Abstract
Abstract. Our fundamental aim is to investigate solar cycle signals in sea level pressure. In order to see if these may relate, especially at high latitudes, to the solar influence on the stratosphere we start by investigating the temperature of the winter polar stratosphere and its dependence on the state of the Sun and the phase of the Quasi-Biennial Oscillation (QBO). We find that the choice of pressure level used to define the phase of the QBO is important in determining how the solar and QBO influences appear to act in combination. Informed by this we carry out a multiple linear regression analysis of zonal mean temperatures throughout the lower stratosphere and troposphere. A combined solar*QBO temporal index exhibits strongly in the lower stratosphere, but in much of the troposphere any influence of the QBO, either on its own or coupled to solar effects is much smaller than the pure solar signal. We use a similar approach to analyse sea level pressure (SLP) data, first using a standard QBO time series dating back to 1953. We find at high latitudes that individually the solar and QBO signals are weak but that the compound solar*QBO temporal index shows a significant signal. This is such that combinations of low solar activity with westerly QBO and high solar activity with easterly QBO are both associated with a strengthening in the polar modes; while the opposite combinations coincide with a weakening. By employing a QBO dataset reconstructed back to 1900, we extend the SLP analysis back to that date and also find a robust signal in the surface SAM; though weaker for surface NAM. Our results suggest that solar variability, modulated by the phase of QBO, influences zonal mean temperatures at high latitudes in the lower stratosphere, in the mid-latitude troposphere and sea level pressure near the poles. Thus a knowledge of the state of the Sun, and the phase of the QBO might be useful in surface climate prediction.
Highlights
Our results suggest that solar variability, modulated by the phase of quasibiennial oscillation (QBO), influences zonal mean temperatures at high latitudes in the lower stratosphere, in the mid-latitude troposphere and sea level pressure near the poles
There is an established body of literature (see Gray et al (2010) for a review), initiated by the pioneering work of Labitzke (1987), which has identified the influence on winter temperatures in the polar lower stratosphere of the quasibiennial oscillation (QBO) in tropical lower stratospheric winds, and of solar activity
Other studies have shown that in the Northern Hemisphere winter extratropics a solar signal in polar winter temperature and wind is QBOphase dependent, moving poleward and downward as winter progresses, taking about 1 month to move from the upper to the lower stratosphere with a faster descent rate under wQBO than eQBO (Matthes et al, 2004; Gray et al, 2004; Lu et al, 2009; Haigh and Roscoe, 2009) showed a similar progression in the Southern Hemisphere late winter. These studies are consistent with the results found in surface polar modes (Northern Annular Mode, NAM, and Southern Annular Mode, SAM) by Haigh and Roscoe (2006) which indicated that, while no statistically significant solar signal was found in either the surface NAM or SAM, when the solar and QBO influences were combined there is a good correlation in SAM and winter NAM
Summary
There is an established body of literature (see Gray et al (2010) for a review), initiated by the pioneering work of Labitzke (1987), which has identified the influence on winter temperatures in the polar lower stratosphere of the quasibiennial oscillation (QBO) in tropical lower stratospheric winds, and of solar activity (measured by sunspot number or some other indicator such as 10.7 cm radio flux). Other studies have shown that in the Northern Hemisphere winter extratropics a solar signal in polar winter temperature and wind is QBOphase dependent, moving poleward and downward as winter progresses, taking about 1 month to move from the upper to the lower stratosphere with a faster descent rate under wQBO than eQBO (Matthes et al, 2004; Gray et al, 2004; Lu et al, 2009; Haigh and Roscoe, 2009) showed a similar progression in the Southern Hemisphere late winter These studies are consistent with the results found in surface polar modes (Northern Annular Mode, NAM, and Southern Annular Mode, SAM) by Haigh and Roscoe (2006) which indicated that, while no statistically significant solar signal was found in either the surface NAM or SAM, when the solar and QBO influences were combined there is a good correlation in SAM and winter NAM. We move on to study signals of solar variability and the QBO in over a century of mean sea level pressure (SLP) data
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