| We present here the first Jicamarca observations of
incoherent scatter radar (ISR) spectra detected from
E- and D-region altitudes.
In the past such observations have not been possible
at Jicamarca due a combined effect of strong equatorial electrojet
(EEJ) clutter and hardware limitations in the receiving system.
The observations presented here were made during weak EEJ
conditions (i.e., almost zero zonal electric field) using an
improved digital receiving system with a wide dynamic range
and a high data throughput.
The observed ISR spectra from E- and D-region altitudes
are, as expected, narrow and get even narrower
with decreasing altitude due to increasing ion-neutral collision frequencies.
Therefore, it was possible to obtain accurate spectral measurements using
a pulse-to-pulse data analysis.
At lower altitudes in the D-region where signal
correlation times are relatively long we used
coherent integration to improve the signal-to-noise ratio of
the collected data samples.
The spectral estimates were fitted using a standard incoherent scatter
(IS) spectral model between 87 and 120 km, and a Lorentzian
function below 110 km. Our preliminary estimates of temperature
and ion-neutral collisions frequencies above 87 km are in
good agreement with the MSISE-90 model.
Below 87 km, the measured spectral widths are larger
than expected, causing an overestimation of the temperatures,
most likely due to spectral distortions caused by atmospheric turbulence. |