T/G Layout 1

storm. With higher resolution observations, it was found that the amplifications in the
wave were associated with the movement of small scale disturbances (short waves)
within the troughs. When these short waves, which appear as constrictions in the
longer wave (figure 20), approach an area of surface low pressure, rapid development
of the cyclonic disturbance occurs.

figure 20.

Interaction: short wave trough and surface low pressure

LL

HH

LL

HH

LL

HH

LL

upper air

upper air

upper air

upper air

upper air

upper air

upper air

L

short wave

trough

L

HH

upper air

warm

L

COLD

COLD

COLD

COLD COLD

initial state

• preexisting
  stationary front
  may not be
  present

approach of short

wave

• note constriction
  in upper air flow
  at trough axis

short wave

interacts with

surface low

pressure

entire wave

develops

a.

b.

c.

d.

L