GGY 181 Lecture Notes: CLIMATE
EARTH/SUN RELATIONSHIP
The world’s climates and their seasonality, or lack of it in the Tropics, are a result of the differential heating of
the land and water surfaces because the Earth is tilted 23.5 degrees on its axis. If the axis was perpendicular to
the Earth’s path around the Sun (the ecliptic), weather and climate would be invariable everywhere. It is the
axial tilt and the fact that the axis is always parallel to itself (parallelism of axis) and points toward Polaris, the
Pole Star, which causes the Earth’s seasonality. Because of axial tilt and parallelism of axis, duration of solar
radiation changes with season. Notice that the North Pole is always in the same position in the diagram below.
http://esminfo.prenhall.com/science/geoanimations/animations/01_EarthSun_E2.html
On the Equinoxes (equal night) (Spring ~ March 21; Fall ~September 23), every latitude receives 12 hours of
light and spends 12 hours in the dark. On the Summer Solstice, the northern hemisphere points toward the sun
and day length increases with latitude to 24 hours of day length above the Arctic Circle (66.5 degrees N). The
opposite is true of the Winter Solstice. On that day, there is 24 hours of darkness above the Arctic Circle, the
southern hemisphere experiences its summer and the Antarctic latitudes are in darkness.
McKnight, 1999
Because the Earth is a sphere, solar intensity changes with latitude. It is most intense (the sun is most nearly
overhead) in the Tropics. Intensity changes rapidly with season in the Mid-latitudes, and radiation is least
intense at all seasons in the high latitudes. This heat surplus in the tropics and heat deficit in the high latitudes
causes the atmosphere to flow, seeking temperature equilibrium and concomitant pressure systems and winds.
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WEATHER AND CLIMATE, VEGETATION AND SOILS
Weather is the condition of the atmosphere on any given day. It could be hot, cold or mild; raining, snowing,
or clear and windy or calm. It is the temperature, moisture content and movement of atmospheric gases at a
particular time. Climate is the long term average of daily weather phenomena of temperature, moisture
(humidity and precipitation), atmospheric pressure (high and low) and wind. Wilmington has a humid temperate
climate, although we have the occasional snow storm, drought or hurricane.
LACEMOPS is an acronym for the eight factors that determine world climates.
Latitude is most
important, but its effects may be moderated or intensified by other factors, such as Elevation and Continentality.
Latitude: Determines intensity and duration of incoming solar radiation, or insolation. Between 23 /12 º
N&S (the Tropics), insolation intensity is always high and duration is a ranges between 11 to 13 hours (12
hours every latitude on the Equinoxes and 12 hours around the equator). Intensity decreases with increasing
latitude, but duration is variable with season because of the Earth's axial tilt.
McKnight, 1999
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Air Masses: Take on the temperature and moisture characteristics of the surface over which they form. They
transport those characteristics to other locations via surface winds and the jet stream. There are four basic
types: maritime Polar (mP) is cool and moist; maritime Tropical (mT) is warm and wet; continental Polar
(cP) is cold and dry; continental Tropical (cT) is hot and dry.
McKnight, 1999
Continentality: Continental interiors have greater temperature extremes with season, especially at mid- and
high latitudes. They are generally subhumid to arid. Whereas, proximity to large bodies of water moderates
temperatures and may cause high humidity and precipitation.
Elevation: Temperatures cool (adiabatically) with increasing elevation, regardless of latitude because air is
thinner at altitude and the immediate source of atmospheric heating is the Earth's land and water surfaces,
which are, of course, ultimately warmed by the Sun. As air masses cool, moisture condenses and clouds
form. Continued cooling produces precipitation.
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Mountain Ranges: Include temperature changes with elevation, but also the Orographic effects of
windward side precipitation and leeward side aridity, as shown below. Adiabatic processes refer to the
cooling of gasses as they rise and experience less pressure through expansion and the heating of gasses as
they descend and experience more pressure as they are compressed. Mountains also block and funnel the
movement of air masses.
