Outline: classical stability analysis, using recent soundings Bjerknes “slice” approach

1. Thermodynamic Applications • Outline: • classical stability analysis, using recent soundings • Bjerknes “slice” approach • conserved variable diagrams

3. Skew T - log-p diagram. Miami, 7 am local, Tuesday

4. Surface parcel properties matter. Denver, 6 am LT & 6 pm

5. Miami eve, CAPE=942 J/kg AM CAPE= 235 J/kg

6. Oklahoma City Cape= 1495 J/kg

7. defines CAPE • Belief that storms are particularly sensitive • to parcel buoyancy and wind shear

8. Parcel method does not account for reaction of Environmental air to the intrusion of a cloud(s). Bjerknes (1938) developed a “slice” method. “Saturated-adiabatic ascent of air through Dry-adiabatically descending environment. Quart. J. Roy. Meteor. Soc., 64, p. 325-330. Helps explain the spacing in between clouds

9. Lorenz, E. 1955: Available potential energy and the maintenance of the general circulation. Tellus, 7, 157-167. APE = energy available for conversion into kinetic Energy (sum of potential, internal, and latent energies). Assumes a closed system. APE turns out to be True enthalphy = enthalpy of a reference state Reference state is one with no conditional instability; All boundary layer air brought to its LNB

10. Lorenz Actual state vs. reference state EQ NP EQ NP

11. Successes of the parcel method: • provides insight into conditions necessary for • convection, or lack thereof • helps explain some general features of • the atmosphere (inter-cloud spacing; • general circulation)

12. Drawbacks of parcel method stability analysis: • ice not represented well • mixing not represented • sondes don’t measure liquid • environmental response not considered Conserved variable diagrams examine mixing and air mass history. Liquid is included have mainly been applied to non-precipitating convection

13. Adiabatic quantities form each coordinate axis; • Plotted data can only change values through irreversible or • diabatic processes • (linear) mixing shows up as a straight line • => Useful for examing mixing processes in clouds JAS,1979

14. “Paluch diagrams”: total water mixing ratio rt vs equivalent potential temperature rt = water vapor + liquid water m.r.

15. Study concludes most cloud air has mixed with environmental air Several km above cloud top. Common in cumuli developing in dry environments (downdrafts develop sufficient neg. buoyancy)

16. Similarly for stratocumulus breakup: “jump” criterion in both e and m.r. Randall, 1980 & Deardorff, 1980

17. Took Paluch’s analysis one step further: A Saturation Point is defined for each data

18. Cloud water is a parcel property • Liquid water potential temperature ll = exp(-Lll/cpT)) The lowest attainable through evaporating all water Saturation point: LCL if unsaturated “sinking evaporation level” if saturated Air parcel specified solely by its Tsl, psl, and psl - p Allows for a treatment of negatively buoyant parcels

19. Particularly elegant analysis of the impact of Cooling through evaporation of rain, and liquid Water loading of an air parcel (Evaporation both cools and moistens; whether a Mixture becomes positively or negatively buoyant Depends on l )

20. If upper air is dry enough, becomes strongly cooled by Evaporation => downdraft.