How the rainfall characteristics of landfalling tropical cyclones (TCs) over China change with the dry-air intrusion is explored through analyzing Tropical Rainfall Measuring Mission (TRMM) and environmental fields. It is found that the rainfall area of landfalling TC is positively correlated to the midlevel environmental relative humidity: the larger the surrounding relative humidity before TC landfall, especially in the southern quadrants of the TC, the larger the rainfall coverage at landfall. Even when situated in a dry environment, the TC may produce severe concentrated rainfall with stronger intensity than in a moist environment. Results show that interaction between synoptic environment and TC is essential for influencing rainfall distribution for landfalling TCs over China. As a TC moves with northward component under two subtropical highs and westerly trough, it is under the influence of significant dry-air intrusion, which results in limited rainfall area. The increasing northwesterly vertical wind shear that is nearly opposite to the TC movement, on the one hand enhances the upshear-side subsidence, which offsets the friction-induced ascent ahead of TC. On the other hand, it strengthens the downshear-side updraft with the corporation of increasing synoptic convergence and results in severe asymmetric rainfall there. When a TC moves under the influences of enhanced subtropical high and monsoonal southwesterlies, it is under the moist environment that causes a larger rainfall area. Influenced by the weaker vertical wind shear with a similar direction as the TC movement, the rainfall distributes relatively symmetrically with heavy rain over the downshear-friction convergence overlapping region at landfall.When a TC makes landfall, its surrounding condition changes dramatically. First of all, the underlying surface changes from ocean to land. Previous observational studies have found that TC rainfall generally has a maximum ahead of the TC center, due to surface friction-induced lower level convergence induced by different magnitudes of radial momentum advection in different quadrants of the TC. Shapiro (1983) used a simple slab boundary layer model to analyze the effect of storm movement on boundary frictional convergence against the observations of radar and wind for Hurricanes Frederic (1979) and Allen (1980) and found that for slow-moving storms, the convergence was located in the front right quadrant, while for fasting-moving storms, it was concentrated more directly ahead of TC. A long-term statistical study also showed that the rainfall maximum tends to locate in the front-to-front-right quadrant of the track, especially in the western North Pacific (WNP;Chen et al., 2006).As the most active basin for TC genesis, the WNP has a favorable environment with warm sea surface temperature and high relative humidity (RH; e.g., Gray, 1968). In addition, a climatological weather systemthe western North Pacific subtropical high (WNPSH)-affects East Asia during the highly active TC season over the WNP. Observ...

In this study, we investigate rainfall characteristics, such as rainfall intensity, rainfall coverage, and the location of heavy rain, associated with tropical cyclones (TCs) that made landfall over China during 2005-2014, using the observations of Tropical Rainfall Measuring Mission and environmental fields. Results show that before landfall, the stronger the TC itself is, the stronger the TC rainfall intensity is in both eyewall and inner rainband regions. However, there is no obvious difference in rainfall intensity in the outer core region for the TCs with different intensity. The coverage of heavy rainfall is also found to be correlated with increasing TC intensity before landfall. It is found that the weak TC with heavy rainfall is usually under strong westward vertical wind shear (VWS), resulting from the impact of enhanced upper-level easterlies associated with a significant northward-shifted South Asia high. In particular, when the TC is located under the right-hand side of the entrance of the upper-level easterly jet, the updraft over the downshear side of the TC circulation is further enhanced under the combined influence of VWS and anomalous upper-tropospheric divergence caused by the jet. The precipitation thus manifests a clear asymmetric feature with severe rainfall over the downshear sector of the weak TC. Our results suggest that the interaction between a weak TC and synoptic systems deserves as much attention as that between a strong TC and surrounding systems in landfalling TC forecasting and research.

The vertical structure of precipitation and its evolution during midlevel dry‐air intrusion (DAI) for landfalling tropical cyclones (LTCs) over China in the past 10 years were examined using several observed Tropical Rainfall Measuring Mission (TRMM) PR products and a reanalysis data set. We show that in the outer region where the environmental midlevel dry air intrudes more easily, the process of environmental DAI has an important effect on the vertical structure and precipitation of LTCs through promoting substantially stratiform precipitation, while inhibiting infrequent intense convective precipitation. Although the total mean rain rate does not change much during the DAI period, both the mean rain rate and area of stratiform precipitation are almost doubled, while the convective precipitation halves compared to the situation prior to the DAI period. Also, the vertical structure of precipitation relative to the vertical wind shear (VWS) is modulated by the dry air, with a clear stratiform precipitation structure in the DAI region, though the dry‐air distribution of LTCs does not depend on the direction of the VWS but rather on the synoptic environmental collocation. Further analysis shows that the mid‐level DAI is favorable to the generation of stratiform precipitation through producing moderate midlevel convergence and less intense low‐level subsidence, which contribute to the mid‐level spin‐up without spinning down the low‐level circulation. At the same time, it helps in maintaining the uniform stratiform precipitation above the melting layer and homogenizing the low‐level circulation, and thus boosts the development of stratiform precipitation in intensity and area in the outer region.