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

Abstract

Abstract. Vertical ascent rate VB of meteorological balloons is sometimes used for retrieving vertical air velocity W, 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 ε, we show that VB can be strongly affected by turbulence, even above the convective boundary layer. For “weak” turbulence (here ε≲10−4 m2 s−3), the fluctuations of VB were found to be fully consistent with W fluctuations measured by middle and upper atmosphere (MU) radar, indicating that an estimate of W can indeed be retrieved from VB if the free balloon lift is determined. In contrast, stronger turbulence intensity systematically implies an increase in VB, not associated with an increase in W 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 VB disturbances, mainly observed in the troposphere, were found to be clearly associated with Ri≲0.25, usually indicative of turbulence, confirming the case studies. The analysis also revealed the superimposition of additional positive and negative disturbances for Ri≲0.25 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 W, and misinterpretations of VB fluctuations can be made if localized turbulence effects are ignored.

Atmospheric Conditions within Big Telescope Alt-Azimuthal Region and Possibilities of Astronomical Observations

“…In this case, typical dynamic Richardson number for these heights should be less than 1 [28]. The estimated 1/Ri changes with height are consistent with data of studies [29], which demonstrate high Ri variability in the lower layers of the atmosphere.…”

Seasonal variations of gravity‐wave parameters over the northern and southern Tibetan plateau radiosonde observatory

“…As expected, the Pearson correlation between the westerly jet (or the precipitation) and the tropospheric VE is very weak over both the northern and southern Tibetan Plateau with a Pearson correlation coefficient smaller than 0.2. Another possible cause of the non‐seasonal feature in the VE is that the complicated environment (shear and convection) over the Tibetan Plateau strongly affects the turbulence drag coefficient of the balloon, which further affects the accuracy of the vertical velocity perturbation extracted from the ascent rate of the balloon (Luce & Hashiguchi, 2020). The tropospheric VE over the Tibetan Plateau (Figure 14c,f) has the smallest amplitude in all three energies.…”

“…The vertical momentum flux is computed with varying height in this section. Since the accuracy of the perturbation vertical velocity extracted from the ascent rate of the balloon is strongly affected by the turbulence drag coefficient of the balloon (Luce & Hashiguchi, 2020), indirect calculation of the momentum flux from the horizontal velocity perturbation and the temperature perturbation is employed.…”

Observing severe precipitation near complex topography during the Yilan Experiment of Severe Rainfall in 2020 (YESR2020)

“…In addition, the GRAW radiosonde was also utilized during YESR2020, providing atmospheric status upstream of the Lanyang River. The concurrent radiosonde release as a network at six sites (Figure 2c) provides the vertical environmental conditions and detailed information of low-level microscale turbulence (Luce and Hashiguchi, 2020) in Yilan.…”