scholarly journals Rossby modes in slowly rotating stars: depth dependence in distorted polytropes with uniform rotation

2020 ◽  
Vol 637 ◽  
pp. A65 ◽  
Author(s):  
C. Damiani ◽  
R. H. Cameron ◽  
A. C. Birch ◽  
L. Gizon
Keyword(s):  
Perturbation Theory ◽  
Radial Force ◽  
Force Balance ◽  
Surface Boundary ◽  
Pressure Perturbation ◽  
Uniform Rotation ◽  
Near Surface ◽  
Depth Dependence ◽  
Special Cases ◽  
Inviscid Case

Context. Large-scale Rossby waves have recently been discovered based on measurements of horizontal surface and near-surface solar flows. Aims. We are interested in understanding why it is only equatorial modes that are observed and in modelling the radial structure of the observed modes. To this aim, we have characterised the radial eigenfunctions of r modes for slowly rotating polytropes in uniform rotation. Methods. We followed Provost et al. (1981, A&A, 94, 126) and considered a linear perturbation theory to describe quasi-toroidal stellar adiabatic oscillations in the inviscid case. We used perturbation theory to write the solutions to the fourth order in the rotational frequency of the star. We numerically solved the eigenvalue problem, concentrating on the type of behaviour exhibited where the stratification is nearly adiabatic. Results. We find that for free-surface boundary conditions on a spheroid of non-vanishing surface density, r modes can only exist for ℓ = m spherical harmonics in the inviscid case and we compute their depth dependence and frequencies to leading order. For quasi-adiabatic stratification, the sectoral modes with no radial nodes are the only modes which are almost toroidal and the depth dependence of the corresponding horizontal motion scales as rm. For all r modes, except the zero radial order sectoral ones, non-adiabatic stratification plays a crucial role in the radial force balance. Conclusions. The lack of quasi-toroidal solutions when stratification is close to neutral, except for the sectoral modes without nodes in radius, follows from the need for both horizontal and radial force balance. In the absence of super- or sub-adiabatic stratification and viscosity, both the horizontal and radial parts of the force balance independently determine the pressure perturbation. The only quasi-toroidal cases in which these constraints on the pressure perturbation are consistent are the special cases where ℓ = m and the horizontal displacement scales with rm.

Along-wind dispersion by horizontal turbulent jets in the upper ocean

2021 ◽  
Author(s):  
Tobias Kukulka ◽  
Todd Thoman
Keyword(s):  
Turbulent Jets ◽  
Surface Boundary ◽  
Surface Boundary Layer ◽  
Near Surface ◽  
Idealized Model ◽  
Eddy Simulation ◽  
Wind Dispersion ◽  
Shear Dispersion ◽  
Coherent Jet ◽  
Local Shear

AbstractDispersion processes in the ocean surface boundary layer (OSBL) determine marine material distributions such as those of plankton and pollutants. Sheared velocities drive shear dispersion, which is traditionally assumed to be due to mean horizontal currents that decrease from the surface. However, OSBL turbulence supports along-wind jets; located in near-surface convergence and downwelling regions, such turbulent jets contain strong local shear. Through wind-driven idealized and large eddy simulation (LES) models of the OSBL, this study examines the role of turbulent along-wind jets in dispersing material. In the idealized model, turbulent jets are generated by prescribed cellular flow with surface convergence and associated downwelling regions. Numeric and analytic model solutions reveal that horizontal jets substantially contribute to along-wind dispersion for sufficiently strong cellular flows and exceed contributions due to vertical mean shear for buoyant surface-trapped material. However, surface convergence regions also accumulate surface-trapped material, reducing shear dispersion by jets. Turbulence resolving LES results of a coastal depth-limited ocean agree qualitatively with the idealized model and reveal long-lived coherent jet structures that are necessary for effective jet dispersion. These coastal results indicate substantial jet contributions to along-wind dispersion. However, jet dispersion is likely less effective in the open ocean because jets are shorter lived, less organized, and distorted due to spiraling Ekman currents.

scholarly journals The role of unsaturated zone in estimating groundwater recharge in arid and semiarid areas as depicted by geochemical tracers

2019 ◽  
Vol 98 ◽  
pp. 12007
Author(s):  
Tianming Huang ◽  
Baoqiang Ma ◽  
Yin Long ◽  
Zhonghe Pang
Keyword(s):  
Groundwater Recharge ◽  
Unsaturated Zone ◽  
Surface Boundary ◽  
Recharge Rate ◽  
Semiarid Area ◽  
Near Surface ◽  
Geochemical Tracers ◽  
Semiarid Areas ◽  
Arid And Semiarid Areas ◽  
Arid And Semiarid

