Meridional circulation dynamics in a cyclic convective dynamo

Surface observations indicate that the speed of the solar meridional circulation in the photosphere varies in anti-phase with the solar cycle. The current explanation for the source of this variation is that inflows into active regions alter the global surface pattern of the meridional circulation. When these localized inflows are integrated over a full hemisphere, they contribute to slowing down the axisymmetric poleward horizontal component. The behavior of this large-scale flow deep inside the convection zone remains largely unknown. Present helioseismic techniques are not sensitive enough to capture the dynamics of this weak large-scale flow. Moreover, the large time of integration needed to map the meridional circulation inside the convection zone, also masks some of the possible dynamics on shorter timescales. In this work we examine the dynamics of the meridional circulation that emerges from a 3D MHD global simulation of the solar convection zone. Our aim is to assess and quantify the behavior of meridional circulation deep inside the convection zone where the cyclic large-scale magnetic field can reach considerable strength. Our analyses indicate that the meridional circulation morphology and amplitude are both highly influenced by the magnetic field via the impact of magnetic torques on the global angular momentum distribution. A dynamic feature induced by these magnetic torques is the development of a prominent upward flow at mid-latitudes in the lower convection zone that occurs near the equatorward edge of the toroidal bands and that peaks during cycle maximum. Globally, the dynamo-generated large-scale magnetic field drives variations in the meridional flow, in stark contrast to the conventional kinematic flux transport view of the magnetic field being advected passively by the flow.Centra-ISTGRPS-UdeMNatural Sciences and Engineering Research Council of CanadaNational Science FoundationUniversity of the Algarveinfo:eu-repo/semantics/publishedVersio

Mixing and general circulation dynamics : theory and observations

Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 1987This thesis studies the role of cross-isopycnal mixing in general circulation dynamics, from both the theoretical and observational points of view. The first two chapters discuss some theoretical aspects of cross-isopycnal mixing in the oceans. In chapter one, an integral constraint relating the interior stratification and air-sea heat fluxes is derived, based on the condition that the total mass of water of given density is constant in a steady state ocean. Two simple models are then used to examine the way the numerically small mixing, together with air-sea fluxes, determines the average vertical density stratification of the oceans, and the deep buoyancy driven circulation. In chapter two, a more complete model of a deep flow driven by cross isopycnal diffusion is presented, motivated by the Mediterranean outflow into the North Atlantic. Mixing in this model is responsible for the determination of the detailed structure of the flow and density field, while in the models of the first chapter it was allowed to determine only the average vertical density stratification. In chapter three, a hydrographic data set from the Mediterranean sea is analyzed by inverse methods. The purpose is to examine the importance of mixing when trying to explain tracer distributions in the ocean. The time-mean circulation and the appropriate mixing coefficients are calculated from the hydrographic data. We conclude that the numerically small cross isopycnal mixing processes are crucial to the dynamics, yet difficult to parameterize and measure using available hydrographic data.NSF grants OCE-8521685 and OCE-8017791 supported me during my studies in the joint program

Hydrographic data collection for Operation James River--1964

Data presented in this report were collected to provide information for verification of an hydraulic model of the James River below the fall line at Richmond, and for calculation of circulation dynamics in the James River

Planetary boundary layer and circulation dynamics at Gale Crater, Mars

The Mars implementation of the Planet Weather Research and Forecasting (PlanetWRF) model, MarsWRF, is used here to simulate the atmospheric conditions at Gale Crater for different seasons during a period coincident with the Curiosity rover operations. The model is first evaluated with the existing single-point observations from the Rover Environmental Monitoring Station (REMS), and is then used to provide a larger scale interpretation of these unique measurements as well as to give complementary information where there are gaps in the measurements. The variability of the planetary boundary layer depth may be a driver of the changes in the local dust and trace gas content within the crater. Our results show that the average time when the PBL height is deeper than the crater rim increases and decreases with the same rate and pattern as Curiosity's observations of the line-of-sight of dust within the crater and that the season when maximal (minimal) mixing is produced is Ls 225°–315° (Ls 90°–110°). Thus the diurnal and seasonal variability of the PBL depth seems to be the driver of the changes in the local dust content within the crater. A comparison with the available methane measurements suggests that changes in the PBL depth may also be one of the factors that accounts for the observed variability, with the model results pointing towards a local source to the north of the MSL site. The interaction between regional and local flows at Gale Crater is also investigated assuming that the meridional wind, the dynamically important component of the horizontal wind at Gale, anomalies with respect to the daily mean can be approximated by a sinusoidal function as they typically oscillate between positive (south to north) and negative (north to south) values that correspond to upslope/downslope or downslope/upslope regimes along the crater rim and Mount Sharp slopes and the dichotomy boundary. The smallest magnitudes are found in the northern crater floor in a region that comprises Bradbury Landing, in particular at Ls 90° when they are less than 1 m s−1, indicating very little lateral mixing with outside air. The largest amplitudes occur in the south-western portions of the crater where they can exceed 20 m s−1. Should the slope flows along the crater rims interact with the dichotomy boundary flow, which is more likely at Ls 270° and very unlikely at Ls 90°, they are likely to interact constructively for a few hours from late evening to nighttime (∼17–23 LMST) and from pre-dawn to early morning (∼5–11 LMST) hours at the norther crater rim and destructively at night (∼22–23 LMST) and in the morning (∼10–11 LMST) at the southern crater rim. We conclude that a better understanding of the PBL and circulation dynamics has important implications for the variability of the concentration of dust, non-condensable and trace gases at the bottom of other craters on Mars as mixing with outside air can be achieved vertically, through changes in the PBL depth, and laterally, by the transport of air into and out of the crater

Characterising two-pathogen competition in spatially structured environments

Different pathogens spreading in the same host population often generate complex co-circulation dynamics because of the many possible interactions between the pathogens and the host immune system, the host life cycle, and the space structure of the population. Here we focus on the competition between two acute infections and we address the role of host mobility and cross-immunity in shaping possible dominance/co-dominance regimes. Host mobility is modelled as a network of traveling flows connecting nodes of a metapopulation, and the two-pathogen dynamics is simulated with a stochastic mechanistic approach. Results depict a complex scenario where, according to the relation among the epidemiological parameters of the two pathogens, mobility can either be non-influential for the competition dynamics or play a critical role in selecting the dominant pathogen. The characterisation of the parameter space can be explained in terms of the trade-off between pathogen's spreading velocity and its ability to diffuse in a sparse environment. Variations in the cross-immunity level induce a transition between presence and absence of competition. The present study disentangles the role of the relevant biological and ecological factors in the competition dynamics, and provides relevant insights into the spatial ecology of infectious diseases.Comment: 30 pages, 6 figures, 1 table. Final version accepted for publication in Scientific Report

A CIRCULATION DYNAMICS MODEL IN THE ECOSYSTEM FOR THE WEST LAKE, HANGZHOU

This paper focuses the researches on an eutrophication model after drainage of wastewater and drawing water from the Qiantang River to West Lake. The model describes the circulation of nutritive matters (such as phosphorus, nitrogen, and carbon) in the ecosystem of the Lake. The model was established according to observed values of water quality and relevant parameters in 1995. The results of model calibration and verification show that the model can reasonably respond to the changes of forcing functions for drawing quantity and temperature of water. The model has been used to forecast the water quality in different drawing quantities. The predictions given by the model are also believed to be useful to comprehensively harness the West Lake.Article信州大学理学部附属諏訪臨湖実験所報告 11: 87-98(1999)departmental bulletin pape