Linear Depolarization Ratios of Columnar Ice Crystals in a Deep Precipitating System over the Arctic Observed by Zenith-Pointing Ka-Band Doppler Radar

Mariko Oue Department of Meteorology, The Pennsylvania State University, University Park, Pennsylvania

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Matthew R. Kumjian Department of Meteorology, The Pennsylvania State University, University Park, Pennsylvania

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Yinghui Lu Department of Meteorology, and Department of Electrical Engineering, The Pennsylvania State University, University Park, Pennsylvania

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Johannes Verlinde Department of Meteorology, The Pennsylvania State University, University Park, Pennsylvania

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Kultegin Aydin Department of Electrical Engineering, The Pennsylvania State University, University Park, Pennsylvania

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Eugene E. Clothiaux Department of Meteorology, The Pennsylvania State University, University Park, Pennsylvania

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Abstract

This study demonstrates that linear depolarization ratio (LDR) values obtained from zenith-pointing Ka-band radar Doppler velocity spectra are sufficient for detecting columnar ice crystals. During a deep precipitating system over the Arctic on 7 December 2013, the radar recorded LDR values up to −15 dB at temperatures corresponding to the columnar ice crystal growth regime. These LDR values were also consistent with scattering calculations for columnar ice crystals. Enhancements in LDR were suppressed within precipitation fallstreaks because the enhanced LDR values of columnar ice crystals were masked by the returns from the particles within the fallstreaks. However, Doppler velocity spectra of LDR within the fallstreak distinguished populations of slower-falling particles with high LDR (>−15 dB) and faster-falling particles with much lower LDR, suggesting that columnar ice crystals with high LDR coexisted with larger isometric particles that produced low LDR while dominating the total copolar reflectivity, thereby decreasing LDR. The measurements suggest that the columnar ice crystals originated in liquid-cloud layers through secondary ice production.

Corresponding author address: Mariko Oue, Dept. of Meteorology, The Pennsylvania State University, University Park, PA 16802. E-mail: muo15@psu.edu

Abstract

This study demonstrates that linear depolarization ratio (LDR) values obtained from zenith-pointing Ka-band radar Doppler velocity spectra are sufficient for detecting columnar ice crystals. During a deep precipitating system over the Arctic on 7 December 2013, the radar recorded LDR values up to −15 dB at temperatures corresponding to the columnar ice crystal growth regime. These LDR values were also consistent with scattering calculations for columnar ice crystals. Enhancements in LDR were suppressed within precipitation fallstreaks because the enhanced LDR values of columnar ice crystals were masked by the returns from the particles within the fallstreaks. However, Doppler velocity spectra of LDR within the fallstreak distinguished populations of slower-falling particles with high LDR (>−15 dB) and faster-falling particles with much lower LDR, suggesting that columnar ice crystals with high LDR coexisted with larger isometric particles that produced low LDR while dominating the total copolar reflectivity, thereby decreasing LDR. The measurements suggest that the columnar ice crystals originated in liquid-cloud layers through secondary ice production.

Corresponding author address: Mariko Oue, Dept. of Meteorology, The Pennsylvania State University, University Park, PA 16802. E-mail: muo15@psu.edu

1. Introduction

Mixed-phase clouds, defined as clouds that are composed of supercooled liquid drops and ice particles within the same volume of air, play a role in ice nucleation and acceleration of ice growth in Arctic cloud systems (Pinto et al. 2001; Rangno and Hobbs 2001). Liquid clouds are often found in multiple layers in deep, ice-precipitating systems over the Arctic, thereby driving complex ice-growth processes (Herman and Goody 1976; Pinto et al. 2001; Verlinde et al. 2013). Recently developed numerical models that are capable of describing particle growth with diverse sizes, aspect ratios, and densities in such mixed-phase clouds (e.g., Harrington et al. 2013; Sulia et al. 2013, 2014) require validation with observations.

