Multiple neutral density measurements in the lower thermosphere with cold-cathode ionization gauges

Cold-cathode ionization gauges were used for rocket-borne measurements of total neutral density and temperature in the aurorally forced lower thermosphere between 90 and 200\ km. A commercial gauge was adapted as a low-cost instrument with a spherical antechamber for measurements in molecular flow conditions. Three roll-stabilized payloads on different trajectories each carried two instruments for measurements near the ram flow direction along the respective upleg and downleg segments of a flight path, and six density profiles were obtained within a period of 22\ min covering spatial separations up to 200\ km. The density profiles were integrated below 125\ km to yield temperatures. The mean temperature structure was similar for all six profiles with two mesopause minima near 110 and 101\ km, however, for the downleg profiles, the upper minimum was warmer and the lower minimum was colder by 20\textendash30\ K indicating significant variability over horizontal scales of 100\textendash200\ km. The upper temperature minimum coincided with maximum horizontal winds speeds, exceeding 170\ m/s.