On the Source of Trends in Atmospheric Water Cycle Components over Indo-Pacific Ocean Basins

Abstract:

Obtaining an accurate baseline of the components of the hydrological cycle is critical for understanding how climate change will affect the energy balance of the earth system. Given that the West Pacific and Indian Ocean basins are home to large water fluxes in the form of ocean evaporation and convective precipitation, any long term changes in the hydrological cycle over these regions are of particular interest. Changes in water cycle closure have been noted in recent years, but trends are limited to the West Pacific region. This work compares the temporal evolution of the main components of the atmospheric water cycle (evaporation, precipitation, and moisture flux divergence) as depicted by multiple satellite, reanalysis, and surface flux products for the period 1998-2015. Analysis suggests that trends in precipitation and in moisture flux divergence are responsible for trends in overall water cycle closure in the West Pacific. Breakpoints also exist in the vicinity of the year 2010, after which differences between reanalysis depictions of lower tropospheric winds are notably reduced, resulting in a closer agreement of moisture flux divergence magnitude among products. When considering overall closure magnitude, West Pacific closure varies dramatically depending on which products are used for precipitation and moisture flux divergence. Product choice affects closure in other tropical ocean basins to a lesser degree, suggesting that temporal changes in either the observing system or the environment in the West Pacific may differ from those in other regions. Breakpoints as well as seasonal and month-to-month variability metrics are analyzed in the context of known environmental and observational changes to hypothesize whether the trends in West Pacific water cycle components are purely observational, physical, or a combination of both, thus allowing us to characterize the temporal stability of individual products and changes in overall water cycle closure.