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The 6-h reanalysis data from the National Centers for Environmental Prediction−National Center for Atmospheric Research dataset with a spatial resolution of 2.5°×2.5° and the tropical cyclone best-track dataset from the China Meteorological Administration (Ying et al., 2014) are used. In addition, the tropical cyclone precipitation dataset identified by objective synoptic analysis (Ren et al., 2001, 2007) is also employed, which partitions the rainfall induced by tropical cyclones from the total rainfall based on station observations from the Chinese mainland, Macau, Hong Kong and Taiwan Island. The dataset also includes rainfall record over land induced by side-swiping tropical cyclones which did not make landfall (fall (Feng et al., 2020), in addition to the rainfall from tropical cyclones that do make landfall. These data have been widely applied in studies of typhoon-induced rainfall over China (Ren et al., 2006; Jiang et al., 2018; Qiu et al., 2019; Liu and Wang, 2020).
Our study has taken more factors into consideration in defining typhoon extreme rainfall, including the number of samples and the representativeness of the tropical cyclones triggering the extreme rainfall, the differences among typhoon-induced torrential rain, heavy torrential rain and extraordinary storms, and extreme rainfall caused by typhoons on Taiwan, Hainan Island and the Chinese mainland. We defined typhoon-induced extraordinary rainstorms in China as a rainfall event in which the 24-h rainfall was ≥600 mm at a single rain gauge station. Statistically, there are 38 records of single-station typhoon extreme rainfall from 1960 to 2019, caused by a total of 26 typhoons. Among these 26 typhoons, 14 resulted in extreme rainfall in Taiwan, 5 resulted in extreme rainfall in Hainan and 7 resulted in extreme rainfall in the Chinese mainland. Seven ERLTC occurred at the same rain gauge station at Ali Mountain, Taiwan Island, which is more than 25% of all the typhoons according to our definition. These typhoons are the main object of study in this paper. We carried out comparative analysis and dynamic diagnosis of the large-scale circulations of selected tropical cyclones using dynamic composite analysis (e analysis (Li et al., 2004). The ERLTC and NERLTC were identified based on the similarities of the season of occurrence (major season, July−September), track (northwestward), and location (Ali Mountain in Taiwan Island) of the tropical cyclones. On this basis, typhoons 9608, 0908, 6312, 1307 and 0813 were selected as associated with ERLTC, whereas typhoons 9417, 1315, 0713, 0505 and 0605 were selected as associated with NERLTC. This research focuses on the precipitation induced by tropical cyclones over land. The term “landfalling tropical cyclones” refers to the landfall of either the center of the tropical cyclone or the tropical cyclone rain belt. Thus, it covers both the landfalling tropical cyclones and side-swiping tropical cyclones in the operational forecasting definition. The average daily rainfall during ERLTC and NERLTC is 1223.0 and 165.7 mm, respectively (Table 1). We are more concerned with the differences between extreme rainfall and ordinary torrential rain accompanied with landfalling typhoons, not the so-called “dry typhoon” which can only generate precipitation over 24-h≤50 mm.
Tropical cyclone
numberExtremes of
daily rainfall
(mm)Time at which extreme
rainfall occurred
(LST, LST=UTC+8)Center of
tropical cycloneCentral
minimum
pressure (hPa)Maximum
wind speed
(m s−1)ERLTC 9608 1748.5 7-31-02:00−8-1-02:00 (121.0°E, 24.9°N) 960 40 0908 1623.5 8-8-20:00−8-9-20:00 (119.8°E, 26.7°N) 975 30 6312 1248.0 9-10-20:00−9-11-20:00 (121.6°E, 25.6°N) 945 55 1307 757.0 7-12-20:00−7-13-20:00 (118.8°E, 26.1°N) 985 30 0813 738.0 9-13-20:00−9-14-20:00 (121.3°E, 25.4°N) 970 33 NERLTC 9417 52.7 8-31-20:00−9-1-20:00 (119.7°E, 25.3°N) 970 35 1315 96.5 8-28-20:00−8-29-20:00 (122.3°E, 26.6°N) 990 23 0713 255.0 9-17-20:00−9-18-20:00 (121.4°E, 26.2°N) 940 50 0505 350.0 7-17-20:00−7-18-20:00 (121.2°E, 24.7°N) 955 40 0605 74.5 7-24-20:00−7-25-20:00 (117.7°E, 24.4°N) 985 28 Table 1. Overview of selected ERLTCs and NERLTCs.
Figure 1 shows the tracks and intensity categories of the tropical cyclones during the ERLTC (Fig. 1a) and NERLTC (Fig. 1b). These tropical cyclones occurred during the peak season of tropical cyclone activity (July−September) and showed a mainly northwestward movement. All these tropical cyclones made landfall or affected Taiwan and the Chinese mainland, reaching the category of a typhoon or above before landfall. To avoid the influence of terrain and to make the tropical cyclone samples more comparable, we selected the tropical cyclones associated with ERLTC and NERLTC in Ali Mountain, Taiwan. This paper focuses on the main differences between the tropical cyclones that bring extreme rainfall and those that bring non-extreme rainfall under similar backgrounds of atmospheric circulation and the same terrain.
Tropical cyclone number | Extremes of daily rainfall (mm) | Time at which extreme rainfall occurred (LST, LST=UTC+8) | Center of tropical cyclone | Central minimum pressure (hPa) | Maximum wind speed (m s−1) | |
ERLTC | 9608 | 1748.5 | 7-31-02:00−8-1-02:00 | (121.0°E, 24.9°N) | 960 | 40 |
0908 | 1623.5 | 8-8-20:00−8-9-20:00 | (119.8°E, 26.7°N) | 975 | 30 | |
6312 | 1248.0 | 9-10-20:00−9-11-20:00 | (121.6°E, 25.6°N) | 945 | 55 | |
1307 | 757.0 | 7-12-20:00−7-13-20:00 | (118.8°E, 26.1°N) | 985 | 30 | |
0813 | 738.0 | 9-13-20:00−9-14-20:00 | (121.3°E, 25.4°N) | 970 | 33 | |
NERLTC | 9417 | 52.7 | 8-31-20:00−9-1-20:00 | (119.7°E, 25.3°N) | 970 | 35 |
1315 | 96.5 | 8-28-20:00−8-29-20:00 | (122.3°E, 26.6°N) | 990 | 23 | |
0713 | 255.0 | 9-17-20:00−9-18-20:00 | (121.4°E, 26.2°N) | 940 | 50 | |
0505 | 350.0 | 7-17-20:00−7-18-20:00 | (121.2°E, 24.7°N) | 955 | 40 | |
0605 | 74.5 | 7-24-20:00−7-25-20:00 | (117.7°E, 24.4°N) | 985 | 28 |