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.

Future climate change of stability indices for the Iberian Peninsula

Abstract: Stability indices evaluate the atmospheric instability which is a basic and precursor ingredient needed for storms to develop. In this study, we evaluated changes of some atmospheric stability indices, namely Convective Available Potential Energy (CAPE), Deep-Layer Wind Shear (SHR06) and Severe Weather Threat (SWEAT), for the Iberian Peninsula, for a future climate scenario (2081–2100), considering the greenhouse gases emission scenario RCP8.5, relative to a historical period (1986–2005). The Weather Research and Forecasting (WRF) was forced by ERA-Interim, for validation purposes, and by the Max Planck Institute (MPI) Earth System Model. The novelty of this approach is the study of extreme weather events through the evaluation of conditions favourable to their development instead of directly studying them. The latter approach may be problematic since these phenomena are known to be poorly reproduced by models due to their relatively low resolution and parametrization processes such as clouds and precipitation. Our approach uses stability indices obtained from simulated variables, such as temperature and winds, which are, generally, much better simulated by models. The WRF-MPI model was validated against WRF-ERA. Overall, the WRF-MPI simulates well the three indices considered here, particularly CAPE, when compared to WRF-ERA. Their spatial patterns were similar, although there is a systematic positive bias in the WRF-MPI. This is minimized when we evaluate climate change by computing differences of WRF-MPI simulations between the future climate scenario and the historical period. In the future, it is estimated a significant increase of CAPE and SWEAT intensity, mainly in summer and autumn. It is also expected a decrease of SHR06 intensity in summer and autumn and an increase in the remaining seasons. Therefore, we may anticipate an increase of the probability of occurrence of environments favourable to the development of severe weather, mainly in the Mediterranean, mostly associated to higher CAPE values.

A Statistical Model for Isolated Convective Precipitation Events

Abstract: To study the diurnal evolution of the convective cloud field, we develop a precipitation cell tracking algorithm which records the merging and fragmentation of convective cells during their life cycles, and apply it on large eddy simulation (LES) data. Conditioning on the area covered by each cell, our algorithm is capable of analyzing an arbitrary number of auxiliary fields, such as the anomalies of temperature and moisture, convective available potential energy (CAPE) and convective inhibition (CIN). For tracks that do not merge or split (termed "solitary"), many of these quantities show generic, often nearly linear relations that hardly depend on the forcing conditions of the simulations, such as surface temperature. This finding allows us to propose a highly idealized model of rain events, where the surface precipitation area is circular and a cell's precipitation intensity falls off linearly with the distance from the respective cell center. The drop-off gradient is nearly independent of track duration and cell size, which allows for a generic description of such solitary tracks, with the only remaining parameter the peak intensity. In contrast to the simple and robust behavior of solitary tracks, tracks that result from merging of two or more cells show a much more complicated behavior. The most intense, long lasting and largest tracks indeed stem from multi-mergers - tracks involved in repeated merging. Another interesting finding is that the precipitation intensity of tracks does not strongly depend on the absolute amount of local initial CAPE, which is only partially consumed by most rain events. Rather, our results speak to boundary layer cooling, induced by rain re-evaporation, as the cause for CAPE reduction, CIN increase and shutdown of precipitation cells.

The Dependence of Storm Longevity on the Pattern of Deep Convection Initiation in a Low-Shear Environment

Abstract: The sensitivity of storm longevity to the pattern of deep convection initiation (e.g., multiple, quasi-linearly arranged initial deep convective cells versus an isolated deep convective cell) is examined using idealized cloud-resolving simulations conducted with a low-shear initial environment. When multiple deep convective cells are initialized in close proximity to one another using either a line of thermals or a shallow airmass boundary, long-lived storms are produced. However, when isolated deep convection is initiated, the resultant storm steadily decays following initiation. These results illustrate that a quasi-linear mechanism, such as a preexisting airmass boundary, that initiates multiple deep convective cells in close proximity can lead to longer-lived storms than a mechanism that initiates isolated deep convection. The essential difference between the experiments conducted is that an isolated initial storm produces a shallower cold pool than when a quasi-linear initiation is used. It is argued that the deep cold pools promote deep forced ascent, systematic convective cell redevelopment, and thus long-lived storms, even in environments with small values of vertical shear. The difference in cold pool depth between the simulations is attributed to differences in the horizontal flux of cold air to the gust front. With a single initial storm, the few convective cells that subsequently form provide only a limited source of cold air, leading to a cold pool that is shallow and incapable of fostering continued updraft redevelopment.

Generation processes of mesoscale convective systems following midlatitude troughs around the Sichuan Basin

Abstract: [1] The generation processes of mesoscale convective systems (MCSs) that occurred over the Sichuan Basin in China were revealed in the early 2008 monsoon season. MCS occurrences detected in METEOSAT geostational satellite images are associated with the traveling of midlatitude troughs after the onset of the Indian monsoon. Three episodes of large-scale MCSs were generated under synoptic conditions of merging southwesterly low-level monsoon flows with a northerly midlatitude air mass following the trough in the leeward of the Tibetan Plateau without direct migration of the vortex generated from the plateau surface. Numerical simulations using a weather research and forecast (WRF) model showed that the MCS was triggered in the evening by strengthening of the low-level wind convergences with horizontal shear between the southerly monsoon flow, with large convective available potential energy, and the northerly dry intrusion. A sudden increase in the northerly winds was confirmed by sonde observation data in the western basin, and the winds were simulated as intrusions passing over the Qinling Mountains when the daytime clouds over the mountain were diminished. Sensitivity experiments by a WRF simulation revealed that the topography of the Sichuan Basin was able to capture the dry intrusion at the bottom to prevent the propagation of disturbances from the plateau and to cause the sudden onset of MCSs apart from the plateau with a heavy precipitation zone.

The Simulated Structure and Evolution of a Quasi-Idealized Warm-Season Convective System with a Training Convective Line

Abstract: This study details the development and use of an idealized modeling framework to simulate a quasi-stationary heavy-rain-producing mesoscale convective system (MCS) A 36-h composite progression of atmospheric fields computed from 26 observed warm-season heavy-rain-producing training line/adjoining stratiform (TL/AS) MCSs was used as initial and lateral boundary conditions for a numerical simulation of this MCS archetypeA realistic TL/AS MCS initiated and evolved within a simulated mesoscale environment that featured a low-level jet terminus, maximized low-level warm-air advection, and an elevated maximum in convective available potential energy The first stage of MCS evolution featured an eastward-moving trailing-stratiform-type MCS that generated a surface cold pool The initial system was followed by rearward off-boundary development, where a new line of convective cells simultaneously redeveloped north of the surface cold pool boundary Backbuilding persisted on the western end of the new lin