System Earth 2a

Atmosphere I

Misha Velthuis

m.velthuis@uva.nl

Tue 10 Sept 2024

Content

Vertical flows

Horizontal flows

Meridional flows

Zonal flows

Presentation

Take home assignment

Looking back

Negative and positive couplings

Negative and positive feedback loops

Dynamic equilibria

Residence time and response time

Forcings and perturbations

Feedback factor

Gaia hypothesis

Driving force

Of course …

Description with image from source (NASA):

The peak energy received at different latitudes changes throughout the year. This graph shows how the solar energy received at local noon each day of the year changes with latitude. At the equator (gray line), the peak energy changes very little throughout the year. At high northern (blue lines) and southern (green) latitudes, the seasonal change is extreme. (NASA illustration by Robert Simmon.)

"Autumnal equinox"

"Autumnal" equinox

Autumnual equinox?

Anyway… on average …

Imbalances

From source: (NASA):

This map of net radiation (incoming sunlight minus reflected light and outgoing heat) shows global energy imbalances in September 2008, the month of an equinox. Areas around the equator absorbed about 200 watts per square meter more on average (orange and red) than they reflected or radiated. Areas near the poles reflected and/or radiated about 200 more watts per square meter (green and blue) than they absorbed. Mid-latitudes were roughly in balance. (NASA map by Robert Simmon, based on CERES data.)

Atmospheric flows

Vertical

Buoyancy

Warm air

Lower density

Higher buoyancy

Pressure gradient

"The atmospheric pressure is a force (F)

determined by the mass (m) of the air column

and the acceleration (a) due to gravity…"

\[F = m.a\]

"If we consider two adjacent columns of air,

of the same volume

one warmer than the other,

the cooler column would have a greater

density, thus more mass and a higher pressure

than the warmer column."

Pressure gradient reversal

Meridional (north-south)

Some key concepts

Tropics (23.5° N/S)

Arctic/antarctic circle (polar circle) (66° N/S)

Subtropical high (30°-35° N/S)

Midlatitudes (between subtropical high and polar circle)

High latitudes (above polar cicles)

Easterlies, westerlies, equatorward, poleward

Meridional flows

Temperature vs altitude

Zonal (west-east)

Coriolis force

Coriolis effect on north-south flows

Coriolis effect on west-east flows

Centrifugal force.

We are all "thrown off" the planet a little bit.

Air moving in the same direction as the earth rotates (moving towards the east) is experiencing slight stronger centrifugal force than static things.

Effective pull away from axis of rotation
Vector decomposition:
- pull away from axis can be decomposed in a vector perpendicular to the surface, and a vector parallel to the surface.
- Force perpendicular to the surface is balanced by gravity. Force parallel to the surface is not.
- Effectively pulling the air south (on the NH) (i.e. to the right).
Air moving in the opposite direction as the earth rotates (moving towards the west) is experiencing weaker centrifugal force than static things. Effectively experiencing centripetal force: pulled towards the axis. Effectively pulled north. (i.e. again to the right). (On the NH).

Jet stream

Geostrophic wind

Weather in midlatitudes

Summary

Vertical flows

Horizontal flows

Meridional flows

Zonal flows