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The occurrence frequencies of dayside ionconics with various conic angles are obtained as a function of altitude fromExos-D (Akebono) observations. We made a model calculation of ion conicevolution to match the observation results. The observed occurrence frequenciesof ion conics with 80° to 90° conicangle are used as an input to the model and the occurrence frequencies of ionconics with smaller conic angles are numerically calculated at higher altitudes.The calculated occurrence frequencies are compared with the observed ones of ionconics with smaller conic angles. We take into account conic angle variationwith altitude in both adiabatic and non-adiabatic cases, horizontal extension ofion conics due to E×B drift, and evolution to elevated conics andion beams in the model. In the adiabatic case, the conic angle decreases withincreasing altitude much faster than was observed. The occurrence frequency ofsmall-angle conics is much larger than the observed value without E×Bdrift and evolution to the other UFIs. An agreement is obtained by assumingnon-adiabatic variation of conic angles with altitude and an ion E×Bdrift to gyro velocity ratio of 0.08 to 0.6, depending on geomagneticactivities. Key words. Ionosphere (particle acceleration) ·Magnetospheric physics (auroral phenomena; magnetopause, cusp, and boundarylayers)

Modeling of occurrence frequencies of ion conics as a function of altitude and conic angle