Introduction to tropical meteorology and deep convection
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Transcript of Introduction to tropical meteorology and deep convection
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Introduction to tropical meteorology and deep convection
Roger K. Smith
University of Munich
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A satpix tour of the tropics
The zonal mean circulation (Hadley circulation), Inter-Tropical Convergence Zone (ITCZ)
Field experiments
Macroscale circulations, The Walker circulation, Monsoons
Synoptic scale weather systems, tropical waves
Moist convection and convective systems
The Madden-Julian Oscillation, Westerly wind bursts
Concluding remarks
Topics
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INDO IR 01010510
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GMS IR 01022621
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GOES IR 00112909
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Principal land and ocean areas between 40°S and 40°N. The shaded areas show tropical highlands (over 1000 m).
From Nieuwolt (1977)
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How does one define the tropics?
Tropic of Capricorn 23.5os
Tropic of Cancer 23.5oN
Maritime continent
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A satpix tour of the tropics
The zonal mean circulation (Hadley circulation), Inter-Tropical Convergence Zone (ITCZ)
Field experiments
Macroscale circulations, The Walker circulation, Monsoons
Synoptic scale weather systems, tropical waves
Moist convection and convective systems
The Madden-Julian Oscillation, Westerly wind bursts
Concluding remarks
Next topic
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Radiative heat balance
Zonally averaged components of the absorbed solar flux and emitted thermal infrared flux at the top of the atmosphere.
(after Vonder Haar and Suomi, 1971, with modifications)
F (
W m
2)
100
0
200
300
90 50 30 10 0 10 30 50 90South Latitude North
Absorbed solar flux
Emitted infrared flux
energy gain
energy loss+
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Mean annual precipitation
Mean annual precipitation as a function of latitude.
(after Sellers, 1965)
2000
1500
1000
500
mm
0
90 60 40 30 20 10 0 10 20 30 40 60 90
North Latitude South
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mean meridional circulation
The mean meridional circulation and main surface wind regimes.
after Defant, 1958
Hadley
circulatio
n
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ITCZ
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ITCZ
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A satpix tour of the tropics
The zonal mean circulation (Hadley circulation), Inter-Tropical Convergence Zone (ITCZ)
Field experiments
Macroscale circulations, The Walker circulation, Monsoons
Synoptic scale weather systems, tropical waves
Moist convection and convective systems
The Madden-Julian Oscillation, Westerly wind bursts
Concluding remarks
Next topic
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Field Experiments in the Tropics 1969 - 1979
Bermuda Oceanographic and Meteorological EXperiment (BOMEX) 1969
Holland & Rasmusson, (1973), MWR, 101, 44-55.
Global Atmospheric Research Programme (GARP) Atlantic Tropical Experiment (GATE) July 1974
GARP: Fleming et al., (1979), BAMS, 60, 649-659. GATE: Kuettner et al. (1974) BAMS, 55, 711-744.
The MONsoon EXperiment (WMONEX December 1978, SMONEX May – August, 1979)
WMONEX: Greenfield & Krishnamurti (1979), BAMS, 60, 649-659.SMONEX: Fein & Kuettner (1980) BAMS, 61, 461-474.
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Field Experiments in the Tropics 1987 -
Australian Monsoon EXperiment & Equatorial Mesoscale EXperiment (AMEX, EMEX) January – February 1987
AMEX Holland et al. (1986), BAMS, 67, 1466-1486. EMEX Webster & Houze (1991), BAMS, 72, 1481-1505.
Tropical Oceans Global Atmosphere Couple Ocean Atmosphere Response Experiment (TOGA COARE) November 1992 – February 1993
Webster & Lucas (1992), BAMS, 73, 1377-1416.
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A satpix tour of the tropics
The zonal mean circulation (Hadley circulation), Inter-Tropical Convergence Zone (ITCZ)
Field experiments
Macroscale circulations, The Walker circulation, Monsoons
Synoptic scale weather systems, tropical waves
Moist convection and convective systems
The Madden-Julian Oscillation, Westerly wind bursts
Concluding remarks
Next topic
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850 mb
200 mb
JJA
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200 mb
850 mbDJF
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Velocity potential
V k
( )k k 2
We can separate the three-dimensional velocity field into a rotational part and a divergent part (see e.g. Holton, 1972, Appendix C.)
rotationalnondivergent
irrotationaldivergent
( ) 0
( ) 0 k2( )
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Upper tropospheric (200 mb) mean seasonal velocity potential indicating the divergent part of the mean seasonal wind which
is proportional to .
(Adapted from Krishnamurti et al., 1973).
