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Center for Nonlinear Studies |
Topic I: Predictability of coupled models in predicting the Two Types of ENSO and their impacts- Forecast skill of the APEC Climate Center (APCC) Multi-Model Ensemble (MME) seasonal forecast system in predicting two main types of El Nino-Southern Oscillation (ENSO), namely Eastern and Central Pacific ENSO, and their regional climate impacts is assessed for boreal winter. The APCC MME is constructed by simple composite of ensemble forecasts from five independent coupled ocean-atmosphere climate models. Based on a hindcast set targeting boreal winter prediction for the period 1982-2004, we show that the MME can predict and discern the important differences in the patterns of tropical Pacific sea surface temperature anomaly between the EP and CP ENSO one and four month ahead. Importantly, the four month lead MME beats the persistent forecast. The MME reasonably predicts the distinct impacts of the EP ENSO, including the strong winter monsoon rainfall over East Asia, the below normal rainfall and above normal temperature over Australia, the anomalously wet conditions across the south and cold conditions over the whole area of USA, and the anomalously dry conditions in capturing its regional impacts, especially, over Australasia and tropical South America at a lead time of one and four months. Nonetheless, forecast skills for rainfall and temperature over East Asia and North America during CP ENSO are comparable to or slightly higher than those during EP ENSO event; Topic II: Impact of initial conditions on ENSO predictions and their teleconnections using CCSM3`-We investigated the impact of initial conditions on prediction skills of regional climate response as well as ENSO prediction itself using coupled seasonal prediction model. Two hindcast experiments reveal that the interannual variabilities on two ENSO predictions and their performance are similar to each other. However, in terms of regional climate responses to ENSO teleconnection patterns, such as the PNA teleconnection structure and spatial anomaly patterns of temperature and rainfall over the North America, the hindcast initialized with three dimensional oceans temperature nudging (3DN_EXP) shows a considerably better performance. The improvement of cold SST bias over the tropical Pacific Ocean is responsible for the intensification of reality of teleconnection patterns in 3DN_EXP and results in the reduced easterly wind bias and even more realistic location of convection activity. This study suggests that it is important to evaluate the location of tropical convective activity and its teleconnection pattern as well as the ENSO prediction itself for the more reliable and accurate seasonal forecast.