Introduction to tropical meteorology and deep convection Roger

Introduction to tropical meteorology and deep convection Roger K. Smith University of Munich

Topics Ø A satpix tour of the tropics Ø The zonal mean circulation (Hadley circulation), Inter. Tropical Convergence Zone (ITCZ) Ø Field experiments Ø Macroscale circulations, The Walker circulation, Monsoons Ø Synoptic scale weather systems, tropical waves Ø Moist convection and convective systems Ø The Madden-Julian Oscillation, Westerly wind bursts Ø Concluding remarks

INDO IR 01010510

GMS IR 01022621

GOES IR 00112909

Principal land 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. 5 o. N Maritime continent Tropic of Capricorn 23. 5 os

Next topic Ø A satpix tour of the tropics Ø The zonal mean circulation (Hadley circulation), Inter. Tropical Convergence Zone (ITCZ) Ø Field experiments Ø Macroscale circulations, The Walker circulation, Monsoons Ø Synoptic scale weather systems, tropical waves Ø Moist convection and convective systems Ø The Madden-Julian Oscillation, Westerly wind bursts Ø Concluding remarks

energy gain + F (W m-2) 300 200 energy loss - Radiative heat balance Absorbed solar flux - Emitted infrared flux 100 0 90 50 30 South 10 0 10 Latitude 30 50 North 90 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 North 40 30 20 10 Latitude 20 30 40 60 90 South Mean annual precipitation as a function of latitude. (after Sellers, 1965)

ley Had n latio circu mean meridional circulation The mean meridional circulation and main surface wind regimes. after Defant, 1958

ITCZ

ITCZ

Next topic Ø A satpix tour of the tropics Ø The zonal mean circulation (Hadley circulation), Inter. Tropical Convergence Zone (ITCZ) Ø Field experiments Ø Macroscale circulations, The Walker circulation, Monsoons Ø Synoptic scale weather systems, tropical waves Ø Moist convection and convective systems Ø The Madden-Julian Oscillation, Westerly wind bursts Ø Concluding remarks

Field Experiments in the Tropics 1969 - 1979 Ø Bermuda Oceanographic and Meteorological EXperiment (BOMEX) 1969 v Holland & Rasmusson, (1973), MWR, 101, 44 -55. Ø Global Atmospheric Research Programme (GARP) Atlantic Tropical Experiment (GATE) July 1974 v GARP: Fleming et al. , (1979), BAMS, 60, 649 -659. v GATE: Kuettner et al. (1974) BAMS, 55, 711 -744. Ø The MONsoon EXperiment (WMONEX December 1978, SMONEX May – August, 1979) v WMONEX: Greenfield & Krishnamurti (1979), BAMS, 60, 649659. SMONEX: Fein & Kuettner (1980) BAMS, 61, 461 -474.

Field Experiments in the Tropics 1987 Ø Australian Monsoon EXperiment & Equatorial Mesoscale EXperiment (AMEX, EMEX) January – February 1987 v AMEX Holland et al. (1986), BAMS, 67, 1466 -1486. v EMEX Webster & Houze (1991), BAMS, 72, 1481 -1505. Ø Tropical Oceans Global Atmosphere Couple Ocean Atmosphere Response Experiment (TOGA COARE) November 1992 – February 1993 v Webster & Lucas (1992), BAMS, 73, 1377 -1416.

Next topic Ø A satpix tour of the tropics Ø The zonal mean circulation (Hadley circulation), Inter. Tropical Convergence Zone (ITCZ) Ø Field experiments Ø Macroscale circulations, The Walker circulation, Monsoons Ø Synoptic scale weather systems, tropical waves Ø Moist convection and convective systems Ø The Madden-Julian Oscillation, Westerly wind bursts Ø Concluding remarks

200 mb JJA 850 mb

200 mb DJF 850 mb

Velocity potential We can separate three-dimensional velocity field into a rotational part and a divergent part (see e. g. Holton, 1972, Appendix C. ) rotational nondivergent irrotational divergent

