Low Convective Available Potential Energy Research Articles

Aerosol influence on cloud macrophysical and microphysical properties over the Tibetan Plateau and its adjacent regions.

This study uses aerosol optical depth (AOD) and cloud properties data to investigate the influence of aerosol on the cloud properties over the Tibetan Plateau and its adjacent regions. The study regions are divided as the western part of the Tibetan Plateau (WTP), the Indo-Gangetic Plain (IGP), and the Sichuan Basin (SCB). All three regions show significant cloud effects under low aerosol loading conditions. In WTP, under low aerosol loading conditions, the effective radius of liquid cloud particles (LREF) decreases with the increase of aerosol loading, while the effective radius of ice cloud particles (IREF) and cloud top height (CTH) increase during the cold season. Increased aerosol loading might inhibit the development of warm rain processes, transporting more cloud droplets above the freezing level and promoting ice cloud development. During the warm season, under low aerosol loading conditions, both the cloud microphysical (LREF and IREF) and macrophysical (cloud top height and cloud fraction) properties increase with the increase of aerosol loading, likely due to higher dust aerosol concentration in this region. In IGP, both LREF and IREF increase with the increase in aerosol loading during the cold season. In SCB, LREF increases with the increase in aerosol loading, while IREF decreases, possibly due to the higher hygroscopic aerosol concentration in the SCB during the cold season. Meteorological conditions also modulate the aerosol-cloud interaction. Under different convective available potential energy (CAPE) and relative humidity (RH) conditions, the influence of aerosol on clouds varies in the three regions. Under low CAPE and RH conditions, the relationship between LREF and aerosol in both the cold and warm seasons is opposite in the WTP: LREF decreases with the increase of aerosol in the cold season, while it increases in the warm season. This discrepancy may be attributed to a difference in the moisture condition between the cold and warm seasons in this region. In general, the influence of aerosols on cloud properties in TP and its adjacent regions is characterized by significant nonlinearity and spatial variability, which is likely related to the differences in aerosol types and meteorological conditions between different regions.

Preconvective environments of severe convective winds over North China and South China

This study aimed to identify the environmental discrepancy between severe convective wind (SCW) and climate background over North China and South China and between SCW occurring in these two regions, which were prone to SCW in China. 17 parameters from 11,727 (13130) climate background soundings and 4404 (2513) SCW soundings in North (South) China were quantitatively investigated. These parameters were grouped as significant important parameters (SIP), moderate important parameters (MIP), and weak important parameters (WIP). The skill in discriminating the environments between SCW and climate background steadily decreased from SIP to MIP and then to WIP. In North China, SCW typically occurred under moderate to severe deep wind shear and low convective available potential energy (CAPE) conditions. However, in South China, SCW tended to occur at low CAPE and moderate deep wind shear, as well as moderate CAPE and moderate to severe deep wind shear. Compared to the background climate, the SCW environment was associated with considerable instability, high shear, and dry and cold air in the middle layer over both North and South China. A substantial variation in wind shear was identified between the SCW and background in North China, whereas a considerable difference in comprehensive conditions involving CAPE and wind shear was detected in South China. The SCW environment is characterized by a steeper lapse rate in the middle layer as well as a higher Total Totals index in North China than in South China, while the opposite was true for CAPE between two regions. In general, the thermal parameter discrimination was larger than the shear metric discrimination when comparing the soundings for the two regions.

Aerosol Impacts on Storm Electrification and Lightning Discharges Under Different Thermodynamic Environments

AbstractThe impacts of aerosol and thermodynamics on electrification and lightning activities have been investigated in detail using the Weather Research and Forecasting Model coupled with a double‐moment microphysics parameterization and an explicit electrification lightning scheme. To obtain a varied combination of convective available potential energy (CAPE) values and aerosol concentrations, a sounding was modified consistently and initiated with five sets of aerosol concentrations that served as cloud condensation nuclei. The simulated electric processes respond to the varying dynamical and microphysical characteristics associated with the different CAPE and aerosol conditions. Under high CAPE circumstances, the augmentation of ice‐phase particle leads to the enhancement of non‐inductive charging primarily through the dynamic processes. Increased aerosol content further invigorates the electrification through microphysical processes. Elevated aerosol loading under low CAPE conditions increases cloud droplet and ice crystal numbers. Larger graupel particle size further leads to the enhanced electric intensity and lightning discharges.

