The Longitudinal Distribution Of Atmospheric Low-frequency Oscillations In Middle-High Latitude And The Impacts Affected By ENSO Events

Firstly,a diagnostic analysis is carried out to investigate the intra-seasonal oscillations(ISO) in Extra-tropical Latitudes by using power spectrum method.The power spectral analysis is performed for the daily Northern 500hPa potential height field data in the mid-high latitudes (20°N～75°N)from 1950 to 2005.The conclusion is received that:(1)The cycle of ISO varies with latitudes.In summer,the longest cycle of ISO locates at 45°N,with period of 52.6 d.However,the cycle of ISO tends to be small in relatively low and high latitude.In winter,the longest cycle of ISO appears around 35°N,with period of 49.9 d, while the shortest cycle of ISO lies around 60°N.(2)The period of ISO varies with latitudes more greatly during ENSO-years,especially in summer.During La Nina years,the location of longest cycle shifts from 35°N to 65°N.(3)The difference of the ISO period between summer and winter during ENSO-years is tiny, thus is great during normal-years and whole-years.(4)In an average,main periods of ISO show a shortening/lengthening tendency during E1 Nino/La Nina event.Secondly,numerical experiments on SSTA induced by E1 Nino/La Nina events are carried out utilizing global spectral model of quasi-geotropic barotropic vorticity equation.Certain conclusions are received by using power spectrum method on model results:(1)The longitudinal variation of ISO-Cycle with heating enforcing is much similar to that without any enforcing either in winter or in summer,which indicates that diabatic heating has little influence on the longitudinal variation of ISO-Cycle.(2)In numerical experiments,high-latitude area(70°N)tends to have a relatively long period of ISO except in summer during La Nina years.(3)As is much the same with the analysis on observed data,main periods of ISO show a shortening/lengthening tendency during E1 Nino/La Nina event.Finally,some theory analysis on Rossby-wave enforced by topography as well as quasi-resonance in forced and dissipative barotropic atmosphere is analyzed in theories,which further substantiate the results of diagnosis and numerical experiments.