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Extreme Solar Proton Events and Polar Nitrates?

Extreme Solar Proton Events and Polar Nitrates?. Harlan Spence (University of New Hampshire) Larry Kepko (GSFC), Joe McConnell (DRI), Peg Shea and Don Smart. Background.

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Extreme Solar Proton Events and Polar Nitrates?

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  1. Extreme Solar Proton Events and Polar Nitrates? • Harlan Spence • (University of New Hampshire) • Larry Kepko (GSFC), Joe McConnell (DRI), Peg Shea and Don Smart

  2. Background Motivation: Some recent work (McCracken et al. [2001, and others) has suggested that impulsive nitrate events in polar ice are results of large solar proton events. Carrington white light of 1859 observed in Greenland ice cores?

  3. Flare, n increase Forbush Decrease Flare, n increase Forbush Decrease “Solar cosmic rays” • Forbush [1946] was the first to observe cosmic rays associated with geomagnetic activity, and suggested a solar source: “These considerations suggest the rather striking possibility that the three unusual increases in cosmic-ray intensity may have been caused by charged particles actually being emitted by the Sun [...]”

  4. Atmospheric Chemistry Cosmic ray particles dissociate O3 and N2. They combine to form “odd nitrates” • NO, NO2, NO3, etc Does this change in atmospheric chemistry make its way down to the Earth’s surface? And can it become entrained in ice?

  5. What makes a good ice core? • Ideally we would like to take our ice cores from a region that has: • High snowfall rates • Low noise (away from the ocean) • Clearly defined annual cycle • Many markers that can be used for dating (volcanoes)

  6. To greener pastures • Central Geasilyfulfills our criteria • Summit has the thickest ice shelf, with minimal ice movement

  7. The GISP-H Core • In June, 1992, a 122-m core was collected at Summit as part of the Greenland Ice Core Science Project 2 (GISP-2) The GISP2 drilling dome on the ice surface. The dome is about 105 feet (32.5 m) in diameter and encloses the lower part of the drilling tower. The dome is connected to nearby surface and buried workshops and living quarters.

  8. The GISP-H Core • Dreschoff and Zeller (U. Kansas) analyzed the core for nitrate and conductivity. • Core was sliced into 1.5 cm segments • Samples were melted, and 2.5 ml injected by hand into a UV absorption cell to analyze nitrate, followed by a conductivity measurement • Resulting dataset contained ~20 samples/year and extended back to ~1577.

  9. SPE Year following SPE Nitrates in Antarctic ice cores As early as 1986, Zeller and Dreschhoff suggested a possible link between solar proton events and impulsive nitrate spikes.

  10. Nitrates in Antarctic ice cores • As early as 1986, Zeller and Dreschhoff suggested a possible link between solar cosmic rays and impulsive nitrate spikes. • Unfortunately: • Sea spray contributes to nitrate deposition • Antarctic ice data are extremely noisy • Resolution was marginallysub-annual • Initial results inconclusive

  11. “BU” Cores • In 2006 we were fortunate to obtain 2 30-m cores from Summit, Greenland Our cores resulted from a project needing only bore holes at Summit, Greenland (special thanks to Sarah Das, WHOI, Joe McConnell, DRI, and Jane Dione, NSF for their help in getting these cores for our project). Jay Kyne drilling an ice core on another expedition to Greenland in summer 2003 Summit Cores were bagged, tubed, boxed, and then transported from Greenland to Scotia, NY via a LC-130 Hercules USAF transport plane.

  12. Continuous Flow Analysis • In the late 90’s glaciologists moved away from labor-intensive hand analysis of cores. • Instead, they moved to a closed, continuous system. • Much faster analysis • Less chance for contamination • Allowed for easy analysis of multiple species • Provides spatial (temporal) resolution an order of magnitude better than previously available.

  13. Continuous Flow Analysis commercial freezer at -20 °F

  14. Continuous Flow Analysis Inner ring underpumped, analyzed Melthead at 35.1 °F Outer ring uverpumped, discarded

  15. Continuous Flow Analysis Nitrate (NO3) is reduced to Nitrite (NO2) in a copperized Cd column

  16. Continuous Flow Analysis Calibration curves are produced by passing NO3 standards through the system before and after core runs Spectrophotometer measures absorption at 540 nm, which is proportional to nitrate+nitrite concentration Capable of measuring < 1ppb

  17. BU Cores Ice Stored at BU Medical Campus in -30 °C deep freeze

  18. BU Cores Cores cut into 4 quarters with a bandsaw... ... And analyzed at BU

  19. BU Results • Each core segment provided 4 independent runs • After the runs, depths are hand-adjusted (mm’s) to align peaks, then averaged to produce a single curve.

  20. GISP-H BU CFA BU CFA vs. GISP-H • The higher resolution afforded by CFA is readily apparent Nitrate (ppb) Depth (m)

  21. GISP-H BU CFA BU CFA vs. GISP-H • The higher resolution afforded by CFA is readily apparent Nitrate (ppb) Depth (m)

  22. GISP-H BU CFA BU CFA vs. GISP-H • The higher resolution afforded by CFA is readily apparent Nitrate (ppb) Depth (m)

  23. GLE #4 19-Nov-1949 GLE #3 25-Jul-1946 Results • Two largest peaks in our record occur in 1946 and 1949

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