Seasonal & Daily TemperaturesSeasonal & Daily Temperatures

This chapter discusses:This chapter discusses:

1.1. The role of Earth's tilt, revolution, & rotatation The role of Earth's tilt, revolution, & rotatation in causing locational, seasonal, & daily in causing locational, seasonal, & daily temperature variationstemperature variations

2.2. Methods & tools for measuring temperatureMethods & tools for measuring temperature

Seasons & Sun's DistanceSeasons & Sun's Distance

Earth's surface is 5 million kilometers further from the sun in Earth's surface is 5 million kilometers further from the sun in summer than in winter, indicating that seasonal warmth is summer than in winter, indicating that seasonal warmth is controlled by more than solar proximity.controlled by more than solar proximity.

Figure 3.1Figure 3.1

Seasons & Solar IntensitySeasons & Solar Intensity

Figure 3.2Figure 3.2

Solar intensity, defined as the energy per area, governs earth's Solar intensity, defined as the energy per area, governs earth's seasonal changes.seasonal changes.

A sunlight beam that strikes at an angle is spread across a greater 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 surface area, and is a less intense heat source than a beam impinging directly.impinging directly.

Solstice & EquinoxSolstice & Equinox

Figure 3.3Figure 3.3Earth's tilt of 23.5° and revolution around the sun creates seasonal Earth's tilt of 23.5° and revolution around the sun creates seasonal solar exposure and heating patterns.solar exposure and heating patterns. A solstice tilt keeps a polar region with either 24 hours of light or 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 A equinox tilt perfectly provides 12 hours of night and 12 hours of day for all non-polar regions.day for all non-polar regions.

24 Hours of Daylight24 Hours of Daylight

Figure 3.4Figure 3.4

Summer north of the artic circle will reveal a period of 24 hour Summer north of the artic circle will reveal a period of 24 hour sunlight, where the earth's surface does not rotate out of solar sunlight, where the earth's surface does not rotate out of solar exposure, but instead experiences a midnight sun.exposure, but instead experiences a midnight sun.

Earth's Tilt & AtmosphereEarth's Tilt & Atmosphere

Figure 3.5Figure 3.5

Earth's atmosphere reduces the amount of insolation Earth's atmosphere reduces the amount of insolation striking earth's surface.striking earth's surface.

Earth's atmosphere and tilt combine to explain variation Earth's atmosphere and tilt combine to explain variation in received solar radiation.in received solar radiation.

Figure 3.6Figure 3.6

Earth's Unequal HeatingEarth's Unequal Heating

Figure 3.7Figure 3.7

Incoming solar radiation is not evenly distributed across all lines of Incoming solar radiation is not evenly distributed across all lines of latitude, creating a heating imbalance.latitude, creating a heating imbalance.

Earth's Energy BalanceEarth's Energy Balance

Earth's annual Earth's annual energy balance energy balance between solar between solar insolation and insolation and terrestrial infrared terrestrial infrared radiation is radiation is achieved locally at achieved locally at only two lines of only two lines of latitude.latitude.

A global balance is A global balance is maintained by maintained by excess heat from excess heat from the equatorial the equatorial region transferring region transferring toward the poles.toward the poles.

Figure 3.8Figure 3.8

Longer Northern Spring & SummerLonger Northern Spring & Summer

Figure 3.9Figure 3.9

Earth reaches its greatest distance from the sun during a northern Earth reaches its greatest distance from the sun during a northern summer, and this slows its speed of revolution.summer, and this slows its speed of revolution.

The outcome is a spring and summer season 7 days longer than that The outcome is a spring and summer season 7 days longer than that experienced by the southern hemisphere.experienced by the southern hemisphere.

Local Solar ChangesLocal Solar Changes

Figure 3.10Figure 3.10

Northern Northern hemisphere hemisphere sunrises are in sunrises are in the southeast the southeast during winter, during winter, but in the but in the northeast in northeast in summer.summer.

Summer noon Summer noon time sun is time sun is also higher also higher above the above the horizon than horizon than the winter the winter sun.sun.

Landscape Solar ResponseLandscape Solar Response

Figure 3.11Figure 3.11

South facing slopes receive greater insolation, providing energy to South facing slopes receive greater insolation, providing energy to melt snow sooner and evaporate more soil moisture.melt snow sooner and evaporate more soil moisture. North and south slope terrain exposure often trigger differences in North and south slope terrain exposure often trigger differences in plant types and abundance.plant types and abundance.

Daytime WarmingDaytime Warming

Figure 3.12Figure 3.12

Solar radiation heats the Solar radiation heats the atmosphere from below by soil atmosphere from below by soil conduction and gas convection.conduction and gas convection.

Winds create a forced convection Winds create a forced convection of vertical mixing that diminishes of vertical mixing that diminishes steep temperature gradients.steep temperature gradients.

Figure 3.13Figure 3.13

Temperature LagsTemperature Lags

Earth's surface Earth's surface temperature is a temperature is a balance between balance between incoming solar incoming solar radiation and outgoing radiation and outgoing terrestrial radiation.terrestrial radiation.

