  The latest MERRA-2 reanalysis of the modern satellite measurements provides
unprecedented uniformity and fidelity for the atmospheric data. In this paper,
these data are used to evaluate five sites for millimeter-wave (mm-wave)
observations. These include two established sites (South Pole and Chajnantor,
Atacama), and three new sites (Ali, Tibet; Dome A, Antarctica; and Summit Camp,
Greenland). Atmospheric properties including precipitable water vapor (PWV),
sky brightness temperature fluctuations, ice and liquid water paths are derived
and compared. Dome A emerges to be the best among those evaluated, with PWV and
fluctuations smaller than the second-best site, South Pole, by more than a
factor of 2. It is found that the higher site in Ali (6,100 m) is on par with
Cerro Chajnantor (5,612 m) in terms of transmission and stability. The lower
site in Ali (5,250 m) planned for first stage of observations at 90/150GHz
provides conditions comparable to those on the Chajnantor Plateau. These
analyses confirm Ali to be an excellent mm-wave site on the Northern Hemisphere
that will complement well-established sites on the Southern Hemisphere. It is
also found in this analysis that the observing conditions at Summit Camp are
comparable to Cerro Chajnantor. Although it is more affected by the presence of
liquid water clouds.
