Michael J. Bodner AOSC 617 31 March 2006

1. Examining the Strength of the Hadley Cell and It’s Influence on the Strength and Displacement of the 200 hPa East Asian Jet Michael J. Bodner AOSC 617 31 March 2006

2. Variations of East Asian Jet Stream (EAJS) influence climate and weather across the Asia-Pacific-America (APA) region(Yang et al. 2002) • PNA pattern • Closely associated with synoptic scale phenomena such as cyclogenesis, blocking and storm track activity • More strongly linked to climate signals of APA than ENSO • Intensification of the EAJS is associated with temperature and precipitation anomalies over North America • Anomalous longitudinal and latitudinal displacements are mostly independent of ENSO

3. Forcing mechanisms which contribute to strength and variability of the East Asian Jet Stream • Diabatic heating over the western tropical Pacific - can influence width, shape and speed of EAJS (Chang 2001) • Orography and land-sea thermal contrast - Influence of Himalayas, Rockies and Andes on mean zonal westerlies (Bolin 1950) • Hadley circulation - Observational (Krishnamurti 1961, Bjerknes 1966) - GCM Model (Hou 1995 and 1998, Chang 1995) - Reanalysis studies (Berbery 1993, Hou 1998)

4. Some of the work done on Hadley circulation influence on subtropical and mid latitude zonal jet • Bjerknes 1966 – Anomalously high SSTs during 1957-58 El Nino event contributed to a stronger Hadley Cell, increased northward transport of angular momentum and stronger than normal westerlies in the mid latitudes. • Hou 1998 – GCM results indicated that intensification and poleward movement of the cross-equatorial Hadley Cell can lead to enhanced vertical shear of the zonal wind in the subtropics and midlatitudes, accompanied by a reduction in the meridional temperature and PV gradients (high zonal index) - A reduction of Hadley cell intensity is associated with increased meridional temperature/PV gradient (low zonal index) - GOES-1 Reanalysis showed similar results during austral winters ▪ Berbery 1993 – used objectively analyzed ECMWF data to show that westerly zonal wind accelerations increase with a strenghening Hadley Cell over SH

5. It’s been demonstrated that a strong Hadley Cell contributes to a strong zonal mean wind (u).But is there any relationship between the strength of the Hadley Cell and the latitudinal/longitudinal displacement of the jet?

6. 200 hPa Average u-wind and Standard Deviation (m sec-1) NCEP Reanalysis Data NDJFM 1958-2001

7. DJF 1997-98 SST Anomaly over Nino 3.4 Region (2.4)

8. DJF 1980-81 SST Anomaly over Nino 3.4 Region (-0.3) DJF 1978-79 SST Anomaly over Nino 3.4 Region (-0.1)

9. To better depict the geometry and strength of the Hadley cell, the divergent component (VΧ) of the wind was calculated at 200 hPa. • Using NCEP Reanalysis data, χ (chi) was obtained from the relationship(Krishnamurti 1973) • Vector and scalar plots of χ (chi) were generated to better depict the shape of the western Pacific Hadley cell show potential areas of strong meridional over turning • Standard deviations of χ (chi) and vertical plots of χ (chi) still need to be done

10. Average Divergence of Chi (Vector and Scalar) 10-5 sec-1 NCEP Reanalysis Data NDJFM 1958-2001

11. Mean Zonal Wind (200 hPa) & Average Divergence of Chi (Vector) 10-5 sec-1 NCEP Reanalysis Data NDJFM 1958-2001

12. Using Grads/GEMPAK software packages and NCEP Reanalysis data, two additional methods of estimating the strength of the Hadley Cell will be attempted. 1) Estimating the maximum value of the mean meridional streamfunction (ψn) by integrating the equation for meridional velocity from the top of the atmosphere downward 2) Using the difference between the upper level meridional wind and the lower tropospheric meridional wind Oort 1996

13. The goal of the project is to use the estimated Hadley Cell strength indicators to… • Test for correlation between the strength of the Hadley cell (using Χ, ψ and/or ∆vn ) and the strength of the 200 hPa zonal mean wind at the points 30N 160W and at 45N 180W. • Apply this procedure to examine ENSO warm and cold winters, both phases of PDO (1958-1978 and 1979-1999) and significant positive/negative jet anomalies from ENSO neutral winters. • Determine whether or not a pattern or prediction index can be identified.

14. References Berbery, E.H., 1993:Intraseasonal interactions between the tropics and extratropics in the southern hemisphere. Journal of Atmospheric Sciences, 50, 1950-1965. Bjerknes, J., 1966: A possible response of the atmospheric Hadley circulation to equatorial anomalies of ocean temperature. Tellus., 18, 820–829. Bolin, B., 1950: On the influence of the earth’s orography on the general character of the westerlies. Tellus, 2, 184-196. Chang, E.K.M., 2001: GCM and observational diagnosis of the seasonal and interannual variations of the Pacific storm track during the cool season. Journal of Atmospheric Sciences, 58, 1784-1800. Chang, E.K.M., 1995: The influence of Hadley circulation intensity changes on extratropical climate in an idealized model. Journal of Atmospheric Sciences, 52, 2006-2024. Hou, A,Y., 1998: Hadley circulation as a modulator of the extratropical climate. Journal of Atmospheric Sciences, 55, 2437- 2457. Hou, A,Y., 1995: Modulation of dynamic heating in winter extratropics associated with cross-equatorial Hadley circulation. Journal of Atmospheric Sciences, 52, 2609-2626. Krishnamurti, T.N., M. Kananitsu, W.J. Koss and J.D. Lee, 1973: Tropical east-west circulations during the northern winter. Journal of Atmospheric Sciences, 30, 780-787. Krishnamurti, T.N., 1961: The subtropical jet stream of winter. Journal of Atmospheric Sciences, 2, 172-191. Oort, A.H., J.J. Yienger, 1996: Observed interannual variability in the Hadley circulation and it’s connection to ENSO. Journal of Climate, 9, 2751-2767. Yang, Song, K.-M. Lau, K.-M. Kim, 2002: Variations of the east Asian jet stream and Asian-Pacific-American winter climate anomalies. Journal of Climate, 15, 306-325.