Climatology of Significant Tornadoes within China and Comparison of Tornado Environments between the United States and China

Abstract A climatology of significant tornadoes [SIGTOR, tornadoes rated (E)F2+ on the (enhanced) Fujita scale] within China and in three subregions, including northern, central, and southern China, is first presented for the period 1980–2016. In total, 129 SIGTOR are recorded in China, with an average of 3.5 per year. The tornado inflow environments of the south-central and southeast regions of the United States (USC and USSE) are compared with those of China and its subregions based on sounding-derived parameters including shear, storm-relative helicity, convective available potential energy (CAPE), lifting condensation level (LCL), etc. Soundings are extracted from the ERA5 reanalysis dataset. The results confirm that the SIGTOR in USSE are characterized by high shear, low CAPE, and low LCL whereas those in USC are characterized by moderate-to-high shear, high CAPE, and high LCL. The thermodynamic conditions of tornadic cases are favorable for China, with moderate-to-high CAPE and low-to-moderate LCL, but their kinematic conditions are much less favorable than in the United States, a fact that is believed to be primarily responsible for the lower tornado frequency and intensity in China. The high CAPE in China is due mostly to high humidity. For three subregions in China, the central China cases account for 60% of total samples, and its environmental features are similar to those of China. The average shear with northern China cases is stronger than that with the other two subregions, and the midlayer is relatively dry. The southern China SIGTOR have the most conducive humidity conditions, but the CAPE and shear there are the lowest. The northern, central, and southern China environments can be considered as representative of midlatitude, subtropical, and tropical regions. Significance Statement We document the climatological characteristics of significant tornadoes (SIGTOR) within China and compare the inflow environments of SIGTOR in China and its subregions with those in the U.S. central and southeastern regions. The availability of hourly high-resolution ERA5 data makes the environments based on extracted proximity soundings much more accurate than possible with earlier reanalyses. The environmental characteristics show systematic differences in the tornado environments of different regions of China and the United States and suggest different roles played by thermodynamic and kinematic conditions for tornado formation. Overall, the environmental differences are consistent with the resulting frequency and intensities of SIGTOR. The findings are helpful toward improving tornado forecasting and warning or even understanding of potential impacts of climate change on SIGTOR, especially in China, where such studies are rarer.

A case study of a derecho storm in dry, high-shear environment

The present study examines the origin and environmental conditions of the severe convective windstorm on September 17, 2017, which affected several countries in the central and southeastern Europe, above all Serbia and Romania. The large area of the damage swath (at least 500 km long) and high wind gusts (up to 40 m/s) would classify this event as a derecho or at least as a storm very similar to derechos (with respect to newer definition proposals). Small-scale bow echoes were found in areas with highest reported wind gusts, and some thunderstorms within the storm-producing convective system were probably supercells. The existence of high wind shear and storm rotation could be also related to the significant rightward deflection of the system with respect to the mean wind and propagation of other thunderstorms and systems observed on that day. In contrary to many other known derecho events, this storm propagated toward a very dry airmass exhibiting only low or moderate convective available potential energy (CAPE) values. This is shown by soundings, ECMWF model outputs, and vertical profiles from the IASI L2 satellite sounder. Several convective parameters (e.g. CAPE, downdraft CAPE, derecho composite parameter, 0-3-km relative humidity, 0-6-km shear) were evaluated and compared with proximity soundings of other described European derechos or with the available climatology. The possibility of a balance between the cold pool-generated horizontal vorticity and the environmental shear is also discussed. It is concluded that identification of low-level humidity sources (with aid of storm-relative wind vectors or streamlines) can be important in forecasting of thunderstorm systems moving toward an airmass, which is seemingly too dry for development and maintenance of deep convection. It is also shown that due to low CAPE values, some composite parameters would not indicate favourable conditions for a long-lived convective system. The lack of radiosonde observations can be partially supplemented by data from the IASI L2 sounder, which profiles can be largely different from model forecasts, showing much drier air in the mid- and upper troposphere in this case. It is concluded that due to the absence of strong synoptic forcing and larger pressure gradient at surface, convective processes played major role in the windstorm development. The presence of high temperature lapse rates at low- and mid-levels, high wind shear and unusually dry pre-storm airmass could be considered as the most important signatures related to the storm severity.

