Convective Available Potential Energy Values Research Articles

The East China Sea Kuroshio Current Intensifies Deep Convective Precipitation: A Case Study

AbstractDeep atmospheric convection is often observed over the Kuroshio in the East China Sea (ECSK). However, the mechanisms by which warm oceanic currents fuel transient deep convection are not fully understood. This study investigates an atmospheric cold front that brought heavy precipitation as it traversed the ECSK in April 2004. The southwesterlies ahead of the cold front advected moist and warm air, creating a zone with high convective available potential energy (CAPE) values. As the cold front approached the ECSK, the pre‐frontal high CAPE values coalesced with those over the warm current that substantially strengthened the deep convection, with precipitation rate increasing from 3 mm hr−1 to 10 mm hr−1. A numerical model well simulated the marked increase in precipitation over the ECSK, permitting the isolation of the ECSK's influence by contrasting the control (CTRL) run with an experiment with smoothed sea surface temperatures (SMTH run). Results show the ECSK contributed to 46% of the precipitation over the warm current. The ECSK was found to amplify ascending motion and elevate neutral buoyancy levels, extending its effect up to the tropopause. Furthermore, the strengthened deep convection significantly lowered the sea level pressure (SLP) over the ECSK and impressed upon the time‐mean SLP field. An additional experiment with lowered SST underscored the high SST's critical role in deep convection. This case study suggests a novel pathway by which the effects of warm oceanic currents influence the upper troposphere under extreme conditions with strong baroclinic instability.

Improving the Representation of Moisture and Convective Instability in Baroclinic-Wave Channel Simulations

Abstract We present an improved approach to generating moist baroclinically unstable background states for f-plane-channel simulations via potential vorticity (PV) inversion. Previous studies specified PV distributions with constant values in the troposphere and the stratosphere, but this produces unrealistic static-stability profiles that decrease sharply with height in the troposphere. Adding moisture to such environments can yield unrealistically large values of convective available potential energy (CAPE) even for reasonable relative humidity (RH) distributions. In our modified approach, we specify a PV distribution that increases with height in the troposphere and the stratosphere, yielding background states with more realistic values of static stability and CAPE. This modification produces environments that are better suited for representing moist processes, namely, deep convection, in idealized extratropical-cyclone simulations. Also, we present a method for introducing moisture that preserves a specified RH distribution while maintaining hydrostatic balance. Our approach allows for a large degree of control over the initial conditions, as background states with different jet strengths and shapes, average temperatures, moisture contents, or horizontal shears can easily be obtained without changing the underlying PV formula and inadvertently producing unreasonable values of static stability or CAPE. We demonstrate the characteristics of idealized extratropical cyclones developing in our background states by adding localized perturbations that represent an upper-level trough passing over a low-level frontal zone. In particular, we illustrate the impacts of horizontal shear, moisture, and grid spacing on baroclinic-wave development.

Control of Stability and Relative Humidity in the Radiative‐Convective Equilibrium Model Intercomparison Project

AbstractThe Radiative‐Convective Equilibrium Model Intercomparison Project (RCEMIP) exhibits a large spread in the simulated climate across models, including in profiles of buoyancy and relative humidity. Here we use simple theory to understand the control of stability, relative humidity, and their responses to warming. Across the RCEMIP ensemble, temperature profiles are systematically cooler than a moist adiabat, and convective available potential energy (CAPE) increases with warming at a rate greater than that expected from the Clausius‐Clapeyron relation. There is higher CAPE (greater instability) in models that are on average moister in the lower‐troposphere. To more explicitly evaluate the drivers of the intermodel spread, we use simple theory to estimate values of entrainment and precipitation efficiency (PE) given the simulated values of CAPE and lower‐tropospheric relative humidity. We then decompose the intermodel spread in CAPE and relative humidity (and their responses to warming) into contributions from variability in entrainment, PE, the temperature of the convecting top, and the inverse water vapor scale height. Model‐to‐model variation in entrainment is a dominant source of intermodel spread in CAPE and its changes with warming, while variation in PE is the dominant source of intermodel spread in relative humidity. We also decompose the magnitude of the CAPE increase with warming and find that atmospheric warming itself contributes most strongly to the CAPE increase, but the indirect effect of increases in the water vapor scale height with warming also contribute to increasing CAPE beyond that expected from Clausius‐Clapeyron.

