GEOG 100 – SUMMER 2007
2A – SECOND WEEK, SECOND LECTURE
EARTH PRESSURE SYSTEMS and GLOBAL WINDS
(IMPORTANT NOTE – SEE 2 DIAGRAMS FOR THIS LECTURE IN THE
CONTENT SECTION. LOOK UNDER “GRAPHS, DIAGRAMS AND MAPS”)
PRESSURE SYSTEMS – HIGHS AND LOWS – THESE ARE MAJOR
DETERMINANTS OF CLIMATE, WHICH IS THE MAJOR DETERMINAT
OF CLIMATE, WHICH DETERMINES THE WORLD BIOMES
– High pressure is characterized by air descending, which is
getting drier as it descend.
It therefore is a zone of little precipitation. High pressure
zones can be in hot regions (subtropical highs) or cold regions (polar highs or cold
Surface air flow moves out of, or diverges, from a high pressure system.
This is because air always flows from High to Low Pressure. So High Pressure
systems, or Highs as they are sometimes called, are characterized by diverging air at
However, there is convergence aloft to feed the air that is descending
into the surface low.
(B) Low Pressure
– Low pressure is air characterized by ascending (rising) air,
which is getting more humid as it rises.
This is because as air rises, it cools, and cool
air has less ability to hold moisture than warm air.
So, as air rises it tends to reach the
dew point, or temperature at which it becomes saturated and cannot hold any more
With the right conditions and the presence of condensation nuclei for
raindrops, precipitation can then occur.
Low pressure zones of rising air, then, are
characterized by a zone of clouds and precipitation.
These low pressure systems, or
Lows as the are sometimes called, can be located in Hot regions (equatorial low) or
cold (sub-polar low) regions.
Because air moves from High to Low pressure, the
surface air flow will always be into a low pressure system.
Thus air converges, or
movies into, into a Low pressure systems.
However, after the converging air rises to
higher elevations, into will eventually move away from the low.
Hence, low pressure
systems have convergence at the surface, but have divergence aloft as the rising air
moves away from the system.
The opposite is true of a High Pressure system, which
is characterized by divergence of air at the surface and convergence aloft.
LOOK AT 2 IMPORTANT DIAGRAMS ON D2L
THAT ARE THE SUBJECT OF THIS LECTURE.
UNDER “CONTENT” UNDERNEATH ALL THE LECTURES LOOK FOR
“GRAPHS, DIAGRAMS, AND MAPS” – UNDER THIS LOOK FOR
“HIGH AND LOW PRESSURE CIRCULATION”