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Characteristics of Precipitation Particle Distribution in Convective Cells around Okinawa Island during the Baiu Period
http://hdl.handle.net/2237/14291
http://hdl.handle.net/2237/14291251c4c9c-b870-4bd8-8eb2-ac9cb506092d
| 名前 / ファイル | ライセンス | アクション |
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k8937_thesis.pdf (4.6 MB)
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| Item type | 学位論文 / Thesis or Dissertation(1) | |||||
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| 公開日 | 2010-10-27 | |||||
| タイトル | ||||||
| タイトル | Characteristics of Precipitation Particle Distribution in Convective Cells around Okinawa Island during the Baiu Period | |||||
| 言語 | en | |||||
| その他のタイトル | ||||||
| その他のタイトル | 梅雨期沖縄域における対流セル内の降水粒子分布特性 | |||||
| 言語 | ja | |||||
| 著者 |
OUE, Mariko
× OUE, Mariko× 尾上, 万里子 |
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| アクセス権 | ||||||
| アクセス権 | open access | |||||
| アクセス権URI | http://purl.org/coar/access_right/c_abf2 | |||||
| 抄録 | ||||||
| 内容記述タイプ | Abstract | |||||
| 内容記述 | Convective cells with low echo-top heights are commonly observed in the humid environments typical of the Baiu season around Okinawa Island. Representative convective cells with low echo-top heights include convective cells in the stratiform and convective rain zones accompanying a precipitation system, as well as isolated convective cells. In recent years, a few studies have reported the convective cells in stratiform rain zones as one of the characteristic convective cell in the humid environments. The precipitation particle distribution and precipitation formation process for these convective cells have not been revealed. The purpose of this study is to clarify distributions of precipitation particles in convective cells, with low echo-top height, developing in a humid environment. We analyzed polarimetric radar variables and ground-based raindrop size distribution (DSD) and estimated DSD parameters for convective cells with low echo-top heights around Okinawa Island during the Baiu period of 2006, using a C-band polarimetric radar and a disdrometer. First, precipitation particle distribution was analyzed for a convective cell in a stratiform rain zone and a convective cell in a convective rain zone, with 30-dBZ echo top less than 6 km above sea level (ASL), associated with a Baiu frontal rainband. The two convective cells were observed by range height indicators (RHIs) of the radar when they passed over the disdrometer. For the convective cell in the stratiform rain zone, analyses of polarimetric radar variables, differential reflectivity (ZDR) and correlation coefficient (ρhv), in an RHI showed that small raindrops predominated in the convective cells below 0・C altitude; ZDR was smaller than 1.5 dB, and ρhv was greater than 0.98, with large radar reflectivity (Zh) below about 3 km ASL. The ground-based DSD showed high number densities of smaller raindrops (1!2 mm in diameter), with few raindrops exceeding 3 mm in diameter. On the other hand, for the convective cells in the convective rain zone, large raindrops contributed to the large radar reflectivity; ZDR greater than 1.5 dB and ρhv smaller than 0.98 predominated, with large Zh greater than 40 dBZ in an RHI below 3 km ASL. The peak of ZDR value were shown particularly below 2 km ASL. The ground-based DSD showed large numbers of raindrops exceeding 3 mm in diameter. To investigated variations in DSD characteristics with time and height, median volume diameter (D0) and normalized intercept parameter (Nw) were estimated for cell lifetime using plan position indicator (PPI) volume scan data. For detailed analyses of time variations, we selected three convective calls, with 30-dBZ echo-top heights less than 6 km ASL, developing over the sea and observed by PPI volume scanning for their lifetimes (a convective cell in the stratiform rain zone of the Baiu frontal rainband, a convective cell in the convective rain zone of the rainband, and an isolated convective cell developing to the south of the Baiu front). To examine DSD characteristics contributing to Zh, the estimated DSD parameters from range bin data of PPIs in a rain region were averaged every 5 dB in Zh. For the convective cell in the stratiform rain zone in the mature stage, the estimated D0 was approximately 1.5 mm with Zh of 45!50 dBZ and did not reach 2 mm even when Zh approached a large value of 50 dBZ; the estimated Nw ranged from 32000 to 100000 mm^"1 m^"3. This indicates that a high number-concentration of small raindrops contributed to large Zh for the convective cell in the stratiform rain zone. For the convective cell in the convective rain zone in the mature stage, the estimated D0 was approximately 2 mm with Zh of 40!45 dBZ; the estimated Nw ranged from 1000 to 10000 mm^"1 m^"3. This indicates that large raindrops contributed to large Zh for the convective cell in the convective rain zone. For the isolated convective cell in the mature stage, D0 was estimated to be approximately 2 mm with Zh of 40!50 dBZ; the estimated Nw ranged from 1000 to 10000 mm^"1 m^"3. This indicates that large raindrops contributed to large Zh for the isolated convective cell. Analyses of variations in the estimated D0 and Nw within cell lifetimes indicated that the D0 values for a given Zh for the convective cell in the convective rain zone and for the isolated convective cell were larger than those for the convective cell in the stratiform rain zone at any given time. The Nw values for the convective cell in the stratiform rain zone were larger than those for the other two cases at any given time. From variations of vertical structure of the radar-estimated D0 and Nw with convective lifetime, we suggested conceivable formation process of raindrops in each of the convective cells. For the convective cell in the stratiform rain zone, a high numberconcentration of small raindrops contributed to the increase in Zh. In the convective cell in the convective rain zone and the isolated convective cell, large raindrops contributed to the increase in Zh and raindrop coalescence processes were predominant at altitudes below 2 km ASL. The significance of these D0 and Nw characteristics was confirmed for 25 cells in the stratiform rain zone, for 28 cells in the convective rain zone, for 14 isolated convective cells from the estimated D0 and Nw for a given Zh using PPI volume scan data. This study characterized precipitation particle distribution for three types of convective cell, with low echo-top heights, representing the humid environment of Okinawa Island during the Baiu period. In particular, the precipitation particle distribution for convective cells in the stratiform rain zone, which differ markedly from convective cells in the convective rain zone and isolated convective cells, were newly characterized. | |||||
| 言語 | en | |||||
| 内容記述 | ||||||
| 内容記述タイプ | Other | |||||
| 内容記述 | 名古屋大学博士学位論文 学位の種類:博士(理学)(課程) 学位授与年月日:平成22年9月28日 | |||||
| 言語 | ja | |||||
| 言語 | ||||||
| 言語 | eng | |||||
| 資源タイプ | ||||||
| 資源タイプ識別子 | http://purl.org/coar/resource_type/c_db06 | |||||
| 資源タイプ | doctoral thesis | |||||
| 書誌情報 |
発行日 2010-09-28 |
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| 学位名 | ||||||
| 言語 | ja | |||||
| 学位名 | 博士(理学) | |||||
| 学位授与機関 | ||||||
| 学位授与機関識別子Scheme | kakenhi | |||||
| 学位授与機関識別子 | 13901 | |||||
| 言語 | ja | |||||
| 学位授与機関名 | 名古屋大学 | |||||
| 言語 | en | |||||
| 学位授与機関名 | Nagoya University | |||||
| 学位授与年度 | ||||||
| 値 | 2010 | |||||
| 学位授与年月日 | ||||||
| 学位授与年月日 | 2010-09-28 | |||||
| 学位授与番号 | ||||||
| 学位授与番号 | 甲第8937号 | |||||
| 著者版フラグ | ||||||
| 値 | publisher | |||||
| URI | ||||||
| 識別子 | http://hdl.handle.net/2237/14291 | |||||
| 識別子タイプ | HDL | |||||
