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)
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 15-18 September 2014 2
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. 15-18 September 2014 3
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. 15-18 September 2014 4
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. 15-18 September 2014 5
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)? 15-18 September 2014 6
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. 15-18 September 2014 7
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. 15-18 September 2014 8
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. 15-18 September 2014 9
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 ~ 15-18 September 2014 10
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 15-18 September 2014 11
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. 15-18 September 2014 12
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. 15-18 September 2014 13
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. 15-18 September 2014 14
Supplemental Slides 15-18 September 2014 15
3-h Precipitaion 15-18 September 2014 16
Radar_2100JST/19-2400JST/20 (dbz) 15-18 September 2014 17
EPT(Equivalent Potential Temperature) : 奄美大島 : 前線の位置 N S N 500m S 15-18 September 2014 18
Vertical Profile at Naze Naze: 09JST/20 At 967hPa (396m) LNB : 401hPa(8km) dlfc : 648m 15-18 September 2014 19
Water Vapor Mass Flux at 500m 15-18 September 2014 20
Vertical profiles of horizontal wind velocity at Naze 2000 1000 (m) 15 (JST) (m s -1 ) 15-18 September 2014 21
Time variations of LHF 400 W/m 2 Black : CTL Red : SST-2 300 W/m 2 200 W/m 2 100 W/m 2 FT=01;07JST FT=06;12JST FT=09;15JST 15-18 September 2014 22
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 = 20696 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 2012 2015 2018 2021 2024 1km-NHM Domain 15-18 September 2014 23
Simulation result_12-h Precipitation Analysis CTL 15-18 September 2014 24
Simulation result in CTL cold pool N PT S S N cold pool 15-18 September 2014 25
降水系を形成する Simulation result 暖湿気塊 in ( 水蒸気 CTL ) の起源 Backward-Trajectory 15-18 September 2014 26
Sensitivity Experiments 15-18 September 2014 27