Showing papers on "Convective available potential energy published in 2021"

Global climatology and trends in convective environments from ERA5 and rawinsonde data

Abstract: Globally, thunderstorms are responsible for a significant fraction of rainfall, and in the mid-latitudes often produce extreme weather, including large hail, tornadoes and damaging winds. Despite this importance, how the global frequency of thunderstorms and their accompanying hazards has changed over the past 4 decades remains unclear. Large-scale diagnostics applied to global climate models have suggested that the frequency of thunderstorms and their intensity is likely to increase in the future. Here, we show that according to ERA5 convective available potential energy (CAPE) and convective precipitation (CP) have decreased over the tropics and subtropics with simultaneous increases in 0–6 km wind shear (BS06). Conversely, rawinsonde observations paint a different picture across the mid-latitudes with increasing CAPE and significant decreases to BS06. Differing trends and disagreement between ERA5 and rawinsondes observed over some regions suggest that results should be interpreted with caution, especially for CAPE and CP across tropics where uncertainty is the highest and reliable long-term rawinsonde observations are missing.

Analysis of a Record-Breaking Rainfall Event Associated With a Monsoon Coastal Megacity of South China Using Multisource Data

Abstract: Monsoon coastal cities often suffer from extreme rain-induced flooding and severe hazard. However, the associated physical mechanisms and detailed storm structures are poorly understood due to the lack of high-resolution data. This study presents an analysis of a thunderstorm that produces extreme hourly rainfall (EXHR) of 219 mm over the Guangzhou megacity on the southern coast of China using integrated multiplatform observations and a four-dimensional variational Doppler radar analysis system. Results indicate that weak environmental flows and convectively generated weak cold pool facilitate the formation of a quasi-stationary storm, while onshore warm and moist flows in the boundary layer (BL) provide the needed moisture supply. The 219-mm EXHR is attendant by a shallow meso- $\gamma $ -scale vortex due to stretching of intense latent heating-induced convergence, which, in turn, helps organize convective updrafts into its core region. Lightning and dual-polarization radar observations reveal active warm-rain (but weak mixed-phase) microphysical processes, with raindrop size distribution (RSD) closer to marine convection. In contrast, another storm develops about 4 h earlier and only 35 km to the northwest, but with more lightning, higher cloud tops, more graupel and supercooled liquid water content, more continental RSD, little evidence of rotation, and much less rainfall; they are attributable to the presence of larger convective available potential energy resulting from the urban heat island effects and less moisture supply in the BL. These results highlight the importance of using multisource remote sensing data sets in understanding the microphysical and kinematic structures of EXHR-producing storms.

The Synoptic Impacts on the Convection Initiation of a Warm‐sector Heavy Rainfall Event over Coastal South China Prior to the Monsoon Onset: A Numerical Modeling Study

Abstract: A series of convection-permitting numerical experiments using the Weather Research and Forecasting (WRF) Model with different model configurations are performed to investigate physical mechanisms governing convection initiation (CI) at the coast of South China (SC) during a warm-sector heavy rainfall event occurred before the South China Sea (SCS) monsoon onset. The simulation results are more sensitive to initial state from the different reanalysis products than the microphysics schemes, horizontal resolutions, initialization time, and lateral boundary conditions with the variation examined. It is found that the speeds of easterly to southeasterly winds in the boundary layer (BL) over northern SCS determine the strength of horizontal convergence of the warm and moist airflows arriving at the coast. The mid-tropospheric divergence over the west coastal areas of SC and its southwest upstream impact vertical motion of the mid-to-lower tropospheric southwesterly airflows when approaching the coast. Differences in such features of upstream airflows in the experiments lead to distinct temporal evolutions of BL dynamic lifting and temperature stratification in the mid-to-lower levels at the CI location, thus the level of free convection and convective available potential energy. The modeling evidence presented shows that the synoptic dynamic and thermodynamic characteristics of the upstream airflows in BL and mid-to-lower troposphere, with local modulation by the coastal mountains, play important roles in determining the time and location of CI, and the distribution and amount of rainfall. Studies on more cases are needed to gain more general and robust conclusions about physical mechanism governing the warm-sector coastal CI.

