Tropical forcing for the interannual variability of the subtropical high

Tropical forcing for the interannual variability of the subtropical high

Pei-Hsuan Chung and Chung-Hsiung SuiDepartment of Atmospheric Sciences, National Central University,Jhong Li, Taiwan

Tim LiDepartment of Meteorology and IPRC, University of Hawaii, Honolulu, Hawaii, USA

Sui, C. -H., P. -H. Chung, and T. Li, 2007: Interannual and interdecadal variability of the summertime western North Pacific subtropical high. Geophys. Res. Lett., 34, 253 L11701, doi:10.1029/2006GL029204.

Time SeriesWNPSHI = H500 anom (120-140E, 10-30N)

OBS AnalysisOBS Analysis

Power Spectrum of WNPSH I ndex

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Periods (Years)

Pow

er

Den

sit

y

Density

95% TEST

2.5 Yrs

3.6 Yrs

Power Spectrum of WNPSH Index

Time Filtering: 2-3-yr and 3-5-yr WNPSH Index

Shading: vertical p-velocity (Pa/s) Vectors: significant W500 (m/s)Color contours: OLR (W/m2) Black contour: H500 (unit: m)

Shading: vertical p-velocity (Pa/s) Vectors: significant W500 (m/s)Color contours: OLR (W/m2) Black contour: H500 (unit: m)

What are the key SSTA forcing dominated in 2-3-yr and 3-5-yr oscillations of the westwarding WNP subtropical

high?

Model Simulation

QTCM Model QTCM : Quasi-equilibrium Tropical Circulation

Model with a single vertical structure of temperature and moisture for deep convection

Intermediate complexity atmospheric model The model formulation makes use of the

constraints placed on the flow by deep convection, as represented by quasi-equilibrium (QE) convective parameterizations

Experiment design

Control SST Run 1958-2005 monthly mean SST to run 50

years simulations and use the middle 30 years results

Prescribe SSTA Run MJJA : Add (High-Low) composite SSTA

in some key regions JFMA and SOND : Climate SST as CTRL Prescribe SSTA Run - Control SSTA Run

2-3-yr oscillation

MJJA SSTA

(High-Low) Comp

CEP RunMC Run

MC Run

CEP Run

Total Run

WNP Run

IO+EP Run

3-5-yr oscillation

MJJA SSTA

(High-Low) Comp

WNP Run

EP+IO Run

Total Run

Discussion

2-3-yr oscillation ~ Total run 3-5-yr oscillation ~ WNP run

(local cold SSTA)

Using “heating” instead of SSTA GCM models