Numerical simulation of a pulse hailstorm in the plateau region in southwestern China

Pulse hailstorms over southwestern China generally produce small hailstones with diameters <20 mm, causing nonnegligible damage to crops. This study examines the mechanisms behind the typical pulse hailstorms which frequently occur in plateau regions in southwestern China. Utilizing radar observations and the Cloud Model 1 (CM1) numerical model developed by George Bryan, the influence of environmental factors on pulse hailstorms and the associated small hailstones is investigated. The results indicate that: firstly, hailstones are primarily generated from frozen droplets, which further grow through collecting supercooled liquid water; secondly, a higher convective available potential energy (CAPE) and lower low-level relative humidity (RH) lead to the raising of convection initiation height; and lastly, higher CAPE values result in smaller hailstones on the surface due to the intensified hailstone melting process caused by higher melting layer and warmer temperatures within the warm layer (>0 °C) in this situation.

Influence of Aerosols on Lightning Activities in Java Island, Indonesia

Lightning is one of the natural disasters that cause significant financial losses and even fatalities. Therefore, it is necessary to understand the characteristics of lightning and related factors take appropriate preventive and mitigation measures. This work investigated the influence of aerosols and atmospheric thermodynamic factors on lightning in Java Island using 16 years of data (1998 - 2013) from the Tropical Rainfall Measuring Mission (TRMM) satellite. Aerosol data were obtained from the Modern Era Retrospective Analysis for Research and Applications version 2 (MERRA-2). Furthermore, convective available potential energy (CAPE) and potential temperature data were taken from the fifth-generation ECMWF atmospheric reanalysis (ERA-5) data. The intensity of lightning strikes in the western part of Java, such as Jakarta and Banten, is higher than in the eastern part, corresponding to the distribution pattern of aerosols, especially sulfate aerosols, sea salt aerosols, and black carbon aerosols. Sea salt aerosols have an inverse relationship with lightning, as these coarse-sized aerosols tend to inhibit convection. An increase in CAPE and potential temperature generally leads to higher lightning intensity. However, in cases where CAPE values are extremely high, such as in Jakarta, the intensity of lightning decreases. A similar pattern can be observed with potential temperature. An inverse relationship between lightning and potential temperature is observed in regions at higher elevations. The peak time for CAPE and potential temperature coincide with the peak intensity of lightning, which typically occurs during the rainy season, while the peak of AOD occurs earlier, during the pre-monsoon (September-October-November). The highest values of sea salt AOD are observed during the dry season (June-July-August) when lightning is minimal. These variations in peak times are particularly evident in the western regions of Java, where AOD values are high. The findings of this study can aid in lightning disaster mitigation efforts on Java Island. HIGHLIGHTS The intensity of lightning strikes in the western part of Java is higher than in the eastern part Sea salt aerosols have an inverse relationship with lightning, as these coarse-sized aerosols tend to inhibit convection An increase in CAPE and potential temperature generally leads to higher lightning intensity The peak time for CAPE and potential temperature coincide with the peak intensity of lightning The highest values of sea salt AOD are observed during the dry season when lightning is minimal GRAPHICAL ABSTRACT

Machine-learning-based investigation of the variables affecting summertime lightning occurrence over the Southern Great Plains

