Simulating acoustic scattering from atmospheric temperature fluctuations using ak-space method

Abstract A self-contained acoustical scintillation instrument is described that has been used to measure flow and turbulence characteristics in two diverse oceanographic settings. This instrument is a battery-operated and internally logging acoustic propagation system that is ideally suited to monitor long-term flow and small-scale effective refractive index fluctuations. When the temperature variability dominates the acoustic scattering, as is the case of a hydrothermal vent plume, then a measure of the vertical buoyancy-driven flow, together with the root-mean-square temperature fluctuations, can be obtained. Results for vent structure Hulk of the Main Endeavour vent field of the Juan de Fuca Ridge show that the long-term (71 days) temperature fluctuations, together with the vertical flow, can be used to estimate heat flux density. Measurements also show oscillations in the log-amplitude variance that result from plume advection by the ambient tidal currents and demonstrate the need for a long time series measurement. When the turbulent velocity dominates the acoustic scattering, as is the case in some energetic bottom boundary layer flows, then the turbulent kinetic energy dissipation rate is derived, assuming isotropic and homogeneous models. The methodology and results are summarized from an application to the Bosporus Canyon of the Black Sea, to monitor the flow and turbulence associated with Mediterranean seawater inflow.

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Profiles of second- to fourth-order moments of turbulent temperature fluctuations in the convective boundary layer: first measurements with rotational Raman lidar

Atmospheric Chemistry and Physics ◽

10.5194/acp-15-5485-2015 ◽

2015 ◽

Vol 15 (10) ◽

pp. 5485-5500 ◽

Cited By ~ 42

Author(s):

A. Behrendt ◽

V. Wulfmeyer ◽

E. Hammann ◽

S. K. Muppa ◽

S. Pal

Keyword(s):

Boundary Layer ◽

Fourth Order ◽

Shot Noise ◽

Temperature Fluctuations ◽

Atmospheric Temperature ◽

Order Moment ◽

Statistical Uncertainty ◽

Temperature Profiles ◽

Raman Lidar ◽

Noise Error

Abstract. The rotational Raman lidar (RRL) of the University of Hohenheim (UHOH) measures atmospheric temperature profiles with high resolution (10 s, 109 m). The data contain low-noise errors even in daytime due to the use of strong UV laser light (355 nm, 10 W, 50 Hz) and a very efficient interference-filter-based polychromator. In this paper, the first profiling of the second- to fourth-order moments of turbulent temperature fluctuations is presented. Furthermore, skewness profiles and kurtosis profiles in the convective planetary boundary layer (CBL) including the interfacial layer (IL) are discussed. The results demonstrate that the UHOH RRL resolves the vertical structure of these moments. The data set which is used for this case study was collected in western Germany (50°53'50.56'' N, 6°27'50.39'' E; 110 m a.s.l.) on 24 April 2013 during the Intensive Observations Period (IOP) 6 of the HD(CP)2 (High-Definition Clouds and Precipitation for advancing Climate Prediction) Observational Prototype Experiment (HOPE). We used the data between 11:00 and 12:00 UTC corresponding to 1 h around local noon (the highest position of the Sun was at 11:33 UTC). First, we investigated profiles of the total noise error of the temperature measurements and compared them with estimates of the temperature measurement uncertainty due to shot noise derived with Poisson statistics. The comparison confirms that the major contribution to the total statistical uncertainty of the temperature measurements originates from shot noise. The total statistical uncertainty of a 20 min temperature measurement is lower than 0.1 K up to 1050 m a.g.l. (above ground level) at noontime; even for single 10 s temperature profiles, it is smaller than 1 K up to 1020 m a.g.l. Autocovariance and spectral analyses of the atmospheric temperature fluctuations confirm that a temporal resolution of 10 s was sufficient to resolve the turbulence down to the inertial subrange. This is also indicated by the integral scale of the temperature fluctuations which had a mean value of about 80 s in the CBL with a tendency to decrease to smaller values towards the CBL top. Analyses of profiles of the second-, third-, and fourth-order moments show that all moments had peak values in the IL around the mean top of the CBL which was located at 1230 m a.g.l. The maximum of the variance profile in the IL was 0.39 K2 with 0.07 and 0.11 K2 for the sampling error and noise error, respectively. The third-order moment (TOM) was not significantly different from zero in the CBL but showed a negative peak in the IL with a minimum of −0.93 K3 and values of 0.05 and 0.16 K3 for the sampling and noise errors, respectively. The fourth-order moment (FOM) and kurtosis values throughout the CBL were not significantly different to those of a Gaussian distribution. Both showed also maxima in the IL but these were not statistically significant taking the measurement uncertainties into account. We conclude that these measurements permit the validation of large eddy simulation results and the direct investigation of turbulence parameterizations with respect to temperature.

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The decay of radar echoes from meteors with particular reference to their use in the determination of temperature fluctuations near the mesopause

Annales Geophysicae ◽

10.1007/s00585-995-1104-x ◽

1995 ◽

Vol 13 (10) ◽

pp. 1104-1106 ◽

Cited By ~ 18

Author(s):

W. Jones

Keyword(s):

Diffusion Coefficient ◽

Kinetic Theory ◽

Decay Time ◽

Temperature Fluctuations ◽

Atmospheric Temperature ◽

Initial Distribution ◽

Correct Result ◽

Radar Echoes ◽

Decay Times ◽

Radar Echo

Abstract. The rate of decay of a radar echo from an ionised meteor train will be governed by the diffusion coefficient of the plasma and this in turn will depend on the temperature. Very recently the temperature fluctuations near the mesopause have been monitored by this means, by the recording of the decay times of underdense trains. The usual derivation of the precise expression relating the underdense echo decay time to the temperature contains two important assumptions, (i) that the train is created with a Gaussian ionisation profile, and (ii) that kinetic theory may be applied to calculate the diffusion coefficient. We investigate the effect of these assumptions, showing that the first assumption is unnecessary, an underdense backscatter echo decaying exponentially with a decay time equal to λ2/(32π2D), where λ is the wavelength and D the diffusion coefficient, independently of the initial distribution. However, the second assumption is shown to be incorrect, and whereas according to kinetic theory D∝T1/2/ρ, where T and ρ are the atmospheric temperature and density, the correct result is D∝Tρ. This leads to an appreciable correction to the results for the temperature fluctuations.

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