Detection of the secondary meridional circulation associated with the quasi‐biennial oscillation

Abstract

[1] The quasi-biennial oscillation (QBO) signal in stratospheric zonal and meridional wind, temperature, and geopotential height fields is analyzed based on the use of the National Centers for Environmental Prediction (NCEP) reanalysis . The multitaper method-singular value decomposition (MTM-SVD), a multivariate frequency domain analysis method, is used to detect significant and spatially coherent narrowband oscillations. The QBO is found as the most intense signal in the stratospheric zonal wind. Then, the MTM-SVD method is used to determine the patterns induced by the QBO at every stratospheric level and data field. The secondary meridional circulation associated with the QBO is identified in the obtained patterns. This circulation can be characterized by negative (positive) temperature anomalies associated with adiabatic rising (sinking) motions over zones of easterly (westerly) wind shear and over the subtropics and midlatitudes, while meridional convergence and divergence levels are found separated by a level of maximum zonal wind shear. These vertical and meridional motions form quasi-symmetric circulation cells over both hemispheres, though less intense in the Southern Hemisphere.

Effects of the quasi‐biennial oscillation on low‐latitude transport in the stratosphere derived from trajectory calculations

“…The advection by the horizontal part of the SMC is less easily identified from the trajectory distributions, probably because isentropic transport is less uniform than the vertical transport. As suggested by Ribera et al [2004], the horizontal circulation anomaly due to the SMC may not always coincide with the phases of the strongest easterly and westerly jets (see Figure 1) that were selected here. Nonetheless, especially in the equinoctial seasons, the width of the latitude range, from which most parcels originate, varies clearly with the phase of the QBO and is narrowest in the selected Easterly phase, as expected.…”

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

“…Based on NCEP reanalysis Ribera et al (2004) reconstructed the spatial and temporal evolution of the several atmospheric variables through a QBO cycle. As they show, the circulation associated with the QBO is linked with negative (positive) temperature anomalies caused by the adiabatic rising (sinking) motions over zones of easterly (westerly) wind shear at the equator.…”

Variability in the speed of the Brewer–Dobson circulation as observed by Aura/MLS

“…The QBO is associated with a secondary meridional circulation anomaly that does not only affect the residual transport to mid-latitudes, but also the vertical ascent in the tropical stratosphere (Reed, 1964;Plumb and Bell, 1982;Choi et al, 2002;Punge et al, 2009;Ribera et al, 2004). Figure 9 shows schematically the QBO associated circulation anomaly as a latitude-height section on the left and the vertical profile of the equatorial zonal wind u on the right.…”

“…The QBO affects also the meridional wind. In fact, it induces a secondary meridional circulation due to thermal wind balance, which affects the meridional branch of the BDC (Plumb and Bell, 1982;Baldwin et al, 2001;Ribera et al, 2004;Punge et al, 2009). More about the QBO can be found in Baldwin et al (2001) and references therein.…”