Tornadic environments in the Iberian Peninsula and the Balearic Islands based on ERA5 reanalysis

AbstractA dataset of 907 tornado and waterspout events recorded from 1980 to 2018 was built to study convective environments in the Iberian Peninsula and Balearic Islands (western Mediterranean). The events were grouped into different categories, distinguishing waterspouts and tornadoes that were stratified by intensity according to the Fujita (F) scale and the Enhanced Fujita (EF) scale. The analysis separated the north‐east (NE) and south‐west (SW) subareas in the region of study, which present different seasonal cycles. For each event, atmospheric profiles from the ERA5 reanalysis data were used to determine convective available potential energy (CAPE), storm‐relative helicity (SRH), vertical wind‐shear (WS), the Universal Tornadic Index (UTI), and the product of wind‐shear and the square root of two times CAPE (WMAXSHEAR). Results showed that the NE events are mostly associated with higher CAPE and lower helicity and wind‐shear than the SW events. Thus, a significant number of SW tornadoes are associated with high‐shear, low‐CAPE environments. Moreover, the low‐shear, high‐LCL tornado environment, which is common inland during warm‐season, is more usual in the NE subarea. Composite parameters such as the UTI and WMAXSHEAR06 are good discriminators between significant and weak tornado events, although WMAXSHEAR06 presents some limitations for the SW events due to low CAPE and weak differences in the WS (0–6 km) between the (E)F1 and (E)F2+ events. This weakness was resolved by using the 0–3 km WS instead of the 0–6 km WS when calculating the WMAXSHEAR. A new threshold for WMAXSHEAR03 is proposed (500 m2⋅s−2) to distinguish between significant and non‐significant tornado environments. Finally, the Szilagyi Waterspout Nomogram, originally developed for the Great Lakes of North America, was successfully tested in the forecasting of waterspout formation for the first time in the western Mediterranean area, although the technique should be adapted to correctly detect cool‐season mid‐latitude waterspouts.

Aerosol Effects on Clouds and Precipitation over Central Europe in Different Weather Regimes

Abstract The response of clouds to changes in the aerosol concentration is complex and may differ depending on the cloud type, the aerosol regime, and environmental conditions. In this study, a novel technique is used to systematically modify the environmental conditions in realistic convection-resolving simulations for cases with weak and strong large-scale forcing over central Europe with the Consortium for Small-Scale Modeling (COSMO) model. Besides control runs with quasi-operational settings, initial and boundary temperature profiles are modified with linear increasing temperature increments from 0 to 5 K between 3 and 12 km AGL to represent different amounts of convective available potential energy (CAPE) and relative humidity. The results show a systematic decrease of total precipitation with increasing cloud condensation nuclei (CCN) concentrations for the cases with strong synoptic forcing caused by a suppressed warm-rain process, whereas no systematic aerosol effect is simulated for weak synoptic forcing. The effect of increasing CCN tends to be stronger in the simulations with increased temperatures and lower CAPE. While the large-scale domain-averaged responses to increased CCN are weak, the precipitation forming over mountainous terrain reveals a stronger sensitivity for most of the analyzed cases. Our findings also demonstrate that the role of the warm-rain process is more important for strong than for weak synoptic forcing. The aerosol effect is largest for weakly forced conditions but more predictable for the strongly forced cases. However, more accurate environmental conditions are much more important than accurate aerosol assumptions, especially for weak large-scale forcing.

