This study investigates the meteorological characteristics and associated human thermal discomfort of downslope windstorms known as 'Vento Norte' (VNOR; 'North Wind' in Portuguese) occurring in the city of Santa Maria, southern Brazil, over 20 years (2004-2023). VNOR events are characterized by unseasonable strong northerly winds, abrupt temperature rises and significant drops in relative humidity. Utilising hourly meteorological data, we identified 189 VNOR episodes, predominantly occurring during austral winter months (June-August), reflecting a seasonal pattern. VNOR events significantly altered local thermal comfort conditions, as demonstrated through a comparative analysis of five biometeorological indices: Effective Temperature with Wind (TEFW), Thermal Discomfort Index (TDI), Temperature-Humidity Index (THI), Human Discomfort Index (HDI) and Humidex (HU). Statistical analyses revealed significant differences between VNOR and non-VNOR periods, with VNOR episodes consistently associated with elevated human thermal discomfort. A detailed examination of representative events further illustrated abrupt changes in meteorological parameters, highlighting the potential for rapid thermal stress in the local population. The present analysis demonstrates the importance of monitoring VNOR phenomena and their thermal impacts and suggests how these downslope windstorms alter local atmospheric conditions, providing an environmental baseline that could support future risk-awareness frameworks and biometeorological monitoring protocols in southern Brazil.

Abstract Taylor diffusion model and forms for the autocorrelation functions are employed to derive turbulent dissipation rates. These formulations contain a numerical coefficient nc and are written in terms of turbulent scales associated with the energy-containing eddies. The derivation generates negative terms in the dispersion parameters that decrease the turbulent dispersion process. The used methodology allows one to connect the negative terms with the inertial range frequencies. The introduction of the inertial range autocorrelation functions in the Taylor diffusion model provides a dispersion parameter with a negative term. Therefore, the negative terms of the dispersion parameters are compared with the negative term of the inertial range dispersion parameter. The comparison provides equations for the turbulent dissipation rates containing the Kolmogorov constant and numerical coefficients. The analysis comparing observed and derived dissipation rate magnitudes selects a magnitude of nc = 2 for the numerical coefficient. Therefore, this value of nc = 2, originated by the choice of the exponential autocorrelation function, seems to be the magnitude that should be used in turbulence models. The present investigation exhibits the non-universal character of the dissipation coefficient and establishes magnitudes for this coefficient that are in accordance with values discovered in the literature.

This study examines a typical episode of a downslope windstorm known as “Vento Norte” (VNOR; “North Wind” in Portuguese) in the state of Rio Grande do Sul, Brazil. The temporal and spatial evolution of the VNOR episode is analyzed by means of sonic anemometer data collected at 10 vertical levels on a 30 m tower, two automated weather stations located at contrasting topographies, and radiosonde data launched twice daily. The primary focus is on the nighttime period that precedes the onset of the VNOR at the surface. The wind and potential temperature profiles showed that this episode was accompanied by a northerly nocturnal low‐level jet peaking at near the terrain slope. A stable boundary layer (SBL) characterized by easterly light winds developed at low elevations in the orographic depression. The Scorer parameter indicated an atmospheric profile favorable to the development of low‐level wave trapping around 500 m. A micrometeorological analysis revealed intense and persistent wave activity near ground level preceding the onset of the VNOR. Wavelet spectral analyses suggested the presence of gravity waves with 5 min time‐scales during this period. These oscillations, initially detected at the tower's high elevations, became more persistent and propagated to the bottom of the SBL as the night advanced. The wave‐like structures were associated with intermittent bursts of turbulence influencing the exchange processes at the surface layer and impacting the SBL flow patterns. This study highlights the dynamics of the VNOR and their multiscale interactions, providing insights into the understanding of the main flow characteristics in such conditions.

