Contributions of Convective and Orographic Gravity Waves to the Brewer–Dobson Circulation Estimated from NCEP CFSR

Contributions of convective gravity waves (CGWs) and orographic gravity waves (OGWs) to the Brewer–Dobson circulation (BDC) are examined and compared to those from resolved waves. OGW drag (OGWD) is provided by NCEP Climate Forecast System Reanalysis (CFSR), while CGW drag (CGWD) is obtained from an offline calculation of a physically based CGW parameterization with convective heating and background data provided by CFSR. CGWD contributes to the shallow branch of the BDC regardless of the season, while OGWD contributes to both the shallow and deep branches except for the summertime, when OGWs hardly propagate into the stratosphere. At 70 hPa, the annual-mean tropical upward mass fluxes from Eliassen–Palm flux divergence (EPD), OGWD, and CGWD are 68%, 7%, and 4% of the total mass flux, respectively. The tropical upward mass flux at 70 hPa shows an increasing trend during the time period from 1979 to 1998, with 28%, 18%, and 6% of the trend driven by EPD, OGWD, and CGWD, respectively. The width of the turnaround latitudes tends to narrow for the streamfunctions induced by OGWD and CGWD but tends to widen for that induced by EPD. The contributions of GWD from MERRA (MERRA-2) to the climatology and long-term trend of the BDC are 7% (7%) and 13% (4%), respectively, somewhat smaller than the contributions of CGWD plus OGWD, which are estimated from CFSR to be 12% and 20%, respectively.

Extra Mass Flux in Fluid Mechanics

The conditions of existence of extra mass flux in single-component dissipative nonrelativistic fluids are clarified. By considering Galilean invariance, we show that if total mass flux is equal to total momentum density, then mass, momentum, angular momentum and booster (center of mass) are conserved. However, these conservation laws may be fulfilled also by other means. We show an example of weakly nonlocal hydrodynamics where the conservation laws are satisfied as well although the total mass flux is different from momentum density.

The detrimental effect of hydrodynamic interactions on the process of Brownian flocculation in shear flow

The problem of Brownian flocculation of spherical particles in strong shearing flow without hydrodynamic interactions is studied in detail using the singular perturbation method. All other types of interparticle interactions, such as van der Waals or Lennard-Jones forces, are also ignored. In the limit of strong external flow, the strength of which is measured by the Péclet number ($Pe\gg 1$), a complicated boundary layer structure for the pair probability density function ($P_{2}$) is identified and the complete stationary spatial distribution of $P_{2}(\boldsymbol {x})$ in the domain is found. The results, in particular the total mass flux in the accumulation process, are compared qualitatively and quantitatively with the case where the spheres interact hydrodynamically and it is demonstrated that the hydrodynamic interactions tend to decrease the rate of flocculation. An explicit simple formula for the flocculation rate for a general form of hydrodynamic interactions is provided. The limit of small Péclet number is also discussed to confirm the conclusion on the detrimental influence of hydrodynamic interactions on the rate of Brownian flocculation in shearing flow.

Experimental study on two-phase pressure drop of air-water in small diameter tubes at horizontal orientation

Experimental results of adiabatic two-phase pressure drop in small diameter tubes are presented in this work. Air-water mixture is used as the working substance. Four test sections made of transparent acrylic tubes of different internal diameters ranging from 3.0 mm to 8.0 mm are used with different test section lengths from 150 mm to 400 mm. The investigation is carried out within the range of mass flux of water 16.58 -3050 kg/m2s, mass flux of air 8.25-204.10 kg/m2s and total mass flux 99.93-3184.69 kg/m2s. Some of the existing correlations for macro and mini-channels are compared with the experimental data. Based on the experimental data; a new correlation has been developed to predict two-phase pressure drop in horizontal channels.

Functions of Step Gating System in the Lost Foam Casting Process

In order to explore whether the step gating system played a role in lost foam casting (LFC) process, this paper simulated the mold filling process of a step gating system with an auxiliary sprue and three side ingates by using the gravity LFC model of the code FLOW-3D, and analyzed its mold filling characteristics in LFC. It is found the mass flux ratio through the bottom-side ingate exceed 82% the total mass flux, much more than through the others. And it is also found the metal temperature of the middle region in the height direction is lower than the upper region or bottom region. The results show that the step gating system is not able to achieve its main roles in LFC. Our results can be used to design gating system in LFC.

