# Presentation: PGYBHPWSB72WJ2GOYCM6KYVETNDQ7R5I

## Coronal mass ejections: observations

**First STEREO workshop**
**Paris **
- March 18 – 20, 2002
- Rainer Schwenn
- Max-Planck-Institut für Aeronomie
- Lindau, Germany

## The first CME observed in 1860?

- This early observation was not confirmed convincingly. However...

## The first CMEs observed in modern times: 

- ...the similarity with Skylab images obtained 113 years later is striking!

- The first CMEs observed in modern times:
- OSO 7 (1971)  and Skylab (1973)

## This was the first published „modern“ CME event, observed 1971 from OSO 7. 

- This was the first published „modern“ CME event, observed 1971 from OSO 7.

## The most popular astronomical picture in history:

- a huge prominence, seen in the He+ line (30.4 nm), from **Skylab **(1973)

- From that time in 1973 on, CMEs were an issue!

## CME?  ...can’t tell what it is, but if I see it I know it...

- CME?  ...can’t tell what it is, but if I see it I know it...

**CME: ****coronal -------- mass ejection****,**
**not: ****coronal mass -------- ejection****!**

- I would still prefer to call them SMEs, that avoids confusion...

## Coronal mass ejections (CMEs)

- The CME of Jan 15, 1996, as seen by LASCO**-C3** on **SOHO**

- Note the CME backside: first observational evidence for disconnection of the cloud!

## Some CMEs are 

- Some CMEs are
- spectacular, indeed!

- Most big CMEs show a characteristic 3-part structure:
-  bright outer loop,
-  dark void
-  bright inner kernel

## Some CMEs are 

- Some CMEs are
- spectacular, indeed!

## Some CMEs are 

- A unique observation by **LASCO-C2.**
- Note the helical structure of the prominence filaments!

- Some CMEs are
- spectacular, indeed!

## Some CMEs are 

- A few hours later a huge ejection occurred. Coincidence?
- A unique observation by **LASCO-C2.**
- Note the helical structure of the prominence filaments!

- The same CME,
- seen as a quick-motion movie

- Some CMEs are
- spectacular, indeed!

## There is a huge variety of CMEs, including slow ones!

- A “balloon-type” CME, observed by **LASCO-C1****, **on June 21, 1998.

- There is a huge variety of CMEs, including slow ones!

- Note the 3-part structure:
- bright outer loop,
- dark void,
- bright inner kernel

*Srivastava** et al.**, 1999*

- This balloon took some 30 hours to finally take off!
- It was the offspring of an eruptive prominence. The ejecta ran away at about the slow wind speed, probably no shock was associated with it.

## There is a huge variety of CMEs, including slow ones!

- There is a huge variety of CMEs, including slow ones!

*Srivastava, 1999*

## Initiation of a balloon type CME

**Prominence ascension**

**YOHKOH brightening**

**GOES C-class flare**

**June 21-22, 1998**

-  Leading Edge(C2+C3)

-   Fe XIV

-  Prominence top (C2+C3)

-  Fe XIV (prom)

-   Fe X (top)

-  H-alpha(top)

-  Prominence Tail (C2+C3)

-  Radio

-  H-alpha(lower)

-  Fe X(lower)

**Distance in Solar Radii**

**Time in Hours**

*Srivastava, 1999*

- It is hard to tell when this event really started !

## Properties of CMEs, 1979 to 1981

- Properties of CMEs, 1979 to 1981

*Howard et al., 1985*

## Properties of CMEs, 1996 to 1998

- Note the small number of slow CMEs! The increased sensitivity of the modern instrumentation has NOT increased the number of slow, faint CMEs.*  *

- Histogram of apparent front speeds of 640 CMEs,
- observed by **LASCO** on **SOHO**

- Properties of CMEs, 1996 to 1998

*St.Cyr et al., 2000*

## Properties of CMEs, 1996 to 1998

- The angular size did not change much with rising solar activity

- Apparent angular size
- of 840 CMEs

*St.Cyr et al., 2000*

- Properties of CMEs, 1996 to 1998

## Properties of CMEs, 1996 to 1998

- At activity minimum, there was a clear preference of equatorial latitudes for CME onset

- The center latitudes of 841 CMEs

- Properties of CMEs, 1996 to 1998

*St.Cyr et al., 2000*

## CMEs and shocks during 2 solar cycles

- CMEs

- shocks

- Only one out of 10 CME shocks hits an *in-situ *observer!
- That means: the average cone angle of a shock front amounts to about 1000,
- Remember that the average cone angle of CMEs is only 500.
- In other words: the shock fronts extend much further than the ejecta!

## How do ejecta and shocks propagate? 

- The spread diminishes with increasing distance: fast ejecta are decelera-ted, the slow ones are accelerated and integrated into the slow solar wind.

- Local speeds of about 400 shocks, observed between 0.3 and 1 AU
- by Helios from 1974 to 1986, compared to LASCO CME speeds.