Kinetic energy budget of active summer monsoon on Southeast Asia

In this paper present and show kinetic energy and convective available potential energy (CAPE) on active summer monsoon on May to August from 1981 to 1990. Result show that kinetic energy usually appear over Bay of Bengal and India area. Because of zonal and meridional components are flow through India area that active monsoon is happen. However, kinetic energy is less available potential energy. The distribution of CAPE in summer and the value of high CAPE located between the equator and 20°N and low CAPE located below equator. The pattern CAPE position distribution fluctuates as an inter-tropical convergence zone.

Can Nor'wester events initiate stratospheric moistening?

The possibility of stratospheric moistening being initiated by deep convective Nor'wester events has been investigated over a period of three years spanning from 2013 to 2015 at a tropical location Kolkata, in India using radiosonde and satellite data. The back trajectories, instability indices, outgoing long wave radiation (OLR), convective available potential energy (CAPE), geopotential height maps, vertical pressure velocity, specific humidity, wind vectors and precipitable water vapour (PWV) have been examined to assess the convective activity prevailing over the atmosphere during these events. Increase in specific humidity, wind velocity at various levels of the lower atmosphere and CAPE values indicate an upwelling of moist air from the troposphere to lower stratosphere during Nor'westers. Decrease in OLR and large differences in the values of instability indices, relative humidity and precipitable water vapour during Nor'westers compared to normal convection also signify high intensity of convection and hence the possibility of higher stratospheric moistening during Nor'wester events.

Simulated Sensitivity of Tropical Cyclone Size and Structure to the Atmospheric Temperature Profile

AbstractThis study uses the WRF ARW to investigate how different atmospheric temperature environments impact the size and structure development of a simulated tropical cyclone (TC). In each simulation, the entire vertical virtual temperature profile is either warmed or cooled in 1°C increments from an initial specified state while the initial relative humidity profile and sea surface temperature are held constant. This alters the initial amount of convective available potential energy (CAPE), specific humidity, and air–sea temperature difference such that, when the simulated atmosphere is cooled (warmed), the initial specific humidity and CAPE decrease (increase), but the surface energy fluxes from the ocean increase (decrease).It is found that the TCs that form in an initially cooler environment develop larger wind and precipitation fields with more active outer-core rainband formation. Consistent with previous studies, outer-core rainband formation is associated with high surface energy fluxes, which leads to increases in the outer-core wind field. A larger convective field develops despite initializing in a low CAPE environment, and the dynamics are linked to a wider field of surface radial inflow. As the TC matures and radial inflow expands, large imports of relative angular momentum in the boundary layer continue to drive expansion of the TC’s overall size.

