persistent wave
1.The cold air could reach low latitude area when the stable meridional circulation pattern controls the Southern Hemisphere. The strong southeast wind to the north of lower layer cold high located behind the long wave trough could form a strong and persistent cross-equator flow in a relatively fixed narrow channel. In some favorable conditions of Northern Hemisphere circulation, this cross-equator flow could turn into southwest flow over the Northwest Pacific and lead to intensification of southwest monsoon.
