Terms in this set (50)
Air in motion measured relative to the Earth's rotating surface
A push or pull on an object computed as mass times acceleration
Newton's second law of motion
A net force is required to cause a unit mass of a substance to accelerate
Air pressure gradient
Change in air pressure with distance
A line plotted on a map joining locations reporting the same air pressure
Pressure gradient force
A force operating in the atmosphere that accelerates air parcels away from regions of high air pressure directly across isobars toward regions of low air pressure in response to an air pressure gradient
An inward-directed force that acts on an object moving in a curved path, confining the object to the curved path
An apparent deflective force arising from the rotation of the Earth on its axis
The resistance an object encounters as it comes into contact with other objects
Friction within fluids such as air and water
Fluid friction arising from the random motions and interactions of molecules composing a fluid such as air or water
Fluid friction arising from eddies within a fluid such as air or water
Atmospheric boundary layer
The atmospheric boundary zone to which frictional resistance is essentially confined
A state of fluid flow characterized by irregular motion
The force that accelerates air downward to the Earth's surface
Balance between the atmosphere's vertical pressure gradient force and the equal, but oppositely directed force of gravity
A hypothetical, unaccelerated horizontal wind that flows along a straight path parallel to isobars or height contours above the atmospheric boundary layer
A hypothetical horizontal wind that blows parallel to curved isobars or height contours, above the atmospheric boundary layer
A dome of air that exerts relatively high surface air pressure compared with surrounding air
A weather system characterized by relatively low surface air pressure compared with the surrounding air
An instrument used to monitor wind direction that consists of a free-swinging shaft with a vertical plate at one end and a counterweight at the other end
An instrument used to monitor wind direction that consists of a cone-shaped cloth bag opened at both ends
A scale of wind speed based originally on visual assessment of the effects of wind on seas and later extended to describe the effects of wind on land-based flexible objects such as trees
An instrument used to monitor wind speed
An instrument that measures wind speed based on the rate of heat loss to air flowing passed a heated wire
A wind sensor designed to measure wind speed and direction
An instrument sensor that emits sound waves to determine wind speed
Weather phenomena operating at the largest spatial scale of atmospheric circulation
Weather phenomena operating at the continental or oceanic spatial scale
Weather phenomena that may influence the weather in only a portion of a large city or county
Weather phenomena that represent the smallest spatial subdivision of atmospheric circulation
What are causes of horizontal air pressure gradients? How do air parcels respond to horizontal air pressure gradients?
Horizontal air pressure gradients are caused by air pressure changes along a surface of constant altitude, such as at sea level. Consequently, horizontal air pressure gradient forces act directly toward lowest pressure and perpendicular to isobars, causing air parcels to move toward lowest pressure.
What is the relationship between the horizontal wind speed and the spacing of isobars on a surface weather map?
Horizontal wind speed is strong where the air pressure gradient is steep, indicated by closely spaced isobars. Horizontal wind speed is light or calm where the horizontal air pressure gradient is weak, indicated by widely spaced isobars.
Why does the Coriolis Effect reverse direction between the Northern and Southern Hemisphere?
The reversal is related to the difference in an observer's sense of Earth's rotation in the two hemispheres. To an observer looking down from high above the North Pole, the planet rotates counterclockwise, whereas to an observer high above the South Pole, the planet rotates clockwise.
How does the Coriolis Effect vary with wind speed and latitude?
The Coriolis Effect influences the wind blowing in any direction, and the amount of deflection varies because of its orientation perpendicular to Earth's axis of rotation. At any latitude in between, some rotation of a tower occurs but not as much as at the poles.
How does the roughness of Earth's surface affect horizontal wind speed and direction within the atmospheric boundary layer?
Friction always opposes motion, acting opposite to the wind direction and increasing with increasing surface roughness. Friction slows horizontal winds blowing within about 1000 m of Earth's surface. A frictional interaction takes place as wind encounters obstacles on Earth's surface. An obstacle on Earth's surface such as trees and houses break the wind into eddies of various sizes to the lee of each obstacle. Consequently, the near surface wind slows. The rougher the surface of the Earth, the greater is the eddy viscosity of the wind.
Give an example of how gravity influences air motion.
Gravity pulls all air downward toward the Earth's surface. Gravity does not modify the horizontal wind because of its vertical direction. Gravity influences air that is ascending or descending, such as the updrafts and downdrafts in convection currents, and gravity is responsible for the downhill drainage of cold, dense air.
What forces are balanced in geostrophic wind?
