Role of ocean and atmosphere variability in scale-dependent
thermodynamic air-sea interactions
Abstract
This study investigates the influence of oceanic and atmospheric
processes in extratropical thermodynamic air-sea interactions resolved
by satellite observations (OBS) and by two climate model simulations run
with eddy-resolving high-resolution (HR) and eddy-parameterized
low-resolution (LR) ocean components. Here, spectral methods are used to
characterize the sea surface temperature (SST) and turbulent heat flux
(THF) variability and co-variability over scales between 50-10000 km and
60 days-80 years in the Pacific Ocean. The relative roles of the ocean
and atmosphere are interpreted using a stochastic upper-ocean
temperature evolution model forced by noise terms representing intrinsic
variability in each medium, defined using climate model data to produce
realistic rather than white spectral power density distributions. The
analysis of all datasets shows that the atmosphere dominates the SST and
THF variability over zonal wavelengths larger than
~2000-2500 km. In HR and OBS, ocean processes dominate
the variability of both quantities at scales smaller than the
atmospheric first internal Rossby radius of deformation (R1,
~600-2000 km) due to a substantial ocean forcing
coinciding with a weaker atmospheric modulation of THF (and consequently
of SST) than at larger scales. The ocean-driven variability also shows a
surprising temporal persistence, from intraseasonal to multidecadal,
reflecting a red spectrum response to ocean forcing similar to that
induced by atmospheric forcing. Such features are virtually absent in LR
due to a weaker ocean forcing relative to HR.