Boundary Layer of Shallow Convection
and Deep Convection
Review of last lecture
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Definition of stratocumulus clouds
Global distribution
Importance for global warming
Vertical structure and formation mechanism of
STBL
Modeling of STBL： non-local forced by surface
heating and cloud-top cooling
Global distribution of shallow convection
and deep convection
Deep convection
Shallow convection
From Shumacher and Houze (2003)
Hadley circulation and cloud types
Tropics
L
Deep convection
H
Trade wind cumulus
Stratocumulus
Walker circulation and cloud types
Deep convection
Trade wind cumulus
Stratocumulus
Trade wind cumulus
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Cloud top height generally
below 4 km
Often associated with light rain
Sometimes topped by
stratocumulus
Deep convection
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Cloud top height above 9 km
Generally associated with rain
Sometimes organized into mesoscale convective systems
Vertical structure of deep convection:
Four components
High θe
Convective updrafts (controlled by
lower troposphere moisture)
Mesoscale updrafts
Low θe
Mesoscale
downdrafts
High θe
Convective downdrafts
Zipser (1977), modified by Houze (1993)
Differences in boundary layer structure
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Stratocumulus has shallow
well-defined BL
Trade wind cumulus has
deep well-defined BL
Deep convection does not
have well-defined BL
Trade wind
cumulus
Deep
convection
Stratocumulus
Differences in boundary layer T and q
Trade wind
cumulus
Deep convection
Differences between shallow convection
and deep convection: Change of
boundary layer T
Shallow/midtop convection: T decreases
Deep convection: T decreases
Differences between shallow convection
and deep convection: Change of
boundary layer q
Shallow/midtop convection: q increases
Deep convection: q decreases
Differences between shallow convection and
deep convection:
Change 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 convection
Self-suppression processes in deep convection
Missing physics III, IV
High θe
Convective updrafts (controlled by lower
troposphere temperature and moisture)
Mesoscale updrafts
Low θe
Missing physics II
Mesoscale
downdrafts
High θe
Convective downdrafts
Missing physics I
Zipser (1977), modified by Houze (1993)
Over-stabilized state: A state far away
from 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)
Summary
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Global distribution of shallow and deep convection
Vertical structure of trade wind cumulus (shallow
convection)
Vertical structure of deep convection. Four
components: convective updraft, convective
downdraft, mesoscale updraft, mesoscale
downdraft
Differences between shallow convection and deep
convection: change of T, q and h in the boundary
layer
Self-suppression processes in deep convection:
Overly stabilized state after deep convection
Problems in current global climate models: lack of
self-suppression processes
Works cited
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http://apollo.lsc.vsc.edu/classes/met455/notes/section2/4
.html
http://www.goesr.gov/users/comet/tropical/textbook_2nd_edition/navmen
u.php_tab_2_page_5.2.0.htm
http://www.atmos.ucla.edu/~bstevens/Research/researc
h.html