Amplitude Of Heat Flux Research Articles

Impact of wave phase difference between soil surface heat flux and soil surface temperature on soil surface energy balance closure

The sensitivity of climate simulations to diurnal variation in the surface energy budget encourages enhanced inspection into the energy balance closure failure encountered in micrometeorological experiments. The diurnal wave phases of soil surface heat flux and temperature are theoretically characterized and compared for both moist soil and absolutely dry soil surfaces, indicating that the diurnal wave phase difference between soil surface heat flux and temperature ranges from 0 to π/4 for natural soils. Assuming that the net radiation and turbulent heat fluxes have phases identical to that of the soil surface temperature, we evaluate potential contributions of the wave phase difference to the surface energy balance closure. Results show that the sum of sensible heat flux and latent heat flux is always less than the available surface energy (i.e., the difference between net radiation and soil surface heat flux) even if all energy components are accurately measured, their footprints are strictly matched, and all corrections related to measurement environments and techniques are made. The energy balance closure ratio is extremely sensitive to the ratio of soil surface heat flux amplitude (A4) to net radiation flux amplitude (A1), and a high value of A4/A1 causes a significant failure in surface energy balance closure. An experimental case study confirms the theoretical analysis.

A simple method for the estimation of thermal inertia

A simple method for estimating thermal inertia using daily amplitude of surface soil heat flux and temperature is proposed. Based on an analytical solution of the diffusion equation where the soil temperature is idealized as a sinusoidal function, the thermal inertia is expressed as a proportional coefficient in a linear equation relating the amplitudes of surface soil (ground) heat flux and temperature. Tests of the proposed method demonstrate that this simple method is potentially useful in the Earth and extra‐terrestrial remote sensing.

The dynamic thermal characteristics of lightweight building elements with a forced ventilated cavity and radiation barriers

This paper presents an analysis of the dynamic thermal characteristics of lightweight building elements (LBEs) with a forced ventilated cavity and radiation barriers. A two-dimensional numerical model was used for the analysis, which was verified with an analytical method and outdoor experiments. The influence of the temperature boundary conditions at the cavity inlet and along the ambient surface of the cavity on the dynamic thermal characteristics of the LBEs was analyzed separately. The influence of the LBE width, the cavity width, the specific air flow rate and the cavity surface emissivities was also demonstrated. Multi-parametric equations were derived for predicting the heat flux amplitude and the decrement factor along the length of the LBE.

Global gyrokinetic particle simulation of turbulence and transport in realistic tokamak geometry

A general geometry model has been developed for the gyrokinetic toroidal code GTC with a number of highly desirable features including a systematic treatment of plasma rotation and equilibrium E × B flow, realistic plasma profiles and corresponding magnetohydrodanamic (MHD) equilibria. A symmetry coordinate system is used to construct a relatively regular mesh in real space for strongly shaped toroidal plasmas, which also facilitates straightforward visualization. By rescaling the radial coordinate, grid size is correlated with the local gyroradius which may vary substantially from the core to the edge. Gyrokinetic transformation of potential and charge density between particle and guiding center positions in general geometry is carefully treated, taking into account the finite ratio of the poloidal to the total field (Bθ/B). The applied equilibrium E × B flow, which is believed to play an important role in determining the turbulence level, is calculated from our global neoclassical particle code GTC-Neo. In the large aspect ratio circular geometry limit, cross benchmarks with the original GTC code show good agreement in real frequency, growth rate, steady-state heat flux and zonal flow amplitude for the ion temperature gradient driven microinstabilities (ITG modes).