Abstract. Lightning is affected by many factors, many of which are not routinely measured, well understood, or accounted for in physical models. Several commonly used machine learning (ML) models have been applied to analyze the relationship between Atmospheric Radiation Measurement (ARM) data and lightning data from the Earth Networks Total Lightning Network (ENTLN) in order to identify important variables affecting lightning occurrence in the vicinity of the Southern Great Plains (SGP) ARM site during the summer months (June, July, August and September) of 2012 to 2020. Testing various ML models, we found that the random forest model is the best predictor among common classifiers. When convective clouds were detected, it predicts lightning occurrence with an accuracy of 76.9 % and an area under the curve (AUC) of 0.850. Using this model, we further ranked the variables in terms of their effectiveness in nowcasting lightning and identified geometric cloud thickness, rain rate and convective available potential energy (CAPE) as the most effective predictors. The contrast in meteorological variables between no-lightning and frequent-lightning periods was examined for hours with CAPE values conducive to thunderstorm formation. Besides the variables considered for the ML models, surface variables and mid-altitude variables (e.g., equivalent potential temperature and minimum equivalent potential temperature, respectively) have statistically significant contrasts between no-lightning and frequent-lightning hours. For example, the minimum equivalent potential temperature from 700 to 500 hPa is significantly lower during frequent-lightning hours compared with no-lightning hours. Finally, a notable positive relationship between the intracloud (IC) flash fraction and the square root of CAPE (CAPE) was found, suggesting that stronger updrafts increase the height of the electrification zone, resulting in fewer flashes reaching the surface and consequently a greater IC flash fraction.

Variations of Pre-monsoon season related atmospheric parameters over Kakinada region

Pre-monsoon showers occur before the beginning of the rainy season. From the months of March to May, they take place, and can be anything from little drizzles to powerful thunderstorms. March, April and May are known as the pre-monsoon season (PRMS). The precipitation patterns recorded in PRMS are critical because they have an impact on a wide range of crop-related operations across the country. During PRMS, the maximum temperature (TMAX), minimum temperature (TMIN), soil moisture, relative humidity, latent heat, convective available potential energy (CAPE), and total precipitable water (TPW) were analysed at Kakinada region. These variables were collected using daily ERA5 reanalysis data for the PRMS from 1981 to 2021. Studying the convection-related characteristics over the Kakinada station during the PRMS was our goal. During the study period, the five years with the highest PRMS rainfall were 1990, 1995, 2008, 2010 and 2016 and the five years with the lowest rainfall were 1990, 1995, 2008, 2010 and 2016. In the months leading up to the monsoon, the Kakinada station experiences CAPE values between 1000 and 6000 J/kg, while TPW values are between 25 and 60 mm. The PRMS values for CAPE and TPW both show that the prerequisites for moderate to severe convection activity have been fulfilled. TPW, soil moisture, relative humidity, and CAPE parameters during PRMS were well estimated using the ARMA and ARIMA models.

Cold Surge Effect on Vertical Profile Atmosphere over Meteorological Station of Ranai Natuna: Case Study Asian Winter Monsoon 2019/2020

During the Asian Winter season, which spans from November to February, the phenomenon of cold surge often occurs, leading to increased convective activity over the western Indonesian Maritime Continent. The location of Natuna Island, situated in the southern part of the South China Sea, is of particular importance for studying cold surges due to their propagation over this area. In this study, the vertical structure of the atmosphere was analyzed using radiosonde observation data collected at the Meteorological Station of Ranai Natuna. The analysis focused on physical parameters such as air temperature and relative humidity, atmospheric kinematics including wind direction and speed, as well as atmospheric thermodynamic parameters such as Lifting Condensation Level (LCL), Level of Free Convection (LFC), Equilibrium Level (EL), Convective Available Potential Energy (CAPE), and Convective Inhibition (CIN). The results indicate that during the passage of a cold surge, air temperature (T) tends to be higher in the lower troposphere, including at the surface, but lower in the middle and upper troposphere. Relative humidity (RH) also tends to be higher during cold surges, with a significant increase in the middle and upper troposphere. In the lower troposphere, the wind direction shifts from east to northeast at a higher speed compared to when a cold surge is absent. Furthermore, the LCL and LFC heights are elevated during the presence of a cold surge, while the EL height shows an insignificant decrease. It is worth noting that intense rainfall occurs, particularly when the cold surge is more pronounced, even though the values of CAPE and CIN do not change significantly.

