Solar Terrestrial Activity Report
Last major update issued on May 28, 2024 at 05:05 UT.
Recent activity
The geomagnetic field was at quiet to unsettled levels on May 27. The high latitude magnetometer at Andenes recorded quiet to unsettled levels. The above 10 MeV proton flux was at background levels at the end of the day.
Solar flux density measured at 20h UT on 2.8 GHz was 170.0 - increasing 39.8 over the previous solar rotation. (Centered 1 year average SF at 1 AU - 183 days ago: 161.17. In comparison SC24 peaked on June 28, 2014 at 145.50. Current SC25 peak: 161.17 on November 27, 2023). The Potsdam WDC planetary A index was 7 (STAR Ap - based on the mean of three hour interval ap indices: 6.8). Three hour interval K indices: 11232112 (planetary), 11243422 (Boulder), 11222103 (Andenes).
The background x-ray flux is at the class C2 level (GOES 16).
At the time of counting spots (see image time), spots were observed in 13 active regions using 2K resolution (SN: 289) and in 10 active regions using 1K resolution (SN: 174) SDO/HMI images.
Region 13685 [S13W73] decayed slowly
and quietly.
Region 13686 [S08W66] decayed slowly and quietly.
Region 13689 [S08W19] decayed slowly and quietly.
Region 13690 [N16E23] was quiet and stable.
Region 13691 [N26E37] produced many C flares. A major flare is
possible due to the magnetic delta configuration in this compact group.
Region 13692 [S09W11] decayed slowly and was mostly quiet.
Region 13693 [N03E22] developed and could produce C flares.
Region 13695 [N27E48] was mostly quiet and stable.
Region 13696 [N08E55] was quiet and stable.
Spotted regions not observed (or interpreted
differently) by SWPC/USAF:
S9739 [N32W08] was quiet and stable.
S9746 [N08W80] was quiet and stable.
New region S9747 [S18E84] rotated partly into
view, probably the return of old AR S9676. The region was the source of an
X2.9 flare at 07:08 UT. A fast full halo CME was associated with this event.
New region S9748 [S24E39] was observed with tiny spots in an
old plage area.
C2+ flares
| Magnitude | Peak time (UT) | Location | Source | Recorded by | Comment |
| C2.3 | 00:20 | 13695 | GOES16 | ||
| C2.3 | 00:30 | 13691 | GOES16 | ||
| C3.8 | 01:24 | 13691 | GOES16 | ||
| C4.4 | 01:50 | 13691 | GOES16 | ||
| C3.9 | 02:35 | 13691 | GOES16 | ||
| C6.9 | 03:17 | S9747 | GOES16 | ||
| C4.6 | 03:59 | 13691 | GOES16 | ||
| C5.5 | 04:25 | N28E48 | 13691 | GOES16 | |
| C2.8 | 05:43 | S9747 | GOES16 | attributed to AR 13691 by SWPC | |
| X2.9 | 07:08 | S9747 | GOES16 | full halo CME, strong type II and weak type IV radio sweeps | |
| C5.9 | 11:33 | S9747 | GOES16 | ||
| C6.7 | 12:27 | S9747 | GOES16 | ||
| C4.4 | 15:13 | S9747 | GOES16 | simultaneous flare behind northwest limb | |
| C4.6 | 15:35 | 13691 | GOES16 | simultaneous flare in AR S9747 | |
| C4.7 | 16:04 | S9747 | GOES16 | ||
| C4.8 | 16:16 | S9747 | GOES16 | ||
| C3.7 | 16:41 | 13691 | GOES16 | ||
| C4.7 | 17:51 | N21E39 | 13691 | GOES16 | |
| C4.5 | 17:53 | S9747 | GOES16 | ||
| C3.5 | 18:18 | 13691 | GOES16 | ||
| C4.7 | 18:27 | 13691 | GOES16 | ||
| C6.0 | 18:50 | 13691 | GOES16 | ||
| C8.9 | 19:16 | N28E39 | 13691 | GOES16 | |
| C3.5 | 20:44 | S9747 | GOES16 | ||
| C3.5 | 22:31 | S9747 | GOES16 | ||
| C3.4 | 23:26 | 13691 | GOES16 | ||
| C3.9 | 23:42 | S9747 | GOES16 | ||
| C4.8 | 00:00 | 13691 | GOES16 |
Coronal mass ejections (CMEs)
May 25-26: No obviously Earth directed CME observed.
May 27: A full halo CME was observed after the X2.9 flare in AR S9747
from a flare site slightly behind the southeast limb. There's a slight
chance of a solar wind shock on May 29-30 and unsettled to minor geogmetic
storm levels.
Coronal holes
[Coronal hole history (since October 2002)]
[Compare today's report to the situation one solar rotation ago:
28 days ago
27 days ago
26 days ago]
A small negative polarity southern hemisphere coronal hole (CH1223) rotated across the central meridian on May 26 and early on May 27.
