摘要
Based on the NCEP/NCAR reanalysis I daily data from 1958 to 2002,climatic characteristics of the 30-60-day intraseasonal oscillations（ISOs） of the zonal wind（u）,meridional wind（v）,and geopotential height（h） over global areas and especially the ISO of v over the subtropical northern Pacific are analyzed using the space-time spectrum analysis and wavelet transform methods.The results show that the ISO of v is very different from those of u and h,with the former representing the meridional low-frequency disturbances,which are the most active in the subtropics and mid-high latitudes,but very weak in the tropics.In the subtropical Northern Hemisphere,the energies of the ISOs of u and h are both concentrated on the waves with wave number of 1 and periods of 30-60 days,while the main energy of the ISO of v is concentrated on the waves with wave numbers of 4-6 and periods of 30-60 and 70-90 days.The westward propagating energies for the 30-60-day oscillations of u,v,and h are all stronger than the eastward propagating energies in the subtropics.In addition,the ISO of v is the strongest（weakest） in summer （winter） over the subtropics of East Asia and northwestern Pacific,while the situation is reversed over the subtropical northeastern Pacific,revealing a ＂seesaw＂ of the ISO intensity with seasons over the subtropics from the northwestern to northeastern Pacific.In the subtropical northwestern Pacific,the interannual and interdecadal changes of the ISO for v at 850 hPa indicate that its activities are significantly strong during 1958-1975,while obviously weak during 1976-1990,and are the strongest during 1991-2000,and its spectral energy is obviously abnormal but ruleless during the ENSO periods.However,in the 2-7-yr bandpass filtering series,the interannual changes of the v ISO over the subtropical northwestern Pacific contain distinct ENSO signals.And in the 9-yr low-pass filtering series,the v ISO changes over the subtropical northwestern Pacific are significantly out of phase with the changes of the Nino-3.4 SST,whereas the v ISO changes in the subtropical northeastern Pacific are significantly in phase with the changes of the Nino-3.4 SST.
Based on the NCEP/NCAR reanalysis I daily data from 1958 to 2002,climatic characteristics of the 30-60-day intraseasonal oscillations（ISOs） of the zonal wind（u）,meridional wind（v）,and geopotential height（h） over global areas and especially the ISO of v over the subtropical northern Pacific are analyzed using the space-time spectrum analysis and wavelet transform methods.The results show that the ISO of v is very different from those of u and h,with the former representing the meridional low-frequency disturbances,which are the most active in the subtropics and mid-high latitudes,but very weak in the tropics.In the subtropical Northern Hemisphere,the energies of the ISOs of u and h are both concentrated on the waves with wave number of 1 and periods of 30-60 days,while the main energy of the ISO of v is concentrated on the waves with wave numbers of 4-6 and periods of 30-60 and 70-90 days.The westward propagating energies for the 30-60-day oscillations of u,v,and h are all stronger than the eastward propagating energies in the subtropics.In addition,the ISO of v is the strongest（weakest） in summer （winter） over the subtropics of East Asia and northwestern Pacific,while the situation is reversed over the subtropical northeastern Pacific,revealing a ＂seesaw＂ of the ISO intensity with seasons over the subtropics from the northwestern to northeastern Pacific.In the subtropical northwestern Pacific,the interannual and interdecadal changes of the ISO for v at 850 hPa indicate that its activities are significantly strong during 1958-1975,while obviously weak during 1976-1990,and are the strongest during 1991-2000,and its spectral energy is obviously abnormal but ruleless during the ENSO periods.However,in the 2-7-yr bandpass filtering series,the interannual changes of the v ISO over the subtropical northwestern Pacific contain distinct ENSO signals.And in the 9-yr low-pass filtering series,the v ISO changes over the subtropical northwestern Pacific are significantly out of phase with the changes of the Nino-3.4 SST,whereas the v ISO changes in the subtropical northeastern Pacific are significantly in phase with the changes of the Nino-3.4 SST.
基金
Supported jointly by the National Basic Research Program of China(2006CB403606)
the National Natural Science Foundation of China(Grant Nos.40575027 and 40905035)
the National Non-Profit Public-Interest Research Project(Grant No. GYHY200806004)