In arid and semiarid area, the recharge rate is relatively limited and the unsaturated zone (UZ) is commonly thick. The moisture in the UZ may represent the water infiltrating from precipitation during the past decades to thousands of years. Therefore, the multiple geochemical tracers in soil moisture, including Cl (chloride mass balance), 3H (tritium peak displacement), NO3, 2H, 18O, can be used to estimate diffuse recharge rate and related recharge characteristics. Based on 45 UZ profiles with maximum depth of 62 m in the Ordos Basin in NW China, a typical arid and semiarid area, we has used multiple geochemical tracers to study the following recharge informations: (1) reconstruction of groundwater recharge history, (2) determination of groundwater recharge mechanism, and (3) assessment of impact of vegetation changes on groundwater recharge. The results show that the soil texture (epically the shallow soil), vegetation and precipitation mainly control the recharge rate. This study also found that shallow groundwater in arid and semiarid areas is often not in equilibrium with near-surface boundary conditions. To estimate present recharge information, the UZ must be considered. The whole recharge process from precipitation to groundwater cannot be well understood unless the UZ have been included in arid and semiarid areas.

scholarly journals Recent development of the Met Office operational ocean forecasting system: an overview and assessment of the new Global FOAM forecasts

2014 ◽  
Vol 7 (6) ◽  
pp. 2613-2638 ◽  
Author(s):  
E. W. Blockley ◽  
M. J. Martin ◽  
A. J. McLaren ◽  
A. G. Ryan ◽  
J. Waters ◽  
...  
Keyword(s):  
Sea Ice ◽  
Forecast Accuracy ◽  
Deep Ocean ◽  
Ocean Model ◽  
Global Ocean ◽  
Surface Boundary ◽  
Observation Window ◽  
Sea Ice Concentration ◽  
Near Surface ◽  
Shelf Sea

Abstract. The Forecast Ocean Assimilation Model (FOAM) is an operational ocean analysis and forecast system run daily at the Met Office. FOAM provides modelling capability in both deep ocean and coastal shelf sea regimes using the NEMO (Nucleus for European Modelling of the Ocean) ocean model as its dynamical core. The FOAM Deep Ocean suite produces analyses and 7-day forecasts of ocean tracers, currents and sea ice for the global ocean at 1/4° resolution. Satellite and in situ observations of temperature, salinity, sea level anomaly and sea ice concentration are assimilated by FOAM each day over a 48 h observation window. The FOAM Deep Ocean configurations have recently undergone a major upgrade which has involved the implementation of a new variational, first guess at appropriate time (FGAT) 3D-Var, assimilation scheme (NEMOVAR); coupling to a different, multi-thickness-category, sea ice model (CICE); the use of coordinated ocean-ice reference experiment (CORE) bulk formulae to specify the surface boundary condition; and an increased vertical resolution for the global model. In this paper the new FOAM Deep Ocean system is introduced and details of the recent changes are provided. Results are presented from 2-year reanalysis integrations of the Global FOAM configuration including an assessment of short-range ocean forecast accuracy. Comparisons are made with both the previous FOAM system and a non-assimilative FOAM system. Assessments reveal considerable improvements in the new system to the near-surface ocean and sea ice fields. However there is some degradation to sub-surface tracer fields and in equatorial regions which highlights specific areas upon which to focus future improvements.

Analysis on Stress-Strain Distribution in Rapid Prototyping

2010 ◽  
Vol 26-28 ◽  
pp. 352-355
Author(s):  
Mao Liang Wu
Keyword(s):  
Strain Distribution ◽  
Influence Factors ◽  
Force Balance ◽  
Force Model ◽  
Theoretic Analysis ◽  
Stress Strain ◽  
Adhesive Layers ◽  
Quantitative Expression ◽  
Special Cases ◽  
Function Relationship

The paper introduces the shrinkage center conception and simplified model of the material solidification. Starting with a micro unit, the paper builds the force model, and derives the formula of the stress-strain principles on the basis of the force balance function, relationship between the strain and displacement and the unit boundary conditions. The theoretic analysis reveals the influence factors and the quantitative expression affecting parts deformation. At last, two special cases, separating layers and complete adhesive layers, are discussed to display the stress-strain distribution under such conditions.

