Chapter 3 Seasonal and Daily Temperatures 2019 Cengage Learning Inc All rights reserved Why Earth Has Seasons 1 of 10 Earth elliptical path around Sun every 365 days and 6 hoursleap year every 4 years ID: 769726
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Chapter 3 Seasonal and Daily Temperatures © 2019 Cengage Learning, Inc. All rights reserved.
Why Earth Has Seasons (1 of 10) Earth: elliptical path around Sun every 365 days and 6 hours—leap year every 4 years) Rotates counterclockwise (eastward) every 24 hours on its axis Distance from Earth to Sun: 150 million km (93 million mi) Closest in January (147 million km) Farthest in July (152 million km)Distance: not the only factor for seasons
The Elliptical Path of Earth
Why Earth Has Seasons (2 of 10) Seasons are regulated by the amount of solar energy. Solar energy at Earth’s surface depends on angle of light received and length of receipt. Direct solar energy leads to more heat. Longer and clearer days lead to more solar energy. Summer in Northern HemisphereWinter in Southern Hemisphere
Sunlight that Strikes a Surface at an Angle
Why Earth Has Seasons (3 of 10)
Why Earth Has Seasons (4 of 10) Seasons in the Northern Hemisphere Summer solstice (Jun 21): Sun is directly above Tropic of Cancer—Northern Hemisphere days are greater than 12 hours. Winter solstice (Dec 21): Sun is directly above Tropic of Capricorn—Northern Hemisphere days are less than 12 hours. Autumnal (Sep 22) and Vernal (Mar 20) Equinox: Sun directly above Equator—all Earth locations have a 12-hour day.
Why Earth Has Seasons (5 of 10) Seasons in the Southern Hemisphere Opposite timing of Northern Hemisphere Closer to Sun in summer but not significant difference from northern hemisphere due to: Greater amount of water (81 percent of total surface area as compared to 61 percent in Northern Hemisphere) absorbing heat Shorter season—spring and summer in North Hemisphere are ~1 week longer
Why Earth Has Seasons (6 of 10)
Why Earth Has Seasons (7 of 10)
Why Earth Has Seasons (8 of 10)
Why Earth Has Seasons (9 of 10)
Why Earth Has Seasons (10 of 10)
Local Seasonal Variations (1 of 2) At middle latitudes in the Northern Hemisphere Objects facing south receive more sunlight than those facing north South facing leads to more evaporation and drier soils Implications for agriculture, skiing, home building, natural vegetation, etc.
Local Seasonal Variations (2 of 2)
Daily Warming and Cooling Air Near the Surface (1 of 15) Each day is like a tiny season with a cycle of heating and cooling. Daytime heating Air is a poor conductor, so initial morning heating only impacts air next to the ground. Around noon, Earth receives the most intense solar rays. Maximum daytime temperature is generally in late afternoon—lag between maximum solar heating and maximum air temperature
Daily Warming and Cooling Air Near the Surface (2 of 15) “Hot” molecules at the ground’s surface move upward in the atmosphere. Wind speeds heat exchange between colder upper air and warmer lower air—forced convection aids mixing. Maximum daily temperature generally occurs between 3:00 and 5:00 pm on cloud-free days. - Earlier with clouds and haze Air temperature depends on soil and vegetation types and moisture content.
Daily Warming and Cooling Air Near the Surface (3 of 15) Highest air temperature reliably observed at 57°C (134°F) in Death Valley, California. Hottest place on Earth—Dallol, Ethiopia—has an average daily maximum temperature of 38°C (100°F). Increased humidity prevents the temperature from climbing as high as in drier climates.
Daily Warming and Cooling Air Near the Surface (4 of 15) Heat energy at the ground’s surface is dissipated. Ground and air cool by radiational cooling creating a radiation inversion. Air above surface is warmer than the ground. Radiation inversions: stronger on clear, long, windless, and dry nights Top of the inversion: ~100 m (330 ft) in middle latitudes and ~1,000 m (3,300 ft) in polar regions
Daily Warming and Cooling Air Near the Surface (5 of 15)
Daily Warming and Cooling Air Near the Surface (6 of 15)
Daily Warming and Cooling Air Near the Surface (7 of 15)
Daily Warming and Cooling Air Near the Surface (8 of 15) Cold air often settles in valleys freezing crops. Farmers often use orchard heaters or wind machines to create convection near the ground.