Polarimetric radar observables offer the capability of identification of hydrometeor species (Hall et al. 1984; Straka and Zrnić 1993; Vivekanandan et al. 1999; and many others), including ice hydrometeors such as pristine crystal habits (e.g., Thompson et al. 2014). Growth of dendritic ice crystals has been frequently observed by scanning polarimetric radars as regions of enhanced differential reflectivity ZDR and specific differential phase KDP near the −15°C temperature level (Kennedy and Rutledge 2011; Andrić et al. 2013; Bechini et al. 2013; Schneebeli et al. 2013; Kumjian et al. 2014; Schrom et al. 2015, manuscript submitted to J. Appl. Meteor. Climatol.). Oue et al. (2015) showed that X-band ZDR, KDP, and correlation coefficient ρHV measurements were useful in identifying riming of graupel and platelike ice particles in Arctic mixed-phase clouds at Barrow, Alaska. Signatures of columnar ice-crystal growth in those observables at low elevation angles are close to those from other ice particles like early-stage aggregates and rimed crystals (e.g., Wolde and Vali 2001; Aydin and Singh 2004). A notable exception is within thunderstorm electric fields, in which columnar ice crystals can be vertically oriented and therefore produce pronounced signatures of negative ZDR and KDP (e.g., Ryzhkov and Zrnić 2007; Hubbert et al. 2014a,b). Strong electric fields and thunderstorms rarely occur in the Arctic, however. These similar characteristics of polarimetric signatures from a variety of ice crystals indicate that distinguishing columns from other crystals in Arctic clouds by ZDR, KDP, and ρHV is difficult.

Linear depolarization ratio (LDR) is a valuable observable in identifying the presence of columnar ice crystals (Matrosov 1991; Matrosov et al. 1996; Aydin and Tang 1997; Reinking et al. 2002). For linearly polarized electromagnetic radiation with the electric field transmitted in the horizontal plane, LDR is defined as the ratio of the cross-polar equivalent reflectivity factor Zvh to the copolar equivalent reflectivity factor Zhh (where here “vh” stands for horizontal transmit/vertical receive):
e1
For backscattering by a particle that is symmetric about the incident horizontally oriented electric field, in theory Zvh is 0 mm6 m−3 (Doviak and Zrnić 1993) and LDR goes to negative infinity. For LDR to be finite there must be some asymmetry in the particle about the electric-field orientation. For example, if the symmetry axis of a spheroidal particle is perpendicular to neither the horizontal nor vertical polarization directions of an incident beam, the particle is not symmetric with respect to the electric field (Matrosov et al. 1996). Alternatively, irregularly shaped hydrometeors can produce values of Zvh that are greater than 0 mm6 m−3 (Doviak and Zrnić 1993). For radar measurements, Zvh is always positive because of cross-coupling of signals (Chandrasekar and Keeler 1993) and therefore LDR is finite even for symmetric particles such as spheres. LDR values depend on the elevation angle of the radar beam; for instance, columns and needles with major axes randomly oriented within the horizontal plane have larger LDR values than do horizontally oriented planar crystals at vertical incidence and have lower values at horizontal incidence (Matrosov 1991; Aydin and Tang 1997; Reinking et al. 2002).

Using Ka-band radar observations of midlatitude clouds, Matrosov et al. (2001) and Reinking et al. (2002) observed higher LDR values from columnar ice crystals than from graupel at vertical incidence. LDR signatures of columnar ice crystals are sometimes suppressed in deep clouds in which large spatial particles dominate the returns (e.g., Matrosov et al. 2012). Rambukkange et al. (2011), Verlinde et al. (2013), and Oue et al. (2015) have shown that Doppler spectrum analysis has the information content to separate the returns from certain classes of ice-particle types in Arctic mixed-phase clouds, suggesting that Doppler spectra may aid in the detection of embedded columnar ice crystals.

The U.S. Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) Program installed a Ka-band ARM zenith-pointing radar (KAZR) at the DOE ARM Climate Research Facility at Barrow, Alaska, on the North Slope of Alaska (NSA) in 2011 (Bharadwaj et al. 2011). During the passage of a deep precipitating system over the NSA, the KAZR detected enhanced LDR values that are associated with temperatures corresponding to the columnar growth regime (e.g., Magono and Lee 1966). This study demonstrates that the LDR signatures combined with Doppler velocity spectrum analysis is sufficient to identify columnar ice crystals in the presence of larger isometric ice particles.