The primary focus of this article is to derive a solution to obtain the asymptotic turbulent dispersion parameter provided by the spectral Taylor statistical diffusion model. Unlike previous articles, which employed the Dirac delta function to solve the eddy diffusivity formula, in this study, we used the Dirac delta function properties to obtain directly the asymptotic turbulent dispersion parameter from the particles’ spatial dispersion variance described in terms of the Eulerian turbulence spectrum and of the scale factor defined formally as the ratio between Lagrangian and Eulerian timescales. From the Kolmogorov 1941 theory, a detailed derivation for this scale factor is presented. Furthermore, using high mean wind speed data generated by local topographic features, a magnitude for the Kolmogorov constant for the neutral atmospheric boundary layer is evaluated. Thus, this magnitude when added to other values obtained from the selected studies found in the literature provides an average value for the Kolmogorov constant that agrees with large eddy simulation data results. Therefore, this average value allows to obtain a more reliable description of this scale factor. Finally, employing analytical formulations for the observed neutral turbulent spectra and for the velocity variances as well as turbulent statistical quantities measured in a surface neutral atmospheric boundary layer, a vertical dispersion parameter is derived. This vertical dispersion parameter when utilized in a simple Gaussian diffusion model is able to reproduce well contaminant observed concentrations.The Gaussian simulated concentrations also compare well with those simulated by a Lagrangian stochastic particle dispersion model that uses observed vertical spectral peak frequency values at distinct levels of the neutral surface boundary layer. Therefore, the present study shows that the observational determination of a single vertical spectral peak frequency is sufficient to obtain a realistic vertical dispersion parameter characterizing the dispersive effect in the turbulent environment of the surface neutral atmospheric boundary layer.

An alternative solution to the asymptotic Taylor statistical diffusion theorem (variance of particle dispersion) and the asymptotic variance quantifying convergence of averages is presented.The solution approach is to identify a representation of the Dirac delta function for large times in the same integral occurring in both variances.This particular function acts as an effective filter and provides a way to obtain an analytical solution.Considering these asymptotic dispersion parameters in a Gaussian diffusion model, analysis of the simulated concentration results shows that the model reproduces well the experimental ground-level concentration data.The variance between the temporal and ensemble averages is evaluated using turbulent observational data collected in a convective boundary layer.The results show that the difference between the temporal and ensemble means is of the order of 5% for an average time window of 1800 s.The present development can be used in a variety of situations involving different types of turbulence.

In this contribution to the Festschrift for Prof. Remo Ruffini, we investigated a formulation of quantum gravity based on the Wheeler-DeWitt (WDW) equation combined with the classical concepts of the branch-cut cosmology, which contemplates as a new scenario for the origin of the Universe, a smooth transition region between the contraction phase, prior to the primordial singularity, and the subsequent expansion phase. Through the introduction of an energy-dependent effective potential, which describes the space-time curvature associated with the embedding geometry and its coupling with the cosmological constant and matter fields, solutions of the WDW equation for the wave function of the Universe are obtained. The Lagrangian density is quantized through the standard procedure of raising the Hamiltonian, the helix-like complex scale factor of branched cosmology as well as the corresponding conjugate momentum to the category of quantum operators. As a novelty, ambiguities in the ordering of the quantum operators are overcome with the introduction of a set of ordering factors α, whose values are restricted to the integers α=[0,1,2], since non-integers have no physical meaning, allowing this way a broader class of solutions for the wave function of the Universe. As another novelty, additional energy-dependent parametrizations are considered, more specifically, in addition to a branched universe filled with underlying background vacuum energy, matter and radiation, in order to make contact with standard model calculations, we additionally supplement the formulation with baryon matter, dark matter and quintessence contributions. As an additional novelty, the boundary conditions for the wave function of the Universe are imposed by assuming the Bekenstein criterion. Our results indicate this way, as a novelty conclusion, the consistency of a topological quantum leap, or alternatively a quantum tunneling, for the transition region of the early universe in contrast to the classic branched cosmology view of a smooth transition.

