Time Introduction Those who have studied the UFO phenomenon have long been aware that the volume and geography of UFO reports vary over time.
Some studies indicate that waves begin long before they attain publicity.
Famous examples are the French and Latin American wave of 1954, and the American wave of 1973. Flaps - shorter duration regional peaks. These may last up to a few months. Flaps occasionally recur in the same geographic area over two or more years. Concentrations - short duration local peaks.