Tad Cook, K7RA, Seattle, reports: Four new sunspots emerged this week and were visible every day.
Spaceweather.com issued a warning on April 22: “A CME is heading for Earth. and it could spark a geomagnetic storm when it arrives on April 25. NOAA forecasters say moderately strong G2-class storms are possible, which means auroras could dip into northern-tier US states from Maine to Washington.”
Average daily sunspot number surged from 7 to 35.1, while average daily solar flux increased from 75 to 78.
Due to seemingly constant solar wind, average planetary A index rose from 5.1 to 16.4, and average daily middle latitude A index went from 4.1 to 13.
Predicted solar flux is 84 on April 23 – 24; 82 on April 25 – 27; 80 on April 28; 78 on April 29 – 30; 68 on May 1 – 2; 78 on May 3; 72 on May 4 – 9; 75 on May 10 – 15; 78 on May 16; 75 on May 17 – 18; 72 on May 19; 70 on May 20 – 23, and 68 on May 24 – 29.
Predicted planetary A index is 10, 8, 25, and 12 on April 23 – 26; 5 on April 27 – May 3; 15 on May 4; 5 on May 5 – 7; 8 on May 8; 5 on May 9 – 10; 8, 12, 20, 30, 15, 12, and 8 on May 11 – 17; 5 on May 18 – 19, and 8, 12 and 5 on May 20 – 22.
Here’s the geomagnetic activity forecast for April 23 – May 18 from F.K. Janda, OK1HH.
The geomagnetic field will be:
quiet on May 1 – 3, 5, 18
quiet to unsettled on April 28 – 30, May 6 – 11, 17
quiet to active on April 26, May 12
unsettled to active April 27, May 16, 18
active to disturbed April 23, (24 – 25,) May (4,) 13 – 14, (15)
Solar wind will intensify on April 23 – 25, (then irregularly between April 26 – May 1), May 3 – 5, (6 – 7, 10 – 11, 16,) 17 – 18, (18)
Remarks:
- Parentheses mean lower probability of activity enhancement.
- Contradictory indications significantly reduce the accuracy of the forecast.
Frank Donovan, W3LPL, says the long-anticipated significant increase in Solar Cycle 25 activity may have begun on April 19.
“As a result, 30- and 20-meter nighttime propagation and 17- and 15-meter daytime propagation is likely to be enhanced through at least April 26. The solar flux index (SFI) is likely to remain at 85 or higher through at least April 26 due to two active regions on the sun’s surface, 2816 and 2817, containing 16 sunspots in all. Two additional active solar regions on the far side of the sun are expected to rotate into view later this week, possibly increasing the SFI and extending enhanced propagation through late April".
See Donovan’s article, “What to Expect During the Rising Years of Solar Cycle 25,” in the May 2021 issue of QST.
Donovan says the new sunspots are fading faster than he’d hoped, but the steady trend of increasing sunspots should soon sustain the solar flux above 80.
Long-distance propagation forecast for Thursday – Friday, April 22 – 23 from Frank Donovan, W3LPL:
“My propagation forecast derived from today’s NOAA/SWPC web pages is published five days a week (M – F) in The Daily DX.
“Propagation at low and mid-latitudes is likely to be normal through Friday. Propagation crossing the auroral oval and polar regions is likely to be mostly normal, with below normal intervals through Friday.
“Today’s latest planetary Kp Index, updated every 3 hours
“N0NBH’s current HF band conditions, updated regularly
“The solar flux index (SFI) is likely to be about 78 through Friday.
“Three active regions containing a total of 17 mostly tiny sunspots are having minimal effect on HF propagation.
“We are exiting the most disturbed weeks of the March – April geomagnetic storm season, when Earth is passing through the part of the interplanetary magnetic field (IMF) with the most frequent, longest duration southward oriented IMF. Approximately twice as many brief minor and moderate geomagnetic storms occur during March and April compared to the quieter IMF during June and July. Brief minor to moderate geomagnetic storms may be triggered with little warning when the IMF rotates to a southward orientation and persists for several hours coincident with the effects of earth-directed coronal hole high-speed streams and coronal mass ejection (CME) enhancements in the solar wind.
“Short-path on 160 and 80 meters from North America to VK/ZL is likely to be normal through Friday. Eighty and forty meter short path propagation to south Asia is likely to be mostly normal at about 0030 UTC Friday. Eighty and forty meter short-path propagation from North America to east Asia after about 0900 UTC is likely to be mostly normal with below normal intervals through Friday.
“Thirty meter propagation through the auroral ovals and across polar regions is likely to be mostly normal with below normal intervals through Friday. Thirty meter propagation is always significantly degraded within a few hours of local noon because of E-region blanketing of long distance F2 propagation. Thirty meter nighttime propagation is likely to improve slightly through Friday, due to solar flux index of 78.
"Twenty meter daytime and evening propagation through the auroral ovals and across polar regions is likely to be mostly normal, with below normal intervals through Friday. Twenty meter northern trans-polar propagation within a few hours of sunrise and sunset will steadily improve with gradually increasing electron density in the polar F2 region through June. Twenty meter night time long distance propagation in the northern hemisphere is likely to improve slightly through Friday due to solar flux index of 78.
"Seventeen and fifteen meter daytime long distance propagation in the northern hemisphere is likely to improve slightly through Friday due to solar flux of 78. Twelve and ten meter daytime long distance propagation is likely to be mostly unreliable and limited to propagation from North America to Southern Africa, South Atlantic, South America, and South Pacific regions.
