Seasonal and Daily temperatures

1
Air in the lower atmosphere is heated from the
ground upward. Sunlight warms the ground, and
the air above is warmed by conduction,
convection, and infrared radiation.
Further warming occurs during condensation as
latent heat is given up to the air inside the
cloud.
2
Energy Balance in radiative terms.
Earths surface receives 147 units of radiant
energy from sun and atmosphere, while it
radiates away 117 units, producing a surplus of
30 units.
The atmosphere receives 130 units of radiant
energy, from sun (19 units) and the earth (111
units), while it loses 160 units, producing a
deficit of 30 units.
The balance is the warming of the atm. through
conduction, convection and latent heat.
3
Particles and Aurora

• Solar wind or plasma is charge traveling through
  space from sun to Earth.
• Solar wind interacts with Earths magnetic field
  and creates auroras
• Aurora borealis (northern lights)
• Aurora australis (southern lights)

4
A magnetic field surrounds the earth just as it
does a bar magnet. It protects the Earth from the
solar wind.
5
The stream of charged particles from the sun
(solar win) distorts the earths magnetic field
into a teardrop shape known as the magnetosphere.
6
The aurora borealis is a phenomenon that forms as
energetic particles from the sun interact with
the earths atmosphere.
7
Seasonal and Daily temperatures

• Chapter 3

8
Why the Earth has seasons

• Earth revolves in elliptical path around sun
  every 365 days.
• Earth rotates counterclockwise or eastward every
  24 hours.
• Earth closest to Sun (147 million km 3668
  Earths circumference at Equator) in January,
  farthest from Sun (152 million km 3793 (3
  increase) Earths circumference at Equator) in
  July.
• Distance not the only factor impacting seasons.

9
Elliptical path
100
103
10

• Our seasons are regulated by the amount of solar
  energy received
• at the earths surface.

Sunlight that strikes a surface at an angle is
spread over a larger area than sunlight that
strikes the surface directly.
Oblique sun rays deliver less energy to a surface
than direct sun rays.
11
Why the Earth has seasons

• The amount of energy that reaches the Earths
  surface is influenced by the distance from the
  Sun, the solar angle, and the length of daylight.
• When the Earth tilts toward the sun in summer,
  higher solar angles and longer days equate to
  high temperatures.

12
As the earth revolves about the sun, it is tilted
on its axis by an angle. The earths axis always
points to the same area in space (as viewed from
a distant star).
Astronomical 1st day of summer in NH
Astronomical 1st day of winter in NH
Tropic of Cancer
Tropic of Capricorn
Astronomical 1st day of spring in NH
2. The second important factor determining how
warm the earths surface becomes is the length of
time the sun shines each day. June (NH tilted
towards sun) vs. December (NH tilted away from
the sun).
13
The relative amount of radiant energy received at
the top of the earths atmosphere and at the
earths surface on June 21 the summer solstice.
Incoming solar radiation
14
During the NH summer, sunlight that reaches the
earths surface in far northern latitudes has
passed through a thicker layer of absorbing,
scattering, and reflecting atmosphere than
sunlight that reaches the earths surface
farther south.
15

How the sun would appear in the sky to an
observer at various latitudes during the June
solstice (June 21), the December solstice
(December 21), and the equinox (March 20 and
September 22).
June
June
June
Equinox
Equinox
Equinox
Dec
June
Equinox
Equinox
Equinox
Dec
June
Dec
Dec
June
Fig. 3-8, p. 63
16
Equinox
Equinox
17
Why the Earth has seasons

• First day of winter
• December 21 is the astronomical first day of
  winter, sun passes over the Tropic of Capricorn
  not based on temperature.
• Seasons in the Southern Hemisphere (SH)
• Opposite timing of Northern Hemisphere (NH)
• Closer (about 3) to sun in January (summer!)
  energy at top of the atmosphere is 7 greater in
  January than July. Does that make summers in SH
  warmer than NH? No, due to
• Greater amount of water absorbing heat ? summer
  is not as hot in SH, and winters are not as cold
  in SH.
• Shorter season (see Fig. 3.9)

18
Local seasonal temperature variations

• In the middle latitudes of the NH, objects facing
  south will receive more sunlight during a year
  than those facing north. This fact becomes more
  apparent in hilly or mountainous country
  ?Southern exposure warmer, drier locations
  facing south. Implications for
• Vegetation south side mostly deciduous, north
  side mostly coniferous.
• Viniculture southern slopes
• Ski slopes northern slopes
• Landscaping plants that like sun over the south
  side
• Architecture homes designed for reducing heating
  and cooling costs.

19
In areas where small temperature changes can
cause major changes in soil moisture, sparse
vegetation on the southfacing slopes will often
contrast with lush vegetation on the northfacing
slopes.
20
Local temperature variations

• Environmental Issues Solar Heating
• In order to collect enough energy from solar
  power to heat a house, the roof should be
  perpendicular to the winter sun.
• For the mid-latitudes the roof slant should be
  45- 50

21
Daily temperature variations

• Each day like a tiny season with a cycle of
  heating and cooling
• Daytime heating
• Air poor conductor so initial heating only
  effects air next to ground
• As energy builds convection begins and heats
  higher portions of the atmosphere
• After atmosphere heats from convection high
  temperature 3-5PM lag in temperature
• Surprisingly, noontime is not usually the warmest
  part of the day. Even though incoming solar
  radiation decreases after noon, it still exceeds
  the outgoing heat energy from the surface for a
  time. Afternoon cloudiness will change the time
  of maximum temperature for the day.

22
On a sunny, calm day, the air near the surface
can be substantially warmer than the air a meter
or so above the surface.
On a night, calm day, the air near the surface
can be substantially colder than the air a meter
or so above the surface.
23
Vertical temperature profiles just above the
ground on a windy night and on a calm night.
Notice that the radiation inversion develops
better on the calm night.
Vertical temperature profiles above an asphalt
surface for a windy and a calm summer afternoon.