Atmósfera (Journal)
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Spatial and temporal variation of acid rain in the Mexico City Metropolitan Zone
Get PDFAt the end of the 1980´s particulates and sulfur dioxide (SO2) were the main atmospheric pollutants in the Mexico City Metropolitan Zone (MCMZ). To reduce emissions, fuel oil was replaced by natural gas at power plants located inside Mexico City. Currently, SO2 levels do not exceed its air quality standard; however, acid rain is present with a high contribution of sulfate (SO42–). In this study, spatial and temporal variations in the chemical composition of rain in Mexico City between 2003 and 2014 were analyzed. Major ions (Na+, NH4+, K+, Mg2+, Ca2+, SO42–, NO3– and Cl–), pH, and electrical conductivity (EC) were analyzed weekly at 16 sampling stations located in the MCMZ. The pH decreased from north to south, with the lowest annual volume weighted mean (VWM) of 4.16 in 2006. Annual ion concentrations were, in decreasing order: NH4+, SO42 –, NO3– and Ca2+ for the entire study period at most of the sampling sites. The highest values for wet atmospheric deposition (kg/ha) were found in the Western area and were the maximum in 2007. Wet deposition had major levels for SO42– and NO3– of 24 and 20 kg/ha, respectively, and were similar to the levels registered in the USA in 2013 and 2014. Considering that external emission sources play a decisive role in acid rain within the City, it is necessary to establish strategies for the emission reductions of acid rain precursors from upwind sources
Impact of updating land surface data on micrometeorological weather simulations from the WRF model
Get PDFLand surface processes play a critical role in governing the surface energy partitioning and the atmospheric circulation within a climate system. Improper representations of present land state, particularly spatially specific fields such as land cover, topographical and biophysical parameters contribute to the uncertainty in the model’s weather simulations extending from local to regional scales. The present study investigates the impact of superior land surface datasets on the performance of the Weather Research and Forecasting (WRF) model in simulating micrometeorological/near-surface weather, particularly sensible variables such as temperature, relative humidity, solar radiation and wind speed. The hypothesis is that the updated land surface datasets would help in improving micrometeorological forecasts over the domain comprising of Punjab, Haryana and Uttarakhand states in India. A land use land cover (LULC) dataset derived from Advanced Wide Field Sensor (AWiFS); an elevation dataset from the Shuttle Radar Topography Mission (SRTM), and a Leaf Area Index (LAI) based on the Moderate Resolution Imaging Spectroradiometer (MODIS), are used in model initialization. Performance evaluation of the model’s simulation is done for controlled (default) and modified land boundary conditions with in situ weather from a network of automatic weather stations (AWS) operated by the Indian Space Research Organization (ISRO). In the modified run, the model more closely captured the temporal evolution of surface level temperature, relative humidity, wind speed, surface pressure and solar radiation. Improvement in 24-hr forecast ranges from 15 to 30% for these near-surface weather variables. Further testing of the model’s performance on its capability to forecast 8-day micrometeorological weather variables revealed that the modified run gave consistent results. The average RMSE values for minimum and maximum temperature, wind speed, relative humidity and precipitation are 2.5 and 3 ºC, 2 m s–1, 18% and 3.5 mm, respectively. The modification helped in increasing the lead-time of the model’s forecast by reducing the propagation error. Thus, this study emphasizes the fact that improved representation of land surface parameters has a definite effect on weather simulations at local to regional scales. For a country like India, where the feedback mechanisms between land and atmosphere are more prominent due to inherent climatic characteristics, it is critical to concentrate and improve on the inputs that represent the initial land state.
