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.

A seamless weather–climate multi‐model intercomparison on the representation of a high impact weather event in the western Mediterranean: HyMeX IOP12

Abstract: High Impact Weather (HIW), particularly Heavy Precipitation Events (HPE), are common phenomena affecting the Western Mediterranean (WMED) especially in the fall period. Understanding and evaluating the capability to adequately represent such events in model simulations is one of the main goals of the Hydrological cycle in the Mediterranean Experiment (HyMeX) and the main motivation of this investigation. In order to gain a better knowledge of the model representation of HPE and related processes we perform a seamless multi-model intercomparison at the event scale. Limited area model runs (grid spacing from 2 to 20 km) at weather and climate timescales are considered, four with parameterized and five with explicit convection. The performance of the nine models is compared by analysing precipitation, as well as convection-relevant parameters. An Intensive Observation Period (IOP12) from the HyMeX-SOP1 (Special Observation Period) is used to illustrate the results. During IOP12, HPE affected the north-western Mediterranean region, from Spain to Italy, as a consequence of Mesoscale Convective Systems (MCSs) which initiated and intensified in the area of investigation. Results show that: (i) the timing of the maximum precipitation seems to be linked with the representation of large-scale conditions rather than differences among models, (ii) Convection Permitting Models (CPMs) exhibit differences among each other, but better represent the short-intense convective events. All four convection-parameterised models produce a large number of weak and long-lasting events. Regional Climate Models (RCMs) capture the occurrence of the event but produce notably lower precipitation amount and hourly intensities than CPMs and Numerical Weather Prediction (NWP) models with parameterized convection. (iii) These differences do not seem to come from mean moisture or Convective Available Potential Energy (CAPE) which are in the same range for all models, but rather from differences in the variability and vertical distribution of moisture and the triggering of deep convection.

Parcel Theory in Three Dimensions and the Calculation of SCAPE

Abstract: Slantwise convective available potential energy (SCAPE) is a measure of the degree to which the atmosphere is unstable to conditional symmetric instability (CSI). It has, until now, been defined by parcel theory in which the atmosphere is assumed to be nonevolving and balanced, that is, two-dimensional. When applying this two-dimensional theory to three-dimensional evolving flows, these assumptions can be interpreted as an implicit assumption that a timescale separation exists between a relatively rapid timescale for slantwise ascent and a slower timescale for the development of the system. An approximate extension of parcel theory to three dimensions is derived and it is shown that calculations of SCAPE based on the assumption of relatively rapid slantwise ascent can be qualitatively in error. For a case study example of a developing extratropical cyclone, SCAPE calculated along trajectories determined without assuming the existence of the timescale separation show large SCAPE values for parcels ascending from the warm sector and along the warm front. These parcels ascend into the cloud head within which there is some evidence consistent with the release of CSI from observational and model cross sections. This region of high SCAPE was not found for calculations along the relatively rapidly ascending trajectories determined by assuming the existence of the timescale separation.

Effects of land-use modification on potential increase of convection: A numerical mesoscale study over south Israel

Abstract: The current research was designed to examine the potential of modified surface conditions in semiarid and arid central-southern Israel to enhance convective development and rainfall. The fifth-generation mesoscale model (MM5), coupled with a sophisticated land-surface submodel, is applied for the three-dimensional high resolution simulations of two convective rain case studies, on October 27, 1990 and October 18, 1987. Three surface conditions are modeled to examine the relative influence of land-use changes, which are present-time land-use (1990s), preirrigation time (1930s), and the hypothetical case of extended irrigated agricultural lands. The main conclusion of the study is that there exists a positive influence of the anthropogenic land-use changes on the enhancement of thermal convection and associated rainfall. Modification of surface parameters from semiarid land conditions to cultivated lands tends to consistently increase the potential for moist convection during the daytime heating hours, as expressed in the evolution of the PBL structure and the growth of convective available potential energy (CAPE), as well as the area-averaged rainfall. The model seems to accurately reproduce the observed atmospheric situations and rainfall, lending confidence to the assertion that these land-atmosphere effects can be quantified with an advanced mesoscale modeling system. This work is the first numerical mesobeta scale 3-D study over the south Israel area with its relatively sharp spatial change in land use as well as in climatic zone. It is believed to be a region, possibly the only in the world, where mesoscale surface and planetary boundary layer processes were suggested as causes for observed anti-desertification gains.

Climatic factors contributing to long-term variations in surface fine dust concentration in the United States

Abstract: . High concentrations of dust particles can cause respiratory problems and increase non-accidental mortality. Studies found fine dust (with an aerodynamic diameter of less than 2.5 µ m) is an important component of the total PM 2.5 mass in the western and central US in spring and summer and has positive trends. This work examines climatic factors influencing long-term variations in surface fine dust concentration in the US using station data from the Interagency Monitoring Protected Visual Environments (IMPROVE) network during 1990–2015. The variations in the fine dust concentration can be largely explained by the variations in precipitation, surface bareness, and 10 m wind speed. Moreover, including convective parameters such as convective inhibition (CIN) and convective available potential energy (CAPE) that reveal the stability of the atmosphere better explains the variations and trends over the Great Plains from spring to fall. While the positive trend of fine dust concentration in the southwestern US in spring is associated with precipitation deficit, the increase in fine dust over the central Great Plains in summer is largely associated with enhanced CIN and weakened CAPE, which are caused by increased atmospheric stability due to surface drying and lower-troposphere warming. The strengthening of the Great Plains low-level jet also contributes to the increase in fine dust concentration in the central Great Plains in summer via its positive correlation with surface winds and negative correlation with CIN. Summer dusty days in the central Great Plains are usually associated with a westward extension of the North Atlantic subtropical high that intensifies the Great Plains low-level jet and also results in a stable atmosphere with subsidence and reduced precipitation.

Clausius–Clapeyron Scaling of Peak CAPE in Continental Convective Storm Environments

Abstract: A thermodynamic constraint on convective available potential energy (CAPE) in continental environments is established using an idealized, one-dimensional model. This theoretical model simplifies the synoptic-scale preconditioning framework for continental severe convection by considering a dry adiabatic column that comes into contact with a moist land surface. A system of equations is derived to describe the evolution of the ensuing surface boundary layer. From these, the maximum value of transient CAPE in the column can be found for any particular combination of surface temperature and moisture. It is demonstrated that, for a given range of surface temperatures, the value of peak CAPE scales with the Clausius-Clapeyron relation.