Atmo 201 Exam 3
Terms in this set (36)
What causes wind?
differences in pressure on a horizontal surface
Pressure Gradient Force
force that causes wind to blow always directed from higher pressure toward lower pressure at right angles to the isobars
ridges (elongated highs)
where the air is war indicates
troughs (elongated lows)
where the air is cold
an apparent force that is due to the rotation of the earth. This force causes the wind to deflect to the right of its intended path in the Northern Hemisphere and to the left of its intended path in the Southern Hemisphere
as wind speed increases what force increases?
what is the force that initially sets the air in motion?
Pressure Gradient Force
what does the Coriolis force do to moving air?
makes the air go right in the northern hemisphere and to the left in the southern hemisphere
what is a geostrophic wind?
when the Coriolis force is equal to the pressure gradient force aka straight wind
why would you not expect to observe a geostrophic wind at the equator?
At the equator there is no Coriolis force, thus there cannot be a geostrophic wind.
Why do upper-level winds in the middle la±tudes of both hemispheres generally blow from the west?
High altitudes winds at mid-latitudes blow from the west because they are inﬂuenced by the earth rotation. But it depends on the scale and time you are talking about
Describe how the wind blows around highs and lows alo² and near the surface (a) in the Northern Hemisphere and (b) in the Southern Hemisphere
a) In the Northern Hemisphere, clockwise around high and counterclockwise around low alo². At the surface, friction induces a component directing toward low pressure. In the free troposphere, the balance is between pressure gradient and the Coriolis forces. Near ground, it is a three balance ‐including friction. (b)In the Southern Hemisphere, the geostrophic wind switches the direction
on a surface weather map why do the winds cross the isobars?
because of the influence of friction
if the earth did not rotate how would surface winds tend to blow?
in a straight line from north to south
why do large thunderstorms and heavy rain showers form along the ITCZ?
over equatorial waters, the air is warm, horizontal pressure gradients are weak, and winds are light, here warm air rises often condensing into huge cumulus clouds and thunderstorms
most of the united states is in what wind belt?
explain how and why the average surface pressure features shift from summer to winter?
As low and high-pressure areas are produced due to the differential heating of the earth's surface (land or sea) by the solar radiation, the inclination of the sun's rays plays an important part in determining the surface pressure. This pressure value shifts with the movement of the sun.
describe how the general circulation helps to explain zones of abundant and sparse precipitation along a line that runs from the equator to the poles
the Hadley cell results from rising air at the equator that sinks at around 30 degrees latitude. Rising air causes clouds and precipitation while sinking air decreases cloud so 30 degrees tends to be where deserts are located
why do upper-level winds tend to blow from west to east
because its usually warmer in the south. the warmer air expands creating a pressure gradient toward the north. air moves north but its pulled by the Coriolis force to the east, resulting in westerly winds aloft
why is the polar jet stream stronger in the winter than the summer
contrasts in temperature produce rapid horizontal pressure changes and strong winds .north-to-south temperature contrasts along the front are greater than they are in the summer.
swiftly flowing air currents. forms directly over the center of the strongest area of horizontal temperature difference, or the front.
how are the polar jet stream and the subtropical jet stream similar?
The polar and subtropical jets are both westerly, meaning they come from the west and blow toward the east. Both jets move north and south with the seasons as the horizontal temperature fields across the globe shift with the areas of strongest sunlight.
why is the polar jet stream stronger in the winter than in the summer?
In the winter the polar jet moves south and becomes stronger because the North Pole gets colder but the equator stays about the same temperature. This increases the temperature contrast and moves the strengthened polar front jet farther south.
what air mass brings the coldest wind to the united states?
arctic air mass
why is continental polar air welcome to the central plains in summer but not welcome in the winter?
in the winter it will bring cold air to the already cold temperatures however it will be welcome in the summer to cool higher temperatures
list the temperatures and moisture characteristics of each of the major air masses
explain how arctic outbreaks can occur in the southern part of the U.S.. Where did the arctic air originate and how is it able to move this far south?
upper-level northerly winds as well as high-pressure anticyclones from Canada/arctic
why do we use upper level isobaric charts?
they are extremely important in forecasting all types of weather including severe weather events. They can also be used to determine the movement of weather systems and to predict the behavior of surface pressure areas
a wind that blows at a constant speed parallel to the curved isobars above the level of frictional influence
centripetal acceleration (is directed at right angles to the wind inward toward the low center)
the gradient wind blowing around the low pressure center is constantly changing direction and is therefore constantly accelerating.
inward directed force that is the result from an imbalance between Coriolis force and pressure gradient force
where is the Coriolis stronger and weaker?
the Coriolis is stronger when it gets closer to the pulls and weakest at the equator
wind flows more or less following a more of less north-south trajectory
where the winds are blowing in a west-to-east trajectory
intertropical convergence zone
The intense incoming solar radiation in the equatorial region creates rising air. The rising air cools condenses and forms a region of intense clouds and heavy precipitation. This area is call the
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