EOG 1200 Module 1 SMU earth sun radiations systems

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Objectives

The objectives of this lab are:

  • To describe differences in seasonal variations at different latitudes on Earth.
  • To explain differences in seasonal variations.

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SAINT MARY’S UNIVERSITY DEPARTMENT OF GEOGRAPHY GEOG 1200 Module 1: EARTH-SUN RADIATION SYSTEM AND SEASONS Objectives The objectives of this lab are: 1. To describe differences in seasonal variations at different latitudes on Earth. 2. To explain differences in seasonal variations. Section 1: Key Terms The following key terms are relevant to this lab. • Equator • Subsolar point • Axial tilt • North Pole • Solar declination • Circle of illumination • South Pole • • Revolution • Arctic Circle Summer Solstice (June 21) Rotation Antarctic Circle • • • Winter Solstice (Dec. 21) • Tropic of Cancer • • Tropic of Capricorn Spring (or Vernal) Equinox (March 21) • Autumnal Equinox (Sept. 22) Note: Dates for solstices and equinoxes are for the Northern Hemisphere. For the Southern Hemisphere the seasonal labels are reversed. Before moving ahead, ensure your understanding of these terms. Most found in Chapter of your textbook. Figure 1 shows the names and positions of the seven important lines of latitude on Earth: Figure 1 Section 2: Describing Seasonal Variations on Earth For this section the amount of insolation (incoming solar radiation), as measured at the top of the atmosphere (TOA), will be used to represent the prime control of seasonal variations on Earth. Differences in seasonal variations at different latitudes on Earth will be described by plotting graphs of insolation over time, with the values to plot to be obtained by reading directly off Figure 2 (next page). 1 Values for the North Pole (W m-2): Figure 2 1. J: 0 F: 0 M: 0 A: 240 M: 450 J: 530 J: 480 A: 290 S: 40 O: 0 N: 0 D: 0 (from Christopherson and Byrne, 2009, Figure 2.10) At each of the latitudes a) – h) below, use Figure 2 above to obtain values of daily insolation (units: Watts per square meter, or W m-2) for each month of the year. Read off the values at the middle of each month’s column, and estimate intermediate values between the lines. For example, the value for January at 40°N would be ~180 W m-2. (If you read off the value for January at 40°N, do you get this answer? Try it now and make sure.) Plot the values on the graphs provided (on a separate sheet) and connect the points with smoothed lines. To help you get started, values for the North Pole are given (above right) and the points have been plotted on the corresponding graph. Go through the North Pole values to confirm you understand how to read values from the graph. Note that the June value must be greater than 500 W m-2 but less than 550 because there is no 550 line shown, so an intermediate value of 530 W m-2 was estimated. a) b) c) 2. North Pole South Pole Arctic Circle d) e) Antarctic Circle 45°N, Halifax’s latitude f) g) h) Tropic of Cancer Equator Tropic of Capricorn Recall that the amount of insolation is being used to represent seasonal variations on Earth, because in simple terms more insolation results in warmer temperatures. Use the completed graphs from Question 1 to summarize seasonal variations by answering these questions: a) Describe how seasonal extremes of insolation (the difference between maximum and minimum values) vary with latitude. 2 b) How do the patterns of seasonal variation at latitudes in the northern hemisphere (e.g., the Tropic of Cancer) compare with the patterns at the corresponding latitudes in the southern hemisphere (e.g., the Tropic of Capricorn)? Section 3: Explaining Seasonal Variations The two key controls on the amount of insolation received at any latitude during the year are 1) the angle of incidence, which determines over how much surface area incoming beams of insolation are spread, and 2) daylength. Subsolar Point and Solar Declination Due to the geometry of the Earth-Sun system, at any time of the year the Sun appears to be directly overhead one point on Earth. That point is called the subsolar point. Beams of insolation arrive perpendicular to the surface only at the latitude of the subsolar point. At all other latitudes, the beams of insolation arrive at an oblique angle. During the year, the subsolar point migrates in a regular and predictable pattern to latitudes north and south of the Equator. The latitude of the subsolar point at a given time is called the solar declination. Solar declination (which has units of degrees) is shown with a dashed line on Figure 2. [Note that for Questions 3 and 4, all of the answers are contained within the list a) – h) in Question 1.] 3. What is the highest latitude in the northern hemisphere to which the subsolar point migrates annually? And the highest latitude in the southern hemisphere? 