Heating the Atmosphere

How do heat and temperature differ? Heat is the ENERGY transferred from one object to another due to a difference in their temperatures. Heat flows from HIGHER to LOWER temperatures. TEMPERATURE is the average kinetic energy of the individual atoms or molecules in a substance.

Energy Transfer Conduction Convection (through movement of a fluid like water or air) Radiation

Conduction Conduction is heat flow through matter by collisions of one molecule with another (molecular activity). The materials have to be TOUCHING. Some materials, like metals, are very good conductors, while others, like air, are very poor. In the atmosphere, conduction is only important at the surface for the air directly in contact with the surface. LEAST IMPORTANT method of heat transfer.

Convection Heat flow through mass movement of a fluid (like water or air) where the molecules or atoms are free to move about or circulate within a substance. Convection depends on unequal heating. As heat is absorbed by some of the fluid, it expands, becomes less dense, and rises due to buoyancy. Colder, denser fluid sinks, flows in (to replace the heated fluid), and becomes heated in its turn, continuing the circulation pattern.

Convection (cont.) In the atmosphere, most of the heat acquired by the lower atmosphere through radiation and conduction is transfered by convection in the air. Convection is also important in the oceans and within the Earth, in the mantle.

Radiation The Sun is ultimately the source of the energy that creates weather. Energy gets from the Sun to Earth via RADIATION (the electromagnetic spectrum, from short wavelengths like x-rays and gamma rays to long wavelengths like radio waves) which travels through space at 300,000 kps.

Radiation (cont.) Radiation is emitted from a source in all directions. Radiation does NOT need a medium through which to travel (no matter needed!) Here are the 4 laws of radiation: All objects, of any temperature, emit radiant energy. Hotter objects radiate more total energy than do cold objects. The hotter the radiating body, the shorter the wavelength of radiation. Objects that are good absorbers of radiation are good emitters as well.

What happens to solar radiation? Absorption Passes through (water and air are transparent to certain wavelengths) Bounces off without being absorbed or transmitted (reflection)

Reflection and Scattering REFLECTION is light bouncing off an object. The reflected light has the same intensity as the incident radiation. SCATTERING disperses light as weaker rays that travel in different directions, although most energy is in the forward direction. Dust and gas molecules scatter light, giving us our blue sky and light on cloudy days. About 50% of the solar radiation that is absorbed at Earth’s surface arrives as scattered light.

Incoming Solar Radiation 50% of incoming solar radiation is absorbed by land and sea 5% is reflected from land/sea interface 20% is absorbed by atmosphere and clouds 20% is reflected from clouds 5% is backscattered to space from the atmosphere

Absorption About 50% of the solar radiation that reaches the top of the atmosphere reaches the surface and is absorbed The atmosphere also plays a major role in heating Earth’s surface.

‘Greenhouse Effect’ The Earth reradiates some of the absorbed solar energy skyward, but at lower temperatures (and longer wavelengths like infrared). The atmosphere (especially water vapor and carbon dioxide) absorbs this energy and in turn radiates it both earthward and skyward. The skyward energy can be absorbed by other gases or it may be lost to space The earthward energy is again absorbed by Earth.

Why do temperatures on Earth vary? We have already looked at differences in how much solar radiation is received at a place due to its latitude. The tropics have warmer temperatures than the polar regions due to more direct solar rays and more daylight.

FACTORS AFFECTING TEMPERATURE A TEMPERATURE CONTROL is any factor that causes temperatures to vary from place to place and from time to time. Other factors beside LATITUDE are HEATING of LAND and WATER, ALTITUDE, GEOGRAPHIC POSITION, CLOUD COVER, and OCEAN CURRENTS.

LAND AND WATER The heating of Earth’s surface controls the temperature of the air above it. Being near a large body of water affects temperatures because land heats more rapidly and to higher temperatures than water does. Land also cools more rapidly and to lower temperatures than water does. The more constant temperature of the water causes the air passing over it to have less temperature change throughout a year than air over land.

Vancouver, BC is at about the same latitude as Winnipeg, Manitoba, so they both have the same solar angle and length of daylight. Vancouver, however, is on the windward Pacific coast while Winnipeg is far inland. The influence of the ocean is that Vancouver’s year-round temperatures are more moderate, cooler in summer and warmer in winter, than Winnipeg’s. “More moderate” also means fewer temperature extremes.

Differences in Hemispheres Another important land and water effect is due to the different amounts of land and water in the Northern and Southern Hemispheres. The Northern Hemisphere has 61% water and 39% land. The Southern Hemisphere has 81% water and 19% land. Which hemisphere would you predict has smaller annual temperature variations (is more moderate)?

Geographic Position Coastal locations where the wind blows onto the land (WINDWARD) or away from the land (LEEWARD) have very different weather. A windward coast gets the moderating influence of the water (cool summers and mild winters) while the leeward coast does not. Mountains can act as barriers, cutting an area off from a moderating influence.

Altitude For the same latitude, higher elevations experience lower overall temperatures than do lower elevations. Understanding check: Denver is far inland but at a high elevation; San Francisco is on the Pacific Coast. They have similar latitudes. What would you expect to be the differences in climate between them?

Cloud Cover Many clouds reflect a significant portion of the sunlight that reaches them back towards space so they have a high albedo. ALBEDO is the fraction of total radiation that is reflected from a surface. How much cloud cover there is strongly affects how much sunlight reaches the Earth’s surface. A cloudy day is a cooler day.

Nighttime Clouds But, clouds at night have the OPPOSITE effect. They act like a BLANKET. Clouds absorb the outgoing radiation from the Earth, trapping it and reradiating some of it back toward the surface. Overall, clouds act to lower daytime temperatures while raising nighttime temps, moderating the daily temperature range.

Ocean Currents The Gulf Stream is a warm current that flows from Florida across the Atlantic Ocean to Great Britain and moderates its climate.

Worldwide Temperature Distribution If you look at world map that show ISOTHERMS, lines that connect points with the same temperatures, you see that temperatures are warmest near the tropics and coldest near the poles, even though there are differences due to the other factors. This shows that the largest influence on temperature is a locations’ latitude.