Extratropical intraseasonal signals along the subtropical westerly jet
as a window of opportunity for subseasonal prediction over East Asia in
boreal summer
Abstract
Previous studies suggest that boreal summer intraseasonal variations
along the subtropical westerly jet (SJ), featuring quasi-biweekly
periodicity, frequently modulate downstream subseasonal variations over
East Asia (EA). Based on subseasonal hindcasts from six dynamical
models, this study discovered that the leading two-three-week prediction
skills for surface air temperature (SAT) are improved significantly in
summer when the SJ has strengthened intraseasonal signals, which are
best demonstrated over the eastern Tibetan Plateau, Southwest Basin, and
North China. The reasons are that the enhanced quasi-biweekly wave and
the associated energy dispersion along the SJ cause more regular
quasi-biweekly periodic variations of downstream SAT, which potentially
increase regional predictability. This study suggests not only that
intraseasonal variations along the SJ could provide a window of
opportunity for achieving better subseasonal prediction over EA, but
also that intraseasonal waves along the SJ are crucial for improving EA
subseasonal prediction.