  The relatively large measured value of theta_13 has opened various
possiblities to determine the neutrino mass ordering, among them using PINGU,
the low-energy extention of the IceCube neutrino telescope, to observe matter
effects in atmospheric neutrinos, or a high statistics measurment of the
neutrino energy spectrum at a reactor neutrino experiment with a baseline of
around 60 km, such as the Daya Bay II project. In this work we point out a
synergy between these two approaches based on the fact that when data are
analysed with the wrong neutrino mass ordering the best fit occurs at different
values of |Delta m^2_31| for PINGU and Daya Bay II. Hence, the wrong mass
ordering can be excluded by a mismatch of the values inferred for |Delta
m^2_31|, thanks to the excellent accuracy for Delta m^2_31 of both experiments.
We perform numerical studies of PINGU and Daya Bay II sensitivities and show
that the synergy effect may lead to a high significance determination of the
mass ordering even in situations where the individual experiments obtain only
poor sensitivity.
