资源环境科技发展态势分析平台

A daily El Nino-Southern Oscillation (ENSO) index is developed based on precipitation rate and is used to investigate subseasonal time-scale extratropical circulation anomalies associated with ENSO-like convective heating. The index, referred to as the El Nino precipitation index (ENPI), is anomalously positive when there is El Nino-like convection. Conversely, the ENPI is anomalously negative when there is La Nina-like convection. It is found that when precipitation becomes El Nino-like (La Nina-like) on subseasonal time scales, the 300-hPa geopotential height field over the North Pacific and western North America becomes El Nino-like (La Nina-like) within 5-10 days. The composites show a small association with the MJO. These results are supported by previous modeling studies, which show that the response over the North Pacific and western North America to an equatorial Pacific heating anomaly occurs within about one week. This suggests that the mean seasonal extratropical response to El Nino (La Nina) may in effect simply be the average of the subseasonal response to subseasonally varying El Nino-like (La Nina-like) convective heating. Implications for subseasonal to seasonal forecasting are discussed.