Convection-parameterized and convection-permitting modelling of heavy precipitation in decadal simulations of the greater Alpine region with COSMO-CLM

Abstract. Heavy precipitation is a challenging phenomenon with high impact on human lives and infrastructure, and thus a better modelling of its characteristics can improve understanding and simulation at climate timescales. The achievement of convection-permitting modelling (CPM) resolutions (Δx&lt;4 km) has brought relevant advancements in its representation. However, further research is needed on how the very high resolution and switching-off of the convection parameterization affects the representation of processes related to heavy precipitation. In this study, we evaluate reanalysis-driven simulations for the greater Alpine area over the period 2000–2015 and assess the differences in representing heavy precipitation and other model variables in a CPM setup with a grid size of 3 km and a regional climate model (RCM) setup at 25 km resolution using the COSMO-CLM model. We validate our simulations against high-resolution observations (E-OBS (ENSEMBLES observations), HYRAS (Hydrometeorologische Rasterdatensätze), MSWEP (Multi-Source Weighted-Ensemble Precipitation), and UWYO (University of Wyoming)). The study presents a revisited version of the precipitation severity index (PSI) for severe event detection, which is a useful method to detect severe events and is flexible for prioritizing long-lasting events and episodes affecting typically drier areas. Furthermore, we use principal component analysis (PCA) to obtain the main modes of heavy precipitation variance and the associated synoptic weather types (WTs). The PCA showed that four WTs suffice to explain the synoptic situations associated with heavy precipitation in winter, due to stationary fronts and zonal flow regimes. Whereas in summer, five WTs are needed to classify the majority of heavy precipitation events. They are associated with upper-level elongated troughs over western Europe, sometimes evolving into cutoff lows, or with winter-like situations of strong zonal circulation. The results indicate that CPM represents higher precipitation intensities, better rank correlation, better hit rates for extremes detection, and an improved representation of heavy precipitation amount and structure for selected events compared to RCM. However, CPM overestimates grid point precipitation rates, which agrees with findings in past literature. CPM systematically represents more precipitation at the mountain tops. However, the RCMs may show large intensities in other regions. Integrated water vapour and equivalent potential temperature at 850 hPa are systematically larger in RCM compared to CPM in heavy precipitation situations (up to 2 mm and 3 K, respectively) due to wetter mid-level conditions and an intensified latent heat flux over the sea. At the ground level, CPM emits more latent heat than RCM over land (15 W m−2), bringing larger specific humidity north of the Alps (1 g kg−1) and higher CAPE (convective available potential energy) values (100 J kg−1). RCM, on the contrary simulates a wetter surface level over Italy and the Mediterranean Sea. Surface temperatures in RCM are up to 2 ∘C higher in RCM than in CPM. This causes outgoing longwave radiation to be larger in RCM compared to CPM over those areas (10 W m−2). Our analysis emphasizes the improvements of CPM for heavy precipitation modelling and highlights the differences against RCM that should be considered when using COSMO-CLM climate simulations.

Evolution of Convective Energy and Inhibition before Instances of Large CAPE

Abstract We analyze the evolution of convective available potential energy (CAPE) and convective inhibition (CIN) in the days leading up to episodes of high CAPE in North America. The widely accepted theory for CAPE buildup, known as the advection hypothesis, states that high moist static energy (MSE) parcels of air moving north from the Gulf of Mexico become trapped under warm but dry parcels moving east from over elevated dry terrain. If and when the resulting CIN erodes, severe convection can occur due to the large energy difference between the boundary layer parcels and cool air aloft. However, our results, obtained via backward Lagrangian tracking of parcels at locations of peak CAPE, show that large values of CAPE are generated mainly via boundary layer moistening in the days leading up to the time of peak CAPE, and that a large portion of this moisture buildup happens on the day of peak CAPE. On the other hand, the free-tropospheric temperature above these tracked parcels rarely changes significantly over the days leading up to such occurrences. In addition, the CIN that allows for this buildup of CAPE arises mostly from unusually strong boundary layer cooling the night before peak CAPE, and has a contribution from differential advection of unusually warm air above the boundary layer to form a capping inversion. These results have important implications for the climatology of severe convective events, as it emphasizes the role of surface properties and their gradients in the frequency and intensity of high CAPE occurrences. Significance Statement Severe convective events, such as thunderstorms, tornadoes, and hail storms, are among the most deadly and destructive weather systems. Although forecasters are quite good at predicting the probability of these events a few days in advance, there is currently no reliable seasonal prediction method of severe convection. We show that the buildup of energy for severe convection relies on both strong surface evaporation during the day of peak energy and anomalous cooling the night before. This progress represents a step toward understanding what controls the frequency of severe convective events on seasonal and longer time scales, including the effect of greenhouse gas–induced climate change.

