Abstract:
Finite-domain wavenumber-frequency analysis and components analysis are applied to analyze the spectrum climatology and inter annual anomaly of diversified propagating boreal summer intra-seasonal oscillation (BSISO) over tropics denoted by tropospheric wind field and convection field, based on the daily outgoing longwave radiation (OLR) data and the second set reanalysis data of NCEP/DOE (daily mean is obtained from 4 times observation). It shows that differences of BSISO climatology and inter-annual anomaly characteristics exist among different elements. Low level wind (850 hPa zonal wind or meridional wind) is more consistent with convection generally. Zonal (Meridional) propagating BSISO climatology characteristics denoted by 850 hPa meridional (zonal) wind is the most similar to those of convection. During the ENSO developing year, the enhanced tendency of eastward propagating mode at the equator reflected by 850 hPa meridional wind is more consistent with convection; the changing tendency of northward propagating mode reflected by both of 850 hPa meridional wind and zonal wind is similar to convection. The weakened tendency of northward propagating mode over eastern Indian Ocean reflected by 850 hPa zonal wind is more significant. During the ENSO decaying year, the weakened tendency of eastward (westward) propagating mode at the equator (off the equator) reflected by 850 hPa zonal (meridional) wind is more consistent with convection; 4 elements (convection, 850 hPa meridional wind, 200 hPa zonal wind and 200 hPa meridional wind) can exhibit the characteristic that the northward propagation over South China Sea and its border is suppressed, i.e., this characteristic is resulted from the combination of atmospheric anomaly between upper and low troposphere. The relationship between eastward propagation of BSISO at the equator and BWA mode of Indian Ocean is only presented by convection, and the other 4 elements of wind filed cannot reflect it. Both of convection and 850 hPa zonal wind can reflect the relationship between northward propagation and the Indian Ocean dipole mode. The northward propagation of BSISO over middle and eastern Indian Ocean and South China Sea weakened (enhanced) under positive (negative) dipole mode. The conclusions above indicate that different results would be obtained from different meteorological elements. This is one of the possible causes that the results are not consistent in the past. For different conditions, proper element should be selected for analyzing tropical BSISO. For example, from the view of the forecasting of regional weather and climate, element which indicates the forecasting area well can be chosen based on diagnoses of the remote relationship between weather in forecasting region and the activity of tropical BSISO.