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Additional affiliations
September 2016 - present
July 2010 - August 2016
August 2005 - July 2010
Education
August 2000 - December 2004
January 1999 - July 2000
July 1994 - June 1998
Publications
Publications (144)
In this paper, we revisit a well-known formulation of temperature structure parameter (CT2\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$C_T^2$$\end{document}), origin...
In this study, we utilize a novel approach to solve the Ekman equations for eddy-viscosity profiles in the stable boundary-layer. By doing so, a well-known expression for the stable boundary-layer height by Zilitinkevich (Boundary-Layer Meteorology, 1972, Vol. 3, 141-145) is rediscovered.
Turbulent fluctuations of the atmospheric refraction index, so-called optical turbulence, can significantly distort propagating laser beams. Therefore, modeling the strength of these fluctuations ( $C_n^2$ C n 2 ) is highly relevant for the successful development and deployment of future free-space optical communication links. In this Letter, we pr...
Plain Language Summary
Low‐level marine clouds in satellite images often reveal vortex streets formed by two rows of counter‐rotating vortices on the leeward side of isolated mountainous islands. This phenomenon is called the “atmospheric von Kármán vortex street” (AVKVS) and has been investigated by satellite observations, laboratory experiments,...
Peak wind gust (Wp) is a crucial meteorological variable for wind farm planning and operations. However, for many wind farm sites, there is a dearth of on-site measurements of Wp. In this paper, we propose a machine-learning approach (called INTRIGUE, decIsioN-TRee-based wInd GUst Estimation) that utilizes numerous inputs from a public-domain reana...
The growing demand for global wind power production, driven by the critical need for sustainable energy sources, requires reliable estimation of wind speed vertical profiles for accurate wind power prediction and comprehensive wind turbine performance assessment. Traditional methods relying on empirical equations or similarity theory face challenge...
Advancements in floating offshore wind energy are unlocking the potential of the coastal waters of Portugal for the installation of wind farms. A thorough evaluation of coastal effects and variability across different time scales is crucial to ensure successful offshore wind farm investments. State-of-the-art atmospheric reanalysis datasets fall sh...
The increasing global demand for wind power underscores the importance of understanding and characterizing extreme ramp events, which are significant fluctuations in wind power generation over short periods, that pose challenges for grid integration. This study focuses on modeling frontal low-level jets (FLLJs) and associated extreme ramp-down even...
This study introduces OTCliM (Optical Turbulence Climatology using Machine learning), a novel approach for deriving comprehensive climatologies of atmospheric optical turbulence strength ($C_n^2$) using gradient boosting machines. OTCliM addresses the challenge of efficiently obtaining reliable site-specific $C_n^2$ climatologies, crucial for groun...
For free-space optical communication or ground-based optical astronomy, ample data of optical turbulence strength ( $C_n^2$ C n 2 ) are imperative but typically scarce. Turbulence conditions are strongly site dependent, so their accurate quantification requires in situ measurements or numerical weather simulations. If $C_n^2$ C n 2 is not measured...
We present a machine learning-based measure-correlate-predict approach that predicts a multi-year time-series of optical turbulence strength ( C n ² ) with high accuracy ( r ¯= 0.78 at 16 locations) based on a single year of in-situ C n ² measurements and reanalysis data.
A mesoscale model is used to systematically investigate how the incoming flow incidence angle affects the development of atmospheric von Kármán vortex streets for non-axisymmetric islands. The analysis is focused on an event observed on the leeward side of Guadalupe Island. By keeping the synoptic conditions the same, several simulations are perfor...
Turbulent fluctuations of the atmospheric refraction index, so-called optical turbulence, can significantly distort propagating laser beams. Therefore, modeling the strength of these fluctuations ($C_n^2$) is highly relevant for the successful development and deployment of future free-space optical communication links. In this letter, we propose a...
Peak wind gust (Wp) is a crucial meteorological variable for wind farm planning and operations. However, for many wind farm sites, there is a dearth of on-site measurements of (Wp). In this paper, we propose a machine-learning approach (called INTRIGUE) that utilizes numerous inputs from a public-domain reanalysis dataset, and in turn, generates lo...
