An observational study of the effects of aerosols on diurnal variation of heavy rainfall and associated clouds over Beijing–Tianjin–Hebei
2020
Abstract. Our previous study found that the observed rainfall diurnal
variation over Beijing–Tianjin–Hebei shows the distinct signature of the effects
of pollutants. Here we used the hourly rainfall data together with
satellite-based daily information of aerosols and clouds to further
investigate changes in heavy rainfall and clouds associated with aerosol
changes. Because of the strong coupling effects, we also examined the
sensitivity of these changes to moisture (specific humidity) variations. For
heavy rainfall, three distinguished characteristics are identified: earlier start time, earlier peak time,
and longer duration; and the signals are robust using aerosol indicators based on both
aerosol optical depth and cloud droplet number concentration. In-depth
analysis reveals that the first two characteristics occur in the presence of
(absorbing) black carbon aerosols and that the third is related to more
(scattering) sulfate aerosols and is sensitive to moisture abundance. Cloud
changes are also evident, showing increases in cloud fraction, cloud top
pressure, the liquid/ice cloud optical thickness and cloud water path and
a decrease in ice cloud effective radius; and these changes are insensitive to
moisture. Finally, the mechanisms for heavy rainfall characteristics are
discussed and hypothesized.
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