Raindrop Size Research Articles

Statistical Characteristics of Raindrop Size Distribution in the South China Monsoon Region (Guangdong Province)

Statistical Characteristics of Raindrop Size Distribution in the South China Monsoon Region (Guangdong Province)

An Equilibrium Raindrop Size Distribution Associated with a Heavy-Rain-Producing Convective System in Japan

An Equilibrium Raindrop Size Distribution Associated with a Heavy-Rain-Producing Convective System in Japan

Characteristics and Variations of Raindrop Size Distribution in Chengdu of the Western Sichuan Basin, China

Knowledge of the microphysical characteristics of precipitation plays a significant role in meteorology, hydrology, and natural hazards management, especially in the western Sichuan Basin (WSB), which is located east of the Tibetan Plateau (TP) in southwestern China and thus has unique terrain conditions and weather systems. Nonetheless, the literature regarding raindrop size distribution (RSD) in the WSB is still very limited. This work investigates RSD characteristics and temporal variations in a site (Chengdu, CD) of the WSB by employing three years of quality-controlled RSD observation collected from a second-generation PARSIVEL disdrometer. The results show that RSD has noticeable seasonal and diurnal variations in CD. Specifically, the broadest mean raindrop spectra can be found in summer and the narrowest in winter, and the raindrop spectra of a day can be the narrowest during 1400–1500 BJT (Beijing Standard Time, UTC+8). In addition, the mass-weighted mean diameter (Dm) is lower in the daytime than in the nighttime, while the logarithm of the generalized intercept parameter (log10Nw, the unit of the Nw is m−3 mm−1) has a larger value in the daytime than in the nighttime. In addition, intercomparisons indicate that the mean Dm of convective rains in CD is smaller than in South China and it is higher than in the eastern slope of TP, East China, and North China; on the other hand, the corresponding mean log10Nw is close to the value at the middle TP. Local empirical relations of shape–slope parameters (μ–Λ) and reflectivity–rain rate (Z–R) are also presented to provide references for optimizing the RSD parameterization scheme and radar precipitation estimation in the local area.

Analysis of Rain Drop Size Distribution to Elucidate the Precipitation Process using a Cloud Microphysics Conceptual Model and In Situ Measurement

Raindrop size distribution (DSD) is an important parameter in rainfall research and can be used for quantitative precipitation estimation (QPE) in meteorology and hydrology. DSD also improves the understanding of the uncertainty of cloud microphysical processes (CMPs) such as ice-based and warm rain growth during climate change. Changes in CMPs impact the generation of precipitation. However, the estimation of CMPs based on in situ observation is difficult because of the complexity of microphysics processes, and most previous studies on the CMP involved approximations to predict the types of microphysical processes affecting precipitation generation based on in situ observations performed in real-time. Therefore, we developed a simple method for understanding the CMPs of precipitation generation using a conceptual model of CMPs and in situ observation DSD data. We employed previously observed DSD parameters and a CMP conceptual model of the DSD observation-based microphysical process. As case studies, we applied DSD observation data obtained in Korea and East Asia to estimate the CMPs. For example, the major CMP of megacities was vapor deposition in Beijing (< 1 mm h−1) and Seoul (< 5 mm h−1), as the strong updraft of the urban heat island effect in megacities results in increased liquid water content, leading to the formation of large number of supersaturated clouds at higher altitudes.

Automatic selection of release plane for Lagrangian-based wind-driven rain studies

Wind-driven rain (WDR) modelling based on Lagrangian particle tracking (LPT) involves the trajectory simulation of raindrops released from a horizontal plane in the computational domain. Usually, the release location is determined in a tedious trial-and-error manner, which impairs the adoption of LPT method for WDR studies in terms of user’s handiness and computational efficiency. In this study, the analytical solution for raindrop trajectories in an unobstructed domain are derived and presented. Based on the analytical solution, the location and sizes of the release plane can be easily determined a priori. A constant scaling factor can be further introduced to address possible obstruction effects by buildings. Unnecessary and expensive repetition of simulations to search for a proper release plane can be avoided, especially for scenario studies involving multiple raindrop sizes. In this paper, the accuracy, efficiency and effectiveness of the proposed automatic selection of release plane based on the analytical solutions are demonstrated based on selected case studies. It is deemed that the proposed innovative procedure for the determination of an effective and appropriate release plane can promote the widespread adoption of LPT approach for WDR studies.