Pre-monsoon Thunderstorm Season Climatology of Convective Available Potential Energy (CAPE) and Convective Inhibition (CIN) over Eastern India

The present work analyses climatological variations of Convective Available Potential Energy (CAPE) and Convective Inhibition (CIN) over the eastern India (Odisha, West Bengal and Jharkhand) during the pre-monsoon season, where thunderstorms are frequent and disastrous. The work utilises European Centre for Medium-Range Weather Forecast (ECMWF) reanalysis data: ERA-5 for 1987-2016, supplemented with information about thunderstorm occurrences over the region from India Meteorological Department (IMD). The CAPE and CIN values can differentiate thunderstorm days (TD) from non-thunderstorm days (NTD), with favourable conditions of convective weather on days of thunderstorms over the region, evident by CAPE and CIN. The coastal areas of Odisha and West Bengal, along with the Jharkhand bordering the northern West Bengal region, have higher CAPE and lower CIN values. The trend analysis of CAPE and CIN has been performed using the non-parametric Mann-Kendall test, which shows an apparent transformation of indices over time for different regions of states for TD and NTD. CAPE shows an increasing trend over the coastal districts of Odisha and West Bengal during TD and for the whole of West Bengal during 12 UTC NTD. The NTD cases show a decreasing trend over Odisha (both 00 and 12 UTC) and 00 UTC over West Bengal. CIN shows an increasing trend for TD and decreasing trend for NTD over whole Odisha, whereas, for West Bengal, trends are positive for coastal regions during TD and negative on the entire state during NTD. For Jharkhand, both the CAPE and CIN values show an increasing trend over the state during NTD, whereas for TD, both increasing/decreasing trends are visible. The analysis complements the observations of thunderstorm occurrence over the region to understand areas with higher potential of thunderstorm occurrence during pre-monsoon season.

Tornadoes in the Tyrrhenian regions of the Italian peninsula: The case study of 28 July 2019

On 28 July 2019 an EF2 tornado affected a small rural area in central Italy causing several damages and one casualty. The tornado was spawned by a thunderstorm embedded in a linear convective system that crossed the central Tyrrhenian regions of Italy. The environment was characterized by high values of convective available potential energy (CAPE) and deep layer wind shear (DLS). The severity of this type of events highlights the importance of carrying out multi-scale integrated analysis on tornado phenomena in the area, one of the most affected by these events in the Mediterranean and on which dedicated studies have not yet been carried out so far.Tornadoes in the area are identified in the years 1990–2021, allowing to perform a synoptic/mesoscale analysis of the main patterns associated to these events. The 32-year analysis is carried out using both radiosonde observations and ERA5 reanalysis.The average synoptic configuration is dominated by an upper level trough over the central Mediterranean Sea and by a low surface pressure area over northwestern Italy, with southwesterly upper-level winds over the Tyrrhenian Sea and higher-than-average northwesterly winds entering the western Mediterranean through the gulf of Lion. Moderate mean values of CAPE (about 700 J Kg−1) and DLS (about 15 m s−1) are found, and the linear shape of the hodograph indicates favorable conditions for multicell systems.High-resolution WRF (Weather Research and Forecasting) model simulations of the 28 July 2019 case study correctly reproduced the event and the structure of the storm. Extreme values of the typical instability parameters/indices denote an environment particularly favorable for tornado formation; some sensitivity tests permitted to evaluate the role of several forcing (Sea Surface Temperature, surface fluxes and orography) in the development and the trajectory of the storm.

