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.

Supersaturation, buoyancy, and deep convection dynamics

Abstract: . Motivated by recent discussions concerning differences of convective dynamics in polluted and pristine environments, the so-called convective invigoration in particular, this paper provides an analysis of factors affecting convective updraft buoyancy, such as the in-cloud supersaturation, condensate and precipitation loading, and entrainment. We use the deep convective period from simulations of daytime convection development over land discussed in our previous publications. An entraining parcel framework is used in the theoretical analysis. We show that for the specific case considered here, finite (positive) supersaturation noticeably reduces pseudo-adiabatic parcel buoyancy and cumulative convective available potential energy (cCAPE) in the lower troposphere. This comes from keeping a small fraction of the water vapor in a supersaturated state and thus reducing the latent heating. Such a lower-tropospheric impact is comparable to the effects of condensate loading and entrainment in the idealized parcel framework. For the entire tropospheric depth, loading and entrainment have a much more significant impact on the total CAPE. For the cloud model results, we compare ensemble simulations applying either a bulk microphysics scheme with saturation adjustment or a more comprehensive double-moment scheme with supersaturation prediction. We compare deep convective updraft velocities, buoyancies, and supersaturations from all ensembles. In agreement with the parcel analysis, the saturation-adjustment scheme provides noticeably stronger updrafts in the lower troposphere. For the simulations predicting supersaturation, there are small differences between pristine and polluted conditions below the freezing level that are difficult to explain by standard analysis of the in-cloud buoyancy components. By applying the piggybacking technique, we show that the lower-tropospheric buoyancy differences between pristine and polluted simulations come from a combination of temperature (i.e., latent heating) and condensate loading differences that work together to make polluted buoyancies and updraft velocities slightly larger when compared to their pristine analogues. Overall, the effects are rather small and contradict previous claims of a significant invigoration of deep convection in polluted environments.

Association of Rainfall and Stability Index with Lightning Parameter over the Indo-Gangetic Plains

Abstract: The Lightning Imaging Sensor (LIS) based satellite lightning grid data for 10 year period (1998-2007) were used to study the association of rainfall and stability index with lightning parameter over Indo-Gangetic plain (IGP) region. The spatial variation of flash rate density (FRD) is found to be (40 fl·km-2·yr-1) higher over northern region of IGP as compare to that of eastern IGP region. The annual variation of FRD exhibits bimodal distributions, while the precipitation rate shows unimodal distributions. The results show that the FRD peaked 2 months (pre-monsoon) in advance to the monsoon months where rainfall peak occurred due to environmental lapse rates more than 7.0°C/km during pre-monsoon which is evident from the temperature profile for correlation coefficient between temperature (700 mb) and FRD with coefficient of 0.70, p ≤ 0.0001 during pre-monsoon. The annual variation of lifted index show negative value over March to September due to intense insolation, convective available potential energy (CAPE) and also availability of moisture. The convective cloud transform into thundercloud with the development of mixed-phase (cloud water + ice) which subsequently produce the lightning. During monsoon, seasonal thermal heating diminishes and even on revival after break monsoon period, K-index is found to be less as the orography does not allow the highly moist air of low temperature to reach to large height above freezing level. They can be referred as maritime clouds of intermediate height with moderate updraft and hence minimum lightning activity during the monsoon season. Lifted index are proved to be indicators of thunderstorm conditions. This is because that rising air parcel is much warmer than its surroundings and can accelerate rapidly and create severe thunderstorms.

Application of Ground-Based Microwave Radiometer in Retrieving Meteorological Characteristics of Tibet Plateau

Abstract: The characteristics of plateau precipitation and atmosphere, once accurately and comprehensively understood, can be used to inform sound air–water resource development practices. In this study, atmospheric exploration of the Tibet Plateau (TP) was conducted using ground-based microwave radiometer (MWR) data collected during the East Asian summer monsoon. Atmospheric temperature, pressure, humidity, and other variables were gathered under clear-sky, cloudy-sky, and rainy-sky conditions. Statistical characteristics of the air parcel height and stability/convection indices such as convective available potential energy (CAPE) and convective inhibition (CIN) were investigated, with a special focus on the rainy-sky condition. Two retrieval applications for characterizing precipitation, namely short-term precipitation forecast and quantitative precipitation estimation were presented. Results showed that CAPE values in the Darlag region reached extremes around 18:00–20:00 (UTC+8) for cloudy-sky and rainy-sky conditions with corresponding peaks of about 1046.56 J/kg and 703.02 J/kg, respectively. When stratiform or convective–mixed precipitation occurs, the precipitable water vapor (PWV) and CAPE values were generally greater than 1.7 cm and 1000 J/kg, respectively. CAPE values are likely to decrease before the occurrence of precipitation due to the release of the latent heat in the atmosphere.

Improved Regional Analyses and Heavy Precipitation Forecasts With Assimilation of Atmospheric Infrared Sounder Retrieved Thermodynamic Profiles

Abstract: This paper describes a procedure to assimilate Atmospheric Infrared Sounder (AIRS)-retrieved thermodynamic profiles into a regional configuration of the Weather Research and Forecasting (WRF) model and validates subsequent precipitation forecasts over the eastern half of the continental U.S. Quality indicators were used to select the highest quality temperature and moisture profiles for assimilation throughout the entire atmosphere in clear and partly cloudy regions and above cloud top in cloudy regions. Separate error characteristics for land and water profiles were also used in the assimilation process. Assimilation of AIRS profiles produced analyses with a better validation to in situ observations than the short-term WRF forecast first-guess field. The AIRS-enhanced initial conditions improved simulation of a severe weather event over Texas and Louisiana from February 12-13, 2007. For this event, assimilation of AIRS profiles produced a more unstable boundary-layer air mass in the warm sector ahead of an advancing midlatitude cyclone, resulting in enhanced convective available potential energy in the model. The simulated squall line and precipitation totals from a forecast initialized with AIRS-enhanced initial conditions more closely reflected ground-based observations than one initialized with a no-AIRS control forecast. The impact of the improved initial conditions through the assimilation of AIRS profiles was further demonstrated through an evaluation of a 37-day period from the winter of 2007. The unstable environment over the Gulf of Mexico and coastal region with the AIRS-enhanced initial conditions resulted in 20%+ improvements in the 6-h accumulated precipitation forecasts out to 48 h over that period.