Lidar and Triple-Wavelength Doppler Radar Measurements of the Melting Layer: A Revised Model for Dark- and Brightband Phenomena

Abstract During the recent Cirrus Regional Study of Tropical Anvils and Cirrus Layers (CRYSTAL) Florida Area Cirrus Experiment (FACE) field campaign in southern Florida, rain showers were probed by a 0.523-μm lidar and three (0.32-, 0.86-, and 10.6-cm wavelength) Doppler radars. The full repertoire of backscattering phenomena was observed in the melting region, that is, the various lidar and radar dark and bright bands. In contrast to the ubiquitous 10.6-cm (S band) radar bright band, only intermittent evidence is found at 0.86 cm (K band), and no clear examples of the radar bright band are seen at 0.32 cm (W band), because of the dominance of non-Rayleigh scattering effects. Analysis also reveals that the relatively inconspicuous W-band radar dark band is due to non-Rayleigh effects in large water-coated snowflakes that are high in the melting layer. The lidar dark band exclusively involves mixed-phase particles and is centered where the shrinking snowflakes collapse into raindrops—the point at which spherical particle backscattering mechanisms first come into prominence during snowflake melting. The traditional (S band) radar brightband peak occurs low in the melting region, just above the lidar dark-band minimum. This position is close to where the W-band reflectivities and Doppler velocities reach their plateaus but is well above the height at which the S-band Doppler velocities stop increasing. Thus, the classic radar bright band is dominated by Rayleigh dielectric scattering effects in the few largest melting snowflakes.

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Measurements and Simulations of Nadir-Viewing Radar Returns from the Melting Layer at X and W Bands

Journal of Applied Meteorology and Climatology ◽

10.1175/2009jamc2033.1 ◽

2009 ◽

Vol 48 (11) ◽

pp. 2215-2226 ◽

Cited By ~ 9

Author(s):

Liang Liao ◽

Robert Meneghini ◽

Lin Tian ◽

Gerald M. Heymsfield

Keyword(s):

Water Content ◽

Doppler Radar ◽

Tropical Rainfall Measuring Mission ◽

Dielectric Constants ◽

Doppler Velocity ◽

Regional Study ◽

Melting Layer ◽

Bright Band ◽

W Band ◽

X Band

Abstract Simulated radar signatures within the melting layer in stratiform rain—namely, the radar bright band—are checked by means of comparisons with simultaneous measurements of the bright band made by the ER-2 Doppler radar (EDOP; X band) and Cloud Radar System (CRS; W band) airborne Doppler radars during the Cirrus Regional Study of Tropical Anvils and Cirrus Layers–Florida-Area Cirrus Experiment (CRYSTAL-FACE) campaign in 2002. A stratified-sphere model, allowing the fractional water content to vary along the radius of the particle, is used to compute the scattering properties of individual melting snowflakes. Using the effective dielectric constants computed by the conjugate gradient–fast Fourier transform numerical method for X and W bands and expressing the fractional water content of a melting particle as an exponential function in particle radius, it is found that at X band the simulated radar brightband profiles are in an excellent agreement with the measured profiles. It is also found that the simulated W-band profiles usually resemble the shapes of the measured brightband profiles even though persistent offsets between them are present. These offsets, however, can be explained by the attenuation caused by cloud water and water vapor at W band. This is confirmed by comparisons of the radar profiles made in the rain regions where the unattenuated W-band reflectivity profiles can be estimated through the X- and W-band Doppler velocity measurements. The brightband model described in this paper has the potential to be used effectively for both radar and radiometer algorithms relevant to the satellite-based Tropical Rainfall Measuring Mission and Global Precipitation Measuring Mission.

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Airflow and Precipitation Properties within the Stratiform Region of Tropical Storm Gabrielle during Landfall

Monthly Weather Review ◽

10.1175/2008mwr2754.1 ◽

2009 ◽

Vol 137 (6) ◽

pp. 1954-1971 ◽

Cited By ~ 14

Author(s):

Dong-Kyun Kim ◽

Kevin R. Knupp ◽

Christopher R. Williams

Keyword(s):

