The Role of Process Coupling in the Time Step Sensitivity of E3SM's Microphysics

Abstract The contribution of surface evapotranspiration (ET) to moist convection, cloudiness, and precipitation along the eastern flanks of the tropical Andes (EADS) was investigated using the Weather Research and Forecasting (WRF) Model with nested simulations of selected weather conditions down to 1.2-km grid spacing. To isolate the role of surface ET, numerical experiments were conducted using a quasi-idealized approach whereby, at every time step, the surface sensible heat effects are exactly the same as in the reference simulations, whereas the surface latent heat fluxes are prevented from entering the atmosphere. Energy balance analysis indicates that surface ET influences moist convection primarily through its impact on conditional instability, because it acts as an important source of moist entropy in this region. The energy available for convection decreases by up to approximately 60% when the ET contribution is withdrawn. In contrast, when convective motion is not thermally driven or under conditionally stable conditions, the role of latent heating from the land surface becomes secondary. At the scale of the Andes proper, removal of surface ET weakens upslope flows by increasing static stability of the lower troposphere, as the vertical gradient of water vapor mixing ratio tends to be less negative. Consequently, moisture convergence is reduced over the EADS. In the absence of surface ET, this process operates in concert with damped convective energy, suppressing cloudiness and decreasing daily precipitation by up to around 50% in the simulations presented here.

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Identifying the tangle of vortex tubes in homogeneous isotropic turbulence

Journal of Fluid Mechanics ◽

10.1017/jfm.2019.487 ◽

2019 ◽

Vol 874 ◽

pp. 952-978 ◽

Cited By ~ 2

Author(s):

Shiying Xiong ◽

Yue Yang

Keyword(s):

Isotropic Turbulence ◽

Time Instant ◽

Small Scale ◽

Homogeneous Isotropic Turbulence ◽

Complex Flow ◽

Time Step ◽

Vortex Sheets ◽

Helical Geometry ◽

Vortex Tubes

We extend the vortex-surface field (VSF), whose isosurface is a vortex surface consisting of vortex lines, to identify vortex tubes and sheets in homogeneous isotropic turbulence. The VSF at a time instant is constructed by solving a pseudo-transport equation. This equation is convected by a given instantaneous vorticity obtained from direct numerical simulation. In each pseudo-time step, we develop a novel local optimization algorithm to minimize a hybrid VSF constraint, balancing the accuracy and smoothness of VSF solutions. This key improvement makes the numerical construction of VSFs feasible for arbitrarily complex flow fields, as a general flow diagnostic tool. In the visualization of VSF isosurfaces in decaying homogeneous isotropic turbulence, the initial curved vortex sheets first evolve into vortex tubes, and then the vortex tubes are stretched and tangled, constituting a complex network. Some vortex tubes exhibit helical geometry, which suggests the important role of vortex twisting in the generation of small-scale structures in energy cascade.

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Mapping of water-related ecosystem services in the uMngeni catchment using a daily time-step hydrological model for prioritisation of ecological infrastructure investment – Part 1: Context and modelling approach

Water SA ◽

10.4314/wsa.v44i4.07 ◽

2018 ◽

Vol 44 (4 October) ◽

Author(s):

CJ Hughes ◽

G De Winnaar ◽

RE Schulze ◽

M Mander ◽

GPW Jewitt

Keyword(s):

Ecosystem Services ◽

Hydrological Model ◽

Severe Drought ◽

Water Shortages ◽

Time Step ◽

Ecological Infrastructure ◽

High Assurance ◽

Daily Time Step ◽

Daily Time

South Africa is a semi-arid country which frequently faces water shortages, and experienced a severe drought in the 2016 and 2017 rainfall seasons. Government is under pressure to continue to deliver clean water to the growing population at a high assurance of supply. Studies now show that the delivery of water may be sustained not only through built infrastructure such as dams and pipelines, but also through investment in ecological infrastructure (EI). A daily time-step hydrological model was used to map areas which should be prioritised for protection or rehabilitation to sustain the delivery of water-related ecosystem services within the uMngeni catchment. We focused on three water-related ecosystem services, i.e.: water supply, sustained baseflow, erosion control/avoidance of excessive sediment losses. The two key types of degradation were modelled, namely, overgrazing and the invasion of upland areas by Black Wattle (Acacia mearnsii). This, Part 1 of a paper in 2 parts, provides a discussion on the role of EI in delivering water-related ecosystem services, describes the motivation for the study, and the methods used in modelling and mapping the catchment. The results of this modelling exercise are presented in Part 2, which also explores and illustrates the potential hydrological benefits of rehabilitation and protection of EI in the uMngeni Catchment.

