Introduction to tropical meteorology and deep convection
Roger K. Smith University of Munich
Thai Meteorological Department Lecture 1 Topics
A satpix tour of the tropics
The zonal mean circul ati on (H adl ey ci rcul ati on) , I nt er- 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 burst INDO IR 01010510 GMS IR 01022621 GOES IR 00112909 EUMETSAT Movie A numerical simulation 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 Cancer 23.5oN
MitiMaritime continent
Tropic of Capricorn 23.5os Next topic
A satpix tour of the tropics
The zonal mean circul ati on (H adl ey ci rcul ati on) , I nt er- 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 energy gain 300 + energy loss )) 2 200
W m Radiative heat balance (( Absorbed solar flux F 100 Emitted infrared flux
0 90 50 30 10 0 10 30 50 90 South Latitude North 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) 2000
1500 mm 1000 Mean annual precipitation
500
0 90 60 40 30 20 10 0 10 20 30 40 60 90 North Latitude South
Mean annual precipitation as a function of latitude.
(after Sellers, 1965) mean meridional ci rcul ati on
The mean meridional circulation and main surface wind regimes .
after Defant, 1958 ITCZ ITCZ Next topic
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 Field Exppperiments in the Tropics
Global Atmospheric Research Programme ( GARP) Atlantic Tropical Experiment (GATE) July 1974 The MONsoon EXpp(eriment (WMONEX December 1978 , SMONEX May – August, 1979) Australian Monsoon EXperiment & Equatorial Mesoscale EXperiment (AMEX, EMEX) January – February 1987 Tropical Oceans Global Atmosphere Couple Ocean Atmosphere Response Experiment (TOGA COARE) November 1992 – February 1993 Next topic
A satpix tour of the tropics
The zonal mean circul ati on (H adl ey ci rcul ati on) , I nt er- 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 200 mb
JJA 850 mb 200 mb
DJF 850 mb Velocity potential
We can separate the three-dimensional velocity field into a rotational part and a divergent part (see e .g . Holton, 1972, Appendix C.)
Vk
rottitational ittilirrotational nondivergent divergent
()kk 2 ()0 ()0k () 2 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). month
OLR < 225 W m2 From L au & Ch an, 1983
Walker circulation Next topic
A satpix tour of the tropics
The zonal mean circul ati on (H adl ey ci rcul ati on) , I nt er- 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 Monsoons July SE Asian Monsoon January Australasian Monsoon South America: January climatology
850 mb wind 200 mb wind An example of monsoon variability
West coast 1963 of India
1971
(From Webster, 1983) Next topic
A satpix tour of the tropics
The zona l mean ci rcul ltiation (H (Hdladley ci rcul lti)Itation), 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 Time-longitude section of vis imagery - latitude band 10 -15 N
01/06
0107
0108 e tim
From Wallace, 1970 Winter MONEX
A B GMS – IR 25 Dec 1978 C Fig. 1.23
MSLP 25 Dec 1978
From Webster, 1983 Winter MONEX
A 250 mb 25 Dec 1978 B C
Fig. 1.24 shaded horizontal wind divergence
A 850 mb 25 Dec 1978
C B
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
Super typhoon Wynnie 11 Aug 1997
TC tracks (1979-1988) Next topic
A satpix tour of the tropics
The zonal mean circul ati on (H adl ey ci rcul ati on) , I nt er- 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 Moist Convection
Trade Cumuli The tropical troposphere
z km
15 -121oC -73oC obdbserved
-150oC +150oC
29oC 77oC
observed
Conclusion: Deep tropical circulations cannot be dry adiabatic The role of diabatic processes
z km 15 Latent heat Radiative cooling opposes adiabatic release Fast warming opposes ascent adiabatic Slow descent cooling
ITCZ subtropical high
Conclusion: Deep convection occupies a small fractional area
Radar reflectivityy() contours (dBZ) of SiltifdSuccessive locations of radar a tropical squall line observed during reflectivity contours in a tropical COPT81 (Ivory Coast, West Africa). squall line. Horizontal cross-section at low levels From Chang et al. (1987) (0.5 – 1.5 km). Radar reflectivityy()pq 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
“Hector”, Darwin, Australia Next topic
A satpix tour of the tropics
The zonal mean circulation (Hadley circulation) , Inter - Tropical Convergence Zone (ITCZ)
Field experi ment s
Macroscale circulations, The Walker circulation, Monsoons
Synoptic scale weather systems, tropical waves
MitMoist convecti on and convecti ve syst ems
The Madden-Julian Oscillation, westerly wind bursts Madden-Julian Oscillation
From JAS, Sept. 1972 Madden-Julian Oscillation MJO
From Webster 1987 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 Westerly wind bursts
GOES-9 12 UTC 2 Dec 1997 10.7 micron image Solution for and Y The extended Held-Hou Model M0
u = UM
z YY
y unknowns Pole Winter Summer Eq. u = 0 Y y Cellcell Cellcell 2 1/2 0 42 5gH M022YY E0 Y 10a gH 3a 2 30 2 0 42 2 M022YY E0 5gH 2a gH a M0 E0 22 Y- Eq. Y0 Y1 Y+ 18a 0
Take 0 = 255 K, = 40 K and H = 12 km Y 2400 km and Streamline dividing the 0.9 K cooler than . Solar heating maximum winter and summer cells in agreement with obs.
Kelvin wave 2 2 dv uY v dY Scale and put y = LEY 22 dv Yv dY Mixed R-GGw wave Parcel 1 2 Now vY () v nnexp 2 Y H ( Y ) motions
dv 1 2 dHn and Yv exp Y dY n 2 dY
dHn Properties of the 2nHn1 () Y Hermite polynomials dY HY()22 YHYnHY () () nnn11Horizontal structure of the Kelvin wave and of a westward propagating Mixed Rossby-gravity wave. A few outstanding problems
Interaction between moist convection and the large-scale flow.
What are the controls on deep convection?
Models usually 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! The End