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In this work, we apply multichannel singular spectrum analysis (MSSA), adata-adaptive, multivariate, non-parametric technique that simultaneouslyexploits the spatial and temporal correlations of the input data to extractcommon modes of variability, to investigate the intermediatequasi-periodicities of the Fe XIV green coronal emission line at 530.3 nm forthe period between 1944 and 2008. Our analysis reveals several significantmid-term periodicities in a range from about one to four years that areconsistent with the so-called quasi-biennial oscillations (QBOs), which havebeen detected by several authors using different data sets and analysismethods. These QBOs display amplitudes varying significantly with time andlatitude over the six solar cycles (18 to 23) covered by this study. A clearNorth-South asymmetry is detected both in their intensity and perioddistribution, with a net predominance of spectral power in the active-regionbelt of the northern hemisphere. On the other hand, while the QBOs with periods> 1.7 years are particularly intense around the polar regions and thereforerelated to the global magnetic field, the ones with shorter periods are mainlygenerated at mid-latitudes, in correspondence with the emergence of activeregions. Our findings indicate that the North-South asymmetry manifested in theuneven latitudinal distribution of QBOs is a fundamental, albeit puzzling,characteristic of solar activity.

Spatio-Temporal Evolution and North-South Asymmetry of Quasi-Biennial Oscillations in the Coronal Fe XIV Emission