Doppler Radar ◽

Tropical Storm ◽

Parameter Study ◽

Melting Layer ◽

Bright Band ◽

Maximum Reflectivity ◽

Stratiform Region ◽

Raindrop Size Distribution ◽

Air Motion ◽

Rainfall Estimates

Abstract Kinematic and microphysical characteristics of a stratiform rainband within Tropical Storm Gabrielle during landfall on 14 September 2001 were investigated using data from a collocated 915-MHz wind profiler and scanning Doppler radar. The curved 60-km-wide rainband was relatively intense with mesoscale updrafts and downdrafts exceeding ±1 m s−1. The bright band is classified as strong, as indicated by reflectivity factors in excess of 50 dBZ and rainfall rates below the bright band peaking at 10–20 mm h−1. The melting layer microphysical processes were examined to understand the relation between brightband processes and precipitation intensity and kinematics (mesoscale downdraft in particular) below the melting layer. The profiler and Doppler radar analyses, designed to maximize vertical resolution of flows within the melting layer, disclose a striking convergence–divergence couplet through the melting layer that implies a prominent cooling-induced finescale circulation. Melting-driven cooling initiates midlevel convergence in the upper part of the melting region, while weak convergence to positive divergence is analyzed within the lower melting layer. A melting-layer parameter study indicates the significance of the level of maximum reflectivity that separates convergence above from divergence below and also reveals a mixture of aggregation and breakup of ice particles, with aggregation being dominant. In this vigorous rainband case, the presence of strong mesoscale downdrafts cannot be ignored for accurate retrievals of raindrop size distribution and precipitation parameters from the Sans Air Motion model. When downdrafts are included, retrieved rainfall estimates were much higher than those under the zero vertical air motion assumption and were slightly less than those from a power-law Z–R relation. The rainfall estimates show a positive correlation with reflectivity factor and brightband intensity (i.e., aggregation degree) but less dependence on brightband height.

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Effects of Multiple Scattering on Attenuation-Based Retrievals of Stratiform Rainfall from CloudSat

Journal of Atmospheric and Oceanic Technology ◽

10.1175/2008jtecha1095.1 ◽

2008 ◽

Vol 25 (12) ◽

pp. 2199-2208 ◽

Cited By ~ 24

Author(s):

Sergey Y. Matrosov ◽

Alessandro Battaglia ◽

Peter Rodriguez

Keyword(s):

Multiple Scattering ◽

Rayleigh Scattering ◽

Absolute Calibration ◽

Radar Rainfall ◽

Retrieval Method ◽

Band Frequency ◽

High Attenuation ◽

Freezing Level ◽

W Band ◽

Scattering Effects

Abstract An attenuation-based method to retrieve vertical profiles of rainfall rates from height derivatives/gradients of CloudSat nadir-pointing W-band reflectivity measurements is discussed. This method takes advantage of the high attenuation of W-band frequency signals in rain and the low variability of nonattenuated reflectivity due to strong non-Rayleigh scattering from rain drops. The retrieval uncertainties could reach 40%–50%. The suggested method is generally applicable to rainfall rates (R) in an approximate range from about 2–3 to about 20–25 mm h−1. Multiple scattering noticeably affects the gradients of CloudSat measurements for R values greater than about 5 mm h−1. To avoid a retrieval bias caused by multiple-scattering effects, a special correction for retrievals is introduced. For rainfall rates greater than about 25 mm h−1, the influence of multiple scattering gets overwhelming, and the retrievals become problematic, especially for rainfalls with higher freezing-level altitudes. The attenuation-based retrieval method was applied to experimental data from CloudSat covering the range of rainfall rates. CloudSat retrievals were compared to the rainfall estimates available from a National Weather Service ground-based scanning precipitation radar operating at S band. Comparisons between spaceborne and conventional radar rainfall retrievals were generally in good agreement and indicated the mutual consistency of both quantitative precipitation estimate types. The suggested CloudSat rainfall retrieval method is immune to the absolute calibration of the radar and to attenuation caused by the melting layer and snow regions. Since it does not require surface returns, it is applicable to measurements above both land and water surfaces.

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Towards the connection between snow microphysics and melting layer: insights from multifrequency and dual-polarization radar observations during BAECC

Atmospheric Chemistry and Physics ◽

10.5194/acp-20-9547-2020 ◽

2020 ◽

Vol 20 (15) ◽

pp. 9547-9562 ◽

Cited By ~ 1

Author(s):

Haoran Li ◽

Jussi Tiira ◽

Annakaisa von Lerber ◽

Dmitri Moisseev

Keyword(s):

Doppler Radar ◽

Precipitation Intensity ◽

Dual Polarization ◽

Radar Observations ◽

Melting Layer ◽

Bright Band ◽

Radar Signatures ◽

Microphysical Processes ◽

The Impact ◽

Precipitation Formation

Abstract. In stratiform rainfall, the melting layer (ML) is often visible in radar observations as an enhanced reflectivity band, the so-called bright band. Despite the ongoing debate on the exact microphysical processes taking place in the ML and on how they translate into radar measurements, both model simulations and observations indicate that the radar-measured ML properties are influenced by snow microphysical processes that take place above it. There is still, however, a lack of comprehensive observations to link the two. To advance our knowledge of precipitation formation in ice clouds and provide new insights into radar signatures of snow growth processes, we have investigated this link. This study is divided into two parts. Firstly, surface-based snowfall measurements are used to develop a new method for identifying rimed and unrimed snow from X- and Ka-band Doppler radar observations. Secondly, this classification is used in combination with multifrequency and dual-polarization radar observations collected during the Biogenic Aerosols – Effects on Clouds and Climate (BAECC) experiment in 2014 to investigate the impact of precipitation intensity, aggregation, riming and dendritic growth on the ML properties. The results show that the radar-observed ML properties are highly related to the precipitation intensity. The previously reported bright band “sagging” is mainly connected to the increase in precipitation intensity. Ice particle riming plays a secondary role. In moderate to heavy rainfall, riming may cause additional bright band sagging, while in light precipitation the sagging is associated with unrimed snow. The correlation between ML properties and dual-polarization radar signatures in the snow region above appears to be arising through the connection of the radar signatures and ML properties to the precipitation intensity. In addition to advancing our knowledge of the link between ML properties and snow processes, the presented analysis demonstrates how multifrequency Doppler radar observations can be used to get a more detailed view of cloud processes and establish a link to precipitation formation.

