<1> A new electrodynamic mechanism for coupling the electrically active mesosphere to the troposphere during disturbed conditions is discussed. It is based on the existence of large V/m mesospheric electric fields that violate local thermodynamic equilibrium in the lower D region. We have suggested a simple electric circuit for troposphere-mesosphere coupling. An order of magnitude increase in the tropospheric conductivity, which has been observed over both seismically active regions and nuclear power plant accidents, acts to redistribute the circuit currents by increasing the tropospheric current, thereby decreasing the current flowing through the mesospheric resistance. This reduces the large electric fields and consequently the electron temperature and effective collision frequency. The net effect is electron cooling in the D region. The resulting variations in the ionospheric conductivities can be remotely sensed with instruments employing radio wave techniques, and they have already been detected in a few experiments.