Vertical Profile Of Radar Reflectivity Research Articles

Using Satellite Observations of Lightning and Precipitation to Diagnose the Behavior of Deep Convection in Tropical Cyclones Traversing the Midlatitudes

AbstractThis study uses a unique combination of geostationary and low‐Earth orbiting satellite‐based lightning and precipitation observations, respectively, to examine the evolution of deep convection during the tropical cyclone (TC) lifecycle. The study spans the 2018–2021 Atlantic Basin hurricane seasons and is unique as it provides the first known analysis of total lightning (intra‐cloud and cloud‐to‐ground) observed in TCs through their extratropical transition and post‐tropical cyclone (PTC) phases. We consider the TC lifecycle stage, geographic location (e.g., land, coast, and ocean), shear strength, and quadrant relative to the storm motion and environmental shear vectors. Total lightning maxima are found in the forward right quadrant relative to storm motion and downshear of the TC center, consistent with previous studies using mainly cloud‐to‐ground lightning. Increasing environmental shear focuses the lightning maxima to the downshear right quadrant with respect to the shear vector in tropical storm phases. Vertical profiles of radar reflectivity from the Global Precipitation Measurement mission show that super‐electrically active convective precipitation features (>75 flashes) within the PTC phase of TCs have deeper mixed phase depths and higher reflectivity at −10°C than other phases, indicating the presence of more intense convection. Differences in the net convective behavior observed throughout TC evolution manifest in both the TC‐scale frequency of lightning‐producing cells and the intensity variations amongst individual convective cells. The combination of continuous lightning observations and precipitation snapshots improves our understanding of convective‐scale processes in TCs, especially in PTC phases, as they traverse the tropics and mid‐latitudes.

Cloud Characteristics in South China Using Ka-Band Millimeter Cloud Radar Datasets

In this study, we investigate the seasonal and diurnal variations in cloud occurrence frequency, as well as cloud vertical structure (CVS) characteristics under different seasons and precipitation intensities over the Guangzhou region in South China, based on the analysis of millimeter-wave cloud radar (MMCR) and ground automatic weather station rainfall observations from May 2019 to August 2021. The results showed that the occurrence frequency of clouds exhibits a bimodal distribution throughout the year, with peaks in March to June and October, reaching its highest occurrence in May at approximately 80% and its lowest from December to February at around 40%. Additionally, there are distinct diurnal variations in occurrence frequency, with the lowest rates occurring around 0005 LST, rapidly increasing after 0006 LST, and peaking during the afternoon to evening hours. Cloud top height (CTH) shows bimodal distributions during the pre-flood and post-flood seasons. The most frequently occurring range of CTH during the pre-flood season is below 3 km, accounting for approximately 43%, while during the post-flood season, it ranges from 11 to 14 km, constituting about 37%. For precipitation clouds, CTH can extend beyond 12 km, with the radar reflectivity decreasing gradually with increasing height. The highest frequencies of radar echoes are observed below 2 km and between 4 and 7 km, exhibiting clear diurnal variations, with echoes mainly below 2 km and between 4 to 6 km during the early morning, intensifying and shifting to higher altitudes during the day and reaching their maximum below 4 km during the afternoon to nighttime hours, while both the frequency and intensity increase in the height range of 4 to 12 km. Vertical profiles of radar reflectivity and cloud ice/liquid water content (IWC/LWC) exhibit similar trends under different precipitation intensities. The main differences are observed below 4 km, where both radar reflectivity and IWC/LWC generally increase with increasing precipitation intensity. These findings contribute to a better understanding of cloud characteristics in the South China region, enhance the accuracy of model simulations, and provide a scientific basis for accurate forecasting and warning of meteorological disasters.

