Solar Terrestrial Activity Report

Last major update issued on April 17, 2005 at 05:40 UTC.

[Solar and geomagnetic data - last month (updated daily)]
[Solar wind and electron fluence charts (updated daily)]
[Solar cycles 21-23 (last update April 4, 2005)]
[Solar cycles 1-20]
[Graphical comparison of cycles 21, 22 and 23 (last update April 4, 2005)]
[Graphical comparison of cycles 2, 10, 13, 17, 20 and 23 (last update April 4, 2005)]
[Historical solar and geomagnetic data charts 1954-2004 (last update February 1, 2005)]
[Archived reports (last update April 15, 2005)]

Recent activity

The geomagnetic field was quiet to unsettled on April 16. Solar wind speed ranged between 401 and 484 km/sec.

Solar flux measured at 20h UTC on 2.8 GHz was 82.9. The planetary A index was 7 (STAR Ap - based on the mean of three hour interval ap indices: 6.9).
Three hour interval K indices: 32112222 (planetary), 32112322 (Boulder).

The background x-ray flux is at the class A5 level.

At midnight there were 3 spotted regions on the visible solar disk. The solar flare activity level was very low. No C class events were recorded during the day. Sub flare activity increased as a fairly active region is approaching the southeastern limb. This region produced a C flare early on April 17.

Region 10750 decayed slowly and quietly, the region could become spotless today.
Region 10752 decayed further and lost all negative polarity spots.
Region 10754 decayed further and could become spotless today if the current rate of decay is sustained.

Coronal mass ejections (CMEs)

April 14-16: No obvious fully or partly Earth directed CMEs were 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

A recurrent coronal hole (CH158) in the southern hemisphere was in an Earth facing position on April 15-17. A coronal hole (CH159) in the northern hemisphere will likely be in an Earth facing position on April 19.

Processed SOHO/EIT 284 image at 01:06 UTC on April 17. The darkest areas on the solar disk are likely coronal holes.

Forecast

The geomagnetic field is expected to be mostly quiet on April 17 and the first half of April 18. Effects from CH158 could reach Earth on April 18 and cause unsettled to active conditions until April 20.

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.

Propagation

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 poor. Trans Atlantic propagation conditions are normally monitored every night on 1470 kHz. Dominant station tonight: Radio Vibración (Venezuela). Some stations from Venezuela and Puerto Rico were audible at local sunrise, however, most of the stations noted then were from North America. WBZ on 1030 and WWZN on 1510 kHz had the best signals.

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
10750 2005.04.05 1 1 S08W66 0020 HSX classification was AXX at midnight, area 0010
10752 2005.04.12 5 4 N02E14 0090 DSO classification was HAX at midnight
10753 2005.04.13 1   N12W45 0010 AXX spotless for the second consecutive day
10754 2005.04.14 5 4 S08E23 0040 DSO classification was CSO at midnight, area 0020
Total spot count: 12 9  
SSN: 52 39  

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)
2004.02 107.0 45.8 49.3 (-2.7)
2004.03 112.0 49.1 47.1 (-2.2)
2004.04 101.2 39.3 45.5 (-1.6)
2004.05 99.8 41.5 43.8 (-1.7)
2004.06 97.4 43.2 41.6 (-2.2)
2004.07 119.1 51.1 40.2 (-1.4)
2004.08 109.6 40.9 39.2 (-1.0)
2004.09 103.1 27.7 37.5 (-1.7)
2004.10 105.9 48.0 (35.6 predicted, -1.9)
2004.11 113.2 43.5 (33.9 predicted, -1.7)
2004.12 94.5 17.9 (31.6 predicted, -2.3)
2005.01 102.2 31.3 (28.9 predicted, -2.7)
2005.02 97.2 29.1 (26.5 predicted, -2.4)
2005.03 89.9 24.8 (24.7 predicted, -1.8)
2005.04 85.2 (1) 23.8 (2) (22.9 predicted, -1.8)

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.


[DX-Listeners' Club]