Circumglobal Teleconnection in Circumglobal Teleconnection in the Northern Hemisphere the Northern Hemisphere

Summer:Summer:

Observation and theoryObservation and theory

Qinghua Ding and Bin WangQinghua Ding and Bin Wang

Department of Meteorology andDepartment of Meteorology and IPRC IPRC

University of HawaiiUniversity of Hawaii

( Wang et al., 2001)

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?

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)

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 CGTIStrong exceeds 0.8 standard deviation

Weak less than -0.8 standard deviation

Search for Teleconnection pattern in northern summer (JJAS, 200hPa)

M/S

CGT

SD &JET stream

One-point corre-lation

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

45E

80E

Composite positive minus negative CGTI: GH at 200 hPa

June

July

August

September

Fig.3

EOFs of 200 hPa GH (JJAS)

Fig.8

Composite differential surface air temperature

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)Conclusion (Observations)

A recurrent circumglobal teleconnection (CGT) pattern in the A recurrent circumglobal teleconnection (CGT) pattern in the summertime midlatitude circulation of the NH has a zonal wavenumber summertime midlatitude circulation of the NH has a zonal wavenumber five structure and is primarily positioned within a waveguide associated five structure and is primarily positioned within a waveguide associated with the westerly jet stream. The CGT anomalies tend to be phase-with the westerly jet stream. The CGT anomalies tend to be phase-locked to preferred longitudes. locked to preferred longitudes.

The CGT pattern represents the second leading EOF mode of interannual The CGT pattern represents the second leading EOF mode of interannual variability of the upper tropospheric circulation. variability of the upper tropospheric circulation.

Accompanying this CGT, significant rainfall and surface air temperature Accompanying this CGT, significant rainfall and surface air temperature anomalies are found in the continental regions of Europe, European anomalies are found in the continental regions of Europe, European Russia, India, East Asia and North America. The CGT may be a source of Russia, India, East Asia and North America. The CGT may be a source of climate variability and predictability in the above midlatitude regions. climate variability and predictability in the above midlatitude regions.

While the CGT has a significant correlation with ENSO, the result While the CGT has a significant correlation with ENSO, the result obtained from partial correlation analysis suggests that the CGT-ENSO obtained from partial correlation analysis suggests that the CGT-ENSO linkage is indirect and is possible via the ENSO’s impact on the Indian linkage is indirect and is possible via the ENSO’s impact on the Indian summer monsoon. summer monsoon.

The variability of the CGT is significantly correlated with the South Asian The variability of the CGT is significantly correlated with the South Asian monsoon and has NO significant linkage with the Arctic Oscillation (AO) monsoon and has NO significant linkage with the Arctic Oscillation (AO) and the variability of the Western North Pacific summer monsoon and the variability of the Western North Pacific summer monsoon (WNPSM). (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 1. The abnormal ISM may excite anomalous central Asian High and downstream Rossby wave trains extending to North Pacific and North America.

2. 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.

3. The interaction between the global wavetrain and the ISM heat source may be instrumental in maintaining the boreal summer CGT.

BT Model Simulation

Barotropic ModelThe 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.

Forcing varies from 0E –350E with 10intervals 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

(a) June, (b) July, (c) August, and (d) September,

Data: climatological 200-hPa zonal flow for the period 1948-2003.

Stationary Rossby wavenumber

Calculation is based on Hoskins and Ambrizzi (1993)

Fig.9

(a) (b)

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)

June

July

August

September

Composite positive minus negative CGTI: GH at 700 hPa

Outline

1. Motivation2. Data and method3. Circumglobal Teleconnection Pattern (CGT) and

the CGT index (CGTI)4. Circulation significance of the summer CGT5. Structure and Climate anomalies associated with

the CGT6. Relations with ISM, ENSO, AO, and WNPSM7. Physical interpretation : A hypothesis8. Barotropic model simulation9. Conclusion

Why Northern Summer teleconnection?

ISM-EASM connectionIndian 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 connectionThe 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