Intercomparisons on the Vertical Profiles of Cloud Microphysical Properties From CloudSat Retrievals Over the North China Plain

AbstractVertical profiles of cloud microphysical properties importantly determine the lifetime and precipitation rate of clouds. The 94‐GHz cloud profiling radar (CPR) onboard the CloudSat satellite can measure the vertical profile of radar reflectivity, from which the microphysical properties of cloud can be retrieved. The retrievals bear variations due to various assumptions and auxiliary products used. This study targets on the mid‐latitude clouds in the northern hemisphere, and intercompares the CloudSat products describing the vertical profiles of cloud microphysics and evaluate the uncertainties for each retrieval algorithm, with further evaluation by aircraft in‐situ observations over the North China Plain region during 2013–2017. For those retrieval products performing phase apportion, the ambient temperature‐based linear apportioning on mixed‐phase clouds can produce reasonable estimation on ice water content, apart from the heavily precipitating clouds. The retrieved liquid water content constrained by cloud optical depth well matched in‐situ observations, however its effective size is overestimated (hereby underestimating the number concentration of water droplets) because of the influence of larger precipitating hydrometeors on size distribution. The CPR‐only retrieval can well produce the effective diameter and number concentration of ice for deep convection clouds, but using additional lidar constraint underestimates the effective diameter due to the intense attenuation by thick clouds. The analysis here suggests the appropriate parameters from various products for different cloud types, and provides guidance for future development of retrieval algorithms on vertical profiles of cloud microphysical properties.

Detection of Bright Band Heights from Vertical Profile of Radar Reflectivity in Akure, South Western Nigeria

Bright band is an important phenomenon that occurs in radar observations of precipitation. It is a layer of intense reflectivity caused by the melting of the snowflakes in the atmosphere. Accurate detection of bright band and its associated properties are essential for the estimation of precipitation rates and characterization of precipitation types as required in Agriculture, Aviation, Navigation, Telecommunication sectors etc. Bright Band Height (BBH) is a vital parameter in the determination of rain height, rain-induced radio signal attenuation and mitigation techniques. This paper presents an empirical study on the measurement of BBH and Zero Degree Isotherm Height (ZDIH) from Micro Rain Radar (MRR) data obtained in Akure, Nigeria. Vertical profile of radar obtained during stratiform rainy events were examined to detect bright bands and its features. Analysis of the result showed that the ZDIH varies between 4.48 and 4.60 km while the BBH also vary from 4.16 to 4.48 km during intense rainy events in September and October 2010. The derived propagation data would be needed for the optimization and improvement of quality of service (QoS) offered by earth-space links during rainy events in Akure and its environs.

Comparison of vertical profile of raindrop size distribution from micro rain radar with global precipitation measurement over Western Java Island

The NASA-JAXA Global Precipitation Measurement (GPM) mission core satellite, launched in February 2014, carries the Dual-Frequency Precipitation Radar (DPR), which retrieves the three-dimensional structure of precipitation from space, including raindrop size distribution (DSD) parameters: mass-weighted mean diameter (Dm, in mm) and normalized DSD scaling parameter for concentration (Nw, in mm−1 m−3). This study compares DSD's vertical structure from the observations of GPM and ground-based radar (24 GHz Micro Rain Radar MRR) for the first time in Indonesia, precisely in Serpong (6.359°S, 106.673°E). The vertical profile of radar reflectivity, Dm, and Nw gradient was used to express the vertical gradient of DSD in rain columns (0.75–3 km). The gradient was calculated using linear regression as a function of parameters and height. Negative values indicated a downward decrease (DD) of parameters toward the surface; while, positive rates indicated a downward increase (DI) pattern. The DI of radar reflectivity from MRR was found more dominant than that of GPM Ku-band and Ka-band, with DI/DD ratios for MRR, Ku-band, and Ka-band at 7.2, 1.1, and 2.2, respectively. The three observations showed that the DI/DD ratio for convective rain was larger than that of stratiform rain. Most of the rain profiles from GPM showed a DI gradient for Nw, with a DI/DD ratio of 1.9, different from the MRR with the ratio of 0.6 only, indicating much more dominantion of DD. Furthermore, the DI/DD ratio for Dm from GPM observation was 0.8, while for MRR it was 4.55. Thus, the vertical structure of DSD from MRR was different from the one obtained by GPM, especially in convective rain. Besides the difference in profile trends, the Nw value of MRR is much larger than GPM; on the other hand, the Dm value of MRR was found much lower. Although there were some differences in DSD's vertical structure between GPM and MRR, both instruments were able to capture seasonal and diurnal variations of the DSD parameters.

