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

Abstract

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.

More or Less: How Do Inhomogeneous Sea‐Salt Aerosols Affect the Precipitation of Landfalling Tropical Cyclones?

“…Previous findings (Shu et al, 2014(Shu et al, , 2018(Shu et al, , 2021 revealed important effects of dry air on the precipitation of LTCs, including reducing convective available potential energy and suppressing deep convective development by promoting evaporative cooling and enhancing the cold downdraft in the boundary layer. The results obtained here deepen the previous findings by presenting an additional radiation-related effect of dry air which lows the TC's environmental humidity, then influences the optical properties of underlying SSAs and finally reduces the updraft and rainfall of the TC.…”

“…When a TC moves from the far open sea to the coastal region, it is usually intruded by environmental dry air from the continent on the west or the WNPSH to the north (Shu et al, 2014(Shu et al, , 2018(Shu et al, , 2021. Fitow made landfall in Zhejiang Province of Southeast China at 1715 UTC 6 October 2013.…”

“…For the landfalling TCs (LTCs) over East Asia, the environmental RHs can be as low as 50%-70% with dry air originating not only in the dry western North Pacific (WNP) subtropical high (WNPSH) but also in the dry mid-to-high-latitude continent (Shu et al, 2014(Shu et al, , 2018(Shu et al, , 2021. Although the state of sea-salt particles relies on the environmental RHs (Zeng et al, 2013), the physical process associated with the inhomogeneity of SSAs has never been considered in research and operational forecast of TCs, which may partly account for the discrepancy between simulation (or forecast) and observation of LTCs.…”

Occurrence of rare lightning events during Hurricane Nicholas (2021)

“…Wind vectors backed with height generally implied dry air intrusion (Figures 9b and 9c). Shu et al (2021) pointed out that this may be an additional reason the upper-level divergence and deep convection strengthened and produced the TLEs. An additional premise to consider is that the TLE producing cell during Case I exhibited the strongest cloud top divergence.…”

Effects of Urban Expansion and Anthropogenic Heat Enhancement on Tropical Cyclone Precipitation in the Greater Bay Area of China

“…This study focuses on the urbanization effect on TCP in the GBA during TC landfall. Following previous studies (Feng & Shu, 2018; Shu et al., 2021), we investigate the TCP characteristics from 18 hr prior to TC landfall to 24 hr after TC landfall. To simulate the TC landfall well and reduce the error caused by the initial conditions to the uncertainty of the physical quantities of the model (T. Yang et al., 2018), the model begins to run at almost 24 hr prior to TC landfall, and ends at around 24 hr after TC landfall.…”