Vertical Structure of the Troposphere/Lower Stratosphere over the southern tip of South America and Antarctica as Evidenced by an EOF Analysis. Part II: Double Tropopauses

A. YUCHECHEN; P. O. CANZIANI; S. BISCHOFF

Foz do Iguaçu

Congreso; 2010 The Meeting of the Americas; 2010

American Geophysical Union

This study complements Part I. In this case, mandatory level ranging from 850 to 50 hPa are also analysed. This time single tropopause is excluded and is replaced by two additional levels, one correspoding to the lower tropopause and the other to the upper one. Again, we shall restrict ourselves to analysing the first three leading EOFs. They account for a slightly lesser percentage of the total variance when compared to Part I, likely owing to the fact that aditional variability has been added after including an extra level. Regarding mandatory levels EOF1 is characterised by a dipole within the domain, since anomalies over Antarctica and South America are in opposite sign. As to mandatory levels, EOF1 direct mode generally shows positive anomalies over South America. With regard to the tropopause, it exhibits an interesting pattern since anomalies for the upper and lower tropopause are in opposite sign. Its direct mode corresponds to a lowered lower tropopause in the vicinities of 30°S over South America and along the shore of the Wilkes Land and in the vicinities of the Ross Sea over Antarctica, and a raised lower tropopause elsewhere. PC1 is moderately dominated by a semiannual cycle, it is statistically trended, and leads to a direct (indirect) mode of EOF1 during the equinoxes (solstices). Such a behaviour for PC1 entails that thicker tropopause layers migrate within the domain throughout the year, and thus a similar behaviour for the enhancement of stratosphere/troposphere exchange (STE) also occurs. The spatial structure for the lower tropopause in EOF2 shows that like-signed anomalies occur all over the domain, whilst the sign of anomalies for the upper tropopause varies depending on the station considered. This can be tied again to STE, perhaps of lesser atmospheric scales. In general, like-sign anomalies are present at all mandatory levels. EOF2 direct mode corresponds to a lowered lower tropopause, and also to lowered mandatory levels. PC2 is not trended, and it is so poorly driven by a semiannual cycle that a palette of other frequencies also contribute to its time evolution. Therefore, a regular behaviour for PC2 throughout the year is hard to be stated. Mandatory levels in EOF3 shows that anomalies over tropical South America are in opposite sign with respect to the anomalies in the rest of the domain. As to the tropopause, the spatial structure resembles the one for EOF2, with an even more heterogenous spatial distribution. EOF3 in its direct mode shows that anomalies at all mandatory levels beyond tropical South America are positive whereas the upper tropopause is lowered. PC3 is weakly trended in a negative fashion, and is also poorly dominated by semiannual cycles.