Abstract
Abstract. Heavy rainfall events causing floods and flash floods are examined in the context of solar wind coupling to the magnetosphere–ionosphere–atmosphere system. The superposed epoch (SPE) analyses of solar wind variables have shown the tendency of severe weather to follow arrivals of high-speed streams from solar coronal holes. Precipitation data sets based on rain gauge and satellite sensor measurements are used to examine the relationship between the solar wind high-speed streams and daily precipitation rates over several midlatitude regions. The SPE analysis results show an increase in the occurrence of high precipitation rates following arrivals of high-speed streams, including recurrence with a solar rotation period of 27 d. The cross-correlation analysis applied to the SPE averages of the green (Fe XIV; 530.3 nm) corona intensity observed by ground-based coronagraphs, solar wind parameters, and daily precipitation rates show correlation peaks at lags spaced by solar rotation period. When the SPE analysis is limited to years around the solar minimum (2008–2009), which was dominated by recurrent coronal holes separated by ∼ 120∘ in heliographic longitude, significant cross-correlation peaks are found at lags spaced by 9 d. These results are further demonstrated by cases of heavy rainfall, floods and flash floods in Europe, Japan, and the USA, highlighting the role of solar wind coupling to the magnetosphere–ionosphere–atmosphere system in severe weather, mediated by aurorally excited atmospheric gravity waves.
Highlights
Extreme rainfall and flash floods have major societal and economic impacts, posing significant natural hazards (Gaume et al, 2009) that increasingly require careful flood risk assessment, mitigation strategies, and recovery management (National Academies of Sciences, 2019)
The cross-correlation analysis applied to the superposed epoch (SPE) averages of green corona intensity, solar wind parameters and daily precipitation rates show correlation peaks at lags spaced by solar rotation period
When the SPE analysis is limited to years around solar minimum (2008–2009), correlation peaks at lags spaced by 9 d are revealed, which is a result of high-speed streams from coronal holes spaced in heliographic longitude by approximately 120◦
Summary
Extreme rainfall and flash floods have major societal and economic impacts, posing significant natural hazards (Gaume et al, 2009) that increasingly require careful flood risk assessment, mitigation strategies, and recovery management (National Academies of Sciences, 2019). Severe weather, including severe winter storms, windstorms, snowstorms, heavy rain events, and explosively developing extratropical cyclones have been examined by Prikryl et al (2018) in the context of solar wind coupling to the MIA system They observed a tendency of significant weather events to follow arrivals of high-speed solar wind streams. The statistical results (Prikryl et al, 2009a, 2016, 2018) and a proposed physical mechanism of Prikryl et al (2009b) were supported by cases of severe weather events, including two flash floods that occurred in Slovakia on 16 and 24 July 2001 (Prikryl et al, 2018; their Fig. 10) Both flash floods closely followed arrivals of solar wind high-speed streams from coronal holes, and a series of convective supercells were associated with atmospheric gravity waves (AGWs) from sources in the highlatitude lower thermosphere that could have reached the midlatitude troposphere. The goal is to demonstrate the statistical link between the solar wind and the occurrence of heavy rainfall and to identify the highlatitude sources of AGWs that may play a role in triggering the convection leading to heavy rainfall, floods, and flash floods
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