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CBS versus GLS stabilization of the incompressible Navier-Stokes equations and the role of the time step as stabilization parameter

Communications in Numerical Methods in Engineering ◽

10.1002/cnm.470 ◽

2001 ◽

Vol 18 (2) ◽

pp. 99-112 ◽

Cited By ~ 44

Author(s):

R. Codina ◽

O. C. Zienkiewicz

Keyword(s):

Stokes Equations ◽

Navier Stokes ◽

Time Step ◽

Navier Stokes Equations ◽

Stabilization Parameter

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Bedrock outcrops: A window for enhanced midwinter recharge

10.5194/egusphere-egu21-8074 ◽

2021 ◽

Author(s):

Stephanie Wright ◽

Kent Novakowski

Keyword(s):

Moisture Content ◽

Element Model ◽

Frozen Soil ◽

Climate Data ◽

Soil Permeability ◽

Time Step ◽

Near Surface ◽

Flow Transport ◽

Winter Time

<p>As midwinter melt and rain-on-snow events become more common occurrences in the northern hemisphere under climate change, incorporating frozen processes when simulating winter-time recharge is increasingly necessary. The activation of infiltration pathways and recharge dynamics of shallow bedrock environments under frozen conditions has received relatively little attention. Over the 2019-2020 winter, hydrogeologic and cryospheric conditions of the surface, unsaturated, and saturated zones were monitored around a low-lying granitic outcrop in eastern Ontario, Canada. Interpretation of the data indicated that the soil-rock contact around outcrop margins was the key pathway enabling midwinter infiltration and recharge. To support this conceptual model and further explore the role of outcrops in enhancing midwinter bedrock recharge, a numerical investigation was undertaken. Measured climate data (hourly time step) was used to govern the surface energy and water balances of a 1D finite difference model that incorporates frozen processes. Measured snow depth, soil moisture content, and soil temperature profiles were simulated. Simulations with vertical infiltration alone could not account for observed increases in moisture content in the deepest soil horizons. This is attributed to additional lateral flow along the unfrozen soil-rock contact that bypasses the frozen soil layers. Preliminary results support the concept that bedrock outcrops provide a window for midwinter infiltration since repeated winter melts reduce frozen soil permeability and inhibits vertical infiltration until the ground thaws. Results from the surface/near-surface simulations are used to guide the development of a 2D finite element model that includes heat and flow transport and ground freeze-thaw. The impacts to bedrock recharge under different rainfall and snowmelt scenarios as well as various outcrop geometries are explored. Results from these numerical experiments help provide greater insight into the processes driving enhanced midwinter bedrock recharge under conditions of warmer winters.</p>

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Improving Time Step Convergence in an Atmosphere Model With Simplified Physics: The Impacts of Closure Assumption and Process Coupling

Journal of Advances in Modeling Earth Systems ◽

10.1029/2019ms001982 ◽

2020 ◽

Vol 12 (10) ◽

Cited By ~ 1

Author(s):

Hui Wan ◽

Carol S. Woodward ◽

Shixuan Zhang ◽

Christopher J. Vogl ◽

Panos Stinis ◽

...

Keyword(s):

Time Step ◽

Atmosphere Model ◽

Process Coupling ◽

Closure Assumption

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Dynamical heating of the X-ray emitting intracluster medium: the roles of merger shocks and turbulence dissipation

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa1221 ◽

2020 ◽

Vol 495 (1) ◽

pp. 784-795 ◽

Cited By ~ 2

Author(s):

Xun Shi ◽

Daisuke Nagai ◽

Han Aung ◽

Andrew Wetzel

Keyword(s):

Temperature Increase ◽

Dominant Role ◽

Tracer Particle ◽

Dissipative Heating ◽

Relative Role ◽

Intracluster Medium ◽

Time Step ◽

X Ray ◽

Accretion Shock

ABSTRACT The diffuse plasma inside clusters of galaxies has X-ray emitting temperatures of a few keV. The physical mechanisms that heat this intracluster medium (ICM) to such temperatures include the accretion shock at the periphery of a galaxy cluster, the shocks driven by merger events, as well as a somewhat overlooked mechanism – the dissipation of intracluster turbulent motions. We study the relative role of these heating mechanisms using galaxy clusters in Lagrangian tracer particle re-simulations of the Omega500 cosmological simulation. We adopt a novel analysis method of decomposing the temperature increase at each time-step into the contribution from dissipative heating and that from adiabatic heating. In the high-resolution spatial–temporal map of these heating rates, merger tracks are clearly visible, demonstrating the dominant role of merger events in heating the ICM. The dissipative heating contributed by each merger event is extended in time and also occurs in the rarefaction regions, suggesting the importance of heating by the dissipation of merger-induced turbulence. Quantitative analysis shows that turbulence heating, rather than direct heating at merger shocks, dominates the temperature increase of the ICM especially at inner radii r < r500c. In addition, we find that many merger shocks can propagate with almost constant velocity to very large radii r ≫ r500c, some even reach and join with the accretion shock and becoming the outer boundary of the ICM. Altogether, these results suggest that the ICM is heated more in an ‘inside–out’ fashion rather than ‘outside–in’ as depicted in the classical smooth accretion picture.