2. Data and methods

The KAZR transmits linearly polarized waves and records the Doppler velocity spectra of both the co-polar and cross-polar signals for each radar sample volume in the column above the radar. The Zhh, Zvh, LDR, and mean Doppler velocity are computed from the two spectra generated from the co-polar and cross-polar signal time series. LDR was computed from received copolar signals that are stronger than −75 dBm and from cross-polar signals that are stronger than −91 dBm. The KAZR data used in this study were collected with a chirp pulse mode: total pulse width of 4 μs, but with a range resolution of 30 m, range gate spacing of 30 m, pulse repetition frequency of 2771.31 Hz, Nyquist velocity of 6.0 m s−1, and time spacing of 3.7 s (Bharadwaj et al. 2013). Owing to cross coupling of signals between the KAZR horizontal and vertical polarizations, the minimum observable LDR value from the KAZR was approximately −21 dB.

To interpret KAZR LDR values, scattering properties for single columnar and needlelike ice crystals were calculated using the discrete dipole approximation of Yurkin and Hoekstra (2011). The sizes and shapes of the columnar ice crystals were defined by means of maximum dimension and aspect ratio. The maximum dimension is the length of the (major) c axis, which is always horizontally oriented (parallel to the surface) in the scattering calculations. The aspect ratio is the ratio of the lengths of the c axis (maximum dimension) to the a axis (thickness). Twenty N1e (long columnar) crystals and 20 N1a (needlelike) crystals were constructed by using the relationships between maximum dimension and thickness that were proposed by Jayaweera and Ohtake (1974) and Auer and Veal (1970), respectively. The backscattering properties for the ice crystals were calculated with crystal rotation angles in the horizontal plane relative to the incident radiation that range from 0° to 90° in 5° increments, effectively simulating random orientation of the columnar crystals in the horizontal plane. The dielectric constant that is associated with each columnar and needlelike ice crystal is 3.1683 + i(6.5053 × 10−4), corresponding to solid ice at a wavelength of 8.40 mm (frequency of 35.6 GHz).

The study period occurred from 1500 to 1545 UTC 7 December 2013. Precipitation fallstreaks from generating cells at the top of a deep precipitating system produced graupel as the ice precipitation fell through multiple liquid-cloud layers (Oue et al. 2015). Some of the lower liquid-cloud layers were in the temperature range from −8° to −3°C where secondary ice formation via the Hallett–Mossop ice multiplication mechanism (Hallett and Mossop 1974) may occur.

3. Results

To identify the presence of liquid-cloud layers during the study period, we made use of cloud-liquid water path (LWP) retrievals from microwave radiometer measurements (Liljegren et al. 2001; Turner et al. 2007) and height-versus-time maps of smallest hydrometeor velocity extracted from the KAZR Doppler spectra (Rambukkange et al. 2011). The LWP in Fig. 1a ranges from 50 to 300 g m−2 during the study period (1500–1545 UTC). The smallest hydrometeor-velocity maps in Fig. 1b are based on the idea that the smallest cloud-particle Doppler velocities are measures of the air vertical motion, whereas precipitation particles have measurable fall speeds (e.g., Wakasugi et al. 1986; Lhermitte 1987; Gossard et al. 1997). Cloud layers through which precipitation falls are revealed by discontinuities in height, especially at cloud top, in smallest hydrometeor velocity (e.g., at 2.5 and 3.0 km). Although it cannot unambiguously be stated that the 2.5- and 3.0-km cloud layers are liquid, Rambukkange et al. (2011) showed, from depolarization lidar, that similar layers embedded in deeper Arctic clouds were liquid.

Fig. 1.
Fig. 1.

(a) Time series of liquid water path retrieved from microwave radiometer measurements, and (b) height-vs-time cross section of smallest hydrometeor velocity extracted from the KAZR Doppler spectra on 7 Dec 2013.

Citation: Journal of Applied Meteorology and Climatology 54, 5; 10.1175/JAMC-D-15-0012.1

Height-versus-time cross sections of KAZR Zhh and LDR (Fig. 2) reveal an enhancement in LDR below a height of 2.2 km during the case-study period. These observed LDR values were as high as approximately −15 dB. The temperature profile recorded by the sounding at 1200 UTC (see Fig. 1 of Oue et al. 2015) reveals that the temperatures at the top of the region with the LDR enhancement fell within the columnar-ice-crystal-growth regime (from −7° to −5°C; Magono and Lee 1966). LDR was highest (from −17 to −15 dB) between the fallstreaks and lowest (from −19 to −18 dB) in the regions within the fallstreaks.

Fig. 2.
Fig. 2.

