Ch 5

• Weather - short-term changes in the temperature, barometric pressure, humidity, precipitation, sunshine, cloud cover, wind direction and speed, and other conditions in the troposphere at a given place and time.
• Front - the boundary between two air masses with different temperatures and densities.
• Warm front - boundary between an advancing warm air mass and the cooler one it is replacing. Because warm air is less dense than cool air, an advancing warm front rises over a mass of cool air.
• Cold front - leading edge of an advancing mass of cold air.
• Atmospheric pressure - force or mass per unit area of air, caused by the bombardment of a surface by the molecules in air.
• Climate - physical properties of the troposphere of an area based on analysis of its weather records over a long period (at least 30 years). The two main factors determining an area’s climate are its average temperature, with its seasonal variations, and the average amount and distribution of precipitation over at least 30 years.
• Ocean currents - mass movements of surface water produced by prevailing winds blowing over the oceans.
• Convection - movement of warmer molecules that rise and become less dense while colder molecules sink and become more dense, ultimately resulting in the transfer of heat.
• Convection cell - cyclical pattern of air that rises and falls due to convection.
• Latitude - distance from the equator.
• Insolation - input of solar energy in a given area.
• Coriolis effect - the deflection of an air mass to the east as it moves north or south away from the equator, or a deflection west as it moves toward the equator. These deflections occur because the earth’s eastward rotation is faster at the equator than at any other point on its surface.
• Gyres - ocean currents that are driven by prevailing winds and the Coriolis effect, rotating clockwise in the northern hemisphere and counterclockwise in the southern hemisphere.
• Greenhouse gases - gases in the earth’s lower atmosphere (troposphere) that cause the greenhouse effect.
• Greenhouse effect - natural effect that releases heat in the atmosphere near the earth’s surface. Water vapor, carbon dioxide, methane, and other gases in the lower atmosphere absorb some of the infrared radiation (heat) radiated by the earth’s surface and release some of it into the lower atmosphere.
• Rain shadow effect - low precipitation on the leeward side of a mountain when prevailing winds move up and over a high mountain or high mountain range and create semiarid and arid conditions on the leeward side of a high mountain range.
• Biomes - terrestrial regions inhabited by certain types of life, especially vegetation.
• Permafrost - perennially frozen layer of soil that forms when the water there freezes. It is found in the arctic tundra.