On the electrical coupling between the troposphere and the mesosphere

4. Effect of Ionospheric D-Region Cooling

[9] During disturbed conditions, the resistance R_t could decrease by an order of magnitude or more due to, e.g., an increase in the level of radiation at ground level in the vicinity of strong earthquakes or during accidents at nuclear power plants with the discharge of radioactive materials [e.g., Fuks and Shubova, 1994; Fuks et al., 1997; Martynenko et al., 1994, 1996]. Consequently, the ratio between R_t and R_m varies, and this leads to a lowering of R_i. If a decreased R_t value satisfies the inequality R_t R_m, then R_i approx R_t (see Figure 4). Then the potential difference, U, across the mesosphere and the large mesospheric electric field intensity, E, become dependent on R_t. A decrease in R_i and R_t results in a decrease in E and consequently in T_e and n_e down to unperturbed values at q =1. Hence a large increase in the tropospheric conductivity may result in local thermodynamic equilibrium in the ionospheric plasma, and in electron cooling in the lower part of the ionospheric D region. This effect of electron cooling is due to electrical coupling between the troposphere and the electrically active mesosphere (see Figure 4). The values of the cooling rates follow a decrease in R_t and lie in the ~0.1- to 1-ms range [e.g., Martynenko, 1999a, 1999b]. These changes are accompanied by a rise in the high-frequency conductivity and by a reduction in the low-frequency (down to DC) conductivity.