A new study of magnetospheric hiss as a spatially and temporally enduring phenomenon is undertaken using a recently developed formalism that allows the representation of hiss by a field distribution function (FDF). This formalism explicitly takes into account the whistler mode relationships and the linear and spin motion of the satellite, so that on a spin-stabilized satellite, it becomes possible to measure the wave propagation direction(s) from the observed fading patterns in the received electromagnetic field data. We have analyzed hiss signals received by electric and magnetic field antennae aboard the DE 1 satellite during a ~ 3-hour period on September 23, 1983. A band of hiss frequencies <2 kHz was observed continuously from 0236 UT to 0539 UT over a range of geomagnetic latitudes from &lgr;m=45¿N to &lgr;m=20¿S and L shells of L=4.3 to L=5.3. Electron density deduced from in situ and remote measurements indicates that during this time the DE 1 satellite was near the boundary of the plasmasphere.

Observations can be summarized as follows: (1) The general character of the electric and magnetic field spectra remained the same throughout the 3-hour-long-period, exhibiting an intensity peak at 1550 Hz. (2) The intensities of both the electric and the magnetic field decreased during this interval by ~30 dB. (3) Well-defined fading patterns at half the spin period (3.04 s) were observed throughout this period. These patterns were stable over a time scale of ~1 min. (4) In addition, a slow fading pattern with a time scale of 30 s was observed approximately 30% of the time. (5) The hiss intensity also showed fading over a time scale of ~10--15 min. The spin fading patterns led to the measurement of wave propagation directions(s). The results of our analysis can be summarized as follows: (1) Near the geomagnetic equator (within ~¿3¿ latitude) we observe a wave normal angle of 60¿¿5¿ with respect to the local geomagnetic field. (2) Away from the equator, wave normal directions range from 30¿ to 80¿ with respect to the local geomagnetic field. (3) All wave normal directions observed over the 3-hour-long period were within ~¿45¿ of the plane normal to the local magnetic meridional plane. Results indicate that the hiss source radiates with initial wave normal angles in the range 30¿<&thgr;0<&thgr;g (Gendrin angle) and 90¿<ϕ0<270¿, contrary to the common assumption that the source emits with wave normal angles closely aligned with the geomagnetic field. The FDF formulation has also permitted elucidation of the statistical nature of hiss. The slow time fading (~30 s) is interpreted in terms of a coherence bandwidth Δ&ohgr; of about 0.2 rad/s. ¿ American Geophysical Union 1988