On the estimation of vertical air velocity and detection of atmospheric turbulence from the ascent rate of balloon soundings

Luce, Hubert; Hashiguchi, Hiroyuki

Vertical ascent rate inline-formulaVB of meteorological balloons is sometimes used for retrieving vertical air velocity inline-formulaW, an important parameter for meteorological applications, but at the cost of crude hypotheses on atmospheric turbulence and without the possibility of formally validating the models from concurrent measurements. From simultaneous radar and unmanned aerial vehicle (UAV) measurements of turbulent kinetic energy dissipation rates inline-formulaε, we show that inline-formulaVB can be strongly affected by turbulence, even above the convective boundary layer. For “weak” turbulence (here inline-formulaε10−4 minline-formula2 sinline-formula−3), the fluctuations of inline-formulaVB were found to be fully consistent with inline-formulaW fluctuations measured by middle and upper atmosphere (MU) radar, indicating that an estimate of inline-formulaW can indeed be retrieved from inline-formulaVB if the free balloon lift is determined. In contrast, stronger turbulence intensity systematically implies an increase in inline-formulaVB, not associated with an increase in inline-formulaW according to radar data, very likely due to the decrease in the turbulence drag coefficient of the balloon. From the statistical analysis of data gathered from 376 balloons launched every 3 h at Bengkulu (Indonesia), positive inline-formulaVB disturbances, mainly observed in the troposphere, were found to be clearly associated with inline-formulaRi0.25, usually indicative of turbulence, confirming the case studies. The analysis also revealed the superimposition of additional positive and negative disturbances for inline-formulaRi0.25 likely due to Kelvin–Helmholtz waves and large-scale billows. From this experimental evidence, we conclude that the ascent rate of meteorological balloons, with the current performance of radiosondes in terms of altitude accuracy, can potentially be used for the detection of turbulence. The presence of turbulence complicates the estimation of inline-formulaW, and misinterpretations of inline-formulaVB fluctuations can be made if localized turbulence effects are ignored.

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Luce, Hubert / Hashiguchi, Hiroyuki: On the estimation of vertical air velocity and detection of atmospheric turbulence from the ascent rate of balloon soundings. 2020. Copernicus Publications.

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