Atmospheric and Oceanic Origins of Tropical Precipitation Variability

Journal of Climate | He et al. [2017]

Abstract

We study the intrinsic atmospheric and ocean-induced tropical precipitation variability using millennial control simulations with various degrees of ocean coupling. A comparison between the coupled simulation and the atmosphere-only simulation with climatological sea surface temperatures (SSTs) shows that a substantial amount of tropical precipitation variability is generated without oceanic influence. This intrinsic atmospheric variability features a red noise spectrum from daily to monthly timescales and a white noise spectrum beyond the monthly timescale. The oceanic impact is inappreciable for sub-monthly timescales but important at inter-annual and longer timescales. For timescales longer than a year, it enhances precipitation variability throughout much of the tropical oceans and suppresses it in some subtropical areas, preferentially in the summer hemisphere. The sign of the ocean-induced precipitation variability can be inferred from the local precipitation – SST relationship, which largely reflects the local feedbacks between the two although non-local forcing associated the El Niño–Southern Oscillation also plays a role.

The thermodynamic and dynamic nature of the ocean-induced precipitation variability is studied by comparing the fully coupled and slab ocean simulations. For timescales longer than a year, equatorial precipitation variability is almost entirely driven by ocean circulation, except in the Atlantic Ocean. In the rest of the tropics, ocean induced precipitation variability is dominated by mixed-layer thermodynamics. Additional analyses indicate that both dynamic and thermodynamic oceanic processes are important for establishing the leading modes of large-scale tropical precipitation variability. On the other hand, ocean dynamics likely dampens tropical Pacific variability at multi-decadal timescales and beyond.

*Full text can be found [here](http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-16-0714.1?af=R).*

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