What were the 'green fireballs' over New Mexico in 1948?

“Between November 1948 and May 1950, hundreds of unusually-colored green fireballs were observed over Sandia Base, Kirtland AFB, Los Alamos, and the broader Albuquerque-Alamogordo corridor — the U.S. nuclear-weapons handling complex of the era. The U.S. Air Force opened a formal investigation under Dr. Lincoln LaPaz of the University of New Mexico.”

The 'green fireballs' were an unusual luminous-phenomenon cluster centered over the U.S. nuclear-weapons complex in New Mexico between November 1948 and May 1950. The Office of Special Investigations' 17th District tabulated more than 209 distinct sightings during this period (sightings #1 through #209, August 1949 to May 1950). The U.S. Air Force retained Dr. Lincoln LaPaz, the University of New Mexico's leading meteoriticist, to determine whether the objects were natural meteoric phenomena. LaPaz concluded that they were not — the predominantly horizontal trajectories, anomalous green color, and absence of recovered meteoritic debris were inconsistent with the meteor hypothesis. His Fourth (December 20, 1948), Sixth, and Seventh (May 23, 1950) Reports on the green-fireball phenomenon are declassified under PURSUE Release 02 as part of the 116-page DOC-141 Sandia Base bundle. The fireballs were investigated by Project SIGN, GRUDGE, and later Blue Book.