Connections in the development of tropical cyclone Mitch (1998): A tribute to the human loss in this calamity
Get PDFTropical cyclone Mitch, which occurred in October 1998 on the Caribbean Sea, is studied. Mitch affected countries in Central America, where it caused great economic and human losses, and the authors believe that the scientific community has not paid enough attention to this phenomenon. Two NE-SE oriented dipole patterns associated with their convergence-divergence zones contributed significantly to its formation and intensification, which are analyzed from the observational synoptic point of view. The most remarkable characteristics of this phenomenon in the mean field occurred between October 18 and November 4, 1998 when another NW-SE dipolar pattern was formed, consisting of a high-level anticyclone from North America (HLA) and a high-level anticyclone from South America (HLC). To discern these patterns, two data sources were used: the NCAR-ds627.0 (ERA-Interim) reanalysis and the NCEP/NCAR reanalysis. The simplest idealization of the NW-SE dipolar vortex is a tropical modon, which is an exact solution of the barotropic vorticity equation (BVE) on a rotating sphere. The role of the HLA and the HLC in the excitation of tropical waves is explored using a numerical spectral method for sutdying the normal mode stability of exact solutions of the BVE. The initiation of the tropical wave at low levels could be associated with disturbances at high levels of the most unstable normal mode
Sea surface temperature, ocean color and wind forcing patterns in the Bay of La Paz, Gulf of California: Seasonal variability
Get PDFMonthly climatologies are used to estimate the mean seasonal cycle of MODIS-Aqua satellite-derived sea surface temperature (SST), surface chlorophyll (Chl-a) and their relationship with surface wind stress curl (from the Cross-Calibrate Multi-Platform, CCMP) in the Bay of La Paz located in the southwestern Gulf of California, a region identified as having high biological productivity and significant seasonal variability. Harmonic fit applied to the monthly climatologies of these variables indicate a best fit with annual and semi-annual constituents. The annual amplitude was the dominant signal in both SST and Chl-a, corresponding to the bay-wide seasonal cycle of warming and cooling associated with the influx of upwelled nutrient-rich coastal waters jointly with the water exchange between the bay and the Gulf of California. Empirical orthogonal function (EOF) decomposition yielded the annual and semi-annual patterns of the seasonal cycle that respond to wind forcing. The EOF1 explained 93% of the SST variance and 48% of the Chl-a variance, showing a homogeneous variability of both variables across the bay and a strong thermal and biological gradient in the vicinity of the Gulf of California with their corresponding amplitude time series representing out-of-phase annual cycles, which corresponded to the regional dynamics of wind forcing pattern. The EOF2 accounted for 6% of the SST variance and 31% of the Chl-a variance, which reached its peak during winter associated with the high Chl-a anomaly values (>1.5 mg m–3) observed along the coast. The intense biological productivity covaried strongly with the wind stress curl annual cycle (R = 0.5, P < 0.05), suggesting that these Chl-a blooms could be associated with coastal currents and upwelling events regulated by the seasonal wind forcing pattern playing an essential role in the modulation of this quasi-permanent biophysical coupling observed in the Bay of La Paz during an annual cycle
Content and composition of dissolved organic carbon in precipitation at the southern part of Mexico City
Get PDFWe present concentrations of dissolved total carbon (TC) and organic carbon (OC) in rainwater samples collected in 2016 in the southern part of Mexico City in a preliminary study. TC ranged from 10 to 25 mgC L–1 and OC – reported as non-purgable organic carbon (NPOC) – varied between 2.5 and 20 mgC L–1. NPOC concentrations were higher in samples collected between May and July and a change in the ratio of NPOC/TC was detected for the second part of the campaign (i.e., August-October). 1H NMR analysis indicated presence of aldehydes, carboxylic and other oxygenated hydrocarbons in the precipitation. An evaluation of air mass back-trajectories suggested no relationship between the organic contents and wind directions. Carbon contents were originated from sources within the basin of Mexico and higher pH of rainwater during the passage of air masses indicates that the sources causing rain neutralization are located in northern parts of the city
Ozone layer adaptive model from direct relationship between solar activity and total column ozone for the tropical equator-Andes-Colombian region
Get PDFDue to the lack of models to predict the ozone layer even after an ample range of total column ozone (TCO) measurements around the globe, a direct relationship between solar activity by means of sunspot number observations and total ozone satellite data for a tropical Andes mountains region at Bogotá-Colombia, is presented. Sunspot number data and 37 years of TCO records from satellite missions Nimbus 7, Meteor 3, Earth Probe and AURA from January 1979 through August 2016, are analyzed. Ozone annual cyclic behavior, which strongly depends on the annual cyclic Sun-Earth distance variation, as well as the dynamics of the solar activity cycles allow to derive a physical-mathematical adaptive model for predicting and reconstructing daily stratospheric ozone over the city of Bogotá, very close to the equator. Results suggest that the ozone layer as a natural indicator of solar activity
Performance evaluation of a coupled method for the estimation of daily global solar radiation on a horizontal surface
Get PDFThe accurate estimation of the amount of global solar radiation potential on the earth’s surface is one of the most important parameters for solar energy investments and long-term climate studies. The most accurate solar radiation data are generally available in some ground stations where they are obtained by using direct measurement. However, the estimation of global solar radiation data can be conducted by some estimation methods in the areas that do not have this information. This study compares and discusses some approaches to identify the most accurate method for daily global solar radiation reaching on a horizontal surface. The comparisons are carried out between some selected conventional empirical methods taken from the related literature, the satellite-based HELIOSAT method and the coupled (hybrid) method which uses both ground data and satellite images. These selected methods have been tested previously and declared most accurate by many researchers for Turkey. The performance results were compared with ground-measured data and all methods were analyzed by using statistical errors in the selected site. According to the last six years of data results, the coupled method is better than the others (except the Angstrom method), with daily difference values (91%) and daily absolute difference values lower than 2.5 MJ m–2 day
