Transcript Chapter 5 Atmospheric motion

Chapters 5
Motion in the Atmosphere
Motion is called Wind or Air Currents
depending on direction of motion and scale
Influenced by global, regional and local factors
Air motion is both an effect of air pressure
differences and a cause of pressure changes
Air circulation patterns are responsible for many
of the climatic zones on earth
related to movement of moisture
Air pressure
Defined as the force exerted over an area
in essence the force of the weight of the air
Pressure is variable- even without air motion
Why?
Amount of air varies from one location to
another due to changes in elevation, thickness
of the atmosphere, and concentration of gases
Tropics
Poles
Elevation differences
Air pressure is measured in units that express
the force
Variable depending on what we want to try to do
with it
Newton = Force to accelerate 1 kg x 1meter
second
Dyne = force to accelerate 1 gram x 1 cm
second
Pressure terms
Pascal = 1N/m2
Bar = 106 dynes/ cm2
millibar = 1/1000 x 1 Bar
inches or mm of mercury are used to measure
the pressure as air displaces the weight of Hg
Air always corrects for force imbalances in the system
Air moves from high pressure toward low pressure
Air parcels moving from opposing directions are said to be
converging
this will create a pressure imbalance if left alone
Air parcels moving away from a central location are said to
be diverging
this too will create an imbalance if left unchecked
Air moves differently depending on a number of forces
acting on it
Pressure gradient = the pressure imbalance between 2
points
Frictional force = the force slowing the motion of the air
as it drags across a surface
Coriolis force = the force exerted on objects in motion
over long distances- created by earth’s rotation
Must look at
pressure at
the surface
and aloft
This map is at
the surface
Coriolis force
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No frictional force to interfere with other forces at
higher elevations in the atmosphere
e.g., coriolis effect (Ce), centripetal force (Cf)
and pressure head (PH)
direction
air wants
to move
direction
air actually
moves
deflection
by coriolis
force
At the surface frictional force interferes to cause crossing
of isobars
Periodic (localized) winds
daily or annual variations in temperature and pressure
cause the development of periodic or localized wind
fields
Several are common, and they vary in duration and
scale
Small scale winds
Land breeze vs Sea breeze
Fohn, Santa Ana, or Chinook winds
Valley vs Mountain breezes
Sea breeze vs land breeze
Develops due to differential heating of land vs water
- during the day, land heats up fast; water slowly
creates convectional lifting over land
wind from the ocean rushes in to fill the void
- during the night, land cools off quickly; water
remains warm
creates a a convection current over the water
air from land rushes in to fill the void
Sea breeze
vs
Land breeze
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Valley vs Mountain breeze
similar to sea vs land breeze
mountain tops heated by sunlight
trigger updrafts in the mountains that draw
air up the slopes from the valley floor below
Valley-breeze
at night, cool air aloft tries to sink, and
slides down the slopes to the lower valley floor,
forcing warmer air to rise
Mountain-breeze
Katabatic winds
includes Santa Ana, Chinook and Fohn winds
cooler drier air from high elevations is rapidly
warmed as it descends to lower elevations
the reverse of the adiabatic process
+7.7°F/1000 ft
Since the air was dry to start, as it warms
it becomes really moisture starved
Absorbs as much water from wherever it can
When funneled through narrow mountain passes
can cause really high velocity winds
Santa Ana Wind
A katabatic wind
Global
circulation
is set up by
radiation
imbalances
related to
latitude and
land vs
ocean mass
distribution
Radiation imbalance sets up a south to north heat
flow-> and a corresponding North to south wind to
compensate for the pressure imbalance
Tropical waves
generally track along the easterly trade winds
move from east to west
Brings tropical moisture to areas that don’t
always have it
Can assist in development of tropical storms
hurricanes, typhoons, cyclones
ITCZ- Intertropical Convergence Zone
along the equator
air converging to fill void left as heated air rises
creates unstable conditions and perpetual rainy
zone
Migrates with the seasonal shift in solar
radiation changes
toward the north in summer
toward the south in winter
in the middle for fall and spring
Trade winds
called the southeasterlies (S) or the
northeasterlies (N) depending upon which
hemisphere you are in
remember it is based on the direction the
wind comes from
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Westerlies
Common in the mid-latitudes (30-60°N-S)
Create and move storm centers form west to east
Interaction with tropical and polar air occurs in
this zone
creates mid latitude cyclonic circulations
low pressure cells that are associated with
frontal boundaries
Monsoonal circulation
180° reversal of wind direction
often associated with seasonal changes
often associated with rainy vs dry seasons
caused by position of H vs L pressure
Ocean thermohaline conveyor belt