The large‐scale frozen‐in anticyclone in the 2011 Arctic summer stratosphere

Abstract

The 2011 Arctic stratospheric final warming was characterized by a large‐scale frozen‐in anticyclone (FrIAC) that rapidly displaced the winter polar vortex, establishing unusually strong polar easterlies. A comprehensive overview of the 2011 FrIAC is provided using meteorological analyses, Microwave Limb Sounder (MLS) N2O observations, and N2O simulations from the Global Modeling Initiative (GMI) 3‐D chemistry and transport model and the Van Leer Icosahedral Triangular Advection (VITA) 2‐D (latitude × longitude) isentropic transport model. A vortex edge diagnostic is used to determine the FrIAC boundary, allowing quantification of several FrIAC properties. The 2011 FrIAC originated over North Africa in late March and traveled eastward and poleward over 2 weeks, forming a strong anticyclone that extended from ~580–2100 K potential temperature (~25–50 km). Low potential vorticity (PV) was transported to the pole with the FrIAC in early April; during May, most of the PV signature decayed due to diabatic processes. A small remnant negative PV anomaly persisted near the pole until mid‐June. Tracer equivalent latitude was low initially and remained low throughout the summer. GMI, VITA, and MLS showed elevated N2O in the FrIAC, although the peak value was smaller in GMI due to a subtropical low bias. The high‐resolution (~20 km) VITA filamentary structure quantitatively matched most of the features observed by MLS when smoothed to match the MLS resolution. The high‐N2O anomaly persisted in the middle stratosphere over 4 months until late August, when it was destroyed by horizontal and vertical shearing, combined with photochemical processes.

Version 1.3 AIM SOFIE measured methane (CH4): Validation and seasonal climatology

“…Shown in Figure are similar maps except for between years 2011 and 2009. Methane is anomalously high throughout the entire year in 2011, which is ascribed to a vigorous final warming and the consequential “frozen‐in” anticyclone with high CH 4 enclosed [ Siskind et al ., ; Allen et al ., ]. The ΔCH 4 | 2011‐2009 in the NH exhibits a pair of much stronger minimum and maximum features in late winter to spring as compared to 2008.…”

Poleward transport variability in the Northern Hemisphere during final stratospheric warmings simulated by CESM(WACCM)

“…This new algorithm consists in a combination of previous methods described in Allen et al . [] and Thiéblemont et al . [].…”

“…In brief, we detect FrIACs by merging the anticyclone detection algorithm, used in Allen et al . [] to characterize the 2011 FrIAC, to the anticyclone/low‐latitude air masses colocation method of Thiéblemont et al . [].…”

“…Consequently, the shape evolution and whole life cycle of FrIACs cannot be characterized using PVEL. The use of PVEL is, however, relevant to follow the early stages of FrIAC development (i.e., spin‐up and “anticyclonic” phases [ Allen et al ., , ]) and is thus sufficient to identify them.…”

“…Observed FrIACs generally occur under strong and abrupt SFWs which are associated to a strong enhancement of planetary wave activity [e.g., Thiéblemont et al ., ]. The detailed modeling studies of the 2005 [ Allen et al ., ] and 2011 [ Allen et al ., ] FrIACs provided a thorough description of the FrIAC life cycle. This can be divided into three phases: (1) a “spin‐up” phase in which the FrIAC develops and is advected to the polar region, (2) an “anticyclonic” phase in which the FrIAC is trapped in the developing summer easterlies and resists the weak vertical wind shear (April–May), and finally (3) a “shearing” phase in which the anticyclonic anomaly decays due to diabatic processes and the tracer anomaly is sheared out by the background wind (beginning by the end of May).…”