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1. Stratocumulus Precipitation Properties Over the Southern Ocean Observed From Aircraft During the SOCRATES Campaign

   https://doi.org/10.1029/2023JD039831  

   Kang, L; Marchand, R T; Wood, R (March 2024, Journal of Geophysical Research: Atmospheres)

   Abstract Precipitation plays an important role in cloud and aerosol processes over the Southern Ocean (SO). The main objective of this study is to characterize SO precipitation properties associated with SO stratocumulus clouds. We use data from the Southern Ocean Clouds Radiation Aerosol Transport Experimental Study (SOCRATES), and leverage observations from airborne radar, lidar, and in situ probes. We find that for the cold‐topped clouds (cloud‐top‐temperature <0°C), the phase of precipitation with reflectivity >0 dBZ is predominantly ice, while reflectivity < −10 dBZ is predominantly liquid. Liquid‐phase precipitation properties are retrieved where radar and lidar are zenith‐pointing. Power‐law relationships between reflectivity (Z) and rain rate (R) are developed, and the derived Z–R relationships show vertical dependence and sensitivity to the presence of droplets with diameters between 10 and 40 μm. Using derived Z–R relationships, a reflectivity‐velocity (ZV) retrieval method, and a radar‐lidar retrieval method, we derive rain rate and other precipitation properties. The retrieved rain rate from all three methods shows good agreement with in‐situ aircraft estimates, with rain rates typically being quite light (<0.1 mm hr⁻¹). We examine the vertical distribution of precipitation properties, and find that rain rate, precipitation number concentration, and precipitation liquid water all decrease as one gets closer to the surface, while precipitation size and distribution width increases. We also examine how cloud base rain rate (R_CB) depends on cloud depth (H) and aerosol concentration (N_a) for particles with a diameter greater than 70 nm, and find thatR_CBis proportional to . 

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2. A CloudSat and CALIPSO‐Based Evaluation of the Effects of Thermodynamic Instability and Aerosol Loading on Amazon Basin Deep Convection and Lightning

   https://doi.org/10.1029/2023JD039818  

   Allen, Dale; Pickering, Kenneth; Avery, Melody; Li, Zhanqing; Shan, Siyu; Morales Rodriguez, Carlos Augusto; Artaxo, Paulo (February 2024, Journal of Geophysical Research: Atmospheres)

   Abstract The Amazon Basin, which plays a critical role in the carbon and water cycle, is under stress due to changes in climate, agricultural practices, and deforestation. The effects of thermodynamic and microphysical forcing on the strength of thunderstorms in the Basin (75–45°W, 0–15°S) were examined during the pre‐monsoon season (mid‐August through mid‐December), a period with large variations in aerosols, intense convective storms, and plentiful flashes. The analysis used measurements of radar reflectivity, ice water content (IWC), and aerosol type from instruments aboard the CloudSat and CALIPSO satellites, flash rates from the ground‐based Sferics Timing and Ranging Network, and total aerosol optical depth (AOD) from a surface network and a meteorological re‐analysis. After controlling for convective available potential energy (CAPE), it was found that thunderstorms that developed under dirty (high‐AOD) conditions were 1.5 km deeper, had 50% more IWC, and more than two times as many flashes as storms that developed under clean conditions. The sensitivity of flashes to AOD was largest for low values of CAPE where increases of more than a factor of three were observed. The additional ice water indicated that these deeper systems had higher vertical velocities and more condensation nuclei capable of sustaining higher concentrations of water and large hydrometeors in the upper troposphere. Flash rates were also found to be larger during periods when smoke rather than dust was common in the lower troposphere, likely because smoky periods were less stable due to higher values of CAPE and AOD and lower values of mid‐tropospheric relative humidity. 

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3. On the Radar Detection of Cloud Seeding Effects in Wintertime Orographic Cloud Systems

   https://doi.org/10.1175/JAMC-D-22-0154.1  

   Zaremba, Troy J.; Rauber, Robert M.; Girolamo, Larry Di; Loveridge, Jesse R.; McFarquhar, Greg M. (January 2024, Journal of Applied Meteorology and Climatology)

   Abstract Recent studies from the Seeded and Natural Orographic Wintertime Clouds: The Idaho Experiment (SNOWIE) demonstrated definitive radar evidence of seeding signatures in winter orographic clouds during three intensive operation periods (IOPs) where the background signal from natural precipitation was weak and a radar signal attributable to seeding could be identified as traceable seeding lines. Except for the three IOPs where seeding was detected, background natural snowfall was present during seeding operations and no clear seeding signatures were detected. This paper provides a quantitative analysis to assess if orographic cloud seeding effects are detectable using radar when background precipitation is present. We show that a 5-dB change in equivalent reflectivity factorZ_eis required to stand out against background naturalZ_evariability. This analysis considers four radar wavelengths, a range of background ice water contents (IWC) from 0.012 to 1.214 g m⁻³, and additional IWC introduced by seeding ranging from 0.012 to 0.486 g m⁻³. The upper-limit values of seeded IWC are based on measurements of IWC from the Nevzorov probe employed on the University of Wyoming King Air aircraft during SNOWIE. This analysis implies that seeding effects will be undetectable using radar within background snowfall unless the background IWC is small, and the seeding effects are large. It therefore remains uncertain whether seeding had no effect on cloud microstructure, and therefore produced no signature on radar, or whether seeding did have an effect, but that effect was undetectable against the background reflectivity associated with naturally produced precipitation. Significance StatementOperational glaciogenic seeding programs targeting wintertime orographic clouds are funded by a range of stakeholders to increase snowpack. Glaciogenic seeding signatures have been observed by radar when natural background snowfall is weak but never when heavy background precipitation was present. This analysis quantitatively shows that seeding effects will be undetectable using radar reflectivity under conditions of background snowfall unless the background snowfall is weak, and the seeding effects are large. It therefore remains uncertain whether seeding had no effect on cloud microstructure, and therefore produced no signature on radar, or whether seeding did have an effect, but that effect was undetectable against the background reflectivity associated with naturally produced precipitation. Alternative assessment methods such as trace element analysis in snow, aircraft measurements, precipitation measurements, and modeling should be used to determine the efficacy of orographic cloud seeding when heavy background precipitation is present. 

