Near-Earth Space: The Van Allen Belts

Nature of the Belts• Discovered early in the space age with a Geiger counter.• Energetic charged particles are trapped in the Earth’s magnetic field.• The inner belt contains protons, and the outer contains electrons.• The inner belt begins at only 100 km or so above ground.

Aurorae

Space Aurora

Aurora Borealis from Yellowknife in Canada

Aurorae• Solar wind particles are generally

repelled by the magnetosphere, but some “sneak” into the atmosphere by running along magnetic field lines toward the poles. (Outer belt)

• Earth atmospheric particles sneak into the belts as well. (Inner belt)

• At ~100km altitude, solar wind particles collide with atmosphere particles to produce an auroral light display.

Comparison of Planetary Magnetic Fields

Equatorial Field(Gauss)

Mercury 0.002

Venus <0.0003

Earth 0.305

Mars (0.0004)

Jupiter 4.2

Saturn 0.20

Uranus 0.23

Neptune 0.06-1.2

The space around the Earth is not exactly crowded, but

there is a great deal of “space debris” in orbit

around Earth.

Cosmic Rays: The penetration of energetic particles from space into the Earth’s atmosphere

The Earth at Night (light pollution)

Sky Appearance

Understanding Sky Color

Sky Color from Two Places

Structure of the Earth’s Atmosphere

The Ozone Layer Component

Antarctic Ozone Hole

Ozone LayerOzone molecule = O3

O3 protects use from harmful solar UV radiation

An efficient O3 destruction mechanism involves chlorofluorocarbons (CFC’s – Cl, F, C):

<chemistry> …

A single Cl atom can be used 1000’s of times to break up ozone molecules!

Catalyst

Ozone Trends

North Pole South Pole

Energy Budget of the Earth

Global Warming: Trends and Effects

• The topic of global warming is complicated. The question is not whether warming exists, but its origin. • Increased greenhouse gases (carbon dioxide, methane, etc) act like a blanket to block the escape of infrared “heat” light.• The Earth has also undergone cycles in the past.• The main concern is the impact and control of warming.

Climate Regulation

Share Question

The Earth's surface absorbs energy from sunlight and then radiates about as much energy back into space. The best proof you can offer for this fact is that the average surface temperature on Earth is

a) warming slowly. b) not warming rapidly. c) half light and half dark. d) warmer at the core than on the surface.

Weather

Primarily driven by solar radiation.Other significant influences include:

1. Land mass and oceans2. Planet rotation3. Atmospheric composition

o Ozoneo Greenhouse effect

4. Volcanic activity

The Hadley Cell: Fundamental circulation pattern because of the fact that planets are

round.

Coriolis Deflection: Planet rotation causes north-south weather circulation to deflect

east-west.

The Coriolis Force

Hadley Cells on the Earth

Volcanoes and Resurfacing

• Magma is less dense than rock, and so rises from the interior

• This breaks through, giving a volcano• Products

– New rocks (esp. basalts)– Ash ( ~1mm )– Cinders (~ 1cm )

• The key point is that volcanoes lead to resurfacing and are evidence of an active planetary interior

Mount St. Helens

Tungurahua (Andes)

Rock TypesIgneous (“ignus”=fire) -

form from crystallization of molten rock– Magma - molten

inside earth– Lava - molten on

surface* Of planetary interest:

– Basalt - fast cooling– Granite - slow cooling

Sedimentary - formed by deposition of small particles which become cemented (e.g., sandstone, shales)

Metamorphic - changed by heat, pressure, and/or chemistry (e.g., marble)

Crustal Plates and Tectonic Activity

• Earth’s surface (or crust) is not a single solid piece, but consists of large and small “plates”

• These plates slowly drift around• At points of convergence, get

volcanoes, mountain ranges, and earthquakes

Crustal Plates

Long Term Plate Drifting

Plate Motion

Volcanic Activity on Earth and Relation to

Motion of Plates

Recycling process and resurfacing effects

Interior Structure of the Earth

Detail of Earth Interior

Seismology

Study of the Earth’s interior from how it carries vibrations

• Types of vibrations– P-waves: pressure waves that travel like sound– S-waves: shear waves, like on a rope

• Terminology:– Focus: point at which the earthquake

originates– Epicenter: surface point above the focus– Seismometer: a device to measure P & S

waves and the strength of earthquakes

Earthquake

Wave Forms

Refraction of traveling sound waves in the Earth reveals its

components

Shuddering of the Earth

Share Question

Earthquakes are an important tool for scientists because their vibrations

a) influence the Earth's orbit about the Sun b) allow the study of the Earth's internal structure c) inform us of the mass of the Earth d) are used to predict the future of plate tectonics

Earth’s Magnetic Field

• Lines of force are somewhat like a bar magnet.

• Its origin and maintenance comes from dynamo activity in the core:Circulation of conducting fluid (e.g.,

molten metals) generates magnetic fields.

So, planetary magnetic fields act like probes of unseen planetary interiors

Earth Dynamo

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The Earth's magnetic dynamo is caused by a combination of convection in its molten core and

a) the Earth's orbit around the Sun b) the Earth's rotation c) lunar tidal action d) the aurora borealis