In this contribution to the Festschrift for Prof. Remo Ruffini, we investigate a formulation of quantum gravity using the Hořava–Lifshitz theory of gravity, which is General Relativity augmented by counter-terms to render the theory regularized. We are then led to the Wheeler–DeWitt (WDW) equation combined with the classical concepts of the branch-cut gravitation, which contemplates as a new scenario for the origin of the Universe, a smooth transition region between the contraction and expansion phases. Through the introduction of an energy-dependent effective potential, which describes the space-time curvature associated with the embedding geometry and its coupling with the cosmological constant and matter fields, solutions of the WDW equation for the wave function of the Universe are obtained. The Lagrangian density is quantized through the standard procedure of raising the Hamiltonian, the helix-like complex scale factor of branched gravitation as well as the corresponding conjugate momentum to the category of quantum operators. Ambiguities in the ordering of the quantum operators are overcome with the introduction of a set of ordering factors α, whose values are restricted, to make contact with similar approaches, to the integers α=[0,1,2], allowing this way a broader class of solutions for the wave function of the Universe. In addition to a branched universe filled with underlying background vacuum energy, primordial matter and radiation, in order to connect with standard model calculations, we additionally supplement this formulation with baryon matter, dark matter and quintessence contributions. Finally, the boundary conditions for the wave function of the Universe are imposed by assuming the Bekenstein criterion. Our results indicate the consistency of a topological quantum leap, or alternatively a quantum tunneling, for the transition region of the early Universe in contrast to the classic branched cosmology view of a smooth transition.

This study investigates a summer heat wave (HW) associated with downslope winds (DWs) affecting the central region of the state of Rio Grande do Sul (RS), Brazil. The temporal evolution of both phenomena is analyzed in the atmospheric boundary layer (ABL) using a combination of micrometeorological and rawinsonde data. For spatial characterization, ERA-5 reanalysis data are used. The HW covered a large area in southern Brazil, Argentina, and Paraguay. The main features of the HW were locally enhanced in the central region of RS by the development of DWs. The establishment of DWs near the surface depends on the dynamics of the ABL and local topographic features. The results showed that DWs that occurred during the HW contributed to the extreme temperatures and were associated with strong northerly winds, low relative humidity, and a drop in the dew points. Together, these extreme events influenced the turbulent and mean flow patterns of the ABL. The increase in turbulent activity associated with the warming of the ABL favored enhanced growth of morning ABL, while at night the simultaneous effects of radiative and turbulence cooling inhibited the formation of a strong stable ABL. The analysis highlights the complex interplay of synoptic and local factors associated with DWs and HW.

The influence of coherent vortices on the turbulence structure above and below a dense plant canopy is investigated using turbulence measurements collected at five levels on top and inside a coniferous forest on an Alpine Plateau. Five different stability regimes, from free convection to very stable stratification, were identified and considered in the analysis. Coherent structures are detected by fitting the vertical velocity auto-correlation functions with a theoretical oscillating function. This allowed to evaluate the coherent vortices characteristic timescales and to discriminate between turbulent data subsets characterized by fine-scale turbulence and subsets in which turbulence is dominated by coherent structures generated at the canopy top. An original methodology to fit cross-correlation function and to single out the most energetic frequency in presence of periodic behaviour is presented and applied to the turbulent momentum flux. The analysis shows how not far from neutral conditions the dominant time scale of the momentum flux is mainly determined by the longitudinal wind velocity component, rather than vertical one, while in free convection and very stable conditions coherent vortices do not seem to influence the momentum transport, dominated by large-scale structures. This is confirmed by the fine-scale turbulence and coherent structures efficiency in turbulence transport throughout the stability regimes.

