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.

The sensitivity of surface energy balance to convective parameterization in a general circulation model

Abstract: This study investigates the interaction between convection and the surface energy fluxes, and its sensitivity to convective parameterization schemes using a general circulation model. Two simulations of the global circulation averaged annually from 1 June 1985 to 31 May 1986 are performed, with particular emphasis on the tropical Pacific. In the control simulation, a convective scheme that parameterizes convection based on low-level moisture convergence is used. A second experiment employs a parameterization scheme that uses the time rate of change of convective available potential energy (CAPE) to determine convection. When the low-level moisture convergence is used as the closure for convective parameterization, convection and low-level convergence occur near the landmass of Southeast Asia. The large-scale circulation is such that a fairly strong surface wind that provides moisture to fuel convection is located in the western tropical Pacific warm pool regions, giving rise to relatively high latent heat flux there. When the time rate of change of CAPE is used to close convective parameterization, convection and its associated low-level large-scale convergence and weak surface wind speed occur in the warm pool region, resulting in low latent heat flux there. Response of surface solar radiative flux to convection is found to bemore » the largest in the surface energy budget. In the experiment, more clouds are produced over the tropical oceans, leading to less solar radiation received on the surface. More clouds in the experiment also lead to less net emission of longwave radiation from the ocean surface due to the cloud greenhouse effect, albeit the magnitude is much smaller than that for solar radiation. The large changes in surface latent heat and solar radiative fluxes from the control run to the experiment suggest that the surface energy balance in the atmospheric general circulation model is highly sensitive to convective parameterization. 44 refs., 10 figs.« less

Influence of convective adjustment time scale on the tropical transient activity

Abstract: The influence of convective adjustment time scale (τ) in simulating the tropical transient activity is examined using the NCAR-Community Atmosphere Model (CAM). In the default configuration of the model, the prescribed value of τ, a characteristic time scale with which convective available potential energy (CAPE) is removed at an exponential rate by convection, is assumed to be 1 h. However, some recent observational findings suggest that it is larger by around one order of magnitude, and subsequent modeling studies showed its impact on mean climate and suggest a value of 8 h. To see if alteration of this time scale could affect the transient features of climate, numerical experiments are conducted in aqua-planet and real-planet frameworks. The analysis includes the tropical intraseasonal variability (ISV), convectively coupled equatorial waves (CCEW), diurnal and sub-diurnal variability of precipitation, and intensity and frequency of rainfall. Two sets of simulations are conducted: one with a time scale of 1 h (CTRL) and another with 8 h (EXPT). EXPT produces more reasonable ISV, with prominent, coherent, and organized eastward propagation. The active phases of the ISV constitute hierarchical substructures embedded within them, which are absent in CTRL. The Kelvin waves become slow, Madden–Julian oscillation (MJO) become energetic, n = 1 equatorial Rossby (ER) and n = 0 eastward inertio-gravity (EIG) waves become prominent, with the increase of τ. On the contrary, the mixed Rossby-gravity (MRG) waves at higher wavenumber regimes become weak. The amplitude of diurnal variability decreases, but the phase remains largely unchanged. At sub-diurnal scales, the variability of precipitation increases. In CTRL, precipitation always occurs in the tropics with light or moderate intensity, which becomes intermittent when τ is increased to 8 h.

Forecasting Convective Downburst Potential Over The United States Great Plains

Abstract: A favorable environment for downbursts associated with deep convective storm systems that occur over the central and eastern continental United States includes strong static instability with large amounts of convective available potential energy and the presence of a mid-tropospheric layer of dry air. However, previous research has identified that over the central United States, especially in the Great Plains region, an environment between that favorable for wet and dry microbursts may exist during the convective season, resulting in the generation of hybrid type microbursts. Hybrid microbursts have been found to originate from deep convective storms that generate heavy precipitation, with sub-cloud evaporation of precipitation a significant factor in downdraft acceleration. Accordingly, a new GOES sounder derived product, the GOES Hybrid Microburst Index, is under development and is designed to assess the potential for convective downbursts that develop in an intermediate environment between a wet type, associated with heavy precipitation, and a dry type associated with convection in which very little to no precipitation is observed at the surface.

A Diagnostic Case Study on the Comparison Between the Frontal and Non-Frontal Convective Systems

Abstract: Two major mesoscale convective clusters of different characters occurred during the heavy rainfall event in Guangxi Region and Guangdong Province on 20 June 2005,and they are preliminarily identified as a frontal mesoscale convective system(MCS1;a frontal cloud cluster) and a non-frontal MCS(MCS2;a warm sector cloud cluster)Comparative analyses on their convective intensity,maintenance mechanism, and moist potential vorticity(MPV) structure were further performedThe convective intensity analysis suggests that the ascending motion in both the frontal MCS1 and the warm sector MCS2 was strong,so it is hard to conclude whether the intensity of the frontal convective cluster was stronger than that of the nonfrontal convective cluster,and their difference in precipitation might result from differences in their moisture conditionsThe comparative analysis of the maintenance mechanisms of matured MCS1 and MCS2 show that in MCS1 there were strong northerly inflows at middle and upper levels,and the convection was mainly maintained through convective-symmetric instability;while in MCS2,the water vapor was abundant,and the convection was maintained by moist convective instabilityThe structural analysis of MPV indicates that(1) the two clusters were both potentially symmetric unstable at middle and low levels;(2) there were interactions between the cold/dry air and the warm/wet air in the frontal MCS1,and the interactions between the upper- and low-level jets in the warm sector MCS2;(3) the high- and low-level jets and moisture condition nearby the convective clusters exerted different impacts on the two types of convective systems, respectively

Investigation of WRF’s ability to simulate the monsoon-related seasonal variability in the thermodynamics and precipitation over southern peninsular India

Abstract: The goal of this study is to evaluate the ability of the state-of-the-art, higher-resolution, convection-permitting, weather research forecasting (WRF) model in predicting the changes in precipitation regimes which come in response to the seasonal changes in the large-scale environmental forcing. The simulation days are selected in the year 2009 and according to four environmental regimes defined by the daily flow direction (Ragi et al. (IEEE Trans Geosci Remote Sens 55:3466–3474, 2017)) using QuikSCAT scatterometer and the comparison of the same with National Center for Environmental Prediction (NCEP) final analysis (FNL) data. The observations used for analysis are from Indian Meteorological Department, Wyoming, TRMM satellite data, and NCEP-NCAR reanalysis data. This study finds that WRF is capable of reproducing the season-specific differences in the precipitating patterns that reflect the different phases of the monsoon. Extensive comparisons to observations point out that the model simulates reasonably well the temperature and the humidity fields, including their diurnal variability and vertical structure. However, the model-produced precipitation and winds do not compare so well, especially the winds. The simulated large-scale monsoon circulation and rainfall patterns indicate a wet bias in the model rainfall simulations than the TRMM rainfall observations over the selected region. In particular, WRF overestimates the rain. The base variables such as outgoing longwave radiation (OLR), latent and sensible heat fluxes, and convective available potential energy (CAPE) and convective inhibition energy (CIN) are nearly in agreement with the observations. In effect, WRF is skilled to represent the variability in different seasons and its spatial distribution, an important characteristic of the precipitation, especially concerning prediction of the monsoon onset. The disagreements between the observed and the model precipitation and winds can be due to the WRF model physics which generates different dynamics and different precipitating systems and initial conditions.