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.

Why does tropical convective available potential energy (CAPE) increase with warming

Abstract: Author(s): Seeley, JT; Romps, DM | Abstract: Recent work has produced a theory for tropical convective available potential energy (CAPE) that highlights the Clausius-Clapeyron (CC) scaling of the atmosphere's saturation deficit as a driver of increases in CAPE with warming. Here we test this so-called "zero-buoyancy" theory for CAPE by modulating the saturation deficit of cloud-resolving simulations of radiative-convective equilibrium in two ways: changing the sea surface temperature (SST) and changing the environmental relative humidity (RH). For earthlike and warmer SSTs, undilute parcel buoyancy in the lower troposphere is insensitive to increasing SST because of a countervailing CC scaling that balances the increase in the saturation deficit; however, buoyancy increases dramatically with SST in the upper troposphere. Conversely, in the RH experiment, undilute buoyancy throughout the troposphere increases monotonically with decreasing RH. We show that the zero-buoyancy theory successfully predicts these contrasting behaviors, building confidence that it describes the fundamental physics of CAPE and its response to warming.

The diurnal cycle of rainfall over New Guinea in convection-permitting WRF simulations

Abstract: . In this study, we examine the diurnal cycle of rainfall over New Guinea using a series of convection-permitting numerical simulations with the Weather Research and Forecasting (WRF) model. We focus our simulations on a period of suppressed regional-scale conditions (February 2010) during which local diurnal forcings are maximised. Additionally, we focus our study on the occurrence and dynamics of offshore-propagating convective systems that contribute to the observed early-morning rainfall maximum north-east of New Guinea. In general, modelled diurnal precipitation shows good agreement with satellite-observed rainfall, albeit with some timing and intensity differences. The simulations also reproduce the occurrence and variability of overnight convection that propagate offshore as organised squall lines north-east of New Guinea. The occurrence of these offshore systems is largely controlled by background conditions. Days with offshore-propagating convection have more middle tropospheric moisture, larger convective available potential energy, and greater low-level moisture convergence. Convection has similar characteristics over the terrain on days with and without offshore propagation. The offshore-propagating convection manifests via a multi-stage evolutionary process. First, scattered convection over land, which is remnant of the daytime maximum, moves towards the coast and becomes reorganised near the region of coastal convergence associated with the land breeze. The convection then moves offshore in the form of a squall line at ∼ 5 m s−1. In addition, cool anomalies associated with gravity waves generated by precipitating land convection propagate offshore at a dry hydrostatic gravity wave speed (of ∼ 15 m s−1) and act to destabilise the coastal/offshore environment prior to the arrival of the squall line. Although the gravity wave does not appear to initiate the convection or control its propagation, it should contribute to its longevity and maintenance. The results highlight the importance of terrain and coastal effects along with gravity waves in contributing to the diurnal cycle over the Maritime Continent, especially the offshore precipitation maxima adjacent to quasi-linear coastlines.

Downscaled estimates of late 21st century severe weather from CCSM3

Abstract: High-resolution dynamical downscaling is used to explore 2080–2090 peak-season hazardous convective weather as simulated from the Community Climate System Model version 3. Downscaling to 4 km grid spacing is performed using the Weather Research and Forecasting model. Tornadoes, damaging wind gusts, and large hail are simulated using a model proxy at hourly intervals for locations east of the U.S. Continental Divide. Future period results are placed into context using 1980–1990 output. While a limited sample size exists, a statistically significant increase in synthetic severe weather activity is noted in March, whereas event frequency is shown to slightly increase in April, and stay the same in May. These increases are primarily found in the Mississippi, Tennessee, and Ohio River valleys. Diurnally, most of the increase in hazardous convective weather activity is shown to be in the hours surrounding local sunset. Peak-season severe weather is also shown to be more variable in the future with a skewed potential toward larger counts. Finally, modeled proxy events are compared to environmental parameters known to generate hazardous convective weather activity. These environmental conditions explain over 80 % of the variance associated with modeled reports during March–May and show an increasing future tendency. Finally, challenges associated with dynamical downscaling for purposes of resolving severe local storms are discussed.

Evaluation of Trigger Functions for Convective Parameterization Schemes Using Observations

Abstract: Realistic simulation of different modes of atmospheric variability ranging from diurnal cycle to interannual variation in global climate models (GCMs) depends crucially on the convection trigger criteria. In this study, using the data from constrained variational analysis by the Atmospheric System Research program for single-column models (SCM), the performance of the commonly used convective trigger functions in GCMs is evaluated based on the equitable threat score (ETS) value, a widely used forecast verification metric. From the ETS score, three consistently better-performing trigger functions were identified. They are based on the dilute and undilute convective available potential energy (CAPE) generation rate from large-scale forcing in the free troposphere (hereafter dCAPE) and parcel buoyancy at the lifting condensation level (Bechtold scheme). The key variables used to define these trigger functions are examined in detail. It is found that the dilute dCAPE trigger function performs the best...