Poster paper for the AGU meeting, 2000 December 15 - 19

Eruptive Events at 30.4 nm: A Further Sample from SOHO EIT

J.B. Gurman
NASA Goddard Space Flight Center
Laboratory for Astronomy and Solar Physics


Although the SOHO Extreme ultraviolet Imaging Telescope (EIT) is normally used to monitor the full disk at 19.5 nm with a 12-minute cadence, we make use of occasional opportunities to observe in the He II Ly alpha resonance line at 30.37 nm (with some contribution from Si XI 30.34 nm) at a somewhat higher cadence. At the current phase of the solar cycle, this affords us the opportunity of amassing some statistics on various kinds of activity observable at 30.4 nm.

I report here on the limb activity visible in these data, including surges, sprays, eruptive prominences, jets, and two classes of phenomena which may not correspond to the classical H I Ba alpha nomenclature for eruptive events: loop jets and fan sprays. The former resemble flare sprays but appear to travel along pre-existing coronal loops, while the latter are not clearly associated with flares, and may represent a manifestation of coronal mass ejections at chromospheric temperatures.

Some background

During the periods 1999 September 27 - October 4, 2000 January 8 - 14, and 2000 March 22 - 25, the SOHO spacecraft was subjected to a series of maneuvers as part of updating the onboard attitude control system (ACS) software to allow closed-loop attitude recovery without the use of gyroscopes. (All three gyroscopes on SOHO are useless since the readout electronics were rendered useless after exposure to extreme cold during the SOHO "vacation" of 1998 June - September.)

During these periods, the LASCO coronagraphs kept their doors closed to prevent contamination, so EIT was able to make use of the entire telemetry bandwidth normally used by both instruments. This in turn allowed us to run, most of the time at 6 - 7 minute cadence, extended time series of images in the 30.4 nm bandpass.

The results reported here are from inspecting those time series, viewed as movies, and from attempting to categorize the eruptive events seen at the limb during those two periods of roughly 7.4, 6.4, and 4.0 days, respectively.

Download a PDF version of the entire poster

Some figures from the current study

  1. A few denizens of the 30.4 nm zoo of eruptive events

  2. Frequencies of the various types of events, for the broadened sample

  3. Frequencies for broad classes of events for all 17.8 days of data

Web curator: Joseph B. Gurman
Responsible NASA official: Joseph B. Gurman, Facility Scientist, Solar Data Analysis Center
+1 301 286-4767

NASA Goddard Space Flight Center
Solar Physics Branch / Code 682
Greenbelt, MD 20771

Last revised 2000 December 05 - J.B. Gurman