Frequency dependence of ionospheric exit points and polarization of daytime whistlers at low-latitude

In order to study the propagation mechanism of whistlers, a new method of wideband direction finding for whistlers, based on the simultaneous measurement of two horizontal magnetic field components and one vertical electric field component using the digital recorders and a fast Fourier transform analyzer, has been adopted for daytime whistlers at low latitude Yamaoka (geomagnetic latitude 25 deg N). It is found that there is a negligibly small frequency dependence of the ionospheric exit point and polarization of daytime whistlers during each occurrence peak with duration of about 2 hr, which lends further support to their propagation in a field-aligned duct in the magnetosphere for each occurrence peak.