CUPRI observations of persistence asymmetry reversals in up‐down vertical type‐I echoes from the equatorial electro jet above Alcântara, Brazil

Abstract

High resolution vertical radar measurements of the equatorial electrojet above Alcântara, Brazil, were made with the Cornell University Portable Radar Interferometer (CUPRI) as part of the Guará Dip Equator Campaign. Type‐I spectra obtained from the main body of the electrojet during strong daytime conditions show a preponderance of upward phase velocities as a function of time. However, the data from a few kilometers higher show a persistence of downward phase velocities. This reversal in sign of the most persistent type‐I peak occurs regularly in our data whenever the electrojet is strongly driven. The persistence of upward phase velocities is similar to that seen earlier at Jicamarca but the reversal in sign of the dominating mode has not been previously observed, nor is it consistent with current electrojet theories. Another unexpected result from the Alcântara data set is that the absolute values of the phase velocities of the type‐I spectra peaks decrease with altitude. This is through a region where the temperature (and hence the acoustic velocity) should be increasing with altitude. Hence, the saturation of the type‐I peak phase velocities is not just a simple function of the acoustic velocity.