Convective organization and its importance to large scale flows

1. Convective organization and its importance to large scale flows Brian Mapes, U of Miami with Baohua Chen (UM) Richard Neale (NCAR) Emily Riley (UM)

2. Organ-ization • From Greek organon • about instrumentality or working order

3. "Organized" convection • (weak) Something is making it patterned • perhaps it is forced or orchestrated • (too strong) It acts as an organ in an organism • it is performing some function • (agnostic) It is far from random in structure • has coherent (contiguous) entities

4. Organized used many ways • multicellular (every cb is) • visual or radar • mesoscale patch or blob • or satellite 'cloud cluster' • line/arc structure as opposed to blobby • patchy on synoptic scale

5. A process view of organization • In PDF language: • Extreme (tail) events in space of {w,T,q,scale,depth} • Vanishingly unlikely in naive multi-normal PDF • Taps an energy source, so natural selection acts • We can treat org as a positive effect • negative rare events (rogue gravity waves) are not reinforced in that way, and also not important • BUT: it doesn't mean optimal always happens • no wild eyed entropy extremal theorems here

6. effect of org. on convection • Thermo: protects penetrative updrafts from getting diluted by modal (mean or env.) air • Dyn: Assists in transfers/loans of energy to exploit metastability (triggered instability) • (Exotic momentum transport effects)

7. Coherent structures • may deserve separate treatment • like we add a 'plume' idealization for very asymmetric moist turbulence • multiplume / cooperating-plume structure an obvious generalization for org. convection

8. LS impacts of organization? • Foreshadowing: one idea "The Maritime Continent...presents a major challenge to models, which tend to systematically underestimate the precipitation in this region. "It is argued that the diurnal cycle ... [and] ... circulation patterns generated by land–sea contrasts are crucial for ... the mean climate."

9. LS impacts of organization? • An observational view: use wide cloud systems as a working definition of organized Emily Riley poster (2nd floor south end)

10. LS impacts of organization? • Observational backdrop: use wide cloud systems as a working definition of organized Emily Riley poster (2nd floor south end)

11. LS impacts of organization? • Observational backdrop: use wide cloud systems as a working definition of organized Exists beyond the margins of where unorganized (narrow) deep conv. can Emily Riley poster (2nd floor south end)

12. LS impacts of organization • May be esp. important in convective margins like • upwind of deep tropics in the trades • e.g. in SE Pacific (Mar-Apr double ITCZ) • W African monsoon MCS dominated • western margin of Indian monsoon • Regions of GCM difficulties/biases?

13. organized convection can survive drynesswhere cu are suppressed 850

14. Example

15. Representative JJA 2006-9 cloudsat radar echo objects<200km in horizontal width

16. now with >200km sample in red

17. GCMs and organized convection • If org is what protects upflow from dilution, then GCMs deep convective plumes tuned to give a realistic stability have org everywhere • GCMs don't lack org, they lack its absence in deep convective onset situations • in the morning over land • in gradually moistening inflows to tropical rain • etc.

18. Our experimental CAM5 version • ZM deep convection turned off • Instead, 2 Park-Bretherton plumes • w/ different environmental mixing rates • Less-dilute plume's activity is an increasing function of organization W • Org. obeys: dW/dt = -W/t + Sources Mapes and Neale 2011, JAMES

19. 2 Sources of Organization Win our CAM5-UW-org-ens version • Source1 is proportional to precip evaporation • Source2 >0 in coastal grid cells (optional) JJA 0.25 degree TRMM climo

20. Results I: Effect of W feedback (when it rains it organizes) obs deep convection less dilute W gets us closer Long-known tradeoff "entrainment dilemma" (Mapes and Neale 2011) unstable mean state stable more dilute precip. variability 

21. Results II: Effect of coastal W source Sense of result obvious (more coastal rain) What the heck??

22. Mystery is local to MC Coastal W source everywhere but in MC

23. Mystery is local to MC Coastal W source only in MC

24. Why less MC rain with coastal W source? • more mass flux in plume #2...

25. ...because Mean Sounding is drier and capped Average in mysterious (less rain w/ coastal org) MC region: 5S-10N, 90E-100E

26. ... CIN > TKE (closure)? With Coast 10-days Hourly Data Without Coast 10-days Hourly Data

27. ...but Mean Sounding is drier so there is re-evap? Average in mysterious (less rain w/ coastal org) MC region: 5S-10N, 90E-100E

28. Perhaps this happens in nature?Too much W? JJA 0.25 degree TRMM climo

29. Summary • Organized convection is coherent structures • Would be vanishingly rare in naive PDF view • Natural selection makes it common • Protects core updrafts in nature's deep convection • Standard GCM deep convection schemes imply org. is ubiquitous (not "missing") • Prognostic W created by rain evap (a positive feedback) helps w/ "entrainment dilemma" • (unwanted tradeoff btw. unstable bias  vs.  variability) • Coastal W source makes most coasts wetter, but core of Maritime continent drier (nonintuitive!)