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Titel |
Evidence for Convective Invigoration from A-Train Observations |
VerfasserIn |
Johannes Mülmenstädt, Daniel Rosenfeld, Odran Sourdeval, Johannes Quaas, Julien Delanoë |
Konferenz |
EGU General Assembly 2016
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Medientyp |
Artikel
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Sprache |
en
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Digitales Dokument |
PDF |
Erschienen |
In: GRA - Volume 18 (2016) |
Datensatznummer |
250135267
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Publikation (Nr.) |
EGU/EGU2016-16112.pdf |
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Zusammenfassung |
The ‘convective invigoration’ hypothesis posits that aerosol affects precipitating clouds by
delaying the onset of precipitation until the cloud has grown above the freezing level,
making more efficient ice-phase precipitation processes available and leading to more
intense precipitation than would have been produced by the same cloud in a less
polluted atmosphere. In the IPCC AR5, evidence for a systematic aerosol effect on
precipitation intensity (i.e., not limited to individual storms) is described as ‘limited and
ambiguous’.
We use a combined dataset of spaceborne radar (CloudSat) and lidar (CALIPSO) retrievals of
precipitation and cloud thermodynamic phase to derive a climatology of rain occurrence from
liquid-phase cloud (‘warm rain’) and ice-phase cloud (‘cold rain’). The cloud-top phase of
precipitating cloud serves as a proxy for rain intensity, with warm clouds preferentially
producing drizzle and cold clouds preferentially producing more intense rain. This proxy is
useful over land, where CloudSat does not retrieve precipitation intensity. In conjunction with
aerosol data, the cloud-top phase can be used to test convective invigoration; according
to the hypothesis, increasing aerosols should lead to an increase in the cold-rain
fraction.
We find that warm rain is extremely rare over the extratropical continents (1.5% of rain
occurrences). Warm rain is rarer in the most polluted tercile of observations (measured by
reanalysis dry AOD) over wide areas of land and ocean outside the tropics, consistent with
expectations under the convective invigoration hypothesis. (In the tropics, the effect is
reversed, presumably due to wet scavenging.) Extrapolating the observed relationship
between warm-rain fraction and reanalysis dry AOD to preindustrial conditions shows a large
anthropogenic aerosol influence on precipitation over the extratropical continents.
We propose this as evidence supporting the convective invigoration hypothesis. |
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