Quantitative relationship between substorm auroral intensity and magnetotail Stretching

Magnetic field line stretching is a key feature in the near-Earth magnetotail during the growth phase of a substorm. The stretched field line ceases abruptly at the onset of substorm and returns to its original dipole-like configuration. The degree of field line stretching is controlled by the solar wind-magnetosphere coupling and may be used as an indicator of the amount of energy available for substorms to occur later. The purpose of this study is to investigate relationship between substorm auroral intensity and magnetic field stretching and to find a practical way of predicting energy dissipation during substorms. We parameterize the intensity of substorms by the total energy deposition from particle precipitation inferred from auroral luminosity in the long wavelength bands of N2 Lyman-Birge-Hopfield auroral emissions (160 - 180 nm) from the Polar ultraviolet imager. The stress of the magnetic field line in the tail is inferred from the magnetotail stretching index, b2i, which is identified by DMSP as the ion precipitating energy flux maximum and is in good relationship with the magnetic field inclination at geosynchronous orbit. We will present quantitative relationships between the two quantities and discuss potential uses of the result in substorm intensity forecasting.