Classification of hydrometeors based on polarimetric radar measurements: development of fuzzy logic and neuro-fuzzy systems, and in situ verification

Includes bibliographical references (page 164).A fuzzy logic and neuro-fuzzy system for classification of hydrometeor type based on polarimetric radar measurements is described in this paper. The hydrometeor classification system is implemented by using fuzzy logic and a neural network, where the fuzzy logic is used to infer hydrometeor type, and the neural network learning algorithm is used for automatic adjustment of the parameters of the fuzzy sets in the fuzzy logic system according to prior knowledge. Five radar measurements, namely, horizontal reflectivity (ZH), differential reflectivity (ZDR), differential propagation phase shift (KDP), correlation coefficient [ρHV(0)], and linear depolarizationratio (LDR), and corresponding altitude, have been used as input variables to the neuro-fuzzy network. The output of the neuro-fuzzy system is one of the many possible hydrometeor types: 1) drizzle, 2) rain, 3) dry and low density snow, 4) dry and high-density crystals, 5) wet and melting snow, 6) dry graupel, 7) wet graupel, 8)small hail, 9) large hail, and 10) a mixture of rain and hail. The neuro-fuzzy classifier is more advantageous than a simple neural network or a fuzzy logic classifier because it is more transparent (instead of a "black box") and can learn the parameter of the system from the past data (unlike a fuzzy logic system). The hydrometeor classifier has been applied to several case studies and the results are compared against in situ observations

Annual report for the CSU-CHILL radar facility

Submitted to the National Science Foundation, Division of Atmospheric Sciences.1 February 1994.Cooperative agreement no. ATM-8919080

Relationships between kinematics, microphysics, and lightning in high plains storms observed during the severe thunderstorm electrification and precipitation study

Summer 2006.Includes bibliographical references (pages 168-169).The Severe Thunderstorm Electrification and Precipitation Study (STEPS) was established to improve our understanding of electrification mechanisms and lightning in High Plains storms. In particular, STEPS focused on investigating anomalous positive cloud-to-ground (CG) lightning, which had been documented to occur more often in this region than in the rest of the U.S. Radar and lightning observations of four storms observed during the STEPS field campaign are analyzed and discussed. The four cases include a predominantly positive CG-producing (PPCG) supercell on 29 June, a supercell on 3 June that produced no CG lightning of either polarity, a negative CG-producing multicellular storm on 19 June, and a PPCG multicellular storm on 22 June. Data from multiple Doppler radars have been synthesized to calculate the three-dimensional wind field, polarimetric radar variables have been combined with thermodynamic soundings to estimate hydrometeor types throughout the echo volumes, and Lightning Mapping Array (LMA) data have been sorted into flashes and studied to determine the flash rates and charge structure for several hours of each storm's lifetime. The purpose of this study is to determine what features are unique for storms that produce predominantly positive CG lightning, and attempt to reveal the processes that lead to this behavior. The 29 June supercell produced large amounts of hail and frequent positive CG lightning, as well as exhibited a large volume of strong (> 10 m S-1) updraft and a deep region of cyclonic vertical vorticity. The charge structure of the 29 June supercell was inverted, with a main region of positive charge centered near 8 km MSL with a negative charge layer above and below. The inferred charge structure in the 3 June case consisted of an inverted dipole, with positive charge beneath upper-level negative charge. A lower negative charge layer was not detected in 3 June and may have been the reason for the lack of CG lightning. This case produced some hail, but not as much hail volume as 29 June, and the updraft volume and cyclonic vertical vorticity were dramatically lower as well. The 19 June multicellular storm exhibited a normal charge structure, with main negative charge centered at 7 km MSL, and positive charge layers above and below, and therefore produced mostly negative CG lightning. The storm produced negligible hail, and had very weak and shallow updrafts, yielding near zero values of strong updraft volume. The 22 June multicellular storm exhibited both inverted and normal charge structures in different regions of the storm complex. The volume of strong updraft was very high, similar to that of 29 June, and the storm produced ample amounts of hail. Both positive and negative CG lightning was observed in this storm complex, but the majority of the CG lightning was of positive polarity. The results indicate that PPCG storms tend to have larger updrafts (both wider and larger in volume), which is consistent with previous studies. Large updrafts and enhanced vertical vorticity also play an important role in the production of large hail. Furthermore, low-level negative charge (below a larger region of positive charge) was observed in the cases that produced positive CG lightning, which may be the impetus needed for the flash to come to ground. This lower negative charge, in essence, represents the lowest charge layer of an inverted tripolar charge structure. The charge structures observed during the production of negative CG lightning were a normal tripole (with negative charge situated between upper and lower positive charge layers) on 19June and an inverted dipole (with negative charge above positive) in the anvil on 22 June. Cloud-to-ground flash rates (of either polarity) decreased when either the lower charge layer of the corresponding tripolar structure was absent, or when the low-level charge layer exhibited an enhanced number of LMA sources, in which case intra-cloud (IC) discharges seemed to be preferred between the two lowest charge layers of the tripole

