10Be CONCENTRATIONS IN SNOW AT LAW DOME, ANTARCTICA FOLLOWING THE 29 OCTOBER 2003 AND 20 JANUARY 2005 SOLAR COSMIC RAY EVENTS

Abstract

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.