified by dual-wavelength ratios (DWRs) reveal temperature regimes where aggregation seems to be triggered. Overall, the aggregation signatures found in the triple-frequency space agree with and corroborate conclusions from previous studies. The combination of DWRs with mean Doppler velocity and linear depolarization ratio enables us to distinguish signatures of rimed particles and melting snowflakes. The riming signatures in the DWRs agree well with results found in previous triple-frequency studies. Close to the melting layer, however, we find very large DWRs (up to 20 dB), which have not been reported before. A combined analysis of these extreme DWR with mean Doppler velocity and a linear depolarization ratio allows this signature to be separated, which is most likely related to strong aggregation, from the triple-frequency characteristics of melting particles.

scholarly journals Spectral Polarimetric Radar Clutter Suppression to Enhance Atmospheric Echoes

2009 ◽  
Vol 26 (9) ◽  
pp. 1781-1797 ◽  
Author(s):  
Christine Unal
Keyword(s):  
Real Time ◽  
Full Range ◽  
Doppler Velocity ◽  
Clutter Suppression ◽  
Depolarization Ratio ◽  
Real Time Processing ◽  
Time Processing ◽  
Reduction Techniques ◽  
Linear Depolarization Ratio ◽  
Atypical Values

Abstract The clutter present in the Doppler spectra of atmospheric targets can be removed by using polarimetry. The purpose is to suppress the Doppler velocity bins where spectral polarimetric parameters have atypical values. This procedure largely improves profiles of moments and polarimetric parameters of atmospheric targets. Several spectral polarimetric clutter-reduction techniques, which are based on thresholding and intended for real-time processing, are discussed in this paper. A new method, the double spectral linear depolarization ratio clutter-suppression technique, is proposed. Very satisfactory performances are obtained with this method, which can be used in the full range of elevations (0°–90°). Spectral polarimetric clutter-suppression techniques for real-time processing were studied for the S-band high-resolution Transportable Atmospheric Radar (TARA) profiler. For this study, precipitation, cloud, and clear-air scattering are considered examples of atmospheric echoes. After successful testing in 2008, the double spectral linear depolarization ratio filter was implemented in the real-time processing of the X-band scanning drizzle radar (IDRA).

scholarly journals Observations of Ice Crystal Habits with a Scanning Polarimetric W-Band Radar at Slant Linear Depolarization Ratio Mode

2012 ◽  
Vol 29 (8) ◽  
pp. 989-1008 ◽  
Author(s):  
Sergey Y. Matrosov ◽  
Gerald G. Mace ◽  
Roger Marchand ◽  
Matthew D. Shupe ◽  
Anna G. Hallar ◽  
...  
Keyword(s):  
Bulk Density ◽  
Elevation Angle ◽  
Winter Season ◽  
Cross Coupling ◽  
Characteristic Size ◽  
Depolarization Ratio ◽  
Aspect Ratios ◽  
W Band ◽  
Validation Experiment ◽  
Linear Depolarization Ratio

Abstract Scanning polarimetric W-band radar data were evaluated for the purpose of identifying predominant ice hydrometeor habits. Radar and accompanying cloud microphysical measurements were conducted during the Storm Peak Laboratory Cloud Property Validation Experiment held in Steamboat Springs, Colorado, during the winter season of 2010/11. The observed ice hydrometeor habits ranged from pristine and rimed dendrites/stellars to aggregates, irregulars, graupel, columns, plates, and particle mixtures. The slant 45° linear depolarization ratio (SLDR) trends as a function of the radar elevation angle are indicative of the predominant hydrometeor habit/shape. For planar particles, SLDR values increase from values close to the radar polarization cross coupling of about −21.8 dB at zenith viewing to maximum values at slant viewing. These maximum values depend on predominant aspect ratio and bulk density of hydrometeors and also show some sensitivity to particle characteristic size. The highest observed SLDRs were around −8 dB for pristine dendrites. Unlike planar-type hydrometeors, columnar-type particles did not exhibit pronounced depolarization trends as a function of viewing direction. A difference in measured SLDR values between zenith and slant viewing can be used to infer predominant aspect ratios of planar hydrometeors if an assumption about their bulk density is made. For columnar hydrometeors, SLDR offsets from the cross-coupling value are indicative of aspect ratios. Experimental data were analyzed for a number of events with prevalence of planar-type hydrometeors and also for observations when columnar particles were the dominant species. A relatively simple spheroidal model and accompanying T-matrix calculations were able to approximate most radar depolarization changes with viewing angle observed for different hydrometeor types.

scholarly journals Benefit of depolarization ratio at λ = 1064 nm for the retrieval of the aerosol microphysics from lidar measurements

2014 ◽  
Vol 7 (11) ◽  
pp. 3773-3781 ◽  
Author(s):  
J. Gasteiger ◽  
V. Freudenthaler
Keyword(s):  
Optical Properties ◽  
Mass Concentration ◽  
Volcanic Ash ◽  
Single Scattering ◽  
Depolarization Ratio ◽  
Complex Relation ◽  
Microphysical Properties ◽  
Lidar Measurements ◽  
Increased Sensitivity ◽  
Linear Depolarization Ratio

