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Some variations of the rainfall in Mexico City from 1954 to 1988 and their statistical significance
No full textSome characteristics of the precipitation such as the beginning and end of the rainy season, as well as their spatial and temporal distributions are studied. The study included data from 23 climatological stations located in the Federal District for the period 1954-1988. Four variables related to the beginning and end of the rainy season were defined, namely the day of the first and last event with 10 mm of accumulated precipitation and the percentage of accumulated precipitation until Julian days 150 and 275. An analysis of variance and principal components was made with these variables, establishing that rainfall in the Federal District (which includes part of Mexico City and its surrounding areas) responds homogeneously through time to the presence of mesoscale meteorological phenomena. The results indicate that precipitation was lower at the beginning and end of the study period, and higher in the middle; additionally, the rainy season starts from west to east and ends from east to west, causing a longer season in the southwest than in the northeast. The spatial distribution shows the greatest rainfall in the southwest due to the effect of the nearby mountains, and the lowest in the northeast.Se estudian algunas características de la precipitación, tales como el principio y final de la estación lluviosa, así como la distribución espacial y temporal de la lluvia, usando datos de precipitación de 23 estaciones localizadas en el Distrito Federal para el periodo 1954-1988. Se definen cuatro variables relacionadas con su comportamiento: el día del primer y último evento de 10 mm de precipitación acumulados y el porcentaje de precipitación acumulada hasta los días julianos 150 y 275. Con estas variables se hace un análisis de varianza y de componentes principales, el cual permite establecer que la precipitación en el Distrito Federal (queincluye parte de la Ciudad de México y áreas circundantes) responde uniformemente en el tiempo a la presencia de fenómenos meteorológicos de mesoescala. Los resultados indican que al principio y final del periodo de estudio la precipitación fue menor que en los años intermedios; adicionalmente, la temporada de lluvias se establece de oeste a este y se retira de este a oeste, causando una temporada más larga en el suroeste que en el noreste. La distribución espacial muestra la mayor precipitación en la parte suroeste debido al efecto de montaña, y la menor en la parte noreste
Characterization and source identification of VOC species in Bogotá, Colombia
No full textIn this article, volatile organic compounds (VOC) were characterized in ambient air at three different monitoring sites within the urban perimeter of Bogotá, Colombia. On-line VOC measurements were conducted using a Synstech Spectras portable gas chromatograph with a temporal resolution of 30 min. Average VOC concentrations were higher at two of the sampling sites, which are characterized by intensive industrial and commercial activities, and high vehicular activity. Analyses of the diurnal behavior of total VOC showed that concentrations tend to be higher in the morning (at around 8:00 LT) and during the evening (around 22:00 LT). Such trends suggest the influence of road traffic activity in the surroundings of the measuring sites on VOC levels. According to our results, alkanes are the most abundant hydrocarbons in the ambient air in Bogotá (about 80% of the total VOC), while alkenes represent only 15% of the total VOC. We computed the ozone formation potential (OFP) using the maximum incremental reactivity (MIR) concept and evaluated the role of each VOC in the O3 formation. These results show that ethene, propene, n-butane, i-pentane and isoprene are the species with the highest OFP (noting that high concentrations are not necessarily linked with elevated O3 production). Finally, we used principal components analysis to identify the sources of different VOC. Our results showed that most of the compounds included in this study are emitted by road traffic. The receptor modeling also shows that the top-five compounds in terms of O3 production come mainly from the exhaust of gasoline vehicles
Improved rainfall estimation over the Indian monsoon region by synergistic use of Kalpana-1 and rain gauge data
Get PDFIn this paper, an attempt has been made to estimate rainfall over the Indian monsoon region by the synergistic use of the geostationary Kalpana-1 satellite-derived INSAT Multispectral Rainfall Algorithm (IMSRA) rainfall estimates and rain gauge data, using a successive correction method in order to further refine the operational IMSRA rainfall estimates. The successive correction method benefits from high spatial and temporal resolutions of the Kalpana-1 satellite and accurate rainfall estimates from rain gauges. A preliminary analysis is done for the southwest monsoon season of 2010 at a daily scale. The successive correction method is applied at a 1º latitude × 1º longitude resolution determined by the spatial autocorrelation analysis. Results are compared with four independent global multisatellite rainfall products, namely the Global Satellite Mapping of Precipitation, the Tropical Rainfall Measuring Mission Multisatellite Precipitation Analysis near-real time and research version rainfall monitoring products, and the Global Precipitation Climatology Project rainfall product. The objectively analyzed rainfall estimates show noticeable improvement over the satellite-based rainfall estimates alone over southern India. Comparison with independent rain gauge observations shows a considerable improvement in terms of correlation, bias and root-mean-square error after objective analysis, especially over the regions where density of rain gauge is fairly good. Overall results reveal that the synergistic use of satellite and in situ observations has potential for more accurate rainfall estimations over the Indian monsoon region