In this contribution, motivated by the quest to understand cosmic acceleration, based on the theory of Hořava–Lifshitz and on the branch-cut gravitation, we investigate the effects of non-commutativity of a mini-superspace of variables obeying the Poisson algebra on the structure of the branch-cut scale factor and on the acceleration of the Universe. We follow the guiding lines of a previous approach, which we complement to allow a symmetrical treatment of the Poisson algebraic variables and eliminate ambiguities in the ordering of quantum operators. On this line of investigation, we propose a phase-space transformation that generates a super-Hamiltonian, expressed in terms of new variables, which describes the behavior of a Wheeler–DeWitt wave function of the Universe within a non-commutative algebraic quantum gravity formulation. The formal structure of the super-Hamiltonian allows us to identify one of the new variables with a modified branch-cut quantum scale factor, which incorporates, as a result of the imposed variable transformations, in an underlying way, elements of the non-commutative algebra. Due to its structural character, this algebraic structure allows the identification of the other variable as the dual quantum counterpart of the modified branch-cut scale factor, with both quantities scanning reciprocal spaces. Using the iterative Range–Kutta–Fehlberg numerical analysis for solving differential equations, without resorting to computational approximations, we obtained numerical solutions, with the boundary conditions of the wave function of the Universe based on the Bekenstein criterion, which provides an upper limit for entropy. Our results indicate the acceleration of the early Universe in the context of the non-commutative branch-cut gravity formulation. These results have implications when confronted with information theory; so to accommodate gravitational effects close to the Planck scale, a formulation à la Heisenberg’s Generalized Uncertainty Principle in Quantum Mechanics involving the energy and entropy of the primordial Universe is proposed.

Circulações atmosféricas induzidas por forçantes de escalas sinótica e meso podem influenciar as características de fluxos turbulentos na camada limite atmosférica (STEFANELLO et al., 2020).Particularmente, escoamentos descendentes, a sotavento de declividades de terreno, requerem uma atenção especial, pois as suas manifestações modificam e intensificam a atividade turbulenta (GARRATT, 1988).Este padrão de escoamento topográfico

Downslope windstorm known as Vento Norte (VNOR; Portuguese for “North Wind”) is a common phenomenon that occurs in southern Brazil during the winter season. Hence, this study attempted to investigate the climatological characteristics of VNOR using seventeen years (2004–2020) of hourly observations collected at seven meteorological stations distributed over the central region of Rio Grande do Sul State. The VNOR windstorm episodes are identified by intense wind gusts and warm air advection from the northern direction. They were selected from the data set obtained during the winter in the city of Santa Maria (SM). Statistical analysis showed that the detected VNOR events were characterized by mean wind gusts ≈15 m.s-1, mean wind direction of 350° and mean air temperature of 27 °C. Average duration of the events was about 9 h, with the longest event lasting 21 h. Characteristics and effects of this phenomenon were compared with those in other locations (meridional and zonal sections). Average values of wind gusts from the northern direction presented a significant increase of ≈200% for the winter period in SM. Nonetheless, a less significant increase in wind gusts was recorded in the meridional (28%) and zonal (41%) sections away from SM. The central location of SM has favorable topographic characteristics for this amplification, with a sharp altitude difference caused by the plateau- plain interface of ≈300 m. Our findings showed that the VNOR phenomenon mainly affects the climate of the southern region of Brazil, with a local amplification in the city of SM.

The air temperature anomaly was analysed in 16 consecutive winters from 2004 to 2019 in southern Brazil using reanalysis data and hourly atmospheric observations. In this study, 13 heat wave (HW) episodes were identified using the percentile methodology. All identified episodes are associated with the occurrence of a downslope windstorm known as Vento Norte (VNOR; Portuguese for ‘North Wind’). The VNOR is characterized by a sharp increase in air temperature combined with constant, strong, gusty winds from the north and a drop in relative humidity. The average duration was about 5 days for HW and 18 h for VNOR being than in 59.5% of the HW hours, the VNOR windstorm was also detected. The main atmospheric variables were compared during the periods of winter, HW and the VNOR windstorm. The analysis showed that HW alters local weather and climate conditions, with the more pronounced features associated with the VNOR flow. A more detailed investigation comparing the atmospheric variables collected north and south of an abrupt change in terrain altitude (400 m) revealed that the main cause of the amplification of the atmospheric variable anomalies in the centre of the state of Rio Grande do Sul was the simultaneous occurrence of HW and VNOR.

