Ozone density profiles obtained with ECC balloon sondes during the first 3 years of a joint INPE/NASA long‐term program of measurements at Natal have been analyzed. Ozone variations with time, as expected, are small. A correlation analysis of ozone and temperature profiles taken concurrently indicates a small correlation coefficient in the troposphere, a positive and increasing correlation between the tropopause and the ozone peak, turning negative above it. Outstanding features of the data are tropospheric densities substantially higher than those measured at other low latitude stations and also a total ozone content that is higher than that given by satellite measurements.

The average ozone profile obtained from 43 balloon flights at Natal is compared to data obtained elsewhere, in particular to an average profile obtained between latitudes ± 30°. At pressures above 100 mbar and below about 15 mbar the ozone density at Natal is higher than predicted by the model.

We analyze a model of fixed in-degree random Boolean networks in which the fraction of input-receiving nodes is controlled by the parameter gamma. We investigate analytically and numerically the dynamics of graphs under a parallel XOR updating scheme. This scheme is interesting because it is accessible analytically and its phenomenology is at the same time under control and as rich as the one of general Boolean networks. We give analytical formulas for the dynamics on general graphs, showing that with a XOR-type evolution rule, dynamic features are direct consequences of the topological feedback structure, in analogy with the role of relevant components in Kauffman networks. Considering graphs with fixed in-degree, we characterize analytically and numerically the feedback regions using graph decimation algorithms (Leaf Removal). With varying gamma , this graph ensemble shows a phase transition that separates a treelike graph region from one in which feedback components emerge. Networks near the transition point have feedback components made of disjoint loops, in which each node has exactly one incoming and one outgoing link. Using this fact, we provide analytical estimates of the maximum period starting from topological considerations.

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