Performance degradation of terahertz channels in emulated rain

The ever-increasing capacity demand (up to Tbps in the foreseeable future) in wireless connectivity can supposed be satisfied by terahertz communications in the band from 100 GHz to 10 THz. This has been studied over short channel distances in laboratories using higher order modulation formats (QPSK, QAM). However, only very few reports on the THz channel performance in outdoor adverse weathers conditions are available due to the involved experimental difficulties. In this article, we report the performance of terahertz channels in emulated rain by utilizing a broadband pulse source and a 16-QAM modulated data stream. We observe that, a not precisely known of raindrop size distribution can be a major source of uncertainty for theoretical precipitation of power attenuation and bit error rate (BER). We also find that the channel degradation in rain is mainly due to power attenuation.

The largest diameter of falling drop in the up-gas flow

This study aimed to investigate the largest diameter of falling drop in the up-gas flow. Due to gravity, the falling drop is common in nature and industry. Drop breakup in the airflow is referred to as secondary atomization, found in numerous practical applications. Critical Weber number is the key dimensionless number marking the beginning of drop breakup. Herein, we explain the different critical Weber numbers between the free-fall raindrops breakup and secondary atomization based on the Rayleigh-Taylor (RT) instability. The theoretical criterion of largest raindrop size is proposed by RT wave number model. In addition, we suggest a map of falling drop size regions, which can well explain the phenomena of the super-large raindrop. The current study is also helpful in the remission of drop entrainment in the washing tower.

Diagnostic Relations for the Intercept Parameter of Exponential Raindrop Size Distribution According to Rain Types Derived from Disdrometer Data and Their Impacts on Precipitation Prediction

The raindrop size distribution observed from ground-based or airborne disdrometers has been widely used to understand the characteristics of clouds and precipitation. However, its variability needs to be studied further and properly considered for improving precipitation prediction. In this study, using disdrometer data, the diagnostic relations for the intercept parameter of the exponential raindrop size distribution N0 are derived for different rain types and the impacts of the diagnostic relations on precipitation prediction are examined. The disdrometer data observed at four sites in South Korea show spatiotemporal variations of N0. Three different derivation methods proposed by previous studies are used to derive the diagnostic relations, and the diagnostic relation that best reproduces the observed N0 is selected. The diagnostic relation is implemented into the WRF single-moment 6-class microphysics (WSM6) scheme, and its impacts are investigated through the simulations of summertime precipitation events in South Korea. Compared to the simulation using the original WSM6 scheme (WSM6-O) where a constant N0 is used, the simulation where N0 is diagnosed by the diagnostic relation using the rainwater content at the lowest level (WSM6-L) yields better precipitation prediction. The WSM6-L simulation represents the variability of N0. Also, the WSM6-L simulation predicts N0 that is on average smaller than the prescribed value in the WSM6-O simulation, agreeing with the observation to some extent. The smaller N0 in the WSM6-L simulation decreases the rainwater production by the accretion of cloud water and the melting of ice hydrometeors, decreasing the rainwater mixing ratio.

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.

An assessment of rainfall kinetic energy functional relationships with GPM DPR

The kinetic energy (KE) of rainfall is an important parameter in estimating the rainfall erosivity factor, an essential parameter in the soil erosion equation. The global precipitation measurement dual-frequency precipitation radar (GPM DPR) can provide radar reflectivity at Ku- and Ka-band frequencies (Zku and Zka), rainfall rate (I, mm h−1), and drop size distribution parameters (mass-weighed mean diameter: Dm in mm and normalized intercept parameter: log10Nw, Nw in m−3 mm−1). The empirical relations between rainfallKEand GPM DPR parameters (KEtime–I, KEmm–Dm, KEtime–Zku, and KEtime–Zka relations) can allow us to estimate the KE at the locations where there are no ground-based measurements. In the present work, long-term measurements of impact type disdrometers located at three different locations (Zhongli, Feitsui, and Hsiayun) in north Taiwan are used to collect the raindrop size distribution (RSD) information of six seasons (spring, mei-yu, summer, autumn, winter, and typhoon). Measured RSDs in six seasons are used to estimate the rainfall intensity, mass-weighted mean diameter, rainfall KE flux (KEtime, J m–2 h−1), KE content (KEmm, J m−2 mm−1), radar reflectivity at Ku- and Ka-band frequencies. For the first time, present study establish and validate the rainfall KE functional relationships with GPM DPR data products (KEtime–I, KEmm–Dm, KEtime–Zku, and KEtime–Zka relations). The empirical relations between rainfall KE and GPM DPR parameters (I, Dm, Zku, and Zka) are established for six seasons of each disdrometer location. Derived KE relations did not show any spatial disparity for a given season, especially the KEmm–Dm, KEtime–Zku, and KEtime–Zka relations. On the other hand, a clear seasonal differences in the rainfall KE relations are noticed at each observational site. The established relations showed reasonable agreement in estimating the KE from the GPM DPR. However, in determining the KE, the KEmm–Dm relation showed outperformance over the remaining three relations (KEtime–I, KEtime–Zku, and KEtime–Zka relations).

