ALBERT

Description: Visualization of local mass transfer coefficients over the dry surface of corrugated-sheet structured packing is essential for optimizing the existing geometry of structured packing and for improving mass transfer efficiency to develop new structured packing. The local flow patterns between packing sheets and the gas-phase mass transfer coefficient at each point over the surface are illustrated by employing a wall-surface reaction model. Different turbulence models are utilized, i.e., a standard κ-ϵ model and three different low-Re-κ-ϵ models. The numerical calculation results with the Lam-Bremhorst low-Re-κ-ϵ turbulence model is found to agree well with experimental data. There are three similar regions with enhanced mass transfer efficiency in each mass transfer unit cell of structured packing. Local mass transfer coefficients at each point over the dry surface in a symmetric mass transfer unit cell of corrugated-sheet structured packings were determined. Computational fluid dynamics simulation results with a Lam-Bremhorst low-Re-κ-ϵ turbulence model and a wall-surface reaction model corresponded well with previous experimental data.

Description: Abstract This study analyzes the summertime precipitation bias over the Central United States and its relationship to the simulated large‐scale environment and the convection scheme in the Energy Exascale Earth System Model Atmosphere Model version 1. This relationship is mainly examined in a set of short‐term hindcasts initialized with realistic large‐scale conditions for the summer of 2011. Besides the uniform 1° model resolution, we adopt Regionally Refined Meshes to increase the model resolution to 0.25° over the contiguous United States. Additional five‐year Atmospheric Model Intercomparison Project simulations are conducted to confirm that the results from the hindcasts are consistent with the climate runs. We find that the summertime dry precipitation bias over the Great Plains and the wet bias over the Rockies cannot be reduced simultaneously by changing resolution or tuning parameters. As for the diurnal cycle, Energy Exascale Earth System Model Atmosphere Model version 1 captures the general diurnal variation of the large‐scale moisture transport and the large‐scale upward motion over the Central United States. However, the diurnal cycle of precipitation over the Great Plains is out of phase with the diurnal variation of the large‐scale environment because the convective precipitation dominates the total precipitation and its diurnal cycle, and it does not directly respond to the local moisture convergence and the large‐scale upward motion. These results reemphasize the importance of improving the coupling of the convection to the large‐scale environment in reducing the summer precipitation bias over the Central United States in climate models with the resolution of ~0.25°.

Description: The evolution of He + -mode electromagnetic ion cyclotron (EMIC) waves is studied inside the geostationary orbit using our global model of ring current (RC) ions, electric field, plasmasphere, and EMIC waves. In contrast to the approach previously used by [22], however, we do not use the bounce-averaged wave kinetic equation but instead use a complete, non bounce-averaged, equation to model the evolution of EMIC wave power spectral density, including off-equatorial wave dynamics. The major results of our study can be summarized as follows. (1) The thermal background level for EMIC waves is too low to allow waves to grow up to the observable level during one pass between the “bi–ion latitudes” (the latitudes where the given wave frequency is equal to the O +  − He + bi–ion frequency) in conjugate hemispheres. As a consequence, quasi-field-aligned EMIC waves are not typically produced in the model if the thermal background level is used, but routinely observed in the Earth's magnetosphere. To overcome this model-observation discrepancy we suggest a nonlinear energy cascade from the lower frequency range of ultra low frequency waves into the frequency range of EMIC wave generation as a possible mechanism supplying the needed level of seed fluctuations that guarantees growth of EMIC waves during one pass through the near equatorial region. The EMIC wave development from a suprathermal background level shows that EMIC waves are quasi-field-aligned near the equator, while they are oblique at high latitudes, and the Poynting flux is predominantly directed away from the near equatorial source region in agreement with observations. (2) An abundance of O + strongly controls the energy of oblique He + -mode EMIC waves that propagate to the equator after their reflection at “bi–ion latitudes”, and so it controls a fraction of wave energy in the oblique normals. (3) The RC O + not only causes damping of the He + -mode EMIC waves but also causes wave generation in the region of highly oblique wave normal angles, typically for θ  〉 82 ∘ , where a growth rate γ  〉 10 − 2 rad/s is frequently observed. The instability is driven by the loss-cone feature in the RC O + distribution function, where ∂ F /∂ v ⊥  〉 0 for the resonating O + . (4) The oblique and intense He + -mode EMIC waves generated by RC O + in the region L ≈ 2 − 3 may have an implication to the energetic particle loss in the inner radiation belt.