Comparison of Solar Wind and CME Data: Current and Previous Solar Minima

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1 Comparison of Solar Wind and CME Data: Current and Previous Solar Minima David Webb 1 & Sarah Gibson 2 1 ISR, Boston College, Chestnut Hill, MA 2 HAO/NCAR, Boulder, CO

2 The What and Why of the Whole Heliospheric Interval (WHI)? Comparison of Current Solar Minimum (23/24) with Previous Minimum (22/23): - How typical was WHI (2008) of current minimum (~2009)? - Previous minimum - Whole Sun Month (WSM ) - Unusually deep (and weak?) and complex - How did it evolve? - Including transients (CIRs and CMEs) Summary & Future Plans Outline 20 May 2010 Webb-SORCE-Keystone, CO 2

3 Overview: What and Why WHI? Internationally coordinated observing and modeling effort Focus on observations originating from Carrington Rotation 2068: March 20 - April 16, Synoptic observing programs: Broad heliospheric coverage, provide context and baseline measurements - Targeted observing campaigns: Coordinated observations run during CROT Observational input from 27 solar, 19 heliospheric, and 21 geospace instruments - ~200 people officially registered (still growing) WHI Science Goals: 1. Connect the origins and effects of solar structure and activity through the solar wind to the Earth and other planetary systems 2. Characterize the 3-D solar minimum heliosphere Hope was WHI would be good example of ground-state solar minimum, but it was early. But also we hoped for sufficient structure/activity to make the connections interesting. 20 May And 2010 that is just what we got! Webb-SORCE-Keystone, CO 3

4 Overview: The Two Sides of WHI CMEs from the active regions CIRs from the low-latitude coronal holes (more later) SOHO EIT 20 May 2010 Webb-SORCE-Keystone, CO 4 Week of WHI Quiet Sun Campaign Sounding rocket (PI Woods) April 10, 2008, solar minimum irradiance spectrum (XUV/EUV)

5 Overview: The Two Sides of WHI Active side SOHO EIT WHI Quiet side Courtesy 20 May 2010 Greg Kopp Webb-SORCE-Keystone, CO 5

6 Time Comparison of Solar Minima during WSM & WHI Periods Magnetic Maps WSM WHI Apr 09 Jul 08 Courtesy G. de Toma WHI 20 May 2010 Webb-SORCE-Keystone, CO 6 Dec 07

7 How typical was WHI of Solar Minimum? Depends what you look at, and how you define minimum If minimum defined as a point in time, WHI was a bit early. But then where exactly was that minimum point? Oct 2008: minimum of 13-month smoothed sunspot number Aug 2008: minimum defined as point where new cycle sunspot number (reversed polarity) is greater than old cycle sunspots WHI (March/April 2008) Courtesy 20 May Tom 2010 Woods 7 Courtesy David Hathaway

8 Comparison of Solar Minima: At the Sun Low-latitude coronal holes more prevalent during WHI EUV N-S asymmetry due to solar B angle microwave WSM WHI Courtesy Giuliana de Toma Courtesy Nat Gopalswamy 8

9 Comparison of Solar Minima: At the Sun Coronal streamer belt is wider and more structured this minimum compared to the last two NORTH POLE SOUTH POLE NORTH POLE 20 MLSO May 2010white light (pb) 1.8 Solar Webb-SORCE-Keystone, Radii, Jan 1980 COto Jan 2009 (Burkepile, 2010) 9

10 Comparison of Solar Minima: At the Sun These differences are evident in comparing WHI to WSM: - Similar low sunspot numbers - Smaller polar coronal holes dipole not as dominant - Wider streamer belt warped heliospheric current sheet (HCS) in solar wind - Low-latitude open flux more fast wind streams at low latitudes in solar wind Cycle 22: Whole Sun Month (WSM) Cycle 23: Whole Heliosphere Interval (WHI) NSO-GONG HAO/MLSO NSO-GONG Courtesy Gordon Petrie 20 May 2010 Webb-SORCE-Keystone, CO 10

11 Themis Hinode Evolution of Current Solar Minima: At the Sun GONG synoptic polarity maps from CR Towards the end of 2008, large low-latitude coronal holes disappeared, and the HCS flattened 2054 Feb. 07 WHI 2064 Dec. 07 WHI 2074 Sep. 08 August May 09 Note that some small mid-latitude coronal holes were still present. 20 May

12 Comparison of Solar Minima: At the Sun... More open magnetic flux at low latitudes in 2008 than in The disappearance of large, low-latitude coronal holes in 2009 did not mean the global field became completely dominated by the dipole, as in The MAS model above exhibited small open field regions at all latitudes in 2009, possibly because of the weak polar field. Low latitude open flux may still be 20 there, May 2010 but on smaller size scales Webb-SORCE-Keystone, implying less of impact COon Earth. 12

13 Comparison of Solar Minima: In the solar wind B less, V similar but higher during WHI WHI vs current solar minimum: - Dominance of high-speed streams during extended declining phase - 2-stream structure weakened and disappeared, and radiation belt intensity dropped soon after WHI WHI Courtesy Cristina Lee et al., SP, May 2010 Webb-SORCE-Keystone, CO 13

14 Solar Wind Comparison: Dominance of CIRs this Cycle Hourly average Wind observations of solar wind protons (top) from the SWE instrument, and suprathermal He (lower) from the EPACT/STEP instrument. Left: ; Right: Courtesy G. Mason 20 May 2010 Webb-SORCE-Keystone, CO 14

15 Comparison of Solar Minima: In the solar wind WHI min WSM min CR CR V N T N a /N p P Ulysses during polar passes: lower magnetic field (35%), density (20%), speed (3%) 20 May 2010 McComas et al., GRL, 35, L18103, 2008 Decline of ecliptic parameters this cycle: N by 45%, B by 15% Courtesy Cristina Lee et al., 2010, Possible Influence of the Source Surface Changes on the IMF Magnitude, in prep.

