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1. First Light Multi-Frequency Observations with a G-band radar

   Lamer, K. ; Oue, M. ; Battaglia, A. ; Roy, R. J. ; Cooper, K. B. ; Dhillon, R. ; and Kollias, P. ( December 2020 , Atmospheric measurement techniques)

   Kneifel, Stefan (Ed.)

   Observations collected during the 25-February-2020 deployment of the Vapor In-Cloud Profiling Radar at the Stony Brook Radar Observatory clearly demonstrate the potential of G-band radars for cloud and precipitation research, something that until now was only discussed in theory. The field experiment, which coordinated an X-, Ka, W- and G-band radar, revealed that the Ka-G pairing can generate differential reflectivity signal several decibels larger than the traditional Ka-W pairing underpinning an increased sensitivity to smaller amounts of liquid and ice water mass and sizes. The observations also showed that G-band signals experience non-Rayleigh scattering in regions where Ka- and W-band signal don’t, thus demonstrating the potential of G-band radars for sizing sub-millimeter ice crystals and droplets. Observed peculiar radar reflectivity patterns also suggest that G-band radars could be used to gain insight into the melting behavior of small ice crystals. G-band signal interpretation is challenging because attenuation and non-Rayleigh effects are typically intertwined. An ideal liquid-free period allowed us to use triple frequency Ka-W-G observations to test existing ice scattering libraries and the results raise questions on their comprehensiveness. Overall, this work reinforces the importance of deploying radars with 1) sensitivity sufficient to detect small Rayleigh scatters at cloud top in order to derive estimates of path integrated hydrometeor attenuation, a key constraint for microphysical retrievals, 2) sensitivity sufficient to overcome liquid attenuation, to reveal the larger differential signals generated from using G-band as part of a multifrequency deployment, and 3) capable of monitoring atmospheric gases to reduce related uncertainty 

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2. Precipitation Growth Processes in the Comma-Head Region of the 7 February 2020 Northeast Snowstorm: Results from IMPACTS

   https://doi.org/10.1175/JAS-D-22-0118.1  

   Varcie, Megan M. ; Zaremba, Troy J. ; Rauber, Robert M. ; McFarquhar, Greg M. ; Finlon, Joseph A. ; McMurdie, Lynn A. ; Ryzhkov, Alexander ; Schnaiter, Martin ; Järvinen, Emma ; Waitz, Fritz ; et al ( January 2023 , Journal of the Atmospheric Sciences)

   Abstract On 7 February 2020, precipitation within the comma-head region of an extratropical cyclone was sampled remotely and in situ by two research aircraft, providing a vertical cross section of microphysical observations and fine-scale radar measurements. The sampled region was stratified vertically by distinct temperature layers and horizontally into a stratiform region on the west side, and a region of elevated convection on the east side. In the stratiform region, precipitation formed near cloud top as side-plane, polycrystalline, and platelike particles. These habits occurred through cloud depth, implying that the cloud-top region was the primary source of particles. Almost no supercooled water was present. The ice water content within the stratiform region showed an overall increase with depth between the aircraft flight levels, while the total number concentration slightly decreased, consistent with growth by vapor deposition and aggregation. In the convective region, new particle habits were observed within each temperature-defined layer along with detectable amounts of supercooled water, implying that ice particle formation occurred in several layers. Total number concentration decreased from cloud top to the −8°C level, consistent with particle aggregation. At temperatures > −8°C, ice particle concentrations in some regions increased to >100 L −1 , suggesting secondary ice production occurred at lower altitudes. WSR-88D reflectivity composites during the sampling period showed a weak, loosely organized banded feature. The band, evident on earlier flight legs, was consistent with enhanced vertical motion associated with frontogenesis, and at least partial melting of ice particles near the surface. A conceptual model of precipitation growth processes within the comma head is presented. Significance Statement Snowstorms over the northeast United States have major impacts on travel, power availability, and commerce. The processes by which snow forms in winter storms over this region are complex and their snowfall totals are hard to forecast accurately because of a poor understanding of the microphysical processes within the clouds composing the storms. This paper presents a case study from the NASA IMPACTS field campaign that involved two aircraft sampling the storm simultaneously with radars, and probes that measure the microphysical properties within the storm. The paper examines how variations in stability and frontal structure influence the microphysical evolution of ice particles as they fall from cloud top to the surface within the storm. 

