:Product: Weekly Highlights and Forecasts :Issued: 2003 Apr 22 2212 UTC # Prepared by the US Dept. of Commerce, NOAA, Space Environment Center # Product description and SEC contact on the Web # http://www.sec.noaa.gov/weekly.html # # Weekly Highlights and Forecasts # Highlights of Solar and Geomagnetic Activity 14 - 20 April 2003 Solar activity ranged from very low to moderate levels. The period began with low level activity on 14 April and very low activity on 15 – 17 April. Region 337 (S12, L= 245, class/area Dko/340 on 20 April) rotated onto the visible disk on 18 April in a growth phase, developing both area coverage and magnetic complexity through 20 April. On 18 April, activity reached moderate levels with Region 337 producing an M1/Sf flare at 1958 UTC. At the end of the period, 19 – 20 April, activity returned to low levels. Early on 19 April, a long duration C1 flare was observed on the east limb. On 20 April, Region 339 (N18, L=338, class/area Cso/20 on 20 April) appeared on the disk and rapidly developed a beta-gamma magnetic configuration. Activity from Region 339 consisted of low C-class flares, the largest being a C4/Sf at 1923 UTC on 20 April. Solar wind data were available from the NASA Advanced Composition Explorer (ACE) spacecraft for most of the summary period. On 14 April, a co-rotating interacting region marked the onset of a large southern coronal hole high speed stream. Bz rotated from negative 10 nT to positive 10 nT before entering a typical oscillating pattern and solar wind speed increased from 500 km/s to near 650 km/s. Solar wind continued to increase on 15 – 16 April and reached a peak value near 800 km/s by midday on the 16th. Solar wind velocity began to decline on 17 April and slowly decreased for the remainder of the period. At the end of the period, velocity was back around 500 km/s. There were no greater than 10 MeV proton events at geo-synchronous orbit during the summary period. The greater than 2 MeV electron flux at geo-synchronous orbit reached high levels on 15 – 20 April. The geomagnetic field ranged from quiet to major storm levels. Activity from the large southern coronal hole high speed stream began late on 14 April with the arrival of a co-rotating interacting region that produced an isolated minor storm period followed by unsettled to active conditions. For the next four days, 15 – 18 April, activity from this high speed stream was at unsettled to minor storm levels with an isolated major storm period on 16 April. By 19 April, activity had subsided to unsettled levels. The period ended on 20 April with quiet to active levels due to elevated solar wind speed and a prolonged period of southward Bz. Forecast of Solar and Geomagnetic Activity 23 April - 19 May 2003 Solar activity is expected to range from very low to moderate levels. With a number of new regions returning to the visible disk, C-class activity is expected with a chance of isolated M-class events. New Regions 337, 338 (S19, L=280, class/area Dso/40 on 20 April), and 339 are all quite active and exhibit some magnetic complexity. No greater than 10 MeV proton events are expected during the forecast period. The greater than 2 MeV electron flux may reach high levels on 27 – 28 April, 02 – 03 May, 08 – 10 May, and again on 15 – 19 May. These high flux levels are all due to returning coronal holes. The geomagnetic field is expected to range from quiet to major storm levels. Activity early in the period is expected to be unsettled to isolated major storm levels due to a combination of a returning coronal hole on 23 April and a weak CME shock. Unsettled to active conditions with the possibility of isolated minor storming is expected to continue through 27 April. Two weaker coronal holes are due to return to a geo-effective position on 29 April – 02 May and 06 – 08 May with unsettled to active conditions expected. On 12 May, a large southern coronal hole is due to return and may result in unsettled to isolated major storm levels from 12 – 18 May.