Land use/land cover change and extreme climatic events in the arid and semi-arid ecoregions of Mexico
Get PDFArid and semi-arid lands in Mexico dominate 60% of the national territory. They harbor many endemic species, as well as a large proportion of the population, and offer diverse ecosystem services. These regions are subjected to anthropogenic impacts derived from agriculture and livestock farming, which have caused land degradation and desertification. In addition, these ecosystems are highly sensitive to climate variability and projected global environmental change. However, information about how land use/land cover change and climate variability processes overlap and synergize each other in these ecoregions is scattered in different publications, and it is desirable to integrate it to provides more complete information for decision making. In this study we describe both land cover and land use changes in the five arid and semi-arid ecoregions in Mexico (Sonoran, Chihuahuan, Tamaulipan, Mexican High Plateau and Tehuacán-Cuicatlán valley) between 2002 and 2011, and their current exposure to droughts, low temperatures, floods and tropical cyclones. These results are discussed in terms of regional climate trends documented in the literature. We found that land use and land cover change differ between ecoregions, with the Sonoran and Chihuahuan ecoregions being the least affected. The overall exposure to extreme climate events is high in all ecoregions except for the Tehuacán-Cuicatlán valley, although each region has different exposure profiles. Observed trends for all ecoregions generally point towards an increase in both maximum and minimum temperatures, while trends for precipitation are less clear. Our results can serve as a guideline for identifying areas where anthropogenic processes of land use and land cover changes and extremes climatic events synergize, to better guide management under a changing environmen
Absolute homogeneity assessment of precipitation time series in an arid region of Pakistan
Get PDFHomogeneity evaluations are usually performed on the total annual precipitation data, which often fails to detect non-homogeneity in seasonal precipitation. Furthermore, it is required to assess homogeneity using multiple methods as the performance of homogeneity testing methods depend on the distribution of the data. This is particularly important for the arid region where distributions of seasonal and annual rainfall are often non-normal. The homogeneity of annual and monthly precipitation datasets of 14 meteorological stations located in the arid region of Pakistan was assessed in this study using the Pettitt’s test, the standard normal homogeneity test (SNHT), the cumulative deviation test, the von Neumann’s ratio test, the Bayesian test, the Worsley’s likelihood ratio test, and Student’s t-test at a 95% confidence level. The rainfall series were categorized into three classes, namely “useful”, “doubtful” and “suspect” based on the results of different homogeneity tests. Results suggest that rainfall time series for most of the months in all the stations are useful. The rainfall time series are found doubtful for the month of June at two stations, for April at one station, and suspect for November at only one station. On the other hand, the annual series were found useful at 12 stations and suspect at two stations. Comparison of different homogeneity tests revealed that SNHT and Worsley’s tests are the most sensitive, and cumulative deviation test is the least sensitive to changes in monthly precipitation data. In the case of annual series, the von Neumann’s test was found most sensitive compared to other tests
Spatial and temporal analysis of thunderstorm and rainfall activity over India
Get PDFThunderstorms are one of the most devastating mesoscale severe weather phenomena, which play an important role in the occurrence of rainfall activity over a region. Therefore, in the present study an attempt has been made to identify the relationship between thunderstorm days (Thn), rainy days (Thr) and rainfall amounts (Trr) for 294 meteorological stations spreading over India, by means of published data (climatological normals) from the India Meteorological Department (IMD) for four periods, 1951-1980, 1961-1990, 1971-2000, and 1981-2010. The analysis has revealed a sharp decrease in the frequency of Thn, while Thr and Trr showed a slight decline. A significant correlation between Thn, Thr and Trr has been observed. Monthly analysis has exhibited a dual peak in the occurrence of Thn and single peak in rainfall activity; however, a time lag of one month in their peak occurrence was detected. These results show that the Indian summer monsoon affects significantly the thunderstorm activity over India. Seasonal analysis suggests that Thn, Thr and Trr are maximum during the monsoon season, while minimum during winters. Apart from this, Thn and Thr, and Thn and Trr have demonstrated a negative relationship during the monsoon, which may be anomalously due to decreasing temperature in India during that season. In addition, the spatial annual and seasonal pattern of the occurrence of Thn, Thr and Trr shows almost a similar pattern during 1951-1980. However, a sharp decline in the frequency of Thn has been observed during subsequent periods over all parts of the country. Likewise, a slight decline in the frequency of Thr and Trr has been observed over India, except in the northeast, where an increasing trend in rainfall activity has been observed. The computed ratio between Thn and Thr (R) has been found maximum during the pre-monsoon, whereas the ratio between Trr and Thn (RTR) during the monsoon season. Regional analysis of Thn, Thr and Trr revealed a wide range of variations in the occurrence of these parameters month after month. It is believed that the results presented in this study will be useful for weather forecasters, aircraft pilots, agriculturists and planners