A strong interaction of charged dust with electrons and ions similar to that leading to formation of polar mesosphere summer echoes (PMSE) assumes to take also place in the lower mesosphere. This assumption predicts extremely low effective conductivity of the region where both positive and negative charges carried by the dust exceed the charges carried by ions and electrons. The low effective conductivity of the mesospheric dusty plasma can explain the existence of V/m vertical electric fields observed in the lower mesosphere and in the vicinity of noctilucent clouds and PMSE. Gravitational sedimentation of charged dust as well as currents of the global atmospheric electric circuit and precipitating high-energy electrons and protons can produce the V/m fields under these conditions. The proposed theory allows understanding the observed behavior of the mesospheric vertical electric fields; their large variability, universal diurnal variation, increasing during solar proton events and geomagnetic disturbances. ¿ 2000 American Geophysical Union