Contributing Factors of the Heavy Rainfall Event at Amami-Oshima Island, Japan, on 20 October 2010

Transcription

1 15-18 September 2014 : Contributing Factors of the Heavy Rainfall Event at Amami-Oshima Island, Japan, on 20 October 2010 Tsuguti and Kato (2014, JMSJ) Hiroshige TSUGUTI and Teruyuki KATO Meteorological Research Institute (MRI) Japan Meteorological Agency (JMA)

2 Table of Contents 1. Overview 2. Purpose 3. Analysis Results p Supply mechanism of low-level humid air p Formation process of low-level humid air 4. Summary and Conclusions September

3 Overview of the Heavy Rainfall Event Geographical Location around Japan China Taiwan One-day Korea 20 Oct 2010 Japan Amami-Oshima Island Naze Ø Ø On 20 October 2010, a heavy rainfall event occurred on Amami-Oshima Island, causing many disasters. The one-day accumulated rainfall amount of 622 mm broke a record (547.1 mm) that had been set on 29 May 1903 at Naze Meteorological Observatory. Ø Although such a rainfall amount is typical of heavy rainfall events during the Baiu(Meiyu) season, this particular instance occurred during the autumn season September

4 Purpose The occurrence of heavy rainfall requires a large amount of low-level humid air. The primary purpose of this study is to determine the supply mechanism and formation process of the low-level humid air that caused the heavy rainfall September

5 Environmental Field Surface Weather Map (09JST 20 Oct 2010) Stationary Front TY1013 (Megi) Amami-Oshima Island Is this True??? Ø This synoptic pattern suggests that low-level humid air was supplied to Amami-Oshima Island from the southern ocean September

6 Supply of low-level humid air 500m_Water Vapor Mass Flux 500m_Specific Humidity 2 Strong East-NorhEasterly Winds 1 Ø The humid air was carried to Amami-Oshima Island during the heavy rainfall event by strong eastnortheasterly winds. Ø Which was the origin of the lowlevel humid air, from south (1)? or north (2)? September

7 Origin of Low-level humid air (Backward-Trajectory) 06JST/20 15JST/20 From North! Ø The back-trajectory placed parcels more than 500 km eastnortheast of the island with less than 500 m change in altitude September

8 Time Variations of PTV/QV of the parcel Ø These changes mean that air was relatively dry and was transformed into humid air as it approached Amami-Oshima Island September

9 Formation Process of the low-level humid air 500m_Virtual Potential Temperature A B B A Ø The convective mixed layer with homogeneous PTV was well developed below 1000 m height September

10 SST and SHF/LHF B A B 40 Wm -2 ~ SST Ø A 2 higher than the annual mean An air-parcel transformation could occur as large SHF/LHF from the sea surface could transform cold dry air into warm humid air. Sensible Heat Flux B A Latent Heat Flux 300 Wm -2 ~ September

11 Numerical Model / Experiment Designs n Model: JMA-NHM (Saito et al., 2006) n Domain: 108(x) X 40(z) [ 2-D simulation ] - horizontal resolution(x): 5 km - vertical resolution(z): variable grid (near surface=40m, model top=13156m) SST A B n Initial Condition: Vertical profile at point B n Lateral Boundary: Open n Surface Boundary (SST): 28 n Physics - Surface: Bulk method (Beljaars & Holtslag, 1991) - Turbulence: MYNN Level 3 (Nakanishi & Niino, 2006) - Cloud Microphysics: Double Moment bulk-type (Predict qc,qi,qr,qs,qg,ni,ns,ng) (No convective parameterization) (Ikawa and Saito, 1991) Initial Vertical Profile of PTV at point B September

12 Simulated PTV in CTL and SST-2 CTL SST-2 Analysis Ø The 2 elevation in SST around Amami-Oshima Island over the annual mean SST was an important factor in enhancing the air-parcel transformation September

13 Schematic Diagram air-parcel transformation Ø Schematic diagram of the study area viewed from the southeast, showing the factors that brought heavy rainfall over Amami-Oshima Island September

14 l Summary and Conclusions Low-level humid air was supplied to the vicinity of Amami-Oshima Island by strong east-northeasterly winds. l The origin of the low-level humid air was more than 500 km east-northeast of Amami-Oshima Island, which was on the northern (cooler) side of a stationary front. l The air was originally relatively dry and was transformed into humid air by receiving a large latent heat flux from the sea surface, which was about 5 warmer than the near-surface temperature. l The SST around Amami-Oshima Island was about 2 higher than the annual mean, which contributed to this transformation September

15 Supplemental Slides September

16 3-h Precipitaion September

17 Radar_2100JST/ JST/20 (dbz) September

18 EPT(Equivalent Potential Temperature) : 奄美大島 : 前線の位置 N S N 500m S September

19 Vertical Profile at Naze Naze: 09JST/20 At 967hPa (396m) LNB : 401hPa(8km) dlfc : 648m September

20 Water Vapor Mass Flux at 500m September

21 Vertical profiles of horizontal wind velocity at Naze (m) 15 (JST) (m s -1 ) September

22 Time variations of LHF 400 W/m 2 Black : CTL Red : SST W/m W/m W/m 2 FT=01;07JST FT=06;12JST FT=09;15JST September

23 Numerical Model / Experiment Designs Initial / Boundary JMA-NHM (Saito et al., 2006) 計算領域 : 800(x) x 600(y) x 50(z) - 水平格子間隔 (x y) : 1 km - 鉛直格子間隔 (z) : 可変格子 * 地表面付近 = 20 m * モデルトップ = m 初期値 : 09JST 20 Oct (FT=15h) 境界値 : メソ客観解析 物理過程 * 地表面過程 : Beljaars&Holtslag(1991) (mswsys(1) = 1255) * 乱流過程 : MYNN Level 3 (mswsys(19)=31001) * 降水過程 : 雲物理過程のみ (mswsys(22)=0, mswsys(18)=-2) MA 1 km-nhm 2009JST km-NHM Domain September

24 Simulation result_12-h Precipitation Analysis CTL September

25 Simulation result in CTL cold pool N PT S S N cold pool September

26 降水系を形成する Simulation result 暖湿気塊 in ( 水蒸気 CTL ) の起源 Backward-Trajectory September

27 Sensitivity Experiments September