Effects of solar wind density on auroral electrojets and brightness under influence of substorms
- 1Institute of Space Science, National Central University, Jhongli City, Taoyuan County 32001, Taiwan
- 2Research Institute for Sustainable Humanosphere, Kyoto University, Uji 611-0011, Japan
- 3Applied Physics Laboratory, Johns Hopkins University, 11100 Johns Hopkins Road, Laurel 20723-6099, USA
Abstract. Using the auroral electrojet indices and Polar Ultraviolet Imager auroral images, we examined two fortuitous events during which the solar wind density had clear enhancements while the other solar wind parameters were relatively constant. Two electrojet enhancements were found in each event. The first electrojet enhancement was likely to be related to a substorm in which an auroral bulge appeared at premidnight. The second electrojet enhancement was driven by the density enhancement in the solar wind. The auroral oval became wider in latitude and the auroral distribution became dispersed after the density enhancement arrived at the Earth. The total auroral power integrated over the entire nightside region from 50 to 80° MLAT, however, did not increase significantly in response to the density enhancement. Our interpretation is that the substorm that occurred prior to the solar wind density enhancement had drained out a significant portion of the stored energy in the magnetotail; therefore, less precipitation energy was deposited into the auroral ionosphere by the density enhancement.