2 Thermodynamic Diagrams There are three desirable characteristics of atmospheric thermodynamic diagrams:The area enclosed by any cyclic process should be proportional to energy or work.The more straight lines the better.The angle between isotherms and dry adiabats should be as large as possible.
3 Emagram—Abscissa is T, ordinate is proportional to ln p Emagram—Abscissa is T, ordinate is proportional to ln p. (From energy/mass).Tephigram—Abscissa is T, ordinate is logarithm of potential temperature, sometimes diagram is rotated (From T-phi)Stuve—Abscissa is T, ordinate is Area is not proportional to energy.Skew T-ln p—Similar to emagram, but temperature lines are skewed to increase the angle with dry adiabats.
4 Convection Parameters Lifted Condensation Level (LCL) – level at which a parcel lifted from the surface will saturateConvective Condensation Level (CCL) –level at which a parcel from the surface heating to its convective temperature will saturateConvective Temperature – the temperature that the surface layer would need to be heated to to convect
5 Convection Condensation Level (CCL) The convection condensation level is the height to which a parcel of air, if heated from below, will rise to until it’s just saturated. It represents the height of the base of cumulus clouds created by surface heating.To determine the CCL, follow the saturation mixing ratio line upward from the surface dewpoint and find the intersection with the T curve.The convective temperature can be found by following a dry adiabat downward from the CCL. It represents the temperature that must be reached for the formation of convective clouds.
6 Lifted Condensation Level The lifted condensation level (LCL) is the height at which a parcel becomes saturated when lifted dry adiabatically. It is found by finding the intersection of the saturation mixing ratio line through the surface dewpoint and a dry adiabat through the surface temperature. It’s actually often more realistic to use an average dewpoint for the area near the surface.
7 Level of Free Convection Level of Free Convection (LFC) – level at which a lifted parcel becomes warmer than its surroundings due to the release of latent heat, and hence buoyant. It is found by starting at the LCL and proceeding upward along a moist adiabat until the temperature of the parcel is greater than its surroundings, that is, it crosses the T curve.
8 Convection Parameters (cont.) Level of Free Convection (LFC) – level at which a lifted parcel becomes warmer than its surroundings, and hence buoyant.Equilibrium Level (EL) – level at which a previously buoyant parcel’s temperature again equals the environmental temperature. This is an approximate height for thunderstorm anvils.
9 Convection Parameter (cont.) Convective Inhibition (CIN) – the “negative” energy area below a parcel’s level of free convection.Convective Available Potential Energy (CAPE) – The “positive” energy area where a parcel is accelerating upward.Equilibrium Level (EL) – level at which a previously buoyant parcel’s temperature again equals the environmental temperature. This is an approximate height for thunderstorm anvils.
11 Stability ParametersAll indices are useful diagnostics but should not be used blindlyLifted index (LI)Showalter index (SI)Total totals (TT)Severe Weather Threat Index (SWEAT)Bulk Richardson NumberStorm Relative Helicity