Raindrop size distribution (DSD) during the passage of tropical cyclone Nivar: effect of measuring principle and wind on DSDs and retrieved rain integral and polarimetric parameters from impact and laser disdrometers

Abstract. Raindrop size distribution (DSD) observations during the passage of landfalling tropical cyclone Nivar by impact (JWD) and laser (LPM and PARSIVEL) disdrometers are used to unveil the DSD characteristics in the eyewall as well as the inner and outer rainbands. Disdrometer measurements collected at the same location are used to study the effect of wind, measuring principle, and hardware processing on the DSDs and, in turn, on estimated rain integral and polarimetric parameters. The concentration of raindrops of diameters between 0.7 and 1.5 mm increases with rain rate (R) in all the regions of Nivar, while the magnitude of the increase is higher in the eyewall than in the inner and outer rainbands. The DSD characteristics reveal that for a given R, relatively larger reflectivity (Z) and mass-weighted mean diameter (Dm) are found in the outer rainband, and smaller Z and Dm are found in the eyewall than in other regions of a tropical cyclone (TC). Raindrops of diameter 3 mm in size are observed frequently in inner and outer rainbands; however, they are infrequent in the eyewall at R greater than 5 mm h−1. The DSDs and estimated rain integral and polarimetric parameters are distinctly different for various disdrometers at similar environmental conditions. Raindrops greater than 3 mm in size are infrequent in the JWD recordings, while they are frequent in the LPM and PARSIVEL, indicating that LPM and PARSIVEL overestimate the raindrop size when the fall path deviates from nadir due to horizontal wind. The wind effect on the recorded DSD as well as estimated rain integral and polarimetric parameters are not uniform in various regions of Nivar for different disdrometers as the measuring principle and hardware processing further influence these effects. Along with the differences in measured DSD spectra, the resonance effects at X band for raindrops greater than 3 mm cause variations in the estimated polarimetric parameters between the disdrometers.

Seasonal differences in raindrop size and causative microphysical processes in continental, orographic and oceanic regions of the Indian subcontinent

Global precipitation measurement dual-frequency precipitation radar observations during 2014–2021 are used for the first time to infer the dominant microphysical processes responsible for the seasonal variations in mass-weighted mean diameter (Dm) in different regions of the Indian subcontinent. Seasonal differences in mean Dm estimated using stratified rain rates for deep systems is pronounced in continental and Western Ghats, while marginal in maritime and Myanmar coast regions. The mean Dm values are larger in pre-monsoon (PM) than in other seasons in all the regions due to prevalence of deepest storms and evaporation. Seasonal differences in Dm observed at the near-surface are originated at raindrop formation altitude (1.5 km below the 0 °C isotherm) and are magnified during the descent of raindrops due to more evaporation in PM over the Arabian Sea, Western Ghats, and Myanmar coast. Raindrop size show contrasting features at the formation altitude and at the near surface in southwest monsoon (SWM) and northeast monsoon (NEM) over Bay of Bengal, foothills of Himalayas, Northwest India, and southeast peninsular India. The breakup of raindrops in NEM results in small Dm at the near surface in NEM than in SWM over the Bay of Bengal and southeast peninsular India. Higher occurrence of convection over Western Ghats, evaporation over foothills of Himalayas and northwest India in NEM results in large Dm values than in SWM. Dm values of shallow rain show considerable seasonal variations over the Arabian Sea and Western Ghats and marginal differences in the Bay of Bengal and Myanmar coast.

