Space Weather

Coronal loops

Intense magnetic field lines trap plasma

http://www.nasa.gov/centers/goddard/images/content 203911main_TRACE_loop_arcade_lg.jpg

Coronal mass ejection

Explosive ejection of gas and plasma from the sun

A space hazard…

Normal conditions

Typical concentration of particles near Earths ~1 particle / cm3Typical velocity ~400 km/sec;

(Protons)

During a solar flare, particle flux increases by a factor > 100,000

Ionized radiation is bad for you…

Sievert – measure of radiation energy absorbed (in gamma ray equivalent) (joules per kg)

Multiply rem x 10 to get mSv

Solar FlareIonized radiation is bad for you…

Notes on the Natural Radiation Hazard at Aircraft Altitudes

In flight there are two principal sources of natural radiation to consider:

1. Galactic Cosmic Rays (GCR) which are always present, and 2. Solar Energetic Particle (SEP) events, sometimes called Solar Cosmic Ray (SCR)

events, which occur sporadically.

GCR provide an inescapable radiation background which varies over the solar cycle of about 11 years. GCR are maximum when solar activity is minimum and vice-versa. The resulting dose equivalent at aircraft also varies quite strongly with altitude and latitude The following table provides estimates of the radiation dose equivalent at the times of a recent solar minimum (10/86) and solar maximum (7/89) for representative high and low latitude locations at 90 degrees west longitude as a function of altitude. These values were obtained through the use of the CARI-6 program developed by the Civil Aeromedical Institute of the Federal Aviation Administration.

Dose Equivalent Rate (micro-sieverts per hour (uSv/h)

Solar Minimum (10/86) Solar Maximum (7/89)

Altitude (x1000

ft)

35 degrees North

Latitude

70 degrees North

Latitude

35 degrees North

Latitude

70 degrees North

Latitude

0 10 20 30 40 50 60 70 80

0.0401 0.190 0.985 3.25 6.78 9.71 11.1 11.4 11.2

0.0412 0.207 1.14 4.06 9.02 13.8 17.1 19.2 20.6

0.0374 0.173 0.875 2.85 5.88 8.36 9.49 9.68 9.44

0.0380 0.181 0.953 3.24 6.99 10.3 12.3 13.3 13.8

We are continually exposed to dose equivalent rates of about 6 to 12 uSv per day at sea-level due to GCR and radiation from the ground which is dependent on our location, as well as radiation from within our own bodies. Thus a two-hour flight at conventional altitudes (20,000 - 40,000 ft) may approximately double one's radiation dose for the day.

Solar particle events of sufficient size to provide significant exposure increases are rare1. In 11 years one could expect up to three events, each of which might produce an equivalent dose rate up to 200 uSv/hr for a few hours at aircraft altitudes. Assuming 3 unusually long duration, maximum events of 1 day each yields a probability of being at altitude on a 2-hour flight during that time of about 1 in 1500.

10 km

20 km

Mostly, it is the mass of the atmosphere that shields us from solar wind radiation, but the magnetic field helps too

The atmosphere protects us from the solar flares

FukashimaReactor #1500 uSv/hr

Interaction of the solar wind and Earth’s magnetic field

All else being equal, this is what the Earth’s field would look like from far away

But the solar wind cannot cross fields lines, so what happens?

Bow shock – where velocity of solar wind drops sharply as it approaches the magnetopauseMagnetopause – delimits boundary between solar wind and Earth’s magnetosphere.Magnetosheath – region between the bow shock and the magnetopause

Outside the bow shock the solar wind wins, Inside the magnetopause the Earth’s field wins, in between is a messy competition

Outside Inside

The magnetic conditions inside and outside the Earth’s magnetosphere are very different

Much quieter inside

Generation of a current sheet in the magneto-tail.

Occurs where the magnetic field switches from south to north, and the field lines are stretched out by the solar wind

Circles show the sense of the magnetic field around parallel wires(with current into page). For a ‘sheet’ of current, the magnetic field Would be given by the red and green lines.

The solar current sheet (or magnetic equator)

Controlled by off-axis dipole, and ~27 day solar rotation.Magnetic equator precesses; from Earth it appears to oscillate

up and down

Some small amount of charged particles can enter magnetopause where field lines and particle trajectories are most nearly parallel

Go to notes on electron orbits in magnetic fields….

Aurora Borealis (northern lights)

From space

Van Allen radiation belts

Outer belt: 4 to 5 Re, electrons

Inner belt: 0.01 to 1.5 Re, protons, particles

1800

180

18

mSv/hour

Multiply rem x 10 to get mSv

1 hour in Van Allen Belt

The South Atlantic Anomaly

SAA is the closest approach of Van Allen radiation belt to the surface.

Happens b/c magnetic pole is tilted relative to Earth’s axis, and b/c Earth’s magnetic field is not uniform

If you are an astronaut or a satellite you want to avoid the area (Hubble shuts down).

SAA is drifting westward ~0.3o per year

Magnetic Fields

Mercury Earth Jupiter Saturn Uranus Neptune

Magnetic Moment /MEarth

1/2700 1 20,000 600 50 25

Surface Field BO (Gauss):

Max/Min:

0.003 ?

0.31 2.8

4.28 4.5

0.22 4.6

0.23 12

0.14 9

Magnetosphere Size Predicted: Observed:

1.2 RM 1.4-1.6 RM

8 RE 6-12 RE

34 RJ 50-100 RJ

16 RS 16-22 RS

20 RU 18-19 RU

20 RN 23-26 RN

Magnetic fields on other planets….

Saturn sometimes sits within Jupiter’s magnetosphere

Jupiter’s radiation belt

(Jupiter’s magnetotail extends beyond Saturn)

Aurora on Jupiter

Io is a major source of plasma-Sulphur dioxides photo dissociates…

Jupiter’s northern lights

Saturn too…