New sunspot group 1057 appeared on March 23; by March 24, it was 38 times its original size. It covered 10 one-millionths of the solar hemisphere on Tuesday, and on Wednesday, it grew to 380 one-millionths. On Thursday, new sunspot group 1058 appeared, and the total area for both groups expanded to 401 millionths of the solar hemisphere. The total sunspot area has not been this large since February 8 when the total was 460 one-millionths (the numbers given for Wednesday are a revision of the numbers for the same day given in yesterday’s ARRL Letter).

The largest area covered during all of 2009 was 380 on October 29, followed by 310 on December 18. March 23-April 3, 2008 was a period of very strong sunspot activity, and on March 26-28, the area covered by three sunspots was 520, 510 and 410 one-millionths of the solar surface.

The average daily sunspot numbers were down nearly 5 points this week to 24.6. Sunspot numbers for March 18-24 were 28, 24, 25, 25, 17, 26 and 27, with a mean of 24.6. The 10.7 cm flux was 85.8, 84.4, 83.5, 84.8, 82.5, 83.9 and 84.4, with a mean of 84.2. The estimated planetary A indices were 5, 4, 7, 2, 2, 2 and 3, with a mean of 3.6. The estimated mid-latitude A indices were 4, 2, 5, 0, 0, 0 and 2, with a mean of 1.9.

The spring equinox was last Saturday, March 20, and HF radio conditions are good with quiet geomagnetic conditions. NOAA and the US Air Force predict solar flux of 88 for today, March 26 and 89 for March 27-31. This is higher than the average solar flux for this week -- 84. Last week it was 87.6 and the week before, it was 78.6. Our reporting week for data at the end of this bulletin is always Thursday-Wednesday, and we haven’t reported a weekly average solar flux above 89 since our February 19th update that had 90.6 on February 11-17.

NOAA predicts a bit more geomagnetic activity -- but not much! -- rising from a planetary A index of 5 on March 26, to 7 on March 27 and 8 for March 28-31. Geophysical Institute Prague expects quiet to unsettled conditions March 26, quiet March 27-29, quiet to unsettled March 30-31 and a return to quiet for April 1 -- the day that NOAA predicts a planetary A index of 5. Last week for the first time we presented the trailing 50-day average of daily sunspot numbers, 27.34. This week it is 28.18.

This weekend is the CQ World Wide WPX SSB Contest. HF conditions should be good.

Harry Gross, KC2FYJ, of Mineola, New York, wrote in with questions about the numbering of sunspot groups, which is different than the sunspot number. Harry asked, “First, what’s the scheme (for example, why is a particular group referred to as 1055)? Is it the 55th group seen in 2010 perhaps? Or is it something more esoteric? Second, how do you decide that a particular group is ‘returning?’ I presume it’s because it’s circled the Sun and is returning on the other side again; however, how can you be certain it’s the same group, since there is a wide (but now narrowing, thanks to STEREO) area were we can’t observe on the far side of the Sun? Couldn’t the group have disappeared, and a new one formed in its place?”

The sunspot groups are numbered consecutively -- starting with 0 -- and when group 9999 emerges, the next new group will be 0 again. I have also seen them expressed as five digits, so the current sunspot 1057 this week would be 11057. If you go here and look at the “Archives” section in the upper right, change the date to June 15, 2002 and click “View.” Note the numbers on the solar image on the left side are up in the 9990+ range. Now click “Forward” on the upper right to advance the date to June 16. Note the piece about Sunspot Zero. I don't know why the image doesn’t show sunspot 2. Perhaps it emerged, was numbered and then faded in less than a day. Perhaps that is also why paging backward does not produce sunspot 9999.

It looks like we went from group 321 to 1057 over the past seven years. If sunspot groups were to continue emerging at the same rate -- which has been slow recently -- it could take us until April 14, 2095 to reach group 0 again -- a pretty rough guess. That will be less than a month and a half short of my birthday at age 143, perhaps around Solar Cycle 32.

I get my information second-hand regarding which groups are returning, and do no direct observation myself. I think they can be recognized possibly from magnetic signatures, and also the timing. It takes about 27.5 days for a complete solar rotation, but it varies with latitude, since the Sun is a big ball of (very hot) gas. At the equator the period is less than 26 days, and toward the poles it is about 36 days. A few references on this are here, here and here.

John Buttolph, N1JB, of Lake Elmore, Vermont, wrote in with information on a Navy map showing letter designations for each time zone. Z or Zulu time (or UTC) as we all know is for the prime meridian, or Greenwich Mean Time. But when it is 1200Z (or 1200 UTC), it is 0400U on the West Coast and 0700R in Newington, Connecticut. Click on the map for greater detail. John wrote, “The world is divided into 24 time zones, and each is assigned a letter. The US Navy, as well as civil aviation, uses the letter Z (phonetically Zulu) to refer to the time at the prime meridian. Proceeding eastward from Greenwich, the zones are designated with the Latin alphabet letters beginning with A or Alfa time (I do not know why the prime meridian time zone was given the last letter of the alphabet rather than the first!). Not all letters of the alphabet are used. For various reasons having to do with population centers and other cultural reasons, the time zones do not strictly follow the meridian lines, and some time zones vary by the half-hour.”

Matt Pastorcich, KJ4NBM, of Mobile, Alabama, was surprised to work John Baylis in Hobart, VK2JB, in Tasmania last Saturday, March 20 at 1246 using PSK31 on 20 meters. That isn’t a promising time for that 9300 mile short path route, and Matt was even more surprised to learn that John was running 2 W into a loop antenna made for 80 meters; Matt uses a vertical. A better time would be 0500-1000, or even better would be 30 meters around 0730-1300 or 40 meters 0800-1200.

Wolf Urban, DK8MZ, in Fuerstenfeldbruck, Germany, wrote to comment on 15 meters. Nearly two weeks ago on Saturday, March 13, he worked Rob Struppeck, V73RS, on the southernmost island of Kwajalein Atoll. Wolf uses a TH3 Yagi at 12 meters high, and said that Rod had a very robust S9 signal on 15 meter SSB. Wolf thinks this is a hopeful sign, and said that “I can’t remember when I last heard such a strong signal from that part of the world, (the most difficult one for the Europeans on the high bands) even during periods of much higher solar activity!”

Don’t miss Carl Luetzelschwab’s, K9LA, excellent monthly propagation column in WorldRadio, available online at no cost. Just right-click on the image of the front cover to download the PDF; you’ll find Carl’s column on ionosphere modeling on page 36.

All times listed are UTC.

Amateur solar observer Tad Cook, K7RA, of Seattle, Washington, provides this weekly report on solar conditions and propagation. This report also is available via W1AW every Friday, and an abbreviated version appears each Thursday in The ARRL Letter. You can find a guide to articles and programs concerning propagation here. Check here for a detailed explanation of the numbers used in this bulletin. An archive of past propagation bulletins can be found here. You can find monthly propagation charts between four USA regions and 12 overseas locations here. Readers may contact the author via e-mail.