the ground, and the air above is warmed by conduction, convection, and 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. 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. 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, 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.

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. FIGURE 2.19 A magnetic field surrounds the earth just as it does a bar magnet.

shape known as the magnetosphere. The stream of charged particles from the sun (solar win) distorts the earth’s magnetic field into a teardrop shape known as the magnetosphere. FIGURE 2.20 The stream of charged particles from the sun— called the solar wind—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. FIGURE 2.22 The aurora borealis is a phenomenon that forms as energetic particles from the sun interact with the earth’s atmosphere.

Seasonal and Daily temperatures Chapter 3 Seasonal and Daily temperatures

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 FIGURE 3.1 The elliptical path (highly exaggerated) of the earth about the sun brings the earth slightly closer to the sun in January than in July. 100% 103%

Our seasons are regulated by the amount of solar energy received at the earth’s surface. ACTIVE FIGURE 3.2 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 (are less intense) to a surface than direct sun rays. Visit the Meterology Resource Center to view this and other active figures at academic.cengage.com/login 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 summer in NH Astronomical 1st day of winter in NH Tropic of Cancer Tropic of Capricorn ACTIVE FIGURE 3.3 As the earth revolves about the sun, it is tilted on its axis by an angle of 231⁄2ｰ. The earth’s axis always points to the same area in space (as viewed from a distant star). Thus, in June, when the Northern Hemisphere is tipped toward the sun, more direct sunlight and long hours of daylight cause warmer weather than in December, when the Northern Hemisphere is tipped away from the sun. (Diagram, of course, is not to scale.) Visit the Meterology Resource Center to view this and other active figures at academic.cengage.com/login 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. FIGURE 3.5 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

reaches the earth’s surface farther south. 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. FIGURE 3.6 During the Northern Hemisphere 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. Sunlight is lost through both the thickness of the pure atmosphere and by impurities in the atmosphere. As the sun’s rays become more oblique, these effects become more pronounced.

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 Dec Equinox June Dec Dec Figure 2.24: The apparent path of the sun across the sky as observed at different latitudes on the June solstice (June 21), the December solstice (December 21), and the equinox (March 20 and September 22). June Fig. 3-8, p. 63

Equinox Equinox TABLE 3.1 Length of Time from Sunrise to Sunset for Various Latitudes on Different Dates in the Northern Hemisphere

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. FIGURE 3.10 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. FIGURE 3.11 On a sunny, calm day, the air near the surface can be substantially warmer than the air a meter or so above the surface.

develops better on the calm night. 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. FIGURE 3.12 Vertical temperature profiles above an asphalt surface for a windy and a calm summer afternoon.