Analysis of CO from spaceborne ACE-FTS (Atmospheric Chemistry Experiment, Fourier Transform Spectrometer) and Aura-MLS (Aura satellite, Microwave Limb Sounder) satellite observations highlights the existence of a sub-peak in CO profiles from late winter to early spring in the polar regions of both the northern and southern hemispheres at the 10 hPa level (i.e., in the middle of the stratosphere). Further analysis of Aura-MLS satellite data demonstrates that air from the mesosphere, which is rich in CO, descends into the stratosphere gradually in early winter. Moreover, while the CO concentration in the upper stratosphere decreases rapidly during late winter, CO concentration in the middle stratosphere changes very slowly. This results in the dramatic emergence of a suspended spherical structure in the stratosphere, defined by high CO concentrations; the satellite observation shows such a sub-peak in the CO concentration profiles. Analysis of the MERRA (the Modern Era Retrospective-analysis for Research and Applications) assimilated data and OH concentrations from Aura-MLS satellite observations suggests that weakening of vertical transport from the mesosphere to stratosphere, enhancement of horizontal exchange, and recovery of the OH concentration may play important roles in reducing CO concentration in the upper stratosphere. However, CO in the middle stratosphere can survive for a relatively long time owing to both the isolation imposed by the transport barrier and the lower OH concentration in the polar regions, thus allowing the sub-peak to persist from late winter to spring.