Tuesday, 29 August 2023
Boundary Waters (Hyatt Regency Minneapolis)
The Dabie Mountain region in East China experiences frequent heavy rainfall every warm season. In this study, we used radar and satellite data to investigate the combined effects of synoptic patterns and topography in determining the spatiotemporal variation of heavy rainfall in the region during the warm seasons of 2008-2020 based on an objective classification method.
The results indicate that heavy rainfall is most likely to occur under three typical synoptic patterns (P1-P3), where P1 and P2 both feature a southwesterly monsoon, while P3 is dominated by a southeasterly monsoon. The diurnal cycles of heavy rainfall under P1 and P3 exhibit a bimodal distribution with a primary peak in the morning and a secondary peak at noon, whereas heavy rainfall of P2 has only one significant morning peak. The morning heavy rainfall peak can be explained by the enhanced moisture transportation due to the inertial oscillation of low-level wind and its interaction with topography. Under P1 and P3, intensified low-level wind leads to a low-level cyclonic circulation over the study region, which strengthens the morning rainfall peak. However, under P2, the cyclonic circulation tends to propagate northeastward, therefore suppresses heavy rainfall after the morning peak as it reaches the northeast side of Dabie mountain.
Based on the statistical results, a heavy rainfall event caused by a mesoscale convective system (MCS) under P1 has been examined by the assimilation of both radar and surface observations into the Variational Doppler Radar Analysis System. The results indicate that the initiation of the MCS resulted from the collisions among three distinct outflow boundaries. The subsequent merge of mesoscale vortexes intensified the newly triggered convection and led to the organization of a south-north-oriented squall line.
The study concludes that under the modulation of synoptic patterns, the diurnal cycle and spatial distribution of heavy rainfall is closely related to the scale interactions between the diurnal varying low-level moisture transportation and local terrains in East China.
The results indicate that heavy rainfall is most likely to occur under three typical synoptic patterns (P1-P3), where P1 and P2 both feature a southwesterly monsoon, while P3 is dominated by a southeasterly monsoon. The diurnal cycles of heavy rainfall under P1 and P3 exhibit a bimodal distribution with a primary peak in the morning and a secondary peak at noon, whereas heavy rainfall of P2 has only one significant morning peak. The morning heavy rainfall peak can be explained by the enhanced moisture transportation due to the inertial oscillation of low-level wind and its interaction with topography. Under P1 and P3, intensified low-level wind leads to a low-level cyclonic circulation over the study region, which strengthens the morning rainfall peak. However, under P2, the cyclonic circulation tends to propagate northeastward, therefore suppresses heavy rainfall after the morning peak as it reaches the northeast side of Dabie mountain.
Based on the statistical results, a heavy rainfall event caused by a mesoscale convective system (MCS) under P1 has been examined by the assimilation of both radar and surface observations into the Variational Doppler Radar Analysis System. The results indicate that the initiation of the MCS resulted from the collisions among three distinct outflow boundaries. The subsequent merge of mesoscale vortexes intensified the newly triggered convection and led to the organization of a south-north-oriented squall line.
The study concludes that under the modulation of synoptic patterns, the diurnal cycle and spatial distribution of heavy rainfall is closely related to the scale interactions between the diurnal varying low-level moisture transportation and local terrains in East China.
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