Evgeni Fedorovich | University of Oklahoma (original) (raw)

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Papers by Evgeni Fedorovich

Quarterly Journal of the Royal Meteorological Society, Dec 27, 2016

We study oscillations that develop in flows along a uniform planar slope in an initially resting ... more We study oscillations that develop in flows along a uniform planar slope in an initially resting stratified fluid as result of sudden application of a surface buoyancy flux. After an oscillatory adjustment (transition), the fluid reaches another steady state that corresponds to a stationary slope flow. The analysis is focused on the temporal evolution of the integral momentum and buoyancy structure in the laminar Prandtl-type slope flow. The main questions addressed are related to physical conditions leading to emerging of the en masse oscillations in the transitioning slope flow, the frequency of these oscillations, and features of their temporal evolution. The persistence of oscillations in Prandtl-type slope flows is found to be associated, somewhat paradoxically, with the fast temporal decay of the surface stress oscillations in the process of the stress approaching a constant value. This relatively rapid evolution of the surface stress progressively weakens damping of the integral momentum and buoyancy oscillations. Extensions of the analyses to the Prandtl slope flow driven by the surface buoyancy and to the turbulent slope flows are proposed and discussed.

Journal of the Atmospheric Sciences, Jul 22, 2020

The turbulence temperature spectrum and structure parameter are related through a widely adopted ... more The turbulence temperature spectrum and structure parameter are related through a widely adopted proportionality coefficient. We formally derive this expression, and present further evidence, to demonstrate that this coefficient is too large by a factor of 2.

HAL (Le Centre pour la Communication Scientifique Directe), 1999

98th American Meteorological Society Annual Meeting, Jan 10, 2018

Entrainment is critical to the development of the atmospheric convective boundary layer (CBL), bu... more Entrainment is critical to the development of the atmospheric convective boundary layer (CBL), but little is known about how entrainment is impacted by the aerosol radiative effect. An aerosol radiation transfer model is used in conjunction with large eddy simulation (LES) to quantify the impact of aerosol shortwave radiative heating on entrainment and thermodynamics of an idealized dry CBL under aerosol-loading conditions. An entrainment equation is derived within the framework of zero-order model (ZOM) with the aerosol radiative heating effect included; the equation is then examined against the LES outputs for varying aerosol optical depth (AOD) and free-atmosphere stratification scenarios. The results show that the heat flux profiles become more nonlinear in shape as compared to the case of the clean (no aerosol pollution) CBL, with degree of nonlinearity being highly dependent on the AOD of the layer for the given type of radiation-absorbing aerosols. As AOD increases, less solar radiation reaches the surface, thus the surface heat flux becomes smaller, and both actual (LES) and ZOM-derived entrainment flux ratios decrease. This trend is opposite to the clean CBL where the LES-predicted flux ratios show an increasing trend with diminishing surface heat flux, while the ZOM-calculated flux ratio remains constant. The modified dimensionless entrainment rate closely follows the-1 power law with a modified Richardson number. The study suggests that including the aerosol radiative effect may improve numerical air quality predictions for heavy air pollution events.

32nd Conf. on Agricultural and Forest Meteorology/22nd Symp. Boundary Layers and Turbulence/ Third Conf. on Atmospheric Biogeosciences (20 – 24 June, 2016), Jun 20, 2016

This paper describes one-dimensional (parallel) laminar and transitional regimes of natural conve... more This paper describes one-dimensional (parallel) laminar and transitional regimes of natural convection in a viscous stably stratified fluid due to temporally-periodic variations in the surface temperature of infinite vertical plates and cylinders. Analytical solutions are obtained for the periodic laminar regime for arbitrary values of stratification, Prandtl number and forcing frequency. The solutions for plates and cylinders are qualitatively similar and show that (i) the flows are composed of two waves that decay exponentially with distance from the surface; a fast long wave and a slow short wave, (ii) for forcing frequencies less than the natural frequency, both waves propagate away from the surface, while (iii) for forcing frequencies less than this natural frequency, the short wave propagates away from the surface while the long wave propagates toward the surface. The analytical results are complemented, for the plate problem, with three-dimensional numerical simulations of flows that start from rest and are suddenly subjected to a periodic thermal forcing. The numerical results depict the transient (start-up) stage of the laminar flow and the approach to the periodicity, and confirm that the analytical solutions provide the appropriate description of the periodic regime for the laminar convection case. Preliminary numerical data are presented for transition from the laminar to turbulent convection. NOMENCLATURE k-nondimensional wavenumber; R-nondimensional radial coordinate; ' T-perturbation temperature; T ∞-ambient temperature; W-nondimensional velocity along the plate; β-buoyancy parameter; θ-nondimensional temperature perturbation; κ-molecular thermal diffusivity; ξ-nondimensional plate-normal coordinate; τ-nondimensional time.