Lightning activity during convective cell mergers in a squall line and corresponding dynamical and thermodynamical characteristics

The convective cell mergers and their impact on lightning activity during an extreme severe squall line system that occurred over the Beijing Metropolitan Region (BMR) have been investigated by using observations from the Beijing Broadband Lightning Network (BLNET), S-band Doppler weather radar, and other meteorological data. During the merger, the external and local multi-cells were connected by triggering new cells between them, and subsequently, cloud bridges formed at 1–5 km AGL. The total flash rate (TFR) of the whole storm decreased slightly at the beginning of the merger, increased sharply later, and peaked when the merger was completed. The TFR of the rear cell reduced to around zero while the TFR of the front cells increased in different degrees, which showed that the merger process exerted different effects on individual cells. Also, the vertical profiles of radar reflectivity illustrated that the merger process tended to weaken the rear cell and strengthen the front cells in spatial scale and intensity, presented as a rear-cell feeding merger. The results from the Variational Doppler Radar Analysis System (VDRAS) are used to derive the corresponding dynamical and thermodynamical processes. The rear-inflow jet (RIJ) penetrated the trailing-stratiform region and extended into the lower layer of the front cells of the storm during the merger period. The resulting strong convergence and updraft of front cells brought water vapor from the bottom to the upper layers, which is conducive to the formation of ice particles, the possibility of noninductive electrification, and the subsequent lightning flashes.

Seasonal characteristics of storms over the Indian subcontinent

Storms are convective cells responsible for the major fraction of convective precipitation. Here, the pre-monsoon and monsoon season characteristics of storms are reported at Lucknow, Patna, Bhopal, and Nagpur in India using equivalent radar reflectivity factor (hbox {Z}_e) given at these radar locations. It is observed that the lifetime, speed of propagation, area, volume, echo top height and thickness lie in ranges 0.3–3 h, 5–60 km hbox {h}^{-1}, 4–184 hbox {km}^2, 8–1600 hbox {km}^3, 2–14 km, and 0.5–16 km respectively. For both seasons, the relationships between radar estimated rain volume (RERV; range 10^4–10^7hbox {m}^3) and area-time integral (ATI; range 1–100 hbox {km}^2 h) are established which are considered as a representative of total precipitation resulted from an individual storm during its life cycle. The results from statistical analysis of RERV-ATI pairs suggest that storms at Lucknow have similar seasonal characteristics at 87% confidence interval while other locations exhibit dissimilarities. In addition, the vertical profiles of radar reflectivity (VPRRs) of storms are constructed at their life phases, namely cumulus, mature and dissipation. It is concluded that the vertical hbox {Z}_e gradient in mixed-phase region (5–8 km) is lower (2–2.9 dBZ hbox {km}^{-1}) at cumulus and dissipation phases than at mature phase (3.6–4.4 dBZ hbox {km}^{-1}) in monsoon season. For pre-monsoon season, this gradient lies between 3.3–5.2 dBZ hbox {km}^{-1} at mature phase. Our results are of great importance for advancing knowledge about storm-scale, which has implications in short-range weather forecasting as well as developing new convective parametrization schemes.

Microphysical Characteristics and Types of Precipitation for Different Seasons over North Taiwan

In this work, long-term (10 years) raindrop size distribution (RSD) measurements from the Joss–Waldvogel Disdrometer (JWD) installed at the National Central University (NCU) (24°58′6″N, 121°11′27″E), Taiwan, and the vertical profile of radar reflectivity were used to analyze the variations in the gamma parameters of six seasons (winter, spring, mei-yu, summer, typhoon, and autumn) and types of precipitation. The normalized gamma distribution of RSD revealed that the highest mean Dm (mass-weighted average diameter) values occurred in the summer, whereas the highest mean log10 Nw (normalized intercept parameter) values were found in the winter. Furthermore, most of the rain falling at a rate of less than 20 mm h−1 occurs in Northern Taiwan. In this study, we used radar reflectivity to differentiate between convective and stratiform systems. It was revealed that the mean Dm values are higher in convective systems, whereas the mean log10 Nw values are higher in stratiform systems. The structure of RSD in stratiform systems remains constant in all seasons; however, convection is similar to maritime type. The microphysical characteristics that are responsible for the different RSD features in different seasons and types of precipitation are illustrated with the help of contoured frequency by altitude diagrams of radar reflectivity.

How do changes in warm-phase microphysics affect deep convective clouds?

