On the stability of the troposphere/lower stratosphere and its relationships with cirrus clouds and three mandatory levels over Buenos Aires

Abstract

An unrotated principal components analysis was carried out to establish the most representative modes for the joint variability between the heights of the upper and lower boundaries of cirrus clouds and three different mandatory levels (850, 500, and 100 hPa), and the associated stability of the troposphere over Buenos Aires. Discussion is limited to the first three most representative structures found, which consists of spatial patterns (or empirical orthogonal functions, EOFs) and their time-evolving coefficients (or principal components, PCs). EOF1 shows a direct (indirect) mode that encompasses the cirrus slightly below (above) its mean position, with 500 and 100 hPa exhibiting a similar behaviour and 850 hPa acting the opposite way. EOF1 is associated with above-normal stability (instability) for direct (indirect) modes (i.e. positive (negative) values of PC1). On a monthly average, this occurs in the austral winter (summer) months. Regarding EOF2, all three mandatory levels experience positive (negative) height anomalies in direct (indirect) modes and cirrus goes up (down) under mild stability (instability). Monthly averages show that PC2 is approximately positive in summer and in early fall and negative the rest of the year. As to EOF3, it is characterized by a stability similar to that of EOF2, with direct (indirect) modes showing lowered (raised) cirrus and all three mandatory levels above (below) normal conditions; on a monthly basis, PC3 is best described as having a semi-annual evolution, with maxima (minima) in March and October (January and August). Overall, EOF1 has the highest stability or instability, depending upon the sign of PC1. These results are the first of their kind worldwide.