The relationship between ELF-VHF waves and magnetic shear at the dayside magnetopause

ELF-VLF waves within the current layer of the dayside magnetopause are studied using ISEE-1 data. The database consists of 272 current layer crossings at the dayside magnetopause from 1977 to 1979. For each crossing, the average intensity of ELF-VLF waves inside the current layer is obtained and the magnetic shear angle across the current layer is calculated from the magnetometer data. It is found that the wave amplitudes (both electric and magnetic fields), after normalization by the average magnetic field strength in the current layer, are proportional to the local magnetic shear angle, i.e. large magnetic shear corresponds to strong wave emission and vice versa. From the dispersion relation of the waves for different shear angles, the phase velocity of the waves increases with the magnetic shear and peaks around 700 Hz to 1 kHz. The dispersion curve of the waves is consistent with that of whistler modes.