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  1. Article: Ensemble-based sensitivity analysis and predictability of an extreme rainfall event over northern Taiwan in the Mei-yu season: The 2 June 2017 case

    Wang, Chung-Chieh / Li, Ming-Siang / Chang, Chih-Sheng / Chuang, Pi-Yu / Chen, Shin-Hau / Tsuboki, Kazuhisa

    Atmospheric research. 2021 Sept., v. 259

    2021  

    Abstract: In the present study, an ensemble-based sensitivity analysis (ESA) on the extreme-rainfall event along the northern coast of Taiwan on 2 June 2017 in the Mei-yu season is performed using the results from 45 forecast members with a grid size of 2.5–5 km. ... ...

    Abstract In the present study, an ensemble-based sensitivity analysis (ESA) on the extreme-rainfall event along the northern coast of Taiwan on 2 June 2017 in the Mei-yu season is performed using the results from 45 forecast members with a grid size of 2.5–5 km. An quasi-stationary rainband associated with the front produced localized rainfall up to 635 mm in 12 h (0000–1200 LST 2 June), causing serious flooding and inundation near the northern tip of Taiwan. With a relatively large spread (i.e., standard deviation or σ), small ensemble mean (~130 mm), and low probability of heavy rainfall in northern Taiwan, the ensemble indicates a lower predictability there, compared to the topographic rainfall over the mountains. However, the ESA allows for identification of several contributing factors to heavy rainfall in northern Taiwan in a quantitative manner as given below.With their impact given in change of (areal-mean) 6-h rainfall amount per one σ increase, these factors include: (1) surface frontal position and moving speed (−16.00 mm per 5 km h⁻¹), (2) position of 700-hPa wind-shift line (+12.59 mm per 0.4° latitude), (3) environmental moisture amount near the surface front (+11.73 mm per 0.92 g kg⁻¹ in mixing ratio), (4) timing and location of frontal low-pressure disturbance (+11.03 mm per 1.38° longitude), and (5) frontal intensity (+9.58 mm per 3 K in equivalent potential temperature difference across 0.5°). While many of the factors identified are interconnected, they tend to increase the local rainfall through lengthening the duration and enhancing near-surface convergence along the northwestern coast of Taiwan over the area immediately upstream.
    Keywords coasts ; latitude ; longitude ; probability ; rain ; research ; standard deviation ; temperature ; topography ; Taiwan
    Language English
    Dates of publication 2021-09
    Publishing place Elsevier B.V.
    Document type Article
    Note NAL-AP-2-clean
    ISSN 0169-8095
    DOI 10.1016/j.atmosres.2021.105684
    Database NAL-Catalogue (AGRICOLA)

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  2. Book ; Online: Idealized simulations of Mei-yu rainfall in Taiwan under uniform southwesterly flow using a cloud-resolving model

    Wang, Chung-Chieh / Chuang, Pi-Yu / Chen, Shi-Ting / Lee, Dong-In / Tsuboki, Kazuhisa

    eISSN: 1684-9981

    2022  

    Abstract: In this study, idealized cloud-resolving simulations are performed for horizontally uniform and steady southwesterly flow at fixed direction–speed combinations to investigate rainfall characteristics and the role of the complex topography in Taiwan ... ...

    Abstract In this study, idealized cloud-resolving simulations are performed for horizontally uniform and steady southwesterly flow at fixed direction–speed combinations to investigate rainfall characteristics and the role of the complex topography in Taiwan during the Mei-yu season without the influence of a front or other disturbances. Eight directions (180 to 285 ∘ , every 15 ∘ ) and eight speeds (5 to 22.5 m s −1 , every 2.5 m s −1 ) are considered, and near-surface relative humidity is also altered (from 55 %–100 %) in a subset of these tests to further examine the effects of moisture content, yielding a total 109 experiments each having a integration length of 50 h . Three rainfall regimes that correspond to different ranges of the wet Froude number ( Fr w ) are identified from the idealized simulations (with a grid size of 2 km ). The low- Fr w regime ( Fr w ≤ ∼ 0.3) is where the island circulation from thermodynamic effects is the main driver of rainfall in local afternoon. The lower the wind speed and Fr w are, the more widespread the rainfall is, as well as its amount. On the other hand, the high- Fr w regime ( Fr w ≥ ∼ 0.4) occurs when the flow of at least 12.5 m s −1 impinges on Taiwan terrain at a large angle (not parallel). This favors the flow-over scenario, and topographic rainfall production becomes dominant through mechanical uplift of unstable air. In this scenario, the faster and wetter the flow is, the heavier the rainfall on the windward slopes is, and maximum amounts typically occur at wind directions from 240–255 ∘ . Between the two regimes above, a third, mixed regime also exists. The idealized results are discussed for their applicability to the real atmosphere.
    Subject code 333 ; 511
    Language English
    Publishing date 2022-06-02
    Publishing country de
    Document type Book ; Online
    Database BASE - Bielefeld Academic Search Engine (life sciences selection)

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  3. Book ; Online: Investigation of an extreme rainfall event during 8–12 December 2018 over central Viet Nam – Part 2

    Wang, Chung-Chieh / Nguyen, Duc Van / Vu, Thang Van / Thi Thanh Nga, Pham / Chuang, Pi-Yu / Truong, Kien Ba

    eISSN: 1684-9981

    An evaluation of predictability using a time-lagged cloud-resolving ensemble system

    2023  

    Abstract: This is the second part of a two-part study that investigates an extreme rainfall event that occurred from 8 to 12 December 2018 over central Viet Nam (referred to as the D18 event). In this part, the study aims to evaluate the predictability of the D18 ... ...

