|Does Low Level Convergence
Upper Level Divergence?
METEOROLOGIST JEFF HABY
When air piles together at the surface, since it can not go into the earth's surface, it has no place to go but up.
The question is, how far does it go up? The classic Dine's compensation model shows low level convergence with
upper level divergence and low level divergence with upper level convergence. The diagram below shows these
As is the case with most processes in meteorology, convergence and divergence have varying magnitudes. To
complete the Dine's compensation model due to dynamic lifting, either the low level convergence must be
strong, the upper level divergence must be strong, or there must be lifting mechanisms in both the lower
and upper levels of the atmosphere. Low level convergence can occur at the same time that upper level
convergence is occurring aloft (e.g. WAA in the PBL with NVA aloft). In this case as shown in the diagram
below, the circulation pattern be as such if the low level convergence is equal to the upper level convergence:
It is important to look at all the processes in the atmosphere that are causing rising and sinking air. Low
level convergence will not necessarily cause a deep layer of rising air in the atmosphere if the low-level
convergence is weak or convergence exists aloft. A cap in the atmosphere can also prevent a deep layer of
rising air when weak low level convergence is present.
Haby sez: The rate of which convergence and divergence produces a dynamical rising or sinking of air depends
on the resultant of all the convergence and divergence process in the atmosphere over a forecast region. Low
level convergence does not always produce a deep layer of rising air.