4. At the Spring (Vernal) Equinox (labeled on Figure 2), what is the latitude of the subsolar point? And at the Autumnal Equinox, the Summer Solstice, and the Winter Solstice? Intensity of Insolation Because the Earth’s surface is curved, the intensity of insolation is not equal at all locations (recall Figure 2.9 in the textbook). Only at the subsolar point is the intensity at its maximum. At all other locations, the more obliquely the surface is oriented to the insolation, the lower the intensity of insolation. Using some simple trigonometry (Equation 1), the intensity of insolation received at different places can be calculated. The answer from Equation 1 will be a percentage of the intensity of insolation re-ceived on a flat surface that is perpendicular to the insolation. Answers will be no smaller than 0 and no larger than 100. Equation 1: X = sin(90 – L) x 100 where: X = intensity of insolation (percent) sin = the sine function L = latitude (°), a positive value whether N or S For Equation 1, first find the answer for (90 – L), then press the sin button, and then multiply that result x 100. The sin function can be found on most calculators, but the calculator must be in degrees mode―not radians mode―for Equation 1 to give correct results. Check your calculator now to see if you get these correct answers: sin(0) = 0, sin(45) = 0.71, and sin(90) = 1. 5. Complete Table 1. This table corresponds to the Spring and Autumn Equinoxes, when the solar declination is 0°. After completing the column for the northern latitudes, ask yourself if there is a shortcut for completing the column for the southern latitudes without doing any more calculations. (There is!) The purpose of completing Table 1 is to show how the intensity of insolation varies with latitude. Table 1: Proportions of Insolation at the Equinoxes Latitude (°N) X = sin (90 – L) x 100 90 75 26 Latitude (°S) X = sin (90 – L) x 100 Latitude (°) 15 66.5°N 30 23.5°N 60 45 45 60 23.5°S 30 75 66.5°S 15 90 X = sin (90 – L) x 100 0° 3 Note that the intensity of insolation is calculated here for the equinox dates when the solar declination is 0°. At other times of the year, the latitude of maximum insolation intensity corresponds to the solar declination, and the intensity of insolation at other latitudes corresponds proportionally. Circles of Illumination At any one time, only (and exactly) one half of the Earth is illuminated by the Sun; that is, the circle of illumination. This is why we have periods of day and night, as the Earth rotates on its axis daily through the circle of illumination. Because of the axial tilt (23½° from vertical), the range of latitudes receiving solar illumination varies during Earth’s annual revolution around the Sun. 6. Figure 3 shows the Earth in two dimensions at the Summer Solstice, with the Northern Hemisphere tilted towards the Sun. On the diagram, lightly shade the half of the Earth that does not receive insolation. To determine the correct half, draw a straight line between the highest point on the circle perimeter (the highest point is below the vertical dashed line at the top of the circle, not at the North Pole, because the Earth is tilted) and the lowest point on the circle perimeter. Then shade the side of Earth facing away from the insolation. Label the unshaded portion of the diagram DAY, and the shaded portion NIGHT. Figure 3 (Summer Solstice) 7. Repeat the circle of illumination exercise for the Autumn Equinox (Figure 4), Winter Solstice (Figure 5), and Spring Equinox (Figure 6). 4 Figure 4 (Autumnal Equinox) Note that the Earth is still tilted on its axis of rotation at an angle of 23.5°. However, to draw the diagrams for the equinoxes on a flat sheet of paper, the perspective (location from which Earth is being viewed) must be changed in comparison to the solstices. Figure 5 (Winter Solstice) Figure 6 (Spring Equinox) 5 8. As shown in Figure 2, there are some latitudes that do not receive any insolation during certain parts of the year. In Figures 3-6, the range of latitudes that do receive insolation falls within the unshaded (DAY) part of the diagram. Consult Figures 3-6 to fill in Table 2 by listing the most northerly and southerly latitudes that receive insolation at the solstices and equinoxes. Give latitude values in degrees (°, including the hemisphere, N or S). Table 2: Range of Latitudes Receiving Insolation Date Most Northerly Latitude Most Southerly Latitude Summer Solstice Autumn Equinox Winter Solstice Spring Equinox Daylength In addition to the angular relationship between Earth surfaces and insolation, daylength is the other principal factor that controls seasonal variations. Figures 3-6 can be used to estimate daylengths at different latitudes. 9. Estimate daylengths for the Summer Solstice by using Figure 3 and these steps: a) Using a ruler with mm markings, measure the full length of each line listed in Table 3, in mm (except the North and South Poles which will be addressed in part e below). Be precise with your measurements. This length is A. b) Measure the length of part of the line that lies within the circle of illumination (the part labeled DAY). This length is B. c) Calculate the proportion of the lengths of the two lines (shorter [B] divided by longer [A]), and express as a decimal value. This result is C. In equation form: C = B/A. d) Multiply C x 24 (hours). The answer is the value D. e) For the North and South Poles, which are actually points not lines, it is not possible to measure line length. However, you can examine Figure 3 and the other answers in the table below to figure out what the daylengths are at the poles. Table 3: Daylengths at the Summer Solstice A North Pole C D Length of line (mm) B Length of line within circle of illumination (mm) C=B/A (no units) D = C x 24 (hours) ―――― ―――― ―――― 63 31.5 0.5 ―――― ―――― ―――― Arctic Circle Tropic of Cancer Equator 12 Tropic of Capricorn Antarctic Circle South Pole If you have done everything correctly, you should find that for the Equator, line B is half the length of line A and the final answer is 12 hours (A = 63 mm; B = 31.5 mm; C = B / A = 0.5; and D = 0.5 x 24 = 12 hours). 