| behind and in front of the positive axis.
4)
Instuble vortex (Stage 3).
Suddenly (the detsils are as
yet obscure, because the chinge is so rapid) thu tangent point
is replaced by two singular points, one negative, lying to the
@ast, the other a neutral point which moves ahead of and relative
to it.
Westerly winds make their appearance for the first time
in an obvious circulation about the negative point, while the
asymptote of convergence extends wéll ahead of the disturbance
joining up with that of the previous vortex of the series, if
there is one.
It is now possible to draw a continuous "equato-
rial front" from one vortex to another in a series such as exists
between 150° E and the China coast when the typhoon szason is
well advanced.
However, st may be difficult to detect a closed
pressure center about the negative point;
though one will
undoubtedly exist, the depression of the barometer in that
central region may be so slignt in comparison with the surround-
ings that it would require very accurate and danse pressure
|
observations, and the careful drawing of isobars at half-millibar
intervils to delineate it.
Tne chahces are that at an early
stage in the deepening process the whole vortical disturbance
Will be mistaken for an easterly wave.
we regard tha vortex as
unstable so long as it deepens, with increasing development of
kinetic energy in the lower layers.
The deepening may be very
Slow so that the vortex may pass from the longitude of Guam to
‘beyond the Philippines as 4a simple weak, but slowly developing
depression.
5001b26b
2n the other hand the deepening may be very rapid
32