SECRETARIA DE PLANEJAMENTO DA PRESIDENCY DA REPUBLICA

CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTIFICO E TECNOLOGICO

' JNASA-CR-176617) TBANSIENT CONVECTION OVER

THE AMAZON-BOLIVIA BEGION AND TEE DYNAMICS

OP DROUGHT OVEB NOBTHEASI BBAZII (Institute

de Pesquisas Espaciais, Sao Jose) 34 p .

HC A03/HF A01 CSCL. 04B 63/47

N86-2J072

Dnclas

08442

INSTIIUTO OE PESQUISAS ESPAGIAIS
1 . Publication N9

INPE-3723-RPE/497

2. Version •

1' -

3. Date

'Nov&iber 1985

4. Origin Program

J)ME TECLIM

5. Distribution

D Internal 0 External

D Restricted

6. Key words - selected by the author(s)

TROPICAL HEAT SOURCE

DROUGHT IN NORTHEAST BRAZILCLIMATE MODELING

1. U.D.C. : 552 . 577 . 38(8 )

8. Titl e INPE-3723-RPE/497

TRANSIENT CONVECTION OVER THE AMAZON/BOLIVIA

REGION AND THE DYNAMICS OF DROUGHT OVER

NORTHEAST BRAZIL

9. Authorship ORIGINAL S3

Julio Buchmann (*) P£ POOR

Pedro Leite da Silva Dias (**)

Antonio Divino Moura

0

Responsible author

10. NO of pages: 31

11. Last page: 29

12. Revised by

Carlos A. Nobre

13. Authorized by

i^-

-^

Marco Antonio Raupv

\ / Director General Y

14. Abstract/Notes

A two-layer, nonlinear, equatorial 6-plane model, in

p-coordinates is used to study the atmospheric response to a large scale

prescribed heat source varying in time. The heat source is meant to

represent a connective burst with total duration of approximately 48

hours over the Amazon/Bolivia region. The boundary conditions used are

meridional velocity zero at 60 S, to = 0 at the top and zero geometric

velocity at the lower boundary. Sensitivity study was done ur.ic/i includes

initial state at rest, compared with realistic initial flow. The scale of

the heat source is 1500km in latitude and longitude and it is centered

at 10°S. Special attention is paid to the distribution and intensity of

the induced vertical motion. The model is integrated for TZJO days and

the preliminary results show agreement with the observed 200mb flow. Of

interest is the establishment of a trough and descending motion to the

northeast of the heat source. A conjucture is thus made that the Amazon

heat source and its fluctuations bear some relationship with the drought

problem over Northeast Brazil.

15. Remarks Archives for Meteorology, Geophysics, ana Bio climatology

Springer-Verlag, Wien I, Molker Bastei 5, A-1011 Wien/Postfach 367.

(*) UFRJ - Universidade Federal do Rio de Janeiro

(**) IAG - Institute Astronomico e Geof-Csico da USP
TRANSIENT CONVECTION OVER THE AMAZON/BOLIVIA REGION AND

THE DYNAMICS OF DROUGHTS OVER NORTHEAST BRAZIL

1 2 3

J-. Buchmann , P.L. da Silva Dias , and A.D. Moura

With 12 figures

1. Departamento de Meteorologia - UFRJ, 22910, Rio de Janeiro, Brazil,

2. Institute Astronomico e Geofvsico - USP, 01051, Sao Paulo, Brazil.

3. Institute de Pesquisas Espaciais/CNPq, 12200, Sao Jose dos Campos,

Brazil.
ABSTRACT

A two-layer, nonlinear, equatorial g-plane model, in

p-coordinates is used to study the atmospheric response to a large scale

prescribed heat source varying in time. The heat source is meant to represen

a convective burst with total duration of approximately 48 hours over the

Amazon/Bolivia region. The boundary conditions used are meridional velocity

zero at 60°N and 60°S, w = 0 at the top and zero geometric velocity at the

lower boundary. Sensitivity study was done which includes initial state at

rest>compared with realistic initial flow. The scale of the heat source is

1500km in latitude and longitude and it is centered at 10°S. Special

attention is paid to the distribution and intensity of the induced vertical

motion.

