Ciência e Natura

Influence of sudden stratospheric warming on Brazil’s rainfall in the years 1988, 2002 and 2019

2024-07-06T14:46:57-03:00

Sudden stratospheric warming (SSW) is a common event in the Northern Hemisphere but very rare in the Southern Hemisphere (SH), where its occurrence was documented in 1988, 2002, and 2019 on the Antarctic continent. Such events can arise when large amplitude planetary waves propagate from the troposphere to the stratosphere, disturbing the polar vortex and causing stratospheric warming within days. The weakening of the polar vortex impacts tropospheric circulation, forcing the Southern (or Northern) Annular Mode to remain negative for longer periods and resulting in climatic anomalies across the hemisphere. During SSW events in Antarctica, climatic anomalies were recorded in the SH. In eastern Australia, during the 2019 SSW, hotter and drier conditions were observed, resulting in wildfires. This study analyzed the spatiotemporal variability of precipitation in Brazil during three SSW events in Antarctica in 1988, 2002, and 2019, using precipitation data from the Brazilian Daily Weather Gridded Data (BR-DWGD) from 1961 to 2020. During these SSW events in Antarctica, the Southern Annular Mode remained negative. This weakening of the Antarctic polar vortex is reflected in anomalous patterns in precipitation maps, highlighting a potential connection between SSW events and climate changes in Brazil.

Application of multiresolution analysis to study the structure of turbulence over the Amazon rainforest

2024-07-06T15:32:15-03:00

In this study, sonic anemometry measurements at 16 vertical levels of the ATTO tower were used to evaluate the temporal variation of the multiresolution (co)spectra of the wind speed and temperature components. This methodology made it possible to visualize, over a large vertical extent, which scales of turbulent movement contribute most to turbulent kinetic energy and turbulent transport of a quantity over the Amazon rainforest. In this respect, it was also possible to identify the turbulent scales most effective in the entrainment process in the early morning. The multiresolution analysis also highlighted the need to determine the scale of the spectral gap in order to obtain more robust estimates of turbulent fluxes, even for the daytime period.

Dexterity of WRF and GFS models in contrast with vertical radiosonde profiles

2024-07-06T15:23:22-03:00

The study focused on evaluating the dexterity of numerical prediction models using radiosonde data, which consists of collecting information from the atmospheric profile, which is fundamental for the initialization of the models. For this analysis, two models, GFS and WRF, were compared with radiosonde observations. The observations used are from the radiosondes launched from the International Airport of Santarém/PA - Maestro Wilson Fonseca. Overall, both models underestimated air temperature measurements at low levels but aligned better at high altitudes. As for the zonal wind, the GFS overestimated at some levels, while the WRF had smaller discrepancies. The models face challenges in predicting air temperature, suggesting limitations in region-specific physics and boundary conditions. Both models had similar performance in the zonal wind forecast. The study highlights the importance of considering such discrepancies in weather forecasting and how these tools can be adjusted to improve their forecasts.

Numerical simulation of Intermittency occurrence during turbulence Collapse

2024-06-16T21:01:58-03:00

This study presents the use of Large Eddy Simulations (LES) in the analysis of laminarization in a turbulent planar Couette flow, induced by the application of a constant cooling rate at the surface. The increase in stratification leads to a reduction in turbulence intensity until the flow becomes laminar. During this process, a regime transition is observed in the flow, from a weakly stable layer to a highly stable layer, where intermittency is detected. The consistency of the results is investigated through the assessment of the turbulent kinetic energy of the flow. The results indicate that the mesh used is adequate, capturing approximately 80% of the turbulent kinetic energy, demonstrating the effectiveness of the LES model in representing turbulence collapse. However, the results also show that further refinements are needed near the surfaces. Moreover, the flow regime transition occurs after the absolute peak of heat flux energy at the surface. Following the transition, intermittency is observed until the suppression of all turbulent flow scales, leading to the laminarization of the flow.

