PHSC 3033: Meteorology
Seasons
Changing Aspect Angle
• Direct Sunlight is more intense and concentrated.
• Solar Incidence Angle is Latitude and Time/Date Dependent
– Daily and Seasonal Variation
Zenith
• There is much less atmosphere to travel through directly
overhead than on the horizon. The sun is more direct and
intense.
Daily Solar Intensity
• By the time the sun gets on the horizon, it is at a grazing
angle and heavily scattered, refracted and absorbed.
Diurnal Temperature
Seasons Reasons
• Earth’s Tilt (Seasonal)
– Tilt of rotational axis with respect to its orbit around sun
– Solar Radiation (Earth’s daily rotation)
• More Direct Sun Light
• Longer Duration of Day Light Hours
• Orbit Variations (Very Long-Term, Small Effects)
– tilt
– eccentricity
– precession
Tilt
Earth’s rotational axis remains fixed with respect to
the stars.
Earth’s Circle of Illumination
50 % of the earth’s
surface is
illuminated
by the sun,
every hour
of every day.
Incident Angle
Winter Solstice
• Sunlight is most direct at the Tropic of Capricorn (23.5 S)
on ~ January 21-22.
Earth From Space - January
.
Earth From Space - July
.
December Solar Insolation
Day Light Hours (June Solstice)
June Solar Insolation
Day Light Hours (Equinox)
Day Light Hours
Combined Annual Average Solar Insolation
Solar Altitude Angle
• Calculation of the Solar Altitude at Local Noon
– What is your Latitude?
– What is the Date?
• For the date and latitude, what is apparent latitude (declination) of the Sun?
– Calculate the distance in degrees between your latitude and the
declination of the sun.
– 90 degrees minus the latitude declination difference will be the
solar altitude at local noon for your location on that date.
Solar Altitude = 90 - |solar latitude - observer latitude|
Solar Altitude Angle (Solstice)
Seasonal Solar Latitude
Solar Altitude Angle
• Solar Altitude at Local Noon, Russellville, AR
– What is your Latitude?
– What is the Date?
• For the date and location, what is apparent latitude (declination) of the Sun?
– Calculate the distance in degrees between your latitude and the
declination of the sun.
– 90 degrees minus the latitude declination difference will be the
solar altitude at local noon for your location on that date.
Solar Altitude at NOON =
90 – [Difference in Latitude on Earth between you and direct sun]
Solar Altitude Angle
• Solar Altitude at Local Noon, Russellville, AR
– What is your Latitude?
– What is the Date?
35 degrees
2011 Jan 19
Solar Altitude Angle
• Solar Altitude at Local Noon, Russellville, AR
– What is your Latitude?
– What is the Date?
35 degrees
2011 Jan 19
• For the Date, What is the apparent latitude (declination) of the Sun? 21o
Solar Altitude Angle
• Solar Altitude at Local Noon, Russellville, AR
– What is your Latitude?
– What is the Date?
35 degrees
2011 Jan 19
• For the Date, What is the apparent latitude (declination) of the Sun? 21o
– Calculate the distance in degrees between your latitude and the
declination of the sun. 35 N + 21 S = 56 degrees
Solar Altitude Angle
• Solar Altitude at Local Noon, Russellville, AR
– What is your Latitude?
– What is the Date?
35 degrees
2011 Jan 19
• For the Date, What is the apparent latitude (declination) of the Sun?
– Calculate the distance in degrees between your latitude and the
declination of the sun. 35 N + 21 S = 56 degrees
– 90 degrees minus the latitude declination difference will be the
solar altitude at local noon for your location on that date.
90 - 56 = 34
Altitude-Azimuth
Russellville 2011 Jan 19
Zenith
Ecliptic (Path of the Sun)
NCP
34 degrees
N
S
W
Solar Altitude Angle
http://aa.usno.navy.mil/AA/data/
Astronomical Applications Dept.
U.S. Naval Observatory
Washington, DC 20392-5420
RUSSELLVILLE, ARKANSAS
W 93 08, N35 17
Altitude and Azimuth of the Sun
Jan 19, 2011
Central Standard Time
Altitude Azimuth
(E of N)
h m
11:40
12:00
12:20
12:40
13:00
o
33.6
34.3
34.5
34.4
33.9
o
167.8
173.4
179.0
184.7
190.3
Solar Altitude and Azimuth Angles
Altitude = tan-1 (h / l)
Azimuth = 180 – tan-1 (w / n)
compass direction
n
N-S line
w
Length of shadow
l
Meter-Stick
Height
h
Thermal Inertia
For Any Given Northern Latitude
• Maximum Daily Solar Insolation Occurs At
• Maximum Yearly Solar Insolation Occurs On
• Hottest Hour of the Day (on average)
• Hottest Month of the Year (on average)
It takes awhile to heat up and cool down!
Solar Homes Application
• Location and Length of Overhangs
• Position Angle of Solar Panels
• Positioning of Foliage and Trees
Summary
• Earth-Sun Geometry
• Seasons
• Solar Energy
– Seasonal (Latitude) Changes
– Diurnal (Daily) Changes