Observed Rainfall Asymmetry in Tropical Cyclones Making Landfall Over China
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JANUARY 2015 Y U E T A L . 117 Observed Rainfall Asymmetry in Tropical Cyclones Making Landfall over China ZIFENG YU College of Atmospheric Sciences, and Pacific Typhoon Research Center, Nanjing University of Information Science and Technology, Nanjing, and Shanghai Typhoon Institute, and Laboratory of Typhoon Forecast Technique, China Meteorological Administration, Shanghai, China YUQING WANG Department of Meteorology, and International Pacific Research Center, University of Hawai‘i at Manoa, Honolulu, Hawaii HAIMING XU College of Atmospheric Sciences, and Pacific Typhoon Research Center, Nanjing University of Information Science and Technology, Nanjing, China (Manuscript received 25 November 2013, in final form 7 August 2014) ABSTRACT In this study, the rainfall asymmetries in tropical cyclones (TCs) that made landfall in the Hainan (HN), Guangdong (GD), Fujian (FJ), and Zhejiang (ZJ) provinces of mainland China and Taiwan (TW) from 2001 to 2009 were analyzed on the basis of TRMM satellite 3B42 rainfall estimates. The results reveal that in landfalling TCs, the wavenumber 1 rainfall asymmetry shows the downshear to downshear-left maxi- mum in environmental vertical wind shear (VWS), which is consistent with previous studies for TCs over the open oceans. A cyclonic rotation from south China to east China in the location of the rainfall maxi- mum has been identified. Before landfall, the location of the rainfall maximum rotated from southwest to southeast of the TC center for TCs making landfall in the regions from HN to GD, TW, FJ, and ZJ. After landfall, the rotation became from southwest to northeast of the TC center from south China to east China. It is shown that this cyclonic rotation in the location of the rainfall maximum is well correlated with a cy- clonic rotation from south China to east China in the environmental VWS between 200 and 850 hPa, in- dicating that the rainfall asymmetry in TCs that made landfall over China is predominantly controlled by the large-scale VWS. The cyclonic rotation of VWS is found to be related to different interactions between the midlatitude westerlies and the landfalling TCs in different regions. The results also indicate that the axisymmetric (wavenumber 0) component of rainfall generally decreased rapidly after landfall in most studied regions. 1. Introduction the 24-h rainfall of 1062 mm at Linzhuang in the Henan province of mainland China caused by landfalling Ty- Landfalling tropical cyclones (TCs) often bring very phoon Nina (7503) in 1975 (Chen et al. 2004). Torrential heavy rainfall to the affected region (Chen and Ding rainfall associated with landfalling TCs is one of the 1979). Many extreme rainfall events are related to most devastating natural disasters in the coastal regions landfalling TCs around the world (Tao 1980; Rappaport of China, inflicting huge losses in property and human 2000). Examples of the record-breaking heavy rainfall lives (Zhang et al. 2009). The regions that suffer most events include the 24-h rainfall of 1248 mm at Baixin in are largely determined by the distribution of rainfall in Taiwan caused by Typhoon Gloria (6312) in 1963 and TCs. Therefore, the spatial distribution of rainfall in a landfalling TC is of particular interest to meteorolo- Corresponding author address: Zifeng Yu, Shanghai Typhoon gists because of its relevance to the rainfall forecasts. Institute, 166 Puxi Road, Xujiahui, Shanghai 200030, China. The rainfall distribution in a TC can be decomposed E-mail: [email protected] into a wavenumber 0 (or an azimuthal mean) component DOI: 10.1175/JAMC-D-13-0359.1 Ó 2015 American Meteorological Society Unauthenticated | Downloaded 10/05/21 07:42 AM UTC 118 JOURNAL OF APPLIED METEOROLOGY AND CLIMATOLOGY VOLUME 54 and a series of lower-wavenumber components (Lonfat Chen et al. (2006) investigated the effects of VWS and et al. 2004). The distribution of rainfall in a landfalling TC storm motion on TC rainfall asymmetries based on is often controlled not only by storm motion and vertical composite analyses. They found that the overall TC wind shear (VWS) for TCs over oceans (Lonfat et al. rainfall asymmetry depended on the juxtaposition and 2004; Chen et al. 2006), but also by other factors such as relative magnitude of the storm motion and the envi- surface conditions (including terrains and coastlines) ronmental VWS over the ocean. Subsequent multicase (Bender et al. 1987; Chang et al. 1993; Yeh and Elsberry analyses of the shear-induced TC asymmetry using the 1993a,b; Linetal.1999, 2002, 2005, 2006; Wu and Kuo satellite-based precipitation estimates have further con- 1999; Wu 2001; Wu et al. 2002; Yu et al. 2010; Yu and Yu firmed the relationship between the spatial distribution of 2012). Therefore, although the rainfall in a landfalling TC TC rainfall and the environmental VWS (Ueno 2007; tends to be dominated by the wavenumber 0 component Wingo and Cecil 2010; Hence and Houze 2011), namely, in general, a