Natural Environments: The Atmosphere - PowerPoint PPT Presentation

1 / 16
About This Presentation
Title:

Natural Environments: The Atmosphere

Description:

Title: PowerPoint Presentation Last modified by: Ranga Created Date: 1/1/1601 12:00:00 AM Document presentation format: On-screen Show Other titles – PowerPoint PPT presentation

Number of Views:28
Avg rating:3.0/5.0
Slides: 17
Provided by: clivegBuE6
Learn more at: http://cliveg.bu.edu
Category:

less

Transcript and Presenter's Notes

Title: Natural Environments: The Atmosphere


1
  • Natural Environments The Atmosphere
  • GG 101 Spring 2005
  • Boston University

Myneni Lecture 04 Orbiting Sphere Jan-28-05 (1
of 16)
Further Reading Chapter 03 of the text book
Outline
- earth-sun geometry
- definitions
- the seasons
- diurnal and seasonal variations
2
Natural Environments The Atmosphere GG 101
Spring 2005 Boston University
Myneni Lecture 04 Orbiting Sphere Jan-28-05 (2
of 16)
Preludio
  • In last lecture, based on the
  • Shape and Rotation of the Earth
  • we were able to devise
  • Geographical Coordinate Systems and Time.
  • In this lecture we will study the
  • Orbit of the earth about the sun
  • which is the first step in understanding the
  • Energy Balance
  • for various locations on the earth and at
    various times of the year.

3
Natural Environments The Atmosphere GG 101
Spring 2005 Boston University
Myneni Lecture 04 Orbiting Sphere Jan-28-05 (3
of 16)
An Example
  • Latitudinal variation in climate regimes
  • Controlled by
  • - Total incoming radiation
  • - Seasonality in radiation
  • How and Why?
  • Earth-Sun Astronomical relationship!

4
Natural Environments The Atmosphere GG 101
Spring 2005 Boston University
Myneni Lecture 04 Orbiting Sphere Jan-28-05 (4
of 16)
Earth-Sun Geometry
  • Spin of the earth about the axis (i.e. rotation)
  • Inclination of the axis of spin relative to the
    axis of orbit around the sun

5
Natural Environments The Atmosphere GG 101
Spring 2005 Boston University
Myneni Lecture 04 Orbiting Sphere Jan-28-05 (5
of 16)
Shape of the Orbit
  • Orbit is an ellipse
  • Period takes 365.25 days to make one
    revolution
  • Direction orbits counter-clockwise looking down
    on the north pole
  • Closest approach - Perihelion 147.5 million
    km
  • Farthest distance - Aphelion 152.5 million km

Earth
Sun
January 3
Aphelion
Perihelion
July 4
Note timing of seasons!
6
Natural Environments The Atmosphere GG 101
Spring 2005 Boston University
Myneni Lecture 04 Orbiting Sphere Jan-28-05 (6
of 16)
Axial Tilt
Angle of tilt 23.5 degrees
Axis of orbit
Axis of Rotation
Direction of Rotation
Axial tilt The angle at which the axis of the
earths rotation is tilted with respect to the
orbit around the sun
Note Combination of axial tilt and orbit around
the sun causes the SEASONS
7
Natural Environments The Atmosphere GG 101
Spring 2005 Boston University
Myneni Lecture 04 Orbiting Sphere Jan-28-05 (7
of 16)
Solar Zenith Angle
SZA
N
S
Angle between a line perpendicular to the surface
and the incoming ray from the sun
8
Natural Environments The Atmosphere GG 101
Spring 2005 Boston University
Myneni Lecture 04 Orbiting Sphere Jan-28-05 (8
of 16)
SZA and Radiation Flux
If the same amount of energy is spread over a
larger area, the intensity of the radiation at
a given point is less Small solar zenith angle
-gt high intensity Large solar zenith angle -gt
less intensity
9
Natural Environments The Atmosphere GG 101
Spring 2005 Boston University
Myneni Lecture 04 Orbiting Sphere Jan-28-05 (9
of 16)
Circle of Illumination Sub-solar Point
(Declination)
Circle of Illumination The half-sphere which is
illuminated by the sun
Sub-solar point The location on the earths
surface where the sun is directly overhead
Declination The latitude of the sub-solar point
at a given time of year (varies between 23.5N
and 23.5S)
10
Natural Environments The Atmosphere GG 101
Spring 2005 Boston University
Myneni Lecture 04 Orbiting Sphere Jan-28-05 (10
of 16)
The Seasons
  • The fixed axial tilt as Earth orbits the sun
  • results in systematic variation in solar
    geometry, the seasons

11
Natural Environments The Atmosphere GG 101
Spring 2005 Boston University
Myneni Lecture 04 Orbiting Sphere Jan-28-05 (11
of 16)
Solstices
Sub-solar point located at tropics of Cancer and
Capricorn (23.5 degrees N and S) Circle of
Illumination extends between 66.5 degrees N and S
12
Natural Environments The Atmosphere GG 101
Spring 2005 Boston University
Myneni Lecture 04 Orbiting Sphere Jan-28-05 (12
of 16)
Equinoxes
Sub-solar point located at Equator Circle of
illumination extends between poles Day-length
equal to 12 hours everywhere
13
Natural Environments The Atmosphere GG 101
Spring 2005 Boston University
Myneni Lecture 04 Orbiting Sphere Jan-28-05 (13
of 16)
Course of the Sub-Solar Point
Varies between 23.5N and 23.5S
14
Natural Environments The Atmosphere GG 101
Spring 2005 Boston University
Myneni Lecture 04 Orbiting Sphere Jan-28-05 (14
of 16)
Another Look at the Seasons
15
Natural Environments The Atmosphere GG 101
Spring 2005 Boston University
Myneni Lecture 04 Orbiting Sphere Jan-28-05 (15
of 16)
Diurnal Seasonal Variations
Maximum solar zenith angle and Daylength
(rotation through circle of illumination) are
controlled by Time of year Latitude (e.g., at
40 degrees north the figure)
16
Natural Environments The Atmosphere GG 101
Spring 2005 Boston University
Myneni Lecture 04 Orbiting Sphere Jan-28-05 (16
of 16)
The Movies
- Seasonal cycle movie
- Sun path movie
Write a Comment
User Comments (0)
About PowerShow.com