Assessing Raindrop Breakup Parameterizations Using Disdrometer Observations

Abstract An intercomparison of raindrop mean diameter frequency distribution (RDFD) is performed for numerical simulations of precipitating cloud systems using an array of models and microphysics schemes. This includes results from the Regional Atmospheric Modeling System (RAMS) double-moment microphysics, the Hebrew University Cloud Model bin microphysics (HUCM) interfaced to the RAMS parent model, and the Weather Research and Forecasting (WRF) Model with the Thompson, Morrison, double-moment 6-class (WDM6), and National Severe Storms Laboratory (NSSL) double-moment schemes. Simulations are examined with respect to the raindrop size distribution (DSD) volume-number mean diameter (Dm) and intercept parameter (Nw). When compared to a suite of disdrometer observations, the RDFD resulting from each microphysics scheme exhibits varying degrees of mean drop size constraints and peaks in the frequency distribution of Dm. A more detailed investigation of the peaked RDFD from the RAMS simulations suggests that the parameterization of raindrop collisional breakup can impose strong limitations on the evolution of simulated drop growth. As such, a summary and comparison of the drop breakup parameterizations among the aforementioned microphysics schemes is presented. While some drop breakup parameterizations are adjusted toward the observations by modifying the threshold diameter for the onset of breakup, this study explores the use of a modified maximum breakup efficiency. This method permits the parameterization to retain its threshold breakup diameter, while limiting the strength of drop breakup and permitting a broader range of drop sizes. As a result, the simulated mean drop sizes are in better agreement with observations.

PHOTOGRAMMETRIC TECHNIQUE FOR ANALYZING RAINDROP SIZE DISTRIBUTION

Rainfall erosivity and rainfall kinetic energy are predominantly affected by the rainfall droplet size distribution characteristics. This study aims to determine the raindrop size distribution with different rainfall intensities in East Malaysia using photographic method and MATLAB image processing tools. A total of five natural rainfall intensities of different ranges were analyzed: 5.51 mm hr-1, 14.20 mm hr-1, 28.80 mm hr-1, 32.41 mm hr-1 and 58.11 mm hr-1. A digital camera with fast capturing mode was used to capture falling raindrops and the droplets were then processed in MATLAB to determine the raindrop size distribution. It was found that the captured raindrop diameters were within the range of 0.1 mm and 5.0 mm, and a higher portion of the raindrops fell between 0.1 mm and 1.0 mm. The results also showed that higher rainfall intensities would promote the formation of larger raindrop sizes, i.e., from 1.0 mm to 5.0 mm, and lower rainfall intensities tended result in higher drop counts in smaller raindrop sizes of &lt;1.0 mm. The modified image processing tools of MATLAB had proved a shorter analysis duration and higher accuracy of the raindrop size determination than the human visual system. The novelty of this study contributes to the understanding of the equatorial rainfall properties. This enhances the study of the rainfall kinetic energy and soil erosion rate estimation. The findings demonstrate the capability of photogrammetric techniques for determination of raindrop size distribution.

Experimental Approach to Developing Equatorial Soil Loss Equation

This paper aims to develop a soil loss equation used within an equatorial climate (2,300 – 6,000 mm of annual rainfall) and hilly terrain based on measured data from the experiment concerning measured erosion outcomes, called Equatorial Soil Loss Equation (EQSLE). The equation under development should consider high equatorial rainfall intensities and challenging topographical conditions, thus introducing the new factors – Equatorial Rainfall Erosivity Factor (Reqt-factor) and Equatorial Slope Length Factor (Leqt-factor). The process included a photogrammetric method and image processing for raindrop size distribution and an experimental plot setup for a length differential study. The final equation has the form of A=Reqt⸱Leqt⸱S⸱K⸱C⸱P for soil erosion estimation in the equatorial region with the involvement slope and hilly terrain. The performance of the Reqt-factor and Leqt-factor are evaluated using the experimental data, and works of literature are carried out for the results. The formation of the two factors has addressed the challenges of high rainfall intensities and extreme terrain conditions faced by Peninsular Malaysia and East Malaysia. In future work, more case studies on the performance of soil loss rate prediction should be conducted to improve the overall performance of EQSLE as well as the respective factors.

The Characteristics of Raindrop Size Distributions in Different Climatological Regions in South Korea

