Chapter 10: Progress Questions

Polar High

A cold-core anticyclone originating in a source region for continental polar air; this shallow system is the product of intense radiational cooling over the snow-covered continental interior of North America, well north of the polar front.

Warm Front

A front that moves in such a way that the cold (more dense) air retreats, allowing relatively warm (less dense) air to advance. May be associated with a broad band of cloudiness and light to moderate precipitation.

Santa Ana Winds

A hot, dry chinook wind that blows from the desert plateaus of Utah and Nevada across the Sierra Nevada and downslope toward coastal southern California. This wind desiccates vegetation and contributes to outbreaks of forest and brush fires.

Air Mass

A huge volume of air covering thousands of square kilometers that has relatively uniform temperature and water vapor concentration (humidity) horizontally. The specific characteristics of an air mass depend on the type of surface over which the air mass forms (its source region) and travels.

Sea Breeze

A relatively cool mesoscale surface wind directed from the ocean toward land in response to differential heating of land and sea; develops during daylight hours.

Lake Breeze

A relatively cool surface wind directed from a large lake toward land in response to differential heating between land and lake; develops during daylight hours.

Extratropical Cyclone

A synoptic-scale low pressure system that occurs in midlatitudes, often forming along the polar front. This low, characterized by fronts and a comma cloud pattern, becomes a cold-core cyclone especially in the later stage of its life cycle.

Front

A transition zone between air masses of contrasting air density, that is, air masses of different temperature, humidity, or both. These are classified as stationary, warm, cold, and occluded.

Cyclone

A weather system characterized by relatively low surface air pressure compared with the surrounding air; same as a Low. Viewed from above, surface winds blow counterclockwise and inward in the Northern Hemisphere but clockwise and inward in the Southern Hemisphere.

Chinook Wind

Air that is adiabatically compressed as it is drawn down the leeward slope of a mountain range. As a consequence, the air is warm and dry, causing rapid temperature rises and reduction in snow cover.

Winter Storm

An extratropical cyclone that produces any combination of frozen or freezing precipitation, including snow, ice pellets or freezing rain.

Air Mass Modification

Changes in the temperature, humidity, and/or stability of an air mass as it travels away from its source region. Occurs primarily by exchange of heat, moisture, or both with the surface over which the air mass travels, radiational heating or radiational cooling, or adiabatic heating or cooling associated with large-scale vertical air motion.

The three-dimensional extension of the Norwegian cyclone model includes warm and cold air streams called

Conveyor belts.

Viewed from above, cold and warm fronts in the Northern Hemisphere rotate ______ around centers of low pressure, with cold fronts typically advancing more rapidly than warm fronts.

Counterclockwise

A Chinook wind is most likely to affect the weather of

Denver, Colorado.

Cold air advection occurs to the ______ of the center of a Northern Hemisphere polar high.

East

Santa Ana winds are hot dry winds of southern California produced by adiabatic compression from higher elevation desert areas to the northeast. Santa Ana winds especially exacerbate the ______ situation.

Fire weather

Cold Air Advection

Flow of air across regional isotherms from relatively cool localities to relatively warm localities.

Cold Front

Front that moves in such a way that relatively cold (more dense) air advances and replaces relatively warm (less dense) air.

Fluids, including air, do not readily mix if their densities are different. The boundaries between neighboring air masses of different densities are called ______. Differences in air-mass density are due to differences in temperature and/or humidity.

Fronts

Winter storms are extratropical cyclones that produce

Frozen precipitation.

In coastal areas, a sea (or lake) breeze is likely to develop if regional winds are weak and the surface air pressure is slightly ______ over the water body than over the adjacent land.

Higher

Fronts slope back from the Earth's surface and over ______ dense air.

More

To the northeast of the center of a mature midlatitude cyclone, surface winds are likely to blow from the

Northeast

Indications that a cold front has passed through your location could include the following: falling air temperature, falling dewpoint, ______ air pressure, and a wind shift from south to the west.

Rising

The warm sector of a mature midlatitude cyclone, where air temperatures and dew-points are relatively high, is usually located to the ______ of the center of the system.

Southeast

Air masses are distinguished from one another on the bases of

Temperature and humidity.

Air Pressure

The weight per unit area of a column of air that extends upward from Earth's surface (or any altitude within the atmosphere) to the top of the atmosphere.

Conveyor Belt Model

Three-dimensional depiction of a mature extratropical cyclone and its corresponding fronts in terms of three interacting airstreams, often referred to as conveyor belts. This model developed out of a better understanding of upper-air circulation in the years since the Norwegian cyclone model.

Air masses acquire their temperature and moisture properties primarily from the

Underlying Earth's surface.

As an air mass migrates from its source region, it begins to modify. Air mass modification is more rapid when the air mass flows over a surface (land or water body) that is ______ than the lowest layer of the air mass.

Warmer