Kinematic and microphysical evolution of the 29 June supercell observed during STEPS

Spring 2003.Also issued as Sarah A. Tessendorf's thesis (M.S.) -- Colorado State University, 2003.Includes bibliographical references.The focus of this thesis is to examine the kinematic and microphysical properties of a severe storm using polarimetric and Doppler radar data. The data were collected during the Severe Thunderstorm Electrification and Precipitation Study (STEPS) that took place between 17 May 2000 and 20 July 2000 in eastern Colorado and western Kansas. One goal of STEPS is to find a relationship between the microphysics and kinematics of severe storms on the High Plains and their unusual positive cloud-to­ ground lightning production. The severe storm observed on 29 June 2000 produced large hail, frequent positive cloud-to-ground lightning, an F1 tornado, and displayed characteristic storm splitting evolution during the sampling period. Unprecedented measurements from three Doppler radars were used to describe the kinematics and rnicrophysics of this storm. Radial components of the wind fields relative to the three Doppler radars were combined to produce the three-dimensional winds in the storm. Bulk precipitation types (e.g., rain, hail) were objectively determined using the multi­ parameter variables available on two of the radars. The Doppler-derived kinematic fields were compared with the microphysical classifications over a nearly three-hour period to examine trends during the lifecycle of the supercell. Results showed that the supercell intensified rapidly while storm splitting occurred. Prior to splitting, there was little cloud-to-ground lightning and little evidence of hail aloft. After storm splitting. hail volume and cloud-to-ground lightning activity quickly intensified. The updraft of this storm pulsated, with maximum speeds to nearly 50 m s·1. The peaks in hail production aloft, largely around -10° C, were well correlated with the updraft fluctuations as well as with peaks in the frequency of positive cloud-to­ ground lightning flashes. These results are consistent with experimental work that shows positive charging in ice-ice collisions around -10° C. The dynamics of the storm-splitting process, in terms of radar-derived updraft and vorticity fields, were shown to be consistent with current conceptual models. The results of this thesis advance our knowledge of supercell evolution and will be used to help determine the electrification mechanisms of severe storms that produce predominantly positive cloud-to-ground lightning.Sponsored by the National Science Foundation under grant ATM-9912051

Investigations of the uncertainties associated with HID algorithms and guiding input to a novel, synthetic polarimetric radar simulator

