  The El Nino southern oscillation (ENSO) behavior can be effectively modeled
as a response to a 2nd-order Mathieu/Hill differential equation with periodic
coefficients describing sloshing of a volume of water. The forcing of the
equation derives from QBO, angular momentum changes synchronized with the
Chandler wobble, and solar insolation variations. One regime change was
identified in 1980. (See floating note)