Abstract. Understanding aerosol effects on deep convective clouds and the derived effects on the radiation budget and rain patterns can largely contribute to estimations of climate uncertainties. The challenge is difficult in part because key microphysical processes in the mixed and cold phases are still not well understood. For deep convective clouds with a warm base, understanding aerosol effects on the warm processes is extremely important as they set the initial and boundary conditions for the cold processes. Therefore, the focus of this study is the warm phase, which can be better resolved. The main question is: How do aerosol-derived changes in the warm phase affect the properties of deep convective cloud systems? To explore this question, we used a weather research and forecasting (WRF) model with spectral bin microphysics to simulate a deep convective cloud system over the Marshall Islands during the Kwajalein Experiment (KWAJEX). The model results were validated against observations, showing similarities in the vertical profile of radar reflectivity and the surface rain rate. Simulations with larger aerosol loading resulted in a larger total cloud mass, a larger cloud fraction in the upper levels, and a larger frequency of strong updrafts and rain rates. Enlarged mass both below and above the zero temperature level (ZTL) contributed to the increase in cloud total mass (water and ice) in the polluted runs. Increased condensation efficiency of cloud droplets governed the gain in mass below the ZTL, while both enhanced condensational and depositional growth led to increased mass above it. The enhanced mass loading above the ZTL acted to reduce the cloud buoyancy, while the thermal buoyancy (driven by the enhanced latent heat release) increased in the polluted runs. The overall effect showed an increased upward transport (across the ZTL) of liquid water driven by both larger updrafts and larger droplet mobility. These aerosol effects were reflected in the larger ratio between the masses located above and below the ZTL in the polluted runs. When comparing the net mass flux crossing the ZTL in the clean and polluted runs, the difference was small. However, when comparing the upward and downward fluxes separately, the increase in aerosol concentration was seen to dramatically increase the fluxes in both directions, indicating the aerosol amplification effect of the convection and the affected cloud system properties, such as cloud fraction and rain rate.

Seasonal variability of warm boundary layer cloud and precipitation properties in the Southern Ocean as diagnosed from A‐Train data

AbstractThe extensive cloudiness and resulting high albedo of the Southern Oceans (SO) are predominantly due to the occurrence of widespread marine boundary layer clouds. Recent work finds correlations between biogenically enhanced cloud condensation nuclei concentrations and cloud droplet number concentrations derived from passive satellite data. The active remote sensors in the A‐Train have created a unique and long‐term record of these clouds that include vertical profiles of radar reflectivity and microwave brightness temperature from CloudSat that can be combined with solar reflectances from Moderate Resolution Imaging Spectroradiometer. We examine this data record using a unique algorithm to infer warm‐topped cloud and precipitation properties. We find seasonal variations in cloud properties where summer season clouds demonstrate higher cloud droplet number concentrations on average and require higher liquid water contents to produce similar precipitation rates.

Understanding Heavy Lake-Effect Snowfall: The Vertical Structure of Radar Reflectivity in a Deep Snowband over and downwind of Lake Ontario

AbstractThe distribution of radar-estimated precipitation from lake-effect snowbands over and downwind of Lake Ontario shows more snowfall in downwind areas than over the lake itself. Here, two nonexclusive processes contributing to this are examined: the collapse of convection that lofts hydrometeors over the lake and allows them to settle downwind; and stratiform ascent over land, due to the development of a stable boundary layer, frictional convergence, and terrain, leading to widespread precipitation there. The main data sources for this study are vertical profiles of radar reflectivity and hydrometeor vertical velocity in a well-defined, deep long-lake-axis-parallel band, observed on 11 December 2013 during the Ontario Winter Lake-effect Systems (OWLeS) project. The profiles are derived from an airborne W-band Doppler radar, as well as an array of four K-band radars, an X-band profiling radar, a scanning X-band radar, and a scanning S-band radar.The presence of convection offshore is evident from deep, strong (up to 10 m s−1) updrafts producing bounded weak-echo regions and locally heavily rimed snow particles. The decrease of the standard deviation, skewness, and peak values of Doppler vertical velocity during the downwind shore crossing is consistent with the convection collapse hypothesis. Consistent with the stratiform ascent hypothesis are (i) an increase in mean vertical velocity over land; and (ii) an increasing abundance of large snowflakes at low levels and over land, due to depositional growth and aggregation, evident from flight-level and surface particle size distribution data, and from differences in reflectivity values from S-, X-, K-, and W-band radars at nearly the same time and location.