    Abstract This is the second part of a two-part study that investigates an extreme rainfall event that occurred from 8 to 12 December 2018 over central Viet Nam (referred to as the D18 event). In this part, the study aims to evaluate the predictability of the D18 event using a time-lagged cloud-resolving ensemble and a quantitative precipitation forecast system. To do this study, 29 time-lagged (8 days in lead time) high resolution (2.5 km) members were run, with the first members run at 12:00 UTC 3 December 2018, and the last member-run at 12:00 UTC 10 December 2018. Between the first and the last members are multiple members that run every 6-h. The evaluated results reveal that CReSS well predict the rainfall fields at the short-range forecast (less than 3 days) for 10 December (rainiest day). Particularly, results show CReSS has high skills in heavy-rainfall QPFs for the 24-h rainfall of 10 Dec with the SSS scores greater than 0.5 for both the last five members and the last nine members. These good results are due to the model having good predicts of other meteorological variables, such as surface wind fields. However, these prediction skills are reducing at extending lead time (longer than 3 days), and it is challenging to achieve the prediction of QPF for rainfall thresholds greater than 100 mm with lead time longer than 6 days. Besides, the ensemble sensitivity analysis of 24-hour rainfall responds to the initial conditions shows that the 24-hour rainfall is very sensitive with initial conditions, not only at the lower level but also at the upper level. The ensemble-based sensitivity is decreased with the increasing lead time. Through the analysis of thermodynamic and moisture sensitivities, it showed that the features of ESA facilitated a better understanding of the sensitivity of a precipitation forecast to the initial conditions, implying that it is meaningful to apply ESA to control initial conditions by work in the future.
    Subject code 910
    Language English
    Publishing date 2023-12-11
    Publishing country de
    Document type Book ; Online
    Database BASE - Bielefeld Academic Search Engine (life sciences selection)

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  4. Book ; Online: Evaluation of Mei-yu heavy-rainfall quantitative precipitation forecasts in Taiwan by a cloud-resolving model for three seasons of 2012–2014

    Wang, Chung-Chieh / Chuang, Pi-Yu / Chang, Chih-Sheng / Tsuboki, Kazuhisa / Huang, Shin-Yi / Leu, Guo-Chen

    eISSN: 1684-9981

    2022  

    Abstract: In this study, the performance of quantitative precipitation forecasts (QPFs) by the Cloud-Resolving Storm Simulator (CReSS) in Taiwan, at a horizontal grid spacing of 2.5 km and a domain size of 1500×1200 km 2 , in the range of 1–3 d during three Mei-yu ...

    Abstract In this study, the performance of quantitative precipitation forecasts (QPFs) by the Cloud-Resolving Storm Simulator (CReSS) in Taiwan, at a horizontal grid spacing of 2.5 km and a domain size of 1500×1200 km 2 , in the range of 1–3 d during three Mei-yu seasons (May–June) of 2012–2014 is evaluated using categorical statistics, with an emphasis on heavy-rainfall events ( ≥100 mm per 24 h). The categorical statistics are chosen because the main hazards are landslides and floods in Taiwan, so predicting heavy rainfall at the correct location is important. The overall threat scores (TSs) of QPFs for all events on day 1 (0–24 h) are 0.18, 0.15, and 0.09 at thresholds of 100, 250, and 500 mm, respectively, and indicate considerable improvements at increased resolution compared to past results and 5 km models (TS < 0.1 at 100 mm and TS ≤ 0.02 at 250 mm). Moreover, the TSs are shown to be higher and the model more skillful in predicting larger events, in agreement with earlier findings for typhoons. After classification based on observed rainfall, the TSs of day − 1 QPFs for the largest 4 % of events by CReSS at 100, 250, and 500 mm (per 24 h) are 0.34, 0.24, and 0.16, respectively, and can reach 0.15 at 250 mm on day 2 (24–48 h) and 130 mm on day 3 (48–72 h). The larger events also exhibit higher probability of detection and lower false alarm ratio than smaller ones almost without exception across all thresholds. With the convection and terrain better resolved, the strength of the model is found to lie mainly in the topographic rainfall in Taiwan rather than migratory events that are more difficult to predict. Our results highlight the crucial importance of cloud-resolving capability and the size of fine mesh for heavy-rainfall QPFs in Taiwan.
    Subject code 910
    Language English
    Publishing date 2022-01-05
    Publishing country de
    Document type Book ; Online
    Database BASE - Bielefeld Academic Search Engine (life sciences selection)

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