The model is integrated for two days and the preliminary results

show agreement with the observed 200mb flow. Of interest is the establishment

of a trough and descending motion to the northeast of the heat source.

A conjecture is thus made that the Amazon heat source and its fluctuations

bear some relationship with the drought problem over Northeast Brazil.
1. Introduction

The Northeast Brazil climate has been the subject of study by

scientists, who have been trying to explain the observed climatic anomalies

due 'to the disruption of the lives of over 30,000,000 people. Two main

lines of research have been followed. The first one considers possible

local effects as the main cause of the anomaly. Along this line, Gomes

Filho [4] studied two mechanisms of formation and maintenance of the

semiarid region: albedo gradients and orographic effects. However this

conclusion is not well established yet. Along the second line of research,

the main cause is due to external mechanisms such as those invoked by

Namias [16], Hastenrath and Heller [8], Kousky [11], Moura and Shukla

[15] and Buchmann [2]. Namias [16] demonstrated a connection between the

700mb circulation pattern over the North Atlantic and the rainfall at

Quixeramobim (state of Ceara). Hastenrath and Heller [8] used a large

number of observations to show that rainfall in the region of Ceara is

closely linked to the meridional displacement of the equatorial trough

zone. Kousky- [J1J showed that: a) frontal systems penetrate the southern

part of Northeast Brazil throughout the year; b) frontal incursion

plays an important role in the December-January maximum in the month

precipitation in the southern part Northeast Brazil; c) in certain

periods, the frontal incursions affect rainfall as far north as Ceara.

Moura and Shukla [15] proposed that a possible mechanism for the occurrence

of severe droughts over Northeast Brazil is the establishment of a

thermally direct local circulation which has the ascending branch at about

10°N and the descending one over Northeast Brazil and the adjoining oceanic

region. Buchmann [2] studied the occurrence of drought and rain
- 2 -

anomalies in the Northeast Brazil, in relation to variations in the

synoptic pressure systems located in middle latitudes of the Northern

Hemisphere, through the mechanism of lateral forcing.

However, there are other mechanisms not yet fully explored.

Because the amount of latent heat released during the rainy season of the

Amazon region is so large (Kasahara and Mizzi,[9] ), one can expect a

significant effect of the local forced circulation on the neighboring

regions, and assume a direct thermal circulation established over the

tropical sector of South America, with maximum upward movement over the

Amazon region and the downward branch of the resulting Walker circulation

affecting Northeast Brazil and the adjacent Atlantic Ocean (Gill, [3] ).

This hypothesis agrees with Bjerknes [1] and Kidson [10] ideas

concerning the relationship between the upper tropospheric high (also

known as Bolivian High after Gutmann and Scwerdtfeger, [5] ), and the

variability of precipitation over Northeast Brazil. Specifically, the

circulation pattern over South America shows large variations in different

time scales: (i) from the Southern Hemisphere summer to winter, the 200mb

circulation changes from a well-defined upper tropospheric anticyclone to

near equatorial westerlies (Kruels et al.,[13]); (ii) convective bursts

during summer make a substantial rearrangement of the upper trospospheric

anticyclone and the accompanying through over Northeast Brazil (Silva Dias

et al., [19] ; Virgi, [21] ), and (iii) the large diurnal variation of

convection seems to have a strong signal in the divergent component of the

upper tropospheric circulation (Silva Dias et a!., [20]). Latent heat

release is a plausible controlling mechanism on the three time scales of

the tropical tropospheric circulation over South America. Due to the
- 3 -

confinement of the precipitation pattern in the central and western part

of Brazil during the summer months, it is reasonable to investigate the

effect of latent heat-induced circulations on Northeast Brazil.

