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

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Presentation on theme: "Extreme Solar Proton Events and Polar Nitrates? Harlan Spence (University of New Hampshire) Larry Kepko (GSFC), Joe McConnell (DRI), Peg Shea and Don Smart."— Presentation transcript:

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 “Solar cosmic rays”  Forbush [1946] was the first to observe cosmic rays associated with geomagnetic activity, and suggested a solar source:  Flare, n increase Forbush Decrease Flare, n increase Forbush Decrease “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 O 3 and N 2. They combine to form “odd nitrates” NO, NO 2, NO 3, 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 Geasily fulfills 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 Nitrates in Antarctic ice cores As early as 1986, Zeller and Dreschhoff suggested a possible link between solar proton events and impulsive nitrate spikes. SPE Year following SPE

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 marginally sub-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). Summit Jay Kyne drilling an ice core on another expedition to Greenland in summer 2003 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 Melthead at 35.1 °F Inner ring underpumped, analyzed Outer ring uverpumped, discarded

15 Continuous Flow Analysis Nitrate (NO 3 ) is reduced to Nitrite (NO 2 ) in a copperized Cd column

16 Continuous Flow Analysis Spectrophotometer measures absorption at 540 nm, which is proportional to nitrate+nitrite concentration Calibration curves are produced by passing NO 3 standards through the system before and after core runs 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 BU CFA vs. GISP-H  The higher resolution afforded by CFA is readily apparent Depth (m) Nitrate (ppb) BU CFA GISP-H

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

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

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

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