Propagation
Long distance low and medium frequency (below 2 MHz) propagation along paths north of due west over upper middle and high latitudes is poor. Propagation on long distance northeast-southwest paths is poor.
Forecast
The geomagnetic field is expected to be at quiet to unsettled levels on May 28-31. On May 29 there's a chance of weak effects from CH1223. On May 29-30 there's a minor chance of shock effects associated with the May 27 X flare.
| Coronal holes (1) | Coronal mass ejections (2) | M and X class flares (3) |
1) Effects from a coronal hole
could reach Earth within the next 5 days. When the high speed
stream has arrived the color changes to green.
2) Effects from a CME are likely to be observed at Earth within 96 hours.
3) There is a possibility of either M or X class flares within the next 48 hours.
Green: 0-30% probability, Yellow: 30-70% probability, Red: 70-100% probability.
Active solar regions
(Click on image for 2K resolution).
4K resolution.
Compare to the previous
day's image. 0.5K image
When available the active region map has a coronal hole polarity overlay where red (pink) is negative and blue is positive.
Data for all officially numbered solar regions according to the Solar Region Summary provided by NOAA/SWPC, all other regions are numbered sequentially as they emerge using the STAR spot number. Comments are my own, as is the STAR spot count (spots observed at or inside a few hours before midnight) and data for regions not numbered by SWPC or where SWPC has observed no spots. SWPC active region numbers in the table below and in the active region map above are the historic SWPC/USAF numbers. SWPC data considered to be not sufficiently precise (location, area, classification) are colored red.
| Active region | SWPC date numbered STAR detected |
Spot count | Location at midnight | Area | Classification | SDO / HMI 4K continuum image with magnetic polarity overlays |
Comment | ||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| SWPC/ USAF |
Magnetic (SDO) |
SWPC | STAR | Current | Previous | ||||||
| 2K | 1K | ||||||||||
| 13685 | 2024.05.15 2024.05.16 |
3 | 4 | 2 | S14W75 | 0150 | DSO | DHO |
 |
 |
location: S13W73 area: 0360 |
| 13686 | 2024.05.16 2024.05.17 |
2 | 4 | 3 | S09W67 | 0060 | CAO | CAO |
 |
 |
location: S08W66 area: 0090 |
| 13688 | 2024.05.19 | S12W56 | |||||||||
| S9724 | 2024.05.19 | S14W59 | |||||||||
| 13689 | 2024.05.19 | 6 | 2 | S07W24 | 0015 |
 |
 |
location: S08W18 |
|||
| S9731 | 2024.05.21 | S24W28 | |||||||||
| 13690 | 2024.05.23 2024.05.23 |
1 | 2 | 1 | N17E21 | 0030 | HSX | HSX |
 |
 |
area: 0060 location: N16E23 |
| 13691 | 2024.05.24 2024.05.25 |
15 | 68 | 32 | N25E34 | 0480 | EKC | DKC |
 |
 |
beta-gamma-delta location: N26E37 area: 0750 |
| 13692 | 2024.05.24 2024.05.25 |
6 | 17 | 10 | S09W11 | 0040 | CAO | CRI |
 |
 |
area: 0060 |
| 13693 | 2024.05.25 2024.05.26 |
4 | 23 | 13 | N06E22 | 0040 | DAO | DAI |
 |
 |
location: N03E22 area: 0160 |
| S9739 | 2024.05.25 | 3 | N32W08 | 0006 | BXO |
 |
 |
||||
| S9740 | 2024.05.25 | N18W31 |
 |
||||||||
| 13696 | 2024.05.25 2024.05.26 |
1 | 3 | 2 | N09E52 | 0010 | HRX | HRX |
 |
 |
area: 0020 location: N08E55 |
| S9743 | 2024.05.25 | S31W32 |
 |
||||||||
| 13694 | 2024.05.26 | S12E31 |
 |
location: S15E35 | |||||||
| 13695 | 2024.05.26 2024.05.26 |
4 | 19 | 6 | N27E46 | 0020 | CRO | DRI |
 |
 |
location: N27E48 area: 0040 |
| S9746 | 2024.05.26 | 2 | N08W66 | 0001 | AXX |
 |
 |
||||
| S9747 | 2024.05.27 | 3 | 3 | S18E84 | 0250 | DAO |
 |
||||
| S9748 | 2024.05.27 | 3 | S24E39 | 0005 | DAO |
 |
|||||
| Total spot count: | 36 | 157 | 74 | ||||||||
| Sunspot number: | 116 | 287 | 174 | (total spot count + 10 * number of spotted regions) | |||||||
| Weighted SN: | 77 | 211 | 128 | (Sum of total spot count + classification weighting for each AR. Classification weighting: X=0, R=3, A/S=5, H/K=10) | |||||||
