Topic
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.
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TL;DR: In this article, a 573-case observational dataset is partitioned into small versus large values of environmental and storm-related variables such as bulk wind shear, convective available potential energy, mean wind, storm motion, and storm relative helicity (SRH).
Abstract: Two shear-based supercell motion forecast methods are assessed to understand how each method performs under differing environmental conditions for observed right-moving supercells. Accordingly, a 573-case observational dataset is partitioned into small versus large values of environmental and storm-related variables such as bulk wind shear, convective available potential energy, mean wind, storm motion, and storm-relative helicity (SRH). In addition, hodographs are partitioned based on the tornado damage scale, as well as where the storm motion falls among the four quadrants. With respect to the 573-case dataset, the largest supercell motion forecast errors generally occur when the (i) observed midlevel (4–5 km AGL) storm-relative winds are either anomalously weak or strong, (ii) observed 0–3-km AGL SRH is large, (iii) supercell motion is fast, (iv) convective inhibition is strong, or (v) the surface–500-mb (1 mb = 1 hPa) RH is low. Moreover, significantly tornadic supercells are biased 1.2 m s−1 ...
15 citations
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TL;DR: In this article, the authors evaluated the potential impact of neglecting ACI on the operational rainfall forecast using ground-based and satellite observations and model reanalysis, and found that the overestimation of light rain (47.84%) and underestimation of heavier rain (31.83, 52.94, and 65.74%) from the model are qualitatively consistent with the potential errors arising from not accounting for ACI.
Abstract: . Aerosol–cloud interactions (ACIs) have been widely recognized as a factor affecting precipitation. However, they have not been considered in the operational National Centers for Environmental Predictions Global Forecast System model. We evaluated the potential impact of neglecting ACI on the operational rainfall forecast using ground-based and satellite observations and model reanalysis. The Climate Prediction Center unified gauge-based precipitation analysis and the Modern-Era Retrospective analysis for Research and Applications Version 2 aerosol reanalysis were used to evaluate the forecast in three countries for the year 2015. The overestimation of light rain (47.84 %) and underestimation of heavier rain (31.83, 52.94, and 65.74 % for moderate rain, heavy rain, and very heavy rain, respectively) from the model are qualitatively consistent with the potential errors arising from not accounting for ACI, although other factors cannot be totally ruled out. The standard deviation of the forecast bias was significantly correlated with aerosol optical depth in Australia, the US, and China. To gain further insight, we chose the province of Fujian in China to pursue a more insightful investigation using a suite of variables from gauge-based observations of precipitation, visibility, water vapor, convective available potential energy (CAPE), and satellite datasets. Similar forecast biases were found: over-forecasted light rain and under-forecasted heavy rain. Long-term analyses revealed an increasing trend in heavy rain in summer and a decreasing trend in light rain in other seasons, accompanied by a decreasing trend in visibility, no trend in water vapor, and a slight increasing trend in summertime CAPE. More aerosols decreased cloud effective radii for cases where the liquid water path was greater than 100 g m−2. All findings are consistent with the effects of ACI, i.e., where aerosols inhibit the development of shallow liquid clouds and invigorate warm-base mixed-phase clouds (especially in summertime), which in turn affects precipitation. While we cannot establish rigorous causal relations based on the analyses presented in this study, the significant rainfall forecast bias seen in operational weather forecast model simulations warrants consideration in future model improvements.
15 citations
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TL;DR: In this article, the authors analyzed how modifications of the convective scheme modify the initiation of tropical depression vortices and their intensification into stronger warm-cored tropical cyclone-like vortice (TCs) in global climate model (GCM) simulations.
Abstract: The authors analyze how modifications of the convective scheme modify the initiation of tropical depression vortices (TDVs) and their intensification into stronger warm-cored tropical cyclone–like vortices (TCs) in global climate model (GCM) simulations. The model’s original convection scheme has entrainment and cloud-base mass flux closures based on moisture convergence. Two modifications are considered: one in which entrainment is dependent on relative humidity and another in which the closure is based on the convective available potential energy (CAPE).Compared to reanalysis, TDVs are more numerous and intense in all three simulations, probably as a result of excessive parameterized deep convection at the expense of convection detraining at midlevel. The relative humidity–dependent entrainment rate increases both TDV initiation and intensification relative to the control. This is because this entrainment rate is reduced in the moist center of the TDVs, giving more intense convective precipitati...
15 citations
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TL;DR: In this paper, the effects of sub-grid-scale land use differences in modifying the stability of prestorm environments has been studied using data from the Department of Energy Cloud and Radiation Testbed (CART) in Kansas and Oklahoma and a mesoscale model.
Abstract: The effects of sub-grid-scale land use differences in modifying the stability of prestorm environments has been studied using data from the Department of Energy Cloud and Radiation Testbed (CART) in Kansas and Oklahoma and a mesoscale model. To quantify the atmospheric instability, three indices were used: the lifted index, the modified K index, and convective available potential energy. The spatial variations of these indices were calculated from simulations using spatially varying and spatially uniform surface fluxes as lower boundary conditions. The CART is approximately 105 km2 in area and is characterized by large areas of contrasting vegetation cover and surface sensible and latent heat fluxes. The spatially varying fluxes were calculated with the SiB2 model using data from the CART. Six days, during which isolated thunderstorms developed, were chosen for the study. The results suggest that sub-grid-scale variations in land use differences do not modify the spatial distribution of the stability indices in the southern Great Plains to any significant degree. Predictions of areas of preferred development of deep convection, based on changes in the indices, are not improved by accounting for sub-grid-scale variations in land use. The indices were found to be potentially useful but imperfect indicators of the occurrence of deep convective precipitation at scales smaller than that of the CART. At the model resolution used (grid spacing of 2.08 km) a close correlation was not found between regions of precipitation and regions with enhanced simulated vertical updrafts related to land-use differences, but a detailed study of local triggering has not been carried out.
15 citations
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TL;DR: In this paper, the authors investigated the sensitivity of nonsupercell tornadogenesis to variations in convective available potential energy (CAPE), outflow boundary vortex sheet strength, and boundary layer vertical shear.
Abstract: Nonsupercell tornadogenesis has been investigated in a three-part numerical study. Building on the results of Parts I and II, Part III addresses the sensitivity of nonsupercell tornadogenesis to variations in convective available potential energy (CAPE), outflow boundary vortex sheet strength, and boundary layer vertical shear. A three-dimensional, nonhydrostatic, quasi-compressible convective cloud model has been employed to examine nonsupercell tornado (NST) development in an environment typical of the Colorado high plains. A strong relationship was shown to exist between the magnitude of the environmental CAPE and the structure and intensity of the misocyclones and nonsupercell tornadoes that developed. As CAPE was increased from 0 to 1700 J kg−1, the simulated vortices markedly contracted and intensified. Multiple CAPE thresholds were identified that yielded markedly different vortex intensity. The highest CAPE runs produced NST families with peak ground-relative surface winds of ∼47 m s−1. V...
15 citations