Makoto INOUE and Masaaki TAKAHASHI (CCSR, Univ. of Tokyo)

1. The relationship between the stratospheric quasi-biennial oscillation (QBO) and tropospheric circulation from the Northern hemisphere autumn to winter Makoto INOUE and Masaaki TAKAHASHI (CCSR, Univ. of Tokyo) 2 July 2008, UAW (Maihama)

2. 1. Introduction The infuence of the stratospheric quasi-biennial oscillation (QBO) on tropospheric circulation over Northern Hemisphere is investigated. In particular, seasonal evolution of zonal wind in the low and middle latitudes from autumn to winter, wave activities and disturbances in mid-latitudes are focused in this presentation. Holton and Tan (1980, 1982) → The connection between QBO and extratropical circulation in Northern Hemisphere winter is investigated. This result shows that polar westerly jet weakens (strengthens) during easterly (westerly) phase of QBO. Naito and Yoden (2006) → They indicated planetary wave activities with the phase of QBO before and after stratospheric sudden warming in Northern Hemisphere winter. 2. Previous studies

3. 3. Data 4. Classification by QBO Sign of 50 hPa zonal wind averaged for 5S-5N u wind v wind omega geopotential height temperature Sep, 1980 – Feb, 2005 ：NCEP/NCAR Reanalysis autumn (Sep-Oct-Nov) Easterly 13 Years (1981, 1982, 1984, 1987, 1989, 1991, 1992, 1994, 1996, 1998, 2000, 2001, 2003) Westerly 12 Years (1980, 1983, 1985, 1986, 1988, 1990, 1993, 1995, 1997, 1999, 2002, 2004) winter (Dec-Jan-Feb) Easterly 12 Years (1981, 1983, 1984, 1986, 1989, 1991, 1994, 1996, 1998, 2000, 2001, 2003) Westerly 13 Years (1980, 1982, 1985, 1987, 1988, 1990, 1992, 1993, 1995, 1997, 1999, 2002, 2004) All figures of composite anomaly are calculated as Easterly years minus Westerly years.

4. 5. Seasonal evolution of zonal-mean zonal wind At high latitudes, significant easterly anomalies are seen in winter. This is just exactly Holton-Tan oscillation. You can see westerly anomalies in mid-latitudes and easterly anomalies in the low latitudes in not only winter but also autumn. This indicates a part of Holton-Tan oscillation starts to form during autumn. In particular, zonal wind anomalies in the mid-latitudes strengthen shifting southward with seasonal march. autumn winter Holton and Tan (1980, 1982) E E E W W E Easterly Years － Westerly Years

5. 6. Effects of waves Acceleration by quasi-stationary waves (10-30 days) ∂u / ∂t Residual circulation Westerly acceleration Easterly acceleration Acceleration by transient waves (< 10 days) Easterly acceleration by stationary waves in 15-25N Westerly acceleration by transient and stationary waves in 25-40N The Transformed Eulerian-mean (TEM) equation Divergence of EP flux

6. global ∂u / ∂t 7. Horizontal distribution In Asian regions, easterly in the low latitudes and westerly in mid-latitudes are apparent at 100 hPa. Extended EP flux (Hoskins et al., 1983) ∂u / ∂t Asia America Acceleration anomalies over America at 25N are strongly responsible for the distribution of global zonal averaged ∂u/∂t . E vector (> 10 days) and u

7. Transient component 8. Local response (Asia and America) Statinary component Asia (60-120E) America (120-60W) Easterly (Left) and westerly (Right) acceleration by quasi-stationary waves (Hoskins et al., 1983) This term S describes the eddy forcing of the mean flow. In Asia, northward fluxes with QBO can be seen in the low latitudes. The trend of zonal wind and zonal wind anomalies in the low and middle latitudes over the Asia are consistent with the signs of S. Easterly and westerly anomalies over Asia are related to quasi-stationary eddies, whereas easterly anomalies over America depends on both stationary and transient eddies. u, EPF

8. 30N Global zonal average KE,EPF (E-W) E-W 9. Disturbances in mid-latitudes with QBO Apparent disturbance in mid-latitudes from the troposphere to stratosphere during the westerly phase of QBO. This disturbance elongates from Africa through the Pacific Ocean in northeast-southwest direction. This implies that stratospheric QBO and perturbation energy in mid-latitudes are connected.

9. 10. Meridional gradient of quasi-geostrophic potential vorticity with QBO Global zonal average, E-W Significant anomalies are observable from the lower stratosphere in the tropics, where QBO is seen, to the troposphere in mid-latitudes. Wind field on a background around here tends to work as a waveguide more strongly during westerly phase of QBO. This result does not conflict northward fluxes near the tropopause over Asia. That is, features of wave propagation are prescribed by the phase of QBO. These anomalies are consitent with enhancement of perturbation kinetic energy in the mid-latitudes during the westerly phase of QBO.

10. 11. Conclusion ・Westerly (easterly) anomalies in mid-latitudes and easterly (westerly) anomalies in the low latitude are seen during the easterly (westerly) phase of QBO in not only winter but also autumn. ・Wave activities in autumn appear to affect the distribution of wind in winter. Both transient and stationary waves are dominant in westerly acceleration at mid-latitudes, while easterly acceleration in the low latitude is responsible for only stationary waves. ・In South and Southeast Asia, apparent easterly anomalies are associated with acceleration by quasi-stationary Rossby wavesduring the easterly phase of QBO. While, easterly anomalies over America depends on both transient and stationary waves. ・The changes of basic field with the phase of QBO prescribe the regions where Rossby waves can propagate and are connected with disturbances in mid-latitudes. Makoto INOUE (CCSR) otenki@ccsr.u-tokyo.ac.jp

11. Appendix 4: Climatological field for∂Q/∂y

12. Appendix 5: Extended EP flux (James, 1994) Extended EP flux (Hoskins et al., 1983) Westerly acceleration Easterly acceleration A local region where E-vector converges will be characterized by the forcing of anticyclonic vorticity to the north of the convergence region and cyclonic vorticity foucing to the south. The signs are reversed for a region of divergence (James, 1994). Therefore, E-vector may be considered as an effective westerly momentum flux (Hoskins et al., 1983). And the above yellow part of S means the barotropic part of the eddy forcing of the mean flow. This direct evaluation yields a field whose large-scale structure is obscured by small-scale noise. This problem is overcome by computing the above term.

13. Appendix 1: 3D convergence of EP flux by quasi-stationary waves, dQ/dy, zonal wind and gepotential height with QBO at 100 hPa

14. Appendix 4: Extended EP flux Extended EP flux (Hoskins et al., 1983) (James, 1994) (Hoskins et al., 1983)

15. Appendix >10days EPF, u, ∂u/∂t in America

18. Appendix 2: 3D EPD and EPF in 6 regions

20. Appendix 1: Total wavenumber with QBO 50hPa 70hPa 100hPa East West