Abstract. A better quantification of aerosol properties is required for improving the modelling of aerosol effects on weather and climate. This task is methodologically demanding due to the diversity of the microphysical properties of aerosols and the complex relation between their microphysical and optical properties. Advanced lidar systems provide spatially and temporally resolved information on the aerosol optical properties that is sufficient for the retrieval of important aerosol microphysical properties. Recently, the mass concentration of transported volcanic ash, which is relevant for the flight safety of aeroplanes, was retrieved from measurements of such lidar systems in southern Germany. The relative uncertainty of the retrieved mass concentration was on the order of ±50%. The present study investigates improvements of the retrieval accuracy when the capability of measuring the linear depolarization ratio at 1064 nm is added to the lidar setup. The lidar setups under investigation are based on those of MULIS and POLIS of the Ludwig-Maximilians-Universität in Munich (Germany) which measure the linear depolarization ratio at 355 and 532 nm with high accuracy. The improvements are determined by comparing uncertainties from retrievals applied to simulated measurements of this lidar setup with uncertainties obtained when the depolarization at 1064 nm is added to this setup. The simulated measurements are based on real lidar measurements of transported Eyjafjallajökull volcano ash. It is found that additional 1064 nm depolarization measurements significantly reduce the uncertainty of the retrieved mass concentration and effective particle size. This significant improvement in accuracy is the result of the increased sensitivity of the lidar setup to larger particles. The size dependence of the depolarization does not vary strongly with refractive index, thus we expect similar benefits for the retrieval in case of measurements of other volcanic ash compositions and also for transported desert dust. For the retrieval of the single scattering albedo, which is relevant to the radiative transfer in aerosol layers, no significant improvements were found.

scholarly journals Projected changes in winter climate in Beskids Mountains during 21st century

Beskydy ◽  
2017 ◽  
Vol 10 (1-2) ◽  
pp. 123-134
Author(s):  
Aleš Farda ◽  
Petr Štěpánek ◽  
Pavel Zahradníček ◽  
Petr Skalák ◽  
Jan Meitner
Keyword(s):  
Water Balance ◽  
21St Century ◽  
Winter Season ◽  
Winter Precipitation ◽  
Balance Budget ◽  
General Increase ◽  
Winter Climate ◽  
Climate Conditions ◽  
Winter Temperatures ◽  
Projected Changes

We have investigated the future changes of climate conditions during the winter season in the Beskids Mountains. During the 21st century mean winter temperature will increase by 2.0–6.3 °C and winter precipitation will increase by 12.5 – to 17.5 % - depending on the scenario. Higher winter temperatures will be reflected in the reduced number of frost days, the number of which may drop by 40 % according to the RCP8.5 scenario. Whilst our study expects general increase in precipitation, higher temperatures will lead to an increased evapotranspiration and also change in the form of precipitation from solid (snow, rime) to liquid (rain, drizzling). Such trends could further propel the unfavorable changes in the water balance budget.

scholarly journals Identifying Insects, Clouds, and Precipitation using Vertically Pointing Polarimetric Radar Doppler Velocity Spectra

2021 ◽  
Author(s):  
Christopher R. Williams ◽  
Karen L. Johnson ◽  
Scott E. Giangrande ◽  
Joseph C. Hardin ◽  
Ruşen Öktem ◽  
...  
Keyword(s):  
Power Spectra ◽  
Department Of Energy ◽  
Cloud Base ◽  
Doppler Velocity ◽  
Polarimetric Radar ◽  
Ka Band ◽  
Ice Particles ◽  
Linear Depolarization Ratio ◽  
Velocity Spectra ◽  
Discrimination Method

Abstract. This study presents a method to identify and distinguish insects, clouds, and precipitation in 35 GHz (Ka-band) vertically pointing polarimetric radar Doppler velocity power spectra and then produce masks indicating the occurrence of hydrometeors (i.e., clouds or precipitation) and insects at each range gate. The polarimetric radar used in this study transmits a linear polarized wave and receives signals in collinear (CoPol) and cross-linear (XPol) polarized channels. The insect-hydrometeor discrimination method uses CoPol and XPol spectral information in two separate algorithms with their spectral results merged and then filtered into single value products at each range gate. The first algorithm discriminates between insects and clouds in the CoPol Doppler velocity power spectra based on the spectra texture, or spectra roughness, which varies due to the scattering characteristics of insects versus cloud particles. The second algorithm distinguishes insects from raindrops and ice particles by exploiting the larger Doppler velocity spectra linear depolarization ratio (LDR) produced by asymmetric insects. Since XPol power return is always less than CoPol power return for the same target (i.e., insect or hydrometeor), fewer insects and hydrometeors are detected in the LDR algorithm than the CoPol algorithm, which drives this need for a CoPol based algorithm. After performing both CoPol and LDR detection algorithms, regions of insect and hydrometeor scattering from both algorithms are combined in the Doppler velocity spectra domain and then filtered to produce a binary hydrometeor mask indicating the occurrence of cloud, raindrops, or ice particles at each range gate. Comparison with a collocated ceilometer indicates that hydrometeor mask column bottoms are within +/-100 meters of simultaneous ceilometer cloud base heights. Forty-seven (47) summer-time days were processed with the insect-hydrometeor discrimination method using U.S. Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) program Ka-band zenith pointing radar observations in northern Oklahoma (USA). All datasets and images are available on public repositories.

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