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| Titel |
Persistent after-effects of heavy rain on concentrations of ice nuclei and rainfall suggest a biological cause |
| VerfasserIn |
E. K. Bigg, S. Soubeyrand, C. E. Morris |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 15, no. 5 ; Nr. 15, no. 5 (2015-03-03), S.2313-2326 |
| Datensatznummer |
250119485
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| Publikation (Nr.) |
 copernicus.org/acp-15-2313-2015.pdf |
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| Zusammenfassung |
| Rainfall is one of the most important aspects of climate, but the extent to
which atmospheric ice nuclei (IN) influence its formation, quantity,
frequency, and location is not clear. Microorganisms and other biological
particles are released following rainfall and have been shown to serve as
efficient IN, in turn impacting cloud and precipitation formation. Here we
investigated potential long-term effects of IN on rainfall frequency and
quantity. Differences in IN concentrations and rainfall after and before
days of large rainfall accumulation (i.e., key days) were calculated for
measurements made over the past century in southeastern and southwestern
Australia. Cumulative differences in IN concentrations and daily rainfall
quantity and frequency as a function of days from a key day demonstrated
statistically significant increasing logarithmic trends (R2 > 0.97). Based on observations that cumulative effects of
rainfall persisted for about 20 days, we calculated cumulative differences
for the entire sequence of key days at each site to create a historical
record of how the differences changed with time. Comparison of pre-1960 and
post-1960 sequences most commonly showed smaller rainfall totals in the
post-1960 sequences, particularly in regions downwind from coal-fired power
stations. This led us to explore the hypothesis that the increased leaf
surface populations of IN-active bacteria due to rain led to a sustained but
slowly diminishing increase in atmospheric concentrations of IN that could
potentially initiate or augment rainfall. This hypothesis is supported by
previous research showing that leaf surface populations of the
ice-nucleating bacterium Pseudomonas syringae increased by orders of magnitude after heavy rain
and that microorganisms become airborne during and after rain in a forest
ecosystem. At the sites studied in this work, aerosols that could have
initiated rain from sources unrelated to previous rainfall events (such as
power stations) would automatically have reduced the influences on rainfall
of those whose concentrations were related to previous rain, thereby leading
to inhibition of feedback. The analytical methods described here provide
means to map and delimit regions where rainfall feedback mediated by
microorganisms is suspected to occur or has occurred historically, thereby
providing rational means to establish experimental set-ups for verification. |
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