Dependence of Rain Drop Size Distribution Parameters on Atmospheric Instability Over a Tropical Location Near the Land‐Sea Boundary

AbstractThe role of atmospheric instability, expressed by Convective Available Potential Energy (CAPE), in determining raindrop size distribution (DSD) parameters have been investigated over an urban tropical location, Kolkata (22.57°N and 88.37°E), India, near the land‐sea boundary. DSD measurements obtained from a ground‐based disdrometer during both pre‐monsoon (March‐May) and monsoon periods (June‐September) have been used in conjunction with CAPE from ERA‐5 data from 2014 to 2018. Based on collocated observations from a K‐band Doppler micro rain radar, rain events are classified as convective or stratiform. The study has shown that enhanced CAPE values significantly influence DSD parameters by increasing mass‐weighted mean diameter (Dm) during convective rain, but it does not impact directly during stratiform rain. For stratiform rain events, the melting layer becomes a significant factor in determining Dm, which decreases with increasing melting layer height. Convective rain exhibits a bimodal DSD pattern for higher CAPE values, while stratiform rain shows a unimodal DSD feature. The present study location provides a unique opportunity to study the combined influences of air mass flows from the hot land region in Chotanagpur plateau and from the sea region of the Bay of Bengal on precipitation features. The investigation reveals the dominance of continental activities during convective precipitation and of maritime airflows on stratiform rain events, which is more visible during the pre‐monsoon season compared to the monsoon period. For the first time, the dual control of CAPE and melting layer on drop size distributions has been demonstrated for convective and stratiform rain events.

Long-term thunderstorm analysis at airports in the Marmara Region: types and favourable atmospheric conditions

In this study, long-term analyses of thunderstorm events occurring in Marmara Region airports were carried out. In the analyses made using airport reports, the events that occurred between 2001-2015 were evaluated in terms of annual, monthly and intra-day changes. While no particular trend was observed in the thunderstorm events annually, more thunderstorms occurred in the summer months after September. In intraday analyses, it was determined that the most thunderstorm events occurred in the 2nd time zone (1100-1900 UTC). Rain also occurred 72% of the times when thunderstorms occurred. The rate of thunderstorm events that occurred without precipitation is 22%. One of the most important results of the study is that the convective available potential energy (CAPE) value was found to be zero in approximately 50% of the thunderstorm events. Non-zero CAPE values were also found to occur mostly (about 90%) in the range of 0 J/kg-1,000 J/kg.

Influences of CAPE on Hail Production in Simulated Supercell Storms

Abstract Lasting updrafts are necessary to produce severe hail; conventional wisdom suggests that extremely large hailstones require updrafts of commensurate strength. Because updraft strength is largely controlled by convective available potential energy (CAPE), one would expect environments with larger CAPE to be conducive to storms producing larger hail. By systematically varying CAPE in a horizontally homogeneous initial environment, we simulate hail production in high-shear, high-instability supercell storms using Cloud Model 1 and a detailed 3D hail growth trajectory model. Our results suggest that CAPE modulates the updraft’s strength, width, and horizontal wind field, as well as the liquid water content along hailstones’ trajectories, all of which have a significant impact on final hail sizes. In particular, hail sizes are maximized for intermediate CAPE values in the range we examined. Results show a non-monotonic relationship between the hailstones’ residence time and CAPE due to changes to the updraft wind field. The ratio of updraft area to southerly wind speed within the updraft serves as a proxy for residence time. Storms in environments with large CAPE may produce smaller hail because the in-updraft horizontal wind speeds become too great, and hailstones are prematurely ejected out of the optimal growth region. Liquid water content (LWC) along favorable hailstone pathways also exhibits peak values for intermediate CAPE values, owing to the horizontal displacement across the midlevel updraft of moist inflow air from differing source levels. In other words, larger CAPE does not equal larger hail, and storm-structural nuances must be examined.