Only a few studies on the overall impact of climate change on offshore wind power production and wind power ramps in the North Sea region have been published. This study focuses on the characteristics of expected wind power production and wind power ramps in the future climate aided by the classification of circulations patterns using a self-organi...
Wind energy is anticipated to play a central role in enabling a rapid transition from fossil fuels to a system based largely on renewable power. For wind power to fulfill its expected role as the backbone – providing nearly half of the electrical energy – of a renewable-based, carbon-neutral energy system, critical challenges around design, manufac...
As wind and solar power play increasingly important roles in the European energy system, unfavourable weather conditions, such as ‘Dunkelflaute’ (extended calm and cloudy periods), will pose ever greater challenges to transmission system operators. Thus, accurate identification and characterization of such events from open data streams (e.g., reana...
Wind energy is anticipated to play a central role in enabling a rapid transition from fossil fuels to a system based largely on renewable power. For wind power to fulfill its expected role as the backbone—providing nearly half of the electrical energy—of a renewable-based, carbon-neutral energy system, critical challenges around design, development...
In this study, we utilize a novel approach to solve the Ekman equations for eddy viscosity profiles in the stable boundary layer. By doing so, a well-known expression for the stable boundary layer height by Zilitinkevich (Boundary-Layer Meteorology, 1972, Vol. 3, 141--145) is rediscovered.
Recently, Basu and Holstlag (2021) proposed a unified f ramework f or describing outer length scales (OLS). By utilizing this framework, we document various characteristics of OLS in nocturnal boundary layers over the US Great Plains.
In this study, the stability dependence of turbulent Prandtl number (Pr t) is quantified via a novel and simple analytical approach. Based on the variance and flux budget equations, a hybrid length scale formulation is first proposed and its functional relationships to well-known length scales are established. Next, the ratios of these length scale...
In the coming decades, the European energy system is expected to become increasingly reliant on non-dispatchable generation such as wind and solar power. Under such a renewable energy scenario, a better characterization of the extreme weather condition ‘Dunkelflaute’, which can lead to a sustained reduction of wind and solar power, is important. In...
Thunderstorm downbursts have been reported to cause damage or failure to wind turbine arrays. We extend a large-eddy simulation model used in previous work to generate downburst-related inflow fields with a view toward defining correlated wind fields that all turbines in an array would experience together during a downburst. We are also interested...
In this study, the stability dependence of turbulent Prandtl number ($Pr_t$) is quantified via a novel and simple analytical approach. Based on the variance and flux budget equations, a hybrid length scale formulation is first proposed and its functional relationships to well-known length scales are established. Next, the ratios of these length sca...
Large-scale weather patterns and their variability can influence both the amount of wind power production and its temporal variation, i.e., wind power ramps. In this study, we use a self-organizing map to cluster hourly sea level pressure into a discrete number of weather patterns. The dependency of wind power production and wind power ramps on the...
In this paper, we revisit a well-known formulation of temperature structure parameter ($C_T^2$), originally proposed by V.~I.~Tatarskii. We point out its limitations and propose a revised formulation based on turbulence variance and flux budget equations. Our formulation includes a novel physically-based outer length scale which can be estimated fr...
We use a database of direct numerical simulations to evaluate parametrizations for energy dissipation rate in stably stratified flows. We show that shear-based formulations are more appropriate for stable boundary layers than commonly used buoyancy-based formulations. As part of the derivations, we explore several length scales of turbulence and in...
In this study, we explore several integral and outer length scales of turbulence which can be formulated by using the dissipation of temperature fluctuations (χ\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\...
We have identified certain fundamental limitations of a mixing-length parametrization used in a popular turbulent kinetic energy-based subgrid-scale model. Replacing this parametrization with a more physically realistic one significantly improves the overall quality of the large-eddy simulation (LES) of stable boundary layers. For the range of grid...
Knowledge about the expected duration and intensity of wind power ramps is important when planning the integration of wind power production into an electricity network. The detection and classification of wind power ramps is not straightforward due to the large range of events that is observed and the stochastic nature of the wind. The development...
The high-fidelity modeling of optical turbulence is critical to the design and operation of a new class of emerging highly-sophisticated astronomical telescopes and adaptive optics instrumentation. In this study, we perform retrospective simulations of optical turbulence over the Hawaiian islands using a mesoscale model. The simulated results are v...
