Atmósfera (Journal)
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Remote sensing of atmospheric nitrogen dioxide in an urban area in central northern Mexico
Get PDFNitrogen dioxide (NO2) was remotely measured in the urban area of San Luis Potosí (México) using the differential optical absorption spectroscopy (DOAS) technique. Measurements were taken from July to August 2015. In this technique, light scattered by the sun through the atmosphere is focused by a telescope onto a linear array-based spectrometer at ground level. During the measurement period, the maximum NO2 levels (2.3 x 1016 molecules/cm2) were found at around 11:00 h, whereas NO2 levels fell on days with wind speeds lower than 1.5 m/s. The NO2 levels were compared and explained with the behavior of meteorological data such as wind speed, relative humidity, and surface temperature obtained from the Weather Research and Forecasting Model (WRF)
The planetary boundary layer physical processes, the secondary thermal baroclinic circulation and inertial oscillation contribution to diurnal variation of the Etesian winds over the Aegean Sea
Get PDFEtesian winds constitute an important climatological phenomenon, which does not only moderate the heat during the summer in the Aegean Sea, but provides a source of clean renewable energy as well. Even though several papers have attempted to explain their dynamical and physical characteristics, the respective processes that drive the diurnal variation of the wind speed are not fully understood. The objective of this paper is to identify the processes responsible for diurnal variation with observed maximum wind speed around noon and minimum around midnight. Analytical solutions of a primitive equation set in Eulerian form, after introducing suitable conditions and approximations, reveal an inertial oscillation over the Aegean Sea. Data based on direct observations, ECMWF IFS high resolution analyses and high-resolution simulations with the Weather Research and Forecasting (WRF) model are utilized to find out the type and structure of the planetary boundary layer (PBL) over the Aegean Sea. This PBL appears to be of a marine character and turbulent mostly during the day but less during the night. The direct impact of local and regional thermally-driven circulations is found to be the main cause of the diurnal variation of the observed wind and partly the inertial oscillation. Results from numerical simulations certify these findings. Furthermore, the momentum and Newtonian heating exchanges by the physical processes inside the PBL, where the gradient wind together with smaller scales of atmospheric motions exist, are also necessary for explaining the variability of the Etesian winds
Historical change of winter chill accumulation in some regions of Turkey
Get PDFDeciduous fruit trees need to be exposed to low winter temperatures for a certain period of time to produce regular crops. In addition to the effects of global warming in many other areas, its effect on cold accumulation is also a reason of concern. As a result, many studies have been carried out in important horticultural areas around the world on the impact of climate change on cold accumulation. In this study, historical changes of cold accumulation calculated using five models were examined in 12 locations in Turkey for the first time. Results show that there was no significant trend in cold accumulation in the provinces of Ankara, Bingöl, Diyarbakır, Malatya, and Tunceli. In some locations, the significance, magnitude, and direction of the chilling trend differed according to the model used. All five models used in the study indicated significant decreases in winter chill accumulation in Şanlıurfa, a site with relatively mild winters. In Erzincan, which has relatively cold winters, increasing trends were detected in cold accumulation calculated according to Utah, Modified Utah, and Positive Utah models. Results show that serious consequences may arise related to the chilling requirement of deciduous fruit trees, especially in regions with mild winters
Using clustering algorithms and GPM data to identify spatial precipitation patterns over southeastern Brazil
Get PDFSoutheastern Brazil comprises an important geoeconomic and populous region in South America. Consequently, it is essential to analyze and understand the precipitation profiles in this region. Among different data sources and techniques available to perform such study, the use of clustering algorithms and information from the Global Precipitation Measurement (GPM) project rises as a convenient yet few exploited alternative. Precisely, this study employs the K-Means, the Hierarchical Ward, and the Self-Organizing Maps methods to cluster the annual and seasonal precipitation data from GPM project recorded from 2001 to 2019. The adopted methods are compared in terms of quantitative measures and the number of clusters defined through a well-established rule. The results demonstrate that the annual and seasonal periods are organized according to different number of clusters. Moreover, the results allow: identify the presence of a spatially heterogeneous distribution in the study area; to conclude that the K-Means algorithm is a suitable clustering method in the context of this investigation when compared to Ward’s Hierarchical and Self-Organizing Maps methods in terms of the Calinski-Harabasz and Davies-Bouldin measures; and that the spatial precipitation distribution over Southeastern Brazil is represented by 10 clusters in annual and summer periods, 11 clusters in autumn and spring and 9 clusters in winter period
Experimental downslope gravity currents over a synthetic topography
Get PDFExperimental lock-release gravity currents are investigated as they propagate downslope over varying synthetic topography. We emulate and investigate the dynamics of thermally driven winds that propagate downslope while interacting with the roughness of a complex topographic surface. The mixing processes between the gravity currents and their surroundings are studied with Particle Image Velocimetry (PIV), and entrainment is quantified. The magnitude of the entrainment coefficient is shown to increase as the roughness of the slope increases. Shadowgraph visualizations qualitatively reproduce this behavior. Finally, pressure fields are estimated from velocity fields, and pressure time series are obtained over synthetic stations along the topographic surface. The arrival of gravity currents is shown to be detected in the pressure time series. This last result may help detect atmospheric gravity currents using only surface pressure measurements
Very high erythemal doses of ultraviolet radiation around solar noon measured in Arica, northern Chile
