The first TMY collection was based on 229 locations in the US and was collected between 1948 and 1980. The second edition of the TMY is called "TMY2". It is based on 239 stations collecting data between 1961 and 1990.
The initial TMY collection was established with 229 locations in the US between 1948 and 1980, while the second edition, "TMY2," expanded to include 239 stations collecting data from 1961 to 1990.