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3. Radar Retrieval Evaluation and Investigation of Dendritic Growth Layer Polarimetric Signatures in a Winter Storm

   https://doi.org/10.1175/JAMC-D-21-0220.1  

   Dunnavan, Edwin L. ; Carlin, Jacob T. ; Hu, Jiaxi ; Bukovčić, Petar ; Ryzhkov, Alexander V. ; McFarquhar, Greg M. ; Finlon, Joseph A. ; Matrosov, Sergey Y. ; Delene, David J. ( November 2022 , Journal of Applied Meteorology and Climatology)

   Abstract This study evaluates ice particle size distribution and aspect ratio φ Multi-Radar Multi-Sensor (MRMS) dual-polarization radar retrievals through a direct comparison with two legs of observational aircraft data obtained during a winter storm case from the Investigation of Microphysics and Precipitation for Atlantic Coast-Threatening Snowstorms (IMPACTS) campaign. In situ cloud probes, satellite, and MRMS observations illustrate that the often-observed K dp and Z DR enhancement regions in the dendritic growth layer can either indicate a local number concentration increase of dry ice particles or the presence of ice particles mixed with a significant number of supercooled liquid droplets. Relative to in situ measurements, MRMS retrievals on average underestimated mean volume diameters by 50% and overestimated number concentrations by over 100%. IWC retrievals using Z DR and K dp within the dendritic growth layer were minimally biased relative to in situ calculations where retrievals yielded −2% median relative error for the entire aircraft leg. Incorporating φ retrievals decreased both the magnitude and spread of polarimetric retrievals below the dendritic growth layer. While φ radar retrievals suggest that observed dendritic growth layer particles were nonspherical (0.1 ≤ φ ≤ 0.2), in situ projected aspect ratios, idealized numerical simulations, and habit classifications from cloud probe images suggest that the population mean φ was generally much higher. Coordinated aircraft radar reflectivity with in situ observations suggests that the MRMS systematically underestimated reflectivity and could not resolve local peaks in mean volume diameter sizes. These results highlight the need to consider particle assumptions and radar limitations when performing retrievals. significance statement Developing snow is often detectable using weather radars. Meteorologists combine these radar measurements with mathematical equations to study how snow forms in order to determine how much snow will fall. This study evaluates current methods for estimating the total number and mass, sizes, and shapes of snowflakes from radar using images of individual snowflakes taken during two aircraft legs. Radar estimates of snowflake properties were most consistent with aircraft data inside regions with prominent radar signatures. However, radar estimates of snowflake shapes were not consistent with observed shapes estimated from the snowflake images. Although additional research is needed, these results bolster understanding of snow-growth physics and uncertainties between radar measurements and snow production that can improve future snowfall forecasting. 

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4. Retrieval and Evaluation of Ice Water Content from the Airborne Wyoming Cloud Radar in Orographic Wintertime Clouds during SNOWIE

   https://doi.org/10.1175/JTECH-D-21-0085.1  

   Deng, Min ; French, Jeffrey ; Geerts, Bart ; Haimov, Samuel ; Oolman, Larry ; Plummer, Dave ; Wang, Zhien ( February 2022 , Journal of Atmospheric and Oceanic Technology)