Buoyant Convection in Geophysical Flows, 1998

17th Symposium on Boundary Layers and Turbulence, May 25, 2006

Persistent katabatic winds, which in basic terms can be described as buoyantly driven, turbulent ... more Persistent katabatic winds, which in basic terms can be described as buoyantly driven, turbulent boundary layer flows along cooled sloping surfaces in a stratified environment, are typical for vast areas of the earth and play an important role in the local and regional climate. Even in their most idealized or elemental forms, these flows conflate two notoriously difficult aspects of atmospheric dynamics: turbulence and natural convection. Although much progress has been made in the conceptual understanding and numerical simulation of ...

EGU General Assembly Conference Abstracts, May 1, 2014

Boundary-Layer Meteorology

Dr. John R. Garratt's name has been synonymous with Boundary-Layer Meteorology-the journal and th... more Dr. John R. Garratt's name has been synonymous with Boundary-Layer Meteorology-the journal and the discipline-for over 40 years. John first joined the Editorial Board of Boundary-Layer Meteorology (BLM) in 1982; he served as an editor of the journal for 25 years and to this day plays a vitally important role in preserving the journal's aesthetic consistency and article quality. Over the course of his career, John made wide-ranging contributions to the discipline with seminal articles on flux-profile relations, landscape heterogeneity, and roughness modelling. He published several review articles that continue to serve as benchmark citations in contemporary research. His textbook "The Atmospheric Boundary Layer", published by Cambridge University Press in 1992, figures prominently in the reference collections of scientists, university instructors, and meteorology practitioners around the world.

This book has been awaited in the atmospheric boundary-layer research community for a long time. ... more This book has been awaited in the atmospheric boundary-layer research community for a long time. John Wyngaard, the author of the book, is by all counts an outstanding figure in the area of atmospheric turbulence studies. His contributions to the field are both numerous and exceptional. As a person, John comprises all the principal qualities of an outstanding scien-tist and academic: curiosity, witty mind, breadth of thinking, depth of understanding, healthy scepticism (also with respect to his own results), and readiness to share his knowledge with colleagues and students. I happened to come across John Wyngaard’s name at the beginning of the 1980s, while I was working on my Ph.D. dissertation in atmospheric boundary-layer modelling. His brilliant scientific articles profoundly shaped my interest in the quantitative aspects of boundary-layer meteorology. Apparently, they played the same role in the scien-tific careers of many other atmospheric boundary-layer researchers worldwide. ...

Analytical solution for katabatic flow induced by an isolated cold strip

Convective boundary layers (CBLs) driven by buoyancy forcings from the bottom or/and from the top... more Convective boundary layers (CBLs) driven by buoyancy forcings from the bottom or/and from the top and capped by temperature (density) inversions are commonly observed in the lower portion of earth’s atmosphere (Holtslag and Duynkerke 1998). During fairweather daytime conditions, the buoyancy forcing in the boundary layer is primarily represented by convective heat transfer from a warm underlying surface. Such buoyancy forcing generates upand downward motions that effectively mix momentum and scalar fields inside the CBL. Due to active mixing, the wind velocity, potential temperature (buoyancy), and concentrations of atmospheric constituents in the main portion of the CBL (often referred to as convectively mixed layer) do not change considerably with height when averaged over horizontal planes or over time. A typical CBL can be subdivided into three separate layers: the surface layer, in which the meteorological variables change fairly rapidly with height; the mixed layer, where mean...

Results are presented from a series of analytical and numerical studies of buoyantly driven flows... more Results are presented from a series of analytical and numerical studies of buoyantly driven flows along heated vertical surfaces immersed in stably stratified fluids. Flows of the studied type are broadly represented in engineering and geophysical applications. First, the classical problem of one-dimensional natural convection flow along a heated wall is revisited for the case of a stably stratified ambient fluid. The study then focuses on laminar natural convection in a viscous stably stratified fluid resulting from temporally periodic variations in the wall surface temperature. Finally, scaling relationships are proposed for the turbulent convection flow along a heated wall and verified based on results of direct numerical simulations.