6 10. Repeat Question 9 for the Autumnal Equinox, using Figure 4 and Table 4. Table 4: Daylengths at the Autumnal Equinox A North Pole C D Length of line (mm) B Length of line within circle of illumination (mm) C=B/A (no units) D = C x 24 (hours) ―――― ―――― ―――― 63 31.5 0.5 ―――― ―――― ―――― Arctic Circle Tropic of Cancer Equator 12 Tropic of Capricorn Antarctic Circle South Pole 7 c) ______________________________ Graphs for Question 1 f) ______________________________ The order of the graphs a) - h) has been chosen to enable summary and comparison in Question 2. 600 Daily Insolation (W per sq. m) Write the name of the line of latitude on the blank line above each graph. Daily Insolation (W per sq. m) 600 500 400 300 200 100 0 M A M J J A S O N 400 300 200 100 M J J A S O N 500 400 300 200 100 F M A M J J A S O N 300 200 100 F M A M J J A S O N D J A S O N D 300 200 100 F M A M J J A S O N D h) ______________________________ 600 500 400 300 200 100 0 0 J 400 J Daily Insolation (W per sq. m) Daily Insolation (W per sq. m) 400 M 500 D 600 500 A g) ______________________________ e) ______________________________ 600 M 0 J D F 600 b) ______________________________ J 100 J 0 A 200 D Daily Insolation (W per sq. m) Daily Insolation (W per sq. m) Daily Insolation (W per sq. m) 500 0 Daily Insolation (W per sq. m) F 600 600 M 300 d) ______________________________ a) North Pole F 400 0 J J 500 500 400 300 200 100 0 J F M A M J J A S O N D J F M A M J J A S O N D Visualizing Physical Geography by Timothy Foresman & Alan Strahler Chapter 1 Discovering the Earth’s Dimensions © Brenda Kean/Alamy Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Chapter Overview The World of Geography The Shape of the Earth Global Location Global Time Mapping the Earth Courtesy of NASA Frontiers in Mapping Technologies Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. What is happening in this photo? The World of Physical Geography Physical geography plays a valuable role in: • Understanding the planet • Addressing issues of sustainability • Population increase • 6.9 billion today • Estimated 10 billion people in 40 years • Integrating the human and physical world Courtesy of NASA Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. The World of Physical Geography The Science of Geography • Geographers study Earth. • Geographers consider: • Spatial considerations (related to physical space) • Temporal considerations (related to changes of time) 1973 2006 USGS, courtesy NASA/Goddard Space Flight Center Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. The World of Physical Geography What are some of the spatial and temporal changes between these two photos? 1973 2006 USGS, courtesy NASA/Goddard Space Flight Center Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. The World of Physical Geography The five essential themes of geography: • Location • Home address • GPS = Global Positioning System • Place • Region • Human-Earth relationships • Movement Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. The World of Physical Geography The Science of Geography: • Physical Geography • Study of the Earth’s living and nonliving systems • Study of landscapes, and natural processes such as weather, climate, and geology • Human Geography • Study of spatial interactions and patterns related to human activity such as social, cultural, and economic topics Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. The World of Physical Geography © John Wiley & Sons Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. The World of Physical Geography The Science of Geography: • Technology, Tools, and Quantitative Methods • Cartography • GIS = Geographical Information Systems • Remote Sensing • Statistics Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. © John Wiley & Sons The World of Physical Geography The World of Systems • Constant Interactions of energy and material between the Earth’s four major systems: • Atmosphere • Hydrosphere • Lithosphere • Biosphere Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. © John Wiley & Sons The World of Physical Geography Methods and Tools for Geography •Eratosthenes • No shadow on summer solstice in Aswan • Earth’s size •Today’s technology • Remote sensing • GIS • GPS • Internet • Web-based mapping tools •Methods • Scientific method Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Courtesy NASA The World of Physical Geography Methods and Tools for Geography • Scientific method = the formal process that a scientist uses to solve a problem, which involves first observing and formulating a hypothesis and then testing and evaluating results Hypothesis = logical explanation for a process or phenomenon that allows prediction and testing by experiment Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. The World of Physical Geography © John Wiley & Sons Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. The World of Physical Geography Methods and Tools for Geography • Steps of the Scientific Method 1. Generate critical inquiry from investigations and field observation. 2. Formalize questions into a testable hypothesis to explain observations. 3. Select method(s) of analysis and control for variables and conditions for experiment. 4. Collect data for controlled experiment. 5. Conduct experiments to test hypothesis. 6. Reject or accept the hypothesis. 7. Document results, provide new scientific facts, and apply them to support theory or greater understanding. Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. The World of Physical Geography Geographic Use of the Scientific Method Step 1: Observe a spatial pattern of vegetative growth that is different on the west side of each of the Hawaiian Islands than on the east side. Step 2: Formalize a hypothesis: • Hypothesis 1 = Vegetation patterns are explained by rock type. • Hypothesis 2 = Vegetation patterns are explained by temperatures. • Hypothesis 3 = Vegetation patterns are explained by rainfall. Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. The World of Physical Geography Geographic Use of the Scientific Method Step 3: Select method of analysis. Use the big island of Hawaii to map the specific 16 × 16 km (10 × 10 mi) square test areas on the west and east sides of the island. Step 4: Collect data: • Vegetation maps from NASA satellites • Geologic maps from USGS • Temperature data from NOAA • Collect rainfall data from NOAA services Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. The World of Physical Geography Geographic Use of the Scientific Method Step 5: Conduct experiments to test hypothesis: • Overlay rock type on the vegetation map to look for patterns. • Look for correlation between rock type and vegetation within grids. • If hypothesis rejected, return to this step to test next hypothesis. Step 6: Reject or accept hypothesis: • No correlation between rock type and temperature with vegetation. • Positive correlation between rainfall and vegetation. Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. The World of Physical Geography Geographic Use of the Scientific Method Step 7: Document results and apply to theory: • Documentation allows others to review for verification. • If sufficient more tests conducted on other islands, the hypothesis may be elevated to a theory. • Theory = a hypothesis that has been tested and is strongly supported by experimentation, observation, and scientific evidence. Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. The World of Physical Geography Geographic Use of the Scientific Method Courtesy NASA Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. The World of Physical Geography Geographic Use of the Scientific Method Courtesy NASA Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. The World of Physical Geography Geographic Use of the Scientific Method Courtesy NASA Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. The World of Physical Geography Geographic Use of the Scientific Method Courtesy NASA Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. The World of Physical Geography Geographic Use of the Scientific Method Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Courtesy NASA The Shape of the Earth Is the Earth round? Courtesy NG Image Collection Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Courtesy NASA The Shape of the Earth The Earth is not a perfect sphere: • Equatorial diameter slightly greater than polar diameter • Poles = the two points on the Earth’s surface where the axis of rotation emerges • Axis = an imaginary straight line through the center of the Earth around which the Earth rotates Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. © John Wiley & Sons Global Location Geographic Grid • Network of parallels and meridians used to fix location on the Earth © John Wiley & Sons Meridian = north-south line on the Earth’s surface, connecting the poles Parallels = east-west circle on the Earth’s surface, lying on a plane parallel to the equator Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Global Location Geographic Grid © John Wiley & Sons Equator is parallel of latitude lying midway between the Earth’s poles; it is designated latitude 0º. Intersection of meridians and parallels makes up the geographic grid. Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Global Location Geographic Grid Latitude • An angular distance for a point north or south of the equator, as measured from the Earth’s center • Like “ladders” • Equator (0o) divides northern and southern hemisphere © John Wiley & Sons Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Global Location Geographic Grid Longitude • The angular distance for a point east or west of the prime meridian. (Greenwich), as measured from the Earth’s center. • Prime meridian is 0o. • Longitude measured eastward or westward from the prime meridian from 0o to 180o. © John Wiley & Sons Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Global Location Longitude • Prime meridian runs through Greenwich, England. © John Wiley & Sons © Dennis di Cicco/Corbis If we are facing north, which side is to the east? What is the latitude and longitude of Point P? Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Global Time Earth’s geographic grid and the rotation of the Earth help define global time. Solar Time • Based on Earth’s rotation • Makes one full turn in a day (24 hours) • Sun rises in the east and sets in the west • Solar noon = reaches its highest angle • Solar timekeeping © Frank Zullo/Photo Researchers, Inc. Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Global Time Solar Time • Sun only shines on half of Earth at one time. • Shines on eastern sides first. • Local time is determined primarily by longitude. When it is noon in Chicago, is it earlier or later in: a. Portland? b. New York? © John Wiley & Sons Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Global Time Standard Time • Designated 24 standard meridians around the globe, at equal intervals from the prime meridian. © John Wiley & Sons Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Global Time Time Zones of the World • Coordinated universal time (UTC) • Bottom figure labels = number of hours of difference between that zone and Greenwich mean time • A negative 7 = seven hours behind Greenwich time • A positive 3 = three hours ahead of Greenwich time Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Global Time Time Zones of the World © US Navy Oceanographic Office Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Global Time Time Zones of the Conterminous United States • Eastern, Central, Mountain, and Pacific • Daylight saving time = clocks set ahead (spring forward) © John Wiley & Sons If it is 3:00 PM in New York City, what time is it in: a. Atlanta? b. Dallas? c. Los Angeles? Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Global Time The International Dateline (IDL) • Follows 180th meridian except through the Aleutian Islands, Alaska and island nation of Kiribati • Move east across IDL, subtract a day © John Wiley & Sons If you flew from Los Angeles to Beijing, would you add or subtract a day? Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Global Time Time Zones of the World © John Wiley & Sons If it is 7 AM Sunday, in New York, NY, what day and time is it in Tokyo, Japan? Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Mapping the Earth Map = a graphic, scaled representative view of the Earth, or any portion of the Earth, as viewed from above, depicting various features of interest. Cartography • Subfield of geography • Representing Earth through maps © John Wiley & Sons Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Mapping the Earth Map scale = the relationship between distance on a map and distance on the ground, given as a fraction or a ratio. Three types of map scale: • Verbal scale, such as 1 cm = 1 km • Representative fraction • 1:50,000 means that 1 unit of map distance equals 50,000 units on the Earth • 1 cm on the map equals 50,000 cm or 500 m or 0.5 km on the ground • Graphic scale • Shows scale on a bar • Stays accurate if map size changes Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. © John Wiley & Sons Mapping the Earth Map Scale Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. © John Wiley & Sons Mapping the Earth Map Projection • A system of parallels and meridians represents the Earth’s curved surface drawn on a flat surface. • Curved surface cannot be projected onto a flat sheet without distortion. • Four main types of projections: • Cylindrical • Conic • Plane • Elliptical (oval) Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. © John Wiley & Sons Mapping the Earth Cylindrical Projection • Wraps a cylinder around the globe so that the paper touches the globe at the equator. • Parallels increases at higher latitude so that the spacing at 60°is double that at the equator, which distorts landmasses, as seen with Greenland. • Example: Mercator project Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. © John Wiley & Sons Mapping the Earth Plane Projection • Produced by projecting a map from a center lit globe onto a piece of paper touching the globe at any point. • Can choose any center point, from which directions and distances are true, but in outer areas, shapes and sizes are distorted. Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. © John Wiley & Sons Mapping the Earth Conic Projection © John Wiley & Sons • Cone sits atop the globe like a cap, with the point of the cone typically situated over one of the poles. • Accuracy is greatest along the circle it touches—the standard parallel. • Good format for mapping mid-latitude regions that are larger east to west than north to south. Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Mapping the Earth Elliptical (Oval) Projection • Central meridian and all parallels are straight lines, with relative sizes represented accurately, but shapes are distorted at the edges. • Often used for thematic or political maps. • Example: Mollweide equal area map Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. © John Wiley & Sons Mapping the Earth Distortions in Map Projections • All maps are distorted. • Mapmaker decides whether to preserve shape, size, or a compromise. • Conformity © John Wiley & Sons • True shape map preserves shape but distorts size. • Example: Mercator projection • Great Circle Route is the shortest distance between two points. Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Mapping the Earth Distortions in Map Projections • Equivalence: Equal-area projection • Preserves size but distorts shape. • Example: Goode’s projection © University of Chicago Press Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Mapping the Earth Distortions in Map Projections • Compromises • Sacrifice equivalency and conformity for the sake of portraying a general balance between the two • Example: Winkel Tripel projection Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. © John Wiley & Sons Frontiers in Mapping Technologies Remote-Sensing Tools • Use of technology to record observations from a distance (e.g., aerial images) • Handheld, aircraft, and satellites capture radio waves, microwaves, infrared energy, and visible wavelengths. • Used for a variety of environmental and land-use issues Population and land use change in Las Vegas between 1973 and 2006. © John Wiley & Sons Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Frontiers in Mapping Technologies Remote-Sensing Tools • Spatial resolution = size of the smallest area, or pixel • Spectral resolution = range of wavelengths captured by the sensors • Important Earth Observing System (EOS) satellites: • Landsat • Weather satellites for