バングラデシュにおける プレモンスーン期およびモンスーン 期の 降水の特徴 寺尾 徹 ( 大阪学院大学情報学部 ) 村田 文絵 ( 地球環境学研究所 ) 林 泰一 ( 京都大学防災研究所 ) P177

Introduction Bangladesh is one of the heaviest rainfall areas. Meso-scale characteristics Diurnal variations. Midnight- early morning peak is found in northeastern part of the country (Ohsawa et al. 2001). Mechanism unknown. Pre-monsoon meso-scale disturbances. Observation plan Instruments with higher temporal resolutions. AWS and raingauges AWS at Dhaka Automatic raingauges: 6 Almost one year obs. Some results is shown today. Pre-monsoon rainfall  -> Ａ Diurnal variations  -> Ｂ AWS obs. case study.  -> Ｃ

AWS Dhaka(ICDDR,B) Data are browsable from everywhere in the world through the network. Raingauges 6-locations ： □ 0.5mm tipping buckets Raingauges are installed in BMD observatories BAY OF BENGAL                                   INDIA (Meghalaya) INDIA (West Bengal) Dinajpur Dhaka Mymensingh Sylhet Chittagong INDIA (Tripura) Rajshahi Locations of AWS and raingauges

2004/07/292005/02/282005/07/22Chittagong Dhaka2004/08/242005/03/042005/07/18 Dinajpur2005/03/012005/07/14 Mymensingh2004/08/012005/03/032005/07/17 Rajshahi2004/08/112005/03/012005/07/15 Sylhet2004/08/052005/07/ /03/032005/07/18Dhaka AWS RGs Obs. time table of AWS and RGs. 30 Jun.- no data

Seasonal march in Bangladesh /Dhaka Rain inc.: Apr->May Sunshine dec. ： May->Jun. Pre-monsoon rainfall begins in May Max. tempSunshine Rainfall

Def. of pre- and mature monsoon Pre-monsoon Jan.->May Mature monsoon Jul.->Dec. Pre-monsoon rain. Northeast>West Chittagong Dhaka Dinajpur Mymensingh Rajshahi Sylhet

Hourly rainfall Pre-monsoon and mature monsoon [1] Rainfall intensity Complicated. Ａ

10-min rainfall Pre-monsoon and mature monsoon [1] Rainfall intensity Intense Short intense downpower Pre>mature monsoon. >5mm/10mi nexceeds 50% of total rain.

1-min rainfall Pre-monsoon and mature monsoon [1] Rainfall intensity Almost same results as 10- min rainfall. Intense

Summary Pre-monsoon and mature monsoon [1] Rainfall intensity Intense rain in pre-monsoon >5mm/10min exceeds 50% of total rain >1mm/min exceeds 50% of total rain BAY OF BENGAL                                   INDIA (Meghalaya) INDIA (West Bengal) Dinajpur Dhaka Mymensingh Sylhet Chittagong INDIA (Tripura) Rajshahi

Pre-monsoon and mature monsoon [2] Diurnal variations UTC(BST-6h) Premonsoon diurnal var. Evident peak Somewhat differs from mature monsoon. Ｂ

Summary I Pre-monsoon and mature monsoon [2] Diurnal variations Diurnal variations in pre-monsoon Central part: afternoon peak. Northern part: Midnight-early morning peak. Steep peak is founr mainly in western part. BAY OF BENGAL                                   INDIA (Meghalaya) INDIA (West Bengal) Dinajpur Dhaka Mymensingh Sylhet Chittagong INDIA (Tripura) Rajshahi Pre-monsoon

Summary II Pre-monsoon and mature monsoon [2] Diurnal variations Diurnal variations in mature monsoon Mymensingh is also in afternoon peak area. BAY OF BENGAL                                   INDIA (Meghalaya) INDIA (West Bengal) Dinajpur Dhaka Mymensingh Sylhet Chittagong INDIA (Tripura) Rajshahi mature monsoon

Case study of pre-monsoon storm. Ｃ AWS

まとめ バングラデシュ各地に AWS と雨量計を設置した AWS×1(2004 年 3 月～ ) 雨量計 ×6(2004 年 8 月～ ) プレモンスーン期とモン スーン期の違いを重視して 解析した プレモンスーン期はモン スーン期に比べて短時間強 雨が多い Chittagong は例外 5mm/10min, 1mm/min の強 雨が降水量の 50% を超える プレモンスーン期にも降水 の日変化が見られる Mymensingh も夜間ピーク 明確なピークが見られる AWS や雨量計を用いてメソ 擾乱を観測することができ た 構造の解明に有効 データを増 やして確認 する必要が ある