convective organization and its importance to large scale flows

Convective organization and its importance to large scale flows

Brian Mapes, U of Miamiwith

Baohua Chen (UM)Richard Neale (NCAR)

Emily Riley (UM)

Organ-ization

• From Greek organon– about instrumentality or working order

"Organized" convection

1. (weak) Something is making it patterned – perhaps it is forced or orchestrated

2. (too strong) It acts as an organ in an organism– it is performing some function

3. (agnostic) It is far from random in structure– has coherent (contiguous) entities

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

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

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)

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

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."

LS impacts of organization?• An observational view: use wide cloud systems

as a working definition of organized

Emily Riley poster (2nd floor south end)

LS impacts of organization?• Observational backdrop: use wide cloud

systems as a working definition of organized

Emily Riley poster (2nd floor south end)

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)

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?

organized convection can survive drynesswhere cu are suppressed

850

Example

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

now with >200km sample in red

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.

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

2 Sources of Organization Win our CAM5-UW-org-ens version

1. Source1 is proportional to precip evaporation2. Source2 >0 in coastal grid cells (optional)

JJA 0.25 degree TRMM climo

Results I: Effect of W feedback (when it rains it organizes)

precip. variability

unst

able

mea

n st

ate

st

able

deep convectionless dilute

more dilute

Long-known tradeoff

"entrainment dilemma"

(Mapes and Neale 2011)

obsW gets us

closer

Results II: Effect of coastal W source

Sense of result obvious (more coastal rain)

What the heck??

Mystery is local to MC

Coastal W source everywhere but in MC

Coastal W source only in MC

Mystery is local to MC

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

...because Mean Sounding is drier and capped

Average in mysterious (less rain w/ coastal org) MC region: 5S-10N, 90E-100E

With Coast10-days Hourly Data

Without Coast10-days Hourly Data

... CIN > TKE (closure)?

...but Mean Sounding is drier so there is re-evap?

Average in mysterious (less rain w/ coastal org) MC region: 5S-10N, 90E-100E

Perhaps this happens in nature?

Too much W?

JJA 0.25 degree TRMM climo

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!)