  Context: Cosmic-ray propagation is strongly dependent on the large-scale
configuration of the Galactic magnetic field. In particular, the Galactic
center (GC) region provides highly interesting cosmic-ray data from gamma-ray
maps and it is clear that a large fraction of the cosmic rays detected at Earth
originate in this region of the Galaxy. Yet because of confusion from
line-of-sight integration, the magnetic field structure in the Galactic center
is not well known and no large-scale magnetic field model exists at present.
Aims: In this paper, we develop a magnetic field model, derived from
observational data on the diffuse gas, nonthermal radio filaments, and
molecular clouds. Methods. We derive an analytical description of the magnetic
field structure in the central molecular zone by combining observational data
with the theoretical modeling of the basic properties of magnetic fields.
Results. We provide a first description of the large-scale magnetic field in
the Galactic center region. We present first test simulations of cosmic-ray
propagation and the impact of the magnetic field structure on the cosmic-ray
distribution in the three dimensions. Conclusions: Our magnetic field model is
able to describe the main features of polarization maps; it is particularly
important to note that they are significantly better than standard global
Galactic magnetic field models. It can also be used to model cosmic-ray
propagation in the Galactic Center region more accurately.
