Introduction to tropical meteorology and deep convection

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



Field experiments





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



Field experiments





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.



Field experiments





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



Field experiments





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



Field experiments





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



Field experiments





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



Field experiments





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

Documents

Introduction to tropical meteorology and deep convection