Natural Environments: The Atmosphere

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• Natural Environments The Atmosphere
• GE 101 Spring 2007
• Boston University

Myneni Lecture 03 Rotating Sphere Jan-22-07 (1
of 15)
Further Reading Chapter 03 of text book
Outline
- 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

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Natural Environments The Atmosphere GE 101
Spring 2007 Boston University
Myneni Lecture 03 Rotating Sphere Jan-22-07 (3
of 15)
Shape of the Earth

• We begin by looking at the earth as a Rotating,
  Orbiting Sphere

N

• 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

12756 km
12714 km
S
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)
Great and Small Circles

• 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 Circles
Small Circles
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Natural Environments The Atmosphere GE 101
Spring 2007 Boston University
Myneni Lecture 03 Rotating Sphere Jan-22-07 (5
of 15)
Parallels and Meridians

• From these concepts we can draw systematic set
  of coordinates on the earths 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
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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

Parallel
Fixed Meridian
Equator
Latitude
Latitude Position measured in degrees of arc
(along a fixed meridian) from the Equator
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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
Fixed Parallel
Meridian
Prime Meridian
Longitude
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
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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

• But, such transformations introduce various
• types of distortions.

• Typically, selection of a projection requires
• trade-off between direction preserving vs.
• area preserving maps.

Equal Angle, Un-equal Areas
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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
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Natural Environments The Atmosphere GE 101
Spring 2007 Boston University
Myneni Lecture 03 Rotating Sphere Jan-22-07 (11
of 15)
Earths 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
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
Sunrise
Solar noon
Sun
Solar night
Sunset
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

• Define time at a point on Earths surface
  relative to passage of Sun
• Angular rate of rotation 360 degrees/ 24 hours
• Therefore, 15 degrees/hour

1100 am
15? West
Solar noon
100 pm

• Problem Does not provide fixed/universal time
  system!!
• Local time varies continuously with longitude

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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

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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 gt
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.