A correlation between auroral kilometric radiation and inverted V electron precipitation

Abstract

Simultaneous observations of energetic electron precipitations and auroral kilometric radiation (AKR) were obtained from the polar orbiting satellites AE‐D and Hawkeye. The Hawkeye observations were restricted to periods when the satellite was in the AKR emission cone in the northern hemisphere and at radial distances ≳7 RE to avoid local propagation cutoff effects. In addition, the AE‐D measurements were restricted to complete passes across the auroral oval in the evening to midnight local time sector (from 20 to 01 hours magnetic local time). This is the local time region where the most intense bursts of AKR are believed to originate. A qualitative survey of AKR and electron particle precipitation shows that AKR is more closely associated with inverted V electron precipitation than with plasma sheet precipitation. Quantitatively, a good correlation is found between the AKR intensity and the peak energy of inverted V events. In addition, in the tail of the most field‐aligned portion (∼0° pitch angle) of the distribution functions of the inverted V events, systematic changes are indicated as the associated AKR intensity increases. When the AKR power flux is weak (<10−17 W/(m² Hz)), the effective tail temperature (T∥) in F(V∥) of the inverted V events is less than 1.8 × 108°K, while for T∥ greater than 1.8 × 108°K the associated AKR power flux is moderate (10−17 to 10−15 W/(m² Hz)) to intense (>10−15 W/(m² Hz)). From a determination of the simultaneous power in the inverted V events and the AKR bursts, the efficiency of converting the charge particle energy into EM radiation increases to a maximum of about 1% for the most intense AKR bursts. However, conversion efficiencies as low as 10−5% are also found. There is some evidence which suggests that the tail temperature, T∥ in F(V∥) of the inverted V events, may play an important role in the efficient generation or amplification of auroral kilometric radiation.