Remote Features Linked to the
South Pacific Subtropical High
(hereafter called the “SP high”)
Richard Grotjahn
Atmospheric Science Program,
Dept. of LAWR, Univ. of California
Davis, CA 95616, USA
Our Prior Work on the SP high
• Working hypothesis
that there are remote
connections to the
subtropical high
• Some connections will
be visible through the
divergent circulation.
• 3 sources of remote
forcing.
• (1) Hadley and Walker
circulations,
• (2) Rossby wave forcing
from East,
• (3) frontal cyclones
Composites of DJF Monthly Anomaly Data:
• Months of stronger highs
minus months of weaker
highs show:
• lower SLP to East (purple)
• More P (green) West or
westward shift of SPCZ
• Dipole (P) & (OLR) S and
SW of high: shift to S.
• More P North of ICZ East
Pacific or Northward shift
• Enhanced P North of
South America
• Green: significant above (1%)
• Purple: significant below (1%)
1-pt correlations of Monthly Anomaly Data:
• P shown, OLR
similar.
• correlation points
respond to events on
the same side as the
correlation point.
• NW side to ICZ
SPCZ
• NE to ICZ & SA
• S & SW sides to
midlatitudes
• Blue: significant above (1%)
• Orange: significant below (1%)
Recent Work: daily mean data
• Data Source:
• NOAA/CDC (Boulder
CO, USA)
• NCEP/NCAR reanalysis
data
• SLP, U, V
• Ud, Vd, Velocity Potential
(VP) from NCL
commands.
• Data record:
• 90-day DJF periods shown
(122 day NDJF similar)
• Drawn from 01/1990
through 08/2002
• Goal:
• Prior work showed remote
links now wish to
establish cause and effect.
Cross-correlation points for SLP & VP
SLP lagged autocorrelations
lag (L) and lead (R) SLP @ pt-8
correlations (CW: 4, 2, 0, -2, -4d)
Velocity Potential (“VP”)
lag (L) and lead (R) SLP @ pt-8 correlations
(CW: 8, 6, 4, 2, 0, -2, -4,-6 d)
Vd - Meridional Divergent Wind
lag (L) and lead (R) SLP @ pt-11
correlations (CW: 4, 2, 0, -2, -4d)
VP cross-correlations for SLP on NE side
DWS cross-correlations for SLP max
DWS cross-correlations for SLP South side
Tentative Conclusions
• Equatorial and NE side of SP high highly correlated with
pressure in equatorial & E Pacific. Stronger SLP on N side
of SP high is followed by lower SLP over SE Asia.
• Stronger SP highs are those SW of the mean position &
reinforced by divergent winds from midlatitude cyclones.
• Weaker E Indonesian convection is followed in a few days
by expansion of Amazonian velocity potential (VP) min.
and westward shift of the SE Pacific VP maximum.
• This last item leads a westward migration of higher than
normal SLP on equatorial side of SP high.
• For many points cross spectrum has strong frequency
~40d. (Presumably MJO-like signal, not shown)
Divergent Wind Components
Vd
Ud
Velocity Potential (left) &
Divergent Wind Speed (right)
SLP lagged autocorrelations
lag (L) and lead (R) SLP @ pt-11
correlations (CW: 4, 2, 0, -2, -4d)
Vd - Meridional Divergent Wind
lag (L) and lead (R) SLP @ pt-8
correlations (CW: 4, 2, 0, -2, -4d)