A Model for the Relationship between Rainfall, GNSS-Derived Integrated Water Vapour, and CAPE in the Eastern Central Andes

Atmospheric water vapour content is a key variable that controls the development of deep convective storms and rainfall extremes over the central Andes. Direct measurements of water vapour are challenging; however, recent developments in microwave processing allow the use of phase delays from L-band radar to measure the water vapour content throughout the atmosphere: Global Navigation Satellite System (GNSS)-based integrated water vapour (IWV) monitoring shows promising results to measure vertically integrated water vapour at high temporal resolutions. Previous works also identified convective available potential energy (CAPE) as a key climatic variable for the formation of deep convective storms and rainfall in the central Andes. Our analysis relies on GNSS data from the Argentine Continuous Satellite Monitoring Network, Red Argentina de Monitoreo Satelital Continuo (RAMSAC) network from 1999 to 2013. CAPE is derived from version 2.0 of the ECMWF’s (European Centre for Medium-Range Weather Forecasts) Re-Analysis (ERA-interim) and rainfall from the TRMM (Tropical Rainfall Measuring Mission) product. In this study, we first analyse the rainfall characteristics of two GNSS-IWV stations by comparing their complementary cumulative distribution function (CCDF). Second, we separately derive the relation between rainfall vs. CAPE and GNSS-IWV. Based on our distribution fitting analysis, we observe an exponential relation of rainfall to GNSS-IWV. In contrast, we report a power-law relationship between the daily mean value of rainfall and CAPE at the GNSS-IWV station locations in the eastern central Andes that is close to the theoretical relationship based on parcel theory. Third, we generate a joint regression model through a multivariable regression analysis using CAPE and GNSS-IWV to explain the contribution of both variables in the presence of each other to extreme rainfall during the austral summer season. We found that rainfall can be characterised with a higher statistical significance for higher rainfall quantiles, e.g., the 0.9 quantile based on goodness-of-fit criterion for quantile regression. We observed different contributions of CAPE and GNSS-IWV to rainfall for each station for the 0.9 quantile. Fourth, we identify the temporal relation between extreme rainfall (the 90th, 95th, and 99th percentiles) and both GNSS-IWV and CAPE at 6 h time steps. We observed an increase before the rainfall event and at the time of peak rainfall—both for GNSS-integrated water vapour and CAPE. We show higher values of CAPE and GNSS-IWV for higher rainfall percentiles (99th and 95th percentiles) compared to the 90th percentile at a 6-h temporal scale. Based on our correlation analyses and the dynamics of the time series, we show that both GNSS-IWV and CAPE had comparable magnitudes, and we argue to consider both climatic variables when investigating their effect on rainfall extremes.

Application of Ground-Based Microwave Radiometer in Retrieving Meteorological Characteristics of Tibet Plateau

The characteristics of plateau precipitation and atmosphere, once accurately and comprehensively understood, can be used to inform sound air–water resource development practices. In this study, atmospheric exploration of the Tibet Plateau (TP) was conducted using ground-based microwave radiometer (MWR) data collected during the East Asian summer monsoon. Atmospheric temperature, pressure, humidity, and other variables were gathered under clear-sky, cloudy-sky, and rainy-sky conditions. Statistical characteristics of the air parcel height and stability/convection indices such as convective available potential energy (CAPE) and convective inhibition (CIN) were investigated, with a special focus on the rainy-sky condition. Two retrieval applications for characterizing precipitation, namely short-term precipitation forecast and quantitative precipitation estimation were presented. Results showed that CAPE values in the Darlag region reached extremes around 18:00–20:00 (UTC+8) for cloudy-sky and rainy-sky conditions with corresponding peaks of about 1046.56 J/kg and 703.02 J/kg, respectively. When stratiform or convective–mixed precipitation occurs, the precipitable water vapor (PWV) and CAPE values were generally greater than 1.7 cm and 1000 J/kg, respectively. CAPE values are likely to decrease before the occurrence of precipitation due to the release of the latent heat in the atmosphere.

