Transport of Air from the Tropical Upper Troposphere into the Extratropical Lower Stratosphere Kenneth Bowman, Cameron Homeyer, Dalon Stone - Texas A&M Laura Pan, Teresa Campos, Andy Weinheimer - NCAR Elliot Atlas - U. of Miami RuShan Gao - NOAA ESRL Fuqing Zhang - Penn State START08 Project Team Extratropical UT/LS Workshop, Boulder, Colorado

START08 Mission Goals A primary goal of START08 is to investigate the mechanisms responsible for layers of low stability (troposphere-like) air in the extratropical LS and their relationship to double tropopauses Data from START08 RF

RF01 GFS Stability Forecast Low stability High stability

RF01 Flight Track

Flight RF01 Static Stability

Flight RF01 O3 and CO Profiles

Flight RF01 O3 vs. CO Other talks have more analysis of trace gases

RF01 Low-PV Particle Initial Positions

Subtropical jet Tropopause break Low-PV air 3 pvu surface Flight path

Flight RF01 Low-PV Back Trajectories

Subtropical jet Low-PV parcels GFS tropopause Tropopause break

RF01 High-PV Particle Initial Positions

Flight RF01 High-PV Back Trajectories

Low- and High-Stability Air Source Regions

Stirring Mechanism Irreversible transport (stirring) occurs due to quasi- horizontal stretching and folding around hyperbolic points in the flow. In large-scale atmospheric flows, hyperbolic points are usually caused by Rossby waves propagating on jets. There is some theory for 2-D flows (adiabatic and isentropic), and there are numerical methods for finding essential flow geometry. To understand how irreversible wave-induced stirring occurs, it is necessary to look at the flow in a reference frame that moves with the wave.

Streamfunction for Idealized Jet + Wave

Streamfunction in Moving Reference Frame

Stirring Mechanism For Rossby waves on a jet, the important parameters for stirring are the speed of the jet U, the speed of the wave c, the amplitude of the wave A, and the time dependence of A Waves typically move slower than the maximum jet speed (U > c) Near the core of the jet, there is a strong barrier to transport across the jet Above and below the core, where U decreases, the barrier weakens

Transport Barrier in a Simple Model From Rypina et al., 2007 c/U ~ 0.46, strong barrier c/U ~ 0.7, no barrier

Flight RF01 Potential Vorticity

Summary and Conclusions START08 sampled a number of low-stability layers in the lower stratosphere with characteristics of tropospheric air. These layers intrude into the stratosphere with layers of stable stratospheric air above and below. Low-stability air sampled during RF01 can be traced back 7–10 days to the tropical upper troposphere. A mass of tropospheric air was transported from the equatorward to the poleward side of the subtropical jet above the jet into the extratropical lower stratosphere by a large amplitude wave event upstream over the Pacific. Transport is highly altitude-dependent due to the vertical structure of the jet.

START08 Mission Goals A primary goal of START08 is to investigate the mechanisms responsible for layers of low stability (troposphere-like) air in the extratropical LS and their relationship to double tropopauses Low stabilityHigh stability

Flight RF01 Static Stability Low stabilityHigh stability