Improved Surface Mass Balance Closure in Ocean Hindcast Simulations

Abstract

Abstract Forced global ocean/sea‐ice hindcast simulations are subject to persistent surface mass flux estimation biases, for example, configurations with an explicit‐free surface may not take into account the seasonal storage of water on land when constraining sea level. We present a physically motivated surface mass flux closure, that results in: reduced watermass drift from initialization; improved Atlantic meridional overturning cirulation intensity; and more realistic rates of ocean heat uptake, in simulations using global ocean/sea‐ice/land (MOM6/SIS2/LM3) model configurations, forced with atmospheric reanalysis data. In addition to accounting for the land storage, the area‐integrated subpolar‐to‐polar (40°–90°N/S) surface mass fluxes are constrained, using a climatological estimate derived from the the CMIP6 historical ensemble, which helps to further improve hindcast performance. Simulations using MERRA‐2 and JRA55‐do forcing, subject to identical hydrologic constraints, exhibit similar reductions in drift.

Keywords

• global ocean simulation
• reanalysis forcing
• hydrologic cycle
• freshwater forcing
• AMOC
• ocean heat content