Download Foundations of Climate Science Lectures 1–3

Foundations of Climate Science
Lectures 1–3
Rodrigo Caballero
Newton’s Laws
• First Law (Law of Inertia): A body at rest tends to stay at
rest while a body in motion tends to stay in motion,
traveling at a constant speed and in a straight line, until
acted upon by an outside force
Newton’s Laws
• Second Law (Law of Momentum): A force exerted on an
object (including a parcel of water or gas) of a given mass
causes the object to accelerate in the direction of the
applied force and in proportion to the force divided by
the objects mass.
• Force equals Mass times Acceleration
F = ma
Important forces in the atmosphere
(and ocean!)
•
•
•
•
Gravity
Pressure gradient
Coriolis
Friction
Pressure gradient
• Pressure: force per unit area
• In fluid, same force/unit are exerted in every direction
• A body (e.g. a fluid parcel) immersed in a pressure gradient
will experience a net force
• Mathematically:
•
NOTE:
is the corresponding acceleration (force per unit mass)
Fig. 6-4, p. 161
Apparent Forces in the Atmosphere
• Coriolis Force
• Centrifugal Force/Centripetal acceleration
Coriolis Force
Mathematically:
Coriolis force is always to the right in the Northern Hemisphere
Fig. 6-9, p. 165
Force balances in the atmosphere
(and ocean)
• Vertical: hydrostatic balance
• Horizontal: geostrophic balance
Geostrophic Balance
•
•
•
A balance is reached between the coriolis force and the pressure
gradient force
If there is no friction then this occurs when the parcel of air is parallel
to the isobars.
At this point there is no net force on the air parcel - no acceleration it now moves with constant velocity.
Surface winds
•
Friction affects winds only close to the earth's surface.
•
Now we must balance three forces - Coriolis, pressure gradient and friction.
•
Net effect is to induce a net inflow around a cyclone, an effect known as convergence
•
Around an anticyclone we get a net outflow, divergence
Fig. 6-18, p. 175
Fig. 6-24, p. 181
Scales of motion
Whether balances apply or not depends on scale (size) of the
system:
Scale (km)
Hydrostatic
Geostrophic
Micro (< 1)
No
No
Meso (1-100)
Pretty much
No
Synoptic (100-1000)
Yes
Yes
Planetary (>1000)
Yes
Yes