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------------------------------------ TTS ---------------------------------------
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Description:

  TTS stands for Trajectory-Tracking Scheme, which is trying to be designed as
  a practical fully Lagrangian linear advection scheme for atmospheric modeling.
  The major focus of TTS is to preserve the large gradient or discontinuity
  existed in the tracer field (e.g., moisture) well.

  In TTS, the continuous air or tracer field is discretized as parcel polygons
  with finite number. The parcels are advected passively by the background wind
  field provided by other components of an atmospheric model (i.e., dynamical
  core).  During the advection, the shape of a parcel polygon will be deformed
  (severely) according to the wind. A curvature guard algorithm has been devised
  to keep good approximation to the continuous curved interface of the parcel by
  discrete straight lines. Also a polygon rezoning procedure is incoporated to
  constrain the computational complexity.

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Authors:

  Li Dong - dongli@lasg.iap.ac.cn

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