Evidence against an Antarctic stratospheric vortex split during the periods of pre-IGY temperature measurements

Historic upper-air observations from Antarctica are inspected to investigate the uniqueness of the vortex split in the Antarctic spring of 2002. No comprehensive meteorological observations are available prior to the International Geophysical Year (IGY) 1957/58, but stratospheric temperature observations from single stations provide evidence of varying strengths against the possibility of a split vortex in 1940 and in the early and middle 1950s.