Onset of EIT waves - based on images. "After" states the time of the last image which didn't show the EIT wave. "Before" is the first frame which contains the wave. So the wave formed somewhere in between these times. EIT times are accurate to +- 2 minutes after September 1997, and are about +-5 minutes before September 1997. 19970401: After 13:46 before 14:00 19970407: After 14:00 before 14:13 19970512: After 04:34 before 04:50 19971103: Perhaps a hint by 04:32, main wave forms after 04:32 and 05:02 19971103: After 08:47 before 09:11 19971103: A little by 10:21, mostly after 10:21 before 10:32 19971104: After 05:40 before 05:57 19971106: After 11:39 before 11:59 19971127: A little by 13:11, mostly after 13:11 before 13:37 19971212: After 22:05 before 22:22 19980121: After 07:36 before 07:55 19980125: After 14:18 before 14:31 19980329: After 02:43 (maybe a little by 02:43) before 02:56 behind-the-limb event 19980420: A little by 09:22, mostly after 09:22 before 09:34 19980423: A little by 05:33, mostly after 05:33 before 05:49 19980427: After 08:06 before 08:21 19980427: A little by 08:51, mostly after 08:51 before 09:05 Maybe something else between 09:05 and 09:21 - can't tell because the images are too close together in time 19980502: After 13:19 before 13:40 19980503: After 21:09 before 21:22 19980506: A little by 07:58, mostly after 07:58 before 08:09 19980509: A little by 03:11, mostly after 03:11 before 03:28 19980511: After 21:35 before 21:50 19980519: After 09:32 before 09:54 19980527: I'm not entirely sure - I guess I'd say after 13:06 before 13:32 19980611: A little by 09:20, mostly after 09:20 before 09:35 19980616: After 17:50 before 18:02 Speeds (starred * events still need to be measured when the archive comes back on line): EIT images listed below are in the directory "eit_waves." 19970401: From 14:00 - 14:18 the speed is around 200 km/sec. Locations in 19970401_eitwaveloc.gif. 19970407: Speeds reaching 350 km/sec, average closer to 250 km/sec. File called 19970407_eitwaveloc.gif, plot of speeds vs. time in 19970407_eitwavespeed.gif (unfortunately, both these figures are copyrighted for the Astrophysical Journal). 19970512: From 04:50 to 05:07, 250 km/sec, roughly isotropic. Figure in sam_19970512.gif, plot of speeds vs. time in 19970512_eitwavespeed.gif (unfortunately, the second figure is copyrighted by AGU). The first file is named for S"am Krucker, who did the study correlating EIT waves and speeds with WIND 3DP electron events - sorry, sam_*.gif files are copyrighted by the American Geophysical Union). 19971103_1: Sorry - no chance of identifying two moving wavefronts, so no derivation of speed. 19971103_2: Between 10:32 and 10:49, average speed of 200 km/sec. File called 19971103_2_eitwavespeed.gif. (The locations of the wavefronts at 10:49 are a bit sketchy - don't completely trust them). 19971104: Wave too fast - EIT didn't catch it in two frames, just some remainders at 06:13 UT. 19971106: Between 11:59 and 12:13, it was going about 480 km/sec. This wave was very sharp in the beginning, tapering off to a more diffuse wave in the second image. File is called sam_19971106.gif (copyright AGU). 19971127: A small brightening at 13:11, a fully developed wave by 13:37 UT. Speed around 175 km/sec, if you believe that the brightening in the image at 13:11 is a wave. File is 19971127_eitwaveloc.gif 19971212: EIT wave images at 22:05 and 22:22 UT, speed around 220 km/sec. File is sam_19971212.gif (copyright AGU). 19980121: I can't find anything in EIT that's obviously measurable. 19980125: 19980125_eitwaveloc.gif 19980329: Behind the limb, so it's hard to see. There's some sort of impulse or something. 19980420: Another behind-the-limb event, something going on, but you can't trace it. 19980423: 19980423_eitwaveloc.gif has the wave at 05:49 and 06:02 UT. Minimum speed on disk is 270 km/sec, velocity off the limb is 250 km/sec. 19980427_1: Too much coronal evolution - you can't really pick out what the wavefronts are. 19980427_2: Three possible wavefronts at 09:06, 09:21 and 09:36 shown in 19980427_2_eitwaveloc.gif. Speed between 09:06 and 09:21 is around 370 km/sec, between 09:21 and 09:36 is 290 km/sec. Whether it has slowed down or not depends on how reliable you think the location of the first wave front is - it could instead be part of the CME, or it could be stray light from the flare. 19980502_1: From Pick et al, 1999: Unfortunately, the image cadence was too low to adequately measure the speed of the wave disturbance. However, a lower limit can be placed on the speed, as the wave was clearly observable in the image at 13:40 UT, and it had travelled nearly to the solar limb by the time of the next image. Based on the location of the wave at 13:40 UT, and the location of disturbances beyond the dimming region at 14:10 UT, a lower limit of 340 km/sec was derived for the wave speed, travelling in the northward direction. File is 19980502_1_eitwaveloc.gif. 19980502_2: A second wave at nearly the same time as the previous one I can't really see. 19980502_3: I'm not really sure what this third one is... 19980503: 19980503_eitwaveloc.gif has wavefronts at 21:23 UT and 21:37 UT, though the second wavefront location might be a little sketchy. Speed on the left half of the front is 450 km/sec, 370 km/sec on the right half. 19980506: This is a difficult event because the flare is very bright so there's a lot of stray light, and because the wave is moving so rapidly at first. 19980506_eitwaveloc.gif shows the location of wavefronts at 08:10 and 08:22 UT. Velocity is 380 km/sec eastward. 19980509: There are no two images with a clear co-linear wave in them. However, the image at 03:11 doesn't have a wave and the image at 03:29 does. A rough "lower limit" of speed can be placed on the eruption by assuming that the wave originated at the outside of the erupting region. Off limb, an apparent speed is 365 km/sec northward, though in the second image the wave isn't very bright. Wave was also seen on disk at the west limb at 3:43, extending N-S and moving eastward. If you believe there's something after it at 04:02 UT (I'm not sure if I do), then it's travelling 175 km/sec eastward. File is 19980509_eitwaveloc.gif 19980511: Event is behind the limb, nothing very measurable. 19980519: Wave locations at 09:55 and 10:07 UT in 19980519_eitwaveloc.gif Speed southward is a steady 150 km/sec. 19980527: Very faint, nothing very obvious to measure. 19980611: Wave off limb, travelling southward in 19980611_eitwaveloc.gif, fronts at 10:00 and 10:09 UT. Speed is ~ 350 km/sec. 19980616: Very strong wave at 18:18 UT. However, in the previous image, it's hard to see if the off-limb stuff is a wave or the actual CME. Therefore, it's not certain. If you measure the loop and assume it's a wavefront, you get speeds reaching 245 km/sec to the south, 560 km/sec to the north. Closer to the disk (lower altitudes), the speeds are 240 to the north and 215 to the south. 19980616_eitwaveloc.gif shows the alleged fronts.