Daily Warming and Cooling Air Near the Surface (9 of 15)
Daily Warming and Cooling Air Near the Surface (10 of 15)
Daily Warming and Cooling Air Near the Surface (11 of 15)
Daily Warming and Cooling Air Near the Surface (12 of 15) Lowest air temperature reliably observed: 89°C (−129°F) at Vostok, Antarctica Coldest place on Earth: South Pole (9,000 ft) with average temperature −46°C (−51°F)
High Temperatures throughout the World
Low Temperatures throughout the World
Daily Warming and Cooling Air Near the Surface (13 of 15) Greatest variation in daily temperature occurs at Earth’s surface Daily range of temperature Largest on clear, dry days in deserts Smallest in areas near water and away from large cities (due to urban heat island effect) Mean (average) daily temperatureReported on weather forecasts 30-year average is called “normal”
Daily Warming and Cooling Air Near the Surface (14 of 15) Main controllers of daily temperature: Latitude Land and water distribution Ocean currents ElevationIsotherms: lines connecting places with same temperature on a mapAnnual range of temperature: difference between warmest and coldest month
Daily Warming and Cooling Air Near the Surface (15 of 15) Annual range of temperature Largest over interior continental land masses Smallest over large bodies of water Larger for inland cities than coastal cities Mean annual temperature: average temperature for the entire year
Average Air Temperature Near Sea Level
Monthly Temperature Data and Annual Temperature Range
Temperature Data
Applications of Air Temperature Data (1 of 2) Heating degree day: an index for fuel consumption Assumes furnace use when mean daily temperature drops below 65°F Subtract mean daily temperature from 65°F Example: 65°F – 64°F = 1 heating degree
Applications of Air Temperature Data (2 of 2) Cooling degree day: an index used in the United States to determine cooling requirements Assumes that cooling use (interior) begins when average daily temperature is greater than 65°F Growing degree day: used by farmers as a guide to planting and for determining the approximate dates when a crop will be ready for harvesting
Mean Annual Total Heating Degree Days Across the United States (Base 65°F)
Mean Annual Total Cooling Degree Days Across the United States (Base 65°F)
Estimated Growing Degree Days for Certain Naturally Grown Agricultural Crops to Reach Maturity Table 3.2 Estimated Growing Degree Days for Certain Naturally Grown Agricultural Crops to Reach Maturity CROP (VARIETY,LOCATION) BASE TEMPERATURE (°F) GROWING DEGREE DAYS TO MATURITY Beans (Snap/South Carolina) 50 1200–1300 Corn (Sweet/Indiana) 50 2200–2800 Cotton (Delta Smooth Leaf/Arkansas) 60 1900–2500 Peas (Early/Indiana) 40 1100–1200 Rice (Vegold/Arkansas) 60 1700–2100 Wheat (Indiana) 40 2100–2400
Air Temperature and Human Comfort (1 of 7) Humans body temperature Stabilized through metabolism Radiant energy is absorbed and emitted Heat is lost and gained by conduction and convection Sensible temperature: perceived temperatureOften higher or lower than actual temperatureWind-chill index (WCI)—how cold it feels
Wind-Chill Equivalent Temperature (°F) (1 of 2) TABLE 3.3 Wind-Chill Equivalent Temperature (°F). A 20-mi/hr Wind Combined with an Air Temperature of 20°F Produces a Wind-Chill Equivalent Temperature of 4 F ° .* AIR TEMPERATURE (°F) WIND SPEED (MI/HR) Calm 40 35 30 25 20 15 10 5 0 –5 –10 –15 –20 –25 –30 –35 –40 5 36 31 25 19 13 7 1 –5 –11 –16 –22 –28 –34 –40 –46 –52 –57 10 34 27 21 15 9 3 –4 –10 –16 –22 –28 –35 –41 –47 –53 –59 –66 15 32 25 19 13 6 0 –7 –13 –19 –26 –32 –39 –45 –51 –58 –64 –71 20 30 24 17 11 4 –2 –9 –15 –22 –29 –35 –42 –48 –55 –61 –68 –74 25 29 23 16 9 3 –4 –11 –17 –24 –31 –37 –44 –51 –58 –64 –71 –78 30 28 22 15 8 1 –5 –12 –19 –26 –33 –39 –46 –53 –60 –67 –73 –80 35 28 21 14 7 0 –7 –14 –21 –27 –34 –41 –48 –55 –62 –69 –76 –82
Wind-Chill Equivalent Temperature (°F) (2 of 2) AIR TEMPERATURE (°F) WIND SPEED (MI/HR) Calm 40 35 30 25 20 15 10 5 0 –5 –10 –15 –20 –25 –30 –35 –40 40 27 20 13 6 –1 –8 –15 –22 –29 –36 –43 –50 –57 –64 –71 –78 –84 45 26 19 12 5 –2 –9 –16 –23 –30 –37 –44 –51 –58 –65 –72 –79 –86 50 26 19 12 4 –3 –10 –17 –24 –31 –38 –45 –52 –60 –67 –74 –81 –88 55 25 18 11 4 –3 –11 –18 –25 –32 –39 –46 –54 –61 –68 –75 –82 –89 60 2517103–4 –11 –19 –26 –33 –40 –48 –55 –62 –69 –76 –84 –91 *Dark-shaded areas represent conditions where frostbite occurs in 30 minutes or less.
Air Temperature and Human Comfort (2 of 7) Frostbite: freezing of the skin Occurs first on hands and feet Hypothermia: rapid, progressive mental and physical collapse due to lowering body temperature First symptom is exhaustion, followed by lack of judgment, stupor, collapse, and death. Most cases occur between 32°F and 50°F.
Air Temperature and Human Comfort (3 of 7) Types of thermometers Liquid-in-glass thermometer: tube with alcohol or mercury inside glass—used for surface air temperature Maximum thermometer: generally a tube with mercury—measures highest temperature Minimum thermometer: generally alcohol as the liquid—measures lowest temperature
Air Temperature and Human Comfort (4 of 7) Types of thermometers Electrical thermometer uses electrical resistance (usually of platinum or nickel) to determine temperature—includes thermocouples and thermistors (ceramic). Radiometer measures emitted radiation. Bimetallic thermometer uses different metals (e.g., brass and iron) to determine temperature
A Section of a Minimum Thermometer
Air Temperature and Human Comfort (5 of 7) Thermograph—measures and records temperature Instrument shelter provides instruments protection from wind, rain, snow, etc. Painted white to reflect sunlight Face north to avoid direct Sun exposure Has louvered sides for air flowMounted ~1.5 m above ground
Air Temperature and Human Comfort (6 of 7)
Air Temperature and Human Comfort (7 of 7)