Atmósfera (Journal)
Not a member yet
881 research outputs found
Sort by
Cyclonic circulation and climatology of SST, CHL and wind stress curl in a semi-enclosed bay (Bahía de La Paz, Gulf of California, Mexico)
Get PDFThe first direct current observations (with the Lowering Acoustic Doppler Current Profiler [LADCP] and surface drifters) in Bahía de La Paz, in the southwestern Gulf of California (GC), concur with previous reports that the main dynamical feature during summer is a closed cyclonic circulation. However, we found that geostrophic calculations overestimate the speed of the orbital velocity: actual speeds (0.20-0.25 m s–1) were ~25-40% lower than those estimated from geostrophic balance (0.25-0.35 m s–1). The reason is that the centrifugal force cannot be neglected in this case. The mean rotation period during ship-borne observations in August 2004 was ~1.4 days, but it varied in the time that surface drifters were inside the bay, from ~1-2 days in June-July to ~2.5-3 days in September-October. The analysis of satellite data (wind velocity, sea surface temperature and chlorophyll) shows that from May to September the wind stress curl is strong and cyclonic, and the surface of the bay is cooler and richer than the adjacent Gulf of California waters, which could be attributed to the positive wind stress curl. This positive wind stress curl on the bay is part of a larger-scale positive wind stress curl distribution that surrounds the southern part of the Baja California Peninsula during summer, probably enhanced in the bay by local topography features. Although there is an exchange of water between the bay and the GC, its effect on the dynamics is poorly known.
A breviary of Earth’s climate changes using Stephan-Boltzmann law
Get PDFEarth’s surface temperature has oscillated greatly throughout time. From near total freezing during the “snowball Earth” (2.9) Ga to an ice-free world in the Paleocene-Eocene thermal maximum 55 (Ma). These changes have been forced by internal (e.g., changes in the chemical composition of the atmosphere) or external (e.g., changes in solar irradiance) drivers that varied through time. Thus, if we understand how the radiation budget evolved at different times, we can approximate past global climate, a fundamental comparison to situate current climate change in the context Earth’s history. Here I present an analytical framework employing a simple energy balance derived from the Stephan-Boltzmann law, that allows for quick comparison between drivers of global temperature at multiple times during the history of our planet. My results show that current rates of increase in global temperature are at least four times faster than any previous warming event
Cold fronts responsible for intense winds in the Santos Basin, Brazilian Southeast Offshore Region
Get PDFThis work aimed to identify the synoptic conditions associated with the cold fronts (CFs) passage that causes intense winds in the Santos Basin. Furthermore, the atmospheric characteristics of the CFs, which generated intense (INTW) and moderate (MODW) winds in the studied area, were identified. For this purpose, INTW and MODW composites of CFs episodes were elaborated. First, the INTW and MODW cases were selected from the 10 m wind intensity observed in the Santos buoy, belonging to the Brazilian National Buoys Program. Satellite images and synoptic surface charts were analyzed to identify the synoptic systems responsible for INTW and MODW in the Santos buoy, keeping only the cases generated by CFs. From the comparison between the composites, it was possible to observe in INTW: (i) a stronger pressure gradient over the Santos Basin, with the isobars presenting an almost meridional position near the basin, which caused the intense winds registered in the buoy; (ii) a baroclinic trough at medium and high levels reaching the Santos Basin region, located westward of the surface system; (iii) stronger 1000-500 hPa layer thickness and dew point temperature gradients over the continent, reaching the Santos Basin region, and (iv) a colder and drier air mass over southern Brazil. On a large scale, the Rossby wave tracings were analyzed, where different wavenumbers were noticed for each composite. In INTW, the wavenumber was 2, while in MODW, it was 2 and 3. Finally, the main characteristics found in the composites were observed in the case studies
Application of vine copulas to estimate dew point temperature
Get PDFIn this study, the accuracy of the copula-based model in the simulation of the dew point temperature in various climates of Iran was investigated, using simulations based on vine copulas such as C-, D-, and R-vine copulas. By examining the various vine copulas and their tree sequences, the best copula and best tree sequence based on AIC, BIC, and log-likelihood were selected. The results show that based on the complete similarity in our case between C-, D- and R-vine copulas, the selected best C-vine copulas fit well the dependence between the minimum and maximum air temperatures and dew point temperature. The simulation results were analyzed using root mean square error (RMSE), Nash-Sutcliffe efficiency (NSE) coefficient, and violin plots. The results show that the copula-based model has high accuracy at all stations. The min (max) RMSE is related to Kerman (Ahvaz) station with RMSE = 0.396 oC (0.617 oC). Also, the min (max) NSE is related to Ahvaz (Urmia) station with NSE = 0.925 (0.955). Also, according to the violin plot, it is possible to appreciate the acceptable certainty of the copula-based model. Due to the diversity of the tree sequences of vine copulas and the use of the rotated states of the internal vine copulas, as well as the possibility of interfering with the effective parameters in high dimensions, the simulation results are reliable and have no restrictions. This model can be used as the best model to estimate dew point temperature due to the full coverage of the range of changes in data
Evaluation of the SACZ index as a prognostic tool based on GFS forecasts