2018 Spring.Includes bibliographical references.A methodology for model evaluation against observations is presented. With the advent of polarimetric radars, the need to produce simulated radar observables from model has also become apparent, in order to directly compare the same quantities between observations and models (e.g. rain rate calculations, hydrometeor identification - HID). To the end of evaluating model performance, for both a spectral bin microphysics (SBM) scheme and bulk microphysics scheme (BMS), a novel, synthetic polarimetric radar simulator created by Matsui et al. (2017) was implemented in this study: POLArimetric Radar Retrieval and Instrument Simulator (POLARRIS). POLARRIS takes in model data and simulates polarimetric radar variables in the forward component (POLARRIS-f), and then the inverse component of POLARRIS (iPOLARRIS) utilizes retrieval algorithms that are also employed in observations to make direct 1-to-1 comparisons between model simulations and observations. This inverse component is novel in its ability to help bridge the gap between model output and observations due to the fact that model output and observations without this framework are not directly comparable. The simulation of ice hydrometeors is not straightforward, and several assumptions are required to create polarimetric data for these species, such as the assumption of the size distribution, particle densities, particle melting, the input axis ratio, and canting angle assumptions. The last two variables are notoriously difficult to pin down for ice hydrometeors. This work aims to narrow down the appropriate inputs for axis ratio and canting angle assumptions that create the most comparable results with observations for three ice hydrometeors: aggregates, ice crystals, and graupel for two different meteorological regimes (mid-latitude supercell and tropical, monsoon MCS). Rain was also carried through as a check on model output. Through various sensitivity tests, it was concluded that, when run through the range of potential values, changes in axis ratio had a larger impact on the resulting polarimetric data than did changes in the canting angle assumptions. With this in mind, the 18 Z integrated hour from the 23 January 2006 monsoon MCS TWP – ICE case and the 22 Z integrated hour mid-latitude supercell from the 23 May 2011 MC3E case were simulated to help determine, for each hydrometeor type, the most appropriate axis ratio value(s) and canting angle assumptions that produced comparable results with observations. It was found using co-variance plots that, for 4ICE, the use of a singular axis ratio, mean canting angle, and degree of particle tumbling often produced differential reflectivity and specific differential phase values that converged to one value. While these values were within the observed values, they did not manage to simulate the breadth of observed values. Reflectivity values were also much too low compared to observations. SBM results, regardless of the type of input assumptions, tended to produce broader ranges for these variables, and also managed to better capture the reflectivity range seen in observations than was the case for the BMS. However, the reflectivity ranges seen in SBM were at times too expansive. The differences between SBM output and BMS output is likely due to the differing inherent assumptions in each microphysical scheme. The sensitivity of the simulated hydrometeors' polarimetric data was also probed against changing axis ratio and canting angle input assumptions. It was found that, in particular, BMS differential reflectivity values were quite sensitive to changes in input assumptions, regardless of the regime (tropical MCS vs. mid-latitude supercell). HID was found to be the most effective method to evaluate the performance of the two different model microphysical schemes (SBM vs. BMS) with respect to observations. Input assumptions that produced the most comparable results with respect to observations for each hydrometeor were compared using HID stacked frequency by altitude (SFAD) diagrams for convective and stratiform precipitation. This analysis found that although the co-variance plots revealed many model shortcomings, the HID proved to be fairly robust, especially for MC3E. The sensitivity of the HID retrieval itself was also investigated with respect to changing inputs (i.e. the membership beta functions) to the HID algorithm. The resulting HID was fairly sensitive to changes in the inputs to HID, particularly for model simulations. Observations seemed less responsive to changes in these input assumptions to HID. Longer simulation time frames, the potential inclusion of simulated melting hydrometeors, and investigation of other radar wavelengths are all suggested to help further utilize this methodology for evaluating model microphysical schemes' abilities to accurately simulate polarimetric data and HID retrievals with respect to observations

Relationship between storm structure and lightning activity in Colorado convection observed during STERO-A

November 1997.Includes bibliographical references.Concurrent measurements from the CSU-CHILL multiparameter Doppler radar, the ONERA VHF lightning interferometer, and the National Lightning Detection Network, obtained during Phase A of the Stratosphere-Troposphere Experiments: Radiation, Aerosols, Ozone (STERAO-A) field project, provided a unique data set with which to study the relationships between convective storm microphysics and associated lightning. Two events have been examined in detail: storms of 10 and 12 July 1996. Both storms underwent major organizational transitions during their lifetimes, identified by sharp changes in total lightning flash rates, dominant cloud-to-ground (CG) flash polarity, or dominant flash type (cloud-to-ground vs. intra-cloud). Both storms also featured relatively high intra-cloud (IC) flash rates. The 10 July 1996·storm evolved from a multicellular line to an intense unicellular storm. The unicellular stage was marked by a sharp peak in IC flash rate as identified by the interferometer. Cloud-to-ground flash rates were low throughout the storm’s lifetime. Small hail was produced during the entire observation period, suggesting storm updraft speeds were significant. The storm of 12 July evolved from an intense multicellular, hail­ producing storm to a weaker rainstorm. Before this transition, hail was being produced and the CG flash rates were low. After the transition, hail was no longer being produced and negative CG flash rates were significantly larger. Storm updraft speeds likely weakened during the transition. These observations are consistent with the elevated-dipole hypothesis to explain low CG production in convective storms, especially if the observed high IC flash rates mostly neutralized any charged core before it descended toward the ground. Alternatively, if significant charging does not occur during wet growth of hail and graupel, both these storms might have produced enough wet-growth ice to prevent the generation of a lower positive charge center that could act to stimulate CG production. However, the radar data, in particular the linear depolarization ratio (LOR) data, suggest that dry growth was more prevalent than wet growth.Sponsored by the National Science Foundation under grant ATM-9321361

