Abstract
Abstract. Superpressure balloons (SPB), which float on constant density (isopycnic) surfaces, provide a unique way of measuring the properties of atmospheric gravity waves (GW) as a function of wave intrinsic frequency. Here we devise a quasi-analytic method of investigating the SPB response to GW motions. It is shown that the results agree well with more rigorous numerical simulations of balloon motions and provide a better understanding of the response of SPB to GW, especially at high frequencies. The methodology is applied to ascertain the accuracy of GW studies using 12 m diameter SPB deployed in the 2010 Concordiasi campaign in the Antarctic. In comparison with the situation in earlier campaigns, the vertical displacements of the SPB were measured directly using GPS. It is shown using a large number of Monte Carlo-type simulations with realistic instrumental noise that important wave parameters, such as momentum flux, phase speed and wavelengths, can be retrieved with good accuracy from SPB observations for intrinsic wave periods greater than ca. 10 min. The noise floor for momentum flux is estimated to be ca. 10−4 mPa.
Highlights
Superpressure balloons (SPB) have been used in both the troposphere and lower stratosphere since the early 1960s (TWERLE Team, 1977)
There are no limits on the range of gravity (buoyancy) waves (GW) frequencies or wavelengths that can be determined using SPBs of the type described here
The uncertainties that are inherent in the instruments carried on the SPB will set a noise floor, below which fluxes cannot be reliably determined
Summary
Superpressure balloons (SPB) have been used in both the troposphere and lower stratosphere since the early 1960s (TWERLE Team, 1977). Nastrom (1980) extended this work by considering the simultaneous wave-induced variations of density and vertical wind He developed an analytical relationship between the amplitude and phase of a SPB in the presence of a sinusoidal gravity wave. When an SPB responds to a gravity-wave-induced displacement of the EDS the equation of motion is such that there is a phase shift between the balloon and the EDS displacement This phase shift is a factor in the retrieval of important GW parameters, including the intrinsic phase speed (i.e., the speed relative to the background wind). In the second part of the paper, we test how well the improved instrumentation on the 12 m SPB is able to detect GW motions and retrieve wave parameters For this aspect we carried out a large number of statistical realizations that covered the full spectrum of GW frequencies. This second part extends the work of Boccara et al (2008) who dealt with Vorcore observations, and in particular only considered the case of hydrostatic waves
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