Circumglobal Teleconnection in the Northern Hemisphere Summer: Observation and theory Qinghua Ding and Bin Wang Department of Meteorology and IPRC University of Hawaii

Why Northern summer teleconnection 500 hPa GPH anomaly: Strong minus weak Indian summer monsoon The Asian summer monsoon is a dominant feature of the NH summer circulation. What is the Teleconnection patterns associated with the Asian summer monsoon? ( Wang et al., 2001) Does a circumglobal teleconnection (CGT) exist in NH summer midlatitude?

Data NCEP/NCAR reanalysis (1948-2003) NOAA extended reconstructed SST (ERSST) (1948-2003) All Indian rainfall index and 29 subdivisions (1948-1998) 160 Chinese station rainfall data (1951-1999) University of Delaware Precipitation and surface air temperature (land-only,1950-1999)

Interannual variation of the CGT Composite strong minus weak CGTI Method The long-term trend and decadal variations with period longer than 8 years are removed. Define a measure of CGT Interannual variation of the CGT Composite strong minus weak CGTI Strong exceeds 0.8 standard deviation Weak less than -0.8 standard deviation

Search for Teleconnection pattern in northern summer (JJAS, 200hPa) SD & JET stream One-point corre-lation M/S CGT

Definition of the CGTI (35-40°N, 60-70°E) (JJAS)

Composite positive minus negative CGTI: GH at 200 hPa June July August September

EOFs of 200 hPa GH (JJAS) Fig.3

Composite differential surface air temperature Fig.8

How does CGTI related to ENSO, AO, and WNPSM indices (JJAS)? NINO-3 AIRI NINO-3 (remove AIRI) AO WNPSM CGTI -0.43 0.69 -0.12 (partial correlation) -0.18 -0.09 In normal ISM years the CGT-ENSO correlation disappears; However, in the absence of El Nino or La Nina, the CGT-ISM correlation remains significant. CGT has no significant association with the Arctic Oscillation (AO) and the variability of the Western North Pacific summer monsoon (WNPSM). ISM acts as a “conductor” connecting the CGT and ENSO.

Conclusion (Observations) A recurrent circumglobal teleconnection (CGT) pattern in the summertime midlatitude circulation of the NH has a zonal wavenumber five structure and is primarily positioned within a waveguide associated with the westerly jet stream. The CGT anomalies tend to be phase-locked to preferred longitudes. The CGT pattern represents the second leading EOF mode of interannual variability of the upper tropospheric circulation. Accompanying this CGT, significant rainfall and surface air temperature anomalies are found in the continental regions of Europe, European Russia, India, East Asia and North America. The CGT may be a source of climate variability and predictability in the above midlatitude regions. While the CGT has a significant correlation with ENSO, the result obtained from partial correlation analysis suggests that the CGT-ENSO linkage is indirect and is possible via the ENSO’s impact on the Indian summer monsoon. The variability of the CGT is significantly correlated with the South Asian monsoon and has NO significant linkage with the Arctic Oscillation (AO) and the variability of the Western North Pacific summer monsoon (WNPSM).

Discussion Mechanisms for maintenance of the CGT Waveguide effects: Hoskins and Ambrizzi (1993) Internal instability of the basic flows: Simmons et al. (1983), Ambrizzi et al (1995) New Hypothesis Connection to Indian summer monsoon Impact of extratropics to ISM

Hypothesis: Interaction between ISM and RWT The abnormal ISM may excite anomalous central Asian High and downstream Rossby wave trains extending to North Pacific and North America. A wave train excited in the jet exit region of the North Atlantic may affect central Asian High and thus the intensity of the ISM. The interaction between the global wavetrain and the ISM heat source may be instrumental in maintaining the boreal summer CGT.

BT Model Simulation Barotropic Model The model is linearized with respect to the 300 hPa summer climate mean streamfunction. The spatial resolution is T42, and the linear damping time scale is (50 day)-1. To suppress the zonal mean component, an additional linear damping, (5 day)-1, was applied to the wave number zero component.

Circum-global wavetrain, which is similar to the Forcing varies from 0E – 350E with 10intervals and 0N-40 N with 5 intervals. One point correlation maps (b-c) reveal a Circum-global wavetrain, which is similar to the observed teleconnection pattern over North Pacific and North America. Statistics of the barotropic model responses to randomly distributed forcing. (a) standard deviation of the responses. (b) One-point correlation with the base point (55E, 40N) (c) One-point correlation with the base point (95W, 45N) .

200 hPa Zonal winds, CGT, and zero zonal wind lines

Stationary Rossby wavenumber (a) June, (b) July, (c) August, and (d) September, Data: climatological 200-hPa zonal flow for the period 1948-2003. Calculation is based on Hoskins and Ambrizzi (1993)

(a) (b) Fig.9

Fig.10

Thank you

Composite of water vapor transportation (1000-300 hPa) and divergence (1000-300 hPa) in August

The AO pattern in the Northern Summer (JJAS) Correlation coefficient of the seasonal mean (JJAS) 200-hPa GH anomalies with the summer (JJAS) AO index defined by Ogi et al., (2004)

Composite positive minus negative CGTI: GH at 700 hPa June July August September

Outline Motivation Data and method Circumglobal Teleconnection Pattern (CGT) and the CGT index (CGTI) Circulation significance of the summer CGT Structure and Climate anomalies associated with the CGT Relations with ISM, ENSO, AO, and WNPSM Physical interpretation : A hypothesis Barotropic model simulation Conclusion

“Silk road” teleconnection Why Northern Summer teleconnection? ISM-EASM connection Indian summer monsoon rainfall is positive correlated with summer rainfall in northern China (Liang 1988; Guo and Wang 1988; Kripalani and Singh 1993), while negative correlated with rainfall in southern Japan (Kripalani and Kulkarni 2001; Krishnan and Sugi 2001). “Silk road” teleconnection Strong ISM years exhibits two equivalent barotropic anticyclonic anomalies : The west of Tibetan Plateau and the northeast Asia (Wang et al. 2001; Krishnan and Sugi 2001; Enomoto et al. (2003). EASM-US connection The first two empirical orthogonal functions (EOFs) of the US summer rainfall are linked to a wavetrain pattern starting from East Asia. (Lau and Weng 2002, Lau et al. 2004a). ISM-North America connections The teleconnection connecting the ISM and EASM is a portion of a global scale wavetrain linking Asia and North America. (Wang et al. 2001)

Composite deference between + and - CGTI: Land rainfall anomalies associated with CGT GPH anomalies