1. Introduction to Space Weather
The Heliosphere:
Transients, Particles
Oct. 15, 2009
CSI 662 / PHYS 660
Fall, 2009
Jie Zhang
Copyright ©

2. Roadmap Part 1: The Sun Part 2: The Heliosphere
Part 3: The Magnetosphere
Part 4: The Ionsophere
Part 5: Space Weather Effects
Part 2: The Heliosphere
Solar wind (steady state)
Solar wind transients: ICMEs, shocks), and energetic particles

3. The Heliosphere: Solar Wind Transients, Energy Particles
CSI 662 / PHYS October
The Heliosphere: Solar Wind Transients, Energy Particles
References:
Kallenrode: Chap. 6, Chap. 7
Prolss: Chap. 6

4. Plasma Physics
1. Shock Waves
Kallenrode: Chap 6.8

5. Solar Wind Transients
The 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
Interplanetary CME (ICMEs)
Corotating interaction region (CIR)
Solar wind transients are responsible for geomagnetic storms
Increased IMF strength
Increased solar wind speed
Most importantly, the presence of southern IMF

6. Corotating Interaction Region (CIR)
When a low latitude coronal hole appears (across the heliographic equator), fast wind exists in the ecliptic plane. The jetline of fast wind is less curved than that of slow wind
Fast streams “catching up” with slow streams, compressing the preceding stream and produce a high pressure region.
The interaction region is at the leading edge of the fast stream
This is 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. Corotating Interaction Region (CIR)

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

9. Interplanetary CME (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. Shock
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 increase.

14. Example of IP Shock

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

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

17. Solar Energetic Particles (SEPs)
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.
Particle acceleration at shock: Kallenrode Chap 7.5

18. The End