Monday, 15 January 2007: 1:30 PM
Wide band power and harmonic amplitude of precipitation
214B (Henry B. Gonzalez Convention Center)
Time series of precipitation from three satellite products (TRMM 3B42, CMORPH, and PERSIANN) and two reanalysis models (the NCEP/DOE Reanalysis-2 and ECPC Seasonal Forecast Model) are examined for their behavior at different frequencies using both harmonic and Fourier approaches. Power spectra generated by fast-Fourier transforms are divided into wide bands comprising the low-frequency (period greater than 30 days), synoptic (period between 2 – 30 days), and high-frequency (period less than 2 days) components. Low-frequency variability is generally the weakest component, but is amplified over the Inter-Tropical Convergence Zone and monsoonal regions. Land areas feature enhanced high-frequency variability and reduced synoptic variability in comparison to the surrounding oceans. The diurnal and semidiurnal harmonics explain very little of the variance, suggesting that the harmonic approach does a poor job of capturing the high-frequency variability of the datasets. Inter-satellite and inter-model differences also indicate biases of the precipitation product algorithms and convective parameterizations, including a strong bias toward low-frequency variability in the Relaxed Arakawa-Schubert parameterization employed by the ECPC Seasonal Forecast Model.