McKnight, 1999
Ocean Currents: In both hemispheres continental West coasts tend to have cool offshore currents because
of Coriolis. East coasts have warm offshore currents. The major exception is the North Atlantic Drift of the
Gulf Stream, which moderates the temperatures of Western Europe, which would be much colder because of
its high latitude. Where a very cold current is dominant at any latitude, arid conditions are found on shore
because little atmospheric moisture is available.
McKnight, 1999
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ENSO (El Niño and the Southern Oscillation) occurs when the usually cold Peru Current off the coast of Peru in
tropical and equatorial waters is submersed beneath much warmer equatorial waters. Air masses that form over
a strong El Nino (named for the Christ child because they usually form around Christmas, not only causes
heavy rains in the windward Andes, but influences dramatic changes in the “normal” climatic patterns in other
parts of the world.
McKnight, 1999
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Pressure Systems: Global and local pressure systems cause the movement of the atmosphere via wind,
which blows from areas of high pressure to low pressure centers. High pressure brings clear skies and no
rain, whereas precipitation generally accompanies low atmospheric
pressure.
McKnight, 1999
Storm Tracks: Includes midlatitude cyclones, also known as cold and warm frontal systems, and tropical
cyclones or hurricanes. Both tend to follow similar paths because of prevailing global wind patterns.
Surface Westerly winds and the polar jet stream in the midlatitudes blow fronts from West to East. NE and
SE Trade winds blow tropical systems eastward.
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Köppen’s Climates (Western Hemisphere)
McKnight, 1999
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Köppen’s Climates (Eastern Hemisphere)
McKnight, 1999.
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Köppen's Climates and Vegetation Types
Vladimir Köppen was a Russian botanist. His and Russia’s interest in maximizing agricultural productivity in
the late 19th century led him to examine the world’s natural potential vegetation regimes, which he used as a
proxy to assign climate types. Because vegetation responds to temperature and moisture, it was an elegant way
to understand climate. Forest types must have adequate moisture and a fairly long growing season. Desert
vegetation, such as cacti, responds to drought. Grasslands don’t receive as much rainfall as forests, hence few
trees. Tundra vegetation survives at high latitudes and elevations with very short growing seasons. Köppen
divided the world into six major climate regimes based on vegetation, with several sub-types based on moisture
and seasonal length.
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Precipitation types respond to climatic, seasonal and topographic or landscape characteristics.
Types of Precipitation
Kostbade and Wheeler, 1993
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Convectional: summer, tropics, mid-latitudes. Warm air rises and cools, usually producing an afternoon
shower, which is usually intense and of short duration.
Mid-latitude Cyclonic: winter; Cold and Warm fronts. Cold dry air moves into areas of warm moist air
and causes it to rise creating an intense, short duration event. For a warm front, the colder air pushes
warmer wetter air over cooler air and causes gentle and long duration precipitation events.
Tropical Cyclonic: summer–hurricanes in the Atlantic and typhoons in Asia. Big counter clockwise
spinning systems that bring high winds, heavy rains and destruction to low and mid-latitude coastal areas.
May move hundreds of miles inland.
Orographic: mountain barriers cause moisture-laden air to be lifted and thus cooled. The precipitation is
always on the windward side, while the leeward side is said to be in the rain shadow.
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Asian Monsoon:
Asian Winter Monsoon: Dry winds blow offshore from the Siberian High Pressure cell, bringing the dry
season.
Asian Summer Monsoon: Indian Ocean moisture flows onshore into a continental low, bringing the wet season.
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VEGETATION is a visible response to climate. Köppen used potential natural vegetation as a proxy for his
world climate classification. It was easy to see where the forests were and to determine the moisture and
temperature requirements of plants (or the absence of plants, which indicates dry and/or cold conditions). It
was much more difficult to map the data of long-term weather patters, although that was done too, most notably
by C. W. Thornthwaite, whose scheme was based on a measurement of evapo-transpiration. The space
composite image of the world’s vegetation does not differentiate among types, only the presence of forests and
grasslands (green) and deserts (yellow), tundra (brown), and ice (white).