significant spatial variability can be induced the downshear-left preference of the rainfall maximum. by various dynamical and thermodynamic processes. TC translation speed becomes an important factor in the Previous studies have shown that rainfall asymmetries low VWS environment. Recently, Reasor et al. (2013), in a TC are affected by the environmental VWS (Marks based on a multicase composite of the asymmetric TC 1985; Merrill 1988; Jones 1995, 2000a,b, 2004; Wang and structure derived from airborne Doppler radar mea- Holland 1996a; DeMaria 1996; Frank and Ritchie 1999, surements, reconfirmed that the impact of storm motion 2001), the planetary vorticity gradient (Peng and Williams on the eyewall convective asymmetry was secondary 1990; Wang and Holland 1996b,c; Bender 1997), the storm compared to the findings from previous studies using motion (e.g., Bender 1997; Peng et al. 1999), the friction- lightning and precipitation data. induced asymmetric boundary layer convergence in a Most of previous studies have focused on the rainfall moving TC (e.g., Shapiro 1983), the asymmetric environ- asymmetries in TCs over oceans. In a numerical study mental moisture distribution (Dunion and Velden 2004), under idealized conditions, Chan and Liang (2003) showed and also the convectively coupled vortex-Rossby waves in the precipitation maximum to the left-front quadrant of the eyewall (Chen and Yau 2001; Wang 2002a,b). a TC when it approached a coastline prior to its landfall. Lonfat et al. (2004) analyzed the global rainfall dis- Chan et al. (2004) investigated the asymmetric distribution tribution in TCs based on the satellite data deduced of convection in TCs making landfall in south China and from the Tropical Rainfall Measuring Mission (TRMM) showed that convection was generally enhanced to the rain estimates. Their results showed the relationships west of the TC center before landfall, namely to the left- between the TC intensity, the geographical location, and front of the storm, which was consistent with the mod- the rainfall asymmetry relative to the storm motion. eling results of Chan and Liang (2003). Shu et al. (2012) However, the storm motion alone could not fully explain investigated the spatial distribution of precipitation in the basin-to-basin variability in the rainfall asymmetry landfalling TCs affecting China using the Geostationary and thus other mechanisms, such as the environmental Meteorological Satellite-5 infrared brightness tempera- VWS, that affect the asymmetric rainfall distribution ture (GMS5-TBB) estimated-rainfall dataset during the have also been investigated intensively (e.g., Rogers period of 2001–09. Their results showed that the envi- et al. 2003; Chen et al. 2006; Lonfat et al. 2007). The ronmental VWS was an important factor contributing to rainfall asymmetry associated with VWS and storm the down-shear rainfall maximum. motion in Hurricane Bonnie (in 1998) was studied based The primary goal of this study is to diagnose the im- on a high-resolution numerical simulation by Rogers pacts of environmental VWS and storm motion on the et al. (2003). Their results suggested that the combination asymmetric rainfall distribution in TCs making landfall of shear and storm motion explained well the rainfall over south and east China through motion-relative and asymmetry in Hurricane Bonnie. The accumulated rain- shear-relative composite analysis of precipitation fields. fall was distributed symmetrically across the track of the We use 9-yr (2001–09) TRMM satellite rainfall esti- storm when the shear was strong and across the track, and mates to examine the differences in the rainfall asym- it was distributed asymmetrically across the track of the metry in TCs making landfall in different regions and storm when the shear was weak and along the track. their detailed changes during landfall. We will also in- Corbosiero and Molinari (2003) observed the maximum vestigate how the rainfall asymmetry is related to envi- occurrence of lightning downshear-left in TCs near the ronmental VWS and storm motion. The details of data coastal regions, similar to the cross-track shear in Hurri- used and the analysis methods are described in section 2. cane Bonnie (1998) described by Rogers et al. (2003). The asymmetric rainfall distributions in landfalling TCs Their results showed that the environmental VWS largely are discussed in section 3. Factors affecting the rainfall controls the asymmetric convective activity in TCs. asymmetry in landfalling TCs, such as the storm motion Unauthenticated | Downloaded 10/05/21 07:42 AM UTC JANUARY 2015 Y U E T A L . 119 and VWS, are examined in section 4. Major results are which are available from the Shanghai Typhoon summarized in section 5. Institute. b. Rainfall analysis method 2. Data and analysis methods The TC rainfall distribution was analyzed using the a. Data Fourier decomposition. The spatial asymmetries were Whereas rain gauge data are routinely available, they created by binning rainfall estimates in 10-km-wide are sparse in many important regions even over land.