Influence of solar UV irradiance on the quasi-biennial oscillation of zonal winds in the equatorial stratosphere

Abstract

The vertical wind profiles in the equatorial stratosphere for 1953-2005 have been examined in relation to variations of solar F10.7 index to reveal influence of solar UV irradiance on the quasi-biennial oscillation (QBO) of zonal winds. Previously it was shown (Gabis, I.P., Troshichev, O.A., 2005. QBO cycle identified by changes in height profile of the zonal winds: new regularities. Journal of Atmospheric and Solar-Terrestrial Physics 67, 33-44) that Stage 1, with the easterly winds above 20-30 hPa and westerly winds below this layer, always starts in solstice (winter or summer) and can be of different but quite quantized (about 3, 9, or 15 months) duration. The present investigation shows that course of the subsequent, after Stage 1 beginning, evolution of the zonal winds depends on intensity of solar UV flux. The easterly winds descend below ∼30 hPa (Stage 2) only under condition of high level of the UV irradiance or steady increase of the UV flux happening in time of the first equinox in course of QBO cycle. If level of UV irradiance is low or UV flux decreases during the equinox, the easterly winds typical of the upper layer, do not descend below 30 hPa, and Stage 1 persists till next equinox. In other words, the stopping of easterly shear zone at ∼30 hPa is defined by the level of UV irradiance in a proper time. Since the length of the QBO cycle is determined by duration of Stage 1, the cycle length (24, 30, or 36 months) can be predicted setting the time of transformation from Stage 1 to Stage 2. © 2006 Elsevier Ltd. All rights reserved.