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流　体　力　学　セ　ミ　ナー　 2013
　 共催： 気象学研究室コロキウム

日時：10月 9日（水） 10:00 から 12:00

場所： 京都大学大学院 理学研究科 1号館 563号室
(地球惑星科学専攻共通大会議室)

講師： Prof. Dale Durran
(Prof. of Atmospheric Sciences,
Dept. of Applied Mathematics,
University of Washington)

講演題目： Atmospheric Predictability: Why Butterflies Don’t Matter

講演要旨：
The seminal paper of Lorenz (1969) established that a fluid system has
limited predictability if the spectral distribution of its energy decays
sufficiently slowly as the scale of motion decreases (i.e., if the
kinetic energy per unit wavenumber has a -5/3 spectrum). According to
Lorenz, predictability is limited by the upscale cascade of errors
beginning at the smallest scales that are not subject to viscous
dissipation. Thus, the flapping of a butterfly’s wings might be
supposed to change the weather on a relatively short time scale.

Nevertheless, numerical weather prediction has been reasonably
successful without accounting for the behavior of butterflies. We will
review the various modifications to the notion of atmospheric
predictability that have been proposed since Lorenz’s paper and present
new results from recent ensemble simulations of strong winter storms.
We will show that after a few modifications, Lorenz’s model is able to
do a surprisingly good job of describing the loss of predictability in
the ensemble forecasts. In the process, we will see why butterflies
are of no practical importance.

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世話人：山田 道夫(京大数理研)， 藤 定義(京大)，松本 剛(京大理)
アドバイザー：船越 満明（京大情報学）、水島 二郎(同志社大工)、
余田 成男（京大理）
連絡先：山田道夫 yamada__at__kurims.kyoto-u.ac.jp
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