Abstract
In this study, the performance of three exponential decay models in estimating intensity change of tropical cyclones (TCs) after landfall over China is evaluated based on the best-track TC data during 1980–2018. Results indicate that the three models evaluated can reproduce the weakening trend of TCs after landfall, but two of them (M1 and M2) tend to overestimate TC intensity and one (M3) tends to overestimate TC intensity in the first 12 h and underestimate TC intensity afterwards. M2 has the best performance with the smallest errors among the three models within 24 h after landfall. M3 has better performance than M1 in the first 20 h after landfall, but its errors increase largely afterwards. M1 and M2 show systematic positive biases in the southeastern China likely due to the fact that they have not explicitly included any topographic effect. M3 has better performance in the southeastern China, where it was originally attempted, but shows negative biases in the eastern China. The relative contributions of different factors, including landfall intensity, translational speed, 850-hPa moist static energy, and topography, to model errors are examined based on classification analyses. Results indicate that the landfall intensity contributes about 18%, translational speed, moist static energy and topography contribute equally about 15% to the model errors. It is strongly suggested that the TC characteristics and the time-dependent decay constant determined by environmental conditions, topography and land cover properties, should be considered in a good exponential decay model of TC weakening after landfall.
Highlights
Tropical cyclones (TCs) can exert severe destructive potential and impacts on human activities and often cause substantial property damage and loss of life after their landfall, in a wellpopulated area with high economic development
Since M3 was originally attempted for TCs making landfall over the South China coast, we show in Figure 9A the mean absolute errors (MAEs) for all TCs samples and samples of TCs making landfall along the South China coast (110.5–117.5°), and in Figure 9B the spatial distribution of biases and tracks for TCs making landfall along the
The mean relative errors (MREs) for landfalling TCs with high moist static energy are smaller than landfalling TCs with low moist static energy in all three models (Figure 10C), which is statistically significant for about 10–15 h after landfall, with the largest contribution over 15%
Summary
Tropical cyclones (TCs) can exert severe destructive potential and impacts on human activities and often cause substantial property damage and loss of life after their landfall, in a wellpopulated area with high economic development. The mean error from M2 increases for the following 18 h (Figure 3A), the mean errors are much smaller than those from M1 Different from those in M1 and M2, the decay constant in M3 is determined by considering the TC intensity, landward translational speed, and 850-hPa moist static energy of the TC at the time of landfall. TCs in the two groups show little difference in intensity at the time of landfall, TCs in the Topo group weaken more rapidly during the first 18 h after landfall than those in the No_topo group (Figure 7D, Table 2) These results strongly suggest that the topographic effect is an indispensable factor affecting the decay rate of landfalling TC over China. The MRE of M3 is slightly lower for TCs in the Topo group and slightly higher for TCs in the No_topo group than that for all landfalling TCs with no significant difference between the Topo and No_topo groups, suggesting that the topography has some minor effects on the performance of M3 (Figure 10D)
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