Solar Terrestrial Activity Report

Last major update issued on April 20, 2004 at 04:20 UTC.

[Solar and geomagnetic data - last month (updated daily)]
[Solar wind and electron fluence charts (updated daily)]
[Solar cycles 21-23 (last update April 2, 2004)]
[Solar cycles 1-20]
[Graphical comparison of cycles 21, 22 and 23 (last update April 2, 2004)]
[Graphical comparison of cycles 2, 10, 13, 17, 20 and 23 (last update April 2, 2004)]
[Historical solar and geomagnetic data charts 1954-2003 (last update January 16, 2004)]
[Archived reports (last update April 18, 2004)]

Recent activity

The geomagnetic field was quiet on April 19. Solar wind speed ranged between 326 and 369 km/sec.

Solar flux measured at 20h UTC on 2.8 GHz was 113.4. The planetary A index was 6 (STAR Ap - based on the mean of three hour interval ap indices: 7.4).
Three hour interval K indices: 22222221 (planetary), 22222231 (Boulder).

The background x-ray flux is at the class B1 level.

At midnight there were 5 spotted regions on the visible disk. The solar flare activity level was low. A total of 2 C class events was recorded during the day.

Region 10593 decayed with a significant loss of penumbral area.
Region 10594 decayed further and could soon become spotless.
Region 10596 developed further and still has a weak magnetic delta structure at the eastern edge of the leading penumbra. A minor M class flare is possible. Flares: C3.3 at 00:34 and C4.7 at 18:30 UTC.

Spotted regions not numbered by NOAA/SEC:
[S391] This region emerged to the north of region 10595 late on April 16 and developed moderately quickly on April 17. Further development was observed on April 18, while the region decayed slowly on April 19 and lost several small spots. Location at midnight: S05E26.
[S394] A new region emerged late on April 19 in the southwest quadrant near the center of the visible disk. Location at midnight: S10W07.

Coronal mass ejections (CMEs)

April 17-19: No fully or partly Earth directed CME observed.

Coronal holes

Coronal hole history (since late October 2002)
Compare today's report with the situation one solar rotation ago: 28 days ago 27 days ago 26 days ago

The northernmost extensions of a coronal hole (CH91) in the southern hemisphere will likely be in a geoeffective position on April 19-20.

Processed SOHO/EIT 284 image at 19:05 UTC on April 19. The darkest areas on the solar disk are likely coronal holes.

Forecast

The geomagnetic field is expected to be quiet on April 20-21 and quiet to active on April 22-23 due to a weak high speed stream from coronal hole CH91.

Long distance low and medium frequency (below 2 MHz) propagation along east-west paths over high and upper middle latitudes is poor. Propagation along long distance north-south paths is fair. [Trans Atlantic propagation conditions are currently monitored every night on 1470 kHz. Dominant stations tonight: Radio Vibración (Venezuela) early on, after 03h UTC CPN Radio (Perú) was strong. Peruvian stations noted on 1500 and 1590 kHz as well].

Coronal holes (1) Coronal mass ejections (2) M and X class flares (3)
Coronal hole indicator CME indicator M and X class flare indicator

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) Material from a CME is likely to impact Earth within 96 hours.
3) There is a possibility of either M or X class flares within the next 48 hours.

Green: 0-20% probability, Yellow: 20-60% probability, Red: 60-100% probability.

Active solar regions (Recent map)

Compare to the previous day's image.

Data for all numbered solar regions according to the Solar Region Summary provided by NOAA/SEC. 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 SEC or where SEC has observed no spots. SEC active region numbers in the table below and in the active region map above are the historic SEC/USAF numbers.

Active region Date numbered SEC
spot
count
STAR
spot
count
Location at midnight Area Classification Comment
10592 2004.04.13 1   S10W21 0010 AXX spotless
10593 2004.04.14 10 9 S18W24 0050 DAI  
10594 2004.04.14 1 1 N15E00 0010 HSX  
10595 2004.04.16 25   S07E27 0080 DAI spotless
instead of numbering a
new region, SEC has
reused 10595. See
S391
10596 2004.04.18 21 23 S09E44 0290 EKI beta-gamma-delta
classification was DKI
at midnight, area 0350
S388 emerged on
2004.04.12
    S07W36     plage
S391 emerged on
2004.04.16
  13 S05E26 0070 DAI beta-gamma
S393 emerged on
2004.04.18
    N07W07     plage
S394 emerged on
2004.04.19
  1 S10W07 0010 HRX  
Total spot count: 58 47
SSN: 108 97

Monthly solar cycle data

Month Average solar
flux at Earth
International sunspot number Smoothed sunspot number
2000.04 184.2 125.5 120.8
cycle 23 sunspot max.
2000.07 202.3 170.1 119.8
2001.12 235.1 132.2 114.6 (-0.9)
2003.03 131.4 61.1 74.0 (-4.3)
2003.04 126.4 60.0 70.1 (-3.9)
2003.05 115.7 55.2 67.6 (-2.5)
2003.06 129.3 77.4 65.0 (-2.6)
2003.07 127.7 83.3 61.8 (-3.2)
2003.08 122.1 72.7 60.0 (-1.8)
2003.09 112.2 48.7 59.5 (-0.5)
2003.10 151.7 65.5 (58.0 predicted, -1.5)
2003.11 140.8 67.3 (55.9 predicted, -2.1)
2003.12 114.9 46.5 (53.3 predicted, -2.6)
2004.01 114.1 37.2 (49.1 predicted, -4.2)
2004.02 107.0 46.0 (44.5 predicted, -4.6)
2004.03 112.0 48.9 (41.7 predicted, -2.8)
2004.04 100.0 (1) 38.1 (2) (39.6 predicted, -2.1)

1) Running average based on the daily 20:00 UTC observed solar flux value at 2800 MHz.
2) Unofficial, accumulated value based on the Boulder (NOAA/SEC) sunspot number. The official international sunspot number is typically 30-50% less.

This report has been prepared by Jan Alvestad. It is based partly on my own observations and analysis, and partly on data from some of these solar data sources. All time references are to the UTC day. Comments and suggestions are always welcome.


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