Two dominant subseasonal variability modes of the eastern Pacific ITCZ



[1] Two subseasonal variability (SSV) modes over the eastern Pacific (EPAC) have been identified based on rainfall observations. The first SSV mode with a dominant period of 40 days has been documented in detail in previous studies. The second SSV mode associated with the EPAC intertropical convergence zone (ITCZ) rainfall, to the best of our knowledge, is documented for the first time, exhibiting a prevailing period of 18 days (hereafter, a 20-d SSV mode). This 20-d SSV mode is largely characterized by northward propagation. While its strongest signals are present over the EPAC, the impacts of this 20-d SSV mode are also discerned over the North American Monsoon, the Gulf of Mexico, and Caribbean Sea. Analysis of the low-frequency variability of these two SSV modes shows that they are anti-correlated on the interannual time scales. The physics responsible for the origins of the two SSV modes over the EPAC are still elusive.