Search

This study derives polarimetric radar vertical profiles and microphysical retrievals for 25 Synoptic Snow (SS) and 23 Lake Effect Snow (LES) cases using the Range‐Defined Quasi‐Vertical Profiles (RD‐QVP), Columnar Vertical Profiles (CVP), and Process‐oriented Vertical Profiles (POVP) methods. For all vertical profile techniques, SS cases exhibit a near‐linear increase in reflectivity from −30 to 0°C whereas ZDR and Kdp locally peak in the dendritic growth layer. LES cases universally exhibit negative ZDR, rather high Z, negligible Kdp, and near‐unity ρhv. Ground measurements from the past OWLeS campaign provide direct evidence that conical graupel may strongly affect these polarimetric measurements in LES bands. Aggregation efficiencies for SS cases are estimated by optimizing the theoretical number concentration (Nt) and mean volume diameter (Dm) steady‐state vertical profiles against radar‐retrieved profiles derived from 20 of the 25 synoptic storm RD‐QVPs. The median estimated aggregation efficiency is approximately 0.15 with a relatively narrow interquartile range that spans from 0.1 to just over 0.2. Values of optimized aggregation efficiencies are nearly independent of the assumed gamma distribution shape parameter. These results are used to derive temperature‐dependent, climatological steady‐state relations for vertical profiles of Nt, Dm, and liquid‐equivalent snowfall rates. These results can be used in numerical weather prediction model aggregation parameterizations and can also provide climatologically representative vertical profiles of radar and microphysical quantities. Plain Language Summary: This study documents the climatology of the vertical profiles of polarimetric radar variables and microphysical parameters in synoptic snow (SS) and lake effect snow (LES) using polarimetric radars in the U.S. The SS vertical profiles show a generally enhanced signal from cloud top to the surface and a noticeable dendritic growth layer signature near −15°C. As for LES vertical profiles, we noticed a negative ZDR pattern with strong Z and weak KDP signals. Further investigation reveals the existence of conical graupel that caused negative ZDR near ground level. This study also summarizes estimated aggregation efficiencies for the SS cases. It shows that the aggregation efficiencies are nearly independent of the commonly used gamma distribution shape parameter. Equations are derived for representing parameters and vertical profiles resulting from aggregation. The overall work from this study provides climatologically representative vertical profiles of radar and microphysical quantities, and can be used as a reference for model parameterization improvement. Key Points: Climatological vertical profiles of synoptic snow and lake effect snow are summarized using polarimetric radarsLake effect snow exhibits negative values of ZDR which are caused by conical graupelSynoptic snow aggregation efficiencies are estimated by combining radar climatology with theoretical relations [ABSTRACT FROM AUTHOR]

Accurate tracking of all components (including core, anvil, and cirrus) of deep convective systems (DCSs) throughout their lifecycle is key to quantifying their impacts on radiative forcing, especially of the anvil and cirrus. Here, a new Full‐tracking Algorithm for Convective Thunderstorm System is developed based on geostationary satellite. It successfully tracks DCSs starting from the initial core to complete dissipation of cirrus detrained from them, and integrates all the related components that split from the initial convective core into a whole DCS. Results show that more than half of the tracked DCSs experience splitting evolutions, with an average of eight sub‐cores during their lifetime. With tracking cirrus generated by DCSs, the lifetime of DCSs is lengthened by up to 10 hr, and their area is enlarged by 16% on average. Generally, long‐lived DCSs have lower cloud top temperature, greater rainfall, and larger area, with more frequent splitting evolutions than short‐lived DCSs. Additionally, DCSs always reach their peaks within 6 hr after initiation regardless of their lifetime. This paper provides a basis for further quantifying the evolution of DCS properties, their impacts on the global radiation budget, and the water cycle in the climate system. Key Points: A novel method is developed to track full components of deep convective systems (DCSs) from their initiation to total cirrus dissipationLifetime of DCSs is extended by up to 10 hr, and their area is enlarged by 16% averagely after continuously tracking their detrained cirrusIntegrated total rainfall amounts are comparably contributed between frequent but small and rare but large DCSs [ABSTRACT FROM AUTHOR]

