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.

Atmosphere-ocean conditions jointly guide convection of the Boreal Summer Intraseasonal Oscillation: Satellite observations

Abstract: The water-vapor and air-temperature profiles from the Atmospheric Infrared Sounder (AIRS), in combination with surface wind from Quick Scatterometer (QuikSCAT) and rainfall and sea surface temperature (SST) from Tropical Rainfall Measurement Mission (TRMM) Microwave Imager (TMI), are used to document surface conditions and vertical moist thermodynamic structures of the 2003-2006 Boreal Summer Intraseasonal Oscillation (BSISO) over the Indo-Pacific warm pool. The composite based on Wheeler and Hendon's intraseasonal oscillation index reveals that Convective Available Potential Energy (CAPE), SST, and surface convergence lead convection in both northward and eastward directions. The preconditioning of CAPE is much earlier than that of SST, implying that the atmosphere internal processes precondition CAPE. On the other hand, the ocean positively feeds back to the atmosphere from bottom up, forming a smooth transition from boundary layer moistening, shallow convection at lower or middle level, to the deep convection all through the troposphere. The preconditioning of the boundary layer moist (dry) anomalies to the subsequent positive (negative) rainfall maximum is as far as 60-90 degrees in longitude (15 degrees in latitude) and quarter-to-half cycle in time. In contrast, this boundary layer preconditioning is virtually undetected from conventional NCEP reanalysis. Finally, the implications of these new findings on the frictional "convective interaction with dynamics'' (CID) theory of intraseasonal oscillation are also discussed.

Idealized mesoscale numerical study of Mediterranean heavy precipitating convective systems

Abstract: The western Mediterranean mountainous areas are prone to heavy precipitating events during the fall season. The ingredients that favour these systems are well known but it is still difficult to understand why a precipitating system can become paroxysmal or to forecast the accurate location of the system. To investigate these predictability issues, an idealized framework to simulate quasi-stationary mesoscale convective systems is set up and serves as a basis for studying the sensitivity of the location and intensity of precipitating systems to the characteristics of the low-level upstream flow over the Mediterranean Sea. High resolution simulations are performed with the non-hydrostatic MESO-NH model for an idealized moist unstable flow but using the real topography. Low-level humidity distribution, convective available potential energy and speed of the flow are varied. It is found that various lifting mechanisms are involved to explain the specific location (orographic lifting, cold pool dynamics, low-level convergence due to deflection of the flow by the Alps). When the speed of the upstream flow is increased (decreased) compared to the CTRL run, the area of precipitation moves downstream (upstream). When the mixing ratio of the environment outside of the jet is less (more) than the CRTL run, the system is located more upstream (downstream). When the instability of the upstream flow is increased (decreased) compared to the CTRL run, the convective system moves upstream (downstream). The cold pool strength increases with slower flow and/or more instability. The maximum of rainfall is obtained when the convective system is over the relief with a strong low-level flow or a weak CAPE. The area covered by heavy precipitation is maximum when CAPE is high or low-level flow is strong.

A Lagrangian Study of Precipitation-Driven Downdrafts*

Abstract: Precipitation-driven downdrafts are an important component of deep convective systems. They stabilize the atmosphere by injecting relatively cold and dry air into the boundary layer. They have also been invoked as responsible for balancing surface latent and sensible heat fluxes in the heat and moisture budget of tropical boundary layers. This study is focused on precipitation-driven downdrafts and basic aspects of their dynamics in a case of radiative‐convective equilibrium. Using Lagrangian particle tracking, it is shown that such downdrafts have very low initial heights, with most parcels originating within 1.5km from the surface. The tracking is also used to compute the contribution of downdrafts to the flux of moist static energy at the top of the boundary layer, and it is found that this is on the same order of magnitude as the contribution due to convective updrafts, but much smaller than that due to turbulent mixing across the boundary layer top in the environment. Furthermore, considering the mechanisms driving the downdrafts, it is shown that the work done by rain evaporation is less than half that done by condensate loading.

Convective initiation and maintenance processes of two back-building mesoscale convective systems leading to heavy precipitation events in Southern Italy during HyMeX IOP 13

Abstract: During Intensive Observation Period 13 (15−16 October 2012) of the first Special Observing Period of the Hydrological cycle in the Mediterranean Experiment (HyMeX), Southern Italy (SI) was affected by two consecutive heavy precipitation events (HPEs). Both HPEs were associated with multi-cell V-shaped retrograde regeneration mesoscale convective systems (MCSs). The life cycle of two MCSs in connection with their dynamic and thermodynamic environments were analysed using a combination of ground-based, airborne and spaceborne observations and numerical simulations. Rain gauges revealed that heavy precipitation occurred in two phases: the first one from 1300 to 1700 UTC (35 mm h –1 ) was caused by a V-shaped system initiating over the Tyrrhenian Sea in the early morning of 15 October. Convection was triggered by the low-level convergence between the south-westerlies ahead of an upper-level trough positioned over south-eastern France and very moist southerlies from the Strait of Sicily. The convection was favoured by high convective available potential energy (1500 J kg –1 ) resulting from warm and moist conditions at low levels associated with high sea surface temperatures in the Sicily Channel. In addition, humidity at mid-level was enriched by the presence of an elevated moisture plume from tropical Africa, favouring the efficiency of the convection to produce more precipitation. The second phase of heavy precipitation (2300 UTC on 15 October to 0200 UTC on 16 October, 34 mm h –1 ) was caused by a MCS initiating over Algeria around 1300 UTC, which subsequently traveled over the Strait of Sicily toward Sicily and SI. Convection was maintained by the combination of large low-level moisture contents and a marked convergence ahead of the cold front. Unlike other MCSs forming in the same region earlier on that day, this huge V-shaped system did affect SI because the strong upper-level flow progressively veered from southwesterly to south-southwesterly.