Fig. 1a shows a typical infrared satellite image with the welldeveloped convection over the Amazon region. Fig. 1b shows the associated

200mb streamlines and the vertical pressure velocity field (u) at 500mb

(thin solid and dashed lines for upward and downward motion, respectively),

as obtained from the National Meteorological Center (NMC) analysis for

January 5, 1981. Similar upper tropospheric situations as well as the

transient behavior are shown in Fig. 6 of Silva Dias et al. [19] .

Upward vertical motion is observed in association with the:upper

tropospheric circulation and sinking motion occurs over Northeast Brazil

when the upper circulation is cyclonic. The satellite imagery qualitatively

agrees fairly well with the NMC vertical motion. In particular, recent model

studies by Silva Dias et al.[19] indicated that transient convection on

the typjcal time and spatial scales over the Amazon region tend to generate

a Walker-type circulation associated with Kelvin waves to the east of the

heat source, an upper tropospheric anticyclone centered to the southwest

of the source and an upper trough over Northeastern Brazil in agreement

with the observed pattern shown in Fig. 1.. However, the model results were

based on the linearized shallow water equations about a basic state at

/

rest. The objective of this paper is to further explore the response of

the atmosphere to transient forcing, in terms of the associated vertical

motion and possible nonlinear effects with a two-level primitive equation

model. The time and horizontal scales of convective bursts, centered at

about 10°S, are assumed to be of approximately 48 hours and of the order of

> i!

1500 km, respectively.
- 4 -

2. Observational Evidence

The summer upper level circulation over tropical South America is

characterized by the anticyclonic flow with large transient variations

(Virji, [21]). In order to analyse the transient behaviour of the upper

circulation and its association with cloudiness, we obtained the vertical

motion at 500mb at 00:00 GMT and 12:00 GMT for January, 1981, based on the

NMC analyses. This choice was based on the particularly intense convective

activity observed in the period (Silva Dias et al., [20]). A mass balanced

kinematic method between 1000mb and 200mb is applied to the gridded data

(horizontal resolution of approximately 5x5) . Infrared geostationary

images processed by the Institute de Pesquisas Espaciais - INPE (Institute

for Space Research) were collected for January, 1981 at times as close as

possible to 00:00 GMT and 12:00 GMT.

The diurnal signal in the vertical motion is clearly evident

during the period with maximum upward motion at 00:00 GMT over the Amazon

region and Central Brazil (approximately 20:00 LT). The diurnal variation

in the vertical motion field ( o> in pressure vertical coordinate) over

tropical South America has been studied by Silva Dias et al. [20], who

showed that the signal is significant from a statistical point of view.

However, as noticed by Virji [21], convective bursts often occur over tropical

South America, frequently in response to penetrating mid latitude systems

(Kousky and Virji,[22]). One such sequence of satellite images (Fig. 2) was

observed from the 22nd to the 25th of January, 1981 with enhanced convective

activity on the 23rd, as shown in the infrared satellite image at 21:16 GMT
- 5 -

(Fig. 2.b). Fig. 3 shows the accompanying upper level wind vectors

(200mb) and the 500mb vertical motion (solid lines for u s 0 and dashed

lines for u < 0). A comparison between the computed vertical motion and

convective activity (Fig.3 and 2,respectively) shows a reasonable

agreement, with maximum upward vertical motion at 00 GMT on the 24th

(Fig. 3c for the u-field and Fig. 2b *or the satellite image).

Several interesting points deserve attention in Fig. 3: (i)

before the convective burst>the anticyclonic circulation is zonally

elongated towards the west with center at approximately 18°S and 75°W

(Fig. 3a); (ii) as the convective activity enhances, a strong cross

equatorial flow over the northern Amazon region is observed (Fig. 3c),

accompanied by enhanced upward vertical motion over Central Brazil (10 S,

55°W); (iii) as the convective activity decreases, the easterly component

is established just off the equator (Fig. 3f); (iv) the center of the

anticyclonic circulation is displaced eastward as the convective activity

enhances (Fig. 3a to 3c), presenting a westward elongation after the

maximum activity (Fig. 3e and 3f); (v) ridging is observed (25°S, 55°W)

during the final period (Fig. 3e and 3f) just south of the most active

region. These general observations were also detected in other periods

of January 1981 and during a particular period of February 1979 (8th to

12th) as discussed by Silva Dias et al. [19] .