In polar regions, where the boundary layer is often stably stratified, atmospheric models produce large biases depending on the boundary-layer parametrizations and the parametri-zation of the exchange of energy at the surface. This model intercomparison focuses on the very stable stratification encountered over the Antarctic Plateau in 2009. Here,...
In the coming decades, both wind and solar power production will be playing increasingly important roles in Europe's energy economy. It is absolutely essential that power grids are resilient against any unusual weather phenomena. One such meteorological phenomenon, "Dunkelflaute", is causing serious concern to the renewable energy industry, which i...
Large-scale weather systems have the potential to modulate offshore wind energy production. The Northern European sea areas have recently seen a rapid increase in wind power capacity and thus there is a need to understand how different weather systems affect offshore production from the perspective of energy system integration. In this study, mean...
In the near future, wind and solar generation are projected to play an increasingly important role in Europe's energy sector. With such fast‐growing renewable energy development, the presence of simultaneous calm wind and overcast conditions could cause significant shortfalls in production with potentially serious consequences for system operators....
Abstract. Knowledge about the expected duration and intensity of wind power ramps is important when planning the integration of wind power production into an electricity network. How to detect and classify wind power ramps is not straightforward due to the large range of events that are observed and the stochastic nature of the wind. The developmen...
In this study, we have identified certain fundamental limitations of a mixing length parameterization used in a popular turbulent kinetic energy-based subgrid-scale model. Replacing this parameterization with a more physically realistic one significantly improves the overall quality of the large-eddy simulations (LESs) of stable boundary layers. Fo...
We develop and study two approaches for the prediction of optical refraction effects
in the lower atmosphere. Refraction can cause apparent displacement or distortion of targets
when viewed by imaging systems or produce steering when propagating laser beams. Low-cost,
time-lapse camera systems were deployed at two locations in New Mexico to measure...
In this study, we explore several integral and outer length scales of turbulence which can be formulated by using the dissipation of temperature fluctuations ($\chi$) and other relevant variables. Our analyses directly lead to simple yet non-trivial parameterizations for both $\chi$ and the structure parameter of temperature ($C_T^2$). For our purp...
In this study, we have proposed an automated classification approach to identify meaningful patterns in wind field data. Utilizing an extensive simulated wind database, we have demonstrated that the proposed approach can identify low‐level jets, near‐uniform profiles, and other patterns in a reliable manner. We have studied the dependence of these...
We use a database of direct numerical simulations to derive parameterizations for energy dissipation rate in stably stratified flows. We show that shear-based formulations are more appropriate for stable boundary layers than commonly used buoyancy-based formulations. As part of the derivations, we explore several length scales of turbulence and inv...
Kolmogorov’s 1941 hypothesis on local isotropy is only applicable for scales smaller than the outer length scales (OLS). By utilizing data from direct numerical simulations and wind tunnel experiments, we quantify OLS in stratified flows.
Severe winds produced by thunderstorm downbursts pose a serious risk to the structural integrity of wind turbines. However, guidelines for wind turbine design (such as the International Electrotechnical Commission Standard, IEC 61400-1) do not describe the key physical characteristics of such events realistically. In this study, a large-eddy simula...
The late afternoon hours in the diurnal cycle precede the development of the nocturnal stable boundary layer. This “evening transition” (ET) period is often when energy demand peaks. This period also corresponds to the time of day that is a precursor to late‐afternoon downbursts, a subject of separate interest. To capture physical characteristics o...
The Monin–Obukhov similarity theory-based wind speed and potential temperature profiles are inherently coupled to each other. We have developed hybrid approaches to disentangle them, and as a direct consequence, the estimation of Obukhov length (and associated turbulent fluxes) from either wind-speed or temperature measurements becomes an effortles...
We propose an approach to estimate a proxy for the outer length scale, and in turn C n 2, by utilizing the ascent rates of radiosondes. For validation, we use observational data from the T-REX field campaign.
Computes Fried number, isoplanatic angle, seeing, and scintillation rate from a vertical profile of Cn2.