Simultaneous Radar Observations of Vertical Profile of Rain Features from Space and Ground at Ku and Ka Bands at a Tropical Location

In this paper parameters of precipitation profiles obtained from precipitation radar aboard tropical rainfall measuring mission satellite and from ground based micro rain radar observations have been compared for different rain events. The dual frequency radar observations of precipitating atmosphere have been utilized to study the vertical profiles of radar reflectivity and rain rate. It is shown that the inclination of the ray path of the satellite borne radar significantly influences the rain rate measurements. The study demonstrates the efficacy of combining space borne and ground-based measurement in obtaining a complete profile of vertical rain structure.

Analyses of Cloud Characteristic during Malaysian 2014 Flood Event

Floods refers to the condition of great overflow of water over a dry land. In malaysia, monsoon flood which cause by the heavy rain in monsoon seasons regularly hits the country. A criteria of the cloud based on horizontal and vertical profile of radar reflectivity have been analyzed in this paper to estimate flood event. The values of the thickness and the size of the cloud are estimated from the analysis. In this paper, we analyze the river basin data and radar data in the duration of flooding time, T for the specific area covered by meteorological radar and rain gauge data. The procedure was applied to 14 days precipitation phenomenon observed in Kota Bharu, Kelantan (Malaysia) from 13 December 2014 until 26 December 2014. The objective of this paper is to analyse the distinctiveness of the cloud during flood events. The result shows that during the critical time of flood disaster, the cloud shows largest size of 13070.6 km2 and the thickness appeared to be the largest at almost 10.2 km during the beginning of the rain fall. The analysis helps us to understand the cloud characteristics hence in future flood estimation model can be constructed and modelled.

Numerical Experiments to Analyze Cloud Microphysical Processes Depicted in Vertical Profiles of Radar Reflectivity of Warm Clouds

Abstract Information about microphysical processes in warm clouds embedded in satellite measurements must be untangled to be used to improve the parameterization in global models. In this paper, the relationship between vertical profiles of horizontally averaged radar reflectivity Zm and cloud optical depth from cloud top τd was investigated using a hybrid cloud microphysical model and a forward simulator of satellite measurements. The particle size distributions were explicitly simulated using a bin method in a kinematic framework. In contrast to previous interpretations of satellite-observed data, three patterns of the Zm–τd relationship related to microphysical processes were identified. The first is related to the autoconversion process, which causes Zm to increase upward with decreasing τd. Before the initiation of surface precipitation, Zm increases downward with τd in the upper part of the cloud, which is considered to be a second characteristic pattern and is caused by the accretion process. The appearance of this pattern corresponds to the initiation of efficient production of raindrops in the cloud. The third is related to the sedimentation and evaporation of raindrops causing Zm to decrease downward with τd in the lower part of the Zm–τd relationship. It was also found that the bulk collection efficiency has a partially positive correlation with the slope factor of Zm with regard to τd and that the slope factor could be a gross measure of the collection efficiency in partial cases. This study also shows that differences in the aerosol concentration modulate the duration of these three patterns and change the slope factor of Zm.

Simultaneous influences of thermodynamics and aerosols on deep convection and lightning in the tropics

AbstractConvective features (CFs) observed by the Tropical Rainfall Measuring Mission satellite between 2004 and 2011 are analyzed to determine the relative roles of thermodynamics and aerosols as they modulate radar reflectivity and lightning. We studied the simultaneous impacts of normalized convective available potential energy (NCAPE) and warm cloud depth (WCD) as well as cloud condensation nuclei concentrations (D ≥ 40 nm; N40) on total lightning density (TLD), average height of 30 dBZ echoes (AVGHT30), and vertical profiles of radar reflectivity (VPRR) within individual CFs. The results show that TLD increases by up to 600% and AVGHT30 increases by up to 2–3 km with increasing NCAPE and N40 for fixed WCD. The partial sensitivities of TLD/AVGHT30 to NCAPE and N40 separately were comparable in magnitude but account for a fraction of the total range of variability (i.e., when the influences of NCAPE and N40 are considered simultaneously). Both TLD and AVGHT30 vary inversely with WCD such that maxima of TLD and AVGHT30 are found for the combination of high NCAPE, high N40, and shallower WCD. The relationship between lightning and radar reflectivity was shown to vary as a function of N40 for a fixed thermodynamic environment. Analysis of VPRRs shows that reflectivity in the mixed phase region is up to 5.0–5.6 dB greater for CFs in polluted environments compared to CFs in pristine environments (holding thermodynamics fixed). This analysis favors a merged hypothesis for the simultaneous roles of thermodynamics and aerosols as they influence deep convective clouds in the Tropics.