Effects of coupling a stochastic convective parameterization with the Zhang–McFarlane scheme on precipitation simulation in the DOE E3SMv1.0 atmosphere model

Abstract: . A stochastic deep convection parameterization is implemented into the US Department of Energy (DOE) Energy Exascale Earth System Model (E3SM) Atmosphere Model version 1.0 (EAMv1). This study evaluates its performance in simulating precipitation. Compared to the default model, the probability distribution function (PDF) of rainfall intensity in the new simulation is greatly improved. The well-known problem of “too much light rain and too little heavy rain” is alleviated, especially over the tropics. As a result, the contribution from different rain rates to the total precipitation amount is shifted toward heavier rain. The less frequent occurrence of convection contributes to suppressed light rain, while more intense large-scale and convective precipitation contributes to enhanced heavy total rain. The synoptic and intraseasonal variabilities of precipitation are enhanced as well to be closer to observations. The sensitivity of the rainfall intensity PDF to the model vertical resolution is examined. The relationship between precipitation and dilute convective available potential energy in the stochastic simulation agrees better with that in the Atmospheric Radiation Measurement (ARM) observations compared with the standard model simulation. The annual mean precipitation is largely unchanged with the use of the stochastic scheme except over the tropical western Pacific, where a moderate increase in precipitation represents a slight improvement. The responses of precipitation and its extremes to climate warming are similar with or without the stochastic deep convection scheme.

Impact of urban sprawls on thunderstorm episodes: Assessment using WRF model over central-national capital region of India

Abstract: Urbanization is the most dominating land use change in the developing countries.There is a considerable growth (30 fold increase) of urban area during recent decades over the central National Capital Region (CNCR) of India. The present study assesses the impact of increasing urban sprawls on precipitation related to thunderstorm and associated meteorological parameters such as convective available potential energy (CAPE) and convective inhibition (CIN) using the Weather Research and Forecast (WRF) model. The study shows that in response to increased convective activity the PBL depth increases by about 400–800 m over urban stations. Furthermore, all sites that got urbanized in the year 2014 showed significantly higher MCAPE of about 10–14% than their values in 1972. Just before the thunderstorm, the maximum CIN (MCIN) value decreases for the urban stations and reaches threshold of MCIN (

Diurnal cycle of summer precipitation over the Eastern Tibetan Plateau and surrounding regions simulated in a convection-permitting model

Abstract: Based on the hourly gauge-satellite merged precipitation data with the spatial resolution of 0.1° × 0.1° during 2013 ~ 2018, we have evaluated the performance of the convection-permitting Weather Research and Forecasting model at Nanjing University (WRF_NJU) in forecasting the precipitation diurnal variation and the associated atmospheric circulation over the eastern Tibetan Plateau and its surrounding regions during summer. Results indicate that WRF_NJU model can well reproduce the diurnal cycle of the summer precipitation in terms of the diurnal peak time, duration and magnitude. In addition, the eastward propagation of rainfall systems with long duration along the eastern Tibetan Plateau (ETP) and its adjacent areas can also be properly captured. The WRF_NJU model can reasonably reproduce the relevant atmospheric circulation during summer as well. However, the model tends to underestimate the summer precipitation amount (PA) and precipitation frequency (PF) over most time of a day. Relatively larger biases in the occurring time and magnitude of PA and PF diurnal peaks can be noted over the ETP and Sichuan Basin. Further analysis suggests that the underestimation of PA over the ETP is attributed to the much lower moisture supply, weaker low-level southwesterly winds and less convective available potential energy (CAPE) in the WRF_NJU model than in ERA5. Over Sichuan Basin, the underestimated PA is related to the weaker upward motion, which is corresponding to the cold biases of surface air temperature in WRF_NJU. Findings of this study provide the basic model biases and may be helpful to further improve the model physical processes.

