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.

Large-scale modes of the tropical atmosphere. Part II: analytical modeling of Kelvin waves using the CAPE closure

Abstract: The thermal assumption of the model is based on the convective available potential energy (CAPE) closure, i.e. increased CAPE, represented by decreased midlevel potential temperature, results in increased precipitation. The dynamic assumption of the model is that the vertical heating profile has the shape of the first baroclinic mode, while the vertical dependence of modeled fields is calculated, i.e. the model is vertically resolved. The modeled modes are free Kelvin waves and convectively coupled Kelvin waves. It is shown that the CAPE closure is not sufficient to produce the observed destabilization of the Kelvin mode, but that the dynamical properties of the model give the observed phase speeds.

On the Two‐Dimensional Steady Upshear‐Sloping Convection

Abstract: A 2-D inviscid steering-level model due to M. W. Moncrieff is reexamined both analytically and numerically. It is found that the thermal effects on the distribution of energy and vorticity play opposite roles in determining the interface slope, with the former being dominant. By separating the two effects, a useful insight is obtained into how the interface is controlled by the internal flow regime. Consequently, a mixed jump and steering-level model is proposed, in which the returning updraught and downdraught are separated by adjacent jump updraught and downdraught. By solving for the internal flow, upshear-sloping convection is obtained in the mixed model. Numerical results indicate that the inferface slope increases towards the vertical, or even becomes downshear-sloping, as (i) the jump outflow becomes shallow, (ii) the lifting condensation level (LCL) becomes low, and/or (iii) the Richardson number (proportional to the ratio between convective available potential energy and kinetic energy in the inflow) increases (except for the cases where the jump outflow is very deep and LCL is very high). These features are discussed in connection with the recent results of A. J. Thorpe et al., and the observed differences between tropical propagating squall lines and mid-latitude steering-level-type squall lines.

Wildfire Pyroconvection and CAPE: Buoyancy’s Drying and Atmospheric Intensification—Fort McMurray

Abstract: The accurate prediction of wildfire behavior and spread is possible only when fire and atmosphere simulations are coupled. In this work, we present a mechanism that causes a small fire to intensify by altering the atmosphere. These alterations are caused by fire-related fluxes at the surface. The fire plume and fluxes increase the convective available potential energy (CAPE) and the chance of the development of a strong pyroconvection system. To study this possible mechanism, we used WRF-Fire to capture fire line propagation as the result of interactions between heat and moisture fluxes, pressure perturbations, wind shear development and dry air downdraft. The wind patterns and dynamics of the pyroconvection system are simulated for the Horse River wildfire at Fort McMurray, Canada. The results revealed that the updraft speed reached up to 12 m/s. The entrainment mixed the mid and upper-level dry air and lowered the atmospheric moisture. The mid-level and upper-level dew point temperature changed by 5–10 ∘ C in a short period of time. The buoyant air strengthened the ascent as soon as the nocturnal inversion was eliminated by daytime heating. The 887 J/kg total increase of CAPE in less than 5 h and the high bulk Richardson number (BRN) of 93 were indicators of the growing pyro-cumulus cell. The presented simulation has not improved the original model or supported leading-edge numerical weather prediction (NWP) achievements, except for adapting WRF-Fire for Canadian biomass fuel. However, we were able to present a great deal of improvements in wildfire nowcasting and short-term forecasting to save lives and costs associated with wildfires. The simulation is sufficiently fast and efficient to be considered for a real-time operational model. While the project was designed and succeeded as an NWP application, we are still searching for a solution for the intractable problems associated with political borders and the current liable authorities for the further development of a new generation of national atmosphere–wildfire forecasting systems.

Supercell convective environments in Spain based on ERA5: hail and non-hail differences

Abstract: Abstract. Severe convective storms, in particular supercells, are occasionally responsible for a large number of property losses and damage in Spain. This paper aims to study the synoptic configurations and pre-convective environments in a dataset of 262 supercells during 2011–2020 in Spain. The events are grouped into supercells with hail (diameter larger than 5 cm) and without hail and the results are compared. ERA5 reanalysis is used to study the synoptic configurations and proximity atmospheric profiles related to the supercell events at the initial time. In addition, temperature, convective available potential energy, convective inhibition, lifting condensation level, level of free convection, height of freezing level, wind shear and storm-relative helicity are obtained for each event. Results show that supercells are more frequent on the Mediterranean coast during the warm season. Some of the variables analyzed present statistically significant differences between hail and non-hail events. In particular, supercells with hail are characterized by higher median values of most-unstable convective available potential energy than supercells without hail.

Quasi-stationary extreme rain produced by mesoscale convective system on the Mei-Yu front

Abstract: A mesoscale convective system (MCS) occurred on the Mei-Yu front in the Jiang-Huai River Basin of China on 7–8 July 2007, which caused extreme rainfall. The MCS formed in an environment of moderate convective available potential energy, high precipitable water, and an almost unidirectional southwesterly low-level jet. The favorable environment for MCS initiation and development featured a low-level convergence between northeasterly wind north of the Mei-Yu front and warm-moist southwesterly airflow. The evaporative cooling generated cold outflow which continuously promoted new convection at the leading edge of the MCS. WRF model simulations reproduced the observed back-building initiation and upscale organization. The flow-parallel MCS was affected by the low-level jet, vertical wind shear, and near-surface cold outflow in a stable nocturnal planetary boundary layer. Stratiform precipitation was reinforced by the downstream propagation of cumulonimbus and advection of ice-phase hydrometeors by the mid-upper level wind. The quasi-stationarity was a product of subtle dynamical balance between the near-surface cold outflow and the background low-level southerly flow. Sensitivity experiments addressed the role of near-surface outflow and diurnal forcing in MCS organization.