Potential Impact of Spring Thermal Forcing Over the Tibetan Plateau on the Following Winter El Nino-Southern Oscillation

Using observational analysis and numerical experiments, we identify that the dipole mode of spring surface wind speed (SWS) over the Tibetan Plateau (TP) could act as a trigger for subsequent winter El Nino-Southern Oscillation events. During the positive phase of spring SWS dipole mode (south-positive and north-negative), a self-sustaining "negative sensible heating-baroclinic structure" prevails over the western TP, which is characterized by negative surface sensible heating anomalies, anomalous low-level anticyclones, and mid-high-level cyclones. The "negative sensible heating-baroclinic structure" stimulates the surface westerly wind anomalies over the tropical western Pacific in May through two pathways, favoring the occurrence of subsequent El Nino events. One is through weakening the zonal monsoon circulation over the tropical Indian Ocean and the Walker circulation over the tropical western Pacific. The other is modulating the air-sea interaction over the North Pacific through triggering Rossby waves. The negative SWS dipole mode tends to induce La Nin & x303;a events.