EOS Microwave Limb Sounder Observations of 'Frozen-in' Anticyclonic Air in Arctic Summer

A previously unreported phenomenon, a 'frozen-in' anticyclone (FrIAC) after the 2005 Arctic spring vortex breakup, was discovered in Earth Observing System (EOS) Microwave Limb Sounder (MLS) long-lived trace gas data. A tongue of low-latitude (high-N2O, low-H2O) air was drawn into high latitudes and confined in a tight anticyclone, then advected intact in the summer easterlies through late August. A similar feature in O3 disappeared by early April as a result of chemical processes. The FrIAC was initially advected upright at nearly the same speed at all levels from approx.660 to 1300 K (approx.25-45 km); increasing vertical wind shear after early June tilted the FrIAC and weakened it at higher levels. The associated feature in PV disappeared by early June; transport calculations fail to reproduce the remarkable persistence of the FrIAC, suggesting deficiencies in summer high-latitude winds. The historical PV record suggests that this phenomenon may have occurred several times before. The lack of a persistent signature in O3 or PV, along with its small size and rapid motion, make it unlikely that a FrIAC could have been reliably identified without hemispheric daily longlived trace gas profiles such as those from EOS MLS.