NTC radiation reflected on magnetopause surface: observations from Cluster large scale configuration

Non Thermal Continuum radiation NTC is an electromagnetic wave of weak intensity steady in time Observations of terrestrial NTC radiations below sim 100 kHz can be classified into two classes A first class corresponds to wave frequencies above the magnetosheath plasma frequency the radiation escaping in the interplanetary medium Corresponding spectral characteristics are a series of narrow banded emissions A second class corresponds to wave frequencies below the plasma frequency of the magnetosheath The radiation bounces at the magnetopause and is trapped in the magnetospheric cavity This class of NTC is often observed in frequency-time spectrograms as a wide and continuous frequency band In this paper we present an event of bounced radiation whose spectral characteristics are similar to those of escaping radiation The Cluster mission which has been launched during the 2000 summer is a constellation of four identical satellites The tetrahedral disposition of the satellites allows a spatial-temporal study of the structures they cross The two main purposes of the WHISPER experiment are to record the natural waves in the bandwidth 2-80 kHz and to make a diagnostic of the electron density using the sounding technique The various working modes and the Fourier transforms calculated on board provide a good time and frequency resolution and allow us to i detect the fine structure of NTC emissions ii derive directivity properties based on spin modulation of the received electric field On July 16 2005 the four Cluster satellites