Cutoff low over the southeastern Pacific Ocean: a case study

Cutoff lows (COLs) are infrequent events in the tropics that can cause extreme rainfall, flash flooding and landslides in arid areas, such as western South America. In this study, the life cycle of a COL in the southeastern Pacific at the beginning of April 2012 was analysed using the ERA-Interim reanalysis dataset. This paper examines: (1) the precursor flow evolution prior to the COL, its development and dissipation by applying the quasi-geostrophic and vorticity equations; and (2) the influence of the COL in the heavy precipitation events over the western Peruvian Andes. During April 2012, the highest amount of precipitation was recorded in Chosica (850 masl) with 37mm on 5 April. Days prior to the formation of the COL, a subtropical trough deepened by the amplification of a ridge over the tropical Pacific and the incursion of cold air from medium and low levels into the trough. The strong cyclonic vorticity advection was intensified by a short-wave trough embedded inside a long-wave one that strengthened the system on 5 April 2012. In the dissipation stage, warm vertical advection predominated, resulting in the reabsorption of the COL by a new trough. Understanding the behaviour COL systems is important for reducing the impact of these extreme weather events on lives and infrastructure in densely populated areas.

Thermo-Solutal Buoyancy Effect on Heat and Mass Transfer in a Backward-Facing Step Channel Under the Influence of Different Shapes of Nanoparticles

Double-diffusive mixed convection in a backward-facing step (BFS) channel for different shapes of nanoparticles is analyzed using velocity–vorticity equations. The effect of four shapes of alumina nanoparticles at volume fractions χ of 1–5% on heat and mass transfer are studied for buoyancy ratios, N from −3 to 3 at Re = 200, Ri = 0.1, and Pr = 6.2. As χ increases, the Nuav decreases for all shapes at N = −3; however, it increases with an increase in N from 1 to 3. At N = 3, the Nu increases by 29% for blades shape, whereas a 28% decrease was noticed for platelets shape. An increase in χ of nanoparticles results in a decrease of Shav for N = 1–3, with a maximum decrease of 57% being observed at N = −3 for cylinders shape. The τav at the bottom wall continues to increase up to a maximum of 400% for platelets shape for N = 3.

Intermezzo: Effects of Increasing Reynolds Number

Effects of increasing fluid speed are analyzed. The Bernouilli and vorticity equations are derived, and the method of matching solutions is described for the Rankine vortex. Cases in which rotational flow is mandatory are explained, and bifurcations, hydraulic jumps, and transitions between stable and unstable behaviors are introduced. The ethical views of Hans Bethe and Edward Teller are contrasted. Other topics include potential flow around both cylinders and spheres and lessons that can be learnt about flow over a wavy streambed.

Effect of External Magnetic Field on Dynamics of Two-dimensional Isotropic Conducting Flow

In this article, the impact of external uniform magnetic field on the dynamic characteristics and mixing parameters of two-dimensional isotropic magnetohydrodynamic (MHD) flow is investigated. For this purpose, the direct numerical simulation (DNS) is applied to two-dimensional incompressible Navier-Stokes and magnetic induction equations by pseudo-spectral method. Governing equations are considered in the N-S vorticity equations to guarantee the incompressibility conditions and remove the pressure term from equations. The Results of the calculations show that the deformation of vortexes by external magnetic field reduces the mixing efficiency. It is also demonstrated that in MHD flow the energy is exchanged by Lorentz force between the flow and the magnetic field in such a way that the kinetic energy decreases and consequently mixing of the fluid is reduced. This energy transfer causes reduction of viscous dissipation of energy and mixing efficiency, despite increasing the total dissipated energy rate.