農業気象

久住山麓の草地斜面上で観測された風の構造と運動量・顕熱フラックスについて

薦田廣章, 小林哲夫, 手嶋準一, 上野豊

2001 年 57 巻 2 号 p. 69-77
発行日: 2001/06/10
公開日: 2010/02/25

DOIhttps://doi.org/10.2480/agrmet.57.69

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久住山麓の草地斜面上における接地気層内の風と気温の構造を, 同斜面上に位置する九州大学農学部附属高原農業実験実習場での2か月の気象観測結果に基づいて解析した。その結果, 次のような特徴が明らかになった。
1) 標高の増加に伴う斜面上の地表風速の増加割合は, 斜面を上昇・下降する風よりも等高線に沿って斜面を横切る風の場合の方が大きかった。
2) 斜面を上昇・下降する風の摩擦速度は, 風速が比較的強い場合は, 平均して斜面を横切る風の値より大きかった。
3) WSWの風の場合, 風速が臨界値を超えて増すと, こぶ状隆起の風下側に位置する斜面上部の風速は, 後流形成の影響を受けて, 斜面下部よりも増加割合は弱まった。
4) 晴天夜間における高度1.5～2.8mの気層内の下向き顕熱フラックスは, 正味放射とほとんど同じか, あるいはしばしばその約2倍になった。この結果は, 地表付近の放射冷却によって形成された冷気の流下層(CADL)がしばしば上空大気のエントレインメントによって暖められたことを示唆する。

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簡易型塩分飛散予測モデルの構築と評価

加藤央之, 赤井幸夫

2001 年 57 巻 2 号 p. 79-92
発行日: 2001/06/10
公開日: 2010/02/25

DOIhttps://doi.org/10.2480/agrmet.57.79

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A simple numerical model, which is based on an atmospheric diffusion model considering the vertical subsidence of sea salt particles and the semitheoretical estimation of their generation and vertical distribution, is proposed to estimate the amount of wind-driven sea salt or sea salt damage at any point along the coastal area under strong onshore wind conditions. The performance of the model was evaluated through sensitivity studies of the calculation methods for the deposition, adsorption and on the vertical distribution pattern of sea salt particles over the ocean used as initial data. The results were compared to data observed under typhoon conditions in Okinawa Prefecture. The estimated initial vertical distribution pattern of sea salt particles for each size class reproduced well the observed pattern under the strong onshore wind conditions. The atmospheric concentration, deposition and adsorption of sea salt particles observed under strong onshore wind conditions over a platform-like topography near the coast can be reproduced by the model when the interception of sea salt particles by the cliff and the observation efficiencies are considered. In the model, the deposition and adsorption of sea salt particles over the coastal area are proportional to the wind speed to the third or fourth power, and they are most sensitive to the wind speed near the coast. These features are reasonably consistent with the results of studies reported in the literature. Through a series of evaluations, it was suggested that this model is useful for the simple evaluation of sea salt damage over a coastal area under a flat or simple topography.

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REA法によるCO₂フラックス長期観測システムの開発

密度変動補正法の検討を含む

鱧谷憲, 文字信貴, 山口浩司

2001 年 57 巻 2 号 p. 93-99
発行日: 2001/06/10
公開日: 2010/02/25

DOIhttps://doi.org/10.2480/agrmet.57.93

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A REA (Relaxed eddy accumulation) system for long-term CO₂ flux measurement was developed. Long term continuous measurements were achieved by applying a repeating intake and exhaust sampling bag system, by adapting a durable electric valve which can withstand frequent switching, and by real time computation of the REA-coefficient using the temperature signal.
Density correction (WPL correction) is shown to be necessary in the REA method as well as in the open path eddy correlation method. A simple correction method using a heat budget was proposed.
Continuous CO₂ flux measurement was made over a cypress forest from October, 1997 to August, 1998, when the system was stuck by a lightning. Typical 10-day averages of CO₂ flux were about -0.05mg m^-2 s^-1 in January and -0.27mg m^-2s^-1 in August.

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画像処理と三次元デジタイザによる葉面傾斜角の測定

本條毅, 庄野浩資

2001 年 57 巻 2 号 p. 101-106
発行日: 2001/06/10
公開日: 2010/02/25

DOIhttps://doi.org/10.2480/agrmet.57.101

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In this study, leaf tip (declination) angles were measured by image processing method and by using a 3-D digitizer. The 3-D digitizer senses magnetic wave from the source and determines the 3-D location of the sensor. While the 3-D digitizer measures the precise position of the leaf, it is time comsuming, especially if there are many leaves. For this reason, we also tested a method to determine general information on leaf tip angles by image processing, we call this the “texture analysis method”. In this procedure, only photos were necessary for the calculation of general characteristics of leaf tip angles.
The 3-D digitizer (Isotrak, POLHEMUS Inc.) was used for the measurement of leaf position of F. benjamiana L. a plant that has about 300 leaves. Within about 60cm from the source, the digitizer showed good precision.
The results of the texture analysis method were compared with measurements of the 3-D digitizer. Generally they showed good agreement and indicated that the texture analysis method was effective for the estimation of leaf tip angles.

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局地気象学における赤外線放射温度計と熱赤外画像計測装置の有効利用

小林哲夫, 谷宏, 黒瀬義孝, 塚本修, 五十嵐大造, 柏木良明, 桑形恒男, 鳥谷均, 森牧人, 脇水健次

2001 年 57 巻 2 号 p. 107-115
発行日: 2001/06/10
公開日: 2010/02/25

DOIhttps://doi.org/10.2480/agrmet.57.107

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