Height-vs-time cross sections on 7 Dec 2013 of (a) copolar equivalent reflectivity factor (Zhh; dB) and (b) LDR from KAZR observables. Black contours represent reflectivity isolines of 4, 8, and 12 dBZ. The vertical dashed lines in each of (a) and (b) at 1512 and 1521 UTC represent the time of the KAZR copolar reflectivity and LDR spectrographs illustrated in Figs. 3 and 4, below.

Citation: Journal of Applied Meteorology and Climatology 54, 5; 10.1175/JAMC-D-15-0012.1

To demonstrate that the drop in LDR within the fallstreaks was the result of fallstreak particles masking the LDR enhancements of the columnar ice crystals that are also present in the same volumes of air, vertical profiles of Doppler velocity spectra are presented in Figs. 3 and 4. These two Doppler velocity spectrographs were observed at 1512:33 and 1521:25 UTC. The spectrograph at 1512:33 UTC cuts through a fallstreak below 2.2-km altitude, whereas the second one at 1521:25 UTC passed through a high-LDR region below 2.2 km (see the dashed vertical lines in Fig. 2). The spectrograph in Fig. 3a (1512:33 UTC) reveals that at least two different ice-particle types were present within the radar sample volumes containing the fallstreak. The faster downward Doppler velocity population (denoted by A in Fig. 3) entered the radar beam at 2.4-km altitude with Doppler velocity of −0.5 m s−1 and reached −2.0 m s−1 at 0.5-km altitude. The LDR values in A were relatively low (−20 dB; Fig. 3b), approaching the cross-polar isolation limit of the KAZR antenna. The slower-falling particles in B were initiated near 0 m s−1 in Doppler velocity at heights somewhere between 2.0 and 2.5 km, consistent with the locations of the liquid-cloud layers. LDR returns from this population exceeded −15 dB. These high-LDR ice particles attained Doppler velocities of −1.0 m s−1 near (0.5 km above) the surface. To examine the contributions of populations A and B to the total Zhh and LDR, we computed profiles of Zhh and Zvh by integrating over the Doppler spectra that correspond to each population and then computed LDR (Figs. 3c,d). The particles in A contributed most to the total Zhh between altitudes of 1.1 and 2.5 km. LDR values for population B reached −14 dB and were approximately 5 dB larger than for A and 3–4 dB larger than for all of the scatterers in the radar sample volumes (dashed line).

Fig. 3.
Fig. 3.

Vertical profiles of Doppler velocity spectra at 1512:33 UTC (dashed lines in Fig. 2) of (a) copolar equivalent reflectivity factor Zhh and (b) LDR. Negative values of Doppler velocity represent downward motion. Also shown are vertical profiles of (c) Zhh and (d) LDR integrated over populations A (gray line) and B (black solid line) as well as over all of the scatterers in the radar sample volume (dashed line). Populations denoted by A and B in (a) and (b) correspond to the profiles shown in (c) and (d).

Citation: Journal of Applied Meteorology and Climatology 54, 5; 10.1175/JAMC-D-15-0012.1

Fig. 4.
Fig. 4.

As in Fig. 3, but for 1521:25 UTC.

Citation: Journal of Applied Meteorology and Climatology 54, 5; 10.1175/JAMC-D-15-0012.1

At 1521:25 UTC, LDR was very high at 1.2–2.2-km altitude (Fig. 2). The spectrograph in Fig. 4 for this time reveals at least two different ice-particle types below 2.3-km altitude (denoted by C and D). The slower-falling particles of population D have larger LDR (>−15 dB) than do the fast-falling particles of population C, similar to population B in Fig. 3. The Zhh for population D dominates total Zhh at 1521:25 UTC outside the fallstreak (1.2–2.1 km), however, in contrast to population B at 1512:33 UTC. As a result, outside the fallstreak LDR exceeds −17 dB, whereas within the fallstreak LDR drops below −17 dB (<1.1 km).