Synoptic-Scale Air–Sea Flux Forcing in the Western North Pacific: Observations and Their Impact on SST and the Mixed Layer

Abstract Decade-long surface meteorological measurements from a Japan Meteorological Agency buoy at 29°N, 135°E are analyzed to elucidate the surface air–sea flux forcing in the western North Pacific Ocean. Besides the well-defined annual cycles, the observed heat and momentum fluxes are dominated by signals related to synoptic-scale weather disturbances. The synoptic-scale heat flux signals have a dominant time scale of 3–14 days, whereas the wind stress signals have a scale of 2–8 days. A comparison between the heat fluxes estimated using the buoy measurements and those from the NCEP reanalysis reveals that the daily NCEP product overestimates both the incoming solar radiation at sea surface and the turbulent heat flux amplitude associated with the individual weather events. The rms amplitude of the synoptic-scale net heat flux of the NCEP product is found to be positively biased by 23%. Despite this amplitude bias, the NCEP product captures the timing and relative strength of the synoptic-scale net hea...

Large Eddy Simulation of Thermally Induced Oscillations in the Convective Boundary Layer

Mesoscale circulations induced by differential boundary layer heating due to surface inhomogeneities on scales of 5 km and more can significantly change the average properties and the structure of the convective boundary layer (CBL) as well as trigger off temporal oscillations. The results of one of the first numerical case studies using large eddy simulation (LES) on the mesoscale suggest that mesoscale circulations exhibit a considerably larger average kinetic energy than convection under homogeneous conditions. This affects turbulent transport processes and should be accounted for in larger-scale models even if their turbulence parameterizations rely on homogeneous control runs of high-resolution models. This case study uses the Hannover parallelized large eddy simulation model (PALM) with prescribed 1D sinusoidal surface heat flux variations on wavelengths from 2.5 to 40 km. The resulting mesoscale circulations are analyzed by means of domain-averaged cross sections, time averaged and normalized with the boundary layer height, as well as power spectra and domain-averaged time series. The simulated mesoscale circulations were periodic. Vertical profiles and time series demonstrate that the onset of the mesoscale circulation triggers off a temporal boundary layer oscillation, whose period and amplitude depend on the surface heat flux perturbation wavelength and amplitude and on the background wind component perpendicular to the surface inhomogeneity orientation. Spectral analysis shows that the mesoscale circulations damp convection equally in all directions. A hypothesis of the oscillation mechanism is briefly discussed.

An Analysis Of Secondary Circulations And Their Effects Caused By Small-Scale Surface Inhomogeneities Using Large-Eddy Simulation

A parallelized large-eddy simulation model has been used to investigate the effects of two-dimensional, discontinuous, small-scale surface heterogeneities on the turbulence structure of the convective boundary layer.Heterogeneities had a typical size of about the boundary-layer heightzi. They were produced by a surface sensible heat flux pattern ofchessboard-type and of strong amplitude as typical, e.g., for the marginalice zone. The major objectives of this study were to determinethe effects of such strong amplitude heat flux variations and to specify theinfluence of different speeds and directions of the background wind.Special emphasis has been given to investigate the secondary circulations induced by the heterogeneities by means of three-dimensional phase averages. Compared with earlier studies of continuous inhomogeneities, the same sizeddiscontinuous inhomogeneities in this study show similar but stronger effects.Significant changes compared with uniform surface heating are only observedwhen the scale of the inhomogeneities is increased to zi. Especially the vertical energy transport is much more vigorous and even the mean emperature profile shows a positive lapse rate within the whole mixed layer. However, the effects are not directly caused by the different shape of the inhomogeneities but can mainly be attributed to the large amplitude of the imposed heat flux,as it is typical for the partially ice covered sea during cold air outbreaks. The structure of the secondary flow is found to be very sensitive to the wavelength and shape of the inhomogeneities as well as to the heatflux amplitude, wind speed and wind direction. The main controlling parameter is the near-surface temperature distribution and the related horizontal pressure gradient perpendicular to the main flow direction. The secondary flow varies from a direct circulation with updraughts mainly above the centre of the heated regions to a more indirect circulation with updraughts beneath the centre and downdraughts above it. For background winds larger than 2.5 m s−1 a roll-like circulation pattern is observed. From previous findings it has often been stated that moderate backgroundwinds of 5 m s−1 eliminate all impacts of surface inhomogeneitiesthat could potentially be produced in realistic landscapes. However, this studyshows that the effects caused by increasing the wind speed stronglydepend on the wind direction relative to the orientation of theinhomogeneities. Secondary circulations remain strong, even for abackground wind of 7.5 m s−1, when the wind direction is orientatedalong one of the two diagonals of the chessboard pattern. On the otherhand, the effects of inhomogeneities are considerably reduced, even undera modest background wind of 2.5 m s−1, if the wind direction isturned by 45°. Mechanisms for the different flow regimesare discussed.