The impact of Saharan dust on the particulate export in the water column of the North Western Mediterranean Sea

Simultaneous measurements of atmospheric deposition and of sinking particles at 200 and 1000 m depth, were performed in the Ligurian Sea (North-Western Mediterranean) between 2003 and 2007, along with phytoplanktonic activity derived from satellite images. Atmospheric deposition of Saharan dust particles was very irregular and confirmed the importance of sporadic high magnitude events over the annual average (11.4 g m−2 yr−1 for the 4 years). The average marine total mass flux was 31 g m−2 yr−1, the larger fraction being the lithogenic one (~37%). The marine total mass flux displayed a seasonal pattern with a maximum in winter, occurring before the onset of the spring bloom. The highest POC fluxes did not occur during the spring bloom nor could they be directly related to any noticeable increase in the surface phytoplanktonic biomass. Over the 4 years of the study, the strongest POC fluxes were concomitant with large increases of the lithogenic marine flux, which had originated from either recent Saharan fallout events (February 2004 and August 2005), from "old" Saharan dust "stored" in the upper water column layer (March 2003 and February 2005), or alternatively from lithogenic material originating from Ligurian riverine flooding (December 2003, Arno, Roya and Var rivers). Those associated export fluxes defined as "lithogenic events", are believed to result from a combination of forcing (winter mixing or Saharan events, in particular extreme ones), biological (zooplankton) activity, and also organic-mineral aggregation inducing a ballast effect. By fertilising the surface layer, mixed Saharan dust events were shown to be able to induce "lithogenic events" during the stratification period. These events would be more efficient in transferring POC to the deeper layers than the spring bloom itself. The extreme Saharan event of February 2004 exported ~45% of the total annual POC, compared to an average of ~25% for the bloom period. This emphasises the role played by these "lithogenic events", and in particular those that are induced by the more extreme Saharan events, in the carbon export efficiency in the North-western Mediterranean Sea.

The impact of Saharan dust on the particulate export in the water column of the North Western Mediterranean Sea

Simultaneous measurements of atmospheric deposition and of sinking particles at 200 m depth, were performed in the Ligurian Sea (North-Western Mediterranean) between 2003 and 2007 along with the historical time records of phytoplanktonic activity from satellite images. Atmospheric deposition of Saharan dust particles was very irregular and confirmed the importance of sporadic high magnitude events over the annual average (11.4 g m−2 yr−1 for the 4 yr). The average marine total mass flux was 31 g m−2 yr−1, the larger fraction being the lithogenic one (~37%). The marine total mass flux displayed a seasonal pattern with a maximum in winter occurring before the onset of the spring bloom. The highest POC fluxes did not occur during the spring bloom nor could they be related to any noticeable increase in the surface phytoplanktonic activity. Over the 4 yr of the study, the strongest POC fluxes were concomitant with large increases of the lithogenic marine flux, which had originated from either recent Saharan fallout events (February 2004, August 2005), or from ''old'' Saharan dust ''stored'' in the upper water column layer (March 2003, February 2005), or alternatively from lithogenic material originating from Ligurian riverine flooding (December 2003, Arno, Roya and Var rivers). These ''lithogenic events'' are believed to result from a combination of physical processes (winter mixing), the aggregation of faecal pellets resulting from zooplankton activity, and also organic-mineral aggregation inducing a ballast effect. However, such an event also occurred in August 2005 without any physical mixing, and was attributed to Saharan dust-induced biological enhancement. POC export provoked by the simultaneous occurrence of winter mixing and an extreme dust event (February 2004, 22 g m−2 deposition) was shown to represent 50% of the total annual POC export at 200 m in the water column that year, as compared to only ~25% for the bloom period. This indicates the importance of atmospheric deposition for POC fluxes in the Mediterranean Sea, which is an area strongly influenced by Saharan dust inputs.

A Theoretical Approach to the Shift Mechanics of Rubber Belt Variators

This paper proposes a theoretical description of the mechanical behavior of rubber belt variators during the speed ratio shift. Comparing with the steady operation, the mass conservation of the belt is completely reformulated considering an elementary dihedral control volume between two planes through the pulley axis and balancing the inside mass variation with the total mass flux through the control surface. On the other hand, the belt equilibrium conditions are similar to the steady case, as the inertia forces due to the shifting motion are negligible with respect to the other forces. Assuming a one-dimensional belt model, it is shown that adhesive regions may appear inside the arc of contact, where the belt sticks to the pulley flanges along spiral-shaped paths. It is demonstrated that this type of contact may occur only for the closing pulleys, differently from the steady drives and from the opening pulleys, where only quasiadhesive internal subregions may be observed at most, where the sliding velocity turns out to be quite small along a more or less extended portion of the arc of contact. Numerical solutions are calculated for all types of conditions, and their characteristics are widely described.

Wall Shear Prediction for Wavy and Annular Air-Water Two-Phase Flow

Non-intrusive pressure drop, film thickness, and wave behavior measurements have been performed for horizontal air-water two-phase flow in round tubes. A databank of over 300 flow conditions in the wavy, wavy-annular, and annular regimes was compiled for three tube diameters (8.8 mm, 15.1 mm, and 26.3 mm). A correlation was developed based on the product of total mass flux, gas superficial velocity, and an empirical friction factor, selected from the lesser of a modified Froude number form and a Reynolds number form. This correlation performed to within 11% mean absolute error across the data range considered. A variety of correlations were also selected from the literature for comparison. Those based on film roughness (Wallis, Hurlburt-Newell), two-phase multipliers (Lockhart-Martinelli, Friedel, Chisholm, Olujic, and Gro¨nnerud), and empirical data fits (Mu¨ller-Steinhagen and Heck) were among those tested. As needed, correlations were rephrased in terms of wall shear to provide a consistent basis for comparison. A complex film roughness model (Hurlburt et al.) was also compared to the experimental data.