Background Pressure Gradient Force Horizontal winds are forced by horizontal differences in pressure between two locations....
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Background Pressure Gradient Force Horizontal winds are forced by horizontal differences in pressure between two locations. This pressure difference over a horizontal distance is referred to as the horizontal pressure gradient (PG₁). The horizontal pressure gradient force (PGF) acts against this gradient, i.e., winds are forced from high pressure to low pressure, and the magnitude (i.e., speed) of the wind is proportional to the strength of the PGF- The PG, may be expressed as: |PG₁ |=|A| where A is the symbol for change, P is pressure, and d is the distance separating the two pressure values used to calculate the pressure change, AP. Coriolis Force Most of our knowledge about the forces influencing wind is derived from Newton's laws of motion. However, these laws are valid only when viewed from a fixed frame of reference. Since the Earth rotates on its axis, our view of air movement is not from a fixed reference frame. Therefore, to compensate for this, we must consider the apparent force that acts upon the air motion in addition to the Newtonian forces (like the PGF) which only partially dictate the wind direction (but entirely dictate wind speed) from the perspective of those on the rotating reference frame (i.e., the Earth). This apparent force, which we only observe because we are bound to a rotating planet, is called the Coriolis force (CF) and would not be apparent from a fixed reference frame. Essentially, as the Earth rotates out from underneath the wind along its original path, the resultant path as viewed by those fixed to the Earth appears curved, and the direction of this curved path (i.e., to the right or left) depends on the hemisphere in which an observer is located. The CF also increases in strength toward each pole. Key characteristics of the CF: 1. The CF is directed to the right in the Northern Hemisphere at a right angle to the airflow. 2. The CF is directed to the left in the Southern Hemisphere at a right angle to the airflow. 3. The CF is larger for higher wind speeds and higher latitudes. Friction Force The friction force (FF) is the most intuitive of the forces that affect the wind. The FF only influences the speed of air near the Earth's surface, on which obstructions of various height and texture (e.g., trees, buildings, grass, etc.) oppose the progress of the wind set into motion by other forces (i.e., PGFh and CF). Therefore, the FF acts in the opposite direction of the wind. Using the equation below, calculate the strength of the PG, between Station A and Station B in the image below if d is 250 km. Write you answer in units of mb per km, however these units do not need to be include in the answer below. |PG₁|=|A| 1016 mb O Station A Station B 1020 mb O 0 250 km What is the direction of the CF if these wind vectors below are in the Northern Hemisphere. Take the top of your screen to be North. N W Left: [Select] 0 Right: [Select] S E What is the direction of the CF if these wind vectors below are in the Southern Hemisphere. Again, take the top of your screen to be North. N W Left: [Select] Right: [Select] What effect will the FF have on the CF? (Note: remember the FF acts to reduce the wind speed) O Friction will have no effect O Friction reduces the Coriolis Force O Friction increases the Coriolis Force Background Pressure Gradient Force Horizontal winds are forced by horizontal differences in pressure between two locations. This pressure difference over a horizontal distance is referred to as the horizontal pressure gradient (PG₁). The horizontal pressure gradient force (PGF) acts against this gradient, i.e., winds are forced from high pressure to low pressure, and the magnitude (i.e., speed) of the wind is proportional to the strength of the PGF- The PG, may be expressed as: |PG₁ |=|A| where A is the symbol for change, P is pressure, and d is the distance separating the two pressure values used to calculate the pressure change, AP. Coriolis Force Most of our knowledge about the forces influencing wind is derived from Newton's laws of motion. However, these laws are valid only when viewed from a fixed frame of reference. Since the Earth rotates on its axis, our view of air movement is not from a fixed reference frame. Therefore, to compensate for this, we must consider the apparent force that acts upon the air motion in addition to the Newtonian forces (like the PGF) which only partially dictate the wind direction (but entirely dictate wind speed) from the perspective of those on the rotating reference frame (i.e., the Earth). This apparent force, which we only observe because we are bound to a rotating planet, is called the Coriolis force (CF) and would not be apparent from a fixed reference frame. Essentially, as the Earth rotates out from underneath the wind along its original path, the resultant path as viewed by those fixed to the Earth appears curved, and the direction of this curved path (i.e., to the right or left) depends on the hemisphere in which an observer is located. The CF also increases in strength toward each pole. Key characteristics of the CF: 1. The CF is directed to the right in the Northern Hemisphere at a right angle to the airflow. 2. The CF is directed to the left in the Southern Hemisphere at a right angle to the airflow. 3. The CF is larger for higher wind speeds and higher latitudes. Friction Force The friction force (FF) is the most intuitive of the forces that affect the wind. The FF only influences the speed of air near the Earth's surface, on which obstructions of various height and texture (e.g., trees, buildings, grass, etc.) oppose the progress of the wind set into motion by other forces (i.e., PGFh and CF). Therefore, the FF acts in the opposite direction of the wind. Using the equation below, calculate the strength of the PG, between Station A and Station B in the image below if d is 250 km. Write you answer in units of mb per km, however these units do not need to be include in the answer below. |PG₁|=|A| 1016 mb O Station A Station B 1020 mb O 0 250 km What is the direction of the CF if these wind vectors below are in the Northern Hemisphere. Take the top of your screen to be North. N W Left: [Select] 0 Right: [Select] S E What is the direction of the CF if these wind vectors below are in the Southern Hemisphere. Again, take the top of your screen to be North. N W Left: [Select] Right: [Select] What effect will the FF have on the CF? (Note: remember the FF acts to reduce the wind speed) O Friction will have no effect O Friction reduces the Coriolis Force O Friction increases the Coriolis Force
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Smith and Roberson Business Law
ISBN: 978-0538473637
15th Edition
Authors: Richard A. Mann, Barry S. Roberts
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