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.

Trends of Convective Available Potential Energy over the Indian region and its effect on rainfall

Abstract: Many studies in recent times have suggested that long-term changes in Convective Available Potential Energy (CAPE) are associated with the changes in convective activity and atmospheric energy budget and, hence, the changes in CAPE could be used as a potential indicator of climate change. Here, we analyse daily radiosonde data of 32 stations over the Indian region from 1984 to 2008 (25 years), to study the climatology and long-term changes in CAPE, lower troposphere moisture content and upper tropospheric temperature. Using gridded daily rainfall data over this region, the relationship between average CAPE and average rainfall as well as the trends in CAPE and its effect on rainfall pattern are also examined during different seasons of this region. All the coastal and island stations, as well as some stations in the foothills of the Himalayas, show higher values of CAPE compared to other inland stations. This study clearly demonstrates that CAPE values have been systematically increasing over most parts of the Indian region during last 25 years. The increase in CAPE is found to be due to increase in low-level moisture content and decrease in upper level temperature over the last 25 years. The seasonal variations show that the CAPE is higher during the monsoon compared to pre-monsoon or post-monsoon seasons and it suggests that thermodynamic conditions favourable for high CAPE together with large-scale dynamics are necessary for organized monsoon convections over this region. In comparison with a large increase in the all-India average of CAPE during monsoon season, which is about 38 J Kg -1 year -1, the all-India summer monsoon rainfall increases about 1.3 mm year -1. The systematic increasing trend in CAPE may be compensating for weakening of monsoon circulation and, thus, maintaining the monsoon rainfall over the Indian region.

Increasing the credibility of regional climate simulations by introducing subgrid‐scale cloud‐radiation interactions

Abstract: The radiation schemes in the Weather Research and Forecasting (WRF) model have previously not accounted for the presence of subgrid-scale cumulus clouds, thereby resulting in unattenuated shortwave radiation, which can lead to overly energetic convection and overpredicted surface precipitation. This deficiency can become problematic when applying WRF as a regional climate model (RCM). Therefore, modifications were made to the WRF model to allow the Kain–Fritsch (KF) convective parameterization to provide subgrid-scale cloud fraction and condensate feedback to the rapid radiative transfer model–global (RRTMG) shortwave and longwave radiation schemes. The effects of these changes are analyzed via 3 year simulations using the standard and modified versions of WRF, comparing the modeled results with the North American Regional Reanalysis (NARR) and Climate Forecast System Reanalysis data, as well as with available data from the Surface Radiation Network and Clouds and Earth's Radiant Energy System. During the summer period, including subgrid cloudiness estimated by KF in the RRTMG reduces the surface shortwave radiation, leading to less buoyant energy, which is reflected in a smaller diabatic convective available potential energy, thereby alleviating the overly energetic convection. Overall, these changes have reduced the overprediction of monthly, regionally averaged precipitation during summer for this RCM application, e.g., by as much as 49 mm for the southeastern U.S., to within 0.7% of the NARR value of 221 mm. These code modifications have been incorporated as an option available in the latest version of WRF (v3.6).

Bow Echo Sensitivity to Ambient Moisture and Cold Pool Strength

Abstract: Bow echo development within quasi-linear convective systems is investigated using a storm-scale numerical model. A strong sensitivity to the ambient water vapor mixing ratio is demonstrated. Relatively dry conditions at low and midlevels favor intense cold-air production and strong cold pool development, leading to upshear-tilted, “slab-like” convection for various magnitudes of convective available potential energy (CAPE) and low-level shear. High relative humidity in the environment tends to reduce the rate of production of cold air, leading to weak cold pools and downshear-tilted convective systems, with primarily cell-scale three-dimensionality in the convective region. At intermediate moisture contents, long-lived, coherent bowing segments are generated within the convective line. In general, the scale of the coherent three-dimensional structures increases with increasing cold pool strength. The bowing lines are characterized in their developing and mature stages by segments of the convectiv...

Severe Convective Wind Environments

Abstract: Nontornadic thunderstorm winds from long-lived, widespread convective windstorms can have a tremendous impact on human lives and property. To examine environments that support damaging wind producing convection, sounding parameters from Rapid Update Cycle model analyses (at 3-hourly intervals) from 2003 were compared with 7055 reports of damaging winds and 377 081 occurrences of lightning. Groundrelative wind velocity was the most effective at discriminating between damaging and nondamaging wind convective environments. Steep surface-based lapse rates (a traditional damaging wind parameter) generally did not discriminate between damaging and nondamaging wind convective environments. Other parameters, such as convective available potential energy, humidity aloft, and lapse rates aloft were moderately discriminating. This paper presents a composite damaging wind algorithm in which the two most discriminatory parameters were combined, yielding more skill than any individual parameter. Damaging wind environments are then examined further through a selection of cases that highlight common severe wind ingredients and failure modes. A primary result is that, even in seemingly favorable environments, when the winds at the top of the inflow layer were either parallel to the convective line or blowing from warm to cold over a front, damaging winds were less likely. In the former case, it appears that the downdraft winds and the cold pool’s gust-front-normal flow are not additive. In the latter case, it appears that convection becomes elevated and does not produce downdrafts that reach the surface. Combining the most discriminatory severe wind parameters with knowledge of these severe wind failure modes may help to improve the situational awareness of forecasters.