1. Section 3.5, 3.5a, 3.5b Overview For Storm-generated Mesoscale processes 1.Local Effects 2.Advective Effects

2. Storm Generated Mesoscale Process Severe storms generate host of mesoscale effects –Promote storm development, severity and longevity, or –Weaken storms

3. Recall From Table 3.3 Local effect includes: –Radiation –Microphysics Downdraft, cold pool production Microburst generation

4. Local Effects Radiation 1.Cloud-radiative effects - may be important in the development of new storms 2.Longer life by enhancing mass circulation 3.Increase total precipiation

5. Local Effects Microphysics –Downdraft, cold pool production –Microburst generation

6. Downdraft, cold pool production Occurs through evaporation and melting Strength of cold pool is important to –Supercell’s behavior and longevity –Squall-line intensity and longevity –Baroclinic vorticity generation in tornadic storms

7. Microburst Generation Particle sizes are important in determining downdraft intensity. –Smaller raindrop has most conducive to strong downdrafts Also, in frontal rainbands, evaporation, sublimation, and melting can have the effect of enhancing the thermal contrast across cold fronts

8. Advective Effects (Overview) From table 3.3 Particle advection, fall and phase changes –Downdrafts generation –Upscale growth Cold pool processes –Cell regeneration –MCS evolution

9. Continuing Overview Momentum transport/ sloping flows –Severe surface winds Vortex tilting/ stretching –Vertical velocity generation –(supercells, MCS mesovortices)

10. Cold pool processes Are responsible for cell regeneration in multicell storms involves cold air outflow from convective downdrafts As it spreads out over a large area and becomes shallow, then the regeneration stops

11. Downdraft Outflows Also important in supercells where forward-flank downdrafts and rear-flank downdrafts produces storm-scale fronts Special case: new mesocyclones may form at the occlusion

12. Schematic Plan View of Tornadic Thunderstorm near the surface

13. Special Case

14. Advection of Condensate Development of trailing stratiform regions of squall lines

15. Schematic Plan View

16. Momentum Transport Vertical transport of horizontal momentum helps to generate covergence at the leading convective line

17. Vortex Tilting

18. Tilting produce vertical vorticity in MCSs

19. Development of Mesovortices in MCSs Interaction between the downdraft and the ambient westerly shear. Another tilting involves perturbation shears

20. Development of Mesovortices in MCSs Buoyancy forces act to generate front-to- rear or rear-to-front flows Tilting of perturbation shears generated by the cold pool is important in the production of line-end vortex pairs in environments with weak-to-moderate shear.

21. Development of Mesovortices in MCSs As squall lines mature, Coriolis effects become important in the development Result: eventual evolution of many squall lines to an symmetric precipitation pattern

22. Effects of the plume of heat and moisture Convective/advective warming of the midtroposphere is the primary mechanism for the generation of the midlevel rear- inflow jets in squall lines Moistening increases buoyancy of secondary convection

23. End