Life cycle of the QBO‐modulated 11‐year solar cycle signals in the Northern Hemispheric winter

This paper provides some insights on the quasi‐biennial oscillation (QBO) modulated 11‐year solar cycle (11‐yr SC) signals in Northern Hemisphere (NH) winter temperature and zonal wind. Daily ERA‐40 Reanalysis and ECMWF Operational data for the period of 1958–2006 were used to examine the seasonal evolution of the QBO‐solar cycle relationship at various pressure levels up to the stratopause. The results show that the solar signals in the NH winter extratropics are indeed QBO‐phase dependent, moving poleward and downward as winter progresses with a faster descent rate under westerly QBO than under easterly QBO. In the stratosphere, the signals are highly significant in late January to early March and have a life span of ∼30–50 days. Under westerly QBO, the stratospheric solar signals clearly lead and connect to those in the troposphere in late March and early April where they have a life span of ∼10 days. As the structure changes considerably from the upper stratosphere to the lower troposphere, the exact month when the maximum solar signals occur depends largely on the altitude chosen. For the low‐latitude stratosphere, our analysis supports a vertical double‐peaked structure of positive signature of the 11‐yr SC in temperature, and demonstrates that this structure is further modulated by the QBO. These solar signals have a longer life span (∼3–4 months) in comparison to those in the extratropics. The solar signals in the lower stratosphere are stronger in early winter but weaker in late winter, while the reverse holds in the upper stratosphere. Copyright © 2009 Royal Meteorological Society