On the Relationship of a Low-Level Jet and the Formation of a Heavy-Rainfall-Producing Mesoscale Vortex over the Yangtze River Basin

Abstract

Dabie vortices (DBVs) are a type of heavy-rainfall-producing mesoscale vortices that appear with a high frequency around the Dabie Mountain over the Yangtze River Basin. For a long time, scholars have found that DBVs tend to form when a low-level jet (LLJ) appears in their neighboring regions. However, the underlying mechanisms of this phenomenon still remain vague. This study furthers the understanding of this type of event by conducting detailed analyses on a long-lived eastward-moving DBV that caused a severe flood in the 2020 summer. It is found that the LLJ in this event was belonged to a nocturnal LLJ type, with its maximum/minimum appeared around 2100/0600 UTC. The diurnal cycle of LLJ affected precipitation and intensity of the DBV notably: As the LLJ intensified, vortex’s precipitation and intensity both enhanced, and vice versa. The LLJ exerted two effects on the DBV’s formation that are opposite to each other. The more important effect is that the LLJ caused intense lower-level convergence around its northern terminus. This convergence directly produced cyclonic vorticity through vertical stretching, which dominates the DBV’s formation and enhances the convection-related upward cyclonic vorticity transport that acted as another favorable factor. The less important effect is that (i) the LLJ induced import of anticyclonic vorticity into the vortex’s central region, which decelerated the DBV’s formation; and (ii) the LLJ-related to strong ascending motions tilted horizontal vorticity into negative vertical vorticity, which reduced the growth rate of cyclonic vorticity.

Impacts of Horizontal Resolution of the Lateral Boundary Conditions and Downscaling Method on the Performance of RegCM4.6 in Simulating the Surface Climate Over Central‐Eastern China

“…Figure 5 further gives the distribution of differences in the simulated total precipitation (TP), convective (CP), and large‐scale precipitation (LSP) in each experiment relative to ERA5 in summer averaged during 1989–1999. As mentioned above, the ERA5 data have good accuracy in the Yangtze River Basin, China (Fu et al., 2021; Zhang et al., 2019) and provide large‐scale and convective precipitation data, which do not exist in gauge observation. From Figures 5a–5d, the differences in TP show very similar features to the gauge observations (not shown), indicating that the ERA5 data can be used to evaluate the model simulation (Chu et al., 2017; Kan et al., 2015).…”

“…To validate the outputs of RegCM4.6, we used the data listed as follows: (a) The fifth generation of ECWMF atmospheric reanalysis data (ERA5) with the horizontal resolution of 0.25° and temporal resolution of 24 hr from 1979 to the present (Copernicus Climate Change Service (C3S), 2017), which is available at https://cds.climate.copernicus.eu/cdsapp%23%21/search%3Ftype%3Ddataset. It has good accuracy in the Yangtze River Basin, China (Fu et al., 2021; Zhang et al., 2019). (b) The daily observed precipitation data set SURF_CLI_CHN_PRE_MON_GRID_0.5_V2.0, which is produced by interpolating the gauge‐observed precipitation at ∼2,400 stations over China from 1961 to the present with the consideration of GTOPO30 (Global Digital Elevation Model Data) topographic distribution onto the grids with the horizontal resolution of 0.5° (Zhao et al., 2014) (available at the site http://data.cma.cn/).…”

“…copernicus.eu/cdsapp%23%21/search%3Ftype%3Ddataset. It has good accuracy in the Yangtze River Basin, China (Fu et al, 2021;Zhang et al, 2019). (b) The daily observed precipitation data set SURF_CLI_CHN_PRE_ MON_GRID_0.5_V2.0, which is produced by interpolating the gauge-observed precipitation at ∼2,400 stations over China from 1961 to the present with the consideration of GTOPO30 (Global Digital Elevation Model Data) topographic distribution onto the grids with the horizontal resolution of 0.5° (Zhao et al, 2014) (available at the site http://data.cma.cn/).…”

A Study on the Mechanisms Accounting for the Generation of a Southwest Vortex That Caused a Series of Severe Disasters during the 2020 Abnormal Meiyu Season

“…Liu et al [26] found that the sequential warm and cold Meiyu front regulated by the North Atlantic Oscillation was responsible for this abnormal Meiyu event. Fu et al [27] claimed that abnormally active mesoscale vortices and low-level jet acted as the direct reasons for a series of heavy rainfall events during the 2020 Meiyu season. The SCB and its surrounding regions were one of the most severely affected areas during the 2020 abnormal Meiyu season, and the SWVs were found to be one of the most important reasons for the torrential rainfall, lightning, and strong winds in this region.…”