Convective intensity, vertical precipitation structures, and microphysics of two contrasting convective regimes during the 2008 TiMREX

AbstractThis study investigates the convective/microphysical properties and precipitation structures of seven rainfall events in southwest Taiwan during the 2008 Terrain‐influenced Monsoon Rainfall Experiment (TiMREX). TiMREX heavy rainfall events (>50 mm d−1) are characterized by upstream low‐level jets, unstable upstream conditions, and a nearly moist neutral stratification within the heavy rain region. Three heavy rainfall events (2, 5, and 16 June) have only weak to moderate convection and little lightning; e.g., less than 10% of their rainfall is associated with intense convective cells (maximum 40 dBZ height > 8 km). Polarimetric radar measurements indicate that large precipitation‐size ice particles well above the freezing level (5 km) are rare in these events. Their vertical profiles of radar reflectivity (VPRR) decrease rapidly above the 0°C level but increase downward below that level. These VPRRs are believed to be associated with weak updrafts and active warm‐rain collision and coalescence processes at low levels with raindrops falling through the updraft. In contrast, the 14 June heavy rainfall event is more intense, is ice‐based, and exhibits continental characteristics; e.g., 60% of its rainfall is contributed by active thunderstorms (>10 flashes min−1). This and other intense storms (26 May and 13 June) have robust lightning (>500 strikes h−1) and pronounced radar reflectivity in the mixed‐phase region, indicating strong updrafts and vigorous ice‐based processes. Significant amounts of large graupel/small hail are present in the mixed‐phase region of these events. Furthermore, their VPRRs decrease or stay constant downward below the freezing level.

Refining the relationship between lightning and convective rainfall over the ocean

AbstractThe lightning stroke density observed by Vaisala's Global Lightning Dataset (GLD360) was compared to maximum reflectivity in the upper and lower troposphere observed by NASA's Tropical Rainfall Measuring Mission Precipitation Radar over remote oceanic regions. We found that GLD360 stroke density is strongly correlated with maximum reflectivity above 0°C and the height of the 30 dBZ isopleth in two ocean basins (best represented by a logarithmic least squares regression). The maximum reflectivity above 0°C increases ~8–10 dBZ and the maximum height of the 30 dBZ isopleth increases ~2.8–3.8 km across the domain of stroke density. Stroke density and the maximum near‐surface reflectivity are also correlated, but the range of the resulting logarithmic relationship is less than that found for maximum reflectivity above 0°C. There is high confidence in the logarithmic regressions as R2 values are generally above 0.9 during the study. A bootstrap resampling approach confirms that the lightning versus rainfall relationship is statistically significant. Vertical profiles of radar reflectivity show that progressively larger values of stroke density are associated with higher reflectivity at most altitudes (most pronounced near 6.5 km mean sea level) and less rapid decreases in reflectivity with increasing height above 0°C. The logarithmic relationships between lightning and rainfall defined in this study have significant utility in creating proxy data sets, such as pseudoreflectivity, for weather analysis and assimilation in numerical weather prediction.

Microwave remote sensing of the 2011 Plinian eruption of the Grímsvötn Icelandic volcano