To understand the microphysical characteristics of rainfall in four different climatological regions (called BOS, BUS, CPO, and JIN) in South Korea, DSDs and their variables, including the mass-weighted mean diameter (Dm) and normalized number concentration (logNw), were examined. To examine the characteristics of DSDs at four sites with different climatology and topography, data measured from Parsivel disdrometer and wind direction from Automatic Weather System (AWS) during rainy seasons from June to August for three years (2018 to 2020) were analyzed. The DSDs variables were calculated using Gamma distribution model. In the coastal area, larger raindrops with a lower number concentration occurred, whereas smaller raindrops with a higher number concentration dominated in the middle land and mountain region. The mountain area of CPO and middle land area of JIN had a larger contribution to the rain rate than that of the coastal area of BOS and JIN in the range of the smallest diameter. The contribution of the drop size to the total number concentration at the CPO and JIN sites was larger (smaller) than that at BOS and BUS in the smallest (larger) diameter. The average shape and slope parameter of gamma model were higher values at the mountain area than at other sites for both rain types, Z-R relation and polarimetric variables were also shown different values at the four studied sites. The intercept coefficient of Z-R relation showed higher values in the mountain area and middle land area than the coastal area. The slope values of Z-R relation were the smallest in the mountain area. The polarimetric variables of ZH and ZDR were shown highest (lowest) value at the coastal region of BOS (mountain area of CPO) site for both rain types. The Dm-rose, which shows the Dm distributions with the wind direction, was used in this study. In the coastal area (mountain and middle land area), the dominant wind was east–southeast (east) direction. The ratio of the smaller diameter to the middle size at BOS was much smaller than that at CPO. In the analysis of the hourly distribution of the Dm and logNw, there were two and four peaks of Dm at BUS and BOS, respectively. There was one peak of the Dm at the CPO and JIN sites. The time variation of the Dm was much higher than that of the logNw.

Evaluation of cloud and precipitation processes in regional and global models with ULTIMATE (ULTra-sIte for Measuring Atmosphere of Tokyo metropolitan Environment): a case study using the dual-polarization Doppler weather radars

We describe a collaborative analysis study involving numerical models and observation data for the Tokyo metropolitan area called the ULTra-sIte for Measuring Atmosphere of Tokyo Metropolitan Environment (ULTIMATE) project. It evaluates cloud microphysics schemes of numerical models using extensive observation data for the Tokyo area. We have access to various remote sensing and in situ data for the Tokyo area for operational and research purposes, particularly by enhancing observations for ground validation of the EarthCARE satellite, which is set to launch in 2023. This study focuses on using the dual-polarization Doppler weather radar, operated by the Japan Meteorological Agency. In terms of numerical models, we use and compare multi-models with single-moment (SM) and double-moment (DM) cloud microphysics schemes; the global non-hydrostatic model, Non-hydrostatic ICosahedral Atmospheric Model (NICAM) and the two regional models with A System based on a Unified Concept for Atmosphere (ASUCA) and Scalable Computing for Advanced Library and Environment (SCALE) are used. In particular, because NICAM can be used as both a global and a regional model, we can immediately test the improved scheme on a global scale for its effect on climatology and the evaluation of climate sensitivity. This paper introduces the methodology for evaluating numerical models by the dual-polarization radar using the observation simulator and compares numerical model results with observations. In particular, we evaluate the simulated rain in the lower level near the ground and the large ice particles just above the melting level. The simulation with NICAM-DM reproduces the comparable polarimetric radar characteristics of rain as the observation. However, the simulations with NICAM-SM and ASUCA-SM show larger raindrop sizes in stronger rain areas compared to the observation. For the larger ice particles just above the melting level around 4 km, NICAM-DM and ASUCA-SM overestimate particle sizes of graupel or snow, while NICAM-SM has a similar size of the ice particles. In future studies, we will use the present results to improve the cloud microphysics scheme, which will be tested on a global model.

Raindrop Size Distribution Prediction by an Improved Long Short-Term Memory Network

The observation of and research on raindrop size distribution (DSD) is important for mastering and understanding the mutual restriction relationship between cloud dynamics and cloud microphysics in a process of precipitation; it also plays an irreplaceable role in many fields, such as radar meteorology, weather modification, boundary layer land surface processes, aerosols, etc. Using more than 1.7 million minutes of raindrop data observed with 17 laser disdrometers at 17 stations in Anhui Province, China, from 7 August 2009 to 30 April 2020, a DSD training dataset was constructed. Furthermore, the data are fitted to a normalized Gamma function and used to obtain its three parameters, i.e., the normalized intercept Nw, the mass weighted average diameter Dm, and the shape factor μ. Based on the long short-term memory network (LSTM), a DSD Gamma distribution prediction network (DSDnet) was designed. In the process of modeling based on DSDnet, a self-defined loss function (SLF) was proposed in order to improve the DSD prediction by increasing the weight values in the poor fitting regions according to the common mean square error loss function (MLF). By means of the training dataset, a DSDnet-based model was trained to realize the prediction of Nw, Dm, and μ minute-to-minute over the course of 30 min, and then was evaluated by the test dataset according to three indicators, namely, mean relative error (MRE), mean absolute error (MAE), and correlation coefficient (CC). The CC of lgNw, Dm, and μ can reach 0.93403, 0.90934, and 0.89741 for 12-min predictions, and 0.87559, 0.85261, and 0.84564 for 30-min predictions, respectively, which means that the DSD prediction accuracy within 30 min can basically reach the application level. Furthermore, the 12- and 30-min predictions of 3 precipitation processes were taken as examples to fully demonstrate the application effect of model. The prediction effects of Nw and Dm are better than that of μ, and the stratiform precipitation is better than the convective and convective-stratiform mixed cloud precipitation.

