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- Author or Editor: S. J. Krivo x

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## Abstract

An estimate of the vertical wind component up to an altitude of 15 km is derived from FPS-16 radar/Jimsphere ascent-rate measurements. The method involves removing ascent-rate profile variations which are not associated with vertical air motions.

Radar noise errors are evaluated by comparing simultaneous measurements by two radars of a single balloon ascent. Radar noise is shown to be a high-frequency phenomenon which can be substantially reduced by smoothing. Ascent-rate profiles are smoothed to reduce the rms noise error to less than 5 cm sec^{−1}. The vertical resolution of the smoothed profiles is ∼250 m.

The contributions of buoyancy and drag to the vertical component of balloon motion are estimated and removed from the smoothed ascent-rate profile. The residual profile contains perturbation amplitudes of up to 40 cm sec^{−1}. The hypothesis that this profile represents the vertical wind component is supported by evidence that several other potential causes of ascent-rate variations are insignificant. It is concluded that useful estimates of sub-synoptic variations in the vertical wind component in clear air below 15 km can be derived from FPS-16 radar/Jimsphere ascent-rate measurements.

## Abstract

An estimate of the vertical wind component up to an altitude of 15 km is derived from FPS-16 radar/Jimsphere ascent-rate measurements. The method involves removing ascent-rate profile variations which are not associated with vertical air motions.

Radar noise errors are evaluated by comparing simultaneous measurements by two radars of a single balloon ascent. Radar noise is shown to be a high-frequency phenomenon which can be substantially reduced by smoothing. Ascent-rate profiles are smoothed to reduce the rms noise error to less than 5 cm sec^{−1}. The vertical resolution of the smoothed profiles is ∼250 m.

The contributions of buoyancy and drag to the vertical component of balloon motion are estimated and removed from the smoothed ascent-rate profile. The residual profile contains perturbation amplitudes of up to 40 cm sec^{−1}. The hypothesis that this profile represents the vertical wind component is supported by evidence that several other potential causes of ascent-rate variations are insignificant. It is concluded that useful estimates of sub-synoptic variations in the vertical wind component in clear air below 15 km can be derived from FPS-16 radar/Jimsphere ascent-rate measurements.

## Abstract

A first-order theory of the fluctuating lift and drag coefficients associated with the aerodynamically induced motions of rising and falling spherical wind sensors is developed. The equations of motion of a sensor are perturbed about an equilibrium state in which the buoyancy force balances the mean vertical drag force. It is shown that, to within first order in perturbation quantities, the aerodynamic lift force is confined to the horizontal, and the fluctuating drag force associated with fluctuations in the drag coefficient acts along the vertical. The perturbation equations are transformed with Fourier-Stieltjes integrals and the resulting equations lead to relationships between the power spectra of the aerodynamically induced velocity components and the spectra of the fluctuating lift and drag coefficients.

Experimental evidence shows that the aerodynamically induced motions of the Jimsphere balloon occur predominantly in the horizontal plane. This implies that the root-mean-square (rms) horizontal lift coefficient is much larger than the rms vertical drag coefficient. The aerodynamically induced motion of the Jimsphere is found to be sinusoidal in nature. The dimenionless frequency (Strouhal number) and nondimensional variance of the induced zonal and meridional velocity components are given as functions of the Reynolds number. The experimental range of the Reynolds number is 1.4 × 10^{5} to 6.6 × 10^{5} The ratio between the rms lift coefficient and the mean, or zero-order, drag coefficient is found to be approximately 0.36.

The theory shows that the Fourier components of the first-order fluctuating horizontal lift coefficient vector lead those of the induced horizontal velocity vector, and that the fluctuating part of the drag coefficient lags the induced vertical velocity for rising balloons and leads the induced vertical velocity in the case of falling balloons. The phase angles of the induced lift and drag associated with the characteristic frequency of oscillation of the Jimsphere are given as functions of the Reynolds number.

The rms lift coefficient of smooth 2 m ROSE balloons operating at supercritical Reynolds numbers is found to be approximately twice the value obtained from wind tunnel data. This result suggests that caution should be exercised when wind tunnel data of constrained bodies are applied to free balloons.

## Abstract

A first-order theory of the fluctuating lift and drag coefficients associated with the aerodynamically induced motions of rising and falling spherical wind sensors is developed. The equations of motion of a sensor are perturbed about an equilibrium state in which the buoyancy force balances the mean vertical drag force. It is shown that, to within first order in perturbation quantities, the aerodynamic lift force is confined to the horizontal, and the fluctuating drag force associated with fluctuations in the drag coefficient acts along the vertical. The perturbation equations are transformed with Fourier-Stieltjes integrals and the resulting equations lead to relationships between the power spectra of the aerodynamically induced velocity components and the spectra of the fluctuating lift and drag coefficients.

Experimental evidence shows that the aerodynamically induced motions of the Jimsphere balloon occur predominantly in the horizontal plane. This implies that the root-mean-square (rms) horizontal lift coefficient is much larger than the rms vertical drag coefficient. The aerodynamically induced motion of the Jimsphere is found to be sinusoidal in nature. The dimenionless frequency (Strouhal number) and nondimensional variance of the induced zonal and meridional velocity components are given as functions of the Reynolds number. The experimental range of the Reynolds number is 1.4 × 10^{5} to 6.6 × 10^{5} The ratio between the rms lift coefficient and the mean, or zero-order, drag coefficient is found to be approximately 0.36.

The theory shows that the Fourier components of the first-order fluctuating horizontal lift coefficient vector lead those of the induced horizontal velocity vector, and that the fluctuating part of the drag coefficient lags the induced vertical velocity for rising balloons and leads the induced vertical velocity in the case of falling balloons. The phase angles of the induced lift and drag associated with the characteristic frequency of oscillation of the Jimsphere are given as functions of the Reynolds number.

The rms lift coefficient of smooth 2 m ROSE balloons operating at supercritical Reynolds numbers is found to be approximately twice the value obtained from wind tunnel data. This result suggests that caution should be exercised when wind tunnel data of constrained bodies are applied to free balloons.