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are contours on a weather map connecting points of equal pressure

On an upper-level map, is cold air aloft generally associated with low or high pressure? What about warm air aloft?

Warm air aloft is associated with high pressure; cold air aloft with low pressure.

What does a steep (or strong) pressure gradient mean?

It indicates a rapid change in pressure over a relatively short distance.

ow does a gentle (or weak) pressure gradient appear on a surface map?

A weak gradient appears as widely spaced isobars.

Explain how each of the following influences the Coriolis Force: (a) wind speed

A. Increasing wind speed increases the Coriolis force.


B. Increasing latitude increases the Coriolis force. Coriolis force is maximum at the poles and zero at the equator.

What is a geostrophic wind?

The geostrophic wind is a theoretical wind that results from a balance between the Coriolis force and the pressure gradient force (PGF). It is a good approximation for the observed wind in middle latitudes more than ~1 km above the surface.

If the clouds overhead are moving from north to south, would the upper-level center of low pressure be to the east or west of you?

East of you. Remember that if you point your nose in the direction the wind blowing, low pressure is located to your left in the Northern Hemisphere.

On a surface map, why do surface winds tend to cross the isobars and flow from higher pressure towards lower pressure?

Because of the influence of friction.

Since there is always an upward-directed pressure gradient force, why doesn't air rush off into space?

Because of what is called hydrostatic balance: the downward force of gravity balances the upward vertical pressure gradient force.

What is an air mass?

An extremely large body of air (dimensions of 1000's by 1000's of kilometers) whose properties of temperature and humidity are relatively uniform in any horizontal direction at any given altitude.

If an area is described as a "good air mass source region," what information can you give about it?

In order for a huge mass of air to develop uniform characteristics, its source region should be relatively flat and of uniform composition with light surface winds.

hot muggy summer weather in the Midwest and East


efreshing, cool, dry breezes after a long summer hot spell on the Central Plains


persistent cold, damp weather with drizzle along the East Coast


drought with high temperature over the Great Plains


record-breaking low temperatures over a large portion of North America


cool weather with showers over the Pacific Northwest


daily afternoon thunderstorms


Why do mid-latitude cyclones tend to develop along the polar front?

The polar front is a region of enhanced temperature gradients. Thus it provides ideal conditions for the formation of mid-latitude cyclones that derive their kinetic energy from the potential energy of horizontal temperature contrasts.

Why is it important that for a surface low to develop or intensify, its upper- level counterpart must be to the left (or west) of the surface storm?

It is only when the upper-level trough is shifted to the west that upper-level divergence is located over the surface low to deepen it. Figure 8.30 of Ahrens nicely shows the relation between the surface cyclone, jet stream, upper-level divergence and vertical motion.

Warm columns

associated with high upper-level heights and ridges;

cold columns

associated with low upper-level heights and troughs.

station pressure

pressure at the elevation of the station


can be a change in speed and/or a change in direction


simply the mass of air above a given level

Ideal Gas Law


isobaric surface

surface along where the pressure is vertical.

pressure gradient

horizontal difference in temp creates a horizontal difference in pressure. Difference in pressure creates a force that causes the air to move from higher pressure to lower pressure.

upper-level maps

are analyzed on isobaric

surface maps



An elongated area of low atmospheric pressure


An elongated area of high atmospheric pressure.

Air Mass

A large body of air that has similar horizontal temperature and moisture characteristics.


The transition zone between two distinct air masses.

Middle-latitude cyclone

A cyclonic storm that most often forms along a front in middle and high latitudes. Not a tropical storm or hurricane.

Which conditions produce the weakest Coriolis force

70° N; wind speed 0 knots

Why do winds have slower speeds at the surface than 5 km above ground level, even if the pressure gradient force is the same?

There is no frictional force aloft to slow the wind.

Which best describes the balance of forces for geostrophic flow?

2 way balance between Coriolis and Horizontal Pressure Gradient.

Wind speeds blow ____ than geostrophic winds around ____ pressure.

The last two are both correct.

The contour lines drawn on a 500 mb chart are lines of constant.


The deepest hurricane/typhoon ever recorded had a sea-level pressure close to?

870 mb

A ridge on an upper-level isobaric chart indicates?

above average heights

What is the effect of curvature on wind speeds if the size of the pressure gradient force is equal everywhere?

Speeds are slower than geostrophic values around troughs, but faster around ridges.

What conditions characterize an air mass source region?

Weak temperature gradients and weak pressure gradients

What significant weather feature often forms between two contrasting air masses?



come together



Land-sea breeze

A coastal breeze that blows from land to sea, usually at night.

At a warm front, the warm air?

rises and cools

Which air mass brings record breaking maximum temperature to Arizona during June?


Longwaves in the middle and upper troposphere usually have lengths on the order of?

thousands of kilometers.

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