Projected changes to severe thunderstorm environments as a result of twenty-first century warming from RegCM CORDEX-CORE simulations

Abstract: Hazardous weather related to the occurrence of severe thunderstorms including tornadoes, high-winds, and hail cause significant damage globally to life and property every year. Yet the impact on these storms from a warming climate remains a difficult task due to their transient nature. In this study we investigate the change in large-scale environments in which severe thunderstorms form during twenty-first century warming (RCP2.6 and RCP8.5) in a group of RegCM CORDEX-CORE simulations. Severe potential is measured in terms of Convective Available Potential Energy (CAPE) and vertical wind-shear during the severe seasons in three regions which are known to currently be prone to severe hazards: North America, subtropical South America, and eastern India and Bangladesh. In every region, environments supportive for severe thunderstorms are projected to increase during the warm season months in both the RCP2.6 and RCP8.5 scenarios during the twenty-first century. The number of days supportive for severe thunderstorms increases by several days per season over the vast majority of each region by the end of the century. Analyzing the CAPE and shear trends during the twenty-first century, we find seasonally and regionally specific changes driving the increased severe potential. Twenty-first century surface warming is clearly driving a robust increase in CAPE in all regions, however poleward displacement of vertical shear in the future leads to the displacement of severe environments over North America and South America. The results found here relate that severe impacts in the future cannot be generalized globally, and that regionally specific changes in vertical shear may drive future movement of regions prone to severe weather.

Characteristics of Raindrop Size Distribution in Seoul, South Korea According to Rain and Weather Types

Abstract: The raindrop size distribution (RSD) is useful in understanding various precipitation-related processes. Here, we analyze disdrometer data collected in Seoul, South Korea from May 2018 to July 2019 to characterize the RSD according to rain and weather types. Rain types are categorized into stratiform, mixed, and convective rain, and weather types into the Changma front (type CF) and low-pressure system (type L). The slope parameter Λ decreases and the intercept parameter N0 fluctuates with rain rate. Among the rain types, the RSD of stratiform (convective) rain shows the steepest (mildest) slope and the smallest (largest) mean diameter. The logarithm of generalized intercept parameter log10Nw and Λ for stratiform rain have considerably dispersed distributions, which may be attributed to the diversity within the stratiform rain type in Seoul. Mixed-type rain has a larger mean value of log10Nw compared to stratiform and convective rain. Regarding the weather types, the RSD of type CF exhibits a milder slope, a larger mass-weighted mean diameter, and a larger radar reflectivity than type L. These differences between the weather types can be explained by the larger convective proportion in type CF (33%) compared to type L (9%). Possible causes for the differences between the RSD characteristics of the two weather types are examined using reanalysis and satellite data. Type CF has a larger convective available potential energy, a higher cloud top, and more active ice microphysical processes than type L, which can lead to different RSD characteristics.

Crucial Role of Mesoscale Convective Systems in the Vertical Mass, Water and Energy Transports of the South Asian Summer Monsoon

Abstract: Convective vertical transport is critical in the monsoonal overturning but the relative roles of different convective systems are not well understood. This study used a cloud classification and tracking technique to decompose a convection-permitting simulation of the South Asian summer monsoon (SASM) into sub-regimes of mesoscale convective system (MCS), non-MCS deep convection (non-MCS), congestus, and shallow convection/clear-sky. Isentropic analysis is adopted to quantify the contributions of different convective systems to the total SASM vertical mass, water, and energy transports. The results underscore the crucial roles of MCSs in the SASM vertical transports. Compared to non-MCSs, the total mass and energy transports by MCSs are at least 1.5 times stronger throughout the troposphere, with a larger contributing fraction from convective updrafts compared to upward motion in stratiform regions. Occurrence frequency of non-MCSs is around 40 times higher than that of MCSs. However, per instantaneous convection feature, the vertical transports and net MSE export by MCSs are about 70-100 and 58 times stronger than that of non-MCSs. While these differences are dominantly contributed by differences in the per-feature MCS and non-MCS area coverage, MCSs also show stronger transport intensities than non-MCSs over both ocean and land. Oceanic MCSs and non-MCSs show more obvious top-heavy structures than their inland counterparts, which are closely related to the widespread stratiform over ocean. Compared to the monsoon break phase, MCSs occur more frequently (~1.6 times) but their vertical transport intensity slightly weakens (by ~10%) during the active phases. These results are useful for understanding the SASM and advancing the energetic framework.

