Decadal variations of Hadley and Walker circulations in the tropics

Preliminary estimate of divergent Hadley and Walker circulation associated with inter-decadal variations in the tropics is made with 50-year reanalysis data and compared with their inter-annual counterparts. Interdecadal and inter-annual components are separated using harmonic analysis and meridional and zonal mass flux stream functions are used to calculate the strength of Hadley and Walker circulations. The magnitude of inter-decadal Hadley and Walker circulation anomalies are shown to be comparable to those associated with dominant inter-annual variations. How superposition of inter-decadal and inter-annual divergent circulations may influence regional climate is discussed.

Nonconforming P1 Finite Element for the Biharmonic Problem and Its Application to Stokes Problem

The aim of this paper is to simulate the two-dimensional stationary Stokes problem. In vorticity-Stream function formulation, the Stokes problem is reduced to a biharmonic one; this approach leads to a formulation only based on the stream functions and therefore can only be applied to two-dimensional problems. The idea developed in this paper is to use the discretization of the Laplace operator by the nonconforming [Formula: see text] finite element. For the solutions which admit a regularity greater than [Formula: see text], in the general case, the convergence of the method is shown with the techniques of compactness. For solutions in [Formula: see text] an error estimate is proved, and numerical experiments are performed for the steady-driven cavity problem.

Worsening Drought of Nile Basin under shift in Atmospheric Circulation, Stronger ENSO and Indian Ocean Dipole

Until now, driving mechanisms behind recurring droughts and hydroclimate variations that controls the Nile River Basin (NRB) remain not well understood. In this study, we demonstrate that recent increasing aridity of NRB is attributed to the growing influence of stronger ENSO and Indian Ocean dipole (IOD), and SST gradient over the Arabian Sea (WTIO) in NRB after 1980s, which have significantly contributed to NRB’s drought severity at inter-annual to inter-decadal timescales. Further, the southward (westward) shift in stream functions and meridional (zonal) winds caused an enhancement in the blocking pattern, with strong anticyclonic waves of dry air that keeps moving into NRB, has resulted in drier NRB, where its streamflow at gauging stations have decreased from 137 to 114.1 m3/s/decade. Contrary to past findings, we show that IOD and WTIO are better predictors of the Nile streamflow than El Niño. Under the combined impact of warming and stronger WTIO and El Niño, future droughts of the NRB will worsen.

Methods: Of Stream Functions and Thin Wires: An Intuitive Approach to Gradient Coil Design

The design of gradient coils is sometimes perceived as complex and counterintuitive. However, a current density is connected to a stream function in fact by a simple relation. Here we present an intuitive open source code collection to derive stream functions from current densities on simple surface geometries. Discrete thin wires, oriented orthogonally to the main magnetic field direction are used to describe a surface current density. An inverse problem is solved and stream functions are derived to find coil designs in the current and stream function domains. The flexibility of the design method is demonstrated by deriving gradient coil designs on several different surface topologies. This collection is primarily intended for teaching, as well as for demonstrating all gradient coil design steps with openly available software tools.

Numerical Study of MHD Natural Convection in Trapezoidal Enclosure Filled With (50%MgO-50%Ag/Water) Hybrid Nanofluid: Heated Sinusoidal from Below

Numerical simulation of MHD free convection in a two-dimensional trapezoidal cavity of a hybrid nanofluid has been carried out in this research. The cavity is heated sinusoidal from the bottom wall, and the inclined walls are cooled while the top wall is isolated. The hybrid nanofluid (MgO-Ag/water) has been used as a working fluid. The numerical simulation has been validated with past papers and met a good agreement. The considered parameters are a range of Rayleigh number (Ra= 103 to 106), Hartmann number (Ha= 0 to 60) and volume fraction (f= 0 to 0.02). The results are presented as isotherms, stream functions, local and average Nusselt numbers, from which it is observed that the strength of the stream functions and isotherms increases with the increase of the Ra and ϕ while the increase in Hartmann number reduce the circulation of the flow and increases the isotherms strength. Also, the Nusselt number is increases with Ra and ϕ while it decreases with Ha.

TRACMASS 7.0 - A Lagrangian trajectory code for atmosphere and ocean sciences

<p>The latest version of the <strong>TRACMASS</strong> trajectory code, version 7.0 will be presented. The latest version includes several new features, e.g. water tracing in the atmosphere, generalisation of the tracer handling, and improvements to the numerical scheme. The code has also become more user friendly and easier to get started with. Previous versions of <strong>TRACMASS</strong> only allowed temperature, salinity and potential density to be calculated along the trajectories, but the new version allows any tracer to be followed e.g. biogeochemical tracers or chemical compounds in the atmosphere. </p><p><strong>TRACMASS</strong> calculates Lagrangian trajectories offline for both the ocean and atmosphere by using already stored velocity fields, and optionally tracer fields. The code supports most vertical coordinate systems, e.g. z-star, z-tilde, sigma, and hybrid sigma-pressure coordinates. Hence, <strong>TRACMASS</strong> supports a range of atmosphere and ocean models such as ECMWF IFS, NEMO, ROMS, MOM, as well as reanalysis products (e.g. ERA-5) or observations (e.g. geostrophic currents from AVISO satellite altimetry). The fact that the numerical scheme in <strong>TRACMASS</strong> is mass conserving allows us to associate each trajectory with a mass transport and calculate the Lagrangian mass transport between different regions as well as construct Lagrangian stream functions. </p><p>A short course on how to set up, configure and run the <strong>TRACMASS </strong>code will be given separately, <strong>SC5.17</strong>.</p>

Time-Periodic Cooling of Rayleigh–Bénard Convection

The problem of Rayleigh–Bénard’s natural convection subjected to a temporally periodic cooling condition is solved numerically by the Lattice Boltzmann method with multiple relaxation time (LBM-MRT). The study finds its interest in the field of thermal comfort where current knowledge has gaps in the fundamental phenomena requiring their exploration. The Boussinesq approximation is considered in the resolution of the physical problem studied for a Rayleigh number taken in the range 103 ≤ Ra ≤ 106 with a Prandtl number equal to 0.71 (air as working fluid). The physical phenomenon is also controlled by the amplitude of periodic cooling where, for small values of the latter, the results obtained follow a periodic evolution around an average corresponding to the formulation at a constant cold temperature. When the heating amplitude increases, the physical phenomenon is disturbed, the stream functions become mainly multicellular and an aperiodic evolution is obtained for the heat transfer illustrated by the average Nusselt number.

Numerical Investigation of Open Cavities with Parallel Insulated Baffles

This research reports the outcome of a numerical investigation of convection in ventilation square cavities contains parallel insulated baffles. The left and right walls of the cavity are kept at the high temperature. Whereas the top, bottom cavity walls, parallel baffles are adiabatic. The opening slots are positioned at the top, bottom corners of the hot vertical walls. The governing Navier-Stokes equations are formulated in the form of vorticity- stream functions. The finite difference method is used to find the values of the primitive variables. The effects of baffles size (Sb − 0.25, 0.50, 0.75), 3 various positions of the parallel baffle, Rayleigh number (103 − 106), Reynolds number (30, 300, 600) are discussed with the flow fields, isotherms, and Nusselt number. It is found that the behavior of ventilation cavities does not only depend on the size of the baffles and its positions. It highly depends on the configuration of the ventilation cavity too. Further, the flow fields are restricted by the largest baffles size of Sb = 0.75.