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Non-Contact Measurement of Human Respiration and Heartbeat Using W-band Doppler Radar Sensor

Sensors ◽

10.3390/s20185209 ◽

2020 ◽

Vol 20 (18) ◽

pp. 5209 ◽

Cited By ~ 3

Author(s):

Heesoo Kim ◽

Jinho Jeong

Keyword(s):

Doppler Radar ◽

Band Pass Filter ◽

Radar Sensor ◽

Pass Filter ◽

Contact Measurement ◽

W Band ◽

Compact Size ◽

Human Respiration ◽

Low Pass ◽

Respiration Signal

This paper presents a W-band continuous-wave (CW) Doppler radar sensor for non-contact measurement of human respiration and heartbeat. The very short wavelength of the W-band signal allows a high-precision detection of the displacement of the chest surface by the heartbeat as well as respiration. The CW signal at 94 GHz is transmitted through a high-gain horn antenna to the human chest at a distance of 1 m. The phase-modulated reflection signal is down-converted to the baseband by the quadrature mixer with an excellent amplitude and phase matches between I and Q channels, which makes the IQ mismatch correction in the digital domain unnecessary. The baseband I and Q data are digitized using data acquisition (DAQ) board. The arctangent demodulation with automatic phase unwrapping is applied to the low-pass filtered I and Q data to effectively solve the null point problem. A slow-varying DC component is rejected in the demodulated signal by the trend removal algorithm. Then, the respiration signal with a frequency of 0.27 Hz and a displacement of ~6.1 mm is retrieved by applying a low-pass filter. Finally, the respiration signal is removed by the band-pass filter and the heartbeat signal is extracted, showing a frequency of 1.35 Hz and a displacement of ~0.26 mm. The extracted respiration and heartbeat rates are very close to the manual measurement results. The demonstrated W-band CW radar sensors can be easily applied to find the angular location of the human body by using a phased array under a compact size.

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A W-band comet-jet Doppler radar prototype

2018 IEEE Radar Conference (RadarConf18) ◽

10.1109/radar.2018.8378557 ◽

2018 ◽

Cited By ~ 1

Author(s):

Ken B. Cooper ◽

Raquel Rodriguez Monje ◽

Maria Alonso-delPino ◽

Robert J. Dengler ◽

Corey J. Cochrane ◽

...

Keyword(s):

Doppler Radar ◽

W Band

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Observational and Modeling Study of Ice Hydrometeor Radar Dual-Wavelength Ratios

Journal of Applied Meteorology and Climatology ◽

10.1175/jamc-d-19-0018.1 ◽

2019 ◽

Vol 58 (9) ◽

pp. 2005-2017 ◽

Cited By ~ 6

Author(s):

Sergey Y. Matrosov ◽

Maximilian Maahn ◽

Gijs de Boer

Keyword(s):

Rayleigh Scattering ◽

Elevation Angle ◽

Characteristic Size ◽

Dual Wavelength ◽

Spherical Particles ◽

Nonspherical Particles ◽

Dual Frequency ◽

Weather Radars ◽

W Band ◽

Differential Reflectivity

AbstractThe influence of ice hydrometeor shape on the dual-wavelength ratio (DWR) of radar reflectivities at millimeter-wavelength frequencies is studied theoretically and on the basis of observations. Data from dual-frequency (Ka–W bands) radar show that, for vertically pointing measurements, DWR increasing trends with reflectivity Ze are very pronounced when Ka-band Ze is greater than about 0 dBZ and that DWR and Ze values are usually well correlated. This correlation is explained by strong relations between hydrometeor characteristic size and both of these radar variables. The observed DWR variability for a given level of reflectivity is as large as 8 dB, which is in part due to changes in mean hydrometeor shape as expressed in terms of the particle aspect ratio. Hydrometeors with a higher degree of nonsphericity exhibit lower DWR values when compared with quasi-spherical particles because of near-zenith reflectivity enhancements for particles outside the Rayleigh-scattering regime. When particle mass–size relations do not change significantly (e.g., for low-rime conditions), DWR can be used to differentiate between quasi-spherical and highly nonspherical hydrometeors because (for a given reflectivity value) DWR tends to increase as particles become more spherical. Another approach for differentiating among different degrees of nonsphericity for larger scatterers is based on analyzing DWR changes as a function of radar elevation angle. These changes are more pronounced for highly nonspherical particles and can exceed 10 dB. Measurements of snowfall spatiotemporally collocated with spaceborne CloudSat W-band radar and ground-based S-band operational weather radars also indicate that DWR values are generally smaller for ice hydrometeors with higher degrees of nonsphericity, which, for the same level of S-band reflectivity, exhibit greater differential reflectivity values.

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