Deep Convection
Shallow cumulus
Photo: Bjorn Stevens
Cumulus congestus
Wikimedia
The large-scale circulation
Cloud Clusters
Hadley/Walker Circulation
Land/Sea Circulation
stratocumulus
tradewinds
trade
winds
EQ
warm, western tropical oceans
cold, eastern subtropical ocean
Clouds are not just visual expressions of the state of the atmosphere, or a collection of small
droplets that produce considerable rainfall, rather, they are a crucial component of the
dynamics of the atmosphere as a whole
Stevens (2005)
New Features
•
Precipitating (often intensely)
•
Updraft velocities can reach 50 m s-1
•
Updrafts and downdrafts (evaporation of condensate)
important
•
Development of anvils
•
Severe weather (pluvials, hail, tornadoes …)
•
Can be more organized (squall lines, mesoscale
convective systems, supercells…)
Cumulonimbus
lifecycle
“Air
Air--Mass
Mass”” Showers:
Credit: K. Emanuel, MIT
1
Microbursts
•
Intense downdraft hits ground,
spreads radially
•
Dry microburst: high cloud
base, light rain evaporates into
downdraft, accelerating it
•
Wet microburst: weight of
suspended rain in wet
conditions accelerates
downdraft
Credit:Wikipedia
Denver, CO - July 1, 1993 12Z
5000
!
25000
Revised Friday, January 30, 2009!
Height (m)
4000
27
20000
3000
15000
2000
10000
Conditional Instability
After sinking through the trade inversion, the air is subjected to friction. This causes its
angular momentum to decrease. As it flows back equatorward, near-surface easterlies result.
1000
5000
0
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Height (m)
Denver, CO - January 2, 1993 0Z
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Denver, CO - July 1, 1993 12Z
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Height (m)
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15000 0
0
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Barrow, AK - July 1, 1993 12Z
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Height (m)
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Kelvin
3152000 320
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350
moist static energy (h)
355
0
10000
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360
saturation moist static energy (h*)
420
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5000
dry static energy (s)
275
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295
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0
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Barrow, AK - January 2, 1993 0Z
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15000
Height (m)
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20000
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290
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0
245305
250310
255315
260320
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270330
275335
280340
285
0 0
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300 280
300
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320
Kelvin
moist static energy (h) Barrow,saturation
moist static
energy 12Z
(h*)
AK - July
1, 1993
5000
400
25000
0
270
0
285
380
Denver, CO - January 2, 1993 0Z
1000
5000
Height (m)
280
340
340
360360380
400
380
420
440
400
460420
440
460
dry static energy (s)
25000
Figure 6.12: Representative observed soundings for 20000
Denver, Colorado, and Barrow, Alaska, for July and
January. The curves plotted show the dry static energy, the moist static energy, and the saturation moist
3000
static energy. The panels on the right cover both the 15000
troposphere and lower stratosphere, while those on
the right zoom in on the lower troposphere to show more detail. Values are divided by c p to give units in
Height (m)
4000
2000
10000
1000
5000
K.
Credit: D. Randall
CAPE
(from LFC to LNB)
Gives upper bound on
updraft vertical velocity
CIN
(from ground to LFC)
Land vs. Ocean
•
2-3 stronger over land (TP) than over oceans (GATE)
•
Often more CAPE over land (but upper bound from CAPE
not reached because of entrainment)
Entrainment dilution
Observations @ 10N, 95W
CRM (colors: vertical mass flux)
Credit: C. Bretherton, UW
Transition to strong
convection
2370
2370
J O UJR
OTS M
PH
I ES
NCCIEESN C E S
ONUARLN O
A FL TOHFETA
HTEMA
OES R
P IHCE S
RCI C
VOLUMEV66
OLUME 66
w/wc
Neelin et al. 2009