Boundary Layer of Shallow Convection Boundary Layer of Shallow Convection and Deep Convectionand Deep Convection

Review of last lectureReview of last lecture

Definition of stratocumulus cloudsDefinition of stratocumulus clouds Global distribution Global distribution Importance for global warmingImportance for global warming Vertical structure and formation mechanism of Vertical structure and formation mechanism of

STBLSTBL Modeling of STBLModeling of STBL ：： non-local forced by surface non-local forced by surface

heating and cloud-top coolingheating and cloud-top cooling

Hadley circulation and cloud typesHadley circulation and cloud types

Deep convection Trade wind cumulus Stratocumulus

HL

Tropics

Walker circulation and cloud typesWalker circulation and cloud types

Deep convection Trade wind cumulus Stratocumulus

Global distribution of shallow convection Global distribution of shallow convection and deep convectionand deep convection

Deep convection

Shallow convection

From Shumacher and Houze (2003)

Trade wind cumulusTrade wind cumulus

Cloud top height generally Cloud top height generally below 4 kmbelow 4 km

Often associated with light rainOften associated with light rain Sometimes topped by Sometimes topped by

stratocumulusstratocumulus

Deep convectionDeep convection Cloud top height above 9 kmCloud top height above 9 km Generally associated with rainGenerally associated with rain Sometimes organized into mesoscale convective systemsSometimes organized into mesoscale convective systems

Zipser (1977), modified by Houze (1993)

Convective updrafts (controlled by lower troposphere moisture)

Mesoscale updrafts

Convective downdrafts

Mesoscale downdrafts

High θe

Low θe

High θe

Vertical structure of deep convection: Vertical structure of deep convection: Four componentsFour components

Differences in boundary layer structureDifferences in boundary layer structure

Stratocumulus has shallow Stratocumulus has shallow well-defined BLwell-defined BL

Trade wind cumulus has Trade wind cumulus has deep well-defined BLdeep well-defined BL

Deep convection does not Deep convection does not have well-defined BLhave well-defined BL

Stratocumulus

Trade wind cumulus

Deep convection

Differences in boundary layer T and qDifferences in boundary layer T and q

Trade wind cumulus

Deep convection

Differences between shallow convection Differences between shallow convection and deep convection: Change of and deep convection: Change of

boundary layer Tboundary layer T

Shallow/midtop convection: T decreases

Deep convection: T decreases

Differences between shallow convection Differences between shallow convection and deep convection: Change of and deep convection: Change of

boundary layer qboundary layer q

Shallow/midtop convection: q increases

Deep convection: q decreases

Differences between shallow convection and Differences between shallow convection and deep convection: deep convection:

Change of boundary layer moist static energy hChange of boundary layer moist static energy h

Moist static energy

h = Cp T + L q + g z

Shallow/midtop convection: h keeps constant

Deep convection: h decreases

Convective wake of deep convectionConvective wake of deep convection

Self-suppression processes in deep convectionSelf-suppression processes in deep convection

Zipser (1977), modified by Houze (1993)

Convective updrafts (controlled by lower troposphere temperature and moisture)

Mesoscale updrafts

Convective downdrafts

Mesoscale downdrafts

Missing physics I

Missing physics II

Missing physics III, IV

High θe

Low θe

High θe

Over-stabilized state: A state Over-stabilized state: A state far awayfar away from quasi-equilibriumfrom quasi-equilibrium

Model atmosphere fluctuates around the quasi-equilibrium state (always drizzle)

The observed atmosphere swings far away from the quasi-equilibrium state (switch between heavy shower and clear sky)

SummarySummary Global distribution of shallow and deep convectionGlobal distribution of shallow and deep convection Vertical structure of trade wind cumulus (shallow Vertical structure of trade wind cumulus (shallow

convection)convection) Vertical structure of deep convection. Four Vertical structure of deep convection. Four

components: convective updraft, convective components: convective updraft, convective downdraft, mesoscale updraft, mesoscale downdraft, mesoscale updraft, mesoscale downdraftdowndraft

Differences between shallow convection and deep Differences between shallow convection and deep convection: change of T, q and h in the boundary convection: change of T, q and h in the boundary layer layer

Self-suppression processes in deep convection: Self-suppression processes in deep convection: Overly stabilized state after deep convectionOverly stabilized state after deep convection

Problems in current global climate models: lack of Problems in current global climate models: lack of self-suppression processesself-suppression processes

Works citedWorks cited

http://apollo.lsc.vsc.edu/classes/met455/notes/section2/4.html

http://www.goes-r.gov/users/comet/tropical/textbook_2nd_edition/navmenu.php_tab_2_page_5.2.0.htm

http://www.atmos.ucla.edu/~bstevens/Research/research.html