A five-year climatological lightning characteristics of linear mesoscale convective systems over North China

The lightning characteristics of 89 linear mesoscale convective systems (MCSs) occurred over the Beijing area from the year of 2007 to 2011 were analyzed by lightning data and S-band radar information. According to different morphology of radar echo, linear MCSs were classified into six categories: leading convective lines with a trailing stratiform region (TS for short), leading stratiform region with a trailing convective region (LS), leading convective lines with no stratiform region (NS), bow echo of leading lines (BE), leading convective lines with a parallel stratiform region (PS), and broken line stratiform (BL). The results showed that linear MCSs occurred frequently over the Beijing area at the summer time, in particular, TS, LS and PS modes totally accounted for 73% of linear MCSs. On the average, lightning mainly concentrated in the linear convective region, and small amount of lightning occurred in the stratiform region. At the mature stage, lightning mainly located in the linear convective region with strong radar echo of TS, LS, and PS MCSs. At the dissipating stage, the lightning gradually increased in the stratiform region of TS MCSs, whereas fewer lightning occurred in the mode of LS MCSs, and positive cloud-to-ground (+CG) lightning accounted for a large percentage in the mode of PS MCSs. From the distribution of +CG/CG in three archetypes of linear MCSs, it is found that PS MCSs with highest the proportion of +CG/CG, and then followed by LS MCSs while the lowest ratio appeared in TS MCSs. The relationship between lightning frequency and volume of 40 dBZ radar echo exhibited linear correlation in three distinct archetypes of linear MCS. Environmental factors of linear MCSs exhibited that high CAPE (Convective Available Potential Energy) value and the larger wind shear of 0–6 km played an important role to sustain the convective development of TS, LS and PS MCSs.

Modeling of Lightning Events using WRF-derived Microphysical Parameters

Numerical simulation of lightning events in Bangladesh has been carried out by using Weather Research and Forecasting Model with Advanced Research Dynamic solver (WRF-ARW). Three major lightning events have been considered for the case study; Case_1, lightning occurrence in Netrokona district in March 24 2017, Case_2, lightning event in Barishal district in April 23 2017, and case_3, lightning event in Sherpur district in April 29, 2018. The model simulation was run in 9 km and 3 km of horizontal resolution using six hourly NCEP-FNL datasets. Yonsei University (YSU) PBL scheme, Rapid Radiative Transfer Model (RRTM) long-wave scheme for radiation, and Kain-Fritsch cumulus parameterization scheme is used for this study. The obtained results from the simulation could reasonably capture the lightning condition of the atmosphere for all the three cases. The WRF simulation give reasonable agreement with the available observational data with some spatial and temporal variations, for example the Convective Available Potential Energy (CAPE) values observed are 1299 J/Kg, 3150 J/kg, 1221 J/kg and CAPE values simulated are 1618 J/kg, 3275 J/kg and 1023 J/kg for case_1, case_2 and case_3 respectively. The regression analysis of the flash count with the microphysical parameters is also studied. It is found that there is strong correlation between the lightning flash counts with the microphysical parameters. This study will help to understand the lightning better and will help to design a better lightning forecasting system.&#x0D; The Dhaka University Journal of Earth and Environmental Sciences, Vol. 8(2), 2019, P 41-50

Characteristics of Extratropical Cyclones That Cause Tornadoes in Italy: A Preliminary Study

Characteristics of extratropical cyclones that cause tornadoes in Italy are investigated. Tornadoes between 2007 and 2016 are analyzed, and statistical analysis of the associated cyclone structures and environments is performed using the JRA-55 reanalysis. Tornadoes are distributed sporadically around the cyclone location within a window of 10° × 10°. The difference in the cyclone tracks partially explains the seasonal variability in the distribution of tornadoes. The highest number of tornadoes occur south of the cyclone centers, mainly in the warm sector, while a few are observed along the cold front. Composite mesoscale parameters are examined to identify the environmental conditions associated with tornadoes in different seasons. Potential instability is favorable to tornado development in autumn. The highest convective available potential energy (CAPE) in this season is associated with relatively high-temperature and humidity at low-levels, mainly due to the strong evaporation over the warm Mediterranean Sea. Upper-level potential vorticity (PV) anomalies and the associated cold air reduce the static stability above the cyclone center, mainly in spring and winter. On average, the values of CAPE are lower than for US tornadoes and comparable with those occurring in Japan, while storm relative helicity (SREH) is comparable with US tornadoes and higher than Japanese tornadoes, indicating that the environmental conditions for Italian tornadoes have peculiar characteristics. Overall, the conditions emerging in this study are close to the high-shear, low-CAPE environments typical of cool-season tornadoes in the Southeastern US.