The linear depolarization ratio σvh/σhh for each of the 40 modeled columnar and needlelike ice crystals was computed from the scattering calculations, where σvh and σhh are the cross-polar and copolar backscattering cross sections at vertical incidence. For each particle, σvh and σhh were first averaged over the 19 rotation angles before taking their ratio. Figure 5 shows σvh/σhh versus aspect ratio at vertical incidence. All of the columnar ice crystals have aspect ratios that are larger than 3.0. The σvh/σhh values for these columns range from −16.0 to −12.6 dB. Columnar ice crystals with large aspect ratios produce the largest σvh/σhh values. We examined canting-angle effects on σvh/σhh. For a canting angle of 10°, the impact on σvh/σhh is less than a 0.2-dB drop in magnitude, whereas for larger canting angles of 20° to 30° the decrease in σvh/σhh ranges from 1 to 2 dB with larger-aspect-ratio particles having a smaller change. This variability in σvh/σhh with canting angle is consistent with the calculations in Matrosov (1991).

Fig. 5.
Fig. 5.

LDR (σvh/σhh) vs aspect ratio for columnar ice crystals. The color shading for circles and triangles represents the maximum dimension associated with the aspect ratio as based on the relationships of Jayaweera and Ohtake (1974) and Auer and Veal (1970), respectively. The results are averages over all 19 rotation angles from 0° to 90° in 5° increments.

Citation: Journal of Applied Meteorology and Climatology 54, 5; 10.1175/JAMC-D-15-0012.1

4. Discussion

During the enhanced-LDR case-study period, ice particles were seeded into liquid-cloud layers, producing further ice growth and new ice nucleation. As a result, two distinct classes of ice particles were present in the radar volumes below 2.5-km altitude. The Doppler velocities for the fast-falling particles in A and C that are illustrated in Figs. 3 and 4 are consistent with fall speeds of small graupel or aggregates (Locatelli and Hobbs 1974). Oue et al. (2015), looking at the same precipitating system but for 30 min earlier, presented evidence from polarimetric radar that similar fallstreaks contained graupel. The comparatively low LDR values and fall speeds of the particles in A and C are consistent with small isometric lump graupel, growing as it falls through the liquid cloud layers.

LDR values from populations B and D are in agreement with the scattering calculations for columnar ice crystals (Fig. 5). Matrosov (1991), Matrosov et al. (2001), Aydin and Walsh (1999), and Reinking et al. (2002) showed that LDR values produced by needle and columnar (aspect ratio > 2) ice crystals at vertical incidence (from −18 to −14 dB) are higher than those for planar crystals (<−24 dB). Although Tyynelä et al. (2011) showed scattering calculations for large aggregates of dendrites with maximum dimensions exceeding 10 mm that produced LDR values at Ka-band wavelengths approaching −10 dB, the downward Doppler velocities in B and D are slower than those of large aggregates of dendrites (Locatelli and Hobbs 1974) and are consistent with those of pristine columnar ice crystals (Jayaweera and Cottis 1969; Heymsfield 1972). We conclude that the measurements from populations B and D are consistent with ice nucleation at approximately 2.5-km altitude and subsequent vapor growth of columnar ice crystals. This conclusion is strengthened by the realization that graupel was falling through liquid cloud layers in the temperature range from −8° to −3°C (1200 UTC Barrow radiosonde; Fig. 1 of Oue et al. 2015) where the secondary ice-production mechanism of Hallett and Mossop (1974) will produce ice-crystal columns/needles via rime splintering. Rangno and Hobbs (2001) reported similar secondary ice production of columns/needles in Arctic stratocumulus clouds.

The radar volumes below 2.5 km contained both graupel and columnar ice. In such a mixture of large isometric particles and small columnar ice crystals, the larger particles will dominate Zhh (denominator of LDR) whereas the small columnar ice crystals will contribute to Zvh (numerator of LDR). Because the faster-falling particles with low LDR from population A dominated the total Zhh, the total LDR for the radar sample volumes within the fallstreaks was suppressed, even though the columnar ice crystals with low reflectivity values produced high Zvh. In contrast, between the fallstreaks the slower-falling particles of population D with high LDR dominated Zhh; therefore, LDR for the radar sample volumes remained high.