Dependence of Warm Season Cloud-to-Ground Lightning Polarity on Environmental Conditions over Sichuan, Southwest China

Abstract: The effects of thermodynamic and moisture factors on cloud-to-ground (CG) lightning polarity in the warm season were discussed. Small convective available potential energy (CAPE) represents relatively shallow convection, which is beneficial to the generation of positive lightning. Large vertical wind shear results in the displacement of upper-level positive ice crystals and promotes the initiation of +CG lightning from positive ice crystals. The dry low- to midlevel troposphere and the high cloud base in the plateau region favor +CG lightning, while the strong thermodynamic conditions in the basin region offset the influence of these moisture factors. In the plateau region, due to the limited cloud thickness, high total column liquid water may mean high cloud water content in the warm cloud region rather than high liquid water content in the mixed-phase region, which is unfavorable for the middle-level positive graupel and thus is unfavorable for the initiation of +CG lightning. In the basin region, the cloud thickness is relatively thicker, the high total column liquid water means that the liquid water content in the warm cloud and the mixed-phase region is both high, which is conducive to the middle-level positive graupel and the +CG lightning.

Urban-climate interactions during summer over eastern North America

Abstract: The urban heat island is a representative urban climate characteristic, which can affect heat-stress conditions and extreme precipitation that are closely connected with human life. Better understanding of urban-climate interactions, therefore, is crucial to ultimately support better planning and adaptation in various application fields. This study assesses urban-climate interactions during summer for eastern North America using regional climate model simulations at 0.22° resolution. Two regional climate model experiments, with and without realistic representation of urban regions, are performed for the 1981–2010 period. Comparison of the two experiments shows higher mean temperatures and reduced mean precipitation in the simulation with realistic urban representation, which can be attributed primarily to reduced albedo and soil moisture for the urban regions in this simulation. Furthermore, the mean temperature and precipitation in the simulation with improved urban representation is also closer to that observed. Analysis of short-duration precipitation extremes for climatologically different sub-regions, however, suggests that, for higher temperatures, the magnitudes of precipitation extremes are generally higher in the simulation with realistic urban representation, particularly for coastal urban regions, and are collocated with higher values of convective available potential energy and cloud fraction. Enhanced sea and lake breezes associated with lower sea level pressure found around these regions, contribute additional water vapor and further enhance dynamic convective development, leading to higher precipitation intensities. Analysis of temperature extremes clearly demonstrates that urban regions experience aggravated heat-stress conditions due to relatively higher temperatures despite reduced relative humidity. Double the number of extreme heat spells lasting six or more days are noted for the coastal urban regions in the study domain. This study, in addition to demonstrating the differences in urban-climate interactions for climatologically different regions, also demonstrates the need for better representation of urban regions in climate models to generate realistic climate information.

Supersaturation, buoyancy, and deep convection dynamics

Abstract: . Motivated by recent discussions concerning differences of convective dynamics in polluted and pristine environments, the so-called convective invigoration in particular, this paper provides an analysis of factors affecting convective updraft buoyancy, such as the in-cloud supersaturation, condensate and precipitation loading, and entrainment. We use the deep convective period from simulations of daytime convection development over land discussed in our previous publications. An entraining parcel framework is used in the theoretical analysis. We show that for the specific case considered here, finite (positive) supersaturation noticeably reduces pseudo-adiabatic parcel buoyancy and cumulative convective available potential energy (cCAPE) in the lower troposphere. This comes from keeping a small fraction of the water vapor in a supersaturated state and thus reducing the latent heating. Such a lower-tropospheric impact is comparable to the effects of condensate loading and entrainment in the idealized parcel framework. For the entire tropospheric depth, loading and entrainment have a much more significant impact on the total CAPE. For the cloud model results, we compare ensemble simulations applying either a bulk microphysics scheme with saturation adjustment or a more comprehensive double-moment scheme with supersaturation prediction. We compare deep convective updraft velocities, buoyancies, and supersaturations from all ensembles. In agreement with the parcel analysis, the saturation-adjustment scheme provides noticeably stronger updrafts in the lower troposphere. For the simulations predicting supersaturation, there are small differences between pristine and polluted conditions below the freezing level that are difficult to explain by standard analysis of the in-cloud buoyancy components. By applying the piggybacking technique, we show that the lower-tropospheric buoyancy differences between pristine and polluted simulations come from a combination of temperature (i.e., latent heating) and condensate loading differences that work together to make polluted buoyancies and updraft velocities slightly larger when compared to their pristine analogues. Overall, the effects are rather small and contradict previous claims of a significant invigoration of deep convection in polluted environments.

