Wednesday, 7 August 2013: 8:45 AM
Multnomah (DoubleTree by Hilton Portland)
A frequency-wavenumber spectral decomposition technique is used to analyze the high-resolution NOAA/Climate Prediction Center morphing technique (CMORPH) precipitation dataset and to explore the differences and similarities of the diurnal variation of warm-season precipitation over the East Asia and North America continents downstream of big topography. Average over all warm-season months (MayAugust) during 2003-2010, it is found that predominant phase speed of precipitation at different time scales over North America is ~20 ms-1, which is larger than ~14 ms-1 over East Asia. Consistent with recent studies of precipitation diurnal cycles over these two regions, it is found that the difference of diurnal phase propragation is mostly due to difference in the mean steering level wind speed over these two regions. The frequency-wavenumber spectral analysis further reveals that a complex multiscale, mutli-modal nature of the warm-season precipitation variation embedded within the diurnal cycle over both continentents, with phase speeds varying from 10 to 30 m/s, and wave periods varying from diurnal to a few hours. At the diurnal frequency regulated by the thermodynamically driven Mountains-Plains Solenoids (MPS), enhanced precipitation in both continents first originates in the afternoon from the eastern edge of big topography which subsequently moves downslope in the evening and reaches the broad plains area over night. More complex diurnal evolutions are seen over East Asian due to more complex multistep terrains east of the Tibetan Plateau and the associated localized MPS circulations. Nevertheless, enhanced variations of precipitation at smaller spatial and temporal scales are evident in the active phase of the dominant diurnal cycle in both continents.
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