THE INFLUENCE OF THE 11-YEAR SOLAR CYCLE ON THE STRATOSPHERE BELOW 30KM: A REVIEW

1. THE INFLUENCE OF THE 11-YEAR SOLAR CYCLE ON THESTRATOSPHERE BELOW 30KM: A REVIEW H. VAN LOON K. LABITZKE 2010/04/13 Pei-Yu Chueh

2. Previously, the signal of the solar cycle had been detected in the temperatures and heights of the stratosphere at 30hPa in the Northern Hemisphere. The global re-analyses show that the signal exists on the Southern Hemisphere too, and that it is almost a mirror image of that on the Northern Hemisphere. • The largest temperature correlations with the solar cycle move from one summer hemisphere to the other, and the largest height correlations move poleward within each hemisphere from winter to summer. • The correlations are weakest over the whole globe in the northern winter. • When the equatorial Quasi-Biennial Oscillation was easterly or westerly, the arctic correlations become positive and large in the west years, but insignificantly small over the rest of the earth. The correlations in the east years are negative in the Arctic but positive in the subtropics and tropics on both hemispheres.

3. The signal of the solar cycle had been detected in the heights of the stratosphere at 30hPa in the Northern Hemisphere. • An independent sample (the last solar cycle) fits the solar curve perfectly. • The amplitude of the signal appears to be dependent on the amplitude of the individual 11-year cycle.

4. The correlation maximum on the Southern Hemisphere appears to be weaker than the one on the Northern Hemisphere. • The Arctic and Antarctic show no evidence of a solar connection; but the interannual variability is large in the polar regions and tends to obscure a solar signal. • The interannual variability is comparatively large in the equatorial regions because of the Quasi-Biennial Oscillation indicate that the SSC affects these regions too, although the signal is obscured by interannual noise

5. Over nearly all of the hemisphere in summer, but in winter only in the Pacific Ocean. • The signal in the Southern Hemisphere is weakest in the southern summer, that is, at the time when the weakest signal is observed on the Northern Hemisphere. • The weak global signal in January–February is associated with the influence of the Quasi-Biennial Oscillation on the dynamics of the unstable winter vortex on the Northern Hemisphere.

6. The largest correlation coefficients move poleward on each hemisphere from winter to summer, and that they are weakest in January–February. • The correlation maximum moves across latitudes farther from the equator on the Northern than on the Southern Hemisphere. • On the equator the correlation coefficients are always smaller than in the tropical and subtropical latitudes, and they are weakest in the months January–March and October–November.

7. Major peak from middle northern latitudes in the northern summer to the middle latitudes on the Southern Hemisphere in the southern summer. The temperature correlations have the same pattern for the annual values as the heights.

8. The solar signal is weak or non-existing on both hemispheres in the northern winter if one uses a full series of stratospheric heights for correlation with the SSC. • But if the data are grouped into years when the QBO in the lower stratosphere (about 45 hPa) was westerly and years when it was easterly, the solar correlations become positive and large in the Arctic in the west years and negative in the east years. • Beyond the Arctic, and as far as the Antarctic, the correlation coefficients approach zero in the west years whereas they are positive and large in the subtropics and tropics in the east years. • The inverse teleconnection pattern is obvious in the east years (Fig. 10 middle), but not in the west years (Fig. 10 bottom).

9. The opposite correlations in the Arctic are then a sign of increased downward motion in the west years, which would be consistent with the warmings in the west years at peaks in the solar cycle. • In the east years the negative Arctic correlations would be indicative of a weakening of the downward motion which normally works against the seasonal radiative cooling.

10. Conclusion • Examination of the global re-analyses of the stratosphere as high as the 10-hPa level reveals a signal of the 11-year sunspot cycle on both hemispheres. • The signal is strongest in the northern summer. • In the northern winter the unstable dynamics of the cyclonic vortex on the Northern Hemisphere counteracts the solar influence in the west years of the Quasi-Biennial Oscillation in the equatorial winds. • The highest correlations between the solar cycle and the stratospheric heights move poleward from winter to summer in both hemispheres. • The highest correlations between the solar cycle and the temperatures in the stratosphere move from one summer hemisphere to the other.