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

Abstract: 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.

On the Diurnal Cycle of Heavy Rainfall over the Sichuan Basin during 10–18 August 2020

Abstract: A sustained heavy rainfall event occurred over the Sichuan basin in southwest China during 10–18 August 2020, showing pronounced diurnal rainfall variations with nighttime peak and afternoon minimum values, except on the first day. Results show that the westward extension of the anomalously strong western Pacific subtropical high was conducive to the maintenance of a southerly low-level jet (LLJ) in and to the southeast of the basin, which favored continuous water vapor transport and abnormally high precipitable water in the basin. The diurnal cycle of rainfall over the basin was closely related to the periodic oscillation of the LLJ in both wind speed and direction that was caused by the combination of inertial oscillation and terrain thermal forcing. The nocturnally enhanced rainfall was produced by moist convection mostly initiated during the evening hours over the southwest part of the basin where high convective available potential energy with moister near-surface moist air was present. The convective initiation took place as cold air from either previous precipitating clouds from the western Sichuan Plateau or a larger-scale northerly flow met a warm and humid current from the south. It was the slantwise lifting of the warm, moist airflow above the cold air, often facilitated by southwest vortices and quasi-geostrophic ascent, that released the convective instability and produced heavy rainfall.

Role of CAPE and CINE in modulating the convective activities during April over India

Abstract: During the month of April, except over northwest India, where rain is normally associated with the intrusion of midlatitudinal westerly systems in the form of western disturbances, other parts of the country receive rain due to enhancement of convective activities in the form of thundershowers, occurring over many parts of the country. The role of Convective Available Potential Energy (CAPE) and Convective Inhibition Energy (CINE) were studied for the occurrence of more convective activities in the month of April 1997 compared to other years. The results reveal that larger values of CAPE and smaller values of CINE in April 1997 over various parts of India compared to other years were responsible for more convective activities and consequently appreciable fall in temperature in April 1997.

Midlatitude Continental CAPE Is Predictable From Large-Scale Environmental Parameters

Abstract: A recent study by Agard and Emanuel (2017) proposed a simple equation for a quantity that scales with convective available potential energy (CAPE) that can be directly calculated from a limited num...

The behavior of high-CAPE (convective available potential energy) summer convection in large-domain large-eddy simulations with ICON

Abstract: . Current state-of-the-art regional numerical weather prediction (NWP) models employ kilometer-scale horizontal grid resolutions, thereby simulating convection within the grey zone. Increasing resolution leads to resolving the 3D motion field and has been shown to improve the representation of clouds and precipitation. Using a hectometer-scale model in forecasting mode on a large domain therefore offers a chance to study processes that require the simulation of the 3D motion field at small horizontal scales, such as deep summertime moist convection, a notorious problem in NWP. We use the ICOsahedral Nonhydrostatic weather and climate model in large-eddy simulation mode (ICON-LEM) to simulate deep moist convection and distinguish between scattered, large-scale dynamically forced, and frontal convection. We use different ground- and satellite-based observational data sets, which supply information on ice water content and path, ice cloud cover, and cloud-top height on a similar scale as the simulations, in order to evaluate and constrain our model simulations. We find that the timing and geometric extent of the convectively generated cloud shield agree well with observations, while the lifetime of the convective anvil was, at least in one case, significantly overestimated. Given the large uncertainties of individual ice water path observations, we use a suite of observations in order to better constrain the simulations. ICON-LEM simulates a cloud ice water path that lies between the different observational data sets, but simulations appear to be biased towards a large frozen water path (all frozen hydrometeors). Modifications of parameters within the microphysical scheme have little effect on the bias in the frozen water path and the longevity of the anvil. In particular, one of our convective days appeared to be very sensitive to the initial and boundary conditions, which had a large impact on the convective triggering but little impact on the high frozen water path and long anvil lifetime bias. Based on this limited set of sensitivity experiments, the evolution of locally forced convection appears to depend more on the uncertainty of the large-scale dynamical state based on data assimilation than of microphysical parameters. Overall, we judge ICON-LEM simulations of deep moist convection to be very close to observations regarding the timing, geometrical structure, and cloud ice water path of the convective anvil, but other frozen hydrometeors, in particular graupel, are likely overestimated. Therefore, ICON-LEM supplies important information for weather forecasting and forms a good basis for parameterization development based on physical processes or machine learning.