The geostrophic wind is a steady, horizontal wind that blows in a straight path parallel to isobars at altitudes above the atmospheric boundary layer. The geostrophic wind results from a balance between the horizontal pressure gradient force and the Coriolis Effect. The Coriolis Effect is significant only in broad-scale circulations so that the geostrophic wind develops only in large-scale weather systems.
Why does the circulation within an anticyclone favor fair weather?
Aloft, horizontal winds converge above the center of the surface high to replace the descending air. Adiabatic compression raises the temperature and saturation vapor pressure of descending air, causing existing clouds to vaporize, and the relative humidity to lower. Skies therefore tend to be clear within anticyclones, and anticyclones are appropriately described as fair weather systems.
Why does the circulation within a cyclone bring stormy weather?
Surface winds converge toward the center of a low. Air does not simply pile up at the center; rather, air ascends in response to converging surface winds and diverging winds aloft. Adiabatic expansion of ascending air lowers the temperature and saturation vapor pressure, thereby increasing the relative humidity of unsaturated air. Clouds and precipitation may eventually develop, so that cyclones are typically stormy weather systems.
Why is radiation fog more likely near the center of an anticyclone than near the center of a cyclone?
Radiation fog usually forms at night when the air is calm and clear. These conditions are typically found at the center of an anticyclone. At the center of a cyclone it is often cloudy and turbulent, which prevents the formation of radiation fog.
Distinguish between the geostrophic wind and the gradient.
Difference between gradient and geostrophic winds generally doesn't exceed 10 - 20%
The pattern of horizontal winds blowing about the center of a high-pressure system implies the existence of a centripetal force. Explain why.
Anything in circular motion about a center implies a centripetal force--that's what keeps it going in a circle.
Why are horizontal winds associated with a sloping pressure surface (e.g., 700-mb surface)?
On a horizontal surface that cuts through the 700-mb surface, there will be a pressure gradient. The wind tends to blow toward lower pressure (toward the north), but in the Northern Hemisphere, the Coriolis force deflects the wind toward the right, generating a wind from the West; the greater the pressure gradient, the stronger the wind.
Describe the relationship between a high pressure system and an air mass.
The two main air masses are high pressure, and low pressure. In the northern hemisphere, the winds are clock-wise around, high pressure; counter clock-wise around low pressure.
High pressure is more dense forcing air towards the earth's surface This action tends to dry the air. Low pressure is less dense, and tends to lift air, in general causing moisture to form.
Along a coastline, cumuliform clouds are more likely with an onshore wind (directed from water to land) than an offshore wind (directed from land to water). Explain why.
Onshore wind will bring lot of moisture from the adjacent water surface (sea). Moreover due to the unequal heating of the land and sea surfaces, air over the land will be warmer and will rise leading to convection.This convection carries the moisture brought about by the on-shore wind leading to the formation of cumuliform clouds. On the other hand ,the offshore wind will be comparatively a dry wind with less moisture. So the air will sink over the land which is an unfavorable condition for cloud formation.
Upper-air support for a developing cyclone requires horizontal divergence. Explain why.
For a surface cyclonic strom to intensity,there must be an upper-level counter part a trough of low pressure that lies to the west of surface low.
Suppose that a cyclone is centered over St. Louis, MO. Describe the type of air mass advection to the southeast and to the northwest of the storm center.
The gradient wind in a cyclone blows counterclockwise and parallel to isobars above the atmospheric boundary layer. Under gradient wind conditions, the horizontal pressure gradient force (PH) is directed radially outward, away from the center of the high
In view of Newton's first law of motion, is the gradient wind a consequence of balanced forces? Explain your answer.
According to Newton's first law of motion, air will remain moving in a straight line unless it is influenced by an unbalancing force. The consequence of Coriolis force opposing pressure gradient acceleration is that the moving air changes direction. Instead of wind blowing directly from high to low pressure, the rotation of the Earth causes wind to be deflected off course. In the Northern Hemisphere, wind is deflected to the right of its path, while in the Southern Hemisphere it is deflected to the left.
What is hydrostatic equilibrium? Is vertical motion of air possible with hydrostatic equilibrium? Explain your answer.
when it is at rest, or when the flow velocity at each point is constant over time. This occurs when external forces such as gravity are balanced by a pressure gradient force. For instance, the pressure-gradient force prevents gravity from collapsing Earth's atmosphere into a thin, dense shell, whereas gravity prevents the pressure gradient force from diffusing the atmosphere into space.
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