Chapter 8 Flashcards
What is air pressure?
The force exerted by air over an area; calculated as Pressure = Force/Area.
How does air pressure change with altitude?
Air pressure decreases exponentially with altitude because there are fewer air molecules above.
What is the Pressure Gradient Force (PGF)?
A force that causes air to move from high to low pressure due to differences in pressure over a distance.
How does temperature affect pressure at different altitudes?
Warm air aloft is associated with high pressure, while cold air aloft is associated with low pressure.
What is the role of PGF in wind formation?
PGF is the primary reason for wind; stronger PGF results in stronger winds.
What are the primary units for measuring air pressure?
Millibar (mb), Hectopascal (hPa), Kilopascal (kPa), and Inches of Mercury (inHg).
What is the difference between station pressure and sea-level pressure (SLP)?
Station pressure is the actual pressure at a location, while SLP is the adjusted value to remove elevation effects.
What are isobars on weather maps?
Lines of constant pressure, spaced typically every 4 mb, showing high and low pressure systems.
What is geostrophic wind?
Wind that flows parallel to isobars in the upper atmosphere due to the balance of PGF and Coriolis force.
What is the Coriolis Force and how does it affect wind?
An apparent force due to Earth’s rotation; deflects winds to the right in the NH and to the left in the SH.
Where is the Coriolis Force strongest and weakest?
Strongest at the poles, weakest (zero) at the equator.
How does friction affect surface winds?
Slows down winds, reducing Coriolis force, causing winds to cross isobars toward low pressure.
What is Buys-Ballot’s Law?
In the NH, if the wind is at your back, low pressure is to your left.
What is gradient wind?
Wind that flows parallel to curved isobars due to a balance of PGF, Coriolis, and centripetal forces.
How do winds circulate around pressure systems in the NH?
Cyclones (low pressure) rotate counterclockwise; Anticyclones (high pressure) rotate clockwise.
How do winds circulate around pressure systems in the SH?
Cyclones (low pressure) rotate clockwise; Anticyclones (high pressure) rotate counterclockwise.
What is the effect of surface convergence in a cyclone?
Air converges and rises, causing cloud formation and precipitation.
What is the effect of surface divergence in an anticyclone?
Air sinks, leading to clear weather.
Why do surface winds cross isobars instead of flowing parallel?
Friction reduces wind speed, weakening Coriolis force, making winds move toward low pressure.
What happens to wind speed when isobars are close together?
Wind speeds increase because PGF is stronger.
How do upper-level winds differ from surface winds?
Upper-level winds flow parallel to isobars, while surface winds cross isobars due to friction.
What happens when warm air meets cold air in the atmosphere?
Warm air rises over cold air, forming pressure gradients that drive wind patterns.
What is the boundary layer in meteorology?
The layer of air near the Earth’s surface (up to ~1 km) affected by friction.
What is the significance of 500 mb charts?
They show mid-tropospheric conditions; high heights = high pressure (warm air), low heights = low pressure (cold air).
How does vertical motion affect weather?
Rising air leads to cloud formation and precipitation, while sinking air leads to clear skies.
