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 radiant energy from sun and atmosphere, while it radiates away 117 units, producinga 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.

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 aurorasAurora 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 teardropshape 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.

100% 103%

Elliptical path

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 energyto a surface than direct sun rays.

1. Our seasons are regulated by the amount of solar energy received at the earth’s surface.

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).

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).

Tropic of Cancer

Tropic of Capricorn

Astronomical 1st dayof summer in NHAstronomical 1st day

of winter in NH

Astronomical 1st dayof spring in NH

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 solarradiation

During the NH summer, sunlightthat reaches the earth’s surface in far northern latitudes has passedthrough a thicker layer of absorbing, scattering, and reflecting atmospherethan sunlight that reaches the earth’s surface farther south.

Fig. 3-8, p. 63

June

Equinox

June June

JuneJune

June

Equinox Equinox

Equinox EquinoxEquinox

Dec

DecDecDec

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).

Equinox Equinox

Why the Earth has seasons

First day of winterDecember 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 slopesSki slopes: northern slopesLandscaping: plants that like sun over the south sideArchitecture: 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 variationsEach day like a tiny season with a cycle of heating and coolingDaytime heatingAir poor conductor so initial heating only effects air next to groundAs energy builds convection begins and heats higher portions of the atmosphereAfter atmosphere heats from convection high temperature 3-5PM; lag in temperatureSurprisingly, 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 inversiondevelops better on the calm night.