Post on 09-Feb-2016
description
Boundary Layer of shallow clouds and Boundary Layer of shallow clouds and deep convectiondeep convection
Review of last lectureReview of last lecture Vertical structure of the atmosphere and Vertical structure of the atmosphere and
definition of the boundary layerdefinition of the boundary layer Vertical structure of the boundary layer Vertical structure of the boundary layer Definition of turbulence and forcings Definition of turbulence and forcings
generating turbulencegenerating turbulence Static stability and vertical profile of virtual Static stability and vertical profile of virtual
potential temperature: 3 casespotential temperature: 3 cases. Richardson . Richardson numbernumber
Boundary layer over oceanBoundary layer over ocean Boundary layer over land: diurnal variationBoundary layer over land: diurnal variation
Shallow clouds Shallow clouds Include stratus, stratocumulus and cumulus cloudsInclude stratus, stratocumulus and cumulus clouds Cloud top height generally below 4 kmCloud top height generally below 4 km Sometimes associated with light rain, sometimes notSometimes associated with light rain, sometimes not
Global distribution of shallow cloudsGlobal distribution of shallow clouds
Do we notice any patterns?Do we notice any patterns?Klein and Hartman, 1993
Vertical structure of shallow cloudsVertical structure of shallow clouds
Intense longwave Intense longwave radiative cooling radiative cooling at cloud top at cloud top drives eddies in drives eddies in BLBL
Eddies pick up Eddies pick up moisture and moisture and maintain cloudmaintain cloud
Eddies also Eddies also entrain warm, dry entrain warm, dry air from above air from above the inversionthe inversion
Entrainment lifts Entrainment lifts the cloud, the cloud, subsidence subsidence lowers itlowers it
Bretherton et al. 2004
Boundary layer of shallow clouds: Boundary layer of shallow clouds: well-definedwell-defined
(From Barnes 1982)
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
Global distribution of deep convectionGlobal distribution of deep convection
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
Boundary layer of deep convection: Boundary layer of deep convection: Not well-definedNot well-defined
Differences between shallow clouds Differences between shallow clouds and deep convection: Boundary layer T and deep convection: Boundary layer T
and qand q
Differences between shallow clouds Differences between shallow clouds 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 clouds Differences between shallow clouds 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 clouds and deep Differences between shallow clouds and deep convection: 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
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 and vertical structure of Global distribution and vertical structure of
shallow cloudsshallow clouds Global distribution and vertical structure of deep Global distribution and vertical structure of deep
convection. Four components: convective convection. Four components: convective updraft, convective downdraft, mesoscale updraft, convective downdraft, mesoscale updraft, mesoscale downdraftupdraft, mesoscale downdraft
Differences between shallow clouds and deep Differences between shallow clouds 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 Problems in current global climate models: lack of self-suppression processesof self-suppression processes