| Relative sunspot number (Wolf number): | 128 | 158 | 139 | ||||||||
Monthly solar cycle data
| Month | Average solar flux | International sunspot number (WDC-SILSO) |
Smoothed sunspot number (4) | Average ap (3) |
|
|---|---|---|---|---|---|
| Measured | 1 AU | ||||
| 2014.02 | 170.3 (cycle peak) |
166.3 | 146.1 (SC24 peak) | 110.5 | 10.70 |
| 2014.04 | 143.9 | 144.8 | 112.5 | 116.4 (SC24 solar max) | 7.88 |
| 2017.09 | 91.3 | 92.3 | 43.6 | 18.2 (-1.3) | 18.22 (SC24 peak) |
| 2019.11 | 70.2 | 68.7 | 0.5 | 2.0 (-0.6) (Solar minimum using 365d smoothing: November 17, 2019) |
4.19 |
| 2019.12 | 70.8 | 68.6 | 1.6 | 1.8 (-0.2) (ISN 13 months smoothed solar minimum) |
3.22 |
| 2022.10 | 133.5 | 132.7 | 95.5 | 98.9 (+2.4) | 11.16 |
| 2022.11 | 123.4 | 120.7 | 80.5 | 101.2 (+2.3) | 9.33 |
| 2022.12 | 147.9 | 143.4 | 112.8 | 106.7 (+5.5) | 10.99 |
| 2023.01 | 182.4 | 176.6 | 144.4 | 113.3 (+6.6) | 8.73 |
| 2023.02 | 167.2 | 163.2 | 111.3 | 117.8 (+3.5) | 14.48 (current SC25 peak) |
| 2023.03 | 157.2 | 155.6 | 123.3 | 121.1 (+3.3) | 14.42 |
| 2023.04 | 145.4 | 146.4 | 97.6 | 122.9 (+1.8) | 13.40 |
| 2023.05 | 155.6 | 159.2 | 137.4 | 124.2 (+1.3) | 10.67 |
| 2023.06 | 161.7 | 166.8 | 160.5 | 125.3 (+1.1) | 8.95 |
| 2023.07 | 176.4 | 182.2 | 160.0 | 124.4 (-0.9) | 8.15 |
| 2023.08 | 153.7 | 157.6 | 114.8 | 124.1 (-0.3) | 7.19 |
| 2023.09 | 154.4 | 156.0 | 134.2 | 123.9 (-0.2) | 14.26 |
| 2023.10 | 142.8 | 141.9 | 99.4 | 124.8 (+0.9) | 8.16 |
| 2023.11 | 153.5 | 150.2 | 105.4 | (125.2 projected, +0.4) | 12.20 |
| 2023.12 | 151.1 | 146.4 | 114.2 | (121.9 projected, -3.3) | 9.60 |
| 2024.01 | 164.6 | 159.3 | 123.0 | (118.5 projected, -3.4) | 5.46 |
| 2024.02 | 172.5 | 168.3 | 124.7 | (117.7 projected, -0.8) | 5.31 |
| 2024.03 | 154.4 | 152.9 | 104.9 | (117.1 projected, -0.6) | 11.03 |
| 2024.04 | 161.3 | 162.6 | 136.5 | (117.1 projected, -0.0) | 9.69 |
| 2024.05 | 190.1 (1) | 127.9 (2A) / 146.8 (2B) / 178.4 (2C) | (118.3 projected, +1.2) | (26.1) | |
| 2024.06 | (117.4 projected, -0.9) | ||||
| 2024.07 | (115.7 projected, -1.7) | ||||
| 2024.08 | (113.8 projected, -1.9) | ||||
| 2024.09 | (112.5 projected, -1.3) | ||||
| 2024.10 | (111.1 projected, -1.4) | ||||
| 2024.11 | (108.6 projected, -2.5) | ||||
1) Running average based on the daily 20:00 UTC observed solar flux value at 2800 MHz
and any corrections applied to that measurement.
2A) Current impact on the monthly sunspot number based on the Boulder (NOAA/SWPC) sunspot number (accumulated daily sunspots / month days).
2B) Boulder SN current month average to date.
2C) STAR SDO 1K Wolf number 30 day average.
3) Running average based on the quicklook and definitive Potsdam WDC ap indices. Values in red
are based on the definitive international
GFZ Potsdam WDC ap indices.
4) Source: WDC-SILSO, Royal Observatory
Of Belgium, Brussels
Solar cycles 24-25
Update on the progress of solar cycle 25 as of April 28, 2024
The big increase in sunspot counts during the April 14-27 interval caused a major uptick in the smoothed SNs and solar flux. It's not yet clear when the next peak will be, anytime between October 28 and December 20, 2023 looks possible. The 365d smoothed solar flux exceeded the June 27 peak on October 28, while the 365d smoothed ISN and NOAA SN both exceeded the June 2023 peak in late October 2023. It should be noted that the current peak using 13-month smoothing is still in June 2023.
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This report has been prepared by Jan Alvestad. It is based on the analysis of data from whatever sources are available at the time the report is prepared. All time references are to Universal Time. Comments and suggestions are always welcome.
SDO images are courtesy of NASA/SDO and the AIA, EVE, and HMI science teams.