Mean Sea Level Height is not really constant. It can vary due to the action of the wind. During La Ninas, the enhanced trade winds push water westward along the equator and pile it up in the western areas. In El Ninos, as the trade easterlies weaken, water sloshes eastward and sea levels rise in the eastern Pacific and fall in the western Pacific. This drop in sea level can cause exposure damage to the sensitive coral in the western Pacific.
Convection is a process of heat transfer involving vertically moving air currents.
It is most favored in unstable air where low level warm air becomes buoyant and rises. Cooler, heavier air from above sinks to replace it. Convection results in clouds and showery type precipitation. In La Ninas, the convection is confined mainly to the western Pacific. In El Ninos, the convection in the tropical Pacific shifts eastward which has an effect on atmospheric jet streams and storm tracks.