The sign of dm2_{31} and the muon-charge asymmetry for atmospheric   neutrinos
  We discuss the possibility to measure the sign of dm2_{31} from matter-induced charge asymmetries in atmospheric neutrino oscillations. The main conclusion is that an impact on the nu_mu survival probability requires the action of the MSW resonance, which becomes visible for baselines above \~7000 km. 
J. Bernabeu and S. Palomares-Ruiz