A pulse of Madden-Julian Oscillation is crossing the Pacific; here's what that means for New Zealand... The Madden-Julian Oscillation or MJO is a pulse of tropical rain & cloud that circumnavigates the Earth every 30-60 days on average. It is forecast to cross the Pacific in the next 2 weeks. In the animation, green colors indicate rising air or the convectively active portion of the MJO pulse where low pressure is more likely to be located. Over the last several months, the existence of La Niña