The best type of graph to illustrate the change in air temperature over a period of time would be a graph.

It would be a line graph. 

if you use a line graph, you can calculate the point and plot them, then draw a line through them and see the falls and rises. 

An informal structure in a bureaucracy would be something like so-called "office politics". where there's a formal structure set up for the organization, but then an informal subculture as well that has a way of organizing the bureaucracy further. this can be positive because it sets up an added degree of organization, albeit informal, within the bureaucracy.