How Do Weak Tropical Cyclones Produce Heavy Rainfall When Making Landfall Over China

Abstract

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.

Observed Vertical Structure of Precipitation Influenced by Dry Air for Landfalling Tropical Cyclones Over China

“…Consistent with the result of Wang (2012) for cyclogenesis, our analysis shows that the midlevel DAI is favorable to the generation of stratiform precipitation through producing moderate midlevel convergence and less intense low‐level subsidence which contribute to the midlevel spin‐up without spinning down the low‐level circulation, or help 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 or areal coverage. The results obtained here deepen the previous finding by Feng and Shu (2018), which showed that the total precipitation in the outer region does not change much as that in the eyewall during TC landfall without providing scientific explanation. Since the stratiform precipitation is found to occur when the young and vigorous convection becomes older or mature (Houze, 1997), the results of this work seems to indicate that the DAI may speed up the lifecycle of the convective system or trigger the transition from convective precipitation to stratiform precipitation.…”

Observed Shear-Relative Rainfall Asymmetries Associated with Landfalling Tropical Cyclones

“…As TCs approach the coast (preland TCs), the rainfall magnitude experiences a slight decrease by about 3%, which is consistent with previous studies [32,37,42]. e contribution from higher wavenumbers to the total rainfall of preland TCs is slightly higher than that of off-shore TCs.…”

“…However, TC rainfall enhancement induced by topographic effect was not evident in other landfalling TC studies [32,42]. Feng and Shu [37] showed that TC experienced a decrease in rainfall intensity during its landfall due to the cutting-off of energy and moisture from the ocean. In contrast, TC rainfall redistribution can be promoted by the interaction between a TC and baroclinic systems.…”

“…Asymmetries in the TC rainfall associated with landfalling can be modulated by not only VWS [30][31][32][33][34], but also some other factors, such as nonuniform surface features including land-sea contrast and local topographic effect [31,32,[34][35][36][37][38][39] and interaction between TCs and synoptic weather systems [38,40,41]. In general, the landfalling TCs regularly had an asymmetry with a downshear to downshear-left rainfall maximum near the coastal regions, which is consistent with the studies for TCs over the ocean [3,19,42].…”

On the Flood Peak Distributions over China

“…Previous studies show that landfalling tropical cyclones can make great contributions to extreme rainfall in inland regions, even though the frequency of occurrence is not as comparative as coastal regions (e.g., Zhang et al, 2018a). This is closely linked to a couple of factors, such as the interplay of tropical cyclone and baroclinic disturbances (i.e., known as extratropical transition, Hart and Evans, 2000), interactions with mid-latitude systems (e.g., easterly, Shu et al, 2018;Feng and Shu, 2018), and impact of regional topography (as demonstrated by Typhoon Nina, Yang et al, 2017). The devastating consequences of Typhoon Nina and the August 1975 flood expose inadequacies of conventional approaches for flood frequency analysis (e.g., fitting historical flood records with assumed distribution function), and highlight the importance of hydrometeorological approaches for Probable Maximum Precipitation (PMP) / Probable Maximum Flood (PMF) analyses for better designs of flood-control infrastructures (e.g., Smith and Baeck, 2015;Yang et al, 2017).…”