Investigation of coupled ocean-atmospheric biennial mechanisms in the tropical Indian and Pacific regions.

摘要

An investigation of the quasi-biennial oscillation convective maximum's intensity and propagation through the tropical Indian and western Pacific Ocean region was undertaken. This was accomplished by using Complex Empirical Orthogonal Functions (CEOFs) and integrated moist static energy (MSE).; Use of these two methods made it possible to identify those unique situations (e.g., amplitude and phase relationships) that identified the years, 1960-1987, as strong, weak, or non-classified years based on air-sea interactions. By using sea level pressure (SLP), sea surface temperature (SST), surface air temperature (SAT), and outgoing longwave radiation (OLR) data, several classification features were found. Three conditions were found to classify a year as strong using CEOF SLP mode 2 anomalies. (1) The phase angle for nearly every May was in the l{dollar}sp{lcub}st{rcub}{dollar} quadrant. (2) The phase angle for nearly every August was in the 2{dollar}sp{lcub}nd{rcub}{dollar} quadrant. (3) There was a maximum low pressure normalized change anomaly of 0.6 over the Philippine Islands during May.; Three conditions were found to classify a weak year using CEOF SLP mode 2 anomalies. (1) The phase angle for nearly every May was in the 2{dollar}sp{lcub}nd{rcub}{dollar} quadrant. (2) The phase angle for nearly every August was in the 3{dollar}sp{lcub}rd{rcub}{dollar} quadrant. (3) The propagation from May through August was toward the southeast. Attempts to classify years not previously classified proved to be unsuccessful.; Plotting of the CEOF phase angles of the four parameters for the strong and weak years for the months of May and August showed that for the May SLP there was a clear distinction between strong and weak years. There was not, however, a clear separation between strong and weak years for the months of May and August for SAT, SST, and OLR.; Comparisons between continental stations and island stations using the integrated moist static energy did show distinct features. The continental stations exhibited a strong annual cycle of the continental heating while the island stations showed a more irregular pattern. Separation of the total MSE into its individual terms showed that for both continental and island stations the latent heating term was the largest contributor to the total MSE.; Correlations of CEOF SLP, SST, and SAT with the integrated MSE were calculated at several locations. The strongest correlation month was June for the first peak in the MSE with the SST, and there was a second peak in the MSE at the end of September or the beginning of October. This second peak in MSE tended to occur only for those years classified as a strong year. As well, the length of the first MSE maxima tended to last longer for strong years.; From the results of CEOF analyses, integrated MSE analyses, and the use of previous conceptual ideas of tropical air-sea interaction, a schematic diagram is presented to show how a strong annual convective maximum year may form, and then how it may lead to a weak convective maximum year, thus leading to a quasi-biennial oscillation.