Most existing cloud models tend to overestimate the size of cloud ice particles and underestimate their concentration. This emphasizes the need to provide a reliable observational reference to optimize cloud model performance, particularly in areas of high concentration of ice at high altitudes. The dual‐polarization radars give the community a unique opportunity to quantify cloud ice with a good accuracy using polarimetric radar retrievals. In this study, we utilize the network of operational WSR‐88D radars to build a climatology of the vertical profiles of radar variables, such as radar reflectivity Z, differential reflectivity ZDR, and specific differential phase KDP as well as the radar‐retrieved vertical profiles of ice water content (IWC) above the melting layer and liquid water content below it, mean volume diameter Dm, and total number concentration Nt of ice and liquid particles. Such climatology was created for continental/marine mesoscale convective systems (MCSs) and tropical cyclones including hurricanes. The dataset includes 13 continental MCSs, 10 marine MCSs, and 11 tropical cyclones. Separate statistics of the "background" vertical profiles and the ones associated with high IWC aloft have been obtained in the course of this study. It is shown that continental MCSs exhibit larger size of ice in lower concentration aloft compared to the marine MCSs and especially tropical cyclones/hurricanes. A combination of high KDP and low Z aloft signifies lower Dm, higher Nt, and often substantial IWC. Key Points: Climatology of the vertical profiles of polarimetric radar variables and microphysical parameters is documented for different storm typesAreas of high ice water content (IWC) in clouds are characterized by high values of specific differential phase combined with low reflectivityTropical clouds have smaller size ice in higher concentration compared to their continental counterparts with comparable IWC [ABSTRACT FROM AUTHOR]

Hypotheses have been proposed for decades about the effect of activated cloud condensation nuclei (CCN) on delaying the warm rain process, invigorating deep convective cloud vertical development, and enhancing mixed‐phase processes. Observational support has been only qualitative with mixed results due to the lack of regional measurements of CCN concentration (NCCN), while simulations have not produced a robust consensus. Quantitative assessments of these relationships became possible with the advent of NCCN retrievals from satellites; when combined with measurements by polarimetric radar and Lightning Mapping Array (LMA), tracking convective cells observed on radar and examining precipitation properties throughout the cells' life cycle has permitted the study of the impact of NCCN on cloud and precipitation characteristics. We composited more than 2,800 well‐tracked cells in the Houston region and stratified them by NCCN, convective available potential energy (CAPE), and urban/rural locations. The results show that increased NCCN invigorates the convection until saturation near NCCN = 1,000 cm3; increasing NCCN from ~400 to an optimum of ~1,000 cm3 increases lightning activity by an order of magnitude. A further increase in CCN decreases lightning rates. Adding CAPE enhances lightning only under low NCCN (e.g., less than 500 cm3). The presence of the urban area enhances lightning for similar NCCN concentrations, although this applies mainly under low NCCN conditions. The urban heat island as manifested by cloud base height cannot explain this observation. It is suspected that the urban ultrafine aerosols contribute to the storm electrification. Plain Language Summary: Deep convective clouds are propelled by rising air currents and are composed of cloud droplets that nucleate on CCN aerosols. Isolating the effects of CAPE and NCCN on cloud properties has been an unresolved challenge. Tracking the time‐height evolution of a large number of individual summer convective storm cells in the Houston area under various CAPE and NCCN shows their relations to the storm's dynamics, precipitation, and electrification processes. The results show that increased NCCN invigorates the convection, produces larger hydrometeors, and enhances lightning. Variability in NCCN was found to be more important than variability in CAPE, cloud base height, and wind shear in explaining the variability of the vigor and electrification of deep convective clouds in the study area. Key Points: Increased CCN invigorates convection, produces larger hydrometeors, and enhances lightningCCN invigoration effect saturates near NCCN = 1,000 cm3 in an environment with similar CAPECCN is more important than CAPE in explaining the variability of the vigor and electrification of storms after convection is initiated [ABSTRACT FROM AUTHOR]