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Planning Project 2: D-region Conductance & Multiple substorms

Our conductance measurements are mostly higher than that made by \cite{Kirkwood1988}, by at least $1.5-2$ times in Pedersen and Hall conductances. The measurements suggest strongly that small-scale conductances are much higher than those predicted by global conductance models. The contribution of D-region to the total conductance is also non-negligible during energetic precipitation. It is highest at the outer radiation belt boundary during growth-phase, the substorm onset, and the expansion phase.

D-region contribution to Hall-conductance is higher than the Pedersen conductance. The charge carriers to ionospheric Hall conductivity are mostly electrons with high mobility in the D-region as opposed to the ions. The Hall conductance contribution reaches a maximum of about 60\% during the expansion phase. Though the D-region Pedersen conductance contribution is low, here we have not taken into account the non-linear effects that can enhance Pedersen conductance in the lower-E and -D region. The increase in conductance has a non-linear dependence on the electric field and electron temperature due to enhanced ion-electron coulomb collisions.

A significant realization that we had during this study is the lack of dependence of D-region conductivity estimates from ISRs on D-region ion chemistry. It is common to attribute uncertainties in any measurement of D-region quantities to the complex D-region chemistry. However, due to the high rate of ion-neutral collisions in the D-region, their mobility becomes insignificant, and electrons are the dominant (if not the only) charge carriers. As ISRs directly measure the D-region's electron concentrations, we can rely on its conductivity estimates without considering the contribution of ions at altitudes below $\sim$ 97 km.

In the future, we ought to expand this study to use ISR-based electric field measurements to estimate Joule heating within the D-region more precisely. And also use the Hall conductance gradients to determine the magnitude of field-aligned currents. Finally, we can conclude that from the perspective of boundary conditions to MI coupling models, neglecting the D-region contribution during magnetically active periods such as a substorm can lead to uncertainty in the conductance values to about 15-60\%.