Strengthened causal connections between the MJO and the North Atlantic
with climate warming
Abstract
While the Madden Julian Oscillation (MJO) is known to influence the
midlatitude circulation and its predictability on
subseasonal-to-seasonal (S2S) timescales, little is known how this
connection may change with anthropogenic warming. This study
investigates changes in the causal pathways between the MJO and the
North Atlantic Oscillation (NAO) within historical and SSP585
simulations of the CESM2-WACCM coupled climate model. Two data-driven
approaches are employed, namely, the STRIPES index and graphical causal
models. These approaches collectively indicate that the MJO’s influence
on the North Atlantic strengthens in the future, consistent with an
extended jet-stream. In addition, the graphical causal models allow us
to distinguish the causal pathways associated with the teleconnections.
While both a stratospheric and tropospheric pathway connect the MJO to
the North Atlantic in CESM2-WACCM, the strengthening of the MJO-NAO
causal connection over the 21st century is shown to be due exclusively
to teleconnections via the tropospheric pathway.