METEOROLOGIST JEFF HABY
Wind is the movement of air. To move the air a force is required. The initiating factor that develops wind
is due to horizontal temperatures differences in the troposphere. Air masses (and air with different temperature
and moisture properties on smaller scales) will have different densities and
these density differences cause pressure differences between the regions the air masses or smaller scale
air regions meet. The force
responsible for moving the air is the
Pressure Gradient Force. There are other factors that influence
the wind speed and direction
centrifugal, etc.) but the Pressure Gradient Force
starts it off. Since temperature differences occur on all scales (global, synoptic, mesoscale, and smaller), wind
patterns are also on all of these scales. Below is a wind glossary that covers many of the various winds and
terminology important to wind in meteorology.
Advection- The horizontal motion of air (parallel to sea level)
Anemometer- An instrument used to measure wind speed
Backing wind- A wind that shifts in a counterclockwise direction with height. For
example, an east wind at 850
mb and a north wind at 700 mb would be a backing wind. Also can be a wind shift at the surface or
a particular pressure level in which over time the wind shifts in a counterclockwise direction at a point
Bora Wind- A cold and dry northeasterly wind that blows down from the mountains along
the eastern shores of the Adriatic Sea.
Calm- A wind speed of less than 3 knots.
Chinook Wind- It is termed a snow eater wind since the warmth and lower humidity
rapidly melt and evaporate snow. A Chinook
is produced by a downsloping wind.
As air downslopes it warms adiabatically and
decreases in relative humidity. The
Chinook is common in the northern plains of the United States in winter.
Convection- A vertical motion of air. The transfer of energy by mixing a fluid.
Coriolis- Coriolis is
the deflection a parcel of air takes relative to the Earth's surface due to Earth's rotation.
Country Breeze- The city tends to be warmer than the surrounding countryside. During
period of clear weather with weak synoptic wind a breeze will blow from the countryside toward the city. The city
air is warmer and thus rises and is replaced by countryside air.
Cyclonic flow- Rotating in the same sense as low pressure. A
cyclonic flow is
counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere.
Derecho- A derecho is
a long line of convective wind gusts originating from evaporationally
cooled high momentum air aloft that accelerates to the surface due to negative buoyancy.
Downsloping Wind- Air that sinks with the terrain as it moves toward
lower elevations. Downsloping air warms adiabatically and decreases in relative humidity.
Eddy- A rotation or spin-off that is embedded within a fluid. Convection
will have eddies at the edges of where air with different temperature and moisture properties is mixing.
Foehn Wind- A warm and dry wind that warms by adiabatic compression as it
moves toward a lower elevation. The process is the same as that that produces a Chinook wind.
Gale Wind- A wind speed ranging from 39 to 54 mph.
Geostrophic Wind- A wind that is balanced by the
Pressure Gradient Force and
remain in geostrophic
balance the wind needs to occur in the middle or high latitudes (since Coriolis is strong enough there) and
needs to flow at a constant speed and direction (to prevent ageostrophic accelerations
and centrifugal accelerations).
Gust Front- A boundary separating downdraft air from a thunderstorm and
the surrounding environmental air. Air tends to be cool and gusty behind the gust front.
Haboob- A severe sandstorm or dust storm with violent winds, occurring
chiefly in Arabia, North Africa, and India during period of dry weather.
Isotach- A line of equal wind speed.
Jet Stream- The Jet Stream is a global upper tropospheric wind belt that separates mid-latitude
air from polar air.
Katabatic Wind- Air that flows under the influence of gravity from
higher toward lower elevations. A air is initially very cold thus it has a high density and is
thus negatively buoyant.
Land Breeze- A wind caused by the differential heating between land and water. During
the night the land cools more than the water. This promotes higher pressure on the land
surface and lower pressure on the water surface. Since air flows from higher toward lower
pressure the wind flow is toward the ocean.
Meridional flow- Meridional flow is a wind flow
through highly amplified troughs and ridges.
Mistral- Extremely cold air in high elevations that blows into the
western Mediterranean basin from the French Alps. Even though the air warms by adiabatic compression, it starts out
so cold that it still ends up being a cold wind.
Mountain Breeze- A wind that blows from the mountains at night due
to differential cooling. The mountains slopes cool more at night than the valley. The cooling air
becomes more dense and then flows toward the valley.
Prevailing Wind- The dominate wind direction at a location for a particular
Santa Ana- A warm and dry wind in southern California. Low pressure to
the south of the area and high pressure to the north of the area set up a dry and adiabatically
compressed wind that comes out of the higher elevations.
Sea Breeze- A sea breeze is a wind caused by the differential heating between land and water. During
the day the land heats more than the water. This promotes lower pressure on the land
surface and higher pressure on the water surface. Since air flows from higher toward lower
pressure the wind flow is from the ocean.
Trade Wind- An easterly band of wind in the tropics. The easterlies are equatorward
from the subtropical highs.
Upsloping Wind- Air that rises with the terrain as it moves toward
higher elevations. Upsloping air cools
adiabatically and increases
in relative humidity.
Valley Breeze- A wind that blows from the valley toward the higher elevations
during the day. The mountain slopes warm more than the valley during the day due to more direct exposure
to the sun. This produces lower pressure along the mountain slopes and thus the flow
is from the higher pressure air in the valley toward the lower pressure air on the mountain slope.
Veering wind- A wind that shifts in a clockwise direction with height. For
example, a south wind at 850
mb and a west wind at 700 mb would be a veering wind. Also can be a wind shift at the surface or
a particular pressure level in which over time the wind shifts in a clockwise direction at a point
Wind- The movement of air. Wind when measured is usually measured as the
horizontal component of the wind speed (parallel to Earth's surface).
Wind Vane- A device used to measure wind direction.
Zonal flow- A zonal flow is a large scale wind flow that is fairly parallel to the
lines of latitude.