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Income and Wealth Distributions from Stochastic Strategy Minority Game

Reports in Advances of Physical Sciences ◽

10.1142/s2424942417400035 ◽

2017 ◽

Vol 01 (01) ◽

pp. 1740003 ◽

Cited By ~ 1

Author(s):

Asim Ghosh ◽

Soumyajyoti Biswas

Keyword(s):

Stationary Distribution ◽

Distribution Functions ◽

Minority Game ◽

Time Step ◽

Self Organized ◽

Pareto’S Law ◽

Economic Interactions

We propose a version of the Minority Game where the agents at each time make investments either in terms of money or stock from their possessions. The amount of investments at each time step, and not the number of people opting for a choice, determines the ‘minority’. The invested money is returned to the stock investors and the invested stock is returned to the money investors in proportion of their respective investments at each time. In this way, agents in the less investment side faces higher demand, and hence are in ‘minority’, receiving higher pay-off for their investments. This dynamics lead the ‘market’ to a self-organized state. We measure the distributions of income of the agents at every step and also the accumulated wealth, both of which have a stationary distribution. The distribution functions follow Pareto’s law when the agents invest random fractions of their wealth. This reflects the role of heterogeneity in economic interactions.

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The Role of Time Step Size in Numerical Stability of Tangent Linear Models

Monthly Weather Review ◽

10.1175/1520-0493(2000)128<1562:trotss>2.0.co;2 ◽

2000 ◽

Vol 128 (5) ◽

pp. 1562-1572 ◽

Cited By ~ 18

Author(s):

Jiang Zhu ◽

Masafumi Kamachi

Keyword(s):

Numerical Stability ◽

Linear Models ◽

Step Size ◽

Time Step ◽

Time Step Size

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A quantitative evaluation of the role of the Argentinean Col and the Low Pressure Tongue East of the Andes for frontogenesis in the South American subtropics

Advances in Geosciences ◽

10.5194/adgeo-22-67-2009 ◽

2009 ◽

Vol 22 ◽

pp. 67-72 ◽

Cited By ~ 1

Author(s):

H. M. J. Barbosa ◽

J. M. Arraut

Keyword(s):

Potential Temperature ◽

Austral Summer ◽

Low Pressure ◽

Spatial Average ◽

South American ◽

The South ◽

Time Step ◽

The Andes ◽

Hourly Data

Abstract. Previous studies have found the South American subtropics to exhibit high climatological frontogenesis in equivalent potential temperature during the austral summer. An important contribution to this pattern is given by frontogenesis over the Argentinean Col (AC), which separates the Northwestern Argentinean Low (NAL) from transient troughs to the south of it. The NAL and the Low Pressure Tongue east of the Andes (LPT) promote efficient transport of Amazonian humidity to the subtropics during the incursion of transient disturbances over the continent. The convergence of this strong warm and humid flow with mid-latitude air brought into the subtropics by the disturbance occurs preferentially in the neighborhood of the AC. The main difficulty in quantifying the contribution of the NAL, AC and LPT structure to frontogenesis in the South American subtropics is the automatic detection of the AC and LPT. In this paper an algorithm developed to this end is briefly presented and applied to obtain statistics on the role of these structures in frontogenesis. Six-hourly data from ECMWF ERA-40 Reanalysis over 21 austral summer periods (December–March) is used. Occurrences of the AC are highly concentrated between 34–39° S and 66–69° W, being present in this region in 42% of the time instants analyzed. The spatial average of the positive values of the frontogenesis over this region was calculated for each time step as a measure of intensity and histograms were built for the cases when the AC was and was not found inside this region. Mean, median and mode are larger for the distribution of cases with the presence of the AC. In addition, we present the frequency of occurrence of the AC as a function of the frontogenesis, showing that it grows with the intensity of the frontogenesis, rising above the 0.955 quantile. We have not found any correlation between the AC frequency and the frontolysis intensity.

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