3. Governing Equations

The fully nonlinear primitive equations above an equatorial

B-plane are discretized in the vertical assuming a two-level model, with
- 6 -

the zonal and meridional wind components and potential temperature defined

at 750mb and 250mb. The geopotential and vertical pressure velocity are

defined at the bottom pressure level(1000mb), 500mb and top (Omb). The

vertical boundary conditions are co = 0 at the top and zero geometrical

velocity at the lower boundary (W= 0). No topographic effects are included.

Thus, there are two vertical modes in the linearized version of this model

(about a basic state at rest): the external (barotropic)and the internal

mode with reversing sign in the vertical (baroclinic). Schuman's horizontal

discretization scheme is applied to the governing equations (Haltiner,

[7] ) and the time differencing scheme is centered in time. The horizontal

boundary conditions are constant in time with v = 0 at 60°N and 60°S. Zonal

periodicity at the equatorial circumference of the earth is also assumed.

The horizontal boundary conditions are not expected to influence the model

results because the time scale of the integration is sufficiently short to

avoid boundary contamination.

The model circulation is forced by a known heat source which is

Gaussian-shaped in the horizontal direction and with time dependence as

shown in Fig. 4, with maximum heating at 24 hours. In the particular case

of the two level model, the heat source is assumed to have the same

intensity at 750mb and 250mb, corresponding to 6°C/day. The choice of

the spatial and temporal scales are based on the satellite imagery. The

heat source intensity is, however, an estimate based on observations in

other tropical regions (Riehl, [17]) because there are no aerological

estimates of the transient characteristics of the Amazon heat source, to

the authors' knowledge.
-

 7

 - n.

The results shown in this paper are confined to the model outputs

at 24 and 48 hours. No initial instabilities were observed in the model

integration because the transient forcing is slowly increasing in time

rather than a switch-on forcing. A carefull observation of the vertical

motion field at frequent intervals (4 hours) shows a very stable and

continuous evolution of the numerical solution.

Numerical solutions including Rayleigh damping and Newtoniancooling were obtained using a characteristic time scale of 10 days. Although

the flow intensity was somewhat reduced compared to the frictionless version,

no major discrepancies were observed up to 2 days of integration time.

Constant radiative cooling of 1.5°C/day was also tested in the model. Since

no available potential energy is generated in this case and the model

contains no moisture physics or radiation interaction, no horizontal motion

is generated by such forcing. In fact, the prescribed heat source can be

interpreted as the combination of both latent heat release and radiative

vertical flux divergence is certainly an important process (Gray and

Jacobson, [6]) due to the typical difference between the vertical profiles of

clear air/cloudy stay radiative cooling rates. In order to keep the thermal

balance, clear regions are associated with sinking motion which approximatelybalances the radiative cooling. Horizontal motion is also generated by the

difference between the radiative cooling rates in cloudy and clear regions,

but this effect is included in the prescribed heat source. Thus, the

results shown below correspond to the frictionless adiabatic version.

4. Model Results

Silva Dias et al. [19] computed how the forced energy-is

partitioned between Kelvin, mixed Rossby-gravity, Rossby and/gravity modes
- 8 -

for the linearized primitive equations about a basic state at rest

assuming different temporal and spatial scales for the heat source. The

characteristics of the response are quite different from the stationary

forcing (Gill, [3] ; Moura and Shukla, [15]). The main findings are: (i)

Rossby wave energy increases as the spatial scale and the latitude of the

forcing increases; (ii) as the forcing time scale decreases, less energy

is excited in the high frequency modes; (iii) as the forcing spatial scale

increases, the energy in gravity modes decreases sharply; (iv) for

fixed time scale of the forcing, the energy in high frequency modes

initially increases with the horizontal scale of the forcing and then

decreases.