Turbulent flow profiles used to estimate the height of the night boundary layer in the Central Amazon

2024-07-06T15:27:12-03:00

The Atmospheric Boundary Layer (ABL) is the portion of the lower troposphere that interacts with and is inﬂuenced by the Earth’s surface. It is a key parameter for micrometeorology, atmospheric chemistry, and other ﬁelds of study. However, estimating the height of the nocturnal boundary layer (NBL) is not trivial, and the techniques used so far have never estimated the top of the NBL with turbulent ﬂux proﬁles (the most appropiate technique for this purpose). This work proposes an innovative methodology for calculating the height of the NBL, using data from 13 three-dimensional sonic anemometers installed on the towers of the ATTO experimental site, located in the central Amazon. Two days were used, one characteristic of the rainy season and the other of the dry season. The results showed that the ﬂux convergence methodology is promising for determining the NBL height. It was observed that, during the dry season, the heights were lower (average of 86.60 m) compared to the rainy season (average of 160.42 m). The higher heights during the rainy season can be attributed to the greater presence of clouds during this period, resulting in a higher amount of longwave radiation emitted by these clouds. This inﬂuences the increase in turbulence due to the available radiative balance and, consequently, resulting in higher NBL heights. These results will be further explored with the use of a larger dataset.

Analysis of synoptic conditions during the forest fires in the Amazon and their impact on the city of São Paulo on august 19, 2019

2024-07-06T15:14:29-03:00

The proposed work aims to evaluate the synoptic conditions during the fire event in the Amazon region in August 2019, which ended up causing the transport of particulates to the southeast region, directly impacting the city of São Paulo on the 19th, transforming the day in night. For the evaluation, the ERA5 reanalysis data was used together with the HYSPLIT model data in order to analyze the trajectory of the air parcels during the event. Based on the evaluations, the passage of a frontal system was observed, whose function was the convergence of humidity and wind flow over the region of São Paulo, favoring the development of cloudiness. In addition, the increase in particulates throughout the atmosphere can contribute as condensation nuclei, favoring the considerable increase in dark clouds during the afternoon in the municipality, directly impacting the reflected radiation, giving a nocturnal appearance to the city.

Use of the counter-gradient term based on Taylor's theory and its influence on precipitation simulation in the Amazon region

2024-07-06T15:36:17-03:00

The Planetary Boundary Layer (PBL) turbulence is parameterized in the Brazilian Global Atmospheric Model (BAM) using G. I. Taylor’s statistical theory, through a PBL parameterization together with the Counter-Gradient term gamma. The use of the gamma generated good results simulating precipitation in the Amazon region.

Tests of photovoltaic modules in a wind tunnel: scale effects and aerodynamic interactions

2024-07-06T15:19:22-03:00

Results of a study carried out in the UNNE wind tunnel to evaluate the aerodynamic loads on panels of a solar park are presented. The experimental study analyses the model scale effects that occur when two models with different characteristics are used. Likewise, the effects of aerodynamic interaction resulting from the relative location of the panels within the park are analysed. Firstly, a preliminary dynamic/numerical evaluation is carried out and then aerodynamic coefficients are experimentally determined, which will allow the quasi-static analysis of the structure of the panel-tracker system.

Comparison of mixing Length parametrizations under different stability conditions in the nocturnal atmospheric boundary layer

2024-07-06T14:53:12-03:00

Mixing length was introduced in the early 20th century to determine turbulent viscosity. Since then, various formulations have emerged, reflecting the complexity of parameterizing turbulent fluxes, especially under strongly stable conditions. This study proposes a new mixing length formulation based on the dissipation of turbulent kinetic energy, avoiding autocorrelation issues. Results show the new formulation behaves consistently, decreasing with stability in weakly stable conditions and increasing in strongly stable conditions. Comparisons with other formulations indicate that this approach offers a more robust description of turbulence in the stable boundary layer (SBL).

Neutral atmospheric boundary layer simulation of the Amazon rainforest using Large-Eddy Simulation

2024-07-06T15:25:09-03:00

The study of the atmospheric boundary layer (ABL) of the Amazon rainforest is important for a better understanding of the biogeochemical phenomena occurring in this region, as well as their local and global impact. Turbulence in the ABL is responsible for mixing chemical components in the canopy, as well as for transporting these substances from the forest floor to the top of the ABL. Large-Eddy Simulation (LES) is one of the main simulation tools for the ABL; however, one of the limitations in its use is in the study of unstable conditions, as the simulation inevitably requires a larger vertical domain, which limits the model's resolution near the surface. To simulate the unstable ABL with adequate resolution in the canopy region, the solution proposed in this work is the use of the One-Dimensional Turbulence (ODT) wall model. When coupled with LES, the ODT replaces the need for mesh refinement near the ground by producing stochastic vortices that mimic the effects of turbulence in this region. In the present work, results of a simulation of the Amazon ABL under neutral stability conditions are presented for a preliminary evaluation. In the vegetation region, the results of mean velocity and shear stress are similar to the GoAmazon field experiment data. On the other hand, the variances and asymmetries show differences that are inherent to the ODT model. In the future, the coupled LES-ODT model may be a useful tool in studies of the unstable Amazonian ABL.

