Why Monsoons Are So Fickle: The Answer Lies in the Spectrum of Random Fluctuations ✎

A monsoon is a giant wind that brings rain from the ocean to the land every summer. But within this regular movement, there are fast fluctuations: rainfall intensifies and weakens with periods ranging from three weeks to three months. To understand these whims, scientists took daily records of special indices that measure monsoon strength and ocean temperature in the tropical Pacific (a phenomenon known as El Niño). There are five such indices in total: three for monsoons in different regions and two for El Niño.

Slow changes were removed from the data, leaving only fast fluctuations. Then they constructed a power spectrum, a graph showing how much energy corresponds to each frequency. It turned out that all five spectra fall onto the same curve, called a stretched exponential. It's as if different musical instruments were playing the same melody, just at different volumes. The shape of the curve indicates that the system exhibits a special type of chaos: Hamiltonian distributed chaos. In such a system, energy is conserved, and disorder arises not from external pushes but from complex internal connections.

For the Indian monsoon, the characteristic oscillation time turned out to be about 32 days, while for other systems it ranged from 143 to 280 days. Interestingly, the Australian monsoon's spectrum resembles El Niño more than it does the Indian monsoon. This suggests that the Australian monsoon and El Niño are parts of one large system. Previously, this was only a hypothesis; now it is confirmed by rigorous calculation. The practical benefit is that climate models can be tested: if a model does not reproduce this spectral shape, it is missing something. And forecasters gain a more reliable basis for predictions several weeks ahead.