Autor a quien debe ser dirigida la correspondencia. ResumenSe evaluaron dos modelos de reducción de escala en la generación de escenarios de cambio climático en el Valle de Mexicali en México. Las técnicas comparadas son un Generador Estocástico de Tiempo Meteorológico (LARS-WG) y un método dinámico-estadístico (SDSM). Cada técnica se evaluó por su habilidad para reproducir algunas características estadísticas del clima observado en el período . Se elaboraron escenarios de cambio climático de temperatura y precipitación para los horizontes temporales 2020 y 2050. El LARS WG y el SDSM son técnicas sencillas que mostraron habilidades diferentes en la simulación de momentos estadísticos del clima observado, siendo ambos más eficientes para simular la temperatura que la precipitación. Para uno de los escenarios considerados se encontró diferencias de 0.1°C y 0.2°C para temperatura máxima y temperatura mínima y del 40.4% al 76.7% para precipitación. Palabras clave: reducción de escala, cambio climático, valle de Mexicali, LARS-WG, SDSM AbstractTwo downscaling models in the generation of climate change scenarios in the Mexicali valley in México were evaluated. The evaluated techniques were the stochastic weather generator (LARS-WG) and the dynamical-statistical model (SDSM). Each technique was evaluated for its ability to reproduce some statistical characteristics of the observed climate during the period 1961-1990. Climate change scenarios of temperature and precipitation for the period 2020 to 2050 were considered. LARS WG and SDSM are simple techniques that showed different abilities in simulating statistical moments of the observed climate, but both were more efficient for simulating temperature than precipitation. For one of evaluated scenarios differences of 0.1°C and 0.2°C for maximum and minimum temperature and 40.4% to 76.7% for precipitation.

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.