How the Environmental Lifting Condensation Level Affects the Sensitivity of Simulated Convective Storm Cold Pools to the Microphysics Parameterization

Abstract Several studies have documented the sensitivity of convective storm simulations to the microphysics parameterization, but there is less research documenting how these sensitivities change with environmental conditions. In this study, the influence of the lifting condensation level (LCL) on the sensitivity of simulated ordinary convective storm cold pools to the microphysics parameterization is examined. To do this, seven perturbed-microphysics ensembles with nine members each are used, where each ensemble uses a different base state with a surface-based LCL between 500 and 2000 m. A comparison of ensemble standard deviations of cold-pool properties shows a clear trend of increasing sensitivity to the microphysics as the LCL is raised. In physical terms, this trend is the result of lower relative humidities in high-LCL environments that increase low-level rain evaporational cooling rates, which magnifies differences in evaporation already present among the members of a given ensemble owing to the microphysics variations. Omitting supersaturation from the calculation of rain evaporation so that only the raindrop size distribution influences evaporation leads to more evaporation in the low-LCL simulations (owing to more drops), as well as a slightly larger spread in evaporational cooling amounts between members in the low-LCL ensembles. Cold pools in the low-LCL environments are also found to develop earlier and are initially more sensitive to raindrop breakup owing to a larger warm-cloud depth. Altogether, these results suggest that convective storms may be more predictable in low-LCL environments, and forecasts of convection in high-LCL environments may benefit the most from microphysics perturbations within an ensemble forecasting system. Significance Statement Computer simulations of thunderstorms can have grid spacings ranging from tens to thousands of meters. Because individual precipitation particles form on scales smaller than these grid spacings, the bulk effects of precipitation processes in models must be approximated. Past studies have found that models are sensitive to these approximations. In this study, we test whether the sensitivity to these approximations changes with the relative humidity in the lowest 1–2 km of the atmosphere. We found that increasing the relative humidity decreases the sensitivity of simulations to the precipitation process approximations. These results can inform meteorologists about the uncertainties surrounding computer-generated thunderstorm forecasts and suggest environmental conditions where using several computer models with different precipitation process approximations may be beneficial.

Characteristics of two different types of thunderstorms in summer over the Nagqu area in China

To investigate further the characteristics of thunderstorms on the Qinghai–Tibet plateau, a plateau vortex (PV) thunderstorm and a local thermoconvective (TC) thunderstorm over the Nagqu area are analyzed using cloud-radar, microwave-radiometer, and raindrop-spectrometer data, and their macrophysical and microphysical evolution characteristics are discussed in terms of thermodynamic processes, microphysical processes, and lightning activities. The results show the following. 1) The cloud layer was deeper in the PV thunderstorm, but the TC thunderstorm had a stronger short-time updraft with a radial velocity exceeding 10 m/s, and the warming from the strong updraft action and latent heat release from the hydromorphic phase change was about twice that of the PV thunderstorm. 2) The water vapor density increased significantly when the thunderstorm cloud passed, and the liquid water content in the middle and lower layers exceeded 4 g/m3. The maximum ice water content in the TC thunderstorm was twice bigger than that in the PV thunderstorm. The trends of raindrop number concentration and rain intensity of the PV thunderstorm were similar, and the average particle size of raindrops was smaller than that of the TC thunderstorm. 3) Both types of thunderstorms accounted for more than 90% of negative cloud-to-ground (CG) lightning, and the regions with black-body temperature (TBB) less than −40 °C and a larger TBB gradient were more favorable for the occurrence of CG lightning. 4) Thermodynamic fields bring water vapor and lift for microphysical processes, and microphysical changes release latent heat to enhance the dynamic effects, which together promote the development of lightning activities. The peak radial velocity and ice-phase particle concentration were more than 10 min ahead of the active peak of the CG lightning. This study reveals the macrophysical and microphysical evolution characteristics of different types of thunderstorms and provides a certain scientific basis for disaster prevention and mitigation regarding thunderstorms over the Nagqu area.