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Brunt-Vaisala Frequency

The Experts below are selected from a list of 216 Experts worldwide ranked by ideXlab platform

Toshitaka Tsuda – 1st expert on this subject based on the ideXlab platform

  • vertical structure of the lower troposphere derived from mu radar unmanned aerial vehicle and balloon measurements during shurex 2015
    Progress in Earth and Planetary Science, 2018
    Co-Authors: Hubert Luce, Lakshmi Kantha, Hiroyuki Hashiguchi, Dale Lawrence, Tyler Mixa, Masanori Yabuki, Toshitaka Tsuda

    Abstract:

    The ShUREX (Shigaraki UAV Radar Experiment) 2015 campaign carried out at the Shigaraki Middle and Upper atmosphere (MU) observatory (Japan) in June 2015 provided a unique opportunity to compare vertical profiles of atmospheric parameters estimated from unmanned aerial vehicle (UAV), balloon, and radar data in the lower troposphere. The present work is intended primarily as a demonstration of the potential offered by combination of these three instruments for studying the small-scale structure and dynamics in the lower troposphere. Here, we focus on data collected almost simultaneously by two instrumented UAVs and two meteorological balloons, near the MU radar operated continuously during the campaign. The UAVs flew along helical ascending and descending paths at a nearly constant horizontal distance from the radar (~ 1.0 km), while the balloons launched from the MU radar site drifted up to ~ 3–5 km in the altitude range of comparisons (~ 0.5 to 4.0 km) due to wind advection. Vertical profiles of squared Brunt-Vaisala Frequency N2 and squared vertical gradient of generalized potential refractive index M2 were estimated at a vertical resolution of 20 m from pressure, temperature, and humidity data collected by UAVs and radiosondes. Profiles of M2 were also estimated from MU radar echo power at vertical incidence at a vertical sampling of 20 m and various time resolutions (1–4 min). The balloons and the MU radar provided vertical profiles of wind and wind shear S so that two independent estimates of the gradient Richardson number (Ri = N2/S2) could be obtained at a range resolution of 150 m. The two estimates of Ri profiles also showed remarkable agreement at all altitudes. We show that all three instruments detected the same prominent temperature and humidity gradients, down to decameter scales in stratified conditions. These gradients extended horizontally over a few kilometers at least and persisted for hours without significant changes, indicating that the turbulent diffusion was weak. Large discrepancies between N2and M2 profiles derived from the balloon, UAV, and radar data were found in a turbulent layer generated by a Kelvin-Helmholtz (KH) shear flow instability in the height range from 1.80 to 2.15 km. The cause of these discrepancies appears to depend on the stage of the KH billows.

  • Characteristics of energy dissipation rate and effect of humidity on turbulence echo power revealed by MU radar-RASS Measurements
    Journal of Atmospheric and Solar-Terrestrial Physics, 2001
    Co-Authors: Jun-ichi Furumoto, Toshitaka Tsuda

    Abstract:

    Abstract We carried out an MU radar-RASS campaign during August 2–6, 1995, and collected both radar echoes and virtual temperatures with good time resolution. We first investigated the accuracy of the Brunt–Vaisala Frequency squared from the RASS temperature profiles, comparing them with radiosonde results launched from the radar site. We then evaluated the turbulence energy dissipation rate (e) by two radar methods: the Doppler spectral width and the radar echo power. Meteorological conditions were very calm throughout the campaign, which is ideal for deriving e by the spectral width method. Under calm conditions, the variation of e from spectral width is mainly influenced by the Doppler spectral width and is less dependent on the Brunt–Vaisala Frequency. On the other hand, e from echo power is mainly determined by the echo power intensity. Though e values from both methods are roughly on the same order, their characteristics differ significantly. e with spectral width did not show large variations with time and height, while e with echo power showed significant fluctuations. We suspect that e from echo power is inaccurate because the refractive-index gradient in the calculation of e is mainly controlled by the humidity gradient in moist regions.

