Statistical properties of small-scale auroral spots near magnetic local noon

Small-scale auroral spots (SsAS) are frequently observed, particularly on the nightside, yet their formation mechanisms remain unclear. Utilizing all-sky imager data from the Chinese Arctic Yellow River Station and radar measurements from the European Incoherent Scatter Scientific Association (EISCAT), we identified 65 SsAS events occurring near magnetic local noon from 2003 to 2009. We found that they are observed only in the 557.7 nm emission band. They can be classified into two types based on their morphology: sporadic SsAS and fence-like SsAS. The occurrence of these events shows clear dependence on the southward interplanetary magnetic field (IMF) B_z, with the fence-like SsAS exhibiting an even more pronounced dependence. Their occurrence also depends on the westward IMF B_y. Additionally, we found that most events (88%) are located on the poleward side of the auroral oval, and the drift motion of these SsAS is consistent with the motion direction of adjacent auroral structures, whose motion is strictly governed by the IMF B_y polarity. These observations indicate that generation of these dayside SsAS may be directly linked to the solar wind energy input through magnetopause reconnection. The EISCAT observations further show that SsAS are accompanied by pronounced electron density gradients. On the basis of these characteristics, we propose that the generation of SsAS may be related to phase mixing of Alfvén waves arising from the density gradients. This study helps elucidate the coupling chain by which solar wind energy is injected into the polar region and subsequently drives ionospheric responses.