5. Conclusions

This study demonstrates that LDR values obtained from Ka-band ARM zenith-pointing-radar Doppler velocity spectra are sufficient for detecting columnar ice crystals. During a deep precipitating system over the Arctic on 7 December 2013, the KAZR recorded LDR values up to −15 dB at temperatures corresponding to the columnar-ice-crystal-growth regime. The LDR values were consistent with scattering calculations for columnar ice crystals, which showed σvh/σhh values ranging from −16.0 to −12.6 dB. The enhancements in LDR were suppressed within precipitation fallstreaks. The KAZR Doppler velocity spectra of LDR distinguished populations of slower-falling particles with high LDR and faster-falling particles with comparatively lower LDR. The available evidence suggests that the slower-falling particles with high (>−15 dB) LDR were columnar ice crystals and that the isometric particles with lower LDR that composed the fallstreak were descending into them. The columnar ice crystals originated within liquid cloud layers, suggesting new ice nucleation through secondary ice production. The LDR values in the fallstreaks were suppressed because the larger isometric particles that compose the fallstreaks produced low LDR values while dominating the total Zhh, thereby decreasing the total LDR.

Acknowledgments

This research was supported by the U.S. Department of Energy’s Atmospheric Science Program Atmospheric System Research, an Office of Science, Office of Biological and Environmental Research program, under Grant DE-FG02-05ER64058 for M. Oue, J. Verlinde, and E. E. Clothiaux and by the National Science Foundation under Grants AGS-1143948 for M. Kumjian and AGS-1228180 for Y. Lu and K. Aydin. The authors thank Nitin Bharadwaj of Pacific Northwest National Laboratory for fruitful suggestions regarding interpretation of the KAZR LDR values.

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  • Matrosov, S. Y., G. G. Mace, R. Marchand, M. D. Shupe, A. G. Hallar, and I. B. McCubbin, 2012: Observations of ice crystal habits with a scanning polarimetric W-band radar at slant linear depolarization ratio mode. J. Atmos. Oceanic Technol., 29, 9891008, doi:10.1175/JTECH-D-11-00131.1.

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  • Oue, M., M. R. Kumjian, Y. Lu, Z. Jiang, E. E. Clothiaux, J. Verlinde, and K. Aydin, 2015: X-band polarimetric and Ka-band Doppler spectral radar observations of a graupel-producing Arctic mixed-phase cloud. J. Appl. Meteor. Climatol., in press.

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  • Rangno, A. L., and P. V. Hobbs, 2001: Ice particles in stratiform clouds in the Arctic and possible mechanisms for the production of high ice concentrations. J. Geophys. Res., 106, 15 06515 075, doi:10.1029/2000JD900286.

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  • Reinking, R. F., S. Y. Matrosov, L. A. Kropfli, and B. W. Bartram, 2002: Evaluation of a slant quasi-linear radar polarization state for distinguishing drizzle droplets, pristine ice crystals, and less regular ice particles. J. Atmos. Oceanic Technol., 19, 296321, doi:10.1175/1520-0426-19.3.296.

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    • Export Citation
  • Ryzhkov, A. V., and D. S. Zrnić, 2007: Depolarization in ice crystals and its effect on radar polarimetric measurements. J. Atmos. Oceanic Technol., 24, 12561267, doi:10.1175/JTECH2034.1.

    • Search Google Scholar
    • Export Citation
  • Schneebeli, M., N. Dawes, M. Lehning, and A. Berne, 2013: High-resolution vertical profiles of X-band polarimetric radar observables during snowfall in the Swiss Alps. J. Appl. Meteor. Climatol., 52, 378394, doi:10.1175/JAMC-D-12-015.1.

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  • Straka, J. M., and D. S. Zrnić, 1993: An algorithm to deduce hydrometeor types and contents from multiparameter radar data. Preprints, 26th Conf. on Radar Meteorology, Norman, OK, Amer. Meteor. Soc., 513–516.

  • Sulia, K. J., J. Y. Harrington, and H. Morrison, 2013: A method for adaptive habit prediction in bulk microphysical models. Part III: Applications and studies within a two-dimensional kinematic model. J. Atmos. Sci., 70, 33023320, doi:10.1175/JAS-D-12-0316.1.

    • Search Google Scholar
    • Export Citation
  • Sulia, K. J., J. Y. Harrington, and H. Morrison, 2014: Dynamical and microphysical evolution during mixed-phase cloud glaciation using the bulk adaptive habit prediction model. J. Atmos. Sci., 71, 41584180, doi:10.1175/JAS-D-14-0070.1.

    • Search Google Scholar
    • Export Citation
  • Thompson, E. J., S. A. Rutledge, B. Dolan, V. Chandrasekar, and B. Cheong, 2014: A dual-polarization radar hydrometeor classification algorithm for winter precipitation. J. Atmos. Oceanic Technol., 31, 14571481, doi:10.1175/JTECH-D-13-00119.1.

