Comparison of the diurnal variations of warm-season precipitation for East Asia vs. North America downstream of the Tibetan Plateau vs. the Rocky Mountains

摘要

A wave-number-frequency spectral decomposition technique is used to analyzethe high-resolution NOAA/Climate Prediction Center morphing technique(CMORPH) precipitation data set and to explore the differences andsimilarities of the diurnal variation of warm-season precipitation in theEast Asia and North America downstream of big topography. The predominantphase speed of precipitation at different time scales for North America,averaged over all warm-season months (May–August) for 2003–2010, is~20 ms?1, which is faster than the speed of~14 ms?1 calculated for East Asia. Consistent with therecent studies of the precipitation diurnal cycles for these two regions,the difference in the diurnal phase propagation is likely due to thedifference in the mean steering level wind speed for these two regions. Thewave-number-frequency spectral analysis further reveals the complex,multi-scale, multi-modal nature of the warm-season precipitation variationembedded within the diurnal cycle over both continents, with phase speedsvarying from 10 to 30 ms?1 and wave periods varying from diurnal to afew hours. At the diurnal frequency regulated by the thermodynamicallydriven mountains–plains solenoids (MPSs), increased precipitation for bothcontinents first originates in the afternoon from the eastern edge of bigtopography and subsequently moves downslope in the evening and reaches thebroad plains area at night. More complex diurnal evolutions are observed inEast Asia due to the more complex, multistep terrains east of the TibetanPlateau and the associated localized MPS circulations. Nevertheless,increased variation of precipitation at smaller spatial and temporal scalesis evident in the active phase of the dominant diurnal cycle for bothcontinents.