Introduction to tropical meteorology and deep convection
Roger K. Smith
University of Munich
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
INDO IR 01010510
GMS IR 01022621
GOES IR 00112909
Principal land and ocean areas between 40°S and 40°N. The shaded areas show tropical highlands (over 1000 m).
From Nieuwolt (1977)
How does one define the tropics?
Tropic of Capricorn 23.5os
Tropic of Cancer 23.5oN
Maritime continent
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
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+
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
mean meridional circulation
The mean meridional circulation and main surface wind regimes.
after Defant, 1958
Hadley
circulatio
n
ITCZ
ITCZ
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
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.
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.
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
850 mb
200 mb
JJA
200 mb
850 mbDJF
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( )
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).
OLR < 225 W m2
month
From Lau & Chan, 1983
Walker circulation
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
MonsoonsJuly
SE Asian Monsoon
January
Australasian Monsoon
South America: January climatology
200 mb wind850 mb wind
(From Webster, 1983)
An example of monsoon variability
1963
1971
West coast of India
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
Time-longitude section of vis imagery - latitude band 10 -15 N
From Wallace, 1970
July
Au
gust
Jun
e0107
01/06
0108
tim
e
Fig. 1.23
GMS – IR25 Dec 1978
MSLP25 Dec 1978
Winter MONEX
AB
C
From Webster, 1983
Fig. 1.24
250 mb25 Dec 1978
850 mb25 Dec 1978
Winter MONEX
A
BC
A
BC
shadedhorizontal wind divergence
From Webster, 1983
The variation of surface pressure at Darwin for the period 23 - 28 Dec. 1978.
Easterly waves over Africa
WV Imagery 17 June 1997 00Z
Tropical cyclones
TC tracks (1979-1988)
Super typhoon Wynnie 11 Aug 1997
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
Moist Convection
Trade Cumuli
The tropical troposphere
z km
29oC
-73oC15
-121oC
observed
observed
-150oC +150oC
77oC
Conclusion: Deep tropical circulations cannot be dry adiabatic
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
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).
Radar reflectivity contours (dBZ) of a tropical squall line observed during COPT81 (Ivory Coast, West Africa).Vertical cross-section along the axis of propagation.
Types of convection
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
From JAS, Sept. 1972
Madden-Julian Oscillation
From Webster 1987
Madden-Julian Oscillation
MJO
Indian Ocean Feb/Mar 2001
06/02 07/02 13/02
17/02 24/02 06/03
West Pacific Ocean – Feb 2001
06/02 09/02 13/02
21/02 24/02 29/02
http://www.bom.gov.au/bmrc/clfor/cfstaff/matw/maproom/OLR/hov.last6mths.anom.S.gif
GOES-9 12 UTC 2 Dec 1997 10.7 micron image
Westerly wind bursts
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
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
The End
Thank you for your interest
Talk available at:http://www.meteo.physik.uni-muenchen.de\~roger\030514-dlr.pdf