Pancake-like and tablet-like distribution functions of energetic electrons in the middle magnetosphere

Abstract. We propose a simple explanation of the prolonged existence of pancake-like electron velocity distributions in the radiation belts. The pancake-like distribution function is characterized by a longitudinal particle velocity (along the magnetic field) of the order of the thermal velocity of the background plasma. The parameters of the tablet-like distribution function with a characteristic longitudinal particle velocity of the order of 20 Alfvèn velocities are refined. Such distribution functions can occur in the middle magnetosphere near the magnetic equator with appropriate sources of energetic particles. The stability of these distributions is examined. The results agree with known experimental data.