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SEATTLE, WA, Mar 4, 2005--This week saw a quiet sun, which will be a frequent observation over the next few years. The average daily sunspot number was down nearly 31 points to 14.9, and average daily solar flux was off 21 points to 76.3. Planetary geomagnetic activity was down just slightly, and mid-latitude activity was just about the same as the previous reporting week.
Unsettled to active geomagnetic conditions were expected during last weekend (February 26-27), due to a strong solar wind. As it turned out, the only day with even slightly unsettled conditions was Monday--the last day of February, and any activity was brief. All week the Interplanetary Magnetic Field (IMF) pointed north, which shielded Earth from any solar wind. The sun was blank most of the week, with only small Sunspot 739 transiting across the visible solar disk.
The spaceweather.com Web site has a review of the IMF Check and how it can affect geomagnetic stability. There’s more about IMF on the Windows to the Universe Web site. Thanks to Jon Jones, N0JK, for passing along this information.
Over the next week expect a rising sunspot count and solar flux, with flux values peaking above 100 around March 11-14. March 6-9 could see some unsettled to active geomagnetic conditions based on activity during the previous solar rotation.
This weekend is the ARRL International DX SSB Contest. Don’t expect great conditions like when the sunspot cycle was higher, but at least we are moving toward the spring equinox and the geomagnetic conditions should be quiet.
Last week’s “Solar Update” stimulated some questions about resources for understanding sporadic-E propagation. The ARRL Propagation page includes a two-part article, “Sporadic-E--A Mystery Solved?” (scroll down to the “Articles” section). You must be an ARRL member and be registered and logged into the ARRL Web site to access these articles. Visit the ARRL Technical Information Service Propagation page for more information concerning propagation and an explanation of the numbers used in each week’s “Solar Update.”
Sunspot numbers for February 24 through March 2 were 17, 15, 27, 12, 11, 11 and 11, with a mean of 14.9. The 10.7 cm flux was 80.3, 78.2, 76.6, 75.8, 75, 73.7 and 74.6, with a mean of 76.3. Estimated planetary A indices were 5, 9, 9, 8, 12, 11 and 12 with a mean of 9.4. Estimated mid-latitude A indices were 4, 9, 9, 6, 8, 10 and 8, with a mean of 6.6.
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