Atmospheric Circulation and Weather

Welcome to Poorna's Pages at the Glendale Community College. You are visiting the Module-4 subpage. This module examines the sediments and sedimentary rocks, metamorphism and metamorphic rocks, streams and landscapes, underground water, deserts and wind action and, because of the increasing concerns about global warming and climate change, and broad summary of what we know about atmospheric circulation and weather.

El Niño etc.

	El Niño/La Niña and Pacific Decadal Oscillations
	NASA's El Niño Watch
	The Southern and Northern Oscillations

Abrupt Climate Change:
Science or Not?

Can global warming bring an Ice Age to Europe?

Ocean and Climate Change Institute

The Fortune Magazine Article — "Pentagon's Weather Nightmare"

William Calvin's Talks/Articles:

	When Climate Staggers
	The Atlantic Monthly Article: "The Great Climate Flip-flop"

Ocean-atmosphere interactions

	modulate surface temperatures,
	shape the earth’s overall weather and climate, and
	create ocean waves and currents.

Atmospheric Circulation and Weather

Ocean-atmosphere interactions (a) moderate surface temperatures, (b) shape the earth’s overall weather and climate, and

(c) create ocean waves and currents. l Atmosphere is the solid earth’s ~110 km thick gaseous envelope; weather is the atmosphere’s state at a given point in time and space; and climate is the weather’s yearly averaged seasonal composite. l In the near-surface region that we are interested in, i.e., the troposphere (it extends to 10-15 km above earth’s surface and carries ~90% of the atmospheric mass), average temperatures decrease as we go up. l The atmosphere — is uniquely rich in N₂ (78%) and O₂ (21%) - Moon and Mars lack an atmosphere, atmosphere of Venus is CO₂-rich (~96%), while Jupiter and Saturn have H and He dominated atmospheres; — evolved in three phases: (1) H, He rich early phase of ~4.5 Ga ago, (2)
CO₂, N₂ and H₂O rich middle phase of ~3.7 Ga ago and (3) N₂ and O₂ rich present phase since ~1.25 Ga ago.
l Where did Earth’s CO₂ go?	― Atmosphere has ~0.03% CO₂, Seawater ~60 times as much. ― Carbonates (e.g., limestones) precipitate in the ocean bottom. Indeed, most of this C is now locked up in limestones and marble.
Oceans have thus depleted the earth’s atmosphere of its CO₂ content. l Three forces mainly drive atmospheric circulation: (a) differential solar heating of earth’s surface, (b) gravity, i.e., equatorial bulge versus polar flattening, and (c) rotation. l As solar heating of the earth’s surface varies with latitude, — earth’s elliptical orbit and 23½^° tilt of spin axis create seasons; and
― evaporation dominates radiation in the tropics while water freezes at the polar latitudes to create icecaps.
l Moisture–laden warm air that rises at the equator cools down and must sink but (a) travels polewards as gravity at the poles exceeds that at equator and (b) begins equatorward return as cold surface air after sinking at the pole, so creating a convective cell. l Being basically unstable, this single cell breaks down into three, at 30° and 60° (N and S) latitudes. This creates (a) high pressure zones of sinking air masses at the 30 N and S latitudes and poles (these latitudes thus have deserts on land and high surface water salinity in the oceans), and (b) low pressure zones of rising air masses at the 60 N and S latitudes and equator (these latitudes thus have rain forests on land and low surface water salinity in the oceans).
		l The Coriolis deflection of these convection cells in the direction of Earth’s spin now creates:
		― westward surface winds (“trade winds”) at 0^°-30^°N and 0^°-30^°S, ― eastward surface winds (“prevailing westerlies”) at 30^°-60^°N & S, and ― westward surface winds (“polar easterlies”) at 60^°-90^°N and S.
		l Equatorial surface air thus flows against earth’s spin direction. Warm surface waters thus stack up on the western margins of tropical/semi-tropical oceans, with the following results: ― Warm surface waters stack up on the western margins of tropical/semitropical oceans. This (a) deepens the thermocline on the western coasts, so producing generally humid climatic conditions on one hand and poor fishing conditions on the other; and (b) creates breeding grounds for tropical storms/cyclones on these western margins. ― Upwelling of cold deep waters on the opposite eastern coasts produces arid climates on one hand but excellent fishing on the other.

Earth's atmosphere

is uniquely rich in N₂ (78%) and O₂ (21%) - Moon and Mars lack an atmosphere, atmosphere of Venus is CO₂-rich (~96%), while Jupiter and Saturn have H and He dominated atmospheres; and

evolved in three phases:

H, He rich early phase of ~4.5 Ga ago,

CO₂ N₂ and H₂O rich middle phase of ~3.7 Ga ago and

N₂ and O₂ rich present phase since ~1.25 Ga ago.

Where did Earth’s CO₂ go?

■

Atmosphere has ~0.035% CO₂, oceans ~60 times as much.

■

Carbonates (e.g., limestones) precipitate in the ocean bottom. Indeed, most of this C is now locked up in limestones and marble.

Oceans have thus depleted the earth’s atmosphere of its CO₂ content.

Three forces mainly drive atmospheric circulation:

differential solar heating of earth’s surface, i.e., tropics receive more solar heat per unit area than higher latitudes;

gravity, i.e., earth's equatorial bulge and polar flattening make gravity greater at the poles than at equator; and

rotation, i.e., linear velocity decreases from equator to the poles.

As for the variation of solar heating of the
earth’s surface with latitude,

	earth’s elliptical orbit and 23½^° tilt of spin axis create seasons; and
	evaporation dominates radiation in the tropics while water freezes at the polar latitudes to create icecaps.

Thus, the moisture-laden warm air that rises at the equator cools down and must sink but (a) travels polewards as gravity at the poles exceeds that at equator and (b) begins equatorward return as cold surface air after sinking at the pole, so creating a convective cell.

Being basically unstable, this single cell breaks down into three, at 30° and 60° (N and S) latitudes. This creates (a) high pressure zones of sinking air masses at the 30° N and S latitudes and poles (these latitudes thus have deserts on land and high surface water salinity in the oceans), and (b) low pressure zones of rising air masses at the 60° N and S latitudes and equator (these latitudes thus have rain forests on land and low surface water salinity in the oceans).

The Coriolis deflection of these convection cells in the direction of Earth’s spin now creates:

westward surface winds (“trade winds”) at 0^°-30^°N and 0^°-30^°S,

eastward surface winds (“prevailing westerlies”) at 30^°-60^°N & S, and

westward surface winds (“polar easterlies”) at 60^°-90^°N and S.

Equatorial surface air thus flows against earth’s spin direction. Warm surface waters thus stack up on the western margins of tropical/semi-tropical oceans, with the following results:

Warm surface waters stack up on the western margins of tropical/semitropical oceans. This

deepens the thermocline on the western coasts, so producing generally humid climatic conditions on one hand and poor fishing conditions on the other; and

creates breeding grounds for tropical storms/cyclones on these western margins.

Upwelling of cold deep waters on the opposite eastern coasts produces arid climates on one hand but excellent fishing on the other.