"Geomagnetic disturbances caused by coronal hole high speed streams are likely to remain mostly brief, minor, and less frequent through at least late 2021. The north-south (Bz) component of the IMF plays a crucial role in triggering brief minor to moderate geomagnetic storms when it persists in a southward orientation (–Bz) with enhanced field strength for several hours coincident with the effects of earth-directed coronal hole high-speed stream or CME enhancements in the solar wind.
“IMF field strength, solar wind speed near earth and geomagnetic activity are likely to be at close to background levels through Friday with a possible enhancement late Friday due to coronal hole high-speed stream effects. There is a slight possibility that an M-Class solar flare may cause a brief sudden ionospheric disturbance and short-wave fadeout on the sun-facing side of the earth late Thursday.
“Geomagnetic storms and earth-directed CMEs strong enough to affect HF propagation are not likely through Friday.
“Mid-latitude northern hemisphere sunset is now 32 minutes later, and the daylight period is 81 minutes longer than it was on March 20.
“Daylight period is increasing by 2 minutes per day, which is steadily lengthening the duration of common daylight between distant locations in the northern hemisphere. Solar elevation in the northern polar region is increasing by about 3° degrees per week, steadily improving 20 meter northern trans-polar propagation through June.
“Today’s Penticton 10.7-centimeter solar flux index is updated at 1700, 2000, and 2300 UTC daily."
Today’s 2-day GFZ Planetary K Index forecast is updated every 3 hours.
Today’s SIDC Daily Bulletin on Solar and Geomagnetic Activity is updated at 1230 UTC daily.
Today’s SWPC Solar Activity Forecast Discussion is updated at 0030 and 1230 UTC daily.
Today’s Australian Space Forecast Centre Summary and Forecastis updated at 2330 UTC daily.
These are perhaps the most useful HF propagation pages for DXers.
The April 2021 NASA solar flux index forecast for Solar Cycle 25 has been published, mostly advancing the date for solar maximum to 2024. The SFI represented by the 50% percentile (green line) is similar to Solar Cycle 24. A double peaked solar cycle — similar to recent Solar Cycles 23 and 24 — could delay solar maximum by a year or more.
Here's slightly updated wording to W3LPL’s May QST article, unconstrained by QST page limits and reflecting NASA’s predicted solar maximum in 2024:
“If the SFI persists below 90 through December 2021, then propagation should improve gradually until a solar maximum weaker than Cycle 24’s arrives in 2024.
“If the SFI persists above 110 through December 2021, then propagation should improve rapidly until a solar maximum similar to Cycle 24’s arrives in 2024.
“If the SFI persists above 125 through December 2021, then propagation is likely to improve more rapidly until a solar maximum stronger than Cycle 24’s arrives in 2024.”
Vote for your favorite May QST article.
N4SO recommends an article in the March-April edition of QEX, “The onset of Solar Cycle 25 and the MGII Index,” by VE6TL.
Jon Jones, N0JK reported an April 20 TEP opening to South America on 6 meters, and sent a long list of stations copied from 2022-2023 UTC, and this report:
“CE6CGX copied me. 10 W, quarter-wave whip. Jon N0JK EM28 KS
“RX at Tue, 20 Apr 2021 20:25:01 GMT."
"From N0JK by CE6CGX Loc FF31qp
"Frequency: 50.314.248 MHz (6m), FT8, –6dB
"Distance: 8846 km bearing 162°”
On April 19 Jon, N0JK, reported that VP8EME in the Falkland Islands was heard on 6 meters by KE8FD and K1TOL around 1800 UTC. “Looks like the summer sporadic-E season has begun,” he observed.
KA3JAW of Easton, Pennsylvania, reported a long 6-meter opening on April 19, 1435 – 1706 UTC. “Best DX range was with N5DG [EM20AB] Hempstead, Texas, at 1,374 miles,” he said.
And from Cuba:
“Hi, CO7WT, Pavel Milanes here from Camagüey Cuba, FL11bj. I’d like to report a huge opening on 6 meters on Saturday, April 17, 2020. I was calibrating my homebrew 6-meter transverter to get access to the magic band (Noise generator, SDR, NanoVNA), and out of the blue, a digital signal came up for a few seconds on my SDR screen. Hmm... weird. No antenna is connected, just coax from the tests, then there it’s a mental calculation spotted the 18.313 MHz, aka 50.313 (32.000 MHz XTAL). That’s FT8! A local ham, I think at first. Connected my antenna (Cushcraft 3 element Yagi) and boom! Loud signals from North America and some from LU and CE on the side/back of the Yagi. Sadly, the transmit side of the transverter is not ready yet. Here are links (1) (2) to some photos on Twitter.
“I spotted at least three beacons, one from W4, and the other was too unstable to decode properly as they come and go. See photos. Some of the ones calling on FT8 had signals dancing up and down in a pattern of a few minutes. I think of sporadic E, as this is the season.”
Sunspot numbers for April 15 – 21 were 22, 44, 28, 15, 36, 54, and 47, with a mean of 35.1. The 10.7-centimeter flux was 72, 76.5, 75.3, 78.1, 85.9, 80, and 78, with a mean of 78. Estimated planetary A indices were 13, 19, 29, 16, 18, 13, and 7, with a mean of 16.4. Middle latitude A index was 11, 15, 20, 13, 15, 10, and 7, with a mean of 13.
For more information concerning radio propagation, visit the ARRL Technical Information Service, read “What the Numbers Mean…,” and check out K9LA’s Propagation Page.
A propagation bulletin archive is available. For customizable propagation charts, visit the VOACAP Online for Ham Radio website.
Instructions for starting or ending email distribution of ARRL bulletins are on the ARRL website.
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