ISSN 1000-0526
CN 11-2282/P
CN 11-2282/P
Archive > Volume 49 Issue 12 > 2023,49(12):1435-1450. DOI:10.7519/j.issn.1000-0526.2023.112701 Prev Next
Preliminary Study on the Refined Characteristics of Rainfall Intensity and Dynamic and Thermodynamic Conditions in the July 2023 Severe Torrential Rain in North China
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Abstract:
Based on the ERA5 reanalysis data and the multi-source observations such as ground national and regional automatic weather stations, dual polarization radar, ground raindrop spectrometer, lightning locator, wind-profiling radar, we analyze the refined characteristics of rainfall intensity, the mesoscale convective system (MCS) responsible for the extreme precipitation, the microphysical features as well as dynamic and thermodynamic conditions of the July 2023 extremely severe precipitation process in North China. The results indicate that the hourly rainfall intensity in this event was characterized by weak in most areas but strong at some stations, and the local hourly and minute-level rainfall intensities both reached the extremity level. The stage feature of the rainfall intensity was obvious, with the rainfall intensity being strongest in the second stage from 08:00 BT 30 to 20:00 BT 31 July. This was caused by several β-MCSs and accompanied by mesoscale processes such as backward propagation and train effect. The severe precipitation was mainly composed of high concentration raindrops with medium diameters, and had a certain amount of low-concentration large particle raindrop samples. Thus, this extreme rainfall event belonged to a mixed type with precipitation of oceanic and continental nature, in which warm clouds collided, coexisting with ice crystal aggregation and melting. In the first stage (from 08:00 BT 29 to 08:00 BT 30 July) and the third stage (from 20:00 BT 31 July to 08:00 BT 2 August) the rainfall intensity was relatively small. The former had a low vertical extension height and weak intensity of MCS, dominated by warm-cloud precipitation, and the raindrops had high concentrations and medium diameters. The MCS responding to the latter developed vigorously, but it moved fast. So, it also had the characteristics of mixed-type oceanic and continental precipitation. The maximum values of integrated precipitable water in the three stages all exceeded 70 mm. In the first stage, the synoptic scale forcing was strong, and the convective available potential energy (CAPE) was around 500 J·kg-1. The vertical height of MCS was relatively low. In the second half period of the second stage, the synoptic scale forcing was weakened, but the unstable convective energy in the central and southern parts of North China was rebuilt again. The CAPE in the upstream region became increased compared to the value in the first stage (600-1000 J·kg-1), causing the extreme-rainfall-related MCS to have developed into a deep wet convective system and the rainfall intensity increased significantly. In the third stage, the synoptic scale forcing was greatly weakened. The convergence of southerly wind pulsations at low level and the large CAPE provided favorable conditions for the vigorous development of MCS.
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