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The eastward displacement of Southwest Vortices (SWVs) profoundly impacts the precipitation in the middle and lower reaches of the Yangtze River Basin (YRB) in summer. At present, the feedback mechanism of latent heating on the persistent eastward movement of SWVs under the influence of the orographic effect of the second‐step terrain in China remains unclear. Therefore, this study focused on clarifying the relationship between orographic effects and the mechanisms governing the persistent eastward movements of SWVs, as well as the feedback effect of latent heating on the eastward‐moving SWVs. In this study, it is revealed that discontinuous maintenance of closed vortex circulation occurs when eastward‐moving SWVs pass over the second‐step terrain region. Specifically, eastward‐moving SWVs first experience dissolution on the windward side, followed by substantial reconstruction of closed vortex circulation on the leeward side when passing over the second‐step terrain region. Moreover, the reconstruction of closed vortex circulation on the leeward side is closely associated with the feedback effect of latent heating, and the microphysical property of cold clouds identified during the vortex intensification determines the dual‐peak feature observed in the vertical constitution of the total latent heating, which is related to two major phase‐transition processes: the condensation of water vapor into liquid‐phase hydrometeors (LCP_vapor) process and the desublimation of water vapor into ice‐phase hydrometeors (LSP_vapor) process. From a potential vorticity (PV) perspective, latent heating promotes the genesis of PV anomalies, which accordingly facilitates the maintenance of a positive "vorticity tower" (i.e., total budget of vorticity) via the tilting effect and the horizontal advection effect of local vorticity. Further sensitivity experiments of latent heating indicated that latent heating associated with the LCP_vapor process fulfills a more important role in sustaining the positive "vorticity tower" than does that associated with the LSP_vapor process during the vortex intensification. Plain Language Summary: This study focused on clarifying the relationship between the orographic effect of the second‐step terrain and the vertical distribution of latent heating, as well as unraveling the feedback mechanism of latent heating on the intensification of vortices downstream of the second‐step terrain. The microphysical properties of cold clouds are further highlighted during the intensification of vortices, and the vertical profile of latent heating exhibits double‐peak features correspondingly. This is associated with two categories of phase‐transition processes: the condensation of water vapor into liquid‐phase hydrometeors (i.e., LCP_vapor) and the desublimation of water vapor into ice‐phase hydrometeors (i.e., LSP_vapor). Further analysis confirms that the topographically enhanced convection downstream of the second‐step terrain provides favorable dynamic conditions for further vertical transportation of water vapor, which substantially facilitates the LCP_vapor and LSP_vapor processes. Latent heating is conducive to the genesis of PV anomalies and facilitates the maintenance of a positive "vorticity tower" via the tilting effect and the horizontal advection effect of local vorticity, which plays crucial roles in strengthening vortices. Key Points: The evolution of vortices indicates the closed vortices is not a continuous maintenance process during the eastward propagation of the SWVsA causal relationship is established between the orographic effect of the second‐step terrain and the latent heating via convectionThe condensation process of water vapor plays the most decisive role in affecting the feedback effect of latent heating [ABSTRACT FROM AUTHOR]

Water vapor transport is a crucial process in modeling and can contribute to errors in precipitation forecasts. To investigate the sensitivity of precipitation to the moisture advection scheme, this study introduced the two-step shape-preserving advection scheme (TSPAS), which has been proven to improve precipitation simulation over steep topography at lower resolutions, into the Southwest Center Weather Research and Forecast (WRF)-based Intelligent Numerical Grid Forecast System (SWC-WINGS) at a convection-permitting resolution. According to experiments conducted throughout the summer of 2021, the precipitation over the eastern slope of the Tibetan Plateau (TP) is highly sensitive to the moisture advection scheme. TSPAS successfully improved precipitation over the eastern slope of the TP, especially for torrential rainfall. The fractions skill score (FSS) is improved by 0.075 (27.78%) for daily precipitation with a threshold of 100 mm. Compared with the experiment with the original WRF advection scheme, the TSPAS reduced the overestimation of precipitation in the topographic region and excessive water vapor transport in a low-level atmosphere. To understand the precipitation improvement contributed by the advection scheme, additional experiments were conducted for a particular precipitation process from two approaches: switching advection schemes during the rainfall evolution and updating the variables related to moisture advection individually. Results demonstrate that the precipitation improvement is mainly contributed by the moisture advection scheme before the precipitation. Among the different variables, the combination of wind and water vapor was the most influential factor causing the precipitation improvement under the TSPAS. [ABSTRACT FROM AUTHOR]