    • Search Google Scholar
    • Export Citation
  • Turner, D. D., S. A. Clough, J. C. Liljegren, E. E. Clothiaux, K. E. Cady-Pereira, and K. L. Gaustad, 2007: Retrieving liquid water path and precipitable water vapor from the Atmospheric Radiation Measurement (ARM) microwave radiometers. IEEE Trans. Geosci. Remote Sens., 45, 36803690, doi:10.1109/TGRS.2007.903703.

    • Search Google Scholar
    • Export Citation
  • Tyynelä, J., J. Leinonen, D. Moisseev, and T. Nousiainen, 2011: Radar backscattering from snowflakes: Comparison of fractal, aggregate, and soft spheroid models. J. Atmos. Oceanic Technol., 28, 13651372, doi:10.1175/JTECH-D-11-00004.1.

    • Search Google Scholar
    • Export Citation
  • Verlinde, J., M. P. Rambukkange, E. E. Clothiaux, G. M. McFarquhar, and E. W. Eloranta, 2013: Arctic multilayered mixed-phase cloud processes revealed in millimeter wave cloud radar Doppler spectra. J. Geophys. Res. Atmos., 118, 13 19913 213, doi:10.1002/2013JD020183.

    • Search Google Scholar
    • Export Citation
  • Vivekanandan, J., D. S. Zrnić, S. Ellis, D. Oye, A. V. Ryzhkov, and J. M. Straka, 1999: Cloud microphysics retrieval using S-band dual-polarization radar measurements. Bull. Amer. Meteor. Soc., 80, 381388, doi:10.1175/1520-0477(1999)080<0381:CMRUSB>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Wakasugi, K., A. Mizutani, M. Matsuo, S. Fukao, and S. Kato, 1986: A direct method for deriving drop-size distribution and vertical air velocities from VHF Doppler radar spectra. J. Atmos. Oceanic Technol., 3, 623629, doi:10.1175/1520-0426(1986)003<0623:ADMFDD>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Wolde, M., and G. Vali, 2001: Polarimetric signatures from ice crystals observed at 95 GHz in winter clouds. Part I: Dependence on crystal form. J. Atmos. Sci., 58, 828841, doi:10.1175/1520-0469(2001)058<0828:PSFICO>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Yurkin, M. A., and A. G. Hoekstra, 2011: The discrete-dipole-approximation code ADDA: Capabilities and known limitations. J. Quant. Spectrosc. Radiat. Transfer, 112, 22342247, doi:10.1016/j.jqsrt.2011.01.031.

    • Search Google Scholar
    • Export Citation
  • Fig. 1.

    (a) Time series of liquid water path retrieved from microwave radiometer measurements, and (b) height-vs-time cross section of smallest hydrometeor velocity extracted from the KAZR Doppler spectra on 7 Dec 2013.

  • Fig. 2.

    Height-vs-time cross sections on 7 Dec 2013 of (a) copolar equivalent reflectivity factor (Zhh; dB) and (b) LDR from KAZR observables. Black contours represent reflectivity isolines of 4, 8, and 12 dBZ. The vertical dashed lines in each of (a) and (b) at 1512 and 1521 UTC represent the time of the KAZR copolar reflectivity and LDR spectrographs illustrated in Figs. 3 and 4, below.

  • Fig. 3.

    Vertical profiles of Doppler velocity spectra at 1512:33 UTC (dashed lines in Fig. 2) of (a) copolar equivalent reflectivity factor Zhh and (b) LDR. Negative values of Doppler velocity represent downward motion. Also shown are vertical profiles of (c) Zhh and (d) LDR integrated over populations A (gray line) and B (black solid line) as well as over all of the scatterers in the radar sample volume (dashed line). Populations denoted by A and B in (a) and (b) correspond to the profiles shown in (c) and (d).

  • Fig. 4.

    As in Fig. 3, but for 1521:25 UTC.

  • Fig. 5.

    LDR (σvh/σhh) vs aspect ratio for columnar ice crystals. The color shading for circles and triangles represents the maximum dimension associated with the aspect ratio as based on the relationships of Jayaweera and Ohtake (1974) and Auer and Veal (1970), respectively. The results are averages over all 19 rotation angles from 0° to 90° in 5° increments.

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