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OLR < 225 W m2
month
From Lau & Chan, 1983
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Walker circulation
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A satpix tour of the tropics
The zonal mean circulation (Hadley circulation), Inter-Tropical Convergence Zone (ITCZ)
Field experiments
Macroscale circulations, The Walker circulation, Monsoons
Synoptic scale weather systems, tropical waves
Moist convection and convective systems
The Madden-Julian Oscillation, Westerly wind bursts
Concluding remarks
Next topic
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MonsoonsJuly
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SE Asian Monsoon
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January
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Australasian Monsoon
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South America: January climatology
200 mb wind850 mb wind
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(From Webster, 1983)
An example of monsoon variability
1963
1971
West coast of India
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A satpix tour of the tropics
The zonal mean circulation (Hadley circulation), Inter-Tropical Convergence Zone (ITCZ)
Field experiments
Macroscale circulations, The Walker circulation, Monsoons
Synoptic scale weather systems, tropical waves
Moist convection and convective systems
The Madden-Julian Oscillation, Westerly wind bursts
Concluding remarks
Next topic
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Time-longitude section of vis imagery - latitude band 10 -15 N
From Wallace, 1970
July
Au
gust
Jun
e0107
01/06
0108
tim
e
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Fig. 1.23
GMS – IR25 Dec 1978
MSLP25 Dec 1978
Winter MONEX
AB
C
From Webster, 1983
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Fig. 1.24
250 mb25 Dec 1978
850 mb25 Dec 1978
Winter MONEX
A
BC
A
BC
shadedhorizontal wind divergence
From Webster, 1983
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The variation of surface pressure at Darwin for the period 23 - 28 Dec. 1978.
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Easterly waves over Africa
WV Imagery 17 June 1997 00Z
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Tropical cyclones
TC tracks (1979-1988)
Super typhoon Wynnie 11 Aug 1997
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A satpix tour of the tropics
The zonal mean circulation (Hadley circulation), Inter-Tropical Convergence Zone (ITCZ)
Field experiments
Macroscale circulations, The Walker circulation, Monsoons
Synoptic scale weather systems, tropical waves
Moist convection and convective systems
The Madden-Julian Oscillation, Westerly wind bursts
Concluding remarks
Next topic
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Moist Convection
Trade Cumuli
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The tropical troposphere
z km
29oC
-73oC15
-121oC
observed
observed
-150oC +150oC
77oC
Conclusion: Deep tropical circulations cannot be dry adiabatic
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The role of diabatic processes
z km
15
Conclusion: Deep convection occupies a small fractional area
Latent heat
release opposes
adiabatic cooling
Radiative cooling opposes adiabatic
warming
ITCZ subtropical high
Fast ascent
Slow descent
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Successive locations of radar reflectivity contours in a tropical
squall line. From Chang et al.
(1987)
Radar reflectivity contours (dBZ) of a tropical squall line observed during COPT81 (Ivory Coast, West Africa).Horizontal cross-section at low levels
(0.5 – 1.5 km).
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Radar reflectivity contours (dBZ) of a tropical squall line observed during COPT81 (Ivory Coast, West Africa).Vertical cross-section along the axis of propagation.
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Types of convection
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A satpix tour of the tropics
The zonal mean circulation (Hadley circulation), Inter-Tropical Convergence Zone (ITCZ)
Field experiments
Macroscale circulations, The Walker circulation, Monsoons
Synoptic scale weather systems, tropical waves
Moist convection and convective systems
The Madden-Julian Oscillation, Westerly wind bursts
Concluding remarks
Next topic
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From JAS, Sept. 1972
Madden-Julian Oscillation
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From Webster 1987
Madden-Julian Oscillation
MJO
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Indian Ocean Feb/Mar 2001
06/02 07/02 13/02
17/02 24/02 06/03
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West Pacific Ocean – Feb 2001
06/02 09/02 13/02
21/02 24/02 29/02
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http://www.bom.gov.au/bmrc/clfor/cfstaff/matw/maproom/OLR/hov.last6mths.anom.S.gif
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GOES-9 12 UTC 2 Dec 1997 10.7 micron image
Westerly wind bursts
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T he extended H eld-H ou M odel
Eq.Y - Y 0 Y 1 Y +
z
Sum m erCell
W interCell
Solar heating m axim umStream line dividing the w inter and sum m er cells
W inter cell
Sum m er cell
Solution for M0 and Y
Eq. Pole
y
u = UM
u = 0 y
24 20
M 0 E02 2
24 20
M 0 E02 2
Y Y10a gH 3a
Y Y2a gH a
YY
1/ 2
20
2
M 0 E0 2 20
5 gHY
3
5 gH
18a
Take 0 = 255 K, = 40 K and H = 12 km Y 2400 km and 0.9 K cooler than . in agreement with obs.
unknowns
Y
Horizontal structure of the Kelvin wave and of a westward propagating Mixed Rossby-gravity wave.
Parcel motions
Kelvin wave
Mixed R-G wave
2 2
u Y vd v
d Y
2 2
Y vd v
d Y
( ) e x p ( )v Y v Y H Yn n 12
2
d v
d YY v Y
d H
d Ynn
e x p 12
2
dHdY
n H Ynn 2 1 ( )
H Y YH Y n H Yn n n 1 12 2( ) ( ) ( )
S c a l e a n d p u t y = L E Y
N o w
a n d
P r o p e r t i e s o f t h e H e r m i t e p o l y n o m i a l s
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Interaction between moist convection and the large-scale flow.
What are the controls on deep convection.
Models don’t get the diurnal variation correct.
No generally accepted theory of the Madden-Julian Oscillation.
Weather forecasting in the tropics is still very difficult compared with that in the middle latitudes.
A few outstanding problems
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The End
Thank you for your interest
Talk available at:http://www.meteo.physik.uni-muenchen.de\~roger\030514-dlr.pdf