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.

Convective environment in pre-monsoon and monsoon conditions over the Indian subcontinent: the impact of surface forcing

Abstract: . Thermodynamic soundings for pre-monsoon and monsoon seasons from the Indian subcontinent are analysed to document differences between convective environments. The pre-monsoon environment features more variability for both near-surface moisture and free-tropospheric temperature and moisture profiles. As a result, the level of neutral buoyancy (LNB) and pseudo-adiabatic convective available potential energy (CAPE) vary more for the pre-monsoon environment. Pre-monsoon soundings also feature higher lifting condensation levels (LCLs). LCL heights are shown to depend on the availability of surface moisture, with low LCLs corresponding to high surface humidity, arguably because of the availability of soil moisture. A simple theoretical argument is developed and showed to mimic the observed relationship between LCLs and surface moisture. We argue that the key element is the partitioning of surface energy flux into its sensible and latent components, that is, the surface Bowen ratio, and the way the Bowen ratio affects surface buoyancy flux. We support our argument with observations of changes in the Bowen ratio and LCL height around the monsoon onset, and with idealized simulations of cloud fields driven by surface heat fluxes with different Bowen ratios.

Interactions between warm rain clouds and atmospheric preconditioning for deep convection in the tropics

Abstract: [1] Positive low- and midlevel moisture and heat anomalies have been observed in many previous studies to occur prior to deep convective events (DCEs) in the tropics. Shallow and midlevel convection has been presumed to supply some of the heat and moisture necessary for atmospheric preconditioning and the generation of convective available potential energy (CAPE) for the development of this deep convection. Other recent studies have also shown that warm precipitating cumulus convection is strongly sensitive to sea surface temperature (SST) and that variability in precipitation efficiency may lead to changes in the amount of cloud water available for moistening the troposphere. In this study, a previously developed multisensor retrieval algorithm for Tropical Rainfall Measuring Mission (TRMM) satellite measurements is applied to investigate the influence of warm rain clouds on atmospheric preconditioning for deep convection. DCEs at three locations across the Pacific Ocean are identified using precipitation maxima for warm seasons from 1998 to 2002. Composites of thermodynamic anomalies are compared to warm rain cloud liquid water path (LWP) anomalies to explore the effects of clouds on low-level temperature and humidity, as well as CAPE generation. Results show that positive anomalies in precipitating warm cloud LWP occur with positive low-level moisture and heat anomalies prior to DCEs. Events composited by the mean SST anomaly highlight the sensitivity of warm precipitating cloud properties to temperature and show corresponding changes in moisture. At anomalously warm SSTs, warm precipitating clouds are more efficient at producing precipitation, leaving less water to evaporate and moisten the atmosphere, which corresponds with observed lower moisture anomalies and decreased CAPE generation.

The Importance of Understanding Mesoscale Model Parameterization Schemes for Weather Forecasting

Abstract: A severe weather outbreak that occurred on 21–23 November 1992 in the southern United States is used to illustrate how an understanding of model parameterization schemes can help in the evaluation and utilization of mesoscale model output Results from a mesoscale model simulation show that although the model accurately simulated many of the observed mesoscale features, there are several aspects of the model simulation that are not perfect Through an understanding of the model parameterization schemes, these model imperfections are analyzed and found to have little effect on the overall skill of the model forecast in this case Mesoscale model output also is used to provide guidance to evaluate the severe weather threat By using the model output to produce hourly calculations of convective available potential energy (CAPE) and storm relative environmental helicity (SREH), it is found that regions with positive CAPE, SREH greater than 150 m2 s−2, and model-produced convective rainfall correspond

An Observational Study of the Development of a Rainband on a Meiyu Front Causing Heavy Rainfall in the Downstream Region of the Yangtze River

Abstract: The mesoscale structure and evolution of a rainband that occurred on 24 June 2001 in the downstream region of the Yangtze River and produced heavy rainfall as much as 110 mm within only two hours in a limited area were studied through detailed analyses of upper-air, surface, and triple-Doppler radar data. The rainband evolved on the north side of a surface Meiyu front. It was oriented in a northeastsouthwest direction nearly parallel to the mean storm motion and the low-level vertical shear. The rainband lasted more than 5 hours and propagated slowly southeastward. The environmental conditions ahead of the rainband were characterized by extraordinary stability below and significant conditional instability in a deep layer above the frontal surface that was approximately 0.5 km above the ground. It was found that significant amount of convective available potential energy (1179-370 J kg-1) could be realized by lifting air parcels in a deep layer (0.7-0.5 km) above the frontal surface. The rainband formed as a core of the storm-relative northeasterly inflow associated with the largescale environment appeared on the backside around an altitude of 4 km. The rapid development of the rainband was associated with the surge of another storm-relative northeasterly inflow from the rear around an altitude of 2 km. The latter inflow appeared to be related to the development of a mesoscale vortex after the formation of the rainband. The air that fed the updrafts of the rainband came from an elevated layer above the frontal surface, rather than from the boundary layer. On the other hand, downdrafts at low-levels were shallow and weak during the formation and development of the rainband and strong outflows under the rainband were absent. It is likely that the horizontal convergence enhanced by the northeasterly inflow around an altitude of 4 km was important in the formation of the rainband by lifting the elevated air that possessed conditional instability. Meanwhile, the lifting of the most unstable air in the vertical column of the atmosphere by the northeasterly inflow around an altitude of 2 km would have aided the rapid development of the rainband and the heavy rainfall.