Get PDFNews media and meteorological bulletins generally report on the ultraviolet index (UVI) to prevent overexposure to the sun. However, this information does not reflect the accumulated damage to the skin induced by the total amount of UVR (ultraviolet radiation) accumulated over time, known as erythemal dose (ED). This study analyzed the UVI and ED measured at ±30 and ±60 minutes around solar noon (SN) in Arica, North of Chile. The results show that SN ED exceeded the Minimum Erythema Dose (MED) for all the skin types. During the summer, shorts exposures to sunlight for up to 1 hour may result in sun exposure up to 10 times greater than the acceptable occupational safe limit for unprotected human skin
Dense fog simulation in southern Brazil using the WRF model with high spatial resolution
Get PDFFog is an atmospheric phenomenon that reduces horizontal visibility to 1000 m or less. These phenomena affect different human activities, mainly those associated with air, maritime, and road transport. Rio Grande city, located in southern Brazil, has one of the main Brazilian ports, and fog occurrences at this location cause several inconveniences, such as the interruption of port activities and increases in operating costs. Thus, a better understanding of fog formation and dissipation, and the consequent improvement in its forecasts, can bring significant help to the port activities in that region. Therefore, this work seeks to evaluate the WRF model’s ability to simulate fog events in Rio Grande city. Four study cases of dense fogs were performed for this goal, as well as a sensitivity test to select the best vertical resolution configuration of the model. Meteorological data from the Rio Grande pilotage station and the Brazilian Coastal Monitoring System buoys were analyzed. Satellite images and synoptic charts were also analyzed for the study cases. The numerical simulations were performed using the WRF model with three nested domains, where 1 km was the highest horizontal resolution. The Fog Stability Index (FSI) and two estimates of horizontal visibility were evaluated. Simulations show promising results, highlighting the ability of the model to identify the fog occurrence in the area of interest and represent aspects of its dissipation process. Furthermore, it is noteworthy that the FSI and the evaluated visibility estimates were sensitive to the occurrence of the events
Spatio-temporal co-variability of air pollutants and meteorological variables over Haqel and Jeddah, Saudi Arabia
Get PDFThis study presents a first simultaneous trend and magnitude assessment of air pollutants (CO, H2S, SO2, NO2, NO, NOx, O3 and PM10) and meteorological variables (rainfall [RF], relative humidity [RH], atmospheric pressure [PR], temperature [TC], wind speed [WS], and wind direction [WD]) in the city of Haqel and at four different locations in the city of Jeddah, Saudi Arabia, for a continuous 5-year period (2008-2012). The spatio-temporal co-variations of air pollutants in terms of their diurnal, weekly, seasonal and annual cycles, and their relationship with meteorological conditions, along with the estimates of the weekend effect, are described. A decreasing annual trend was observed for most air pollutants analyzed except for O3 and PM10. The CO, NO2, NO and NOx displayed a strong weekend effect. A percentile-based change analysis displayed an increase in concentrations for O3 (PM10) in the lower (higher) percentiles from the first to second half of the study period. The study identified 12 cyclonic weather events during the 5-year time period associated with high PM10 concentrations (> 500 µg m–3) relative to a mean value of 102 µg m–3, with a standard deviation value of 179 µg m–3. The study also analyzed the impacts of several mid-latitude anti-cyclonic events on air pollutant concentrations and found a significant change in air pollutant concentrations (CO, SO2, NO2, NO, NOx, O3 and PM10) and meteorological variables (RH, PR, TC, WS, and WD) associated with stagnant upper air conditions during the atmospheric blocking
Structural change points of NDVI in Mexico driven by climate oscillations (edited by Dr. P. Ordóñez)
No full textBased on the climatology of air temperature, precipitation, and the normalized vegetation index (NDVI), a regionalization of Mexico for the rainy season is presented through a non-parametric clustering algorithm known as DBSCAN. Thirty years of data, spanning from 1984 to 2013, are used to detect structural change points with the Mann-Kendall and Pettitt non-parametric tests applied on the NDVI, mean daily precipitation, 99th percentile precipitation, and mean daily air temperature. The relative predictive importance of the parameters examined was estimated using a Machine-Learning Random Forest algorithm that allows establishing a connection between changes in the NDVI and changes in air temperature, average precipitation, and extreme precipitation for some regions. Modulation by large-scale climate phenomena, such as the Atlantic Multidecadal Oscillation (AMO) and the Pacific Decadal Oscillation (PDO), as well as interannual modulation by El Niño/Southern Oscillation (ENSO) are explored. Structural change points in the series appear to be modulated mainly by the phase shift of the AMO and those of the ENSO and PDO in 1997
Subsurface temperature change attributed to climate change at the northern latitude site of Kapuskasing, Canada
Get PDFSubsurface temperatures have been measured in different regions of the world, usually near the surface up to a depth of about a hundred meters. In this work a forward model calculation for a Northern Hemisphere soil temperature site at Kapuskasing, Canada, is presented, employing the solution of the differential equation of heat conduction through a semi-infinite homogeneous solid, subject to surface boundary conditions determined by surface air temperature. In this way, a detailed analysis is made of the subsurface temperature as a function of ground depth and for the time interval ranging from 1970 to the future (including the next century), for different scenarios of climate change. From these results, it was possible to determine the following characteristic quantities: (a) the depth where the surface perturbation (practically) finishes (in the range of about 180-200 m); (b) the depth where the subsurface temperature changes its slope from negative to positive; (c) the temperature change at the surface for the years where data exist; (d) the thermal gradient at steady state in the starting year (1880); (e) the temperature differences extrapolated at surface and at a 20 m depth, this last value corresponding to the depth at which seasonal and diurnal temperature variations are negligible; (f) the heat flow at surface to the inner part of the soil attributed to climate change, and (g) the temperature changes at surface for the 100 years interval (1980-2080) and mainly for the next century (2080-2180), for each site and for each IPCC Representative Concentration Pathway (RCP) scenario. As an example, the impact of the change in mean annual soil temperature due to global warming in near-surface geothermal energy is described