Unformatted text preview: Seasonal & Daily Temperatures Seasonal This chapter discusses: 1. The role of Earth's tilt, revolution, & rotatation The in causing locational, seasonal, & daily temperature variations temperature 1. Methods & tools for measuring temperature Seasons & Sun's Distance Seasons Figure 3.1 Earth's surface is 5 million kilometers further from the sun in Earth's summer than in winter, indicating that seasonal warmth is controlled by more than solar proximity. controlled Seasons & Solar Intensity Seasons Figure 3.2 Solar intensity, defined as the energy per area, governs earth's Solar seasonal changes. seasonal A sunlight beam that strikes at an angle is spread across a greater surface area, and is a less intense heat source than a beam impinging directly. impinging Solstice & Equinox Solstice Earth's tilt of 23.5° and revolution around the sun creates seasonal Earth's solar exposure and heating patterns. solar A solstice tilt keeps a polar region with either 24 hours of light or darkness. darkness. A equinox tilt perfectly provides 12 hours of night and 12 hours of day for all non-polar regions. day Figure 3.3 24 Hours of Daylight 24 Figure 3.4 Summer north of the artic circle will reveal a period of 24 hour Summer sunlight, where the earth's surface does not rotate out of solar exposure, but instead experiences a midnight sun. exposure, Earth's Tilt & Atmosphere Earth's Figure 3.5 Figure 3.6 Earth's atmosphere reduces the amount of insolation Earth's striking earth's surface. striking Earth's atmosphere and tilt combine to explain variation in received solar radiation. in Earth's Unequal Heating Earth's Figure 3.7 Incoming solar radiation is not evenly distributed across all lines of Incoming latitude, creating a heating imbalance. latitude, Earth's Energy Balance Earth's
Earth's annual Earth's energy balance between solar insolation and terrestrial infrared radiation is achieved locally at only two lines of latitude. latitude. A global balance is maintained by excess heat from the equatorial region transferring toward the poles. toward Figure 3.8 Longer Northern Spring & Summer Longer Figure 3.9 Earth reaches its greatest distance from the sun during a northern Earth summer, and this slows its speed of revolution. summer, The outcome is a spring and summer season 7 days longer than that experienced by the southern hemisphere. experienced Local Solar Changes Local
Northern Northern hemisphere sunrises are in the southeast during winter, but in the northeast in summer. summer. Summer noon time sun is also higher above the horizon than the winter sun. sun. Figure 3.10 Landscape Solar Response Landscape Figure 3.11 South facing slopes receive greater insolation, providing energy to South melt snow sooner and evaporate more soil moisture. melt North and south slope terrain exposure often trigger differences in plant types and abundance. plant Daytime Warming Daytime Solar radiation heats the Solar atmosphere from below by soil conduction and gas convection. conduction Figure 3.12 Winds create a forced convection Winds of vertical mixing that diminishes steep temperature gradients. steep
Figure 3.13 Temperature Lags Temperature
Earth's surface Earth's temperature is a balance between incoming solar radiation and outgoing terrestrial radiation. terrestrial Peak temperature lags after peak insolation because earth continues to warm until infrared radiation exceeds insolation. insolation.
Figure 3.14 Nighttime Cooling Nighttime Figure 3.15 Figure 3.16 Earth's surface has efficient radiational cooling, which creates a Earth's temperature inversion that may be diminished by winds. temperature Evening length, water vapor, clouds, and vegetation affect earth's nighttime cooling. earth's Cold Dense Air Cold Figure 3.17 Nighttime radiational cooling increases air density. On hill slopes, denser air settles to the valley bottom, creating a thermal belt of warmer air between lower and upper cooler air. thermal Protecting Crops from Below Protecting Figure 3.18 Figure 3.19 Impacts of radiational cooling can be diminished by orchard Impacts heaters creating convection currents to warm from below and by wind machines mixing warmer air from above. wind Protecting Crops from Above Protecting
Crops subjected Crops to below freezing air are not helped by convection or mixing, but by spraying water. spraying The cold air uses much of its energy to freeze the water, leaving less to take temperatures below 0° C that damage the crop. damage Figure 3.20 Controls of Temperature Controls Earth's air temperature is governed by length of day Earth's and intensity of insolation, which are a function of: and 1) latitude Additional controls are: Additional 2) land and water 3) ocean currents 4) elevation January Isotherms January Latitude Latitude determines that earth's air temperatures are warmer at the equator than at the poles, but land and water, ocean currents, and elevation create additional variations. variations.
Figure 3.21 July Global Isotherms July
The southern The hemisphere has fewer land masses and ocean currents that encircle the globe, creating isotherms that are more regular than those in the northern hemisphere. hemisphere.
Figure 3.22 Daily Temperature Range Daily Earth's surface Earth's efficiently absorbs solar energy and efficiently radiates infrared energy, creating a large diurnal temperature range (max min) in the lower atmosphere. atmosphere.
Figure 3.23 Regional Temperatures Regional Regional differences in Regional temperature, from annual or daily, are influenced by geography, such as latitude, altitude, and nearby water or ocean currents, as well as heat generated in the urban area. generated Figure 3.24 Heating Degree Day Heating Figure 3.25 Temperature data are analyzed to determine when living space will Temperature likely be heated (e.g. when below 65° F) and how much fuel is required for that region. required Cooling & Growing Degree Days Cooling Figure 3.26 Daily temperature data are also used to determine cooling loads for Daily living space above 65° F, as well as growing hours for specific crops above a base temperature. above Recording Thermometer Recording Figure 3.27 Figure 3.28 Non-digital thermometers recorded maximum and minimum Non-digital temperature using simple designs to temporarily trap the mercury or a marker along the thermometer scale. mercury Technological Upgrades Technological Pen and lever recording drums Pen required regular calibration for accurate data. accurate
Figure 3.29 Modern weather stations Modern predominantly use digital data recording techniques that are less likely to introduce data error and generate data more readily analyzed by computers. analyzed Figure 3.30 ...
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This note was uploaded on 03/13/2010 for the course ATOC 245 taught by Professor Aparisa during the Spring '10 term at McGill.
- Spring '10