ATOC 1050 EXAM 2 CU BOULDER WITH
COMPLETE SOLUTIONS
Which force controls the movement of air? - ANSWER-The pressure gradient force, the
coriolis force, the frictional force, and the gravitational force. (and we also talked briefly
in chapter 8 about the role the centrifugal force plays for curved flow)
What causes the pressure gradient force? In which direction does it act? - ANSWER-
The pressure gradient force exists anywhere pressure changes with distance. The
pressure gradient force acts from high pressure to low pressure.
What causes friction in moving air? In which direction does the force of friction act? -
ANSWER-Friction in air occurs when faster moving molecules collide with slower
moving molecules or the earths surface, causing air to slow down. Friction acts opposite
the direction of air motion
What is the coriolis force? In what direction does it act in the Northern Hemisphere? -
ANSWER-The coriolis force is an apparent force associated with the rotation of the
earth. It acts on objects in motion across the Earths surface, and it acts to the right of
the direction of motion in the northern hemisphere.
What is geostrophic balance? - ANSWER-Geostrophic balance is the force balance that
exists when the horizontal pressure gradient force is equal and opposite to the coriolois
force.
Hydrostatic Balance? - ANSWER-the force balance that exists when the vertical
pressure gradient force is equal and opposite to the gravitational force
Jetstream - ANSWER-the band of strong winds that circles the globe in middle latitudes
just below the tropopause. Its horizontal position is associated with strong horizontal
surface temperature gradients in the troposphere.
Between what altitudes is the jet stream typically formed? - ANSWER-the average
altitude of the core of the jet stream is typically around 300mb (30,000 ft), but as low as
500 mb.
How is the pressure gradient force related to the wind speed? - ANSWER-In the
absence of other forces, the pressure gradient force is proportional to wind speed.
What does a strong pressure gradient force look like on a sea-level pressure map? -
ANSWER-the pressure gradient force is strong where isobars are close together and
weak where they are far apart.
, Given that the vertical pressure gradient force acts upward, why don't air molecules ugly
off into space? - ANSWER-Gravity acts to hold air on earth, balancing the upward
pressure gradient force.
Name the three types of turbulence that occur in the atmosphere. - ANSWER-
Mechanical, thermal, shear-induced
Mechanical Turbulence - ANSWER-develops when air collides with ground objects
thermal turbulence - ANSWER-develops when warm plumes of air rise and mix with air
above
shear-induced turbulence - ANSWER-develops when wind speed changes with
distance (typically with height) and the faster moving air mixes with the slower moving
air.
On a hot summer day, air flows off the southeast coast of the US and over the Atlantic.
What should happen to the depth of the friction layer once the air moves over the
ocean? - ANSWER-the depth of the friction layer will decrease since mechanical
turbulence is reduced because the water is smooth compared to the land surface
What is a typical depth of the friction layer in the atmosphere? - ANSWER-the friction
layer varies in depth. On a night with weak winds, the boundary layer over a large lake
may only extend upward a few hundred meters, while the boundary layer over a city on
a hot, windy afternoon may extend upward a few thousand meters.
The Coriolis Force (4 key properties) - ANSWER-1. causes objects to deviate to the
right of their direction of motion in the northern hemisphere (and to the left in the
southern hem); 2.affects the direction an object will move across the earth's surface, but
has no effects on its speed; 3. is strongest for fast moving objects and zero for
stationary objects; 4. is zero at the equator and maximum at the poles.
What forces are important for horizontal air motion in the boundary layer? At 7 km
above the ground? - ANSWER-in the boundary layer: horizontal pressure gradient
force, coriolis force, friction at 7km : horizontal pressure gradient force, coriolis force
When air is in geostrophic balance, what is the relationship between the direction of flow
and the height gradient on a constant pressure map? What about the direction the flow
and isobars on a constant height map? - ANSWER-the direction of flow is parallel to the
height contours (perpendicular to the height gradient) on a constant pressure map when
air is in geostrophic balance. The direction of flow is parallel to the isobars
(perpendicular to the pressure gradient) on a constant pressure map when air in
geostrophic balance.
