Dayside magnetospheric interactions inferred from dayside diffuse aurora and throat aurora

Optical aurora can be classified into two broad categories, i.e., diffuse and discrete auroras. Recent studies based on optical observations obtained on the dayside reveal some important processes occurred in the dayside magnetosphere and are reviewed in this paper. Dayside diffuse auroras (DDAs) are classified into unstructured and structured DDAs. Unstructured DDAs predominantly occur in the morning but structured ones are mainly observed near magnetic local noon (MLN). Because structured diffuse auroras have been suggested to be associated with cold plasma structures in the magnetosphere, distribution and generation of cold plasma structures in the dayside outer magnetosphere are discussed based on the detailed observational properties of DDAs. A particular discrete auroral form, i.e., throat aurora, is defined during study on DDA. Detailed observational properties of throat aurora are presented, which suggest that throat auroras are ground signatures for localized magnetopause indentations that are most likely caused by localized high-speed jets impacting on the magnetopause. Studies on throat aurora reveal that the transient structures locally generated in the magnetosheath can frequently cause indentations on the subsolar magnetopause, trigger reconnection, result in a serial of responses in geospace, and thus will play important role on solar wind-magnetosphere coupling.