what causes the seasons and associated changes in insolation?
TRANSCRIPT
WHAT CAUSES THE SEASONS ANDASSOCIATED CHANGES IN INSOLATION?
SUN
December 22 June 21
September 21
March 21
Sun on horizon z = 90°
Sun on horizon z = 90°
March & September 21
SUN
Sun overhead z = 0°
N
Equator 0°
Antarctic Circle 66.5°S
Tropic ofCancer 23.5°N
Arctic Circle 66.5°N
Tropic ofCapricorn 23.5 °S
S
Noon z = Lat
WHAT DO WE KNOW SO FAR?
Zenith Angle at noon on these twodays is exactly equal to a location’sLatitude.
Gainesville, 29.5°NSouthampton, 52°NPerth, W.A., 32°S
Old SchoolGeography
N
March & September 21
SUN
Sun overhead z = 0°Equator
Antarctic C.
Cancer
Arctic C.
Capricorn
S
WHAT IS THE SUB-SOLAR POINT?
Sub-solar point is the latitude at which the noon day Sun appears directly overhead (z=0) at noon.
WHAT IS THE ZENITH ANGLE AT NOON ANYWHERE IN THE WORLD?
WHAT IS THE ZENITH ANGLE AT NOON ANYWHERE IN THE WORLD?
Z = LATITUDE OF LOCATION – LATITUDE OF SUB-SOLAR POINT
Thus on March and September 21:Z at Noon = Latitude of location - 0
WHAT IS THE SUB-SOLAR POINT FOR ANY DAY OF THE YEAR?
ANALEMMA
Latit
ude
of S
ub-s
olar
poi
nt
Equator
23.5°N
23.5°S
WHAT THE *%$* ?
SUN
December 22 June 21
September 21
March 21
N
S
N
s
Sun on horizon z = 90°
Sun on horizon z = 90°
June 21
SUN Sun overhead z = 0°
EquatorCancer
Antarctic
S
U
N
N
s
Sun on horizon z = 90°
Sun on horizon z = 90°
June 21
SUN Sun overhead z = 0°
EquatorCancer
Antarctic
S
U
N Equator: z = 23.5°
N
s
Sun on horizon z = 90°
Sun on horizon z = 90°
June 21
SUN Sun overhead z = 0°
EquatorCancer
Antarctic
S
U
N
WHERE IS THE SUN OVERHEAD (z=0) AT NOON?
23.5°N
N
s
Sun on horizon z = 90°
Sun on horizon z = 90°
June 21
SUN Sun overhead z = 0°
EquatorCancer
Antarctic
S
U
N
WHAT IS NOONTIME Z IN GAINESVILLE?
Lat = 29.5°
Z = <29.5°= 29.5 – 23.5 = 6°
Small Zenith Angle: Sun Close ToOverhead – Higher Proportion ofSolar Constant – More Energy – HOT!
N
s
Sun on horizon z = 90°
Sun on horizon z = 90°
June 21
SUN Sun overhead z = 0°
EquatorCancer
Antarctic
S
U
N
WHAT IS NOONTIME Z IN SOUTHAMPTON?
Lat = 52°N
Z = <52°= 52 – 23.5 = 28.5°
Small Zenith Angle: Sun Closer ToOverhead – Higher Proportion ofSolar Constant – More Energy – WARM!
N
s
Sun on horizon z = 90°
Sun on horizon z = 90°
June 21
SUN Sun overhead z = 0°
EquatorCancer
Antarctic
S
U
N
WHAT IS NOONTIME Z IN PERTH, W.A.?
Lat = 32°SZ = >32°
= 32 + 23.5 = 8.5°
Large Zenith Angle: Sun Further FromOverhead – Lower Proportion ofSolar Constant – Less Energy – COOLER!
SUN
December 22 June 21
September 21
March 21
N
S
N
s
Sun on horizon z = 90°
Sun on horizon z = 90°
December 22
Sun overhead z = 0°
Equator
Capricorn
Arctic SUN
S
U
N
Z = >0°= 0 + 23.5 = 23.5°
WHERE IS THE SUN OVERHEAD AT NOON?
23.5°S
N
s
Sun on horizon z = 90°
Sun on horizon z = 90°
December 22
Sun overhead z = 0°
Equator
Capricorn
Arctic SUN
S
U
N
Z = >29.5°= 29.5 + 23.5 = 53°
WHAT IS ZENITH ANGLE AT GAINESVILLE?
N
s
Sun on horizon z = 90°
Sun on horizon z = 90°
December 22
Sun overhead z = 0°
Equator
Capricorn
Arctic SUN
S
U
N
Z = >52°= 52 + 23.5 = 75.5°
WHAT IS ZENITH ANGLE AT SOUTHAMPTON?
N
s
Sun on horizon z = 90°
Sun on horizon z = 90°
December 22
Sun overhead z = 0°
Equator
Capricorn
Arctic SUN
S
U
NZ = < 32°= 32 - 23.5 = 23.5°
WHAT IS ZENITH ANGLE AT PERTH, W.A.?
WHAT IS THE SUB-SOLAR POINT TODAY?La
titud
e of
Sub
-sol
ar p
oint
Equator
23.5°S
21.5°S
Gainesville latitude ~ 29.5°NZ = 29.5 + 21.5 = 51°
BOTTOM LINE
BOTTOM LINE
March and September:Z at noon – Lat.
BOTTOM LINE
March and September:Z at noon = Lat.
Summer (Jun. in N, Dec. in S):Z at noon = Lat -23.5°
BOTTOM LINE
March and September:Z at noon = Lat.
Summer (Jun. in N, Dec. in S):Z at noon = Lat -23.5°
Winter (Dec. in N, Jun. in S):Z at noon = Lat +23.5°