DE-2 and AE-C satellite measurements of plasma and neutral densities have been used to derive time constants for momentum transfer to the neutrals from ions in the high-latitude thermosphere. The momentum transfer time constants for solar cycle maximum (DE-2) and for solar cycle minimum (AE-C) have been averaged and binned according to geomagnetic latitude and local time to provide a quantitative measure for the tightness of ionneutral momentum coupling in the altitude range 250-350 km. During solar maximum conditions, the neutrals respond relatively rapidly to forcing from the ions. with e-folding time-constants of the order of 1-3 hours. For solar minimum conditions, however, the time constants are typically about an order of magnitude larger, implying that the neutrals are relatively insensitive to ion-drag forcing and that the winds are controlled principally by the large-scale, day-to-night pressure gradient. The measurements are compared with model calculations of the time constants using the Chiu (1975) and MSIS-83 semi-empirical models for electron (ion) density and neutral composition. respectively. Since thermospheric general circulation models (TGCMs) rely on these two semi-empirical models for their parameterizations of the ion drag momentum source. the comparisons enable an important TGCM input to be critically examined. The agreement between the derived time constants and the corresponding values obtained from the semi-empirical models is reasonable for solar maximum. At solar minimum, however, the model time constants are significantly smaller than the experimentallyderived values. The discrepancy is principally due to the overestimation of the polar ionospheric densities by the Chiu model. TGCM calculations which use a polar ionosphere based on the Chiu semi-empirical model therefore exaggerate the importance of the ion drag momentum source at solar minimum by a significant margin.
This paper presents a method for dry calibration of an electromagnetic flowmeter (EMF). This method, which determines the voltage induced in the EMF as conductive liquid flows through a magnetic field, numerically solves a coupled set of multiphysical equations with measured boundary conditions for the magnetic, electric, and flow fields in the measuring pipe of the flowmeter. Specifically, this paper details the formulation of dry calibration and an efficient algorithm (that adaptively minimizes the number of measurements and requires only the normal component of the magnetic flux density as boundary conditions on the pipe surface to reconstruct the magnetic field involved) for computing the sensitivity of EMF. Along with an in-depth discussion on factors that could significantly affect the final precision of a dry calibrated EMF, the effects of flow disturbance on measuring errors have been experimentally studied by installing a baffle at the inflow port of the EMF. Results of the dry calibration on an actual EMF were compared against flow-rig calibration; excellent agreements (within 0.3%) between dry calibration and flow-rig tests verify the multiphysical computation of the fields and the robustness of the method. As requiring no actual flow, the dry calibration is particularly useful for calibrating large-diameter EMFs where conventional flow-rig methods are often costly and difficult to implement.
The radial radiative heat flux and its divergence are determined both exactly and approximately for homogeneous suspensions of small particles. Scattering is assumed to be small compared to absorption and the absorption coefficient is taken to be inversely proportional to wavelength. The exact solution is reduced to an infinite series of single integrals. The optically thin and the next higher order behavior appear in closed form as the first two terms in the series. Two approximate solutions are also developed. One is in good agreement with the exact solution while the other is not. Finally, a closed form approximate relation is derived for the dimensionless heat flux at the surface. This expression, which also gives the emissivity or absorptivity of the medium, is in excellent agreement with the exact result.
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