- How do ejecta and shocks propagate?

- LASCO
- CMEs

- Helios shocks

## How do ejecta and shocks propagate? 

- C3

- Helios

- Comparison of shock speeds determined by
- Interplanetary scintillation technique (IPS),
- In-situ measurements by Helios,
- Average propagation speeds between Sun and Helios

-  Apparently, strong deceleration of the very fast events occurs close to the sun.
- The slow ones are decelerated more gradually.

*Woo et al., 1985*

- How do ejecta and shocks propagate?

## How do ejecta and shocks propagate? 

**in 1997**

**Nov.4th  **

- Note the decelerating track
-  of the Nov. 4th, 1997 CME

- Brightness distributions in limited latitudinal slices plotted vs radial distance reveal acceleration/deceleration of features in the corona, e.g. CMEs

*Sheeley et al., 1999*

- How do ejecta and shocks propagate?

## CMEs and shock waves near the Sun

- What is this feature (in the NW): a density wave driven by the subsequent CME?

- Where is the shock with respect to the CME?
- Why can’t we see it, even with our most sensitive instruments?

## A shock wave near the Sun?

- Does this moving kink in the pre-existing radial features indicate the propagation of an otherwise invisible shock wave?

*Sheeley et al., 1999*

## Tracers of shock waves: Radio type II bursts

*Kaiser et al., 1998 *

## Propagation of shock waves from the Sun towards Earth 

*Kaiser et al., 1998 *

- Propagation of shock waves from the Sun towards Earth

- Where and how are they accelerated/decelerated?
- Answers might come from radio wave observations,
- especially for improving space weather forecasts.

## Radio bursts as remote sensors of shock waves

- Height-time diagram of the May 3rd, 1999, CME, as determined from **LASCO**, and from drift rates of type II radio emission.

- The CME shock runs ahead of and simultaneously to
- the metric type II shock.
- They cannot be the same!

- Maybe they can!

*Reiner et al., 2000*

## The events of April 4, 2000

- The events of April 4, 2000

- Based on EIT images, none of the several events seemed worth particular attention ...

## The events of April 4, 2000

- ... nor did the halo CME alert the predictors

- The events of April 4, 2000

## The event of April 4, 2000, unnoticed at first...

- From: Simon Plunkett
- Subject: Halo CME on 2000/04/04
- LASCO and EIT observed a full halo event on 2000/04/04. This is presumably the cause of the shock that was observed at ACE today. The CME was first observed in a C2 frame at 16:32 UT, following a data gap of about ninety minutes. The leading edge of the CME had already left the C2 field of view
- at this time. Measurements in C3 indicate a plane-of-sky speed of 984 km/s at PA 260 (W limb). The event was brightest and most structured ov er the West limb, where a bright core was observed behind the leading edge. The appearance was more diffuse and fainter in the east.
- EIT observed a C9 flare in AR 8933 (N18 W58) at 15:24 UT, that was probably associated with this flare. A large area of dimming between AR 8933 and AR 8935 (S07 W34) was also observed in EIT around the same time.
- Apologies for the late delivery of this message. I was on travel earlier this week and did not see the event until today.

## The storm of April 6, 2000: one of the strongest in the solar cycle, unpredicted!

- GOES-X-rays

- Dst-Index

- Kp-Index

- B

- Bz

- SW density

- flare

- shock

- cloud ?

- The storm of April 6, 2000: one of the strongest in the solar cycle, unpredicted!

**The April 4./6. 2000 events**
- C 9.8 flare:                 	  	  April 4, 16:37
- Arrival of energetic particles at 1 AU: 	none
- Shock at 1 AU:            	   	  April 6, 16:02
- Travel time:                	       	       47.5 hours
- Initial CME speed:		         	         980 km/s
- Average travel speed:      	         	         880 km/s
- Shock speed at 1 AU:         	         	         810 km/s
- Kp max: 	                     		                      8
- Dst min:	                		            -310 nT

- Aurora in Essen, Germany, on April 7, 2000 at 01:00

- The biggest storm of the present solar cycle,
- caused by a middle-class solar event -
- that’s what I call “geoefficient”...!

- Conclusions: Don‘t trust observers and predictors: they might be lacking relevant data or ignoring them, or they are biased, or on vacations, or...

## A never ending discussion: flares vs CMEs

- A solar flare, as observed by **TRACE**

- CMEs, as observed by LASCO C3

- One the cause of the other?

## The “old” paradigm: the “solar flare myth”

*Gosling, 1993*

## The modern paradigm

*Gosling, 1993*

- Flares and CMEs are probably symptoms of a more basic **“magnetic disease”** of the Sun (*Harrison)*

## Explosive onset of a CME

- For this CME we were lucky to observe the onset in
- unprecedented detail, using data from several instruments:
- MICA, SUMER, EIT

## The onset of a fast CME (600 km/s) was revealed!

## The onset of a fast CME (600 km/s) was revealed!

**SUMER slit ****(1 sec ****x**** 300 sec)**

*Innes et al., 2000*

- SUMER happened to take UV spectra in the “right” location. Pure chance!

