Abstract
AbstractBasin‐integrated precipitation minus evaporation (P − E) in the Pacific is near neutral while the Atlantic shows net evaporation. We link this P − E asymmetry to atmospheric moisture fluxes across the boundaries of the ocean drainage basins. Adopting an objective approach based on a comparison between actual fluxes and a zonally averaged circulation, we show that the asymmetry is dominated by moisture fluxes associated with the monthly mean flow at low latitudes rather than by differences in moisture fluxes into the Southern Ocean and Arctic catchments. In boreal summer, the eastward moisture flux, due to the Asian Summer Monsoon flow, opposes the zonal mean westward flux in the Trade Winds and results in more positive P − E over the Pacific than both the Atlantic and Indian Oceans, even in the annual mean. Our analysis reveals that moisture flux across Southeast Asia, rather than across Central America, is the dominant factor in the P − E asymmetry.
Highlights
The contrast between Atlantic and Pacific sea surface salinity (SSS) is linked to the time-mean asymmetry in P − E where the Atlantic P − E ≈ −0.5 Sv (1 Sv ≡ 109 kg s−1) and the Pacific is near neutral. Craig et al (2017) have shown the consistency of these estimates obtained from a range of atmospheric and oceanic analysis techniques
Adopting an objective approach based on a comparison between actual fluxes and a zonally averaged circulation, we show that the asymmetry is dominated by moisture fluxes associated with the monthly mean flow at low latitudes rather than by differences in moisture fluxes into the Southern Ocean and Arctic catchments
Our analysis reveals that moisture flux across Southeast Asia, rather than across Central America, is the dominant factor in the P − E asymmetry
Summary
The contrast between Atlantic and Pacific sea surface salinity (SSS) is linked to the time-mean asymmetry in P − E (precipitation minus evaporation) where the Atlantic P − E ≈ −0.5 Sv (1 Sv ≡ 109 kg s−1) and the Pacific is near neutral. Craig et al (2017) have shown the consistency of these estimates obtained from a range of atmospheric and oceanic analysis techniques. Point (2) assumes that all Atlantic-to-Pacific atmospheric moisture transport across Central America is evaporated from the subtropical Atlantic and precipitated across the tropical Pacific (Leduc et al, 2007; Richter & Xie, 2010). This Eulerian understanding of the hydrological cycle ignores long-range atmospheric transport and potential remote sources of moisture and will be addressed in a separate paper. We will address the time-mean P − E asymmetry To this end, we evaluate, in a quantitative and objective manner, the contributions of the moisture fluxes across catchment boundaries to the asymmetry using the zonally averaged state as a reference point. Our analysis notably reveals that the moisture flux across Southeast Asia is the dominant factor in the P − E asymmetry
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