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Unit 2: Chapter 2 Radiation Balance and the Thermal Environment

Terms in this set (68)

What is atmospheric temperature?
A measure of the kinetic energy contained within a unit of geographical space within air
What is air temperature?
The degree of warmth of a portion of the atmosphere
What is the standard altitude at which air temperature is measured?
About 1.2 metres above the ground surface
How is air temperature measured?
with a thermometer
What are the 3 large-scale geographic factors that influence air temperature?
Latitude, seasons/length of day and time of day
What is the maritime vs. continental effect?
The difference in annual and daily temperature that exists between coastal locations and those that are surrounded by bodies of land
What is specific heat?
The amount of energy it takes to raise one gram of a substance by one degree Celsius
Which specific heat is higher, water or land?
Water specific heat is five times greater than land specific heat
As water evaporates from the ocean, energy is transferred to the atmosphere in the form of....?
Latent heat
Why do high latitudes in the Southern hemisphere not experience the same extreme temperature range as those in the Northern hemisphere?
Because the Southern hemisphere is covered by more water than the Northern Hemisphere, and thus more of a maritime effect occurs in the Southern hemisphere than the northern hemisphere (where the continental effect dominates)
What are 4 factors which influence air temperature?
seasonality, angle of incidence, latitude and proximity to large bodies of water
Why does a temporal lag exist on an annual and daily basis between when the receipt of the highest amount of radiation occurs and when the warmest temperature takes place?
Because insolation is first absorbed by the surface of Earth before it is re-radiated as longwave radiation
What are the 3 ways the surface can gain/energy heat?
1. Shortwave/longwave radiation
2. Conduction (if the air is warmer than the surface)
3. Latent heat (if condensation/freezing takes place on the surface
What are the 3 ways the surface can lose heat/warm the air?
1. Longwave radiation
2. Conduction (if the surface is warmer than the air)
3. Latent heat (if evaporation occurs)
When are both the losses and gains of the surface temperature happen most?
During the daylight
Why is there is a lag of up to four hours between the period of maximum incoming radiation and the period of maximum surface temperature?
Because time must elapse before the soil warms up
Why is there is a lag between incoming and outgoing radiation for ground surface temperatures?
Because surface temperatures have to reach a certain level before longwave radiation becomes significant.
When is ground surface energy lost faster?
At night
Why is the air temperature's daily cycle process different than ground temperature's?
Because air is mobile and convection causes continual air movement
Describe the daily patterns of air temperatures (3)
1. Temperatures are lowest at times of lowest net radiation
2. Minimum temperatures are reached just at sunrise
3. Highest some time after maximum net and incoming radiation
What happens to the air during temporary or lower atmospheric temperature inversions?
Air is prevented from moving upward, lower air is stable. If it lasts for a long time air pollutants can be trapped near the ground
What is radiation inversion?
The most common type of temperature inversion. Caused by intense radiative cooling of the ground surface which causes cooling of lower atmosphere immediately above it.
Describe what happens to the air at higher altitude areas?
Thin atmosphere reflects and scatters less radiation
Absorbs much lower amounts of radiation, but radiation levels at ground surface can be very high
absorbs lower amounts of water vapour, carbon dioxide and little terrestrial radiation
Greenhouse effect is weakened
Nighttime/daytime heating becomes more intense with higher altitudes
Large daily range of temperature but lower mean temperatures with increased altitude
When does the minimum daily temperature usually occur?
About one half hour after sunrise
Why are urban surface temperatures warmer than rural temperatures during the day?
Because drier surfaces have less water to evaporate than most soils do
Why do maximum air and ground temperatures occur several hours after maximum daily insolation?
Ground temperatures respond to absorption of radiation by the surface and this response takes some time to develop
Also the warming of the atmosphere by longwave radiation is intense at high latitudes and surface temperatures can be high
However as the atmosphere retains little energy, radiative cooling by outgoing longwave radiation is also intense, thus temperature ranges are very large
What are the characteristics of temperature inversion?
Inversions reverse the normal environmental lapse rate so that temperatures increase with height. They are commonly caused by radiative cooling of the surface which in turn cools the lower air
Why does radiation fog often form over vegetated areas?
Fog can only form if water vapour is present in the air to be condensed when dew point is reached
Because of the greater amounts of water evaporated from the vegetation, fogs can be denser over vegetation than non vegetated areas where the air contains lower levels of vapour
How does altitude affect intensity of radiation and temperature regimes?
Absorption of short wave and longwave radiation is less because of the thinner atmosphere, and smaller amounts of shortwave are scattered.
Therefore, direct beam radiation is intense at higher latitudes and surface temperatures can be very high
However as the atmosphere retains little energy, radiative cooling by outgoing longwave radiation is also intense, thus temperature ranges are very large
How does latitude influence net radiation and annual temperature range?
Latitudes changes the angles of incoming solar radiation relative to the surface and causes variations in day length.
Lowe incident angles reduce radiation intensity but this reduction is offset by increased day lengths during summers in both hemispheres
This results in radiation levels being greater for the year as a whole in lower latitudes, although daily totals of radiation are seasonally greater at high latitudes than equatorial or tropical regions
What is topography?
the shape and configuration of the surface—landforms such as hill slopes, valley areas, and plateaus and the more detailed aspects of slope angle and orientation.
What are two major effects of topography?
it redistributes insolation at the Earth's surface, thereby influencing local temperature regimes.
