Hindawi Publishing Corporation Advances in Meteorology Volume 2015, Article ID 383712, 11 pages http://dx.doi.org/10.1155/2015/383712 Research Article The Impact of Typhoon Danas (2013) on the Torrential Rainfall Associated with Typhoon Fitow (2013) in East China Hongxiong Xu1 and Bo Du2 1 State Key Laboratory of Severe Weather, Chinese Academy of Meteorological Sciences, Beijing 100081, China 2ChinaMeteorologicalAdministrationMeteorologicalObservationCenter,Beijing100081,China Correspondence should be addressed to Hongxiong Xu; [email protected] Received 30 September 2014; Revised 20 January 2015; Accepted 20 January 2015 Academic Editor: Hann-Ming H. Juang Copyright © 2015 H. Xu and B. Du. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. When typhoon Danas (2013) was located at northeast of Taiwan during 6–8 October 2013, a torrential rainfall brought by typhoon Fitow (2013) occurred over the east of China. Observations show that the rainband of Fitow, which may be impacted by Danas, caused the rainfall over north of Zhejiang. The Advanced Research version of the Weather Research and Forecast (ARW-WRF) model was used to investigate the possible effects of typhoon Danas (2013) on this rainfall event. Results show that the model captured reasonably well the spatial distribution and evolution of the rainband of Fitow. The results of a sensitivity experiment removing Danas vortex, which is conducted to determine its impact on the extreme rainfall, show that extra moist associated with Danas plays an important role in the maintenance and enhancement of the north rainband of Fitow, which resulted in torrential rainfall over the north of Zhejiang. This study may explain the unusual amount of rainfall over the north of Zhejiang province caused by interaction between the rainband of typhoon Fitow and extra moisture brought by typhoon Danas. 1. Introduction III et al. [12] and Carr III and Elsberry [13]proposedfour conceptual models of track-altering binary tropical cyclones Extreme rainfall is responsible for a variety of societal that occurred in the Pacific Ocean. impacts, including flash flooding that can lead to damage, If there is another typhoon near the area of disaster, injury, and fatalities [1]. Tropical cyclones (TCs) are often the effects of binary tropical cyclone interaction make the heavy rain producers [2]. Thus, it is of great interest to process of precipitation become much more complicated. accurately predict extreme rainfall caused by TCs. However, Studies [14, 15] showed that BTC processes may associate heavy rainfall (including TCs rainfall) interweaves multiscale with torrential rainfall in favorable environment conditions. nonlinear interactions among different physical processes Wu et al. [14] found that tropical Storm Paul (1999) plays an and weather systems [3–5]. Such interactions include envi- important role in impeding the movement of Rachel, thus ronmental moisture transport and binary TC (BTC) interac- becoming one of the key factors in enhancing the rainfall tion [6]. amount in southern Taiwan. Xu et al. [15]foundthatGoni Binary tropical cyclones (BTCs) can interact with each (2009, 08 W) transported a large amount of moisture and other when they are close enough [7–10]. Their interaction energy into Morakot (2009, 09 W). The interaction between depends on the distance of two TCs, the differences in Goni and Morakot accounts for about 30% of precipitation TC size, intensity, and the variations in the currents [11]. over Taiwan. Based on the results of numerical experiments, Shin et al. In this study, we discussed the role of the circulation [10] suggested that the critical separation distance of binary associated with Danas (2013) played in the extreme rainfall vortices is slightly less than twice the radius at which the caused by Fitow (2013). Specifically, the purpose of this paper relative vorticity of one vortex becomes zero. Concerning is to quantify the distant effects of typhoon Danas on the theobservationsofbinarytropicalcyclonesandrealistic extreme rainfall brought by rainband of Fitow in the east of flow patterns surrounding tropical cyclones, studies by Carr China on 8–10 October 2013. In Section 2, we described the 2 Advances in Meteorology 584 586 586 574 574 588 ∘ 578 590 ∘ 578 590 40 N 592 40 N 582 592 584 582 594 582 584 586 ∘ ∘ 30 N 586 30 N 584 584 584582 586 586 578 584 578 586584 582 ∘ ∘ 584 582 20 N 20 N 582 586 584 586 586 584 ∘ 586 ∘ 10 N 10 N ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ 100 E 110 E 120 E 130 E 140 E 100 E 110 E 120 E 130 E 140 E 20 20 (a) 00Z060CT2013 (b) 12Z060CT2013 574 586 574 586 ∘ 578 588 ∘ 574 578 