Please i have a geography question based on atmospheric pressure and wind direct
ID: 107134 • Letter: P
Question
Please i have a geography question based on atmospheric pressure and wind direction. I was told to find the surface wind direction and wind speed of oregon on March 15, 2015. Sorry i couldn't show you what the map look like. But after i located Oregon which is in the West coast and below washington, i found out that the wind direction was South-East (SE) with 5 knots according to the station model i saw. Now they are asking me about "what is the upper atmosphere wind direction over Oregon?
-What does this question mean? are they asking me about the city on top of oregon wind direction, or since i found the oregon wind direction to be SE, are they asking what is the upper atmosphere of that wind direction would be; which is EAST from SE? Sorry my english is not too good.
Explanation / Answer
For better understanding of the question, we will discuss the below points.
Atmospheric Circulation Pressure Belts
• The movement of air in the atmosphere due to the uneven distribution of temperature over the surface of the earth is known as Atmospheric Circulation.
• Air expands when heated and gets compressed when cooled. This results in variations in the atmospheric pressure. The result is that it causes the movement of air from high pressure to low pressure, setting the air in motion.
• Atmospheric pressure also determines when the air will rise or sink.
Wind
• Air in horizontal motion is wind.
• The wind redistributes the heat and moisture across the planet, thereby, maintaining a constant temperature for the planet as a whole.
• The vertical rising of moist air cools it down to form the clouds and bring precipitation.
Atmospheric Pressure
• The weight of a column of air contained in a unit area from the mean sea level to the top of the atmosphere is called the atmospheric pressure.
• The atmospheric pressure is expressed in units of millibars.
• At sea level the average atmospheric pressure is 1,013.2 millibars.
• Due to gravity the air at the surface is denser and hence has higher pressure.
• Pressure is measured with the help of a mercury barometer or the aneroid barometer.
• The pressure decreases with height. At any elevation it varies from place to place and its variation is the primary cause of air motion, i.e. wind which moves from high pressure areas to low pressure areas
Vertical Variation of Pressure
• In the lower atmosphere the pressure decreases rapidly with height. The decrease amounts to about 1 mb for each 10 m increase in elevation.
• It does not always decrease at the same rate the vertical pressure gradient force is much larger than that of the horizontal pressure gradient.
• But, it is generally balanced by a nearly equal but opposite gravitational force. Hence, we do not experience strong upward winds.
Horizontal Distribution of Pressure
• Small differences in pressure are highly significant in terms of the wind direction and velocity. Horizontal distribution of pressure is studied by drawing isobars at constant levels. Isobars are lines connecting places having equal pressure. In order to eliminate the effect of altitude on pressure, it is measured at any station after being reduced to sea level for purposes of comparison.
• Low pressure system is enclosed by one or more isobars with the lowest pressure in the center. High-pressure system is also enclosed by one or more isobars with the highest pressure in the center.
Explanation:
The wind blows from high pressure to low pressure. The wind at the surface experiences friction. In addition, rotation of the earth also affects the wind movement. The force exerted by the rotation of the earth is known as the Coriolis force. Thus, the horizontal winds near the earth surface respond to the combined effect of three forces – the pressure gradient force, the frictional force and the Coriolis force. In addition, the gravitational force acts downward. The differences in atmospheric pressure produce a force. The rate of change of pressure with respect to distance is the pressure gradient. The pressure gradient is strong where the isobars are close to each other and is weak where the isobars are apart. The small heat lows that form on clear hot days. Given a steep lapse rate caused by cool air aloft over a hot surface, little horizontal air movement, few or no clouds, and the noonday sun heating flat arid soil surfaces to high temperatures, the air in contact with the ground becomes super-heated and highly unstable. This surface layer of air builds until something triggers an upward movement. Once started, the hot air rises in a column and draws more hot air into the base of the column. Circulation begins around this heat low and increases in velocity until a small vigorous whirlwind is created. Dust devils are usually of short duration and are so named because they are made visible by the dust, sand and debris that they pick up from the ground. A gust is usually result of rapid and irregular fluctuation of varying intensity in the upward and downward movement of air currents.It may be associated with a rapid change in wind direction.Therefore the upper atmosphere of winf direction plays an important role in determining the effect of the wind in that particular area.