ALBERT

Notes: Transient changes in polarizability during collisions between atoms and molecules give rise to interaction-induced rototranslational Raman scattering: the scalar component of the collision-induced polarizability Δα00 accounts for isotropic scattering, while the second-rank component ΔαM2 accounts for collision-induced depolarized scattering. We have evaluated the changes in electronic polarizability due to interactions between an atom and a molecule of D∞h symmetry in fixed configurations, with nonoverlapping charge distributions. We have cast the resulting expressions into the symmetry-adapted form used in spectroscopic line shape analyses. Our results are complete to order R−6 in the atom–molecule separation R. To this order, the collision-induced change in polarizability of an atom and a D∞h molecule reflects not only dipole-induced–dipole (DID) interactions, but also molecular polarization due to the nonuniformity of the local field, polarization of the atom in the field due to higher multipoles induced in the molecule, hyperpolarization of the atom by the applied field and the quadrupolar field of the molecule, and dispersion. We have analyzed the dispersion contributions to the atom–molecule polarizability within our reaction-field model, which yields accurate integral expressions for the polarizability coefficients. For numerical work, we have also developed approximations in terms of static polarizabilities, γ hyperpolarizabilities, and dispersion energy coefficients. Estimated polarizability coefficients are tabulated for H, He, Ne, and Ar atoms interacting with H2 or N2 molecules. The mean change in polarizability Δα¯, averaged over the orientations of the molecular axis and the vector between atomic and molecular centers, is determined by second-order DID interactions and dispersion. For the lighter pairs, dispersion terms are larger than second-order DID terms in Δα¯. In both Δα00 and ΔαM2, first-order DID interactions dominate at long range; other interaction effects are smaller, but detectable. At long range, the largest deviations from the first-order DID results for Δα00 areproduced by dispersion terms for lighter species considered here and by second-order DID terms for the heavier species; in ΔαM2, the largest deviations from first-order DID results stem from the effects of field nonuniformity and higher multipole induction, for atoms interacting with N2.

Notes: A new algorithm that determines the evolution of a surface eroding under reactive-ion etching is presented. The surface motion is governed by both the Hamilton–Jacobi equation and the entropy condition for a given etch rate. The trajectories of "shocks'' and "rarefaction waves'' are then directly tracked, and thus this method may be regarded as a generalization of the method of characteristics. This allows slope discontinuities to be accurately calculated without artificial diffusion. The algorithm is compared with "geometric'' surface evolution methods, such as the line-segment method.

Notes: Abstract Observations are presented for internal gravity waves and their breaking at a height of 23.5 m over the ocean in surface-based inversions which are formed because of the advection of warm air over cold water. The spectral and cospectral analyses of velocity and temperature fluctuations were made to establish the characteristic features of the waves. Flow visualization photographs of smoke released during the breaking of a wave are also presented. Comparison between the turbulent energies present during and after breaking of a wave indicates enormous mixing and dispersion occurring during breaking.

Notes: Abstract A parabolic shaped Thermal Internal Boundary Layer (TIBL) develops at the coast because of the temperature discontinuity between land and water. The TIBL is shown to play a significant role in determining where a coastal elevated plume fumigates to the ground. Six TIBL models available in the literature were identified and statistically compared. Two data bases obtained from the TIBL experiments, one at eastern Long Island, the other at the Kashimaura area of Japan, were used for statistical comparisons. Statistical methods of t, F and R were used to determine bias, scatter and correlation. The data were also classified according to wind speed (low and high) and stability (unstable, neutral, isothermal and stable onshore flow) to determine whether some models worked better under certain conditions. These limited data indicated that a formulation which included heat flux and wind speed together with overwater lapse rate, all raised to the half power, performed the best. Classifications according to wind speed and thermal stability also showed that the heat flux type of equation worked reasonably well.

Notes: Abstract Analysis of the mean wind, equivalent potential temperature and virtual potential temperature profiles observed by the National Center for Atmospheric Research (NCAR) Electra aircraft and obtained from dropwindsondes and ship-launched radiosondes were made in conjunction with synoptic observations to study the structure of the monsoon boundary layer over the Arabian Sea during MONEX 79. Comparison of mean profiles indicates the monsoon boundary layer to be much different from the trade wind boundary layer. Results confirm the existence of a boundary-layer jet known as East African or Somali Jet. Regions of multiple cloud layers at roughly the height of the capping inversion layer were associated with the jet. Regions in which a more well-mixed layer was observed showed a jet structure depressed in height. A free-jet surface-layer model appears to describe the mean wind structure of this jet observed during the present study and by others. An approximate balance of forces was found in the monsoon boundary layer between friction, advective acceleration, Coriolis and pressure gradient forces. Friction and advective acceleration terms were significant in the lower levels of the boundary layer. Forces in a typical trade wind boundary layer were found to be approximately one order of magnitude smaller than those observed in the monsoon boundary layer.

Notes: Abstract Lagrangian integral time scales were calculated from crosswind concentration distributions of oil-fog smoke released from a continuous point source over the ocean during stable atmospheric conditions assuming an exponential correlation function. Variance of the lateral velocity fluctuations, Σ v 2, and the energy dissipation rate, ɛ, were obtained from simultaneous Eulerian measurements at the beach. An Eulerian energy dissipation scale defined as Σ v 2/ɛ was then computed. The ratio of the Lagrangian integral scale to the Eulerian energy dissipation scale was found to be close to 1. This ratio was also estimated to be 1 based on physical and dimensional considerations regarding the cascade of energy. Length scales for longitudinal, lateral and vertical directions were interpreted with a model based on similarity considerations applicable for over-water atmospheric flows.

Notes: Abstract The calibration of a sailplane variometer to measure vertical velocity fluctuations in the atmospheric boundary layer is described. Its usefulness is demonstrated with typical results from a boundary-layer development study. The atmospheric calibrations gave the ratio of standard deviations of vertical velocity fluctuations measured by a standard tower-mounted turbulence instrument to the values measured by variometer as 2.5 m s−1 V−1.

Notes: Abstract Formation and breaking of internal gravity waves contributing to a very significant increase in turbulence in the atmospheric surface layer over the Atlantic Ocean off Long Island, New York are reported. Contrary to the bursts that are characteristically of short duration, this increase in turbulence lasted for more than one hour and was typical of what one would observe during unstable atmospheric conditions. However, mean temperature profiles indicated strong stable conditions.

Notes: Abstract The applicability of the log-linear profile relationship over rough terrain to a height of 126 m is investigated. Simultaneous hourly averaged mean wind and temperature profiles measured at the Brookhaven meteorological tower during stable conditions are used in the analysis. The tower was surrounded by fairly homogeneous vegetation to a height of about 8 m. The results indicate that the log-linear profile relationship is valid at least for a height of 126 m for stabilities with Richardson numbers less than the critical value of 0.25. The mean value of α in $${{\partial u} \mathord{\left/ {\vphantom {{\partial u} {\partial z}}} \right. \kern-\nulldelimiterspace} {\partial z}} = \left( {{{u_ * } \mathord{\left/ {\vphantom {{u_ * } k}} \right. \kern-\nulldelimiterspace} k}} \right)\left( {1 + \alpha \left( {{z \mathord{\left/ {\vphantom {z L}} \right. \kern-\nulldelimiterspace} L}} \right)} \right)$$ is found to be about 5.2 for these stabilities. The log-linear profile relation is found to be applicable for profiles observed beyond the critical stability; but the height of validity seems to decrease to about 100 m and the mean value of α is about 1.6.