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| Titel |
Sensitivity of high-temperature weather to initial soil moisture: a case study using the WRF model |
| VerfasserIn |
X.-M. Zeng, B. Wang, Y. Zhang, S. Song, X. Huang, Y. Zheng, C. Chen, G. Wang |
| 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 ; 14, no. 18 ; Nr. 14, no. 18 (2014-09-16), S.9623-9639 |
| Datensatznummer |
250119032
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| Publikation (Nr.) |
 copernicus.org/acp-14-9623-2014.pdf |
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| Zusammenfassung |
Using a succession of 24 h Weather Research and Forecasting model (WRF)
simulations, we investigate the sensitivity to initial soil moisture of a
short-range high-temperature weather event that occurred in late July 2003
in East China. The initial soil moisture (SMOIS) in the Noah land surface
scheme is adjusted (relative to the control run, CTL) for four groups of
simulations: DRY25 (−25%), DRY50 (−50%), WET25 (+25%) and WET50
(+50%). Ten 24 h integrations are performed in each group.
We focus on 2 m surface air temperature (SAT) greater than 35 °C
(the threshold of "high-temperature" events in China) at 06:00 UTC (roughly
14:00 LT in the study domain) to analyse the occurrence of the
high-temperature event. The 10-day mean results show that the 06:00 UTC SAT
(SAT06) is sensitive to the SMOIS change; specifically, SAT06 exhibits an
apparent increase with the SMOIS decrease (e.g. compared with CTL, DRY25
generally results in a 1 °C SAT06 increase over the land surface
of East China), areas with 35 °C or higher SAT06 are the most
affected, and the simulations are more sensitive to the SMOIS decrease than
to the SMOIS increase, which suggests that hot weather can be amplified
under low soil moisture conditions. Regarding the mechanism underlying the
extremely high SAT06, sensible heat flux has been shown to directly heat the
lower atmosphere, and latent heat flux has been found to be more sensitive
to the SMOIS change, resulting in an overall increase in surface net
radiation due to the increased greenhouse effect (e.g. with the SMOIS
increase from DRY25 to CTL, the 10-day mean net radiation increases by 5 W m−2).
Additionally, due to the unique and dynamic nature of the western
Pacific subtropical high, negative feedback occurs between the regional
atmospheric circulation and the air temperature in the lower atmosphere
while positive feedback occurs in the mid-troposphere.
Using a method based on an analogous temperature relationship, a detailed
analysis of the physical processes shows that for the SAT change, the SMOIS
change affects diabatic processes (e.g. surface fluxes) more strongly than
the adiabatic process of subsidence in the western Pacific subtropical high
in the five groups of simulations. Interestingly, although diabatic
processes dominate subsidence during the daytime and night-time separately,
they do not necessarily dominate during the 24 h periods (e.g. they are
dominant in the WET and CTL simulations only). Further, as the SMOIS
decreases, the SAT06 increases, which is largely due to the reduced cooling
effect of the diabatic processes, rather than the warming effect of
subsidence.
Unlike previous studies on heatwave events at climate timescales, this
paper presents the sensitivity of simulated short-term hot weather to
initial soil moisture and emphasises the importance of appropriate soil
moisture initialization when simulating hot weather. |
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