Integrated display and analysis tool for multi-variable radar data

Fall 2004.Also issued as author's thesis (M.S.) -- Colorado State University, 2005.Includes bibliographical references.Doppler and polarimetric radars provide valuable information about the kinematics and microphysics of storms. However, radar products, such as Doppler­ derived wind vectors and hydrometeor identification, which assist with in-depth analysis of storms, have not been readily available in (near) real-time. The goal of this project is to develop and integrate radar algorithms currently used in post¬ processing with meteorological observations to develop a near real-time integrated display and analysis tool for use in nowcasting. This software has been linked to and is now available for real-time radar operations at the CSU-CHILL radar facility. This methodology was also developed for a network of four Doppler radars, including one polarimetric radar, along the Northern Colorado front range. The four radars include two National Weather Service WSR-88D radars (KFTG and KCYS) and two research radars (PAWNEE and CSU-CHILL) operated by Colorado State University. These four radars form three dual-Doppler pairs, in which the radial velocities can be synthesized to obtain three-dimensional wind vectors. The analysis also incorporates algorithms for hydrometeor identification and rainfall rate estimation using the polarimetric measurements from CSU-CHILL, as well as ram rate calculation using standard midlatitude Z-R relationships. The software was successfully tested at the CSU-CHILL radar facility during the summer of 2004 using data from three of the radars. CHILL data were available within 3 minutes after a volume scan, WSR-88D was displayed approximately 12 minutes after the start of a volume scan, therefore the dual-Doppler winds lagged by 13-15 minutes after the start of the first volume scan. Among other things, users have the ability to zoom in and out of interesting radar features, change the grid resolution and origin, create vertical cross sections, contour data, and archive data as they use the software in real-time. Despite the lag time, the tool helped diagnose areas of intense rainfall and possible hail, updrafts, and wind field features such as mesocyclones and convergence lines. Two case studies from June 2004 are used to demonstrate the utility of the software in this thesis. The software was found to be a valuable resource for assisting scientists with the real-time analysis and visualization of copious amounts of data from a network of multi-variable radars. This tool could be especially useful during large field experiments, especially those in which one research aircraft requires guidance from ground-based radars.Sponsored by the National Science Foundation under grant ATM-0121546 and award no. 0313747

Observations of winter storms with a video disdrometer and polarimetric radar

Spring 2007.Includes bibliographical references (pages 104-110).With efforts to upgrade the operational NEXRAD radars to include polarimetric capability underway, there are growing interests in developing radar-based algorithms for classifying hydrometeor types, quantifying winter precipitation, and improving the parameterization of winter precipitation in numerical forecast models. The capabilities of polarimetric radars, such as to better quantify warm season precipitation, have been demonstrated in various studies. However, these tasks are further complicated for winter precipitation by the need to know hydrometeor phase and bulk density of ice particles. In this study, data collected with a two-dimensional video disdrometer and S-band dual polarization radar during the Winter Icing and Storms Project 2004 (WISP04) storms are examined in support of ongoing research to develop radar-based algorithms for cold season precipitation. The capability to match radar-measured and disdrometer-based calculations of radar reflectivity factor and differential reflectivity is essential for retrieving hydrometeor characteristics with radar. During the WISP04, the disdrometer provided detailed information regarding hydrometeor size, number concentration, terminal velocity, and shape during the precipitation events. In this study, bulk ice particle density is estimated using an empirical relationship derived from disdrometer measurements of precipitation volume and rain gauge measurements of precipitation mass. Reflectivity and differential reflectivity, as measured by radar and computed from disdrometer observations are compared, and the combined dataset is used to examine storm microphysical properties. The measurements and computed values show good agreement and reveal that the radar detected subtle changes in the characteristics of winter precipitation. Additionally, sensitivity of the scattering computations to assumed ice particle characteristics is examined, and particle size distributions from radar measurements are retrieved for comparisons with the disdrometer observations