  • Spectral analysis of temperature and Brunt-Vaisala Frequency fluctuations observed by radiosondes
    Journal of Geophysical Research, 1991
    Co-Authors: Toshitaka Tsuda, T. E. Vanzandt, Masahiro Mizumoto, Susumu Kato, Shoichiro Fukao

    Abstract:

    We observed profiles of the temperature, T, and Brunt-Vaisala Frequency squared, N2, from 0 to 30 km in altitude using radiosondes with 150 m height resolution launched from the MU observatory, Japan (34°51′N, 136°06′), from September 27, 1986, to February 24, 1989. We analyzed vertical wavenumber spectra of the normalized temperature T/T and N2 fluctuations in the 2.0–8.5 km (troposphere) and 18.5–25.0 km (lower stratosphere) altitude ranges and compared them with model spectra based on saturated gravity wave theory. In the winter stratosphere the slope of the mean T/T spectra in the wavenumber range from 7.0×10−4 to 2.0×10−3 (cycles per meter) was very close to the −3 predicted by the model, and the spectral amplitudes were 1.3–1.9 times larger than the predicted values, which is within the possible range of variability of the model. On the other hand, in the summer stratosphere the spectral slope ranged from −2.2 to −2.4, which is more gradual than the model, and the spectral amplitudes were only 0.4 to 0.5 of the predictions. The spectral shape in the troposphere did not show a significant difference between summer and winter. The spectral amplitudes, however, exceeded the model values by factors of about 3.2 and 1.9 in winter and summer, respectively. The overall shape of the profile for fluctuations with vertical scales from 150 to 900 m was generally similar to the shape of the background value of N4, consistent with the saturated gravity wave model, but the details of the altitude variations were rather complicated. That is, just below the tropopause usually exceeded the model by a factor of 2 to 4, and it became significantly smaller than the model in the summer stratosphere and in a region above 25 km in winter.

Veniamin Perov – 2nd expert on this subject based on the ideXlab platform

  • application of a new spectral theory of stably stratified turbulence to the atmospheric boundary layer over sea ice
    Boundary-Layer Meteorology, 2005
    Co-Authors: Semion Sukoriansky, Boris Galperin, Veniamin Perov

    Abstract:

    A new spectral closure model of stably stratified turbulence is used to develop a K–e model suitable for applications to the atmospheric boundary layer. This K–e model utilizes vertical viscosity and diffusivity obtained from the spectral theory. In the e equation, the Coriolis parameter-dependent formulation of the coefficient C 1 suggested by Detering and Etling is generalized to include the dependence on the Brunt-Vaisala Frequency, N. The new K–e model is tested in simulations of the ABL over sea ice and compared with observations from BASE as simulated in large-eddy simulations by Kosovic and Curry, and observations from SHEBA.

P.c. Westlake – 3rd expert on this subject based on the ideXlab platform

  • Trapped internal waves produced by a submerged slender body moving in a stratified fluid
    , 1996
    Co-Authors: W.g. Price, P.c. Westlake

    Abstract:

    Analytical solutions are obtained for the disturbance generated by a singularity moving horizontally in a layer of a three layer fluid, each layer possessing a constant Brunt-Vaisala Frequency. A radiation condition is enforced using an artificial damping mechanism. The singularity solution is developed into a continuous source/sink line distribution which is used to model a prolate spheroid. The disturbance velocity field generated by the body displays the characteristics associated with the propagation of trapped internal waves. The disturbance calculated on the fluid’s surface is compared with those obtained using a constant density three layer fluid model and a constant Brunt-Vaisala Frequency model. The patterns produced by the current model described herein display significant departures from previous patterns.

  • Internal waves produced by a submerged slender body moving in a stratified fluid
    , 1994
    Co-Authors: W.g. Price, P.c. Westlake

    Abstract:

    Solutions are obtained for the velocity components generated by a singularity moving horizontally in a fluid of constant Brunt-Vaisala Frequency. A radiation condition is enforced using an artificial damping mechanism. Two solutions are combined to produce a Rankine ovoid and a continuous line distribution is used to model a prolate spheroid. The distribution velocity field generated by the body displays the characteristics associated with the propagation of internal waves. The disturbance velocities calculated on the fluid’s surface are compared with those obtained from a three layer model. The patterns produced display significant differences.