On the Efficiency of Baroclinic Eddy Heat Transport across Narrow Fronts*

A simple theory is developed that relates the amplitude of eddy heat (or density) flux across a narrow front to the basic frontal parameters. By assuming that heat is transported primarily by baroclinic eddy pairs, an analytical expression for the cross-front eddy heat flux is derived as u9r9 5 ceVmDr, where u9 and r9 are deviations from the temporal or spatial mean cross-front velocity and density, Dr is the density change across the front, Vm is a scale for the alongfront velocity (which may be interpreted as the maximum alongfront velocity for a front with density change Dr over a horizontal scale of the deformation radius, assuming a deep level of no motion), and ce is an efficiency constant. Similar expressions for the eddy heat flux have been proposed previously, based on scaling or energetics arguments, but neither an a priori estimate for the value of the efficiency constant ce nor a clear dynamical understanding of what determines its value has been forthcoming. The theory presented here provides a dynamically based means of estimating the efficiency constant, which may be approximately interpreted as the ratio of the speed at which eddies propagate away from the front to the alongfront velocity, resulting in ce 0.045. Eddy-resolving numerical models are used to test this theoretical estimate for both unforced and forced frontal problems. For a wide range of parameters the cross-frontal heat transport is carried primarily by heton-like eddy pairs with values of ce between 0.02 and 0.04, in general agreement with the theory. These values of ce are also consistent with numerous previously published laboratory and numerical studies.

Emanation and dispersal of tritiated water from disposal shafts

The source level of contamination induced by the presence of tritiated water (HTO) in the Bandelier tuff near Los Alamos, New Mexico has been seen to decrease in all directions at the same rate. This decrease in radioactivity with distance from the source has been measured around three different disposal shafts and found to be slower than the decrease in emanation rate with distance from the source. Physical factors, suspected of influencing HTO emanation, were entered as independent variables in a regression equation including measurements taken over a 14-month period. The physical variables studied were of thermal, hydrological, and meteorological origin. Only four variables were retained as significant. Air concentrations of HTO show a maximum during the warmer months and an overall minimum during the colder months. Emanation of HTO, shown to be strongly associated with daily heat flux amplitude, also at a maximum in summer and at noon, more than counterbalances higher dissipation due to increased turbulence occurring during the same period. More than 76% of the variation in air concentration of HTO was associated with the regression on emanation, wind direction, wind velocity and turbulence.

Non-linear waves in helium II

The evidence of non-linear terms in Landau's two-fluid theory of helium II, provided by some non-linear wave experiments, is assessed. The non-linear relationship between heat flux and wave amplitude is found. The standard discontinuity relations derived from the energy equation and superfluid equation of motion are compared with recent experimental results on shock waves.

Fin performance in an oscillating temperature environment

An analytical solution is presented to describe the performance of a straight convecting fin operating in an oscillating temperature environment. The solution involves the amplitude parameter, A, and the frequency parameter, B, in addition to the steady-state convection-conduction parameter, N. The effects of these parameters on the amplitude and phase angle of spatial temperature and base heat flux are discussed. For most practical finned surfaces, i.e. N < 2, the time-average fin efficiency is found to be practically independent of B in the range 0·01–10 but increases as A increases. This is in contrast with the previously reported study of periodic variation of base temperature wherein, for N < 1, the time-average fin efficiency was found to reduce significantly with the increase of parameters A and B in the same range.