COMPLETE SOLUTIONS
Which force controls the movement of air? - ANSWER-The pressure gradient force, the
coriolis force, the frictional force, and the gravitational force. (and we also talked briefly
in chapter 8 about the role the centrifugal force plays for curved flow)
What causes the pressure gradient force? In which direction does it act? - ANSWER-
The pressure gradient force exists anywhere pressure changes with distance. The
pressure gradient force acts from high pressure to low pressure.
What causes friction in moving air? In which direction does the force of friction act? -
ANSWER-Friction in air occurs when faster moving molecules collide with slower
moving molecules or the earths surface, causing air to slow down. Friction acts opposite
the direction of air motion
What is the coriolis force? In what direction does it act in the Northern Hemisphere? -
ANSWER-The coriolis force is an apparent force associated with the rotation of the
earth. It acts on objects in motion across the Earths surface, and it acts to the right of
the direction of motion in the northern hemisphere.
What is geostrophic balance? - ANSWER-Geostrophic balance is the force balance that
exists when the horizontal pressure gradient force is equal and opposite to the coriolois
force.
Hydrostatic Balance? - ANSWER-the force balance that exists when the vertical
pressure gradient force is equal and opposite to the gravitational force
Jetstream - ANSWER-the band of strong winds that circles the globe in middle latitudes
just below the tropopause. Its horizontal position is associated with strong horizontal
surface temperature gradients in the troposphere.
Between what altitudes is the jet stream typically formed? - ANSWER-the average
altitude of the core of the jet stream is typically around 300mb (30,000 ft), but as low as
500 mb.
How is the pressure gradient force related to the wind speed? - ANSWER-In the
absence of other forces, the pressure gradient force is proportional to wind speed.
What does a strong pressure gradient force look like on a sea-level pressure map? -
ANSWER-the pressure gradient force is strong where isobars are close together and
weak where they are far apart.
, Given that the vertical pressure gradient force acts upward, why don't air molecules ugly
off into space? - ANSWER-Gravity acts to hold air on earth, balancing the upward
pressure gradient force.
Name the three types of turbulence that occur in the atmosphere. - ANSWER-
Mechanical, thermal, shear-induced
Mechanical Turbulence - ANSWER-develops when air collides with ground objects
thermal turbulence - ANSWER-develops when warm plumes of air rise and mix with air
above
shear-induced turbulence - ANSWER-develops when wind speed changes with
distance (typically with height) and the faster moving air mixes with the slower moving
air.
On a hot summer day, air flows off the southeast coast of the US and over the Atlantic.
What should happen to the depth of the friction layer once the air moves over the
ocean? - ANSWER-the depth of the friction layer will decrease since mechanical
turbulence is reduced because the water is smooth compared to the land surface
What is a typical depth of the friction layer in the atmosphere? - ANSWER-the friction
layer varies in depth. On a night with weak winds, the boundary layer over a large lake
may only extend upward a few hundred meters, while the boundary layer over a city on
a hot, windy afternoon may extend upward a few thousand meters.
The Coriolis Force (4 key properties) - ANSWER-1. causes objects to deviate to the
right of their direction of motion in the northern hemisphere (and to the left in the
southern hem); 2.affects the direction an object will move across the earth's surface, but
has no effects on its speed; 3. is strongest for fast moving objects and zero for
stationary objects; 4. is zero at the equator and maximum at the poles.
What forces are important for horizontal air motion in the boundary layer? At 7 km
above the ground? - ANSWER-in the boundary layer: horizontal pressure gradient
force, coriolis force, friction at 7km : horizontal pressure gradient force, coriolis force
When air is in geostrophic balance, what is the relationship between the direction of flow
and the height gradient on a constant pressure map? What about the direction the flow
and isobars on a constant height map? - ANSWER-the direction of flow is parallel to the
height contours (perpendicular to the height gradient) on a constant pressure map when
air is in geostrophic balance. The direction of flow is parallel to the isobars
(perpendicular to the pressure gradient) on a constant pressure map when air in
geostrophic balance.
