Space weather

1.

Space Weather

2.

Coronal loops
Intense magnetic field lines trap
plasma
http://www.nasa.gov/centers/goddard/images/content 203911main_TRACE_loop_arcade_lg.jpg

3.

Coronal mass ejection
Explosive ejection of gas and plasma from the sun
A space hazard…

4.

Normal conditions
Typical concentration of particles near Earths ~1 particle / cm3
Typical velocity ~400 km/sec;
(Protons)

5.

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

6.

Ionized radiation is bad for you…
Sievert – measure of radiation energy
absorbed (in gamma ray equivalent)
(joules per kg)

7.

Ionized radiation is bad for you…
Solar Flare
Multiply rem x 10 to get mSv

8.

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.
The atmosphere protects us from the solar
flares
Dose Equivalent Rate (micro-sieverts per hour (uSv/h)
Solar Minimum (10/86)
10 km
20 km
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 sealevel 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.
Fukashima
Reactor #1
500 uSv/hr
Mostly, it is the mass of the atmosphere that shields us from
solar wind radiation, but the magnetic field helps too
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

9.

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

10.

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

11.

Bow shock – where velocity of solar wind drops sharply as it approaches the magnetopause
Magnetopause – 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

12.

The magnetic conditions inside and outside the
Earth’s magnetosphere are very different
Outside
Much quieter inside
Inside

13.

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.

14.

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

15.

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

16.

Go to notes on electron orbits in magnetic fields….

17.

18.

Aurora Borealis (northern lights)

19.

From space

20.

21.

22.

Van Allen radiation belts
Outer belt: 4 to 5 Re, electrons
Inner belt: 0.01 to 1.5 Re, protons, particles

23.

1800
180
18
mSv/hour

24.

1 hour in Van Allen Belt
Multiply rem x 10 to get mSv

25.

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

26.

Magnetic fields on other planets….
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
1.2 RM
8 RE
34 RJ
16 RS
20 RU
20 RN
Predicted:
1.4-1.6 R M 6-12 RE 50-100 RJ 16-22 RS 18-19 RU 23-26 RN
Observed:
Saturn sometimes sits within Jupiter’s magnetosphere

27.

Jupiter’s radiation belt
(Jupiter’s magnetotail extends beyond Saturn)

28.

Aurora on Jupiter

29.

Jupiter’s northern lights
Io is a major source of plasmaSulphur dioxides photo dissociates…

30.

Saturn too…