Weekly cycles of air pollutants, precipitation and tropical cyclones in the coastal NW Atlantic region

Direct human influences on climate have been detected at local scales, such as urban temperature increases and precipitation enhancement(1-3), and at global scales(4,5). A possible indication of an anthropogenic effect on regional climate is by identification of equivalent weekly cycles in climate and pollution variables. Weekly cycles have been observed in both global surface temperature(6) and local pollution(7) data sets. Here we describe statistical analyses that reveal weekly cycles in three independent regional-scale coastal Atlantic data sets: lower-troposphere pollution, precipitation and tropical cyclones. Three atmospheric monitoring stations record minimum concentrations of ozone and carbon monoxide early in the week, while highest concentrations are observed later in the week. This air-pollution cycle corresponds to observed weekly variability in regional rainfall and tropical cyclones. Specifically, satellite-based precipitation estimates indicate that near-coastal ocean areas receive significantly more precipitation at weekends than on weekdays. Near-coastal tropical cyclones have, on average, significantly weaker surface winds, higher surface pressure and higher frequency at weekends. Although our statistical findings limit the identification of cause-effect relationships, we advance the hypothesis that the thermal influence of pollution-derived aerosols on storms may drive these weekly climate cycles.