Estimation of CO2 exchange in the pampa biome: obtaining experimental parameters for use in modeling

2024-07-06T15:08:46-03:00

Due to the urge to reduce greenhouse gas emissions in agricultural systems, studies are being conducted in the fields of the Pampa biome to understand the dynamics of carbon exchanges and propose mitigation measures. In this study, a model was calibrated to estimate the net ecosystem exchange (NEE) of CO2 in the native fields of the Pampa biome used for livestock, based on classical equations of ecosystem respiration and carbon assimilation through photosynthesis. For this purpose, NEE data obtained using the Eddy Covariance (EC) technique from a native field at the Santa Maria site in the years 2015 and 2016 were used to obtain the parameters utilized in the model. The parameters were obtained for each season, and the model was evaluated for the years 2019 and 2020 for both the Santa Maria site and the Aceguá site, located about 300 km from Santa Maria. The results showed that the model was able to estimate the NEE for the Santa Maria site with an average R² = 0.80 and RMSE 0.08 g C m-2 30 min-1, and for the Aceguá site with R² = 0.75 and RMSE 0.10 g C m-2 30 min-1. However, the model showed higher R² and higher RMSE during the summer and spring periods and lower values in winter and autumn at both sites. This model can be used to estimate the NEE of CO2 in the native fields of the Pampa biome as a basis for predicting CO2 absorption/emission across different seasons.

A TKE analysis for the roughness sublayer of an Amazon forest under unstable atmospheric conditions

2024-07-06T15:29:10-03:00

The equation of turbulence kinetic energy (TKE) quantiﬁes the intensity of turbulence, the mechanisms generating it, transporting it, and dissipating it. Given the well-known diﬃculty in applying Monin-Obukhov Similarity Theory in the roughness sublayer, the development of new approaches to understand the ﬂow in this region of the atmosphere is necessary. By calculating the terms of TKE and their balance using a reduced TKE diagram, we sought to investigate the characteristics of turbulence over an Amazon forest located at the ATTO Project experimental site. To do so, using data from three sonic anemometers at heights of 35m, 50m and 81m installed on one of the experiment towers and collected between August and October 2021 for the daytime period, we computed the terms of mechanical production P , thermal production B, storage S, vertical turbulence transport T^v, and dissipation ε_e of TKE. At the chosen analysis height (66m - average between the two upper sonic anemometers) and after quality control, we obtained 42 one-hour blocks. It was observed that in over 90% of the cases, ε_e was the largest term. The second-largest term was B (≈ 57%) and the third was P (≈ 40%), showing a certain balance regarding production mechanisms. However, upon balancing them, the existence of a residual term, not explained by T^v, was found. This residual was predominantly negative, which may indicate the effect of vegetation and topography on the ﬂow. It was also noted that in 70% of the blocks, the transport of TKE was upwards. S, on the other hand, is at least 2 orders of magnitude smaller than P , being negligible. Additionally, we calculated the dimensionless standard deviation for vertical wind speed, which showed good agreement with what is expected in the inertial sublayer (ISL).

Performance Evaluation of Historical Simulations from CMIP6 Models in Representing Precipitation Regime in Southern Brazil

2024-07-06T15:17:36-03:00

This study assesses the performance of historical simulations from CMIP6 models in representing precipitation patterns in southern Brazil between 1982 and 2014, comparing these simulations with ERA5 reanalysis data. The results demonstrate a generally good agreement in the amplitudes of seasonal precipitation between CMIP6 and ERA5, except for Winter, where climate models underestimated rainfall percentiles. During the Summer, the ACCESS-CM2 and BCC-ESM1 models exhibited the strongest correlations. In the Winter and Autumn seasons, the NorESM2-MM model demonstrated the best performance in terms of correlation and standard deviation. However, for the Spring season, despite some models exhibiting strong correlation, there were disparities in the standard deviation.