Extratropical stratoshere-troposphere exchange in a 20-km-mesh AGCM yr21-01-10 00Z yr21-01-11 00Z yr21-01-12 00Z Extratropical stratoshere-troposphere exchange in a 20-km-mesh AGCM Ryo Mizuta (Meteorological Research Institute / AESTO) Hiromasa Yoshimura (Meteorological Research Institute) E-mail: rmizuta@mri-jma.go.jp

Introduction Transport and mixing processes around UTLS region includes very fine filamental structures, but these cannot be simulated by conventional GCMs. We had to restrict to regional models or two dimensional models in order to represent these processes. Water vapor image (Meteosat) Isentropically advected “controur” of PV isolines of 4 days before Appenzeller et al. (1996)

AGCM with the grid size of 20km Long-term simulations by a high-resolution AGCM improve the representation of regional-scale phenomena like tropical cyclones and that of local climate, due to better representation of topographical effects and physical processes. OBS Model Surface temperature climatology Precipitation climatology OBS Model

In addition to near-surface phenomena, the model can resolve yr21-01-10 00Z yr21-01-11 00Z yr21-01-12 00Z L In addition to near-surface phenomena, the model can resolve sharp tropopause filamental structures near the tropopause PV 315K [PVU=10-6Km2s-1kg-1 ] Using this high-resolution model, we have investigated where and how the transport and mixing occur what depends on the model resolutions PV Water Vapor

Climate Simulation on the Earth Simulator JMA/MRI AGCM -- used both for the operational numerical weather prediction and climate researches TL959 (grid size of about 20km, 1920x960) 60 vertical layers with top at 0.1hPa (interval is ~900m at 250hPa) Dynamics: Semi-Lagrangian Scheme (Yoshimura, 2004) Cumulus parameterization:prognostic Arakawa-Schubert (Randall and Pan,1993) Radiation: Shibata et al. (1999), Gravity wave drag: Iwasaki et al. (1989) Time integrations over 20 years (as the “control” run against the global warming simulation) using climatological SST Pick up one January and one July of a certain year because very huge data size is required The horizontal resolution dependence is also examined using the coarse resolution (200km) model (TL95L40, almost the same settings as the TL959 model). spin-up 20-year integration Jan Jul

Model Climatology zonal-mean U・T (DJF) ERA40 Reanalysis (1979-1998) TL959L60 (20years) TL959L60 – ERA40 ＋ － ■ ■ 95% significant difference The model's ability of simulating the present-day climate has been confirmed from global scale through small scale in the sense of seasonal mean (Mizuta et al. 2006).

Model Climatology Jet stream Storm tracks U300 [m/s] NH DJF stddev of Z300 2.5-6days bandpass-filtered (DJF) ERA40(1979-1998) TL959L60 (20years)

Quantification of Transport by Passive Tracer Advection 1. Tracer initialized to 1 only above the 2PVU tropopause 2. Tracer advection for 24 hours without source/sink 3. Compare with the tropopause at final time Gray (2006) χ= 1 at PV > 2 (PVU) χ= 0 at PV < 2 (PVU) χ at PV < 2 : ST 1 – χ at PV > 2 : TS Semi-Lagrangian advection scheme, same as the model dynamical core 3D online calculation initialized to 0 or 1 at 00UTC every day Averaged over 30-day calculations Day 1 2 3 4 30 31

Vertical distribution (20N-90N, Jan) Strat.  Trop. Trop.  Strat. Net TL959 TL95 TL959 TL95 TL95 TL959 Less transport in each direction above 400hPa in the high-resolution model, but more exchange below 500hPa. Net transport does not much depend on model resolution. Vertically integrated amount is consistent with the residual mean stratospheric circulation (1-2 x 1010 kg/s S  T)

Exchange in the lower levels Exchange in the lower levels is not well simulated in the low-resolution model, because tropopause folding is simulated only in the high-resolution model.  less exchange in the lower level of the low-resolution model. TL959 TL95 ---- PV=2PVU TL959 yr21-01-11 00Z

Horizontal Distribution (Jan) StratosphereTroposphere TroposphereStratosphere Horizontal Distribution (Jan) 200-350hPa TS transport around the subtropical jet over Eurasia ST transport in northern winter around the storm tracks at lower altitude 400-700hPa

July TL95 TL95 TL95 TL959 Vertical distribution is similar to January, with upward shift of the peak because of higher tropopause Transport occurs mainly around the Pacific and the Atlantic at 200hPa, due to Rossby wave breaking (Postel and Hitchman 1999) weaker in the lower altitudes due to weak storm activity TL959 TL959 Strat.  Trop. Trop.  Strat. Net 150-200hPa 250-450hPa

Contributions of the PV nonconservative terms A nonconservative process has to work for transport across PV surface Gravity-wave drag Convective momentum transport (Diffusion) Shortwave Radiation Longwave Radiation Heat release by Large-scale condensation Heat release by Convection (Diffusion) will move to the stratosphere in Δt --- stored as monthly-averaged data (except for diffusion) will move to the troposphere in Δt

Contribution by Longwave (300hPa, Jan)

Contributions of the PV nonconservative terms Jan Jul Estimated transport by the effect of longwave can explain over half of TST The other contributions are too small to explain the transport

Summary Amount of exchange estimated by passive tracer has resolution dependence. In the high-resolution model, less exchange at higher levels --- due to better representation of sharp tropopause more exchange at lower altitudes --- due to better representation of small-scale structures net transport have small resolution dependence Net stratosphere to troposphere transport below 400hPa large over the Pacific and Atlantic storm track in January Net troposphere to stratosphere transport above 300hPa near the subtropical jet over Eurasia in January around the Pacific and the Atlantic in July Large part of this transport estimated from PV change by vertical difference of longwave radiation. Please check Mizuta and Yoshimura (2009, JGR) for more detail !