Shortwave radiative flux variability through the lens of the Pacific
Decadal Oscillation
Abstract
The variability of the shortwave radiative fluxes at the surface and top
of atmosphere (TOA) is examined in a pre-industrial modelling setup
using the Pacific Decadal Oscillation (PDO) as a possible pacemaker of
atmospheric decadal-scale variability. Within models from the Coupled
Model Intercomparison Project – Phase 6, downwelling shortwave
radiation at the surface, the net shortwave fluxes at the surface and
TOA, as well as cloud radiative effects show remarkably similar patterns
associated with the PDO. Through ensemble simulations designed with a
pure PDO pattern in the North Pacific only, we show that the PDO relates
to about 20-40% of the unforced year-to-year variability of these
shortwave fluxes over the Northern Hemispheric continents. The SST
imprint on shortwave-flux variability over land is larger for spatially
aggregated time series as compared to smaller areas, due to the blurring
effect of small-scale atmospheric noise. The surface and TOA radiative
flux anomalies associated with the PDO index range of [-1.64; 1.64]
are estimated to reach up to ±6Wm-2 for North America, ∓ 3Wm-2 for India
and±2Wm-2 for Europe. We hypothesise that the redistribution of clouds
in response to a North Pacific PDO anomaly can impact the South Pacific
and North Atlantic SSTs.