Application of Site Amplification Factors to Determine the Local Magnitude from Borehole Seismic Stations in Taiwan

2020 ◽  
Author(s):  
Tz-Shin Lai ◽  
Yih-Min Wu ◽  
Wei-An Chao
Keyword(s):  
Site Effect ◽  
Site Amplification ◽  
Force Balance ◽  
Earthquake Catalog ◽  
Local Magnitude ◽  
Broadband Seismometer ◽  
Near Surface ◽  
Amplification Factors ◽  
Attenuation Function ◽  
Borehole Seismic

<p>Since the inception of 62 borehole seismic arrays deployed by Central Weather Bureau (CWB) in Taiwan until the end of 2018, a large quantity of strong-motion records have been accumulated from frequently occurring earthquakes around Taiwan, which provide an opportunity to detect micro-seismicity. Each borehole array includes two force balance accelerometers, one at the surface and other at a depth of a few ten-to-hundred (30-492) meters, as well as one broadband seismometer is below the borehole accelerometer. In general, the background seismic noise level are lower at the downhole stations than surface stations. However, the seismograms recorded by the downhole stations are smaller than surface stations due to the near-surface site effect. In Taiwan, the local magnitude (M<sub>L</sub>) determinations use the attenuation function derived from surface stations. Therefore, the M<sub>L</sub> will be underestimated by using current attenuation function for downhole stations. In this study, we used 19079 earthquakes to investigate the site amplification at subsurface materials between downhole and surface stations. Results demonstrate the amplification factors ranging from 1.11 to 5.74, provide the site effect parameter at shallow layers and have a strong relationship with Vs30. Further, we apply the amplification factors to revise the station local magnitude for downhole station. The revised M<sub>L</sub> at downhole stations correlate well with the M<sub>L</sub> at surface stations. Implement of the downhole station in the M<sub>L</sub> determination, it enhances the ability to detect the micro-earthquake and makes the earthquake catalog more comprehensive in Taiwan.</p>

On the radial force balance in the quiet time magnetotail current sheet

2016 ◽  
Vol 121 (5) ◽  
pp. 4017-4026 ◽  
Author(s):  
A. V. Artemyev ◽  
V. Angelopoulos ◽  
A. Runov
Keyword(s):  
Current Sheet ◽  
Radial Force ◽  
Force Balance ◽  
Quiet Time ◽  
Magnetotail Current Sheet

scholarly journals Impact of debris cover on glacier ablation and atmosphere-glacier feedbacks in the Karakoram

2015 ◽  
Vol 9 (2) ◽  
pp. 2259-2299 ◽  
Author(s):  
E. Collier ◽  
F. Maussion ◽  
L. I. Nicholson ◽  
T. Mölg ◽  
W. W. Immerzeel ◽  
...  
Keyword(s):  
Coupled Model ◽  
Surface Boundary ◽  
Glacier Surface ◽  
Near Surface ◽  
Mass Fluxes ◽  
Surface Boundary Conditions ◽  
Boundary Layer Development ◽  
Debris Cover ◽  
The Difference ◽  
Strong Control

Abstract. The Karakoram range of the Hindu-Kush-Himalaya is characterized by both extensive glaciation and a widespread prevalence of surficial debris cover on the glaciers. Surface debris exerts a strong control on glacier surface-energy and mass fluxes and, by modifying surface boundary conditions, has the potential to alter atmosphere-glacier feedbacks. To date, the influence of debris on Karakoram glaciers has only been directly assessed by a small number of glaciological measurements over short periods. Here, we include supraglacial debris in a high-resolution, interactively coupled atmosphere-glacier modelling system. To investigate glaciological and meteorological changes that arise due to the presence of debris, we perform two simulations using the coupled model from 1 May to 1 October 2004: one that treats all glacier surfaces as debris-free and one that introduces an simplified specification for mapping debris thickness. The basin-averaged impact of debris is a reduction in ablation of ~7%, although the difference exceeds 2.5 m w.e. on the lowest-altitude glacier tongues. The modest reduction in mean mass loss results in part from non-negligible sub-debris melt rates under thicker covers and from compensating increases in melt under thinner debris, and may help to explain the lack of distinct differences in recent elevations changes between clean and debris-covered ice. The presence of debris also strongly alters the surface boundary condition and thus heat exchanges with the atmosphere; near-surface meteorological fields at lower elevations and their vertical gradients; and the atmospheric boundary layer development. These findings are relevant for glacio-hydrological studies on debris-covered glaciers and contribute towards an improved understanding of glacier behaviour in the Karakoram.

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