- EIT images, taken every 12 minutes, show but the scenario

## The onset of a fast CME (600 km/s) was revealed!

- Expansion speeds up to 600 km/s in all directions were measured.That indicates 3-D explosive reconnection at a site in the corona.

*Innes et al., 2000 *

- Line-of-sight plasma flow observations using SUMER spectra.

## Limb CMEs and „halo“ CMEs

- A series of dramatic CMEs observed by LASCO C3 on SOHO

- Halo CMEs, if pointed towards (not away from!) the Earth, may cause disturbances of the Earth‘s geomagnetism: Geomagnetic Storms.

## Halo CMEs: a new quality from SOHO

-  We can now watch earthward pointed CMEs early on

- Towards or away from Earth? That can only be decided using simultaneous disk observations

## A SOHO discovery: EIT waves

- In conjunction, there was a halo CME launched towards Earth.

- In H-alpha, similar features had been seen long ago: “Moreton-waves”.
- They are not the same!

## EIT waves and coronal shock waves

- EIT** **waves are usually much slower
- than type II waves

- That indicates that the EIT-waves are NOT the coronal shock waves causing radio bursts

*Klassen et al., 2000*

## Radio signals („bursts“) as remote sensors

- The “two-shock concept”: a CME driven shock wave
- runs ahead of a flare generated blast wave

- If this concept is correct, why do we never see the blast wave in-situ? Does it die out before it reaches us?

## Ejected plasma clouds in space

- Magnetic clouds imply large-scale rotations of the magnetic field vector

## Ejected plasma clouds in space

- Note the 180 deg rotation of the magnetic field direction through the cloud!

- A typical “magnetic cloud”, following a fast shock wave

## The signatures of plasma clouds/driver gas with respect to the ambient solar wind:

- ion and electron temperature depressions,
- tangential discontinuities in density, temperatures, and field,
- helium abundance enhancements (up to 30 %!),
- unusual ionization states (Fe16+, He+, etc),
- counterstreaming of energetic electrons and protons,
- counterstreaming of suprathermal electrons (BDEs),
- magnetic cloud signatures:
- 		anomalous field rotation,
- 		strong magnetic field,
- 		very low plasma beta,
- 		low variance of the magnetic field.
**Usually, only a subset of these signatures is observed.**

- Ejected plasma clouds in space

## Ejected plasma clouds in space

- Topologies of 3D reconnection

- Another artist at work...

## Do global or sympathetic CMEs exist?

- Do global or sympathetic CMEs exist?

## Global or sympathetic CMEs ?

- A perfect halo CME with symmetric lobes enclosed

- Global or sympathetic CMEs ?

- The „cat‘s head halo“

## The lobes are due to 

- An extended flux rope CME seen from the front or the back side.
- Note the 2D rope structure and the engulfing 3D halo CME structure.

- The lobes are due to
- a projection effect!

- Global or sympathetic CMEs ?

## CME mythology: do global CMEs or sympathetic CMEs exist?

**My answer is: No**.
- They are probably just head-on flux rope halo CMEs.
- Let’s see what they look like from different perspectives, i.e., SMIE, STEREO, SDO, and Solar Orbiter.

## How to predict travel times of halo CMEs? 

- As a better proxy for the unknown speed component towards Earth, we try to use the „expansion speed“ vexp and derive an empirical relation.

**V front**

**V exp.**

**V min**

- The apparent „front speed“ vfront   depends on the ejection direction.

- How to predict travel times of halo CMEs?

## An empirical function was derived: an improved prediction tool!

- presently used

- improved

- For 95 cases, the halo expansion speed and the travel times to 1 AU were determined.
- An empirical function was derived: **a****n improved ****prediction tool!**

- How to predict travel times of halo CMEs?

## Close relatives of “global” CMEs: Cannibals!

- 2 succeeding halo CMEs, “cannibalizing” a limb CME

*Gopalswamy, 2000*

- Let’s see what they look like from different perspectives, i.e., SMIE, STEREO, SDO, and Solar Orbiter!

## Questions to be addressed in the future:

- Where are the shock fronts relative to the CME?
- How does the 3 part CME structure transform into what is encountered *in-situ*?
- Types of CMEs: continuous spectrum or qualitative differences?
- Acceleration/deceleration profiles from Sun to Earth?
- Can proxy data be found for predicting arrival and effects at Earth?
- How to predict CMEs/flares before they occur (time, location, strength, topology)?

- The STEREO mission is the next logical step for finding the answers

## Coronal mass ejections: observations

**First STEREO workshop**
**Paris **
- March 18 – 20, 2002
- Rainer Schwenn
- Max-Planck-Institut für Aeronomie
- Lindau, Germany