Rossby-Haurwitz wave perturbations under tropical forcing
Get PDFThis study explores the zonal flow in the form of Legendre polynomials. The basic flow is divided into a zonally symmetric flow and a Rossby-Haurwitz (RH) wave. Several features of this (more realistic) zonal flow make it particularly interesting, such as the midlatitude westerly jet streams and an easterly wind around the equator, which closely resembles the mean horizontal flow at 200 mb of the December-February period. The zonal flow is combined with the RH wave, in order to test the blocking formation mechanism on early stages for the northeastern Pacific. A numerical simulation has been performed using a linear barotropic model with tropical forcing and damping to check the extra-tropical response of the mechanism of eddies reinforcement of the ridge along the western coast of North America.Este trabajo explora el flujo zonal en forma de polinomios de Legendre. El flujo básico se divide en un flujo zonal simétrico y una onda de Rossby-Haurwitz (RH). Varias características (más realistas) de este flujo zonal lo hacen particularmente interesante, como las corrientes en chorro con dirección oeste en latitudes medias y un viento con dirección del este alrededor del ecuador, muy similar al flujo medio horizontal del periodo diciembre-enero a 200 mb. El flujo zonal se combina con la onda RH para evaluar las etapas tempranas del mecanismo de acciones de bloqueo en el Pacífico nororiental. Se llevó a cabo una simulación numérica utilizando un modelo barotrópico lineal con forzamiento tropical y disipación para analizar la respuesta extratropical del mecanismo de reforzamiento de torbellinos en los sistemas de alta presión a lo largo de la costa occidental de Norteamérica
Surface temperature forecast skill comparison for the west coast of Saudi Arabia
Get PDFGiven the growing interest of the general public in accessing commercial weather forecasts through various media outlets and the available impetuses for promoting tourism in Saudi Arabia (SA), a first attempt is made to present a forecast skill comparison for surface temperature in four cities (Wejh, Yenbo, Jeddah, and Gizan) along the west coast of SA, for the 61-day transitional period (from January 16 to March 16) between the December-January-February (DJF) and the March-April-May (MAM) seasons. A simple skill score comparison method is used to assess the next-day city forecasts for surface temperature from six commercial weather forecast providers based on the operational numerical weather prediction (NWP) model outputs. All the NWP model forecast providers performed better than the respective daily climatology (Clm) for each station. Depending upon the station and the provider, the absolute average maximum daily surface temperature difference between the forecasts and the observations was less than 2 ºC. Daily surface temperature forecasts from two versions of an atmospheric-ocean general circulation model are also compared to assess their performance for these coastal locations.Debido al interés creciente del público general por acceder a servicios comerciales de pronóstico meteorológico a través de diversos medios de comunicación, y al impulso que ha cobrado la promoción del turismo en Arabia Saudita (AS), se hace un primer intento de comparar aptitudes para el pronóstico de la temperatura superficial en cuatro ciudades situadas en la costa oeste de AS (Wejh, Yenbo, Jeddah, y Giza), centrado en la fase de transición de 61 días (del 16 de enero al 16 de marzo) entre los periodos diciembre-enero-febrero y marzo-abril-mayo. Se utiliza un método sencillo de comparación de puntajes para evaluar los pronósticos de temperatura superficial de 24 h realizados por seis proveedores comerciales de pronósticos del tiempo basados en un modelo numérico. Todos los proveedores que utilizaron el modelo numérico de predicción del tiempo obtuvieron mejores resultados que la climatología diaria para la estación correspondiente. Dependiendo del proveedor y la estación, la diferencia absoluta en los promedios de temperatura máxima entre los pronósticos y las observaciones fue menor a 2 ºC. Los pronósticos diarios de temperatura superficial obtenidos a partir de dos versiones de un modelo de circulación general océano-atmósfera también se comparan para evaluar su desempeño en estas localidades costeras
MESOSCALE CONVECTIVE SYSTEMS IN NW MEXICO DURING THE STRONG ENSO EVENTS OF 1997-1999
