Meteorology: Understanding the Atmosphere Ackerman and Knox
Climate Spatial Scales
Global climate is the largest spatial scale. We are concerned with the global scale when we refer to the climate of the globe, its hemispheres, and differences between land and oceans. Energy input from the sun is largely responsible for our global climate. The solar gain is defined by the orbit of Earth around the sun and determines things like the length of seasons. The distribution of land and ocean is another import influence on the climatic characteristics of the Earth. Contrasting the climate of the Northern Hemisphere, which is approximately 39% land, with the Southern Hemisphere, which only has 19% land, demonstrates this (see the table below). The yearly average temperature of the Northern Hemisphere is approximately 15.2C, while that of the Southern Hemisphere is 13.3C. The presence of the water reduces the annual average temperature. The land reduces the winter average temperature while increasing the average temperature during summer. As a result, the annual amplitude of the seasonal temperature is nearly twice as great for the Northern Hemisphere. The Northern Hemisphere has a large variation in the monthly mean temperature.
The land absorbs and loses heat faster than the water. Over land, the heat is distributed over a thin layer, while conduction, convection and currents mix the energy over a fairly thick layer of water. Soil, and the air near it, therefore follow radiation gains more closely than water. For this reason, continental climates have a wider temperature variation. We observed this in Chapter 3 by comparing the seasonal cycles of temperatures for different regions of the globe.
The average temperatures of the Northern Hemisphere and Southern Hemisphere for winter, summer and the year. The Annual Range is give as well as the differences between the Hemispheres. Differences between the Hemispheres are caused by the differences in the distribution of land and water.
The major factors that determine global climate
also influence climate on a regional scale. Regional climates are influenced
by water bodies and mountain ranges. Lakes exert a moderating influence on
local climate, in a manner similar to how oceans affect larger climate.
The Great Lakes are a good example for demonstrating the impact of lakes on
climate. We saw in Chapter 7 how the Great Lakes effect snow
fall. The Great Lakes also influence the temperature of the
region. The figure below shows the average land temperature versus
the average surface lake temperature in the Southern Lake Michigan region. The
temperature of the water is lower than the land from mid-March to August.
Largest differences occur from mid-May to early June. The water
temperature is greater than that of the land from late August to mid March,
with the largest differences in late November and early-December in late
autumn and winter. Exchanges of heat and moisture above the lakes
is the key to weather modification by the Great Lakes. The
influence of large water bodies on the weather of surrounding regions is most
marked when the temperature differences are greatest. .
Large mountains influence regional
climates. They provide barriers for the air. Large mountain ranges
that are oriented east-west can block cold air outbreaks from reaching regions
that are more southern. You can observe this by comparing the annual mean
temperature of a city south of large mountain barrier with a city at a similar
latitude but with no mountain barrier. Lahore, India, (31.5N)
located south of the Himalayan Mountain Range has an average temperature of
12.8C, while the temperature of Austin, TX USA (30.25N) has an average
temperature of only 10.4C.
Variations in climate can be observed over a
short distance. Small-scale climates are referred to as microclimates.
Examples of microscale climates include the climate of a cornfield, a house, a
patio, or a sand dune. Microclimates can be very different across
a particular region. Topography, presence or absence of water, exposure to the
sun, and soil conditions are important factors that determine microclimates.