Get PDFThe South Atlantic Convergence Zone (SACZ) is an atmospheric phenomenon typical of summertime where a band of nebulosity causes intense or persistent rainfall in many regions of Brazil. SACZ episodes can be responsible for many natural disasters. Besides, the impacts of rainfall on water availability and consequently on the energy sector are extensive. The main objective of this study was to investigate the implementation of the SACZ index as an objective forecasting tool using input data from the Global Forecast System (GFS) model. Initially, we compared the index with the SACZ events identified by the Center for Weather Forecasting and Climate Studies (CPTEC ) from 2017 to 2021. Results showed that the index represented all events identified SACZs by CPTEC. Finally, we used data from the GFS 0.25 Degree from 2017 to 2021 to calculate Accuracy, Probability of detection, and False alarm ratio to evaluate the SACZ index as a prediction tool. Three thresholds are defined for the binary classification of a possible SACZ event. Results showed that above the most sensitive threshold (h1), within 10 days in advance, the sign of a possible SACZ can be detected. For the intermediate threshold (h2), a forecast of 96 h can detect a sign. For the most specific threshold (h3), the index can detect the event within 72 h in advance with a probability of detection of almost 90%. The SACZ index proved to be an efficient tool for detecting the dynamics of the phenomenon and can be used to assist operationally and in decision-making
The influence of snow cover on Ozone Monitor Instrument formaldehyde observations
Get PDFFormaldehyde (HCHO) is measured from space using backscattered ultraviolet sun-light. Because of HCHO’s short lifetime, space-based observations of HCHO can serve as a proxy for volatile organic compounds, helping to characterize their global emissions and distributions. HCHO satellite observations rely on Air Mass Factor (AMF) calculations to transform fitted slant columns into vertical column densities. Most HCHO satellite products do not explicitly consider the presence of snow on the ground during the calculation of AMFs. In this study, we leverage information from the MODIS bidirectional reflectance distribution function (BRDF), MODIS snow cover information, and the Interactive Multisensor Snow and Ice Mapping System to evaluate the impact of ground snow on Ozone Monitoring Instrument (OMI) HCHO retrievals. We focus our analysis on the year 2005. We compare AMFs computed using daily MODIS BRDF to AMFs computed using OMI’s surface reflectance climatology, the baseline for NASA’s OMHCHO product. Over snow-covered regions, both sets of AMFs show significant differences. We observe two different behaviors. Regions with permanent snow cover (Greenland and Antarctica) show smaller AMFs calculated with MODIS BRDF than with the OMI climatology resulting in a 6% median annual increase of HCHO VCDs. Over regions with seasonal snow cover, the situation is more complex with more variability in the differences during the year. For example, a February 2005 case study over Europe shows that the NASA OMHCHO VCDs (calculated using the OMI Lambertian climatology) are on average 16% larger than HCHO columns retrieved using daily MODIS BRDF information
Solution of advection-diffusion-reaction problems on a sphere: High-resolution numerical experiments
Get PDFThe implicit and unconditionally stable numerical method proposed in Skiba (2015) is applied to solve linear advection-diffusion-reaction problems and nonlinear diffusion-reaction problems on a sphere. Numerical experiments carried out on a high-resolution spherical mesh show the effectiveness of the method in modelling linear advection-diffusion processes on a sphere (dispersion of pollution in the atmosphere), and nonlinear diffusion processes (propagation of nonlinear temperature waves, blow-up regimes of combustion, and chemical reactions in the Gray-Scott model). The method correctly describes the mass balance of a substance in forced and dissipative systems and conserves the total mass and norm of the solution in the absence of forcing and dissipation
Classification of wintertime daily atmospheric circulation patterns over Brazil
Get PDFThis study presents a synoptic classification at surface and at 500 hPa during winter (June, July, and August) over Brazil, in order to identify the main synoptic-scale meteorological systems that influence the weather of this period. Through principal components analysis for the 1979-2020 period, five main synoptic patterns were identified, which predominated during winter and are practically the same for each of the three analyzed months. The most frequent synoptic pattern is associated with the climatological mean-field, represented by two of the most characteristic systems of low-level atmospheric circulation in South America: the South Atlantic Subtropical High and the North-Western Argentinean Low. There are two other synoptic patterns related to a classical cold front over the southern and southeastern regions of Brazil. Finally, two other synoptic patterns are associated with a blocking anticyclone and a cyclogenetic process over the Atlantic Ocean, respectively, both of which correspond to the most frequent synoptic pattern related to cold waves and cold surges (friagens) over Brazil
Occurrence and characteristics of snowfall on the highest mountain of Mexico (Citlaltépetl volcano) through the ground’s surface temperature
Get PDFSnow has great environmental importance. Its physical properties influence the ground temperature; its long-term accumulation adds to the mass of glaciers and is also a clear indicator of climate variability. However, despite the frequency of snowfall in tropical high-mountain environments, its quantitative study is very scarce, and it is non-existent in the case of Mexico. Due to the altitude of a large part of the Mexican territory and the high ecosystem value of the snow, in this work we analyze the temporality, accumulation, and duration of the snow cover on the highest mountain in the country. The data obtained through continuous monitoring of the surface temperature of the ground allowed us to identify that snowfall occurs with greater frequency and volume during the summer and autumn months, while during the winter snowfall of less intensity occurs. The accumulation values are mostly less than 30 cm thick, and the duration of the snowpack is on average less than two weeks; however, there are episodes of greater depth and duration
Urban atmospheric humidity excesses and deficits in two Mexican metropolises: Guadalajara and Puebla
Get PDFComparative studies of atmospheric humidity between urban and suburban and urban-rural environments are scarce, and their results are very scattered and inconclusive. In this paper, we compare differences in atmospheric temperature, relative humidity and absolute humidity measured at the limits between the urban canopy and the boundary layer in two elevated metropolises in Mexico: Guadalajara and Puebla. Results show that variations in relative humidity contrasts between different environments have an inverse relationship with the temperature variations. In Guadalajara, the urban excesses of absolute humidity are predominant from May to September. In Puebla the urban-suburban contrasts are lower than in Guadalajara, following a daily cycle and being negative between noon and 18:00 LT. From March to September urban-rural differences in Puebla are positive between 10:00 and 18:00 LT, and weak during the nocturnal period