Basin-scale wind transport during the MILAGRO field campaign and comparison to climatology using cluster analysis

Abstract

Abstract. The MILAGRO field campaign was a multi-agency international collaborative project to evaluate the regional impacts of the Mexico City air pollution plume as a means of understanding urban impacts on the global climate. Mexico City lies on an elevated plateau with mountains on three sides and has complex mountain and surface-driven wind flows. This paper asks what the wind transport was in the basin during the field campaign and how representative it was of the climatology. Surface meteorology and air quality data, radiosondes and radar wind profiler data were collected at sites in the basin and its vicinity. Cluster analysis was used to identify the dominant wind patterns both during the campaign and within the past 10 years of operational data from the warm dry season. Our analysis shows that March 2006 was representative of typical flow patterns experienced in the basin. Six episode types were identified for the basin-scale circulation providing a way of interpreting atmospheric chemistry and particulate data collected during the campaign. Decoupling between surface winds and those aloft had a strong influence in leading to convection and poor air quality episodes. Hourly characterisation of wind circulation during the MILAGRO, MCMA-2003 and IMADA field campaigns enables the comparisons of similar air pollution episodes and the evaluation of the impact of wind transport on measurements of the atmospheric chemistry taking place in the basin.

PM1 Chemical Characterization during the ACU15 Campaign, South of Mexico City

“…Given that sulfate is formed in a regional scale [13,18], a larger fraction of this component could also indicate that the aerosol was more aged than in other sites during previous campaigns, which is consistent with the patterns of air circulation that have been described in the Mexico City basin by de Foy et al [35] during the month of April 2003 for the MCMA03 campaign. The same patterns were observed during the MILAGRO campaign in 2006 [36], and are expected to have occurred during ACU15 because the three campaigns occurred in the dry season. In general, northerly surface winds in the morning meet a southwest flow from a mountain gap south east of the Mexico City basin, which generate a convergence zone in the afternoon where the highest ozone concentrations of the day are detected.…”

“…The same patterns were observed during the MILAGRO campaign in 2006 [36], and are expected to have occurred during ACU15 because the three campaigns occurred in the dry season. In general, northerly surface winds in the morning meet a southwest flow from a mountain gap south east of the Mexico City basin, which generate a convergence zone in the afternoon where the highest ozone concentrations of the day are detected.…”

Cluster Analysis of the Wind Events and Seasonal Wind Circulation Patterns in the Mexico City Region

“…A comparison of the wind patterns WP1-WP7 with those reported by de Foy et al [16] shows the following important similarities and differences, which are also summarized in …”

“…De Foy et al [16] reported a cluster analysis carried out to identify the main wind circulation modes in the metropolitan area of Mexico City for the period of the MILAGRO campaign (March 2006) and also for a period of 10 years before, but considering only the warm dry season (15 February to 15 May). They also used the hourly wind data reported by the meteorological network REDMET.…”

“…Salcido et al [1] performed the first long-term micrometeorological campaign in surface carried out in a three station network in Mexico City throughout 2001. Finally, de Foy et al [16] reported a basin-scale study of the wind transport during the MILAGRO campaign and its comparison to climatology using cluster analysis on the period of March 2006 and in the period 1998-2006 of hourly surface wind data from the Mexico City atmospheric monitoring network (RAMA) for the warm dry season. They showed that March 2006 was representative of typical flow patterns experienced in the basin, and they could identify six episode types for the basin-scale circulation.…”