Geoscience Reference
In-Depth Information
Marine West-Coast Climates (
Cfb
,
Cfc
)
In order to visualize how the marine west-coast climate functions,
go to the
Geo Media Library
and select
Marine West-Coast Cli-
mates (Cfb, Cfc)
. In this animation, you will be able to see how
the migrating midlatitude storm track brings moisture off the east-
ern Pacific Ocean into the region. This animation is similar to the
humid subtropical hot-summer climates (
Cwa
,
Cwb
) animation
you previously viewed in that it will show airflow and associated
cloud development. As you watch the animation, notice the re-
lationship between cyclones and moisture flow, as well as the
effect that the Cascade Mountains have on precipitation intensity.
Once you complete the animation, be sure to answer the ques-
tions at the end to test your understanding of this concept.
the ground for extended periods of time. In contrast, summer
temperatures are usually warm and can even be hot for brief
periods of time.
D
climates are found almost exclusively in the
Northern Hemisphere because no large landmasses are pres-
ent at corresponding latitudes in the Southern Hemisphere.
The only places you will see
D
climates in the Southern Hemi-
sphere are in highland areas. (W
hy does this distribution of D
climates make sense?
)
KEY CONCEPTS TO REMEMBER ABOUT
MESOTHERMAL (C) CLIMATES
1.
Three major mesothermal
(C)
climate subcategories are
recognized: (a) humid subtropical hot-summer climates
(
Cfa
,
Cwa
); (b) Mediterranean dry-summer climates
(
Csa
,
Csb
); and (c) marine west-coast climates (
Cfb
,
Cfc
).
Humid Continental Climates
Like the mesothermal
C
climates, microthermal
D
climates can be initially subdi-
vided into three categories. The most southerly of these sub-
categories are the humid continental hot-summer climates
(
Dfa
,
Dwa
), which are located in the central and eastern parts
of North America and Eurasia (Figure 9.2). Two subclassi-
fications are recognized in these climates: one is moist (
⩾
6
cm [2.5 in.] of average rainfall each month) over the entire
year (
Dfa
), whereas the other is dry (
<
6 cm [2.5 in.] of rain-
fall per month) in the winter (
Dwa
). The primary weather-
producing system in humid continental hot-summer climates
is the midlatitude jet stream, which steers cyclones through
these regions. Given the continental locality of this climate,
the annual range of temperature is high, ranging from warm,
periodically hot summers to cold winters. Most precipitation
falls during the summer, when mT air masses invade from the
south. Winters are relatively dry because cP and cA air masses
dominate the region. In these climate zones, the dominant
vegetation is deciduous forest (Figure 9.10).
Poleward of the humid continental hot-summer climates
(
Dfa
,
Dwa
) are the humid continental mild-summer climates
(
Dfb
,
Dwb
). These climate regions range across central and
eastern North America, western Europe, central Asia, and
the far east of Asia (Figure 9.2). These regions are known for
having a wide annual temperature range due to the effects
of Earth-Sun geometry. In places like the upper Midwest
in the United States, average high temperatures in July are
>
27°C (80°F), with about 10 cm (4 in.) of rain. In contrast,
average high temperatures in January are about
-
5°C (23°F)
and most precipitation is snow. In northern Michigan this cli-
mate is associated with northern hardwood and pine forests
(Figure 9.11).
2.
The humid subtropical hot-summer climates (
Cfa
,
Cwa
)
occur on the southeastern side of continents in places
like South Carolina and China. These regions have am-
ple year-round precipitation, but have a distinct sum-
mer peak due to the influx of mT air by offshore STH
Pressure Systems. Vegetation consists predominantly
of pines and deciduous trees.
3.
The Mediterranean dry-summer climates (
Csa
,
Csb
) oc-
cur on the southwest coast of North America and in the
Mediterranean region. These climates have a warm but
narrow temperature range due to their relatively low-
latitude coastal location. The summer dry season is as-
sociated with dominance by the STH Pressure System.
Vegetation consists of a mix of trees and grass.
4.
The marine west-coast climates (
Cfb
,
Cfc
) occur in
coastal zones poleward of their Mediterranean counter-
parts. Thus, they have a wider temperature range that
is, on average, cooler. These regions receive ample an-
nual precipitation, but have a distinct winter wet sea-
son due to passage of midlatitude cyclones. Vegetation
consists largely of needle-leaf trees.
Microthermal (
D
) Climates
At this point, let's turn to the climate zones that are more con-
tinental in their character by focusing on
D
climates. These
climate zones are typically located poleward of
C
climates,
ranging from about 35° to 60° N and S latitude (Figure 9.2).
D
climates are known as “microthermal” because they have
winters sufficiently cold to ensure that snow can remain on