   As part of the analysis following the Seeded and Natural Orographic Wintertime Storms (SNOWIE) project, the ice water content (IWC) in ice and mixed-phase clouds is retrieved from airborne Wyoming Cloud Radar (WCR) measurements aboard the University of Wyoming King Air (UWKA), which has a suite of integrated in situ IWC, optical array probes, and remote sensing measurements, and it provides a unique dataset for this algorithm development and evaluation. A sensitivity study with different idealized ice particle habits shows that the retrieved IWC with aggregate ice particle habit agrees the best with the in situ measurement, especially in ice or ice-dominated mixed-phase clouds with a correlation coefficient (rr) of 0.91 and a bias of close to 0. For mixed-phase clouds with ice fraction ratio less than 0.8, the variances of IWC estimates increase (rr = 0.76) and the retrieved mean IWC is larger than in situ IWC by a factor of 2. This is found to be related to the uncertainty of in situ measurements, the large cloud inhomogeneity, and the retrieval assumption uncertainty. The simulated reflectivity Ze and IWC relationships assuming three idealized ice particle habits and measured particle size distributions show that hexagonal columns with the same Ze have a lower IWC than aggregates, whose Ze–IWC relation is more consistent with the observed WCR Ze and in situ IWC relation in those clouds. The 2D stereo probe (2DS) images also indicate that ice particle habit transition occurs in orographic mixed-phase clouds; hence, the retrieved IWC assuming modified gamma particle size distribution (PSD) of aggregate particles tends to have a greater bias in this kind of clouds.

    

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5. Evaluation of ARM tethered-balloon system instrumentation for supercooled liquid water and distributed temperature sensing in mixed-phase Arctic clouds

   https://doi.org/10.5194/amt-12-6845-2019  

   Dexheimer, Darielle ; Airey, Martin ; Roesler, Erika ; Longbottom, Casey ; Nicoll, Keri ; Kneifel, Stefan ; Mei, Fan ; Harrison, R. Giles ; Marlton, Graeme ; Williams, Paul D. ( January 2019 , Atmospheric Measurement Techniques)

   Abstract. A tethered-balloon system (TBS) has been developed and is beingoperated by Sandia National Laboratories (SNL) on behalf of the U.S.Department of Energy's (DOE) Atmospheric Radiation Measurement (ARM) UserFacility in order to collect in situ atmospheric measurements withinmixed-phase Arctic clouds. Periodic tethered-balloon flights have beenconducted since 2015 within restricted airspace at ARM's Advanced MobileFacility 3 (AMF3) in Oliktok Point, Alaska, as part of the AALCO (AerialAssessment of Liquid in Clouds at Oliktok), ERASMUS (Evaluation of RoutineAtmospheric Sounding Measurements using Unmanned Systems), and POPEYE(Profiling at Oliktok Point to Enhance YOPP Experiments) field campaigns. Thetethered-balloon system uses helium-filled 34 m3 helikites and 79 and104 m3 aerostats to suspend instrumentation that is used to measureaerosol particle size distributions, temperature, horizontal wind, pressure,relative humidity, turbulence, and cloud particle properties and tocalibrate ground-based remote sensing instruments. Supercooled liquid water content (SLWC) sondes using the vibrating-wireprinciple, developed by Anasphere Inc., were operated at Oliktok Point atmultiple altitudes on the TBS within mixed-phase clouds for over 200 h.Sonde-collected SLWC data were compared with liquid water content derivedfrom a microwave radiometer, Ka-band ARM zenith radar, and ceilometer at the AMF3, as well as liquid water content derived from AMF3 radiosonde flights. The in situ data collected by the Anasphere sensors were also compared with data collected simultaneously by an alternative SLWC sensor developed at the University of Reading, UK; both vibrating-wire instruments were typically observed to shed their ice quickly upon exiting the cloud or reaching maximum ice loading. Temperature sensing measurements distributed with fiber optic tethered balloons were also compared with AMF3 radiosonde temperature measurements. Combined, the results indicate that TBS-distributedtemperature sensing and supercooled liquid water measurements are inreasonably good agreement with remote sensing and radiosonde-basedmeasurements of both properties. From these measurements and sensorevaluations, tethered-balloon flights are shown to offer an effective methodof collecting data to inform and constrain numerical models, calibrate andvalidate remote sensing instruments, and characterize the flight environmentof unmanned aircraft, circumventing the difficulties of in-cloud unmanned aircraft flights such as limited flight time and in-flight icing. 

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