México es un país vulnerable a los eventos climáticos extremos; sin embargo, el impacto no es uniforme en todo el territorio, por lo que se analizan y modelan las temperaturas extremas de 12 ciudades de México con la suposición de que existe un clima no estacionario en todas las regiones del país. A partir de la base climatológica disponible de temperaturas máximas y temperaturas mínimas, se estimó una tendencia temporal con las pruebas no paramétricas de Mann-Kendall y el método de pendiente de Sen, y se utilizó la distribución generalizada de valores extremos (GEV) para modelar ambas temperaturas. Para evaluar la fortaleza de los modelos propuestos con la incorporación de una covariable, se utilizaron tanto la prueba de razón de verosimilitud como los criterios de información de Akaike y de Bayes, y se estimaron los niveles de retorno para escenarios temporales futuros. Se detectó una tendencia al calentamiento urbano, tanto con las pruebas no paramétricas como con la distribución GEV, aunque con comportamiento heterogéneo. En la serie de temperatura máxima, la mitad de las ciudades analizadas se mostró no estacionaria; de éstas, la ciudad de Guadalajara, situada en el centro-occidente del país, presentó tendencia negativa. En el caso de las temperaturas mínimas la tendencia fue más uniforme: 90% de las ciudades se mostraron no estacionarias con tendencia positiva y sólo el 10% (una zona urbana al oriente de la zona metropolitana del Valle de México [Milpa Alta] y una ciudad costera del Golfo de México [Veracruz]) mostraron una serie estacionaria. Se concluye que los periodos de retorno de extremos térmicos estimados en un clima cambiante varían temporalmente, por lo que la modelación estadística debe tomar en cuenta ese comportamiento en razón de su importancia para valoraciones de riesgos y propósitos de adaptación.
The objective was to analyze how representative tropospheric NO 2 column densities are of surface NO 2 measurements under different atmospheric stability conditions in the air basin of two border cities: Calexico, United States, and Mexicali, Mexico. NO 2 columns were measured by the Ozone Monitoring Instrument (OMI) on the NASA Aura satellite. NO 2 concentrations and meteorological parameters were also measured on the surface for comparison. Specifically, the correlations between OMI and surface NO 2 concentrations under different atmospheric stability conditions according to the Pasquill-Gifford (P-G) and Monin-Obukhov (M-O) classification schemes were determined for 2017 and 2018. During the passage of the satellite through the study area (11:00-13:00 UTC−8), unstable conditions were documented in both years.Good correlation was found between the surface NO 2 and OMI NO 2 column observations in the second semester of each year, particularly under unstable conditions as diagnosed by the P-G and M-O schemes applied in the first and second year, respectively. However, a weakening of these conditions occurs during the autumn-winter period. In both cases, the highest determination coefficients were found for Calexico, with values of 0.48 and 0.36 in 2017 and 2018, respectively; for Mexicali, the determination coefficients were 0.23 and 0.35, respectively. Under each atmospheric stability scheme, the mechanical and convective turbulence caused a decreasing trend in wind speed and solar radiation over the course of second semester of 2017 and in friction velocity, temperature, and sensible heat flux over the course of the same period for 2018. The negative trend of these parameters during the analyzed time frames helped to reduce the influence of unstable atmospheric conditions, favoring better correlations between satellite and surface NO 2 measurements. The methodology applied and results obtained herein can enable us to better understand the representativeness of OMI NO 2 data in arid border zones with extreme meteorological conditions.
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