MERGE SP: Trajectory analysis of atmospheric transport of 10Be to the polar region and implication for the past solar activity reconstructions

Studying past solar activity can help us to improve the forcing used to drive paleoclimate simulations, and therefore improve our understanding of the climate variability in the past. Cosmogenic radionuclides, such as 10Be in ice cores, are excellent tools to reconstruct past solar activity (e.g. Muscheler et al., 2007). Due to its cosmic ray origin, the production rate of 10Be is modulated by the solar and geomagnetic shielding, hence providing useful information on changes of solar activity. However, the interpretation of the 10Be data is hampered by the uncertainty introduced by the transport and scavenging processes of the 10Be from their origin to the archives. One open question is the source region of 10Be deposited in polar areas and the varying weather/climate
influences on the 10Be records. Because of the geomagnetic shielding, the solar modulation of 10Be is strongest at high latitudes. If the 10Be deposited in the polar region originated mainly from latitudes pole-wards of 60°, interpreting the variability of measured '0Be data from the ice cores as global production variability would lead to an overestimation of the solar modulation (referred as "polar bias"). While some general circulation model (GCM) studies have detected a polar bias, stating that polru 10B e records were dominated by 10Be produced at polar latitudes (e.g. Field et al., 2006), otherssuggest no such polar bias (Heikkila et al., 2009). Similarly, unidentified climate imprints on 10Be records could lead to erroneous solar activity reconstructions. This leads to the question that whether 10Be transport processes wi11 result in such polar bias effects on 10Be deposition in Greenland and how we can quantify and correct for climate/circulation impacts on the 10Be data.

The aim of this project is to improve the interpretation of 10Be records from polar ice cores by tracing back the origin of the 10Be. To fill this knowledge gap, we propose to apply the HYSPLIT (HYbrid Single-Particle Lagrangian Integrated Trajectory) model to study the 10Be transport pathways and their variability to polar regions. T
he main objectives are:
1) To quantify the contribution of source regions at different latitudes to the measured 10Be deposition in the Greenland for winter (December) and summer (July) seasons and how this influences the 10Be deposited in Greenland.
2) To investigate the circulation/climate influences on the 10Be deposition from a model perspective.