From routine observations by means of highly sensitive all-sky cameras and tilting-filter photometers, a total of 20 low-latitude aurora events in Japan were identified during the high solar activity period of 1999--2004. This indicates that the invisible-level auroras appear rather frequently in the northern sky of Japan during magnetic storms. These auroras are characterized by an enhancement in red (630.0 nm) emissions in the northern sky during magnetic storms, probably at geomagnetic latitudes higher than ~40--50¿. We show examples of stable auroral red (SAR) arcs, which are typically observed during the recovery phase of storms. We also found several red aurora events that occurred at the initial phase of magnetic storms. Intensifications as well as equatorward motion of the auroras were observed in association with storm time substorms. Green line emissions (557.7 nm) were often enhanced (~1 kR) not only in the northern sky but also in the whole sky. Some auroras show weak enhancements (~10 R) of N2+1N (427.8 nm) in the northern sky in the morning hours. We discuss possible causes of these emissions in light of magnetospheric disturbances and thermospheric dynamics.