Rainfall changes due to warming of the Indo-Pacific Ocean and corresponding changes in the Madden Julian Oscillation. The shining sun depicts areas of declining rainfall while the rain clouds show where rainfall is increasing. Credit: Roxy M. Koll, Indian Institute of Tropical Meteorology, et al., Nature
Roxy, M.K., P. Dasgupta, M.J. McPhaden, T. Suematsu, C. Zhang, and D. Kim, 2019: Twofold expansion of the Indo-Pacific warm pool warps the MJO life cycle. Nature, 575, 647-651. https://doi.org/10.1038/s41586-019-1764-4
A new study published in the journal Nature (Roxy et al., 2019) shows that warming of the Indo-Pacific Ocean is altering rainfall patterns across the globe, contributing to declines in rainfall along the U.S. West Coast and parts of the East Coast. The research, involving NOAA scientists and others from India, Japan, and the U.S., reports that the warm pool of water spanning the western Pacific and eastern Indian Ocean has doubled in size over the past century. This “Indo-Pacific warm pool”, which is already the warmest part of the global ocean, is expanding each year by an area the size of California. The expansion is changing a key weather and climate feature called the Madden Julian Oscillation (MJO), which is characterized by a band of rain clouds that develops approximately every 30 to 60 days over the tropical Indian Ocean and then moves eastward into the Pacific Ocean. Warming of the Indo-Pacific Ocean has changed the life cycle of the MJO, which now spends several days less time over the Indian Ocean and several days more time over the west Pacific.
The MJO influences everything from monsoons in India to heat waves and flooding in the United States (see figure). Climate model simulations indicate that continued warming of the Indo-Pacific Ocean is highly likely, which may further intensify changes in MJO life cycle and global rainfall patterns associated with it. Predicting the development of individual MJO events may help with extended range weather forecasting at lead times of two to four weeks, which is why understanding its behavior in a changing climate is so important.