AAVSO: Solar Bulletin April, 2001

Sudden Ionospheric Disturbance Report

From the April 2001 Solar Bulletin

Michael Hill, SID Analyst
114 Prospect St
Marlborough, MA 01752 USA
noatak@aol.com

Sudden Ionospheric Disturbances (SID) Recorded During April 2001

(Analysis performed by Michael Hill, SID Analyst)
Date	Max	Imp	Date	Max	Imp	Date	Max	Imp
010401	1100	3+	010413	1207	2+	010422	0817	1
010401	1901	1+	010414	0505	1+	010422	1015	1+
010402	0930	2	010414	1745	3	010422	2042	2+
010402	0950	2	010415	0407	2	010422	2120	1-
010402	1015	2	010415	0610	2+	010423	0125	1+
010402	1121	3	010415	0756	2	010423	1016	1+
010402	2150	2+	010415	0847	2+	010423	2118	2+
010403	1235	1+	010415	1103	1+	010424	0540	2+
010403	1648	1-	010415	1400	3+	010424	0700	2+
010403	1745	2+	010416	0624	2	010424	1218	2+
010403	1850	2	010417	1220	2+	010424	1245	2+
010404	0643	3	010417	1404	3	010424	1809	2+
010404	0820	2+	010417	2143	2+	010425	0510	2
010404	1033	3+	010419	1135	2+	010425	1148	2
010404	1201	1-	010420	0507	2+	010425	1345	2+
010404	1225	2+	010420	1303	2	010425	1543	2+
010405	0510	2	010420	1410	1+	010425	1830	1+
010405	0805	2	010420	1658	1	010426	1245	3
010405	0921	2+	010420	1824	2	010427	0658	1
010406	1919	2+	010420	1918	2	010427	1915	2+
010409	0930	2+	010420	1958	3	010428	0931	2
010410	0518	2+	010420	2135	2	010428	2013	1+
010410	1455	2+	010421	1705	1+	010429	1638	1
010411	1320	3	010421	1809	1	010429	1744	2
010411	1855	2	010421	2206	1+	010429	1924	2
010412	0303	1+	010421	2237	2
010412	1015	3	010422	0520	1+

The events listed above meet at least one of the following criteria

Reported in at least two observer reports
Visually analyzed with definiteness rating = 5
Reported by overseas observers with high definiteness rating

Observer	Code	Station(s) monitored
J Winkler	A50	NAA, NPM, xxx
D Overbeek D Toldo	A52	NAA, NWC, xxx
A Stokes	A62	NAA
J Ellerbe	A63	ICV
A Panzer	A83	NAA
W Moos	A84	ICV, FTA, GBZ
M Hill	A87	NAA
J Mandaville	A90	NPM
T Poulos	A95	NAA
R Battaiola	A96	HWU
J Wallace	A97	NAA
M King	A99	GYA

Importance	Duration (min)
1-	< 19
1	19 – 25
1+	26-32
2	33-45
2+	46-85
3	86-125
3+	> 125

Solar Events

April was another fairly active month, although not as active as last month by any means. The thing I noticed most about the data this month was that there were a lot of very long SID events. This of course corresponded to a lot of large flares. Of the 210 Goes-8 Flares recorded, 8 of them were X-Class and 39 of them were M-Class. Out of the 8 X-Class flares two of them were very large. One was an X17.1 on the 2nd and the other was an X14.4 on the 15th.

Corresponding to this, out of the 79 SID events reported, three of them had an importance rating of 3+ , eight of them had an importance rating of 3, and twenty six of them had an importance rating of 2+. A lot of long duration events!

The X-Class flare on the 2nd resulted in an average rating of 2+, and the X-Class flare on the 15th resulted in an average rating of 3.

Once again I have included a bar graph showing the recorded Goes - 8 flares. It was mentioned last month that the graphs for the time period of 7/00 to 3/01 were posted on the web site. This was never attended to by me, but should be there this month. Also of note - there will be a new article to accompany the antenna article posted a few months back. This one is a series of e-mails between a few of our members about the effects of VLF signal propogation. It is very enlightening and I encourange all of you to read it. It really sheds some light onto some of the effects we see when monitoring VLF signals for SID events.