Get PDFThis study presents an analysis of the summertime mesoscale convective systems (MCSs) that developed in northwestern Mexico during the strong ENSO events of 1997-1999. From the analysis of geostationary data, results indicate that the largest number of MCSs was associated with the 1997 El Niño event throughout a longer active period. During the La Niña event of 1999 fewer MCSs were observed, which had developed over a shorter active period. The occurrence of the MCSs is linked to the location of the ridge and the anti-cyclonic anomalies at 500 hPa and 200 hPa, respectively
DOWNSCALING STANDARDIZED PRECIPITATION INDEX VIA MODEL OUTPUT STATISTICS
Get PDFThis study investigates the possible impacts of future climate change on meteorological drought events in Turkey by using a new statistical downscaling technique based on polytomous logistic regression, denoted as the model output statistics (MOS) technique. It is designed to downscale the drought classes of the 12-month Standardized Precipitation Index (SPI). The main goal of a downscaling procedure is to determine the influences of large-scale climatic variability and the projected changes on the local scale-regional variables. The large-scale predictors used in this study were obtained from the output of the Second Generation Canadian Coupled General Circulation Model (CGCM2) simulations, run from 1940 to 2100 for three socioeconomic scenarios, namely control, with the constraint of the 20th century atmospheric concentration of greenhouse gases, and the SRES A2 and B2 scenarios. Observations from 96 meteorological stations were used to estimate 12-month SPI values for the period 1940-2010, leaving the last 10 years for validation against the results simulated by the CGCM2. The MOS results derived from the control climate simulation agree with the observed patterns for present climate. The MOS results derived from future climate scenarios lead to conclude that there is a decreased probability of very wet and extremely wet conditions. In addition, the probabilities of near-normal conditions will decrease in the Black Sea coast and will increase towards the Marmara Transition and continental eastern Anatolia regions.
Variation of the 0+ ion density during low and high solar activity as measured by the SR0SS-C2 satellite
Get PDFThe O+ ion density measured by the SROSS-C2 satellite during solar minima (year 1995, F10.7 = 77) and maxima (year 2000, F10.7 = 181) has been analyzed for studying diurnal, seasonal, latitudinal and geomagnetic variations. The study region covers an area encompassed between 5-35º N latitude and 65-95º E longitude over India at a ~500 km altitude (F2 region). The year 2000 shows significant enhancement in the annual average of O+ ion density and attainment of post sunset secondary enhancement compared to 1995. Attributed to photoionization, daytime shows a maximum ionization compared to nigttime. However, attainment of post sunset secondary maxima is attributed to the strong pre-reversal enhancement in the vertical E × B drift. The effect of geomagnetic activity Kp through the E × B drift dynamic movement on O+ ion density distribution studies indicates periodicities of seven and nine days in 1995 and 2000, respectively, and polynomial dependencyof the O+ ion density on geomagnetic activity Kp. Further on, stratification of the O+ ion density accordingto latitude (5-35º N) indicates high density in mid-latitudes (12-24º N) compared to high and low latitudes,except in the winter of 1995, which shows a distinct trend (i.e., density decreases with increasing latitude).Se analiza la densidad del ion O+ medida por el satélite SROSS-C2 durante el mínimo solar de 1995 (F10.7 = 77)y el máximo solar de 2000 (F10.7 = 181) para estudiar variaciones diurnas, estacionales, latitudinales y geomagnéticas. El área de estudio abarca una región comprendida entre los 5 y 35º de latitud norte, y los 65 y 95º de longitud oeste sobre la India a una altura de ~500 km (región F2). El año 2000 muestra un aumento significativo en cuanto al promedio anual de densidad del ion O+ y un aumento secundario posterior a la puesta del sol en comparación con 1995. Durante el día la ionización alcanza un máximo atribuido a la fotoionización. Sin embargo, la ocurrencia de un máximo posterior a la puesta del sol se atribuye a un fuerte aumento previo a la reversión en la desviación vertical E × B. El efecto geomagnético de la actividad Kp a través del movimiento dinámico de la derivación E × B en los estudios de distribución de densidad del ion O+ indica periodicidades de siete y nueve días en 1995 y 2000, respectivamente, así como dependencia polinómica de la densidad del ion O+ en la actividad geomagnética Kp. Más aún, la estratificación de la densidad del ion O+ de acuerdo con la latitud (5-35º N) indica alta densidad en latitudes medias (12-24º N) en comparación con laltitudes bajas y altas, excepto en el invierno de 1995, que muestra un tendencia diferente (i.e., la densidad decrece conforme se incrementa la latitud)
Retrospective health impact assessment for ozone pollution in Mexico City from 1991 to 2011