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

Abstract: 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.

Severe convection-related winds in Australia and their associated environments

Abstract: Severe surface wind gusts produced by thunderstorms have the potential to damage infrastructure and are a major hazard for society. Wind gust data are examined from 35 observing stations around Australia, with lightning observations used to indicate the occurrence of deep convective processes in the vicinity of the observed wind gusts. A collation of severe thunderstorm reports is also used to complement the station wind gust data. Atmospheric reanalysis data are used to systematically examine large-scale environmental measures associated with severe convective winds. We find that methods based on environmental measures provide a better indication of the observed severe convective winds than the simulated model wind gusts from the reanalysis data, noting that the spatial scales on which these events occur are typically smaller than the reanalysis grid cells. Consistent with previous studies in other regions and idealised modelling, the majority of severe convective wind events are found to occur in environments with steep mid-level tropospheric lapse rates, moderate convective instability and strong background wind speeds. A large proportion of events from measured station data occur with relatively dry environmental air at low levels, although it is unknown to what extent this type of environment is representative of other severe wind-producing convective modes in Australia. The occurrence of severe convective winds is found to be well represented by a number of indices used previously for forecasting applications, such as the weighted product of convective available potential energy (CAPE) and vertical wind shear, the derecho composite parameter and the total totals index, as well as by logistic regression methods applied to environmental variables. Based on the systematic approach used in this study, our findings provide new insight on spatio-temporal variations in the risk of damaging winds occurring, including the environmental factors associated with their occurrence.

Calibration of Kain–Fritsch cumulus scheme in Weather Research and Forecasting (WRF) model over Western Luzon, Philippines

Abstract: Calibration of the cumulus parameterization scheme for localized areas is one method that can improve numerical weather prediction rainfall forecast accuracy Calibration for model development, however, is a time-consuming procedure that requires numerous simulations The utilization of an efficient method for calibrating complex dynamical models can help mitigate the heavy computational costs involved In this study, five parameters in the Weather Research and Forecasting (WRF) Kain–Fritsch cumulus scheme were calibrated based on rainfall verification in the northwest and the southeast regions of the Philippines Two optimization methods—Multiple Very Fast Simulated Annealing (MVFSA) and Adaptive Surrogate Modeling-Based Optimization (ASMO)—were used to find the best parameter set values Both methods generated a higher coefficient of downdraft (Pd), lower entrainment (Pe), and longer convective available potential energy (CAPE) consumption time (Pc), which were found to result in better skill scores than the default WRF Precipitation amount in both calibrated models decreased leading to an overall less wet bias Precipitation skill score in the northwestern Philippines significantly improved by 35%, while that of the southeastern Philippines only increased by 3% In addition, model calibration had no significant effect on the simulated temperature and wind speed The results show that calibration of the cumulus parameterization scheme yields better results for convective rainfall rather than rain from stratiform clouds, which is expected since the cumulus parameterization scheme represents the effects of sub-grid-scale convective processes

Geographic Shift and Environment Change of U.S. Tornado Activities in a Warming Climate