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SOILS are climate and vegetation dependent and not just dirt. Particular soils form in a mineral parent material
under particular climate and vegetation regimes. Most people assume (wrongly) that the mineral their most
important component. However, the same mineral parent material may form very different soils under different
temperature, moisture and vegetation regimes. So, soil not only supports and provides nutrients for plants, it is
in turn modified by the climate it forms in and the vegetation (with its roots, litter and plant acids) that the soil
supports.
There are ten major soil families with thousands of variations based on climate, vegetation, mineral content,
slope, human disturbance and many other factors.
Much of the scientific work on soils is divided into two disciplines: pedology and agronomy. A pedologist is
interested in soil formation and typology for a variety of purposes from straight classification to engineering.
An agronomist is interested in soil for producing crops.
The major soil families are generally referred to by the following names, which are a combination of Greek
word roots with the suffix sol for soil. They generally have diagnostic layers or horizons that reflect their age
and other conditions. Some may have all horizons, others may be absent. For example, aridisols generally lack
horizonation.
The following list comes from a USDA document called Soil Taxonomy: The Seventh Approximation, which
was the seventh attempt to make sense of the huge variety of soils in the world. That it’s called an
“approximation” tells us that there is still much work to be done.
Major Soil Families of the USDA’s Seventh Approximation of Soil Classification
1. Alphasols: These soils are generally located in areas of deciduous forest with high aluminum content
and an acidic ph. Good agricultural soils, but they require soil amendments, such as fertilizers and
calcium carbonate or lime to decrease their acidity.
2. Ultisols: These are old or ultimate soils with high clay content. They are often worn out by heavy
agricultural use, as in Europe and the eastern US. If they’re red, they’re iron-rich; if they’re yellow,
they’re aluminum rich.
3. Histosols: Histos for tissue means that these are almost not soil because they contain mostly partially
decayed vegetation as in northern bogs, which are wet and cool, but they’re also are found in swamps
and marshes at mid- and low latitudes.
4. Vertisols: these have very high clay content, thus they shrink and swell and may invert. Texas has
vertisols and tractors have been reported to turn over in some of the cracks. These soils also cause road
beds and foundations to crack.
5. Aridisols: These arid desert soils are very fertile when irrigated but tend to be sandy and gravely. Too
much irrigation makes them too salty for agriculture.
6. Entisols: These recent soils have not been forming long. They may be very fertile, as in flood plain
soils or areas of recent volcanic or glacial deposition.
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7. Inceptisols: These are also young soils, at their inception, but in the sense that they form very slowly in
high latitudes or elevations where there is little vegetation, such as tundra, or on steep slopes.
8. Spodosols: These are boreal forest soils. Because they support conifers which drop acid producing
needle litter, the moisture that passes through them causes the nutrients to be washed, or leached, from a
sub-surface layer, giving it a white or ashy layer, from the Russian, spodos for ash.
9. Mollisols: These are the grassland soils, named for the mollifying effect of the grass roots on the deep,
nutrient rich yet low moisture soil body. They’re found in large areas with low precipitation in a few
places. Most famously the Russian Steppe, the African Sahel, and the American Great and High Plains.
10. Oxisols: These tropical rain forest soils are deeply weathered and oxidized by constant warmth and
moisture. They support the rain forest trees and vines, but are essentially devoid of organic material and
are not good for agriculture. Also known as laterites.
11. Unclassified Highland or Mountain Soils: These tend to be stony and poorly developed, especially at
higher elevations because of limited vegetation and steep slopes.
Major Soil Families
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McKnight, 2002
Using the thematic maps in the front of your atlas, compare the world’s climate, vegetation, soils and landform
maps. There is a striking degree of overlap for most regions.