Get PDFAir pollution is the main environmental issue in Mexico City, where ozone is one of the most damaging pollutants for human health. In this work we present a retrospective health impact assessment (HIA) study split up by age groups for evaluating the benefits of ozone regulatory strategies from 1991 to 2011 in Mexico City. Since people move from one place to another during the day, which may affect their potential exposure to pollutants, we consider time-dependant spatial population distributions during the day. Ozone data is made up of observations taken with hourly frequency from January 1, 1991 to December 31, 2011, at approximately 22 stations of the monitoring network of Mexico City. Interpolated values for unknown locations are also taken into accountin the HIA. The Cressman objective analysis method is applied for interpolating the observed ozone concentrationsfrom monitoring stations to grids of convenient resolution. We demonstrate that different age groupspresent different spatial patterns of exposure, being the working-age people (between 18 and 64 years) the mostbenefited. We also confirm the hypothesis that, in general, people move to less polluted regions during the day.La contaminación atmosférica es el principal problema ambiental en la ciudad de México, donde el ozono es uno de los contaminantes que mayor daño causa a la salud humana. En este trabajo se presenta un análisis retrospectivo del impacto sanitario de las políticas regulatorias de contaminación por ozono desde 1991 hasta 2011 en la zona metropolitana del Valle de México. El estudio se divide en grupos etarios, ya que éstos presentan diferencias respecto a la vulnerabilidad. Dado que las personas se mueven de un lugar a otro durante el día, lo cual puede afectar su exposición potencial a los contaminantes, se consideran distribuciones espaciales de población variables durante el día. Los datos de ozono consisten en registros tomados con frecuencia horaria desde el 1 de enero de 1991 hasta el 31 de diciembre de 2011, en 22 estaciones de la red de monitoreo atmosférico de la ciudad de México. Sin embargo, considerar estos registros es insuficiente; también es necesario interpolar los valores para localizaciones no medidas. El análisis objetivo de Cressman fue el método utilizado para llevar a cabo la interpolación de concentraciones de ozono hacia retículas de resolución conveniente. Se demuestra que los diferentes grupos etarios presentan diferentes patrones espaciales de exposición, y que las personas en edad laboral (de 18 a 64 años) son las más beneficiadas. También se confirma la hipótesis de que en general las personas se mueven hacia regiones menos contaminadas durante el día
Measurements of net all-wave radiation at a tropical location, Ile-Ife, Nigeria
Get PDFHourly averaged net all-wave radiation data spanning a complete three-year period (2010-2012) at a meteorological station located inside the Obafemi Awolowo University campus in Ile-Ife (7.52º N, 4.52º E), Nigeria is presented in this study to investigate its diurnal and seasonal variations. Using a high-sensitivity four-component net radiometer, the data represents so far the most consistent and detailed information available for a tropical location in West Africa. From the dataset, hourly maxima of the net radiation occurred at 14:00 LT (GMT + 1), whose values increased considerably from 337.6 ± 146.4 Wm–2 in July, which is the peak of the wet season, to 441.7 ± 82.4 Wm–2 in March, the end of the dry season. April and October, both of which mark the beginning and end of the raining season at Ile-Ife have recorded the highest values of 584.7 and 612.2 Wm–2, respectively. There was strong intra/inter-seasonal variation observed in the monthly mean values of the net radiation due mainly to the fluctuations in cloudiness and humidity. In the study area, the data indicated a net radiative heating taking place at the surface, whose annual trend follows a bimodal distribution. The present data supports the results published in earlier studies by other authors.Se presentan datos de radiación neta en todas las longitudes de onda promediados cada hora, registrados en una estación meteorológica situada en el campus de la Universidad Obafemi Awolowo, Ile-Ife (7.52º N, 4.52º E),Nigeria, durante un periodo completo de tres años (2010-2012), para estudiar sus variaciones diurnas y estacionales. Esta información, obtenida con un radiómetro neto de alta sensibilidad de cuatro componentes, representa hasta hoy la información más consistente y detallada disponible para una localidad tropical de África Occidental. De acuerdo con los datos obtenidos, la radiación neta máxima ocurrió a las 14:00 LT (GMT + 1),y sus valores se incrementaron de manera considerable de 337.6 ± 146.4 Wm–2 en julio, que es el pico de la estación lluviosa, a 441.7 ± 82.4 Wm–2 durante marzo, en el final de la estación seca. En los meses de abril y octubre, que marcan el principio y fin de la estación lluviosa en Ile-Ife, se han registrado los valores más altos de radiación neta: 584.7 y 612.2 Wm–2, respectivamente. Se observó una importante variación inter e intraestacional en los valores medios mensuales de radiación neta, debida principalmente a fluctuaciones de nubosidad y humedad. En el área de estudio, los datos revelaron la presencia de calentamiento radiativo neto en la superficie, cuya tendencia anual sigue una distribución bimodal. Los datos de este estudio respaldan los aportados por otros autores