The results obtained with the two-level nonlinear primitive

equation model are essentially similar to the linear situation shown in

Silva Dias et al. [19] , primarily concerning the rotational contribution

and the Kelvin component to the east of the source. Figs. 5 and 6 show the

250mb wind field at 24 and 48 hours,respectively, for a heat source

centered at 10°S, with symmetrical e-folding width of the order of 1500km.

The corresponding vertical motion field at 500mb is shown in Figs 7 and 8.

The development of the upper tropospheric anticyclone and the trough over

Northeast Brazil is well depicted by the model (compare with Fig. 4 of

Silva Dias et al.H9] ). The heating over the Amazon region initially

induces subsidence over Northeast Brazil,although the forcing function

is quite wide. It is interesting to note the preferred location of the

downward motion. As time increases, a slight ascending motion can be

detected over Northeast Brazil. However, with smaller scale forcing, the

/

subsidence over this region is emphasized as shown in the vertica/1 motion
- 9 - .

field at 24 hours for a heat source located at 15 S and with a

meridionally elongated source (zonal and meridional e-folding width of

700 Icn and 1500 km, respectively), as shown in Fig. 9.

Possible nonlinear effects were also studied by prescribing an

initial condition with a more realistic zonal flow with subtropical jets

located at about 35° to the north and south of the equator, attaining

35 ms~ . In this case the wind field at 48 hours at 250mb is shown in Fig.

10 and the deviation from the initial flow is shown in Fig. 11. The basic

characteristics of the forcing are the same of Figure 6. The main

difference from the no initial flow case is due to the stronger meridional

component to the south of the upper anticyclone. This effect implies a

larger distortion of the zonal flow (ridging) and therefore we might

expect important downstream amplification of the wave train if longer

time scale forcing is applied or if a succession of convective bursts occurs

(Lau and Lim, [M] ). The upper westerlies to the east of the heat source

are also evident in Figs. 5, 6, 9 and 10. This upper level configuration

seems to be related to free Kelvin modes according to Silva Dias et al.,

[191 and recently found in satellite data by Salby et al [18] .

The model results seem to corroborate observed characteristics

of the tropospheric circulation over tropical South America during

actively convective episodes, as presented in Section 4. In particular,

there is correspondence with the intense cross equatorial flow at the

initial stages of the forcing (Fig. 5), the slow turning of the wind to

easterlies south of the equator (Fig. 6) and the westward displacement of

the upper anticyclone center at the latter stages (Fig. 6). The case with
- 10 -

initial zonal flow indicates that nonlinear interactions might be relevant

in emphasizing the observed ridging at the final stages of the convective

burst,as observed in Figs. 3e e 3f.

5. Conclusion

The nonlinear primitive equation model simulation of the transient

heat source reproduced most of the results obtained with the linear shallow

water equations of Silva Dias et-al. H9! . However, the results also

indicate that the induced subsidence occurs preferentially over Northeast

Brazil primarily for meridionally elongated heat sources. These results

indicate that a regional Walker type circulation with ascending motion

over Northeast Brazil may take place. Thus, excessive convection over

central and western South America may induce an unfavourable dynamical

situation for convection over the Northeast region. The model is able to

simulate the basic features of the observed characteristics of the

transient convection episodes (Section 2). The nonlinear effects up to 2

days seem to be confined to higher latitudes where the upper anticyclonic

circulation interacts with the upper westerlies, intensifying the

ridging mechanism. The intensification of the equatorial westerlies to the

east of the forcing (Fig. 6)doesnot seem to be evident in the observations

(Fig. 3) although westerlies are observed. This can be due to the

rotational constraints imposed on the analyses and assimilation scheme

used by NMC. It is interesting to note that transient forcing is more

realistic than stationary forcing over tropical South America. According

to the linear model partition of energy, discussed in the previous

section, more energy in fast modes is expected for highly transient
J 11:-

forcing and therefore more intense vertical motion teleconnections are

expected through gravity wave activity.

