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Data Processing: Wheeler-Kiladis Space-Time Spectra

===> Under Development <===

NCL version 5.0.1 is required to use the wkSpaceTime and wkSpaceTime_cam interfaces.

The following four libraries must be loaded prior to use.

load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/gsn_code.ncl"
load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/gsn_csm.ncl"
load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/contributed.ncl"
load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/diagnostics.ncl"

*********************   REFERENCES  *********************
  Wheeler, M., G.N. Kiladis
     Convectively Coupled Equatorial Waves:
     Analysis of Clouds and Temperature in the
     Wavenumber-Frequency Domain
     J. Atmos. Sci., 1999,  56: 374-399.
----

   Hendon, H.H., and M.C. Wheeler 
     Some space-time spectral analyses
     of tropical convection and planetary-scale waves. 
     J. Atmos. Sci., 2008, in press.

----
  Hayashi, Y.
     A Generalized Method of Resolving Disturbances into
     Progressive and Retrogressive Waves by Space and
     Fourier and TimeCross Spectral Analysis
     J. Meteor. Soc. Japan, 1971, 49: 125-128.

wkSpaceTime_1.ncl:

Default Mode using the wkSpaceTime_cam interface.

wkSpaceTime_2.ncl: This illustrates using several of the options to change the default behavior. The data used were from ERA40 1999-2001 on a T85 grid. The original data were at a sampling rate of 4x per day (ie: every 6-hours). In this example The sampling rate was reduced (decimated) to 2x per day (ie: every 12 hours). This may be needed if memory is a problem.

Matt Wheeler commented on the spectral peaks in zonal wind (200 or 850hPa) for low westward-propagating wavenumbers (1-4) and periods in the range of about 4-6 days. (See the rightmost symmetric power figure.) "These are best described as resulting from global Rossby-Haurwitz waves. These are global and barotropic, and are not observable as peaks in the spectrum of OLR or precip. Despite the fact that they are not equatorially-trapped, their dispersion relation can be well-approximated by the same dispersion relation as used for the equatorially-trapped Rossby waves, provided the equivalent depth is set to ~10km, and you assume some global advecting basic state wind speed (~ 15 m/s). We discuss this more in the paper Hendon and Wheeler (2008, JAS - in press)."

wkSpaceTime_3.ncl: This illustrates using the direct interface, wkSpaceTime for calculations and plotting. The data used were from NCEP Reanalysis 2001-2005 on a 2.5x2.5 degree grid 4x per day. This is the interface that is most commonly used.

Data Processing: Wheeler-Kiladis Space-Time Spectra

NCL is a product of the Computational & Information Systems Laboratory at the National Center for Atmospheric Research (NCAR), with support from NSF Contact webmaster

NCL is a product of the Computational & Information Systems Laboratory at the National Center for Atmospheric Research (NCAR), with support from NSF
Contact webmaster