Large‐scale nonturbulent motions are investigated using high‐resolution direct numerical simulations of the turbulent Ekman layer at a moderate Reynolds number. In particular, the role of stable stratification effects in the generation and amplification of large‐scale oscillations in the wind‐speed components and buoyancy is analysed. Eulerian autocorrelation functions (EAFs) and spectral analysis help to describe and characterize such modes as meandering‐like structures. Focus is given to the strong stability cases, where vertical turbulent motions are damped and large‐scale modes drive near‐wall patterns of flow laminarization. Horizontal meandering arises in the near‐wall region when the ratio of vertical wind‐speed variance to horizontal wind‐speed variance decreases to small orders of magnitude. In the case of strong stratification, the characteristic features of meandering motion were identified as negative lobes in the EAF, with corresponding low‐frequency peaks in the horizontal wind speed and buoyancy spectra. The Ekman configuration used reproduced the development of meandering‐like structures satisfactorily in strong stable conditions, as indicated by field observations of the stable boundary layer and its dependence on the level of stratification. At strong stability, the Rotta model constant, which represents the relationship between the dissipation and return to isotropy terms in the velocity variance budget, is shown to vary with stability.

The aim of this paper is to analyse the thermal effects in a wind tunnel experiment to simulate the planetary boundary layer (PBL). Experiments were performed in the wind tunnel of the Laboratory of Constructions Aerodynamics at the Federal University of Rio Grande do Sul, Porto Alegre, Rio Grande do Sul State, Brazil. This wind tunnel is a closed return low-speed wind tunnel specifically designed for dynamic and static studies on civil construction models. As a novelty, one of the experimental sections of the wind tunnel was equipped with a metal sheet with Peltier elements coupled to it. In other words, thermal effects generating new flow patterns become feasible and open pathways to compare wind tunnel simulations to those in the PBL. Furthermore, measurements obtained with the smooth floor of the wind tunnel were repeated under the same conditions with the addition of the roughness in the floor, and the mechanical turbulence generated by the surface roughness significantly amplified the exchange of momentum and heat between the regions located in vertical direction of the wind tunnel boundary layer. In the presence of turbulent heat flux near the surface, thermal effects contribute to the increase of the turbulence intensity. Turbulent energy spectra for flow velocities and different heights were obtained using the Hilbert–Huang transform method, and the observed convective turbulence energy spectra behavior reproduced those measured in an unstable surface PBL.

The sudden increase in air temperature associated with strong gusty winds of northerly direction is a phenomenon occasionally observed during the cold season in the central region of Rio Grande do Sul (RS) state, located in extreme southern Brazil. This geophysical flow, which is known as Vento Norte (VNOR; Portuguese for “North Wind”), promotes temperature variations that depart significantly from the local cold-season climatology. In this study, eleven years of surface meteorological observations collected at seven weather stations distributed over central RS are employed to investigate the regional extension of the effects of the VNOR windstorm. The analysis revealed that the sharp increase in temperature and in wind magnitude caused by VNOR is observed over a rather wide region of central RS. However, it is in the vicinities of the city of Santa Maria, located just south of an abrupt drop in terrain elevation, that the most intense VNOR effects are observed suggesting a downslope enhancement of the windstorm. A detailed investigation of the meteorological data also showed that the duration of the VNOR windstorm is well correlated with the magnitude of the maximum wind gusts, with the most intense VNOR events also lasting longer. VNOR events occur more frequently in the period between the morning (0700 LST) and early afternoon (1400 LST). The onset of the windstorm is detected predominantly during overnight and morning hours, with 70% of VNOR cases initiating between 0000 and 1000 LST. Regarding the VNOR demise, 66% of the windstorms dissipate between early afternoon and early evening hours (1200–1900 LST). Results from this study are applicable in the areas of atmospheric diffusion and local weather forecasting.