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4. Microphysical and Kinematic Characteristics of Anomalous Charge Structure Thunderstorms in Cordoba, Argentina

   https://doi.org/10.3390/atmos13081329  

   Medina, Bruno; Carey, Lawrence; Deierling, Wiebke; Lang, Timothy (August 2022, Atmosphere)

   Some thunderstorms in Cordoba, Argentina, present a charge structure with an enhanced low-level positive charge layer, and practically nonexistent upper-level positive charge. Storms with these characteristics are uncommon in the United States, even when considering regions with a high frequency of anomalous charge structure storms such as Colorado. In this study, we explored the microphysical and kinematic conditions inferred by radar that led to storms with this unique low-level anomalous charge structure in Argentina, and compared them to conditions conducive for anomalous and normal charge structures. As high liquid water contents in the mixed-phase layer lead to positive charging of graupel and anomalous storms through the non-inductive charging mechanism, we explored radar parameters hypothesized to be associated with large cloud supercooled liquid water contents in the mixed-phase layer and anomalous storms, such as mass and volume of hail and high-density graupel, large reflectivity associated with the growth of rimed precipitation to hail size, and parameters that are proxies for strong updrafts such as echo-top and Zdr column heights. We found that anomalous storms had higher values of mass and volume of hail in multiple sub-layers of the mixed-phase zone and higher frequency of high reflectivity values. Low-level anomalous events had higher hail mass in the lower portion of the mixed-phase zone when compared to normal events. Weaker updraft proxies were found for low-level anomalous events due to the shallow nature of these events while there was no distinction between the updraft proxies of normal and anomalous storms. 

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5. Estimating Ice Water Content for Winter Storms from Millimeter-Wavelength Radar Measurements Using a Synthesis of Polarimetric and Dual-Frequency Radar Observations

   https://doi.org/10.1175/JTECH-D-23-0143.1  

   Oue, Mariko; Ryzhkov, Alexander V; Matrosov, Sergey Y; Bukovčić, Petar; Kollias, Pavlos (January 2025, Journal of Atmospheric and Oceanic Technology)

   Abstract The potential of millimeter-wavelength radar-based ice water content (IWC) estimation is demonstrated using a Ka-band Scanning Polarimetric Radar (KASPR) for the U.S. northeast coast winter storms. Two IWC relations for Ka-band polarimetric radar measurements are proposed: one that uses a combination of the radar reflectivityZand the estimated total number concentration of snow particlesN_tand the other based on the joint use ofZ, specific differential phaseK_DP, and the degree of rimingf_rim. A key element of the algorithms is to obtain the “Rayleigh-equivalent” value ofZmeasured at the Ka band, i.e., the correspondingZat a longer radar wavelength for which Rayleigh scattering takes place. This is achieved via polarimetric retrieval of the mean volume diameterD_mand incorporating the relationship between the dual-wavelength ratio DWR_S/KaandD_m. Those techniques allow for retrievals from single millimeter-wavelength radar measurements and do not necessarily require the dual-wavelength ratio (DWR) measurements, if the DWR–D_mrelation and Rayleigh assumption for Ka-bandK_DPare valid. Comparison between the quasivertical profile product obtained from KASPR and the columnar vertical profile product generated from the nearby WSR-88D S-band radar measurements demonstrates that the DWR_S/Kacan be estimated from the two close radars without the need for collocated radar beams and synchronized antenna scanning and can be used for determining the Rayleigh-equivalent value ofZ. The performance of the suggested techniques is evaluated for seven winter storms using surface disdrometer and snow accumulation measurements. Significance StatementIce water content (IWC) estimation using millimeter-wavelength radar measurements has been challenging for decades, because of the complexity of snow particle properties and size, which can cause complex scattering at the shorter radar wavelengths. The suggested polarimetric techniques overcome this difficulty via utilizing specific differential phaseK_DPwhich is higher at millimeter wavelengths than at centimeter wavelengths. This study proposes new IWC relationships for Ka-band polarimetric radar measurements and evaluates them using a Ka-band Scanning Polarimetric Radar (KASPR) and a nearby NEXRAD (S-band) polarimetric radar for the U.S. northeast coast winter storms. The proposed techniques can be applied to other millimeter-wavelength radars and shed light on the millimeter-wavelength polarimetric radar IWC estimation. 

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