High-altitude resolution stratospheric measurements with the arecibo 430-MHz radar

Abstract

The potential of the Arecibo 430-MHz radar for the study of stratospheric dynamics and turbulence has been recently established. In the past the instrumented resolution of the system has been larger than 300-600 m. The present paper describes instrumental modifications which have enabled us to obtain a resolution of 150 m, the maximum allowed by the transmitter bandwidth. Such a gain in resolution is very important for stratospheric studies, since it is expected that turbulence occurs at these altitudes in layers with thickness between a few tens to a few hundred meters. Furthermore, a complementary coded pulse scheme has been used for the first time. Such a code has the advantage of generating no pulse side lobes, an important property for defining the quiet regions existing in between turbulent layers. Decoding is performed digitally. The high data processing rate is taken care of by the use of a preprocessor. Power spectra of the signals corresponding to 256 altitudes are evaluated on line by means of an array processor peripheral connected to the processing computer. Useful echoes have been obtained from 10 km to about 30 kin. The existence of layers of turbulence has been demonstrated, and their separation has been determined, but the thickness of some of them has still not been fully resolved. The separation of the layers varies as a function of altitude, changing from a few hundred meters at lower stratospheric heights to a few kilometers at 25- to 30-kin altitudes. The results obtained show the importance of high resolution when using radars to obtain wind information from the Doppler shift of turbulence echoes.