- Free convective layer
In
atmospheric sciences , the free convective layer (FCL) is the layer of conditional or potential instability in thetroposphere . It is a layer of positivebuoyancy (PBE) and is the layer where deep, moist convection (DMC) can occur. On anatmospheric sounding , it is the layer between thelevel of free convection (LFC) and theequilibrium level (EL). The FCL is important to a variety of convective processes and to severe thunderstorm forecasting.It is the layer of instability, the "positive area" on
thermodynamic diagrams where an ascendingair parcel is warmer than its environment. Integrating buoyant energy from the LFC to the EL gives theconvective available potential energy (CAPE), an estimate of the maximum energy available to convection. The depth of the FCL is expressed by the formula:: FCL = ZEL - ZLFC or : FCL = PEL - PLFC
Deep, moist convection is essentially a
thunderstorm , it iscumulus congestus cloud s orcumulonimbus cloud s. An air parcel ascending from the near surface layer (mixed layer or boundary layer) must work through the stable layer ofconvective inhibition (CIN) when present. This work comes from increasing instability in the low levels by raising thetemperature ordew point , or by mechanical lift. Without the aid of mechanical forcing, a parcel must reach itsconvective temperature (Tc) before moistconvection (cloud ) begins near theconvective condensation level (CCL}, whereas with dynamic lift,cloud base begins near thelifted condensation level (LCL). This will remain as shallow, moist convection (smallcumulus cloud s) until breaking through the convective inhibition layer, after which DMC ensues as a parcel hits the LFC and enters the FCL, if thermal or mechanical forcing continues. At the level of neutral buoyancy (the EL), a parcel is cooler than the environment and is stable, so it slow down, eventually ceasing at themaximum parcel level (MPL).References
* Blanchard, David O. (Sep 1998). Assessing the Vertical Distribution of Convective Available Potential Energy. "
Weather and Forecasting ", 13 (3): 870–877.See also
*
Atmospheric thermodynamics
*Mixed layer External links
* [http://www.crh.noaa.gov/lsx/science/pdfppt/convective_indices.pdf Atmospheric indices] (
National Weather Service St. Louis)
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