Tropical systematic and random error energetics based on NCEP (MRF) analysis-forecast system — A barotropic approach

Abstract

Systematic and random error and their growth rate and different components of growth rate budget in energy/variance form are investigated at wavenumber domain for medium range tropical (30‡S-30‡N) weather forecast using daily horizontal wind field of 850 hPa up to 5-day forecast for the month of June, 2000 of NCEP (MRF) model. Part I of this paper deals with the study at physical domain. The following are the major findings in this paper: •Tropical systematic error is associated with large scale wave of wavenumber 2, unlike the tropical random error, in which case dominant spectra of random error are observed at higher spectral band of wavenumbers 4–7 in comparison to that of systematic error. •Systematic error growth rate peak is observed at wavenumber 2 up to 4-day forecast then the peak is shifted to wavenumber 1 at 5-day forecast. Random error energy shows maximum growth at wavenumber 4 for 2-day forecast, wavenumber 6 for 3–4 day forecasts and at wavenumber 7 for 1-day and 5-day forecasts. •In the error growth rate budget, flux of systematic error shows the net increase of error energy at wavenumber 1 through the triad interactions with the pairs of waves of other wavenumbers. Flux and pure generation of random error energy are found to be accumulated at wavenumber 4. Resolving the possible triads in wavenumber 4 associated with these terms, it is shown that the wave receives more energy from the pairs of waves of different wavenumbers than it loses, leading to the error energy peak at wavenumber 4. However, the significant triad interaction occurs among the wavenumber 2 and higher wavenumbers in systematic error energy flux.