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Long Term Measurements of Solar Wind Fe Charge States: Charge State Distributions

This study examines the variations in iron charge states in the solar wind over a period of several years, and their correlation with solar wind speed. The results show a trend of the iron charge state moving in the opposite direction to the solar wind speed.

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Long Term Measurements of Solar Wind Fe Charge States: Charge State Distributions

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  1. Long Term Measurements of Solar Wind Fe Charge States:Charge State Distributions Mark Popecki, A. Galvin, L. M. Kistler,H. Kucharek, E. Moebius, K. Simunac, P. Bochsler, L. M. Blush, B. Klecker

  2. slow fast Von Steiger et al., (2000) Solar Wind Fe Charge State Expectations • Four types (Schwenn, 2006) • Fast solar wind (coronal holes) • Slow solar wind (near helmet streamers • Slow solar wind (active regions) • ICME solar wind • <QFe> slow> <QFe>fast • ICME QFe ~16+ • Small variations in mean charge state compared to SEPs

  3. Q Fe STEREO A solar wind speed/100 (km/s) STEREO A Fe Charge States vs. Solar Wind SpeedLatter Half of 2008 • Limited period of time • Solar wind speed is inversely related to Q Fe

  4. 2007/143 May 22-24 ICME S/W speed / 100 and < QFe > Iron charge states and solar wind speeds :2007 (DOY 022) -2009 (DOY 230), STEREO A • The top trace is the iron charge state, averaged over 2 hour periods. • The average charge states typically ranged between 8+ and 11+. • A prominent exception occurred during the 2007/143 May 23 ICMEs. The average charge state was ~13+ to 14+. • The bottom trace is the 2 hour averaged solar wind speed from STEREO A. • An upward trend occurred in the beginning of 2008, maximizing at DOY 2007 400 (early February, 2008). • A long decline below the 2007 levels followed, until August of 2009. • Variations in the solar wind speed have decreased compared to early 2007. 2009 2007 2008

  5. QFe S/W speed 2009 2007 2008 Mean Iron Charge State and Solar Wind Speed:2007 (DOY 022) -2009 (DOY 230), STEREO A • The smoothed trendline in the iron charge states is shown in blue (left axis) with the smoothed trendline for the solar wind speed. • The iron charge state tends to move in the opposite direction to the solar wind speed in a large scale sense. • The charge state in 2008/2009 has not completely recovered to the early 2007 levels, even though the average solar wind speed has gone lower than it was in 2007.

  6. QFe S/W speed 2009 2007 2008 Mean Iron Charge State and Solar Wind Speed:2007 (DOY 022) -2009 (DOY 230), STEREO A • The smoothed trendline in the iron charge states is shown in blue (left axis) with the smoothed trendline for the solar wind speed. • The iron charge state tends to move in the opposite direction to the solar wind speed in a large scale sense. • The charge state has not completely recovered to the early 2007 levels, even though the average solar wind speed has gone lower than it was in 2007.

  7. QFe S/W speed 2009 2007 2008 Iron Charge State and Solar Wind Speed:A change in the Fe charge state distribution in the 410-435 km/s S/W speed range • Fe charge histograms were calculated for two periods in 2007 and 2008 for which solar wind speeds were 410 - 435 km/s. • The Fe charge state histogram for 2008 is narrower and has less high charge content than in the 2007 period.

  8. Summary Changes in Fe charge state distributions with solar wind speed • In the 2007-2009 period, the solar wind speed trended up, then down again. • The mean Fe charge state varied inversely, consistent with von Steiger et al. (2000). • However, in the second low speed period, the mean Fe charge state was lower than the first. • For the speed range 410 - 435 km/s, the Fe charge state distribution in the second period was narrower than in the first, due to a deficit in higher charge states. • Is the slow solar wind in the second period from a different source than the first?

  9. Solar Wind Speeds: Recent Solar Min and Max • STEREO A: 2007/045-2009/230 • ACE: 1998-2005.5 • Speeds in the 2007-2009 period (solar min) are typically lower than the 1998-2005 period (solar max)

  10. 2007 vs 2008 for 410-435 km/s normSTA_2007_133-222_2008_190-258_ST tail data.txtqoftdata.xls

  11. NSO/GONG synoptic coronal hole plots for selected Carrington rotations • Red/green areas are coronal holes: red negative polarity, green positive polarity • Neutral line is in black • Isolated coronal holes disappear with time • Polar coronal hole extensions shrink • Neutral line flattens (less tilted current sheet) • Reduced exposure to coronal hole solar wind? Galvin et al., 2009

  12. One hour averages of solar wind speed and iron charge state from STEREO A • Smoothed lines - 655 hour averages (~Carrington rotation)

  13. STEREO A Fe Charge States vs. Solar Wind Speed • Average Fe charge state generally shows an anticorrelation with solar wind speed (sources: fast or slow s/w, coronal holes or active region). • Typical values of charge state are between 9+ and 10+. • Only one period of high charge states exists: May 22-24, 2007 (ICME).

  14. 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 < QFe > 0 200 400 600 800 Solar Wind Speed (STEREO A, km/s)

  15. 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 < QFe > 0 200 400 600 800 Solar Wind Speed (STEREO A, km/s) Solar Wind Speed vs. Iron Charge State STEREO A 2007-2009 • The mean iron charge states are plotted against corresponding solar wind speeds for the 2007-2009 period. • Variations in charge state are generally related to solar wind speed, but with a broad spread of approximately 1-2 charge units. • The mean Q Fe goes up at low speed, as von Steiger et al. (2000) reported.

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