An assessment of the ratio of ultraviolet-B to broadband solar radiation under all cloud conditions at a subtropical location

Adam, M. El-Nouby; Ahmed, Emad A.

doi:10.1016/j.asr.2015.11.030

Cited by 6 publications

(4 citation statements)

References 66 publications

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Section: Introductionmentioning

confidence: 99%

Variability of winter and summer surface ozone in Mexico City on the intraseasonal time scale

Barrett¹,

Raga²

2016

Preprint

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Abstract. Surface ozone concentrations in Mexico City frequently exceed the Mexican standard and have proven difficult to forecast due to changes in meteorological conditions at its tropical location. The Madden-Julian Oscillation (MJO) is largely responsible for intraseasonal variability in the tropics. Circulation patterns in the lower and upper troposphere and precipitation are associated with the oscillation as it progresses eastward around the planet. It is typically described by phases (labeled 1 through 8), which correspond to the broad longitudinal location of the active component of the oscillation with enhanced precipitation. In this study we evaluate the intraseasonal variability of winter and summer surface ozone concentrations in Mexico City was investigated over the period 1986&#8211;2014 to determine if there is a modulation by the MJO that would aid in the forecast of high pollution episodes. Over 1&#8201;000&#8201;000 hourly observations of surface ozone from five stations around the metropolitan area were standardized and then binned by active phase of the MJO, with phase determined using the Real-time Multivariate MJO Index. Highest winter ozone concentrations were found in Mexico City on days when the MJO was active and in phase 2 (over the Indian Ocean), and highest summer ozone concentrations were found on days when the MJO was active and in phase 6 (over the western Pacific Ocean). Lowest winter ozone concentrations were found during active MJO phase 8 (over the eastern Pacific Ocean), and lowest summer ozone concentrations were found during active MJO phase 1 (over the Atlantic Ocean). Anomalies of reanalysis-based cloud cover and UV-B radiation supported the observed variability in surface ozone in both summer and winter: MJO phases with highest ozone concentration had largest positive UV-B radiation anomalies and lowest cloud cover fraction, while phases with lowest ozone concentration had largest negative UV-B radiation anomalies and highest cloud cover fraction. Furthermore, geopotential height anomalies at 250&#8201;hPa favoring reduced cloudiness, and thus elevated surface ozone, were found in both seasons during MJO phases with above-normal ozone concentrations. Similar height anomalies at 250&#8201;hPa favoring enhanced cloudiness, and thus reduced surface ozone, were found in both seasons during MJO phases with below-normal ozone concentrations. These anomalies confirm a physical pathway for MJO modulation of surface ozone via modulation of the upper-troposphere.

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Section: Introductionmentioning

confidence: 99%

Variability of winter and summer surface ozone in Mexico City on the intraseasonal time scale

Barrett¹,

Raga²

2016

Preprint

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“…All of these studies noted a primary relationship between ozone concentration in Mexico City and ultraviolet (UV) radiation, where days with more UV radiation were associated with elevated surface ozone concentrations. Furthermore, UV radiation received at the surface is strongly modulated by cloud cover (El-Nouby Adam and Ahmed, 2016). However, as yet, no study has explored surface ozone variability in Mexico City on the intraseasonal (30-60 day) timescale, despite known relationships between the leading mode of atmospheric intraseasonal variability, the Madden-Julian Oscillation (MJO; Madden and Julian, 1971), and tropical cloud cover (Riley et al, 2011) and circulation (Madden and Julian, 1972;Zhang, 2005).…”

Section: Introductionmentioning

confidence: 99%

“…The problem of the incidence of high surface ozone events is exacerbated in Mexico City, a megacity with 21 million inhabitants, because of the intense solar radiation received at its relatively high elevation (more than 2200 m above sea level) and tropical latitude (19.4 • N) (Lei et al, 2007). Furthermore, the city is located in a basin, effectively preventing efficient ventilation of the polluted air (Fast and Zhong, 1998;Whiteman et al, 2000;Zhang et al, 2009). …”

Section: Introductionmentioning

confidence: 99%

“…However, intensive field campaigns limited to 1 month, cannot address the seasonal and intraseasonal variability of the high surface ozone within the city. Past studies have examined the variability of surface ozone in Mexico City at different timescales, e.g., hourly (Raga and Le Moyne, 1996;Huerta et al, 2004;Lei et al, 2007), daily (Fast and Zhong, 1998), weekly (Stephens et al, 2008), monthly (Rodríguez et al, 2016), and seasonal (Thompson et al, 2008). All of these studies noted a primary relationship between ozone concentration in Mexico City and ultraviolet (UV) radiation, where days with more UV radiation were associated with elevated surface ozone concentrations.…”

Section: Introductionmentioning

confidence: 99%

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Variability of winter and summer surface ozone in Mexico City on the intraseasonal timescale

Barrett

Raga

2016

Atmos. Chem. Phys.

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Abstract. Surface ozone concentrations in Mexico City frequently exceed the Mexican standard and have proven difficult to forecast due to changes in meteorological conditions at its tropical location. The Madden-Julian Oscillation (MJO) is largely responsible for intraseasonal variability in the tropics. Circulation patterns in the lower and upper troposphere and precipitation are associated with the oscillation as it progresses eastward around the planet. It is typically described by phases (labeled 1 through 8), which correspond to the broad longitudinal location of the active component of the oscillation with enhanced precipitation. In this study we evaluate the intraseasonal variability of winter and summer surface ozone concentrations in Mexico City, which was investigated over the period 1986-2014 to determine if there is a modulation by the MJO that would aid in the forecast of high-pollution episodes.Over 1 000 000 hourly observations of surface ozone from five stations around the metropolitan area were standardized and then binned by active phase of the MJO, with phase determined using the real-time multivariate MJO index. Highest winter ozone concentrations were found in Mexico City on days when the MJO was active and in phase 2 (over the Indian Ocean), and highest summer ozone concentrations were found on days when the MJO was active and in phase 6 (over the western Pacific Ocean). Lowest winter ozone concentrations were found during active MJO phase 8 (over the eastern Pacific Ocean), and lowest summer ozone concentrations were found during active MJO phase 1 (over the Atlantic Ocean). Anomalies of reanalysis-based cloud cover and UV-B radiation supported the observed variability in surface ozone in both summer and winter: MJO phases with highest ozone concentration had largest positive UV-B radiation anomalies and lowest cloud-cover fraction, while phases with lowest ozone concentration had largest negative UV-B radiation anomalies and highest cloud-cover fraction. Furthermore, geopotential height anomalies at 250 hPa favoring reduced cloudiness, and thus elevated surface ozone, were found in both seasons during MJO phases with abovenormal ozone concentrations. Similar height anomalies at 250 hPa favoring enhanced cloudiness, and thus reduced surface ozone, were found in both seasons during MJO phases with below-normal ozone concentrations. These anomalies confirm a physical pathway for MJO modulation of surface ozone via modulation of the upper troposphere.

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Spatio-temporal estimations of ultraviolet erythemal radiation in Central Chile

González-Rodríguez

Rodríguez‐López

Jiménez

et al. 2022

Air Qual Atmos Health

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An assessment of the ratio of ultraviolet-B to broadband solar radiation under all cloud conditions at a subtropical location

Cited by 6 publications

References 66 publications

Variability of winter and summer surface ozone in Mexico City on the intraseasonal time scale

Variability of winter and summer surface ozone in Mexico City on the intraseasonal time scale

Variability of winter and summer surface ozone in Mexico City on the intraseasonal timescale

Spatio-temporal estimations of ultraviolet erythemal radiation in Central Chile

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