CHARACTERISTICS OF THE SOLAR-WIND CONTROLLED AURORAL EMISSIONS

We performed a, high-time resolution (5 min) correlative study of the energy deposition rate in the northern auroral zone with the concurren t solar wind plasma and interplanetary magnetic field (IMF) observatio ns for a 4 month period from March 30 to July 29, 1996. Amoral power, inferred by auroral emissions, was derived from images acquired by the ultraviolet imager (UVI) on board the Polar satellite, and the interp lanetary parameters were based on Wind observations. It is found that dayside aurorae in the afternoon sector (65 degrees-80 degrees magneti c, latitude (MLAT) and 1300-1800 magnetic local time (MLT)) are more a ctive for large IMF cone angles and large solar wind electric fields. This result can be attributed to the manifestation of the antiparallel magnetic field merging in different locations and the partial ''penet ration'' of the IMF on the dayside magnetopause. The integrated nights ide (60 degrees-75 degrees MLAT and 2000-0100 MLT) auroral brightness is moderately correlated with the north-south component of the IMF and the solar wind Speed with correlation coefficients of 0.49 and 0.35, respectively. The mean nightside auroral power is found to be approxim ately linearly proportional to the IMF B-z with a constant slope of 2 GW/nT. The solar wind speed, however, affects the nightside auroral po wer for both polarities of IMF B-z. Interestingly, the solar wind dyna mic pressure shows no effect on the nightside auroral brightness. All these findings indicate that both reconnection and viscous-like intera ction mechanisms play an important role in producing auroral emissions in the night sector. It is also found that the nightside auroral brig htness responds to the southward turning of the IMF with a peak delay time of similar to 60 min. This result favors the model of loading-unl oading magnetosphere. We also found that a negative IMF B-y condition favors the nightside auroral activity, and we attributed this effect t o the partial penetration of the IMF B-y. Finally, the response functi on for nightside aurora is given as similar to VB(T)(4)sin(4)(theta(c) /2) with a median correlation coefficient of 0.63, indicating: that th ere may be other factors other than the solar wind and IMF responsible for lightening up the northern-southers hemispheric sky.