第80回流体懇話会のご案内
平成14年10月3日
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日時：10月25日（金） 16：15〜17：45
場所：電気通信大学 東4号館8階AV会議室(802号室)
講師：D.G. Dritschel（University of St Andrews）
演題：THE QUASI-GEOSTROPHIC ELLIPSOIDAL MODEL
内容：A new reduced model, the ``Ellipsoidal Model'' (ELM), is
introduced to approximate, in a relatively simple way, the interaction
of vortices in three-dimensional rotating, stratified "quasi-geostrophic"
flows. We consider a fluid having uniform background rotational and
buoyancy frequencies. Then it is well known that an ellipsoid of
uniform "potential vorticity" is an exact, rotating solution of the
full equations. Moreover, it remains an exact solution even when an
external linear flow is added (such as one of uniform horizontal
strain and vertical shear), although in this case the shape of the
ellipsoid generally changes in time.
When two or more ellipsoids are considered however, the flow induced
by one ellipsoid is only approximately linear in the vicinity of
another, and so the vortices do not remain precisely ellipsoidal. An
approximation is therefore required. Miyazaki and co-workers used a
Taylor-series expansion of the flow induced by distant vortices,
retaining only the locally linear part. However, it turns out that
this is just part of the flow which preserves the ellipsoidal shape of
a given vortex. Here, we discuss a simple, accurate procedure which
extracts the full contribution of distant vortices --- in effect using
all of the terms in the Taylor-series expansion.
Numerical comparisons with the full equations verify that the ELM is
a highly accurate approximation except during strong vortex
interactions like merger. This generally close comparison has
permitted us to map out the conditions leading to a strong vortex
interaction for two vortices having equal potential vorticity (a 5
parameter problem).
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流体懇話会事務局（電気通信大学）
FAX:0424-84-3327
e-mail：nagare@maekawa.mce.uec.ac.jp
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