Similar model simulations have also been performed with zonally

elongated heat sources located over the eastern equatorial Pacific Ocean.

These model results are expected to represent the El Nino type of anomaly.

The model results also seem to indicate a preferred subsidence region

over most of equatorial South America on the time scale of two days

(Fig. 12). These results are in agreement with the observed negative

correlation between precipitation over the eastern Pacific Ocean and over

tropical South America (Kousky et al., [1^]).
*

t2.

ACKNOWEDGEMENTS

The authors are grateful to Dr. Vernon E. Kousky, Mr. J.P.

Bonatti, Mr. Manoel A. Gan and Mrs. Iracema F. Cavalcanti. Research support

was available through FINER grants to INPE and IAG-USP. Partial support

for this work was provided by NASA grant NAG 5-127. The first author

also benifitted from a post-doctoral fellowship provided by CNPq. We

are also grateful to Dr. C. Nobre for editorial comments and suggestions.
r .:

References

[1] Bjerkness, J. : Atmospheric teleconnections form the equatorial Pacific.

Mon. Wea. Rev.. 97, 163-172, 1969.

[2] Buchmann, J.: A study of the influence of extratropical meteorological

phenomena on climatic variability in northeast Brazil. Doctoral

dissertation presented at COPPE/UFRJ, 123 pp [available from COPPE/

UFRJ-C.P. 1191,20000 - RJ, Brazil] (in Portuguese), 1981.

[3] Gill, A.E.: Some simple solutions for heat induced tropical circulation.

Quart. J. Roy. Meteor. Soc.. 106, 447-462, 1980.

[4] Gomes Filho, M.F.: A study of differential albedo and orographical

influence on the atmospheric circulation: Application to Northeast

Brazil. Master thesis presented at the Institute for Space Research,

INPE. INPE-1640-TDL/015, 86 pp [Available from INPE - C.P. 515, 12200

Sao Jose dos Campos, SP, Brazil] (in Portuguese), 1979.

[5] Gutman, G.J. and Schwerdtfeger, W.: The role of latent and sensible

for the development of a high pressure system over the subtropical

Andes in the summer. Meteorol. Rundch., 18, 69-75, 1965.

[6] Gray and Jacobson: Diurnal variations of deep cumulus convection.

Mon. Wea. Rev.. 105. 1171-1188, 1977.

[7] Haltiner, G.J.: Numerical weather prediction. New York: John Wiley &

Sons, Inc., 317 pp., 1971.

[8] Hastenrath, S. and Heller, L.: Dynamics of hazards in Northeast Brazil.

Quart. J. Roy. Meteor. Soc.. 103, 77-92, 1977. '
- 14 -

[9] Kasahara, A. and Mizzi, A.: Temporal variations of the divergence field

in the E.C.M.W.F. level III-B analysis data. National Center of

Atmospheric Research. P.O. Box 3000, Boulder, Co. 80.307, 1984.

[10] Kidson, J.W.: Tropical eigenvector analysis and Southern Oscillation.

Mon. Wea. Rev., 103. 187-196, 1975.

[11] Kousky, V.E.: Frontal influences on northeast Brazil. Mon. Wea. Rev., 107,

1140-1153, 1979.

[12] Kousky, V.E., M. Kagano and I.F.A. Cavalcanti: The Southern Oscillation:

oceanic-atmospheric circulation changes and related rainfall

anomalies. Accepted in Tell us, 1983.

[13] Kruels, R., Fraedrich and E. Ruprecht: An aerological climatology over

South America. Meteor. Rundsch., 28, 17-24, 1975.

[14] Lau, K.M. and H. Lim: On the dynamics of equatorial forcing of climate

telecommunications. J. Atmos. Sci., 41, 161-176, 1984.

[15] Moura, A.D. and Shukla, J.: On the dynamics of droughts in Northeast

Brazil: Observations, theory and numerical experiments with a general

circulation model. J. Atmos. Sci.. _38, 2653-2675, 1981.

