Convective available potential energy

About: Convective available potential energy is a research topic. Over the lifetime, 936 publications have been published within this topic receiving 43773 citations. The topic is also known as: CAPE.

Effects of Moist Froude Number and CAPE on a Conditionally Unstable Flow over a Mesoscale Mountain Ridge

Abstract: In this study, idealized simulations are performed for a conditionally unstable flow over a two-dimensional mountain ridge in order to investigate the propagation and types of cloud precipitation systems controlled by the unsaturated moist Froude number (Fw) and the convective available potential energy (CAPE). A two-dimensional moist flow regime diagram, based on Fw and CAPE, is proposed for a conditionally unstable flow passing over a two-dimensional mesoscale mountain ridge. The characteristics of these flow regimes are 1) regime I: flow with an upstream-propagating convective system and an early, slowly moving convective system over the mountain; 2) regime II: flow with a long-lasting orographic convective system over the mountain peak, upslope, or lee slope; 3) regime III: flow with an orographic convective or mixed convective and stratiform precipitation system over the mountain and a downstream-propagating convective system; and 4) regime IV: flow with an orographic stratiform precipitatio...

Environmental controls on storm intensity and charge structure in multiple regions of the continental United States

Abstract: A database consisting of approximately 4000 storm observations has been objectively analyzed to determine environmental characteristics that produce high radar reflectivities above the freezing level, large total lightning flash rates on the order of 10 flashes per minute, and anomalous vertical charge structures (most notably, dominant midlevel positive charge). The storm database is drawn from four regions of the United States featuring distinct environments, each with coinciding Lightning Mapping Array (LMA) network data. LMAs are able to infer total lightning flash rates using flash clustering algorithms, such as the one implemented in this study. Results show that anomalous charge structures inferred from LMA data, significant lightning flash rates, and increased radar reflectivities above the freezing level tend to be associated with environments that have high cloud base heights (approximately 3 km above ground level) and large atmospheric instability, quantified by normalized convective available potential energy (NCAPE) near 0.2 m s−2. Additionally, we infer that aerosols may affect storm intensity. Maximum flash rates were observed in storms with attributed aerosol concentrations near 1000 cm−3, while total flash rates decrease when aerosol concentrations exceed 1500 cm−3, consistent with previous studies. However, this effect is more pronounced in regions where the NCAPE and cloud base height are low. The dearth of storms with estimated aerosol concentrations less than 700 cm−3 (approximately 1% of total sample) does not provide a complete depiction of aerosol invigoration.

The dynamical structure of two‐dimensional steady convection in constant vertical shear

Abstract: A nonlinear regime of two-dimensional steady convection in unidirectional flow of constant vertical shear is examined theoretically, the main objective being to determine the organization of the updraught and downdraught system. The asymptotic solution for the travel speed of the system and the remote flow obtained by Moncrieff and Green is used as lateral inflow and outflow boundary conditions. The internal flow and the shape of the interface separating the updraught and downdraught branches of the circulation are determined as solutions of a free-boundary problem. The orientation of the flow is basically determined by the ratio of convective available potential energy (CAPE) to the square of the cloud layer shear expressed as R=CAPE/½ (Δ U)2. In all realistic ranges of R the interface slopes downshear, the slope being little affected by compressibility, by the negative vorticity generated in an interfacial boundary layer and by different values of R in the updraught and downdraught branches. Quasi-steady storms are thus not adequately described by two-dimensional dynamics. Certain three-dimensional effects appear essential to significantly advance the theory of severe storms, and these are discussed with reference to existing numerical and observational models. Steady convection can exist only if the values of R in the updraught and downdraught branches lie within a limited range, a result of considerable significance in cloud physical terms.

Modes of isolated, severe convective storm formation along the dryline

Abstract: Patterns of the formation of isolated, severe convective storms along the dryline in the southern plains of the United States during the spring over a 16-year period were determined from an examination of the evolution of radar echoes as depicted by WSR-57 microfilm data. It was found that in the first 30 min after the first echo, more than half of the radar echoes evolved into isolated storms as isolated cells from the start; others developed either from a pair of cells, from a line segment, from a cluster of cells, from the merger of mature cells, or from a squall line. Proximity soundings were constructed from both standard and special soundings, and from standard surface data. It was found that the estimated convective available potential energy and vertical shear are characteristic of the environment of supercell storms. The average time lag between the first echo and the first occurrence of severe weather of any type, or tornadoes alone, was approximately 2 h. There were no significant diff...

Urban signatures in the spatial clustering of summer heavy rainfall events over the Beijing metropolitan region

Abstract: The climatology of summer heavy rainfall events over the Beijing metropolitan region during 2008–2012 is investigated with the aid of an observational network of rain gauges and the Weather Research and Forecasting model. Two “hot spots” of higher frequency of summer heavy rainfall events are observed. One is located over the urban core region and the other resides in the climatological downwind region. Two comparative sets of model runs are designed to assess the effect of land surface properties with and without the presence of the city on the model simulation results. By comparing the two sets of model runs, the changes of rainfall statistics, behaviors of storm cells, and variables related to convection due to urbanization are analyzed and quantified. The intensity of heavy rainfall is increased over the urban and downwind region, corresponding to the locations of the two observed hot spots based on rain gauges. The changes of rainfall statistics suggest that the probability distribution of rainfall is shifted toward a heavier upper tail distribution. The Lagrangian properties of storm cells are examined using a newly developed Storm-Cell Identification procedure. High-echo storm cells tend to split approaching the city and merge in the downwind region. The level of free convection and the height of the planetary boundary layer are significantly increased over the urban region and maximum convective available potential energy is decreased. Increased sensible heat flux from the urban surfaces plays a dominant role in the modification of simulated rainfall from a climatological perspective.