Utilizing the so-called Thorpe scale as a measure of the turbulence outer scale, we propose a physically-based approach for the estimation of Cn2 profiles in the lower atmosphere. This approach only requires coarse-resolution temperature profiles (a.k.a., soundings) as input, yet it has the intrinsic ability to capture layers of high optical turbul...
This function computes friction velocity (u*), sensible heat flux (wT), and Obukhov length (L) from three-level wind speed data. For a detailed description of the proposed approach, please refer to:
Basu, S. (2018). "A simple recipe for estimating atmospheric stability solely based on surface‐layer wind speed profile", Wind Energy, 21(10), 937-941...
Downburst events initialized at various hours during the evening transition (ET) period are simulated to determine the effects of ambient stability on the outflow of downburst winds. The simulations are performed using a pseudo-spectral large eddy simulation model at high resolution to capture both the large-scale flow and turbulence characteristic...
The wind energy community is gradually recognizing the significance of atmospheric stability in both power production and structural loading. However, estimating stability requires temperature gradient data which are not commonly measured by the wind farm developers or operators. To circumvent this problem, we propose a simple approach á la Swinban...
We analyzed several multiyear wind speed datasets from 4 different geographical locations. The probability density functions of wind ramps from all these sites revealed remarkably similar shapes. The tails of the probability density functions are much heavier than a Gaussian distribution, and they also systematically depend on time increments. Quit...
A newly developed coupled modeling approach is utilized to simulate optical wave propagation over an urban area. The simulated results are validated against a time-lapse imagery-based unique dataset of refractive index gradient.
Atmospheric modeling shows that strong refractive index gradients can appear in the surface layer during certain periods of the diurnal cycle. These gradients and associated turbulence can significantly impact laser beam propagation.
Downburst events initialized at various hours during the evening transition (ET) period are simulated to determine the effects of ambient stability on the outflow of downburst winds. The simulations are performed using a pseudo-spectral large eddy simulation model at high resolution to capture both the large-scale flow and turbulence characteristic...
Accurate and timely model simulations of rainfall in cities are of critical importance for reliable prediction of water levels and flows, overflow from sewers, and predicting urban flood events. Ongoing development of forecasting systems are happening for the cities of Aalborg, Helsinki, Rotterdam, and Stockholm in the framework of the MUFFIN (Mult...
Severe winds from thunderstorm outflows pose a challenge to wind turbine arrays. They can cause significant power ramps and disruption in energy production. They can also cause extreme structural damage to turbines as was seen in the severe storm event over the Buffalo Ridge Wind Farm on July 1, 2011. At this southwestern Minnesota site, blades fro...
The late afternoon hours in the diurnal cycle precede the development of the nocturnal stable boundary layer. This so-called evening transition (ET) period is often when energy demands peak. To capture physical characteristics of the wind fields in the atmospheric boundary layer (ABL) - particularly the interplay of shear and turbulence - during th...
Utilizing synthetically generated random variates and laboratory measurements, we document the inherent limitations of the conventional structure function approach in limited sample size settings. We demonstrate that an alternative approach, based on the principle of maximum likelihood, can provide nearly unbiased structure function estimates with...
Accurate simulation and forecasting of over-the-horizon propagation events are essential for various civilian and defense applications. We demonstrate the prowess of a newly proposed coupled mesoscale modeling and ray tracing framework in reproducing such an event. Wherever possible, routinely measured meteorological data from various platforms (e....
In several recent large-eddy simulation studies, the lowest grid level was located well within the roughness sublayer. Monin–Obukhov similarity-based boundary conditions cannot be used under this scenario, and in this note we elaborate on this fundamental problem and suggest potential solutions.
In this Letter, via idealized and realistic case studies, we have documented the limitations of several conventional metrics in validating C n 2 profile predictions. We have introduced the (normalized) Kantorovich metric as a viable alternative and demonstrated its prowess.
In this Letter, an artificial neural network (ANN) approach is proposed for the estimation of optical turbulence ( C n 2 ) in the atmospheric surface layer. Five routinely available meteorological variables are used as the inputs. Observed C n 2 data near the Mauna Loa Observatory, Hawaii are utilized for validation. The proposed approach has demon...