not as warm as that moving northward in advance of it.
A warm core low decreases intensity with height or
completely disappears and are often replaced by
anticyclones aloft. The heat lows of the southwestern
United States, Asia, and Africa are good examples of
warm core lows. Newly formed waves are generally
warm core because of the wide-open warm sector.
Systems that retain their closed circulations to
appreciable altitudes and are migratory are called
dynamic lows or highs. A dynamic low is a
combination of a warm surface low and a cold upper
low or trough, or a warm surface low in combination
with a dynamic mechanism aloft for producing a cold
upper low or trough. It has an axis that slopes toward
the coldest tropospheric air. (See figure 3-22.) In the
final stage, after occlusion of the surface warm low is
complete, the dynamic low becomes a cold low with the
axis of the low becoming practically vertical.
The dynamic high is a combination of a surface
well-developed ridge, or a combination of a surface
cold high with a dynamic mechanism aloft for
producing high-level anticyclogenesis. Dynamic highs
have axes that slope toward the warmest tropospheric
air. (See fig. 3-22.) In the final stages of warming the
cold surface high, the dynamic high becomes a warm
high with its axis practically vertical.
Q3-11. What is the term that defines the formation of
an anticyclone or the intensification of an
What is the direction of the windflow around a
How do temperatures change within a cold
Low pressure due to intense heating over the
southwestern United States is an example of
which type of low-pressure system?
LEARNING OBJECTIVE: Define tertiary
circulations affect local weather and wind
direction and speed.
Tertiary (third order) circulations are localized
circulations directly attributable to one of the following
causes or a combination of them: local cooling, local
heating, adjacent heating or cooling, and induction
Many regions have local weather phenomena
caused by temperature differences between land and
water surfaces or by local topographical features. These
weather phenomena show up as circulations. These
tertiary circulations can result in dramatic local weather
conditions and wind flows. The most common tertiary
circulations are discussed in this lesson. However, there
are numerous other circulations and related phenomena
in existence around the world.
The term monsoon is of Arabic origin and means
season. The monsoon wind is a seasonal wind that
blows from continental interiors (or large land areas) to
the ocean in the winter; they blow in the opposite
direction during the summer. The monsoon wind is
most pronounced over India, although there are other
regions with noticeable monsoon winds.
Monsoon winds are a result of unequal heating and
cooling of land and water surfaces. During winter a
massive area of cold high pressure develops over the
extensive Asiatic continent. This high pressure is due
primarily to cold arctic air and long-term radiation
cooling. To the south, the warm equatorial waters exist
and, in contrast, the area has relatively lower surface
pressures. The combination of high pressure over Asia
Figure 3-22.Vertical slope of low -pressure systems.