40 N 590 40 N 578 588 590 582 592 582 592 586 584 584 ∘ ∘ 586 30 N 584 582 30 N 588 584 586 584582 582 584 582 ∘ ∘ 584 20 N 584 20 N 588 586 586 586 ∘ ∘ 584 10 N 10 N ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ 100 E 110 E 120 E 130 E 140 E 100 E 110 E 120 E 130 E 140 E 20 20 (c) 00Z070CT2013 (d) 12Z070CT2013 Figure 1: 500 hPa geopotential height (contour, unit: dagpm) and wind (vector) at (a) 0000 UTC 06 October 2013, (b) 1200 UTC 06 October 2013, (c) 0000 UTC 07 October 2013, and (d) 1200 UTC 07 October 2013. ∘ 34 N ∘ 30 N ∘ 26 N ∘ ∘ ∘ ∘ ∘ ∘ ∘ 114 E 116 E 118 E 120 E 122 E 124 E 126 E 20 60 100 140 180 220 260 300 340 380 420 460 500 (mm) Figure 2: The observed 48 h accumulated rainfall (unit: mm) ending at 0000 UTC 08 October 2013. Advances in Meteorology 3 ∘ ∘ 32 N 32 N ∘ ∘ 29 N 29 N ∘ ∘ 26 N 26 N ∘ ∘ ∘ ∘ ∘ ∘ 118 E 120 E 122 E 118 E 120 E 122 E (a) 16 UTC 06 (b) 19 UTC 06 ∘ ∘ 32 N 32 N ∘ ∘ 29 N 29 N ∘ ∘ 26 N 26 N ∘ ∘ ∘ ∘ ∘ ∘ 118 E 120 E 122 E 118 E 120 E 122 E 10 20 30 40 50 60 70 10 20 30 40 50 60 70 (c) 22 UTC 06 (d) 01 UTC 07 Figure 3: Radar mosaic reflectivity (DBZ) at (a) 16 UTC 06, (b) 19 UTC 06, (c) 22 UTC 06, and (d) 01 UTC07. model configuration and design of numerical experiments FNL analysis. It shows a South Asian anticyclone over the used in this study. We presented the results of numerical Tibetan Plateau in southwestern China, and a west wind simulations in Section 3. Finally we summarize conclusions trough extended from north of China to Sichuan province in Section 4. (Figure 1(a)). In the mid-latitudes over the Japan Sea, there was a subtropical anticyclone. During the typhoon Fitow 2. Overview of 8–10 October 2013 landfall over east of China (Figures 1(b), 1(c),and1(d)), Torrential Rainfall subtropical anticyclone moved to east. Warm and moisture of typhoon interacted with cold air after the westerly trough. Figure 1 shows 500 hPa geopotential height and wind from This condition was favorable for the development of convec- the National Centers for Environmental Prediction (NCEP) tion and result of rainfall. 4 Advances in Meteorology ∘ ∘ ∘ ∘ ∘ ∘ Typhoon Fitow hit north of Fujian province during 6– 75 E 90 E 105 E 120 E 135 E 150 E ∘ 8 October 2013 and produced extreme rainfall and brought D01 40 N about catastrophic flash flooding to Zhejiang province. The ∘ observed 48 h rainfall is shown in Figure 2. The extreme 40 N rainfall areas are mainly located in the coast and north of ∘ 30 N Zhejiang province. The exceptional rainfall with a record D02 ∘ 03 amount of 700 mm (northeast of Zhejiang) exceeded the 60- 30 N D year recurrence. The southeast coast of mainland China expe- ∘ 20 N riences several hits of landfalling typhoons every year [15]. 20∘ However, the amount of rainfall over Zhejiang (especially, N north of Zhejiang) brought by Fitow is quite rare. Thus, it is of 10∘ great interest to explore the possible mechanism responsible N 10∘ for the unusual heavy rainfall. N Radar mosaic reflectivity (Figure 3) shows a quasistation- ∘ ∘ ∘ ∘ ∘ ary rainband, which was nearly in east-west direction over 90 E 100 E 110 E 120 E 130 E the north of Zhejiang province. Along the band, there were several echo centers of 45–55 dBz embedded in line, which corresponded to the north rainband of typhoon Fitow. Inside 500 1000 2000 3000 4000 5000 the north rainband, there was another rainband occurring 1500 2500 3500 4500 over the south of Zhejiang province. The inner echo band Figure 4: Topography (color-shaded, m) for the model domain. The wasalsocomposedofalotofechocenters.Insidethetwo outer box is d01 (30 km). The inner boxes are d02 (10 km) and d03 radar echo bands, there were a few echo blocks extending (3.3 km). to the eyewall along the radial, which corresponded to the connecting spiral rainband. Studies have shown that rainbands of a TC moving slowly The model physical options include the Thompson micro- outward along the radial [16–18] may remain stationary physics scheme [24], the YSU planetary boundary layer with new cells forming on the upwind edge [19, 20]. This scheme [25], the Kain-Fritsch cumulus parameterization process also occurred to the rainbands of typhoon Fitow scheme [26, 27], the Noah land surface model [28, 29], the (Figure 3). The north rainband remained stationary over rapid radiative transfer model [30]longwave,andtheDudhia Zhejiang province. However, the south rainband moved shortwave radiation scheme [31]. The cumulus parameteri- further to the south when typhoon Fitow was to the south- zationschemewasnotappliedtothefinest(3.3km)grid west. The two rainbands were maintained by a different domain to explicitly resolve the convective rainfall.