Application of CCM SOCOL-AERv2-BE to cosmogenic beryllium isotopes: description and validation for polar regions
Authors: Golubenko Kseniia , Rozanov Eugene , Kovaltsov Gennady , Leppänen Ari-Pekka , Sukhodolov Timofei , Usoskin Ilya 
Published: December 2021

Abstract. The short-living cosmogenic isotope 7Be, which is produced by cosmic rays in the
atmosphere, is often used as a tracer for atmospheric dynamics, with precise
and high-resolution measurements covering the recent decades. The long-living
isotope 10Be, as measured in polar ice cores with an annual resolution,
is a proxy for long-term cosmic-ray variability, whose signal can, however,
be distorted by atmospheric transport and deposition that need to be properly
modeled to be accounted for. While transport of 7Be can be modeled with
high accuracy using the known meteorological fields, atmospheric transport of
10Be was typically modeled using case-study-specific simulations or
simplified box models based on parameterizations. Thus, there is a need for a
realistic model able to simulate atmospheric transport and deposition of
beryllium with a focus on polar regions and (inter)annual timescales that is
potentially able to operate in a self-consistent mode without the prescribed
meteorology. Since measurements of 10Be are extremely laborious and
hence scarce, it is difficult to compare model results directly with
measurement data. On the other hand, the two beryllium isotopes are believed
to have similar transport and deposition properties, being different only in
production and lifetime, and thus the results of 7Be transport can be
generally applied to 10Be. Here we present a new model, called CCM
SOCOL-AERv2-BE, to trace isotopes of 7Be and 10Be in the atmosphere
based on the chemistry–climate model (CCM) SOCOL (SOlar Climate Ozone Links),
which has been improved by including modules for the production, deposition,
and transport of 7Be and 10Be. Production of the isotopes was modeled
for both galactic and solar cosmic rays by applying the CRAC (Cosmic Ray
Atmospheric Cascade) model. Transport of 7Be was modeled without
additional gravitational settling due to the submicron size of the background
aerosol particles. An interactive deposition scheme was applied including
both wet and dry deposition. Modeling was performed using a full nudging to
the meteorological fields for the period of 2002–2008 with a spin-up period
of 1996–2001. The modeled concentrations of 7Be in near-ground air were
compared with the measured ones at a weekly time resolution in four nearly
antipodal high-latitude locations: two in the Northern (Finland and Canada) and
two in the Southern (Chile and the Kerguelen Islands) Hemisphere. The model results
agree with the measurements in the absolute level within error bars, implying
that the production, decay, and lateral deposition are correctly reproduced.
The model also correctly reproduces the temporal variability of 7Be
concentrations on annual and sub-annual scales, including the
presence and absence of the annual cycle in the Northern and Southern Hemisphere,
respectively. We also modeled the production and transport of 7Be for a
major solar energetic particle event (SPE) on 20 January 2005, which appears
insufficient to produce a measurable signal but may serve as a reference event
for historically known extreme SPEs. Thus, a new full 3D time-dependent
model, based on CCM SOCOL, of 7Be and 10Be atmospheric production,
transport, and deposition has been developed. Comparison with real data
on the 7Be concentration in the near-ground air validates the model and its
accuracy.