The sub-glacial Plinian explosive eruption of the Grímsvötn volcano, which occurred on May 2011, is for the first time analyzed and quantitatively interpreted by using ground-based weather radar data and the Volcanic Ash Radar Retrieval (VARR) physically-based technique. The prevailing southerly winds stretched the erupted plume toward the Artic pole, thus preventing the ash cloud to move toward continental Europe and threatening the airline traffic (different from the less explosive Eyjafjöll eruption on April and May 2010). The 2011 Grímsvötn eruption has been continuously monitored by the Keflavík C-band weather radar, located at a distance of about 260km from the volcano vent. The VARR methodology is summarized and applied to available radar time series to estimate the coarse ash particle category, volume, fallout, concentration and the plume maximum height, every 5min within the volcano vent surroundings (i.e. an area of about 100×100km2 around the volcano). Due to the large distance from the volcano, fine-grained ash cannot be detected and estimated by the Keflavík C-band weather radar. Estimates of the eruption discharge rate, based on the retrieved ash plume top height, are provided together with an evaluation of the total erupted mass and volume. Deposited ash at ground is also retrieved from radar data by empirically reconstructing the vertical profile of radar reflectivity and estimating the near-surface ash fallout. Radar-based ash retrieval results can be compared with available satellite microwave radiometric imagery in order to show the potential contribution and limitations of these microwave remote sensing products to the understanding and modeling of explosive volcanic ash eruptions. Spaceborne microwave brightness temperatures show a correlation with ash columnar content, derived from VARR, depending on the millimeter-wave frequency and on the spatial averaging. Microphysical sensitivity of satellite microwave brightness temperatures to plume fine and coarse ash suggests their exploitation in synergy with satellite thermal infrared radiometer and ground-based microwave radar observations.

Comparison of polarimetric signatures of hail at S and C bands for different hail sizes

In this study, severe hail cases in Oklahoma/USA are investigated by analyzing the data simultaneously collected by two closely located polarimetric weather radars operating at S and C bands. Polarimetric radar variables measured in the presence of hail at C band are quite different from the ones at S band due to more pronounced effects of resonance scattering and much stronger impact of attenuation. The differences are particularly strong in melting hail below the freezing level, but they can be substantial even at higher altitudes where hail is dry or grows in wet regime. As a consequence, the algorithms for hail detection and determination of its size developed at S band can't be directly applied to C band. Differences between vertical profiles of radar reflectivity Z, differential reflectivity ZDR, and cross-correlation coefficient ρhv in hail-bearing parts of the storms have been examined for large and giant hail. It is shown that in the presence of hail, ZDR(C) is usually higher than ZDR(S) and ρhv(C)<ρhv(S). The height of radar resolution volume with respect to the freezing level has to be taken into account in polarimetric hail detection/sizing. It is also demonstrated that giant hail is commonly associated with pronounced depression of ρhv in the areas of hail generation above the freezing level and the corresponding drop in ρhv at C band is much stronger than at S band. These results are compared to C-band polarimetric data collected in hail-bearing thunderstorms in Austria, where additional small hail size reports are available.

Relationships between lightning flash rates and radar reflectivity vertical structures in thunderstorms over the tropics and subtropics

Relationships between the vertical profile of radar reflectivity and lightning flash rates are investigated using 13 years of Tropical Rainfall Measuring Mission (TRMM) observations during 1998–2010. First the Radar Precipitation Features (RPFs) are defined by grouping raining areas detected by the TRMM Precipitation Radar (PR). Then the characteristics of radar reflectivity and lightning flash rate are calculated in each RPF using PR and Lightning Imaging Sensor (LIS) observations. Using these RPFs, temperatures at 20, 30, and 40 dBZ radar echo tops, used as proxies of the maximum convective intensity of precipitation systems, are examined as indicators of the probability of lightning. Although 30 and 40 dBZ echo top temperatures are better indicators of the probability of lightning than the 20 dBZ echo top temperature, there is a large regional variation in the temperature thresholds, especially between land and ocean. In general, oceanic thunderstorms have higher 20 dBZ echo top and larger horizontal extent than those over land. However, radar reflectivity is more likely to exceed 30 and 40 dBZ at cold temperatures over land than over ocean. The correlations between flash rates and radar echo top temperatures, areas and volumes of radar reflectivity, and ice water contents in the mixed phase region are analyzed using RPFs with at least one flash. In agreement with previous studies, the correlations with the echo top temperatures are low, but the correlations between flash rates and areas and volumes of high radar reflectivity in the mixed phase region are much higher. There is a high correlation between the flash rates and the volumes with radar reflectivity greater than 30, 35, or 40 dBZ in the mixed phase region, but the correlation coefficient varies significantly between thunderstorms over different regions, especially between land and ocean. These results are confirmed by repeating the analysis for regions of the storms defined as convective, thus eliminating the contribution from large areas of stratiform radar echo that have much less lightning.