Transcript Seasonal and Daily temperatures

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.
Energy Balance in radiative terms.
Earth’s surface receives 147 units of
The atmosphere receives 130 units of
radiant energy from sun and atmosphere,
radiant energy, from sun (19 units) and
while it radiates away 117 units, producing
the earth (111 units), while it loses 160
a surplus of 30 units.
units, producing a deficit of 30 units.
The balance is the warming of the atm. through conduction, convection and latent heat.
Particles and Aurora
Solar wind or plasma is charge
traveling through space from sun to
Earth.
 Solar wind interacts with Earth’s
magnetic field and creates auroras

 Aurora borealis (northern lights)
 Aurora australis (southern lights)
A magnetic field surrounds the earth just as it does a bar magnet.
It protects the Earth from the solar wind.
The stream of charged particles from the
sun (solar win) distorts the earth’s
magnetic field into a teardrop
shape known as the magnetosphere.
The aurora borealis
is a phenomenon
that forms as
energetic particles
from the sun interact
with the earth’s
atmosphere.
Chapter 3
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
Earth’s circumference at Equator) in January,
farthest from Sun (152 million km = 3793 (3% increase)
Earth’s circumference at Equator) in July.
 Distance not the only factor impacting seasons.

Elliptical path
100%
103%
1. Our seasons are regulated by the amount of solar energy received
at the earth’s 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.
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.
As the earth revolves about the sun, it is tilted on its axis by an angle. The earth’s axis
always points to the same area in space (as viewed from a distant star).
Astronomical 1st day
of winter in NH
Astronomical 1st day
of summer in NH
Tropic of Cancer
Tropic of Capricorn
Astronomical 1st day
of spring in NH
2. The second important factor determining how warm the earth’s 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).
The relative amount of radiant energy received at the top of the earth’s
atmosphere and at the earth’s surface on June 21 — the summer solstice.
Incoming
solar
radiation
During the NH
summer, sunlight
that reaches the
earth’s surface in
far northern
latitudes has
passed
through a thicker
layer of
absorbing,
scattering, and
reflecting
atmosphere
than sunlight that
reaches the
earth’s surface
farther south.
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
Equinox
Dec
Equinox
June
Dec
June
Dec
Equinox
June
Fig. 3-8, p. 63
Equinox
Equinox
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)
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.
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.
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°
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.
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.
Vertical temperature profiles
above an asphalt surface for a
windy and a calm summer
afternoon.
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.