Height-integrated conductivity in auroral substorms - 2. Modeling

Calculations of height-integrated conductivity from 31 individual Dynamics Explorer (DE 2) substorm crossings presented by Gjerloev and Hoffman [this issue] are used to compile empirical models of the height-integrated Peders en and Hall conductivities (conductances) in a bulge-type auroral substorm. Global auroral images obtained by Dynamics Explorer 1 (DE 1) were used to select substorms displaying a typical bulge-type emission pattern and each individual DE 2 pass was positioned with respect to key features in the obs erved emission pattern. The conductances were calculated for each DE 2 pass using electron precipitation data and a monoenergetic conductance model. A ll passes were divided into six different sectors, and average conductance profiles were carefully deduced for each of these sectors. Using a simple b oxcar filter, smoothed average sector passes were calculated and from linea r interpolation between these, two-dimensional conductance models were comp iled. The characteristics of our models are (1) the Hall conductance maximi zes in the high-latitude part of the surge at 48 mho with a Hall to Pederse n ratio of 2.4; (2) two channels of enhanced conductance are overlapping in local time near midnight and are fairly separated in latitude; (3) the con ductance has a sharp gradient at the high-latitude boundary in the premidni ght sector while in the postmidnight sector a broad region of low conductan ce stretches up to 10 degrees invariant latitude poleward of the local peak ; and finally, (4) the enhanced conductance region displays a characteristi c broadening toward dawn primarily owing to a poleward shift of the high-la titude boundary.