1. 7 March 2004Milagro Collaboration 1 Update on Solar Science Jim Ryan, Abe Falcone, James Ledoux

2. 7 March 2004Milagro Collaboration 2 Huge X28 solar flare occurred on 29 October 2003, largest on record. Major signal (decrease) in Milagro, even, arguably, in the raw trigger rate (middle panel below). Signal is in the form of a Forbush Decrease—a “sweeping up” of galactic CR in the heliosphere by the CME. Direct solar particles are small component (in valley).

3. 7 March 2004Milagro Collaboration 3 Signal shows up in other NMs. (Time scaling of Apatity data by eyeball.)

4. 7 March 2004Milagro Collaboration 4 Direct Solar Particles? Yes, but effect is not large Need to correlate structure at lowest point with signals in NMs. Whopping signal from some low cutoff stations, i.e., South Pole.

5. 7 March 2004Milagro Collaboration 5 Sorry for compressing the plots to match time scales. Milagro HT scalers South Pole NM The solar origin of the bumps in the valley of the scaler data could be confirmed with some careful correlation with several stations.

6. 7 March 2004Milagro Collaboration 6 Haleakala (red) and Climax (blue) have significantly different cutoffs and see different responses of the heliosphere to solar activity on a long term basis. Haleakala modulates less but still sees isolated events, e.g. 10/03 at right edge. 1995-2004 12.9 GV 3.0 GV Long term effects of CMEs

7. 7 March 2004Milagro Collaboration 7 Shorter term effects: Climax (bottom) stays down longer w.r.t. Haleakala and recovers more slowly (effect not large on these time scales over cutoff range). How does Milagro add to this? Trigger threshold is possibly much higher than Haleakala cutoff (12.9 GV).

8. 7 March 2004Milagro Collaboration 8 Significant Items Solar protons at depth of Forbush decrease on 29 October, with no big onset like 15 April 2001. Significant Forbush decrease even in triggered rate, but seemingly short- lived w.r.t. scalars and NMs.

9. 7 March 2004Milagro Collaboration 9 Scientific Pay Dirt Forbush decreases are poorly understood above 15 GV. –Previous identifications from underground detectors are dubious. –Which trigger rate of ours is > 15 GV? If our triggered threshold corresponds to ~20-50 GV, then we are measuring the differential backfilling of the heliosphere with galactic cosmic rays, never seen before on these time scales.

10. 7 March 2004Milagro Collaboration 10 Thumbnail Hypothesis for Forbush Decrease Publication At ~50 GV the gyroradius at 1 AU is about 0.2 AU compared to 0.02 AU for a 5 GV proton. The diffusion of galactic protons back into 1 AU is therefore more rapid (on scale of hours not days, months or years)., a new probe into the transport of galactic cosmic rays in the heliosphere.Finally, a new probe into the transport of galactic cosmic rays in the heliosphere.

11. 7 March 2004Milagro Collaboration 11 Evidence The duration of the decrease and its recovery are typically momentum independent. We see that the triggered rate (middle) (assuming small corrections) recovers faster.

12. 7 March 2004Milagro Collaboration 12 Further Work (growing list) Look at other trigger-criteria rates (different cutoffs). Need longer baseline to study recovery (met corrections critical here). ModelModel effective proton threshold for different channels. Compare to Climax, Haleakala, IMP to obtain direct solar particle spectrum from 50 MeV to 50 GeV. Analyze event data to quantify azimuthal anisotropy of decrease (unprecedented).

13. 7 March 2004Milagro Collaboration 13 Meeting Opportunities “When the Sun Went Wild” session at the Denver Solar Physics Division Meeting of the AAS in Denver in June (1). Abstracts due March 17! Will have to circulate draft abstract next week (ouch). Will probably be a bit bland at this stage.

14. 7 March 2004Milagro Collaboration 14 Missed Opportunities Late May AGU meeting in Montreal, but others are coming along. JR might go anyhow (semester ended) to hear what’s going on perhaps with TBD data in hand.

15. 7 March 2004Milagro Collaboration 15 Journal Opportunities Call for a special volume of J. Geophys. Res. on this period of solar activity. Call went out for someone to organize and has been deathly quiet since. It will probably happen one way or the other.

16. 7 March 2004Milagro Collaboration 16 Collaborations Approached by Cliff Lopate (UNH, Climax, Haleakala), Jack Lockwood (UNH, Durham, Mt. Washington) and Bill Webber (NMSU, IMP) to collaborate on an analysis of the direct solar particles. Our signal is not huge, but is probably there when compared to timing of increases at NMs and spacecraft. Yet to be demonstrated, but at least we see the end of the spectrum.

17. 7 March 2004Milagro Collaboration 17 Need to get our data out first somehow prior to multi-instrument paper. I suggest first a Forbush decrease analysis, since our direct particle signal is weak and would be best used in the context of other data. Milagro direct solar particle data might be publishable alone but should wait to see. Decrease anisotropy paper should be strictly Milagro, or at least lead.