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| Titel |
Persistence of Heat Waves and its Link to Soil Moisture Memory |
| VerfasserIn |
Ruth Lorenz, Eric B. Jaeger, Edouard L. Davin, Sonia I. Seneviratne |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250038629
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| Zusammenfassung |
| In this study, we assess the role of soil moisture for heat wave persistence using simulations
with the regional climate model COSMO-CLM. We perform a control run as well as three
different sensitivity experiments with prescribed soil moisture contents (constant at
plant wilting point, respectively field capacity, and prescribed to the mean seasonal
cycle).
Several studies have investigated changes in the frequency of hot summer days but very
few investigated changes in their persistence. We use two different heat wave thresholds for
the definition of hot days, either defined by the 90th-percentile of the control run or by the
90th-percentile of the respective sensitivity experiment. When the threshold is set to the
90th-percentile of the respective sensitivity experiment, we can infer from a difference in heat
wave statistics between the sensitivity and the control experiments that they are characterized
by a different number of threshold exceedances and, hence, a different mean length of
threshold exceedances (i.e. hot day persistence). When using the 90th-percentile of
the CTL experiment, on the other hand, a difference in heat wave length may also
simply be induced by a modified temperature density function in the sensitivity
experiment (e.g. change in mean temperature). In this study, we investigate differences
in heat wave duration in the experiments using both hot day thresholds. With the
joint analysis of the two measures, it is possible to disentangle variations in heat
wave duration caused by differences in the intrinsic persistence of daily maximum
temperatures, and those due to differences in the corresponding probability density
functions.
We identify that simulations with prescribed soil moisture, even for constant dry
conditions, present a lower intrinsic heat wave persistence than simulations with interactive
soil moisture. Correspondingly, with prescribed soil moisture, the autocorrelation of daily
maximum temperature is significantly decreased (by 20% for 5-day lags to more than 50%
for 20-day lags), and the number of short exceedances increases while longer exceedances are
less frequent. This effect is related to the impact of soil moisture memory in the interactive
simulation. Such effects may be overlooked when using the 90th-percentile of the control run
for the definitions of hot days. Our results highlight the key role of soil moisture memory for
the persistence of heat wave events, beside the known effects of soil moisture on heat wave
intensity.
References: Lorenz, R., E.B. Jaeger, and S.I. Seneviratne, 2010: Persistence of heat waves
and its link to soil moisture memory. Submitted to Geophys. Res. Lett. |
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