Contributions of substorm injections to SYM-H depressions in the main phase of storms

Substorm injections bring energetic particles to the inner magnetosphere. But the role of the injected population in building up the storm time ring current is not well understood. By surveying Los Alamos National Laboratory geosynchronous data during 34 storm mainphases, weshowevidence that at least some substorm injections can contribute to substorm-time scale SYM-H/Dst depressions in the main phase of storms. For event studies, we analyze two typical events in which the main-phase SYM-H index exhibited stepwise depressions that are correlated with particle flux enhancement due to injections and with AL index. A statistical study is performed based on 95 storm time injection events. The flux increases of the injected population (50-400 keV) arefoundproportional to the sharpSYM-Hdepressions during the injection interval. By identifying dispersionless and dispersive injection signals, we estimate the azimuthal extent of the substorm injection. Statistical resultsshowthat the injection regions of these storm time substorms are characterized with an azimuthal extent larger than 06:00 magnetic local time. These results suggest that at least some substorm injectionsmaymimicthe large-scaleenhancedconvectionandcontribute to sharp decreases of Dst in thestorm main phase.