Life-cycle of the ‘frozen-in anticyclone' in the 2005 Arctic summer stratosphere

Immediately following the breakup of the 2005 Arctic spring stratospheric vortex, a tropical air mass characterized by high nitrous oxide and low water vapor was advected poleward, merging with the decaying Aleutian high, and became trapped in the summer easterly circulation. This feature, known as a “frozen-in anticyclone (FrIAC)”, was observed in Earth Observing System (EOS) Microwave Limb Sounder (MLS) N2O and H2O anomalies that circled westward around the pole for nearly five months, from late March to late August 2005. The processes associated with the formation and lifecycle of the FrIAC are examined here using meteorological analyses, high-resolution (~20 km) isentropic advection simulations, and results from the Global Modeling Initiative (GMI) chemistry and transport model. The lifecycle of the FrIAC is divided into four phases corresponding to spin-up (March – early April); quasi-solid-body rotation (early April – early June); shearing phase (early June – late July); and final demise (late July – August). By providing continuous high-resolution synoptic views during the entire lifecycle of the FrIAC, the model simulations reveal many details of the transport and mixing not visible in gridded MLS data and provide a stringent test of the quality of both transport schemes and wind analyses in the stratosphere. The model simulations are found to be in general reliable. However, important differences between model and observations may help improve knowledge of winds and ability to model transport.