장기간(1997~2013) 라디오존데 관측 자료를 활용한 집중호우 시 연직대기환경 유형 분류

Heavy rainfall (<TEX>$</TEX><TEX>></TEX><TEX>30mm\;hr^{-1}$</TEX>) over the Korean Peninsula is examined in order to understand thermo-dynamic characteristics of the atmosphere, using radiosonde observational data from seven upper-air observation stations during the last 17 years (1997~2013). A total of 82 heavy rainfall cases during the summer season (June-August) were selected for this study. The average values of thermo-dynamic indices of heavy rainfall events are Total Precipitable Water (TPW) = 60 mm, Convective Available Potential Energy (CAPE) = <TEX>$850J\;kg^{-1}$</TEX>, Convective Inhibition (CIN) = <TEX>$15J\;kg^{-1}$</TEX>, Storm Relative Helicity (SRH) = <TEX>$160m^2s^{-2}$</TEX>, and 0~3 km bulk wind shear = <TEX>$5s^{-1}$</TEX>. About 34% of the cases were associated with a Changma front; this pattern is more significant than other synoptic pressure patterns such as troughs (22%), migratory cyclones (15%), edges of high-pressure (12%), typhoons (11%), and low-pressure originating from Changma fronts (6%). The spatial distribution of thermo-dynamic conditions (CAPE and SRH) is similar to the range of thunderstorms over the United States, but extreme conditions (supercell thunderstorms and tornadoes) did not appear in the Korean Peninsula. Synoptic conditions, vertical buoyancy (CAPE, CIN), and wind parameters (SRH, shear) are shown to discriminate among the environments of the three types. The first type occurred with high CAPE and low wind shear by the edge of the high pressure pattern, but Second type is related to Changma front and typhoon, exhibiting low CAPE and high wind shear. The last type exhibited characteristics intermediate between the first and second types, such as moderate CAPE and wind shear near the migratory cyclone and trough.

A climatology of convective available potential energy in Great Britain

ABSTRACTDeep moist convection (DMC) requires three ingredients: instability, moisture and lift. One measure that incorporates two of these, instability and moisture, is convective available potential energy (CAPE). A 10‐year climatology of CAPE over Great Britain is presented covering the period 1 June 2002–31 May 2012, based on a 9‐km grid spacing implementation of the Weather Research and Forecasting (WRF) model, with two‐way interactive nesting. Appropriate tests are carried out to verify model reliability by comparing simulated and observed CAPE. CAPE is found to be highly variable both spatially and temporally, the highest values being produced during Spanish plume events. A strong relationship is confirmed between surface temperature and CAPE magnitude, the highest CAPE across Great Britain during this period locally exceeding 3000 J kg−1. In an average year, 15 days produce CAPE in excess of 500 J kg−1 somewhere in Great Britain, 4 days &gt; 1000 J kg−1 and 1 day &gt; 1500 J kg−1. Three main CAPE seasons are identified: ‘land dominated CAPE’ between April and September, ‘sea dominated CAPE’ between September and January and ‘low CAPE’ from January to April. The southern North Sea witnesses significant CAPE all year round because of a combination of favourable synoptic situations, including warm air plumes in spring/summer and cold air incursions over warmer seas in winter. CAPE is not a direct predictor of thunderstorm incidence, due in part to the confounding effect of convective inhibition (CIN). However, at the annual scale, when comparing against an existing days of thunder climatology, we observe a close correspondence with &gt;500 J kg−1 CAPE frequency.

Variability of Updraft and Downdraft Characteristics in a Large Parameter Space Study of Convective Storms

AbstractOver 200 convective storm simulations are analyzed to examine the variability in storm vertical velocity and updraft area characteristics as a function of basic environmental parameters. While it is known that bulk properties of the troposphere such as convective available potential energy (CAPE) and deep-layer wind shear exert significant influence over updraft intensity and area, additional parameters such as the temperature at the cloud base, the height of the level of free convection (LFC), and the vertical distribution of buoyancy also have an effect. For example, at low CAPE, updraft strength is strongly related to the vertical distribution of buoyancy, and also to the bulk environmental wind shear. More generally, updraft area and its temporal variability both tend to increase in environments where the LFC is raised. Additionally, in environments with persistent storms, downdraft strength is sensitive to the bulk shear, environmental temperature, and LFC height. Using multiple linear regression methods, the best combinations of environmental parameters explain up to 81% of the interexperiment variance in second-hour mean peak updraft velocity, 74% for midlevel updraft area, and 64% for downdraft velocity. Downdraft variability is explained even less well (49%) when only persistent storms are considered. These idealized simulation results show that it is easier to predict storm updraft characteristics than those of the downdraft.

