Download CME Propagation Instructor Solution

CME Propagation
Instructor Solution
Activities
Activity 1 : Solar Wind & The Shape Of IMF
Question 1: What are the ranges of particle number densities in solar winds
and in a CME bubble?
Solar Wind
CME Bubble
:
:
Nr ≃ 15 − 20 cm−3
Nr ≃ 35 − 55 cm−3
Question 2: Why is the solar wind spiral in shape? What will be the shape
of the solar wind jet if the sun were not spinning?
While the solar wind particles themselves move radially outward from the sun, because of sun’s rotation the locus of all such particles emerging from the same spot on
the sun forms a spiral pattern. This situation is analogous to a garden water sprinkler
where sun is the sprinkler and the solar wind is the water jet. If the sun were not
spinning the shape of solar wind would be straight line directed radially outward.
Activity 2 : CME Propagation Speed
Question 3: What is the CME propagation speed in km/s, as calculated
from the snapshots? Show your calculation and take the average of the
values.
vcme
r
t
1AU = 1.4959 × 108 km
∆r
(1 AU − 0.5 AU)
0.5 AU
=
=
=
= 1037 km/s
∆t
(20 hrs)
20 hrs
∆r
( km)
0.5 AU Mar 05, 8:03
1.0 AU Mar 06, 4:04 7.479 × 107
1.5 AU Mar 07, 4:04 7.479 × 107
∆t
( s)
vcme
km/s
7.206 × 104
8.64 × 104
1037
865
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Question 4: Look at the color code in the velocity plot and answer the following
questions
(i) What is the maximum radial speed of CME plasma particles in km/s?
vrmax ≃ 850 − 1000 km/s
(ii) What is the typical speed of solar wind plasma particles in km/s?
vr ≃ 400 − 500 km/s
Question 5: As the CME propagates through space it leaves a cavity behind
itself. This can be seen as the dark blue region behind it representing very
low particle number density. Why is the region behind the CME empty?
Hint: Examine your answers to the previous question.
It is clear from the answers to the previous questions that the CME plasma travel
2-2.5 times faster than the solar wind plasma. So it sweeps the solar wind plasma
infront of it leaving behind a cavity.
Question 6: Assuming that the CME bubble does not accelerate as it propagates through the heliosphere, calculate the CME propagation time to the
orbits of various planets. We are assuming circular orbits with radii equal
to the mean distances between the sun and the planets.
The CME propagation time is : Tcme = r/vcme ; vcme ≃ 950 km/s = 3.42 × 106 km/hr.
Table 1: CME Propagation Time
Planet Orbital Radius
( AU)
Propagation
Time
Planet Orbital Radius
( AU)
Propagation
Time
Mercury
0.387 AU
16.9 hrs
Jupiter
5.203 AU
9 days − 11 hrs
Venus
0.723 AU
1 day − 7 hrs
Saturn
9.523 AU
17 days − 8 hrs
Earth
1.00 AU
1 day − 20 hrs
Uranus
19.209
34 days − 23 hrs
Mars
1.524 AU
2 days − 18 hrs
Neptune
30.087
54 days − 18 hrs
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Activity 3 : CME & The IMF
Question 7: Why is the IMF spiral in shape, in the absence of CME?
Hint: In a highly conducting fluid like the solar plasma, the magnetic field lines are frozen
in the fluid and are dragged along by the moving fluid.
Since the IMF is dragged along by the solar wind it takes the same shape as the trails of the
solar wind, a spiral shape.
Question 8: How does the shape of IMF change as the CME bubble propagates
through it?
The fast moving CME plasma sweeps all the solar wind plasma between itself and the
sun. So the magnetic field line behind a CME bubble is straight because of the absence of
spiral structure due to solar wind. The field remains pinned to the CME plasma and gets
stretched sideways as the CME spreads out.
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