Ra. Plumb et al., INTRUSIONS INTO THE LOWER STRATOSPHERIC ARCTIC VORTEX DURING THE WINTER OF 1991-1992, JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES, 99(D1), 1994, pp. 1089-1105
Investigations of the kinematics of the lower stratospheric Arctic vor
tex during the winter of 1991-1992 using the contour advection with su
rgery technique reveal three distinct events in which there was substa
ntial intrusion of midlatitude air into the vortex, in apparent contra
diction of the view that the polar vortex constitutes an isolated air
mass. Two of these events, in late January and mid-February, were well
documented. They were predicted in high-resolution forecasts by the E
uropean Centre for Medium-Range Weather Forecasts, most clearly in exp
erimental forecasts with reduced diffusion. Direct confirmation of the
presence of the intrusions and of their calculated locations was prov
ided by aerosol observations from the airborne differential absorption
laser lidar aboard the NASA DC-8, taken as part of the second Airborn
e Arctic Statospheric Expedition campaign; aerosol-rich air of midlati
tude origin was seen in the expected position of the intrusions. The r
eality of the February event was also confirmed by in situ measurement
s from the NASA ER-2. Such events may be significant for the chemical
processes taking place within the winter vortex. The intrusions were e
vidently related to the meteorology of the northern stratosphere durin
g this winter and in particular to persistent tropospheric blocking ov
er the northeastern Atlantic Ocean and western Europe and concomitant
ridging into the lower stratospheric vortex in this region. Neverthele
ss, preliminary investigations have indicated that such events are not
uncommon in other northern hemisphere winters, although no such event
s were found in the southern hemisphere during the Antarctic winter of
1987.