Abstract During the cold season, episodes of a windstorm known as Vento Norte (VNOR) are frequently observed in the city of Santa Maria, situated in the central region of Rio Grande do Sul (RS). The onset of this windstorm is characterized by strong gusts with northerly component which are accompanied by a sharp increase in temperature and abrupt drying. A methodology based on the observed behavior of the standard deviation of temperature during VNOR was successful in identifying the onset and demise of the windstorm. Additionally, the research shows the results of different micrometeorological variables during the event. Early morning and evening atmospheric profiles exhibit an elevated mixed layer over central RS in association with the strong VNOR winds, indicating the presence of mechanically-forced mixing during nighttime hours.

Considering the influence of the downslope windstorm called "Vento Norte" (VNOR; Portuguese for "North Wind") in planetary boundary layer turbulent features, a new set of turbulent parameterizations, which are to be used in atmospheric dispersion models, has been derived. Taylor's statistical diffusion theory, velocity spectra obtained at four levels (3, 6, 14, and 30 m) in a micrometeorological tower, and the energy-containing eddy scales are used to calculate neutral planetary boundary layer turbulent parameters. Vertical profile formulations of the wind velocity variances and Lagrangian decorrelation time scales are proposed, and to validate this new parameterization, it is applied in a Lagrangian Stochastic Particle Dispersion Model to simulate the Prairie Grass concentration experiments. The simulated concentration results were shown to agree with those observed.

Paddy fields are significant anthropogenic sources of methane (CH4) emissions. In southern Brazil, rice is grown in lowland flooded areas once a year, followed by a long fallow period. This study aimed to measure CH4 fluxes in a rice paddy field in southern Brazil during the rice-growing season of 2015/2016 and the following fallow period. The fluxes were estimated using the eddy covariance (EC) technique and soil chamber (SC). Diurnal and seasonal variations of CH4 fluxes and potential meteorological drivers were analyzed. The CH4 fluxes showed distinct diurnal variations in each analyzed subperiod (vegetative, reproductive, pre-harvest, no rice, and land preparation), characterized by a single-peak diurnal pattern. The variables that most influenced methane emissions were air and surface temperatures. In the growing season, the rice vegetative stage was responsible for most of the measured emissions. The accumulated annual emission estimated was 44.88 g CH4 m−2 y−1, being 64% (28.50 g CH4 m−2) due to the rice-growing season and 36% (16.38 g CH4 m−2) due to the fallow period. These results show the importance of including fallow periods in strategies to mitigate methane emissions in flood irrigated rice-growing areas.

The correct simulation of pollutant dispersion in coastal regions demands understanding the turbulence structure of the thermal internal boundary layer (TIBL), which typically occurs in daytime when maritime air is advected over the continent. Such a structure is investigated using 10 levels of turbulence observations made at a 140-m micrometeorological mast installed at 3500 m from the shoreline in south-eastern Brazil, with TIBL dimensionless vertical profiles of the turbulence parameters commonly used in Lagrangian and Eulerian dispersion models determined. To accomplish that, the TIBL height z(i) is estimated using a vertical-flux-convergence approach, developed here. The values experimentally obtained for z(i) agree with those predicted by a widely-used model for TIBL growth. In general, the normalized turbulent profiles evaluated for the TIBL differ from those previously obtained in the convective boundary layer (CBL). The horizontal eddy diffusivities evaluated for the TIBL are larger than those typically observed in the CBL, while the vertical ones are similar for both boundary layers. Finally, it is shown that CBL similarity relationships can be used to describe turbulent parameters as long as the proper empirical constants are used.