It also significantly influences the movement of local air flows
Describe the continental climate
Hot in summer but cold in winter
Annual ranges of temperature are large, but large daily temperature ranges
Describe the maritime climate
Small annual temperature ranges, but daily temperature ranges are small
What is one of the major affects of topography?
it redistributes insolation at the Earth's surface, thereby influencing local temperature regimes. I
How does topography redistribution insolation at the Earth's surface?
by altering the angle and duration of the sun's rays because of changes in slope inclination and aspect (compass orientation).
Why do sloping areas receive more intense radiation than valley flats?
because they are inclined at a sharper angle relative to incoming solar rays.
What is a valley breeze?
When air over valley slopes is heated and rises by convection up the valley sides
What is adiabatic cooling?
when the warm air over valley slopes (valley breeze) cools down
What is a mountain breeze?
The reverse of valley breeze, happens at night when surfaces and air at high elevations lose heat rapidly through radiative cooling; then cold dense air flows back downslope
What are katabatic winds?
Powerful and large-scale examples of cold air drainage - these winds flow to lower elevations under the force of gravity, common in Greenland, Antartica and Alaska (known as taku)
What is slope aspect?
The orientation of the slope - whether it faces north, south, east, or west
Why is aspect an important variable in plant geography?
Because it is related to how intensely the sun strikes a given slope
What is an adret slope?
The slope that faces the sun most directly, or the slope which solar radiation arrives at a high angle
What is the ubac slope?
low-sun slope, normally has cooler microenvironment with less evaporation
In the northern hemisphere, which slope do trees grow more often?
the north facing ubac slopes
What is vertical zonation?
The change in vegetation that occurs with respect to elevation rather than latitude
What is the alpine tree line and where does it occur?
It occurs at high elevations in the mountains, above which are only scattered tundra, bare rocks and even perpetual snow - exists in all major mountain ranges
What is the circumpolar tree line?
The highest latitude at which trees can grow
What is the Krumholz zone?
Meaning "crippled wood", where trees are often bent in a particular direction that reflects prevailing winds
What is plant succession?
The natural changes that occur in a biome of a particular place over time, because of an array of vegetation, given the regional lclimate, water and soil variables
What is the difference between primary and secondary succession?
Primary - when plant succession begins on freshly deposited sediment
Seconndary - when plant succession occurs in an area that was disturbed through fire or other catastrophic event
Which slopes receive more insolation North of the Tropic of Cancer and why?
the sun always shines from the south, and therefore slopes that face south will receive more insolation than slopes that face north.
What happens to south-facing slopes in the northern hemisphere during midsummer?
soils dry out enough to impair the vigour and cover of the vegetation
The weakening of the vegetation through water stress can reach a point where it is no longer able to protect the soil.
Erosion and gullying from precipitation and runoff are often more intense
Second, soils may dry out so much that evapotranspiration is in fact eventually reduced because there is little moisture left.
Reduced evapotranspiration means less transfer of latent heat to the atmosphere; this lack of a heat escape intensifies the heating of the soil surface even more.
What are the four main factors that influence global patterns of isotherms
Latitude (general effects on insolation)
Continental-ocean contrasts
Ocean currents
Altitude
When does temperature inversion occur?
When warm air lies atop cooler air next to the ground
What are the seasonal temperature contrasts for places located well inland and far from oceans?
They are stronger from winter to summer than those near oceans (NOT unstable)
What are the different thermal qualities of water and soil
Water: Has high specific heat (about 5x more than land), raising the temperature by 1 degree takes 5x more energy. Able to store large amounts of heat energy and releases it slowly
Soil: Heats up more rapidly, but distributed less evenly because of water's thermal conductivity, and because sunlight can penetrate to some depth. Temperature rises quickly in the surface, and is also lost quickly to the atmosphere
How do clouds affect local energy budgets?
They reflect incoming shortwave radiation back to space by scattering it as diffuse radiation to the surface.
Clouds break insolation into direct beam radiation and diffuse radiation
Reflection of shortwave radiation by clouds will cause depletion of amounts of radiation by reaching the surface
Clouds also direct longwave radiation to the surface (counter radiation) which heats the lower atmosphere
Where is the most continental region of B.C and why?
Peace River East of the Rockies, because of its distance from the ocean, barriers to Pacific air by Cordillera, influence of Arctic conditions/summer heating over interior plains
Where is the most maritime region of Canada?
The outer coast of B.C. (not Maritime provinces) because of exposure to coastal thermal qualities of Pacific water, air masses and prevailing westerly flow
How does aspect influence temperature?
By redistributing energy at the surface
How do slope angles cause variations in radiation and temperatures?
By influencing the angle of inclination of the sun's rays to the surface
Why are vegetation zones on south or southwest facing slopes of mountains in the northern hemisphere generally higher in elevation?
Because temperatures decrease and precipitation increases with an increase in elevation. The environmental gradient is paralleled by transitions to more cold tolerant and moist tolerant plat species, and are clearly marked altitudinal zonation of vegetation. Vegetation zones are pushed upwards relative tot heir altitudinal position
What are the climatic and sol conditions on southwest slopes?
They are drier and warmer at a given altitude,
Where is cold air drainage most likely to occur?
In topographic depressions
Why do fruit tree growers sprinkle trees with water, causing ice to form on trees, as protection against freezing damage during heavy overnight frosts?
When water freezes on plants it releases latent heat of fusion, and the energy release rate is enough to prevent temperature of plants from falling below 0 degrees (most plants survive but suffer lower temperature and frost damage)
Why are isotherms in the southern hemisphere generally aligned in a more E-W pattern?
Because of expanses of ocean and relatively small continental areas. Thermal contrasts between land and ocean are less than i the northern hemisphere and contrasting seasonal shifts in isotherms are not so marked.
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