16 Comparison of Solar Minima: In the wind Black = 2008 White = 1996 Tokumaru et al., JGR, 2010 Left: STEL IPS solar wind speed distr. over 2 full cycles w/wso neutral lines Right: Comparison of speed vs latitude 16 bins at last two minima.

17 Comparison of Solar Minima: In the wind For last 2 cycles: Top: SSN Middle: WSO polar field Bottom: STEL speeds as f(area) Tokumaru et al., JGR, 2010 STEL IPS map showing start in 2003 of high speed wind at low latitudes. 20 May 2010 Webb-SORCE-Keystone, CO 17

18 Comparison of Solar Minima: At the Earth Because of recurring high-speed streams, relativistic electrons in outer radiation belt (GOES geosynchronous orbit) were elevated for much of % increase (71% log) for WHI vs. WSM (faster wind) 20 May 2010 Gibson et al., JGR, 114, A09105,

19 Comparison of Solar Themis Minima: At the Earth Hinode As the high-speed streams disappeared, radiation belts fell to record lows, and cosmic rays reached record highs WHI Courtesy Dan Baker Courtesy R. Mewaldt 20 May 2010 Webb-SORCE-Keystone, CO 19

20 Themis Hinode Comparison of Solar Minima: Summary 20 May Gibson et al., JGR, 114, A09105, 2009

21 Variation of Coronal Mass Ejections at Solar Minima 20 May 2010 Webb-SORCE-Keystone, CO 21

22 Total Coronal Mass - MLO MK; Burkepile et al., SOHO23, 2009 Minimim coronal mass similar in 1986 and 2009: ~ 5 x g. 20 May 2010 Webb-SORCE-Keystone, CO 22

23 CME Occurrence Rate over the Solar Cycle Robbrecht et al., ApJ, May 2010 Webb-SORCE-Keystone, CO 23

24 STEREO and SOHO CME Rates Jan 1996 Jan 1997 Jan 1998 Courtesy C. St Cyr & H. Xie 24

25 Total LASCO CME Mass Per Rotation; Howard et al., SOHO23, 2009 Note: Total mass at solar max ~100x that at minimum. No significant difference at beginning and end of cycle 23 (red horizontal line is to guide the eye)

26 CME Rates: WHI vs WSM Cremades et al. CME (day -1 ) Faint CME (day -1 ) Jet (day -1 ) Str. Swell (day -1 ) Total (day -1 ) WHI (LASCO) WHI (COR1) WHI (total) WSM (LASCO) A really different minimum? Dissimilar cadence - FOV? Instrumental limitations + projection issues 26

27 Summary: WHI vs. WSM Cremades et al. More ejecta More jets WHI Less ambiguity in source identification Less than 20% produced by Ars Ejecta at all position angles Jets at polar latitudes Less Parkerian solar wind WSM Less ejecta More streamer swelling events Large uncertainties due to poor coverage, bad cadence More than 40% produced by ARs Predominance at equatorial latitudes Non-radial jets Alignment at 135º and 315º No significant MCs or ICMEs at Earth. No strong magnetic field or flux. 27

28 Solar Minima Studies: Summary The current solar minimum is not just long and deep, but also extended and complex WHI illustrates certain aspects of this solar minimum well: - Quiet side irradiance (as low as any this minimum) - Low-latitude coronal holes high-speed streams geospace periodicities The length of this cycle allows us to probe Sun-Earth physical processes 1. In 2008 geospace was forced by high-speed streams, even though solar irradiance, activity, and IMF were lower than 1996 allows us to isolate the effects of fast solar wind 2. In 2009 solar magnetic flux moved to smaller spatial scales; high-speed streams no longer periodically forced the Earth allows us to study the Sun-Earth system at its quietest Coronal density/mass was similar at last two minima - CME rates and masses were similar - CME mass/year less at end of SC May 2010 Webb-SORCE-Keystone, CO 28

29 Solar Minima Studies: Future Plans Modeling and connecting observations post-whi via internet: New IAU International Working Group on Comparative Solar Minima: IAU Proceedings of JD 16 in Highlights of Astronomy, Vol. 15, 2010: Upcoming special issue of Solar Physics on WHI/Minima-related topics IAU Symposium 286 on Comparative Magnetic Minima: Characterizing Quiet Times in the Sun and Stars; Mendoza, ARG, October WHI continue to encourage new participants! 20 May 2010 Webb-SORCE-Keystone, CO 29