[16] Namias, J.: Influence of northern hemisphere general circulation on

drought in Northeast Brazil. Tell us, 24, 336-343, 1972.

[17] Riehl, H.: Climate and weather in the tropics. London, Academic Press,

611pp., 1979.

[18] Salby, M.L., D.L. Hartmann, P.L. Bailey and J.C. Gille: Evidence for

;

equatorial Kelvin modes in Nimbus-7 LIMS. J. Atmos. Sci., 41, 220-235,

1984. /
- 15 -

[19] Silva Dias, P.L., W.H. Scubert and M. DeMaria: Large-scale response of

the tropical atmosphere to transient convection. J. Atmos. Sci., 40,

2689-2707, 1983.

[20] Silva Dias, P.L., J.P. Bonati and V.E. Kousky: Diurnally forced tropical

tropospheric circulation over South America. Submitted to Mon. Wea.

Rev., 1985.

[21] Virji, J.: A preliminary study of summertime tropospheric circulation

patterns over South America from cloud winds. Mon. Wea. Rev., 109,

599-610, 1981.

[22] Virgi, H. and Kousky, V.E.: Regional and global aspects of a low

latitude frontal penetration in Amazonas and associated tropical

activity. Paper presented at the First International Conference on

Southern Hemisphere Meteorology. Sao Jose dos Campos, SP, Brazil,

1983.

Author's address: Dr. Prof. Pedro L. da Silva Dias, Departmento de Meteorologia,

Universidade de Sao Paulo - USP, Caixa Postal 30627, 01051 Sao Paulo,

S.P. Brazil.
Figure Legends

Fig. 1a - Infrared satellite image for 01/05/81 at 21:16 GMT. (SMS-2).

Fig. 1b - 200mb streamlines (solid lines with arrows) and 500mb vertical

motion in 10~"mbs on 01/06/81 at 00:GMT.

Fig. 2 - Infrared satellite image of (a) 01/23/81 at 12:16 GMT (SMS-2),

(b) 01/23/81 at 21:16 GMT, (c) 01/24/81 at 12:16 GMT, (d) 01/24/81

at 21:16 GMT,(e) 01/25/81 at 09:16 GMT, (f) 01/25/81 at 21:17

GMT.

Fig. 3 - 200mb wind vectors and vertical motion in pressure coordinate in

10~'*mbs" (sinkingmotions are represented by dashed lines and upward

motion,by sollid lines) on (a) 01/23/81 at 00:GMT (Vmax = 66 m/s),

(b) 01/23/81 at 12:GMT (Vmax = 71 m/s), (c) 01/24/81 at 00:GMT

(Vmax = 77 m/s), (d) 01/24/81 at 12:GMT (Vmax = 72 m/s), (e)

01/25/81 at 00:GMT (Vmax = 75 m/s), (f) 01/25/81 at 12:GMT

(Vmax = 68 m/s).

Fig. 4 - Time dependence of heat source. Tmax = 24 hours in the model

computations.

Fig. 5 - Wind flow at 250mb after 24 hours for a heat source centered at

10°S and 60°W with symmetrical e-folding width of 1500 km.

Maximum vector corresponds to 1.98ms" .

Fig. 6 - Same as Fig. 5 but at 48 hours. Vmax = 4.94ms~ .

"» _i Fig. 7 - Vertical p-velocity in 10 mbs at 500mb after 24 hours.

Fig. 8 - Same as Fig. 7 but after 48 hours.

Fig. 9. - Same as Fig.7 but for a heat source centered at 15°S and'zonal
- 17 -

e-folding width of 700 km and meridional width of 1500 km.

Fig. 10 - Same as Fig. 5 but at 48 hours for realistic initial flow.

Vmax = 19.82 ms "1.

Fig. 11 - Difference between 250mb wind field at 48 hours and initial flow.

Vmax = 4.96 ms~ .

_ •» -1

Fig. 12 - Vertical p-velocity in 10 mbs ' at 48 hours for a heat source

located at the Equator and 130°W.
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(f)

s s

f c . Si -