Multi-sensor analysis of convective activity in central Italy during the HyMeX SOP 1.1

Abstract. A multi-sensor analysis of convective precipitation events that occurred in central Italy in autumn 2012 during the HyMeX (Hydrological cycle in the Mediterranean experiment) Special Observation Period (SOP) 1.1 is presented. Various microphysical properties of liquid and solid hydrometeors are examined to assess their relationship with lightning activity. The instrumentation used consisted of a C-band dual-polarization weather radar, a 2-D video disdrometer, and the LINET lightning network. Results of T-matrix simulation for graupel were used to (i) tune a fuzzy logic hydrometeor classification algorithm based on Liu and Chandrasekar (2000) for the detection of graupel from C-band dual-polarization radar measurements and (ii) to retrieve graupel ice water content. Graupel mass from radar measurements was related to lightning activity. Three significant case studies were analyzed and linear relations between the total mass of graupel and number of LINET strokes were found with different slopes depending on the nature of the convective event (such as updraft strength and freezing level height) and the radar observational geometry. A high coefficient of determination (R2 = 0.856) and a slope in agreement with satellite measurements and model results for one of the case studies (15 October 2012) were found. Results confirm that one of the key features in the electrical charging of convective clouds is the ice content, although it is not the only one. Parameters of the gamma raindrop size distribution measured by a 2-D video disdrometer revealed the transition from a convective to a stratiform regime. The raindrop size spectra measured by a 2-D video disdrometer were used to partition rain into stratiform and convective classes. These results are further analyzed in relation to radar measurements and to the number of strokes. Lightning activity was not always recorded when the precipitation regime was classified as convective rain. High statistical scores were found for relationships relating lightning activity to graupel aloft

A comparison of X-band polarization parameters with in-situ microphysical measurements in the comma head of two winter cyclones

Since the advent of dual-polarization radar, methods of classifying hydrometeors by type from measured polarization variables have been developed. However, the deterministic approach of existing hydrometeor classification algorithms of assigning only one dominant habit to each volume does not properly consider the distribution of habits present in that volume. During the Profiling of Winter Storms (PLOWS) field campaign the NSF/NCAR C-130 aircraft, equipped with in-situ microphysical probes, made multiple passes through the comma head of two cyclones as the Mobile Alabama X-band (MAX) dual-polarization radar performed range-height indicator scans in the same plane as the C-130 flight track. On 14-15 February and 21-22 February 2010, 579 and 202 coincident data points, respectively, were identified when the plane was within 10 s (~1 km) of a radar gate. Using the axis ratio (α), sphericity (β), maximum dimension D, and projected area A of the in-situ imaged crystals, the habit of each particle was identified. For all particles that occurred for times within different binned intervals of radar reflectivity (ZHH) and of differential reflectivity (ZDR), the reflectivity-weighted contribution of each habit, and the frequency distributions of α and β were determined. Habits with less circular shapes (bullet rosettes and aggregates) had greater contributions to the reflectivity compared to other habits when ZHH > 7 dBZ and ZDR > 2 dB. The presence of bullet rosettes and aggregates for similar ZHH and ZDR supports previous studies that bullet rosettes are the favored crystal species for aggregate formation. While irregular particles made up 40% of the observed shapes, only 55% of the ZHH-ZDR bins had irregular particles contribute over 40% of the reflectivity. Additionally, over 88% of the bins did not have a single habit contribute over 75% to the reflectivity. These findings show the general lack of dominance of a given habit for a particular ZHH and ZDR, and suggest that determining the probability of specific habits in radar volumes may be more suitable than the deterministic methods currently used