ozone, temperature, clouds • Terra Courtesy of NASA Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Frontiers in Mapping Technologies Geographical Information Systems (GIS) • A combination of software, data, and operational organization • Provides the capacity to capture and communicate spatial relationships among geographic features, values, and objects in digital databases Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. © John Wiley & Sons Frontiers in Mapping Technologies Geographical Information Systems (GIS) • A useful analysis tool • Designed to answer questions with spatial information: • What is the best route to deliver packages? • Which wells will be polluted by underground aquifer contamination? • What property values will suffer from loan defaults in one neighborhood as compared to another? © John Wiley & Sons Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Frontiers in Mapping Technologies Geographical Information Systems (GIS) • Geocoding: These questions are answered by merging conventional data with their geographic locations. • GIS maps are common feature in public hearings. © John Wiley & Sons Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Frontiers in Mapping Technologies Global Positioning Systems (GPS) • Accurately determines geographic location • Consists of 24+ satellites that orbit Earth • Receivers work by measuring and triangulating time delay of signals from a minimum of three (usually four or more) GPS satellites. • Handheld devices and phones automatically enable GPS data to be recorded. • openstreetmap.org • Represents a creative approach to citizen-led data collection for mapping world’s streets • Available for free Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Frontiers in Mapping Technologies Geobrowsers and 3-D Mapping • Internet mapping • Uses: • Reporting on humanitarian issues • Tracking eco-disasters 1. What does a geographer see? 2. If the resolution of Blue Marble is 1 square kilometer, how can geographers keep track of 8.5 million points to discern changes in land use? Courtesy NASA Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Frontiers in Mapping Technologies Geobrowsers and 3-D Mapping • Computer programs that access and query geographic data draped over a computer-generated globe • Google Earth 1. Explain how spaceage technologies have affected the field of geography. 2. What do you think we can expect from these technologies in the future? Courtesy NASA Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Visualizing Physical Geography by Timothy Foresman & Alan Strahler Chapter 2 The Earth’s Global Energy Balance © Zuma Press Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Chapter Overview Electromagnetic Radiation Insolation over the Globe Solar Energy and the Earth’s Atmosphere The Global Energy System © Zuma Press What type of energy is being captured? Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. The Earth’s Global Energy Balance Solar Energy • Every second, the Sun provides us with energy to meet the world’s energy demands for 10 days! • Currently, world economy is driven by burning of fossil fuels, which are nonrenewable. • Solar energy is a fast-growing industry. © Zuma Press Generating 64 megawatts of solar thermal energy is the Solar One power plant in Nevada. Should we build more solar plants? Explain. Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Electromagnetic Radiation • Electromagnetic radiation = wave form of energy radiated by any substance possessing internal energy; it travels through space at the speed of light. • Wavelength is the measured distance separating one wave crest from the next wave crest. © John Wiley & Sons, Inc. Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Electromagnetic Radiation Electromagnetic Spectrum • Defines the entire range of wavelengths for all energy Can you locate shortwave (SW) radiation in the figure? SW = energy in the range of 0.2 to 3 μm Find longwave (LW) radiation. LW = energy in the range of 3 to 5 μm © John Wiley & Sons, Inc. Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Electromagnetic Radiation Radiation and Temperature •Hot objects radiate more energy than cooler objects. • Hotter objects emit shorter wavelengths. Can you locate shortwave (SW) radiation? Find longwave (LW) radiation. LW = emitted from earth Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. © University of Chicago Press Electromagnetic Radiation Solar Radiation •Shortwave (SW) radiation • Emitted from the sun • Ultraviolet, visible, and infrared radiation • Distance of Earth’s orbit from Sun optimal for life • Solar constant • Flow rate of solar energy • Measured outside atmosphere • Watts/meter squared (W/m2) © National Council for Geographic Education Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Insolation over the Globe Energy received from the sun varies each day and over a year, and it varies by latitude. Daily Insolation Insolation = flow rate of incoming solar energy, as measured at the top of the atmosphere Daily insolation depends on: • Angle of sunlight: • Subsolar point = noon Sun directly overhead at this one point • Declination = latitude of the subsolar point • Day length Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Insolation over the Globe Daily Insolation • Day length also determines daily insolation • Circle of illumination = separates day and night • Equator always experiences 12 hours of day length • Poles experience either 24 hours or 0 hours • Other latitudes have varying day length each day Considering solar angle, when is insolation greatest? © John Wiley & Sons, Inc. Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Insolation over the Globe Seasonal Change • Earth revolves around the sun every 365.242 days: • Orbit is counterclockwise and is an ellipse. • Perihelion: point in orbit when Earth is closest to Sun. • Aphelion: point in orbit when Earth is farthest from Sun. © John Wiley & Sons, Inc. Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Insolation over the Globe Seasonal Change The Tilt of the Earth’s Axis: • Earth has seasons because of the tilt of the axis. • Axis aims toward Polaris (North Star). • Axis tilted at an angle of 23½° from a right angle to plane of the ecliptic. © John Wiley & Sons, Inc. Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Insolation over the Globe Seasonal Change Equinox: time when subsolar point falls on equator and circle of illumination passes through both poles Winter solstice: solstice occurring on December 21 or 22, when the subsolar point is at 23½° S; December solstice Summer solstice: solstice occurring on June 21 or 22, when the subsolar point is at 23½° N; June solstice © John Wiley & Sons, Inc. Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Insolation over the Globe Equinox • Circle of illumination passes through both poles • Subsolar point at equator • Day and night of equal length everywhere on the globe • Occurs twice per year • Vernal equinox: March 21 • Autumnal equinox: September 23 Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. © John Wiley & Sons, Inc. Insolation over the Globe Solstices • Circle of illumination grazes Arctic and Antarctic Circles • June solstice: • North Pole has 24 hours of daylight; day length increases from equator to North Pole. • Arctic Circle is southern point of 24 hours days. • N hemisphere tilted © John Wiley & Sons, Inc. toward the sun. • Subsolar point = 23.5°N Is this the start of winter or (Tropic of Cancer). summer in the: Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. 1. Southern hemisphere? 2. Northern hemisphere? Insolation over the Globe December Solstice • South Pole has 24 hours of daylight; day length increases from equator to South Pole. • Arctic Circle is southern point of 0 hour days. • Northern hemisphere tilted away from the sun. • Subsolar point = 23.5°S (Tropic of Capricorn). Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. © John Wiley & Sons, Inc. Is this the start of winter or summer in the: 1. Southern hemisphere? 2. Northern hemisphere? Insolation over the Globe Annual Insolation by Latitude • Annual insolation decreases from equator (more direct rays) to poles (oblique rays) • Solar insolation is strongest near the equator and weakest near the poles • Seasonal changes in day length vary by latitude © John Wiley & Sons, Inc. At ___latitude, the solar radiation would be spread out over twice as much area as at the equator. Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Insolation over the Globe Seasonal changes in day length by latitude © John Wiley & Sons, Inc. June solstice • Farther north of equator, the longer the days • 12 hours at equator • 24 hours at North Pole December solstice • Further north of equator, shorter days • 0 hours at South Pole Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Insolation over the Globe The Earth’s Diverse Environments by Latitudes Latitude zones: decreasing insolation from equator to poles Equatorial: intense insolation, day and night roughly equal Tropical: high annual insolation Subtropical: large annual insolation © NG Image Collection © NG Image Collection Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. © John Wiley & Sons, Inc. Insolation over the Globe The Earth’s Diverse Environments by Latitudes Midlatitude: strong seasonal contrasts in insolation and length of day © NG Image Collection © The Image Works Arctic/subarctic, Antarctic: enormous variation in annual insolation, extreme variation in day length © John Wiley & Sons, Inc. Polar: greatest change Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Solar Energy and the Earth’s Atmosphere Composition of the Atmosphere • 97% lies within 30 km (19 mi) or earth’s surface © SPL/Photo Researchers, Inc. Layers of the Atmosphere by Temperature •Troposphere • Lowest layer of the atmosphere, where human activity and most weather takes place • Temperature usually decreases with height Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Solar Energy and the Earth’s Atmosphere Layers of the Atmosphere by Temperature • Stratosphere • Layer of atmosphere directly above the troposphere, where temperature slowly increases with height © SPL/Photo Researchers, Inc. • Ozone layer protects humans from ultraviolet radiation • Mesosphere = coldest near top of this layer • Thermosphere = hottest layer Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Solar Energy and the Earth’s Atmosphere Layers of the Atmosphere by Composition • Homosphere • Heterosphere © SPL/Photo Researchers, Inc. Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Solar Energy and the Earth’s Atmosphere Composition of the Atmosphere Permanent gases • 78% nitrogen • 21% oxygen • Argon © John Wiley & Sons, Inc. Variable gases • Carbon dioxide (CO2): needed by green plants, absorbs long-wave radiation • Water vapor varies up to 2%, absorbs heat • Ozone (O3): ozone layer in the stratosphere Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Solar Energy and the Earth’s Atmosphere Aerosols = tiny particles present in the atmosphere that are so small and light that the slightest air movements keep them aloft. •Global dimming: • Reduction in industrial pollution has led to increase in solar insolation. • Decrease in atmospheric particles lowers the reflectance of the Sun’s incoming energy. • Temperatures may increase, adding to existing warming trend. © Science Central Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Solar Energy and the Earth’s Atmosphere Absorption, Scattering, and Reflection Absorption = process in which electromagnetic energy is absorbed when radiation strikes molecules or particles in a gas, liquid, or solid, raising its energy content. © John Wiley & Sons, Inc. Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Solar Energy and the Earth’s Atmosphere Absorption • 16% of incoming solar radiation is absorbed in the atmosphere • Carbon dioxide • Water vapor holds latent heat • Clouds absorb shortwave radiation © John Wiley & Sons, Inc. Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Solar Energy and the Earth’s Atmosphere Scattering • Process by which particles and molecules deflect incoming solar radiation in different directions on collision; atmospheric scattering can redirect solar radiation back to space • Diffuse radiation © John Wiley & Sons, Inc. Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Solar Energy and the Earth’s Atmosphere Reflection • Albedo = proportion of solar radiation reflected upward from a surface. Intermediate albedo: forests, fields, bare ground © NG Image Collection High albedo: Snow and ice, also clouds Albedo of water depends on the angle of incoming radiation. © Jeremy Woodhoue Masterfile Low albedo: black asphalt paving Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Solar Energy and the Earth’s Atmosphere Reflection • Losses of incoming solar energy are much lower with clear skies (left) than with cloud cover (right) because clouds both reflect and absorb solar radiation. Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. © A. N. Strahler The Global Energy System The Earth’s Energy Output • Incoming energy • Shortwave from the sun • Greenhouse effect: • Absorption of outgoing longwave radiation by components of the atmosphere and reradiation back to the surface, which raises surface temperatures. • Reradiation is also known as counterradiation. Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. The Global Energy System Greenhouse Gases © John Wiley & Sons, Inc. Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. The Global Energy System Why might the greenhouse effect be stronger in humid regions, such as the Amazon Basin, than in dry regions? © John Wiley & Sons, Inc. Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. The Global Energy System Greenhouse Effect • Without the natural warming process of the greenhouse effect, the Earth would be too cold for human habitation. Enhanced Greenhouse Effect • Levels of greenhouse gases in the atmosphere increase as a byproduct of human activities, the greenhouse effect warms the Earth more, disrupting our climate. Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. © John Wiley & Sons, Inc. The Global Energy System Net Radiation and the Global Energy Budget • Net radiation is the difference between incoming and outgoing radiation. • Outgoing energy: • Reflected SW • LW radiation emitted from earth • Incoming energy: • SW from the sun © John Wiley & Sons, Inc. • LW energy from greenhouse gases • Net radiation increase has resulted in temperature increase of about 1o C in the past century Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. The Global Energy System Human Impacts on the Global Energy Balance 1. Rising Concentrations of Greenhouse Gases • Carbon dioxide (CO2): • Trend since 1958 • Trend since 1860s • Methane (CH4) • Nitrous oxides (N2O) 2. Changes to surface albedo © John Wiley & Sons, Inc. Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. The Global Energy System Human Impacts on the Global Energy Balance 3. Air Pollution • • • • Hazy Asian Atmosphere Asian Brown Cloud 10% reduction in crop yields Dark soot particles had lowered the albedo of snow pack in the region Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. © UNEP Assessment Report Courtesy NASA The Global Energy System Human Impacts on the Global Energy Balance 4. Thinning of Ozone Layer in the Stratosphere • Ultraviolet radiation is damaging to life, so, absorption of UV radiation by ozone layer protects life on Earth’s surface • Does not impact warming • Ozone hole Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Courtesy NASA The Global Energy System 4. Thinning of Ozone Layer Ozone hole forms through a chemical process • VERY cold air + CFCs (human caused) + O3 = Breakdown of O3 • Primarily forms over Antarctica during their late winter after it has been very cold Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. © John Wiley & Sons, Inc. The Global Energy System 4) Thinning of Ozone Layer • Data collection: • Aircraft (remote sensing) • Balloons with sensors • Satellites Courtesy NASA Courtesy NASA Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Courtesy NASA The Global Energy System 4. Thinning of Ozone Layer • Montreal Protocol treaty • 23 nations signed in 1987. • By 1999, scientists confirmed that concentrations had topped out in 1997 and were beginning to fall. Why should the U.S. government fund both satellites and field work to conduct climate change research? Courtesy NASA Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc.
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