Atmospheric Lifting Mechanisms Flashcards
What happens when an air mass is lifted?
When an air mass is lifted, it cools adiabatically (by expansion). When the cooling reaches the dew-point temperature, moisture in the saturated air can condense, forming clouds and perhaps precipitation.
What are the Four principal lifting mechanisms
- Convergent lifting results when air flows toward an area of low pressure.
- Convectional lifting happens when air is stimulated by local surface heating.
- Orographic lifting occurs when air is forced over a barrier such as a mountain range.
- Frontal lifting occurs as air is displaced upward along the leading edges of contrasting air masses.
What is Convergent lifting?
Air flowing from different directions forces lifting and displacement of air upward, initiating adiabatic processes.
Air flowing from different directions into the same low-pressure area is converging, displacing air upward in convergent lifting. All along the equatorial region, the southeast and northeast trade winds converge, forming the intertropical convergence zone (ITCZ) and areas of extensive convergent uplift, towering cumulonimbus cloud development, and high average annual precipitation
What is Convectional lifting
Air passing over warm surfaces gains buoyancy and lifts, initiating adiabatic processes
When an air mass passes from a maritime source region to a warmer continental region, heating from the warmer land surface causes lifting and convection in the air mass. Other sources of surface heating might include an urban heat island or the dark soil in a ploughed field; the warmer surfaces produce convectional lifting. If conditions are unstable, initial lifting continues and clouds develop.
What is Orographic lifting
The uplift of a migrating air mass as it is forced to move upward over a mountain range—a topographic barrier. The lifted air cools adiabatically as it moves upslope; clouds may form and produce increased precipitation.
Stable air forced upward in this manner may produce stratiform clouds, whereas unstable or conditionally unstable air usually forms a line of cumulus and cumulonimbus clouds.
What is a Rain Shadow?
The area on the leeward slope of a mountain range where precipitation receipt is greatly reduced compared to the windward slope on the other side. (See Orographic lifting.
What is the Chinook wind?
Chinook wind
North American term for a warm, dry, downslope airflow; characteristic of the rain-shadow region on the leeward side of mountains; known as föhn or foehn winds in Europe.
What is a front?
The leading edge of an advancing air mass is its front.
What is a cold front?
The leading edge of an advancing cold air mass; identified on a weather map as a line marked with triangular spikes pointing in the direction of frontal movement. (Compare Warm front.)
What is a warm front?
Warm front
The leading edge of an advancing warm air mass, which is unable to push cooler, passive air out of the way; tends to push the cooler, underlying air into a wedge shape; identified on a weather map as a line marked with semicircles pointing in the direction of frontal movement. (Compare Cold front.)
Characteristics of a cold front
The steep face of an advancing cold air mass reflects the ground-hugging nature of cold air, caused by its greater density and more uniform characteristics compared to the warmer air mass it displaces
What happens to the warm, moist air in advance of a cold front?
Warm, moist air in advance of the cold front lifts upward abruptly and experiences the same adiabatic rates of cooling and factors of stability or instability that pertain to all lifting air parcels.
What happens a day or two ahead of a cold fronts arrival?
A day or two ahead of a cold front’s arrival, high cirrus clouds appear. Shifting winds, dropping temperature, and lowering barometric pressure mark the front’s advance due to lifting of the displaced warmer air along the front’s leading edge. At the line of most intense lifting, usually travelling just ahead of the front itself, air pressure drops to a local low.
What typically happens in the aftermath of a cold fronts passage?
The aftermath of a cold front’s passage usually brings northerly winds in the Northern Hemisphere and southerly winds in the Southern Hemisphere as anticyclonic high pressure advances. Temperatures drop and air pressure rises in response to the cooler, denser air; cloud cover breaks and clears.
How is a cold front depicted?
a cold front is depicted as a line with triangular spikes that point in the direction of frontal movement along an advancing air mass.
