1. Introduction to Space Weather Interplanetary Transients
The Heliosphere:
Interplanetary Transients
March 08, 2012
CSI 662 / PHYS 660
Spring, 2012
Jie Zhang
Copyright ©

2. Roadmap Part 1: Sun Part 2: Heliosphere CH5: The Solar Wind
Part 3: Magnetosphere
Part 4: Ionosphere
Part 5: Space Weather Effects
CH5: The Solar Wind
CH6: Interplanetary Transients

3. CH6: Interplanetary Transients
CSI 662 / PHYS Mar. 08, 2012
CH6: Interplanetary Transients
6.1. Corotating Interaction Regions
6.2. Interplanetary Coronal Mass Ejections
6.3. Shock Waves
6.4. Solar Energetic Particles
Plasma-10: Shock Wave Models

4. CH6: Interplanetary Transients
References and Reading Assignment:
KAL CH (on CIRs)
KAL CH (on ICMEs)
KAL CH (on Interplanetary Shocks)
KAL CH (on Shock Theory)

5. Introduction
The magnetic field of background solar wind generally follows the Archimedean spiral, characterized by the large scale sector magnetic structures and heliospheric current sheet
They are usually steady and thus “quiet”; do not cause space weather disturbances
Space weather is caused by solar wind transients, or highly disturbed solar wind.
Solar wind transients are in two forms
Corotating interaction region (CIR)
Interplanetary CME (ICMEs)
Solar wind transients are responsible for geomagnetic storms
Increased IMF strength
Increased solar wind speed
Most importantly, the presence of southward IMF (Bz)

6. CH 6.1. CIR
When a low latitude coronal hole appears (across the heliographic equator), fast wind exists in the ecliptic plane. The magnetic field of the fast wind is less curved than that of the slow wind
The fast stream “catches up” with the slow stream, compressing the preceding stream and producing a high pressure region.
This interaction region is at the leading edge of the fast stream, commonly called “corotating interaction region” or CIR
Since low-latitude coronal holes can live over several solar rotations, this structure can recur several times.

7. CH 6.1. CIR

8. CH 6.2. Interplanetary CME (ICME)
A CME propagates into the interplanetary space, plowing through the ambient solar wind
The magnetic structure of an ICME at 1 AU is similar to that in its solar origin, which is a highly helical flux rope.
At 1 AU, it is also called magnetic cloud
highly organized magnetic field is observed, e.g., smooth rotation
Large scale, crossing the Earth for ~ 24 hours
Magnetic Cloud

9. CH 6.2. ICME
A Fast ICME pushes through the interplanetary plasma, and produces a shock wave ahead of it.
A CME driven shock is efficient in accelerating energy particles
In addition to geomagnetic storms, CMEs are also responsible for energetic particle storms.
ICME driven shock

10. SW Observations Direct solar wind observations are routine now
ACE (Advanced Composition Explorer) (1997-present) spacecraft at Lagrangian point 1
WIND (1994-present) spacecraft (complicated orbit, sampling different parts of space)
Measuring
Magnetic field (3-D)
Plasma velocity (3-D), density, temperature
Particle energy, abundance, charge state, composition

11. Example

12. In Situ Observations of the 2008 Feb. 4 CME
Credit: Brian Woods

13. CH 6.3. Shock Waves
A Shock is a discontinuity separating two different regimes in otherwise continuous medium.
It is associated with a disturbance moving faster than the signal speed in the medium (in a gas the signal speed is the speed of sounds; in space plasma: Alfven speed)
At the shock front the properties of the medium change abruptly.
In a hydrodynamic shock, temperature and density increase
In a magnetohydrodynamic shock, magnetic field strength also increases.

14. Example of IP Shock

15. Shock Wave Theory Kallenrode: Chap 6.8 Rankine-Hugoniot Equations:
Relate parameters between upstream and downstream
M: Mach number (shock speed/signal speed)

16. Time-variation of SEP fluxes
CH 6.4. Solar Energetic Particles (SEP)
SEP with energies ranging from a few Kev to several Gev
Because traveling close to the speed of light, they reach the Earth in tens of minutes of the eruption
Small SEPs are caused by flare related acceleration
Large SEPs from CME-driven shocks
Time-variation of SEP fluxes

17. CH 6.4. SEP Large SEPs are accelerated by CME-driven IP shocks.
They can last for several days because of the continuing driving of the shock
Particle energy is gained from the kinetic energy of the shock front.
Refer to Kallenrode Chap 7 for details, if you are interested.

18. The End