Proximity soundings for severe convection for Europe and the United States from reanalysis data

Proximity soundings from reanalysis data have been created for significant severe thunderstorms in the United States and Europe, along with corresponding soundings not associated with severe thunderstorms. The probability of a combination of convective available potential energy (CAPE) and deep tropospheric wind shear being associated with significant severe thunderstorms has been calculated for both areas. Probabilities of significant severe storms are higher for high CAPE and shear in Europe, but those large scale environmental conditions are experienced much more frequently in the US, so that the overall number of events is much higher in the US. Probabilities of significant storms are approximately constant for constant values of CAPE⁎Shear for each of the datasets. High values of 0–1 km wind shear and low lifted condensation levels are associated with higher probabilities that significant severe thunderstorms will be associated with significant tornadoes. A subset of the US data, taken from the southeastern US in the cool season, produces probabilities that are much closer to the European values than the overall US data. The environments also are closer to European values with relatively low CAPE and low lifted condensation levels. From the southeastern US data, it is shown that the probability of severe convection occurring with moderate values of CAPE⁎Shear is much higher in the cool season than in the warm season. It is suggested that the higher probabilities result from stronger synoptic forcing and stronger and more frequent boundaries to initiate convection.

Observational aspects and analysis of events of severe thunderstorms during April and May 2006 for Assam and adjoining states – A case study on ‘Pilot Storm Project’

A Pilot project on ‘Severe Thunderstorm Observation and Regional Modeling (STORM)’ was undertaken by the Department of Science and Technology during April and May 2006. Regional Meteorological Centre, Guwahati too participated in this project and attempted to monitor each and every severe thunderstorm event. A total of 62 events have been identified on 30 days during 1st April to 25th May. The experiment was restricted upto 25th May in view of onset of monsoon on 27th May. Significant features of all these events are discussed in detail. Satellite imagery and radar echoes of selected events are included to describe the developments of these events. Thermodynamic state of atmosphere along with prevailing synoptic situation associated with the events has been discussed broadly. Results of the study confirm that the ‘Assam valley’ along Brahmaputra river experiences maximum number of events. Lower Assam is more prone to these events as compared to upper and south Assam. High thermodynamic instability, inhomogeneity in horizontal distribution of air temperatures and moisture near ground level and Convective Available Potential Energy (CAPE) value at four stations namely Guwahati, Agartala, Siliguri and Dibrugarh are the key factors in presence of the favourable lower level convergence exhibited by cyclonic circulation over sub-Himalayan West Bengal and adjoining west Assam moving eastwards along Brahmaputra valley with divergence aloft for occurrence of severe thunderstorm over this region. Also In some cases severe thunderstorm outbursts happen in the environment of very low CAPE value also due to proximity of complex terrain feature of this region.

The dependence of aerosol effects on clouds and precipitation on cloud‐system organization, shear and stability