Abstract: Even with ever-increasing societal interest in tornado activities engendering catastrophes of loss of life and property damage, the long-term change in the geographic location and environment of tornado activity centers over the last six decades (1954–2018), and its relationship with climate warming in the U.S., is still unknown or not robustly proved scientifically. Utilizing discriminant analysis, we show a statistically significant geographic shift of U.S. tornado activity center (i.e., Tornado Alley) under warming conditions, and we identify five major areas of tornado activity in the new Tornado Alley that were not identified previously. By contrasting warm versus cold years, we demonstrate that the shift of relative warm centers is coupled with the shifts in low pressure and tornado activity centers. The warm and moist air carried by low-level flow from the Gulf of Mexico combined with upward motion acts to fuel convection over the tornado activity centers. Employing composite analyses using high resolution reanalysis data, we further demonstrate that high tornado activities in the U.S. are associated with stronger cyclonic circulation and baroclinicity than low tornado activities, and the high tornado activities are coupled with stronger low-level wind shear, stronger upward motion, and higher convective available potential energy (CAPE) than low tornado activities. The composite differences between high-event and low-event years of tornado activity are identified for the first time in terms of wind shear, upward motion, CAPE, cyclonic circulation and baroclinicity, although some of these environmental variables favorable for tornado development have been discussed in previous studies.

Spatio-Temporal Variability of Pre-monsoon Convective Events and Associated Rainfall over the State of Odisha (India) in the Recent Decade

Abstract: The state of Odisha is situated on the eastern coast of India and is highly vulnerable to massive convective activity in the pre-monsoon season (PM), i.e., from March to May; however, there is a scarcity of studies in this context using long-term datasets. Therefore, an in-depth investigation of the variability in convective events and associated rainfall during PM over the state of Odisha has been carried out for the period 2009–2018 using the European Centre for Medium-Range Weather Forecasts (ECMWF) fifth-generation reanalysis (ERA5) datasets. The convective events (severe and moderate) identified using two sets of threshold values of three different convective indices, i.e., convective available potential energy (CAPE), the K Index, and the Total Totals Index, show an increasing trend in recent years, with South Coastal Odisha (SCO) and North Coastal Odisha (NCO) showing the highest increase. Subsequently, the spatial distribution of rainfall suggests that the maximum convective precipitation (CP) is experienced over NCO and adjacent eastern districts of North Interior Odisha (NIO). The spatial distribution of the 2 m temperature suggests that there exists a strong temperature gradient between the western and eastern portions of the state. However, the gradient weakens for the years associated with the anomalous distribution of CP. The distinct tropospheric temperature difference between the lower levels (LL) and upper levels (UL) clearly suggests that the warming (cooling) of LL is associated with high (low) CP over the region. This is further established by the coherent signature of specific humidity. The frozen hydrometeors (cloud ice and snow) are the major facilitators for the occurrence of CP over the study region. The moisture transport (MT) is associated primarily with the anomalous distribution of spatial rainfall. The years with suppressed convective activity have a distinct signature of a negative MT anomaly along with anomalous north-easterly winds (as against the typical south-westerly flow). It is also demonstrated that the anomalous MT scenario is highly modulated by the land–sea temperature contrast over the region.

Study of statistical estimated parameters using ERA5 reanalysis data over Khulna region during monsoon season

Abstract: Thunderstorms are extreme localized weather phenomena that form primarily as a result of intense atmospheric convection. These are characterized by heavy rainfall, lightning and thunder. Thunderstorms occur in monsoon season over some parts of the world, and they can be found in the rain bands of many convective systems. Thunderstorms are a natural weather occurrence that results in significant damage to property and people all over the world. Lifted index, K index, total totals index, humidity index (HI), total precipitable water (TPW), convective available potential energy, deep convective index, S index, maximum temperature and rainfall parameters are investigated over Khulna region in Bangladesh during the monsoon season. We have measured all the above parameters using daily ERA5 reanalysis data for the monsoon season from 2011 to 2020. High TPW values (~ > 60 mm) and low HI values (~ < 20 K) are observed during July and August months over Khulna region. DCI values greater than 30 °C are observed which indicates highly favorable for severe convection-related thunderstorms. We have experimented ARMA model to estimate four parameters. The major motive behind this is to compare the accuracy of the ARMA model data to ERA5 data. For obtaining reliable statistical estimates of thunderstorm parameters, the ARMA model proved to be extremely useful.

