  Vallis proposed a simple model for El-Nino weather phenomenon (referred as
Vallis system) by adding an additional parameter p to the Lorenz system. He
showed that the chaotic behavior of the Vallis system is related to the El-Nino
effect. In the present article we study fractional version of Vallis system in
depth. We investigate bifurcations and chaos present in the fractional Vallis
system along with the effect of variation of system parameter p. It is observed
that the range of values of parameter p for which the Vallis system is chaotic,
reduces with the reduction of the fractional order. Further we analyze the
incommensurate fractional Vallis system and find the critical value below which
the system loses chaos. We also synchronize Vallis system with Bhalekar-Gejji
system.
