Study of the nose event on 11 April 2002 with UBK method

Nose event, which names after the nose-like shape of structures in ion spectrograms observed by satellite in the inner magnetosphere, refers to the deep inward penetration of ions from magnetotail at discrete energy bands. Nose events have been studied extensively both with observations and simulations since first discovered in 1970s. In this study we use the UBK method to model the different L-shell penetration characteristics for a multi-band nose event observed by Cluster/CODIF on April 11, 2002. The modeled open-closed orbit separatrices are generally smaller than the observed L-shell penetrations for outbound crossing; the difference varies from −2.02 to −0.62 RE for different energy channels of H+ bands and from −1.88 to −1.10 RE for O+ band. The average difference is −1.46 RE. The separatrices for the inbound crossing are generally larger than those of outbound crossing and are more consistent with the observed L-shell penetration depths. The modeled open-closed orbit separatrices are smaller than the observed L-shell penetrations for 6.5–17.1 keV energy channels of H+ bands but larger for 4.0–5.1 keV (due to closed banana orbits region) and 21.7–35.2 keV (due to energy increasing) energy channels of H+ bands. For O+ band, the difference between the modeled open-closed orbit separatrix and observed L-shell penetrations of 4.6 keV energy channel is larger (due to closed banana orbits region), the difference of 7.4 keV energy channel is smaller. The overall average difference is 0.043 RE for nose structures of inbound crossing. The discrepancies between the model and observation may come from the magnetic field and electric potential models we used. The formation of multi nose event and relations to the observed plasma flow vortices are discussed, the local intense E Y may relate to the formation of the observed multi nose structures.