Chapter 8 - Air pressure and winds Flashcards
Why does air pressure decrease with height more rapidly in cold air than in warm air?
Warm air spread out more and have higher density. Cold air has low density and is dense at the bottom.
On an upper-level chart, is cold air aloft generally associated with low or high pressure? What about warm air aloft?
Cold air aloft –> low atmospheric pressure. Hot air aloft –> high atmospheric pressure.
Explain why, in the northern hemisphere, the average height of contour lines on an upper level isobaric chart tends to decrease northward.
Generally colder air in the north.
Explain how the following affect the Coriolis force: (a) rotation of earth (b) wind speed (c) latitude?
(a) Deviation from straight path (b) increase the deviation (c) increase in deviation
What factors influence the angle at which surface winds cross the isobars?
Altitude, gravity, Coriolis force, friction affecting wind speeds. The angle is approx. 30° near the ground and increases with height.
Since there is always an upward-directed pressure gradient force, why doesn’t the air rush off into space?
The upward-directed pressure force is nearly always balanced with downward force of gravity = hydrostatic equilibrium.
Explain how on a 500 mbar chart you would be able to distinguish a through from a ridge.
Ridge = where the isobars are high Through = where the isobars are low
Suppose an aircraft using a pressure altimeter flies along a constant pressure surface from a standard temperature into warmer-than-standard air without any corrections. Explain why the altimeter would indicate an altitude lower than the aircraft’s true altitude.
Warm air expands, which means that the same pressure will be at an higher altitude. That’s why the altimeter will show a lower altitude by just measuring the pressure.
If the wind aloft is blowing parallel to curved isobars, with the horizontal pressure gradient force being of greater magnitude than the Coriolis force, would the wind flow be cyclonic or anticyclonic?
Cyclonic flow (northern hemisphere)
The Coriolis force causes winds to deflect to the right of their intended path in the Northern hemisphere, yet around a surface low-pressure area, winds blow counterclockwise, appearing to bend to their left. Explain why.
Coriolis force decrease because of friction. –> pressure gradient force > Coriolis force –> cyclonic flow.
As a cruise ship crosses the equator, the entertainment director exclaims that water in a tub will drain in the opposite direction now that the ship is in the Southern hemisphere. Give two reasons why this is not true.
Coriolis force is not so strong in a small scale, and especially not at the equator.
