Abstract
This paper presents measured data related to the question of how constant are “constant-level” balloons. The simultaneous use of two balloon-borne instruments, a radio altimeter and a pressure sensor, operating on entirely different principles, help to distinguish between sensor noise and true balloon altitude fluctuation. Four types of superpressure balloon altitude changes at the level of 150 mb were observed: (i) neutral buoyancy oscillations (NBO) with a period of about 200 sec and with peak-to-peak amplitude of up to 50 m, (ii) short-term oscillations with a period of ∼1.2 hr and peak-to-peak amplitudes of up to 80 m, (iii) diurnal half-cycle (day observations only) with an amplitude of up to 150 m, and (iv) possible trends of up to 120 m per day.
The data were obtained during four superpressure-balloon 150-mb flights in the Southern Hemisphere. These balloon flights were part of a test program for the TWERL Experiment. NCAR's GHOST balloons and navigation system were used, with the final version of the TWERLE radio altimeter and an early version of the pressure sensor.
The data are presented with a discussion of their limitations, mainly aliasing, ambiguity, and the absolute accuracy of the pressure sensor. A theoretical analysis of the NBO, with a spectrum analysis of supporting ground radar data, are given in the Appendix.
