Remote Features Linked to the South Pacific Subtropical High

Remote Features Linked to the South Pacific Subtropical High

(hereafter called the “SP high”)

Richard GrotjahnAtmospheric 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 autocorrelationslag (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 Windlag (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 ComponentsVd Ud

Velocity Potential (left) & Divergent Wind Speed (right)

SLP lagged autocorrelationslag (L) and lead (R) SLP @ pt-11 correlations (CW: 4, 2, 0, -2, -4d)

Vd - Meridional Divergent Windlag (L) and lead (R) SLP @ pt-8

correlations (CW: 4, 2, 0, -2, -4d)