Peak temperature lags Peak temperature lags after peak insolation after peak insolation because earth because earth continues to warm continues to warm until infrared until infrared radiation exceeds radiation exceeds insolation.insolation.

Figure 3.14Figure 3.14

Nighttime CoolingNighttime Cooling

Figure 3.15Figure 3.15

Earth's surface has efficient radiational cooling, which creates a Earth's surface has efficient radiational cooling, which creates a temperature inversion that may be diminished by winds.temperature inversion that may be diminished by winds.

Evening length, water vapor, clouds, and vegetation affect Evening length, water vapor, clouds, and vegetation affect earth's nighttime cooling.earth's nighttime cooling.

Figure 3.16Figure 3.16

Cold Dense AirCold Dense Air

Nighttime radiational cooling increases air density.Nighttime radiational cooling increases air density.

On hill slopes, denser air settles to the valley bottom, creating a On hill slopes, denser air settles to the valley bottom, creating a thermal belt of warmer air between lower and upper cooler air.thermal belt of warmer air between lower and upper cooler air.

Figure 3.17Figure 3.17

Protecting Crops from BelowProtecting Crops from Below

Impacts of radiational cooling can be diminished by orchard Impacts of radiational cooling can be diminished by orchard heaters creating convection currents to warm from below and by heaters creating convection currents to warm from below and by wind machines mixing warmer air from above.wind machines mixing warmer air from above.

Figure 3.18Figure 3.18Figure 3.19Figure 3.19

Protecting Crops from AboveProtecting Crops from Above

Crops subjected Crops subjected to below freezing to below freezing air are not helped air are not helped by convection or by convection or mixing, but by mixing, but by spraying water.spraying water.

The cold air uses The cold air uses much of its much of its energy to freeze energy to freeze the water, leaving the water, leaving less to take less to take temperatures temperatures below 0° C that below 0° C that damage the crop.damage the crop.

Figure 3.20Figure 3.20

Controls of TemperatureControls of Temperature

Earth's air temperature is governed by length of day Earth's air temperature is governed by length of day and intensity of insolation, which are a function of:and intensity of insolation, which are a function of:

1)1) latitudelatitude

Additional controls are:Additional controls are:2) land and water2) land and water3) ocean currents3) ocean currents4) elevation4) elevation

January IsothermsJanuary Isotherms

Figure 3.21Figure 3.21

Latitude Latitude determines that determines that earth's air earth's air temperatures temperatures are warmer at are warmer at the equator than the equator than at the poles, but at the poles, but land and water, land and water, ocean currents, ocean currents, and elevation and elevation create additional create additional variations.variations.

July Global IsothermsJuly Global Isotherms

The southern The southern hemisphere hemisphere has fewer land has fewer land masses and masses and ocean currents ocean currents that encircle that encircle the globe, the globe, creating creating isotherms that isotherms that are more are more regular than regular than those in the those in the northern northern hemisphere.hemisphere.

Figure 3.22Figure 3.22

Daily Temperature RangeDaily Temperature Range

Figure 3.23Figure 3.23

Earth's surface Earth's surface efficiently efficiently absorbs solar absorbs solar energy and energy and efficiently efficiently radiates infrared radiates infrared energy, creating a energy, creating a large diurnal large diurnal temperature temperature range (max - range (max - min) in the lower min) in the lower atmosphere.atmosphere.

Regional TemperaturesRegional Temperatures

Regional differences in Regional differences in temperature, from annual or temperature, from annual or daily, are influenced by daily, are influenced by geography, such as latitude, geography, such as latitude, altitude, and nearby water or altitude, and nearby water or ocean currents, as well as heat ocean currents, as well as heat generated in the urban area.generated in the urban area.

Figure 3.24Figure 3.24

Heating Degree DayHeating Degree Day

Figure 3.25Figure 3.25

Temperature data are analyzed to determine when living space will Temperature data are analyzed to determine when living space will likely be heated (e.g. when below 65° F) and how much fuel is likely be heated (e.g. when below 65° F) and how much fuel is required for that region.required for that region.

Cooling & Growing Degree DaysCooling & Growing Degree Days

Figure 3.26Figure 3.26

Daily temperature data are also used to determine cooling loads for Daily temperature data are also used to determine cooling loads for living space above 65° F, as well as growing hours for specific crops living space above 65° F, as well as growing hours for specific crops above a base temperature.above a base temperature.

Recording ThermometerRecording Thermometer

Figure 3.27Figure 3.27

Non-digital thermometers recorded maximum and minimum Non-digital thermometers recorded maximum and minimum temperature using simple designs to temporarily trap the temperature using simple designs to temporarily trap the mercury or a marker along the thermometer scale.mercury or a marker along the thermometer scale.

Figure 3.28Figure 3.28

Technological UpgradesTechnological Upgrades

Figure 3.29Figure 3.29

Pen and lever recording drums Pen and lever recording drums required regular calibration for required regular calibration for accurate data.accurate data.

Modern weather stations Modern weather stations predominantly use digital data predominantly use digital data recording techniques that are recording techniques that are less likely to introduce data error less likely to introduce data error and generate data more readily and generate data more readily analyzed by computers.analyzed by computers.

Figure 3.30Figure 3.30