PHOENIX — The Sandra Day O’Connor Federal Courthouse here is a visual triumph of modern architecture. Designed by the acclaimed architect Richard Meier, it is a sleek steel and glass structure of impressive dimensions and design whose undulating roof resembles, from a distance, an approaching jagged wave — a sort of apparition in a city in the desert.

But inside, a great expanse of the courthouse is hot, even for Arizona, where “hot” is not employed lightly.

In the summer here, the midday temperature rarely dips below 100 degrees, and it does not change much at night. Life in these months is best lived indoors, and in most public places air-conditioners are set so low that, after a few minutes, visitors might wish they had brought along a light jacket.

Not in the towering atrium of the courthouse. Baristas in the food kiosk wear shorts and tank tops. Deputy federal marshals who provide security during high-profile proceedings — like the civil rights trial of Sheriff Joseph M. Arpaio of Maricopa County, which ended on Thursday — change their posts every hour so everyone gets some time inside the air-conditioned courtrooms.