J. of Atmos. and Oceanic Tech. Vol 17, June 2000, p
862-878
The Sensitivity of Relocatable Local Area Models to
Temporal Interpolation Noise at Open Boundaries
Sylvia J. Murphy
National Center for Atmospheric Research, Boulder, Colorado
Timothy R. Keen
Naval Research Laboratory, Stennis Space Center, Mississippi
The feasibility of utilizing regional model data to force the open
boundaries of a relocatable local area model (RLAM) is investigated
mathematically and numerically. The error associated with the
interpolation in time of a periodic signal at the open boundaries of a
numerical ocean circulation model can generate high-frequency noise in the
interior of the model domain. This error is investigated for the tidal
signal represented by a sine wave with a period of 12 h and an amplitude of
1 m. The original time series is subsampled and reconstructed using
first- and third-order polynomial interpolations. The power spectra of the
reconstructed time series contain additional peaks, regardless of sample
interval or interpolation order. The pattern of error growth with
increasing sample interval is examined.
Several suites of numerical model simulations are described. These
include an idealized basin forced at the open boundaries by semidiurnal
tide and residual (storm surge) water-level time series. Also presented
is a realistic representation of the southern Middle Atlantic Bight forced
with the semidiurnal tide plus residual used for the idealized basin, and a
multiconstituent tide plus storm surge. In all the numerical experiments,
the error increases by one order of magnitude with each sample interval
increase. The spectral periods at which error is introduced into the model
are examined. The use of a multiconstituent tide significantly increases
the error magnitudes as well as the overall variability. Neither rotational
nor frictional effects change the pattern of interpolation error growth.
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Hongjun Zhang:
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