Physical and Dynamical Characteristics of Thunderstorms Over Bangladesh Based on Radar, Satellite, Upper-Air Observations, and WRF Model Simulations

Abstract: The physical and dynamical characteristics of pre-monsoon (March–May) thunderstorms (TS) are investigated over Bangladesh using the Weather Research and Forecasting (WRF) model. The model was run for 24-h using 6-hourly data sets as initial and lateral boundary conditions. The Milbrandt cloud microphysics scheme, Krain–Fritsch cumulus scheme, and Yonsei University planetary boundary layer are found to be the best combination by comparing the root mean square error of rainfall from 18 sensitivity experiments. The synoptic condition and atmospheric instability associated with three TS cases have been analyzed based on mean sea level pressure, convective available potential energy (CAPE), and thermodynamic indices. CAPE is found between 500 and 2700 J kg−1 at 0000 UTC for the TS cases. The presence of low-level southerly wind from the Bay of Bengal and upper-level westerly or north-westerly wind with speeds ranging from 5 to 30 m s−1 is found during the storms. The cloud characteristics and intensity were investigated based on Doppler Weather Radar and INSAT 3DR satellite observations. Cloud micro-physical hydrometeors and other composite features (e.g., cloud top and core precipitation altitude, length of squall line) were also studied by the model and then compared with available observed values. For 24-h rainfall, 2 × 2 contingency tables are computed using Model Evaluation Tools. Categorical skill scores such as proportion correct, frequency bias index, probability of false detection, false alarm ratio, and Gilbert skill score were calculated to evaluate the model's performance. The forecast goodness is found to be reasonably satisfactory after analyzing the significance of the skill scores.

Simulating the Effects of Surface Energy Partitioning on Convective Organization: Case Study and Observations in the US Southern Great Plains

Abstract: Author(s): Dai, Y; Williams, IN; Qiu, S | Abstract: Realistic cloud-resolving simulations were performed to study the effects of surface energy partitioning (surface sensible and latent heat fluxes) on the organization of isolated convection into larger mesoscale convective systems (MCSs) near the US Southern Great Plains. The role of cold pools in mediating surface-convection interactions was explored. Better organized MCSs tended to occur in the experiments with perturbed wetter soil (and more active vegetation), regardless of the effects of soil moisture on the diurnal timing of convective triggering. Wetter soil led to shallower boundary layers and more convective available potential energy than drier soil. The roles of cold pools on convection are lifecycle-stage dependent: A dry surface allows more numerous colliding cold pools, thereby aiding in convective triggering by reducing entrainment in the early stages, and providing gust-front uplift in later stages. However, horizontal propagation of the cold-pool density current can outrun the convective system, creating a slantwise updraft and thus weakening the gust front uplift in later stages. This effect calls into question previous cold pool parameterizations, in which the gust front uplift is mainly proportional to the negative buoyancy of cold air. Lastly, both the model and observation show an enhancement of surface latent heat flux during the passage of a gust front at night, suggesting that a positive feedback between the surface and convection helps MCSs to persist into the nighttime.

Climatology of the dynamic and thermodynamic features of upper tropospheric cyclonic vortices in Northeast Brazil

Abstract: The purpose of this study is to analyze the dynamic/thermodynamic features of the center and periphery of upper tropospheric cyclonic vortices (UTCV) in Northeast Brazil (NEB). An algorithm was developed to identify the vortex climatology using ERA-Interim, while rainfall impact was assessed using the Climate Prediction Center dataset, from 1980 to 2016. The algorithm was validated by comparison UTCV’s positions obtained by subjective analysis, showing good performance regarding positioning and seasonality. One of the preferential regions of UTCV occurrence was the semiarid region of NEB, which may indicate these systems have a strong influence on the water deficit in the region. Air subsidence and mass divergence at the center and upward motions and convergence on the periphery of the system were observed. Two conceptual skew-t diagrams were generated and the results bring a new perspective about UTCV thermodynamic features, some of which are: in the center, associated with subsidence, low convective available potential energy (CAPE) values and low humidity concentration were detected in a large atmospheric layer due to the subsidence generated by mass convergence at high levels. In contrast, the edge region presented high CAPE values and high atmospheric moisture content, related to the mass convergence in lower troposphere. The advances in knowledge about dynamic/thermodynamic characteristics of this meteorological system generate perspectives for better simulations, improving its predictability. In addition, the proposed algorithm is of great value for future climatological studies of UTCV.