To further assess and enhance the capabilities of regional models for high-resolution climate simulation in the east of Southwestern China (ESWC), the present study investigated two nested simulations (with D01 as the outer domain and D02 as the inner domain) of summer rainfall and temperature over the ESWC from 1998 to 2019. These simulations were conducted using the Weather Research and Forecasting (WRF) model coupled with various boundary layer parameterization schemes. The findings indicated that different parameterization schemes can lead to biases in the simulated mean annual rainfall. Specifically, the D01 domain exhibited a noticeable wet bias, while the D02 domain showed a dry bias in the Sichuan Basin and the lower altitudes of Chongqing. A wet bias was predominantly found in the complex terrain areas of Chengkou, Shizhu and Wulong in Chongqing, as well as in Guizhou. Overall, the YSU scheme in D01 and the MYJ scheme in D02 demonstrated the smallest bias in rainfall simulations. Regarding temperature simulations, a noticeable warm bias was present in D01 for the Sichuan Basin, with a cold bias in other areas. In D02, a warm bias was observed for most regions. The MYJ scheme exhibited the least bias, while the YSU scheme showed the greatest bias in both domains. The WRF model skillfully reproduced the interannual variability of rainfall and temperature in the midwest of Chongqing and most of Hubei. The YSU scheme outperformed others in rainfall simulation, while the MYJ scheme excelled in temperature simulation. These results suggest that the choice of an optimal scheme may vary depending on the meteorological parameter of interest, especially after model resolution is enhanced to the convective scale. Therefore, it is crucial to select the most suitable local scheme based on operational requirements. [ABSTRACT FROM AUTHOR]

Diurnal variation in regional precipitation in Central and East China has been broadly identified in previous study. This study focused on clarifying not only the differences in the diurnal variation concerning the local precipitation occurred in the Dabie Mountain (DBM) region and the regional precipitation occurred through the middle‐lower reaches of the Yangtze River Basin, but also the association mechanism between diurnal variation in local precipitation with differing duration and diurnal modulation of ambient circulations driven by large‐scale background synoptic force or local‐scale orographic force of the DBM. It was found that cases of short duration precipitation (SDP, duration <6 h) and cases of long duration precipitation (LDP, duration ≥6 h) exhibit vastly different patterns of diurnal variations. Further investigation revealed that the primary pattern of the ambient circulation responsible for SDP and LDP is the recycling transformation between a closed cyclonic circulation to a cyclonic wind shear, and the recycling movement of a closed cyclonic circulation in the lower troposphere respectively. Although the diurnal variation in LDP exhibited greater orographic regional differences between the west slope (WS) region and the east slope (ES) region in comparison with that of SDP, topographical sensitivity experiments of the DBM and detailed analysis of background synoptic systems associated with LDP indicated that this regional orographic difference shows closer association with eastward propagation of background synoptic systems than orographic effects of the DBM. Respective strengthening of upward vertical motion at different levels of the troposphere during diurnal variation in SDP and LDP cases provide substantial evidences to reconfirm the close association with orographic force in lower the troposphere for SDP cases and background synoptic force in middle troposphere for LDP cases. Further quantitative diagnosis also confirmed that the orographic effects of the DBM is conducive to cause marked differences in the diurnal variation in SDP cases between the WS region and the ES region via adjustment of the upslope wind over the former and the circumventing wind over the latter. [ABSTRACT FROM AUTHOR]