886 
speeds, but consist of lines of flow (direction only) with 
the speeds indicated by isopleths or by feathers on the 
arrows. It is possible, with these charts, to identify 
areas of convergence and divergence with reasonable 
reliability and also to pick out sloping surfaces of well- 
marked wind discontinuity. Short-period forecasts of 
good reliability can be made by an experienced fore- 
caster using this method, but much more satisfactory 
results appear to be possible if the streamline charts are 
related to the isobaric charts. Sen [8] in India has ad- 
vanced the method a stage further by assuming the 
equatorial circulation to consist of a Karman vortex 
street, the location of each vortex bemg determined 
with the assistance of streamline charts and the surface 
isobaric chart. This conception mvolves the existence 
in the Northern Hemisphere of a line of anticyclonic 
vortices near the equator and a line of cyclonic vortices 
to the north, with the corresponding zones of weak 
anticyclonic and cyclonic pressure centres, respectively, 
to mark their positions. From the spacing ratio of the 
“street,” the stability or instability of the system is 
determined, and developments are forecast accordingly. 
The distribution of humidity is brought into the dis- 
cussion of the degree of development that is expected to 
take place. It is necessary, however, to assume that the 
geostrophic balance of wind and pressure holds to 
within a few degrees of the equator, which is not in 
accordance with the experience of most workers in the 
region. 
TROPICAL METEOROLOGY 
The recognition of convection and orographic effects 
is, of course, of great importance, but since these are 
not features peculiar to’ the equatorial zone they will 
not be discussed here. It must be remarked, however, 
that by far the greater amount of rain and thunder- 
storms arises from these effects so that their recogni- 
tion is of primary importance to the forecaster. 
REFERENCES 
1. Crosstey, A. F., Memo CHM/1946/1 of the Conference of 
Empire Meteorologists. London, His Majesty’s Stationery 
Office, 1946. 
2. —— “On the Relation between Wind and Pressure.’ Quart. 
J. R. meteor. Soc., 74:379-382 (1948). 
3. Forvrr, D. H., Analysis and Forecasting in the South-West 
Pacific Area. Melbourne, Australian Meteorological Serv- 
ice (Section IV). 
4. Freeman, J. C., Jr., “An Analogy between the Equatorial 
Easterlies and Supersonic Gas Flows.” J. Meteor., 5:138- 
146 (1948). 
5. Gress, W. J., Tropical Weather Research Bull. No. 12. 
R.A.A.F. Meteorological Services, Sept. 1945. 
6. Grimes, A., “The Movement of Air across the Equator.” 
Mem. Malay. meteor. Serv., Singapore, No. 2 (1938). 
7. Rosssy, C.-G., ‘Planetary Flow Patterns in the Atmos- 
phere.”’ Quart. J. R. meteor. Soc., (Supp.) 66:68-87 (1940). 
8. Sen, S. N., ‘Monsoon Cyclones.” Sct. Cult., 9:90 (1943); 
“‘Atmospheric Vortex Street.’ Ibid., 9:453-455 (1944). 
9. TreLoar, H. M., Tropical Weather Research Bull. No. 12. 
R.A.A.F. Meteorological Services, Sept. 1945. 