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 m-2 From Lau & Chan, 1983

Walker circulation

Next topic Ø A satpix tour of the tropics Ø The zonal mean circulation (Hadley circulation), Inter. Tropical Convergence Zone (ITCZ) Ø Field experiments Ø Macroscale circulations, The Walker circulation, Monsoons Ø Synoptic scale weather systems, tropical waves Ø Moist convection and convective systems Ø The Madden-Julian Oscillation, Westerly wind bursts Ø Concluding remarks

July Monsoons

SE Asian Monsoon

January

Australasian Monsoon

South America: January climatology 850 mb wind 200 mb wind

An example of monsoon variability West coast of India 1963 1971 (From Webster, 1983)

Next topic Ø A satpix tour of the tropics Ø The zonal mean circulation (Hadley circulation), Inter. Tropical Convergence Zone (ITCZ) Ø Field experiments Ø Macroscale circulations, The Walker circulation, Monsoons Ø Synoptic scale weather systems, tropical waves Ø Moist convection and convective systems Ø The Madden-Julian Oscillation, Westerly wind bursts Ø Concluding remarks

Time-longitude section of vis imagery - latitude band 10 -15 N June 01/06 July 0107 August time 0108 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 C B 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 00 Z

Tropical cyclones Super typhoon Wynnie 11 Aug 1997 TC tracks (1979 -1988)

Next topic Ø A satpix tour of the tropics Ø The zonal mean circulation (Hadley circulation), Inter. Tropical Convergence Zone (ITCZ) Ø Field experiments Ø Macroscale circulations, The Walker circulation, Monsoons Ø Synoptic scale weather systems, tropical waves Ø Moist convection and convective systems Ø The Madden-Julian Oscillation, Westerly wind bursts Ø Concluding remarks

Moist Convection Trade Cumuli

The tropical troposphere z km 15 -121 o. C -73 o. C observed -150 o. C 29 o. C q +150 o. C 77 o. C observed Conclusion: Deep tropical circulations cannot be dry adiabatic

The role of diabatic processes z km 15 Latent heat release opposes adiabatic cooling Fast ascent Radiative cooling opposes adiabatic warming Slow descent ITCZ subtropical high Conclusion: Deep convection occupies a small fractional area

Successive locations of radar reflectivity contours in a tropical squall line. From Chang et al. (1987) Radar reflectivity contours (d. BZ) of a tropical squall line observed during COPT 81 (Ivory Coast, West Africa). Horizontal cross-section at low levels (0. 5 – 1. 5 km).

Radar reflectivity contours (d. BZ) of a tropical squall line observed during COPT 81 (Ivory Coast, West Africa). Vertical cross-section along the axis of propagation.

Types of convection

Next topic Ø A satpix tour of the tropics Ø The zonal mean circulation (Hadley circulation), Inter. Tropical Convergence Zone (ITCZ) Ø Field experiments Ø Macroscale circulations, The Walker circulation, Monsoons Ø Synoptic scale weather systems, tropical waves Ø Moist convection and convective systems Ø The Madden-Julian Oscillation, Westerly wind bursts Ø Concluding remarks

Madden-Julian Oscillation From JAS, Sept. 1972

Madden-Julian Oscillation MJO From Webster 1987

Indian Ocean Feb/Mar 2001 06/02 17/02 07/02 13/02 24/02 06/03

West Pacific Ocean – Feb 2001 06/02 21/02 09/02 24/02 13/02 29/02

http: //www. bom. gov. au/bmrc/clfor/cfstaff/matw/maproom/OLR/hov. last 6 mths. anom. S. gif

Westerly wind bursts GOES-9 12 UTC 2 Dec 1997 10. 7 micron image

A few outstanding problems Ø Interaction between moist convection and the large-scale flow. Ø What are the controls on deep convection. Ø Models don’t get the diurnal variation correct. Ø No generally accepted theory of the Madden-Julian Oscillation. Ø Weather forecasting in the tropics is still very difficult compared with that in the middle latitudes.

The End Thank you for your interest Talk available at: http: //www. meteo. physik. uni-muenchen. de~roger30514 -dlr. pdf