10 Be concentrations in snow at Law Dome, Antarctica following the 29 October 2003 and 20 January 2005 solar cosmic ray events
2007
Recent model calculations have attempted to quantify the contribution of
major energetic solar cosmic ray (SCR) events to 10 Be production. In this
study we compare modeled 10 Be production by SCR events to measured
10 Be concentrations in a Law Dome snow pit record. The snow pit record
spans 2.7 years, providing a quasi-monthly 10 Be sampling resolution which
overlaps with the SCR events of 29 Oct 2003 and 20 Jan 2005. These
events were calculated to increase monthly 10 Be production in the polar
atmosphere (>65° S geomagnetic latitude) by ~60% and ~120% above the
GCR background, respectively. A strong peak in 10 Be concentrations (>4σ
above the 2.7 y mean value) was observed ~1 month after the 20 Jan 2005
event. By contrast, no signal in 10 Be concentrations was observed following
the weaker 29 Oct 2003 series of events. The concentration of 10 Be in ice
core records involves interplay between production, transport, and deposition
processes. We used a particle dispersion model to assess vertical and meridional
transport of aerosols from the lower stratosphere where SCR production of
10 Be is expected to occur, to the troposphere from where deposition to the ice
sheet occurs. Model results suggested that a coherent SCR production signal
could be transported to the troposphere within weeks to months following both
SCR events. We argue that only the 20 Jan 2005 SCR event was observed
in measured concentrations due to favorable atmospheric transport, relatively
high production yield compared to the 29 Oct 2003 event, and a relatively high
level of precipitation in the Law Dome region in the month following the event.
This result encourages further examination of SCR signals in 10 Be ice core data.
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