1. Natural Environments: The Atmosphere GE 101 – Spring 2007 Boston University Myneni Lecture 03: Rotating Sphere Jan-22-07 (1 of 15) Outline Further Reading: Chapter 03 of text book - Introduction - Latitudes and Longitudes - Map Projections - Time

2. Natural Environments: The Atmosphere GE 101 – Spring 2007 Boston University Myneni Lecture 03: Rotating Sphere Jan-22-07 (2 of 15) Earth as Rotating Sphere Let us begin to lay the foundation for the first part of the course, which is - Energy balance of the earth system that is, What energy comes in, how it changes form, what goes out The energy source for the earth is the sun. Therefore, we need to look at the earth-sun “astronomical relationship” We begin by looking at the earth as a Rotating, Orbiting Sphere From this we will be able to answer many questions about the basic climate of the earth - Why are there seasons? - Why is there such a temperature difference between the equator and poles? - What effect does this temperature difference have on the circulation of the atmosphere and oceans

3. Natural Environments: The Atmosphere GE 101 – Spring 2007 Boston University Myneni Lecture 03: Rotating Sphere Jan-22-07 (3 of 15) We begin by looking at the earth as a Rotating, Orbiting Sphere 12756 km 12714 km N S - Approximately spherical - Actually an “oblate ellipsoid” - Slightly compressed from north to south - Slightly bulging from east to west - But, we treat it as a sphere Shape of the Earth The Blue Marble

4. Natural Environments: The Atmosphere GE 101 – Spring 2007 Boston University Myneni Lecture 03: Rotating Sphere Jan-22-07 (4 of 15) Because earth is effectively a sphere, the geometry, (meaning, how we define where we are on the sphere) is more difficult than if the earth was flat. We introduce two concepts for drawing lines on the surface - Great CirclesSmall Circles Great and Small Circles

5. Natural Environments: The Atmosphere GE 101 – Spring 2007 Boston University Myneni Lecture 03: Rotating Sphere Jan-22-07 (5 of 15) From these concepts we can draw systematic set of coordinates on the earth’s surface called “Meridians and Parallels” Parallels -Parallel to one another - Intersect meridians at 90-degree angles Meridians - Not parallel to one another - Intersect at the poles Parallels and Meridians

6. Natural Environments: The Atmosphere GE 101 – Spring 2007 Boston University Myneni Lecture 03: Rotating Sphere Jan-22-07 (6 of 15) Geographical Coordinate System: Latitude From these sets of lines, we can define a “geographic coordinate system” based on the relation of our position on the globe to the fixed meridians and parallels Equator ParallelFixed Meridian Latitude Position measured in degrees of arc (along a fixed meridian) from the Equator

7. Natural Environments: The Atmosphere GE 101 – Spring 2007 Boston University Myneni Lecture 03: Rotating Sphere Jan-22-07 (7 of 15) Geographical Coordinate System: Longitude Prime Meridian Fixed ParallelMeridian Longitude Position measured in degrees of arc (along a fixed parallel) from a fixed meridian Called the “Prime Meridian” - passes through Greenwhich, England and is defined as 0-degrees longitude

8. Natural Environments: The Atmosphere GE 101 – Spring 2007 Boston University Myneni Lecture 03: Rotating Sphere Jan-22-07 (8 of 15) Geographical Coordinate System: Example Location of point P is: 50 degrees North, 60 degrees West So P would be located….?

9. Natural Environments: The Atmosphere GE 101 – Spring 2007 Boston University Myneni Lecture 03: Rotating Sphere Jan-22-07 (9 of 15) Maps and Projections To make life easier, cartographers usually represent three-dimensional objects in two dimensions using cartographic projection systems, that is, maps Typically, selection of a projection requires trade-off between direction preserving vs. area preserving maps. But, such transformations introduce various types of distortions. Equal Angle, Un-equal Areas

10. Natural Environments: The Atmosphere GE 101 – Spring 2007 Boston University Myneni Lecture 03: Rotating Sphere Jan-22-07 (10 of 15) Common Projections: Goodes Preserves area but not shape

11. Natural Environments: The Atmosphere GE 101 – Spring 2007 Boston University Myneni Lecture 03: Rotating Sphere Jan-22-07 (11 of 15) Earth’s Rotation Rotation of the earth produces “time” We count time with respect to the position of the sun either over a: - Fixed point, which is “solar time” - will discuss later - Imaginary point, which is “standard time” - will discuss later Remember, the Earth spins in a counter-clockwise direction when looking down on the North pole (one revolution or 360 degrees defines 1 day)

12. Natural Environments: The Atmosphere GE 101 – Spring 2007 Boston University Myneni Lecture 03: Rotating Sphere Jan-22-07 (12 of 15) Solar Time Sunrise Sunset Solar night Solar noon Sun Solar Time: time relative to position of sun over a fixed point Midpoint of the day (i.e. when the sun is highest overhead) called “solar noon” Midpoint of night (i.e. when the earth has rotated 180-degrees from solar noon) Sunrise and sunset = time when earth rotates into and out of illumination

13. Natural Environments: The Atmosphere GE 101 – Spring 2007 Boston University Myneni Lecture 03: Rotating Sphere Jan-22-07 (13 of 15) Problem with Solar Time 11:00 am 1:00 pm 15  West Solar noon Define time at a point on Earth’s surface relative to passage of Sun Angular rate of rotation = 360 degrees/ 24 hours Therefore, 15 degrees/hour Problem: Does not provide fixed/universal time system!!  Local time varies continuously with longitude

14. Natural Environments: The Atmosphere GE 101 – Spring 2007 Boston University Myneni Lecture 03: Rotating Sphere Jan-22-07 (14 of 15) Standard Time Therefore, we create something called ‘Standard Time” Define “time zones” - swaths of approximately 15-degree longitude where we define time to be the same everywhere - “Standard time” - time as defined by a given time zone - “Standard meridian” - imaginary longitude whose solar time is defined to be the standard time for an entire time zone

15. Natural Environments: The Atmosphere GE 101 – Spring 2007 Boston University Myneni Lecture 03: Rotating Sphere Jan-22-07 (15 of 15) U.S. Time Zones US Time Zones Eastern time ~ 75W Central time ~ 90W Mountain time ~105W Pacific time ~ 120W Note – within any time zone Local solar time > standard time E of standard meridian, and vice versa “Daylight savings time” is a political construct which relates to an arbitrary selection of the time for a given time zone. Hawaii and Arizona follow Standard Time all year long.