Precipitation suppression due to an increase of aerosol number concentration in stratiform cloud is well‐known. It is not certain whether the suppression applies for deep convection. Recent studies have suggested increasing precipitation from deep convection with increasing aerosols under some, but not all, conditions. Increasing precipitation with increasing aerosols can result from strong interactions in deep convection between dynamics and microphysics. High cloud liquid, due to delayed autoconversion, provides more evaporation, leading to more active downdrafts, convergence fields, condensation, collection of cloud liquid by precipitable hydrometeors, and precipitation. Evaporation of cloud liquid is a primary determinant of the intensity of the interactions. It is partly controlled by wind shear modulating the entrainment of dry air into clouds and transport of cloud liquid into unsaturated areas. Downdraft‐induced convergence, crucial to the interaction, is weak for shallow clouds, generally associated with low convective available potential energy (CAPE). Aerosol effects on cloud and precipitation can vary with CAPE and wind shear. Pairs of idealized numerical experiments for high and low aerosol cases were run for five different environmental conditions to investigate the dependence of aerosol effect on stability and wind shear. In the environment of high CAPE and strong wind shear, cumulonimbus‐ and cumulus‐type clouds were dominant. Transport of cloud liquid to unsaturated areas was larger at high aerosol, leading to stronger downdrafts. Because of the large vertical extent of those clouds, strong downdrafts and convergence developed for strong interactions between dynamics and microphysics. These led to larger precipitation at high aerosol. Detrainment of cloud liquid and associated evaporation were less with lower CAPE and wind shear, where dynamically weaker clouds dominated. Transport of cloud liquid to unsaturated areas was not as active as in the environment of high CAPE and strong shear. Also, evaporatively driven differences in downdrafts at their level of initial descent were not magnified in clouds with shallow depth as much as in deep convective clouds as they accelerated to the surface over shorter distances. Hence the interaction between dynamics and microphysics was reduced, leading to precipitation suppression at high aerosol. These results demonstrate that increasing aerosol can either decrease or increase precipitation for an imposed large‐scale environment supporting cloud development. The implications for larger‐scale aspects of the hydrological cycle will require further study with larger‐domain models and cumulus parameterizations with advanced microphysics.

The influence of the land surface on the transition from dry to wet season in Amazonia

Analysis of the fifteen years of European Centre for Medium Range Weather Forecasts (ECMWF) reanalysis suggests that the transition from dry to wet season in Southern Amazonia is initially driven by increases of surface latent heat flux. These fluxes rapidly reduce Convective Inhibition Energy (CINE) and increase Convective Available Potential Energy (CAPE), consequently providing favourable conditions for increased rainfall even before the large-scale circulation has changed. The increase of rainfall presumably initiates the reversal of the cross-equatorial flow, leading to large-scale net moisture convergence over Southern Amazonia. An analysis of early and late wet season onsets on an interannual scale shows that a longer dry season with lower rainfall reduces surface latent heat flux in the dry and earlier transition periods compared to that of a normal wet season onset. These conditions result in a higher CINE and a lower CAPE, causing a delay in the increase of local rainfall in the initiating phase of the transition and consequently in the wet season onset. Conversely, a wetter dry season leads to a higher surface latent heat flux and weaker CINE, providing a necessary condition for an earlier increase of local rainfall and an earlier wet season onset. Our results imply that if land use change in Amazonia reduces rainfall during dry and transition seasons, it could significantly delay the wet season onset and prolong the dry season.

The meteorology of high‐intensity rainfall events over the west Mediterranean region

The meteorological situations in which heavy rainfall events occur over the western Mediterranean region are presented and discussed. The study of such situations has been made looking for mechanisms able to maintain convection during larger intervals than the life cycle of a single convective cell. These mechanisms have been analysed firstly from a thermodynamic standpoint, involving the determination of stability, precipitable water mass, convective available potential energy (CAPE), and bulk Richardson number (bRi). This permits definition of some features of these events and establishment of some thresholds for different variables. Secondly, resort has been made to objective analysis focused on the diagnosis of spatial and temporal distributions of quasi‐geostrophic forcing for vertical motion, convective instability, water vapour divergence/convergence at low levels and CAPE. Following this analysis compound maps were obtained, showing the zones of superimposition of the above four variables. These z...

Convective Available Potential Energy in the Environment of Oceanic and Continental Clouds: Correction and Comments

In 1980, Zipser and LeMone estimated the convective available potential energy (CAPE) for the Thunderstorm Project cumulonimbus environment to be about 3000 J per kg. By assuming the most adiabat reported by Byers and Braham (1949) to be that of an undilute parcel rather than a reference moist adiabat, a significant error was introduced. On the basis of recent calculations made under similar conditions in Oklahoma and Florida, CAPE is now estimated to be considerably lower. These lower CAPE estimates shed doubt on the suggestion that differences in CAPE account for differences in the vertical velocities in convective updrafts over land and over the ocean.