Coronal Mass Ejections

So how often does the Earth get 'hit' by a CME? The SOHO satellite which gives us pictures like the one above, watches the Sun round the clock and since 1996 it has detected thousands of these explosions. Most of them shoot out sideways and are not directed towards Earth. Some of them, however, head right towards Earth. They look like a sudden 'halo' of light expanding from nearly all around the edge of the Sun at the same time. Scientists look for these Halo CME events and note them carefully. Usually, within a few days, the CME produces effects here at Earth.

To see how often Earth gets in the way, lets look at the table below compiled by Dr. Chris St.Cyr (Naval Research Lab/LASCO).

Study the list, and answer the questions at the end.

Appearance

Speed

Description of the Event

Date

Time [UT]

[km/s]

 

1998/06/01

11:27

272

Small bright front; falls apart in C2

1998/06/01

15:00

364

Jet. Part of continuous E limb activity?

1998/06/02

02:04

249

Material; falls apart in C2

1998/06/02

02:59

254

Bright thick (flat?) structured arcade

1998/06/02

08:08

1383

Bright streamer eruption; mega prom material

1998/06/02

21:06

882

Structured material w/no obvious front

1998/06/03

12:02

604

Thick structured loop; mega concave-out

1998/06/04

02:04

1717

Halo CME. Extremely bright & structured

1998/06/04

06:31

880

Serrated edge in C2; not much front in C2

1998/06/04

09:36

217

Asymmetric narrow loop(?) w/core

1998/06/04

21:00

517

Non-radial ragged material

1998/06/04

21:27

652

Thick ragged loop w/structured core

1998/06/04

22:28

422

Structured material

1998/06/05

01:30

499

Faint filled mound feature

1998/06/05

07:02

755

Faint loop w/trailing structured loop(s)

1998/06/05

10:28

431

Bright structured non-radial material

1998/06/05

12:01

412

Halo CME. Starts as concentric loops

1998/06/06

08:27

494

Non-radial fan

1998/06/06

12:27

271

Faint material precedes slowly rising faint loop

1998/06/06

all day

537

Several blobs or loops ejected?

1998/06/07

09:32

516

Halo CME. Bright structured halo (doily)

1998/06/07

19:27

392

Non-radial material falls apart in C2

1998/06/08

08:01

143

Faint loop precedes brighter structured cloud

1998/06/08

15:27

560

Bright structured in NE from swelling streamer

1998/06/09

05:55

255

Thick arcade

1998/06/09

08:27

197

Thin loop

1998/06/09

09:27

314

Second thick arcade overlaps previous

1998/06/09

11:27

508

Third structured arcade w/core; overlaps earlier

1998/06/10

03:55

667

Bright & structured in SE; doily?

1998/06/10

11:27

483

Blob precedes concave-out

1998/06/10

16:06

421

Cloud /some structure

 

 

 

 

  1. How many days worth of observations are recorded?
  2. How many Halo CMEs were recorded during this time?
  3. What is the average number of days between the sightings?
  4. How many ejections of material were seen?
  5. What fraction of coronal mass ejections are Halo CMEs?
  6. What is the average (mean) speed of a CME?
  7. What is the median speed of a CME?
  8. What is the mode speed of a CME?