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Extratropical stratoshere-troposphere Extratropical stratoshere-troposphere exchange in a 20-km-mesh AGCMexchange in a 20-km-mesh AGCM
Ryo Mizuta(Meteorological Research Institute / AESTO)
Hiromasa Yoshimura(Meteorological Research Institute)
E-mail: [email protected]
Appenzeller et al. (1996)
Water vapor image (Meteosat)
Isentropically advected “controur” of PV isolines of 4 days before
• 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.
IntroductionIntroduction
AGCM with the grid size of 20km 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.
Surface temperature climatology
Precipitation climatology OBS Model
OBS Model
• In addition to near-surface phenomena, the model can resolve
– sharp tropopause– filamental structures near
the tropopause
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L
L
L
PV
Water Vapor
• Using this high-resolution model, we have investigated
– where and how the transport and mixing occur
– what depends on the model resolutions
PV 315K [PVU=10-6Km2s-1kg-1 ]
Climate Simulation on the Earth SimulatorClimate 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 integrationJan Jul
Model ClimatologyModel Climatology
ERA40 Reanalysis (1979-1998) TL959L60 (20years) TL959L60 – ERA40
zonal-mean U ・ T (DJF)
■ ■ 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).
Jet stream
Storm tracks
ERA40(1979-1998) TL959L60 (20years)
stddev of Z300 2.5-6days bandpass-filtered (DJF)
U300 [m/s] NH DJF
Model ClimatologyModel Climatology
Quantification of Transport by Passive Tracer AdvectionQuantification of Transport by Passive Tracer Advection
• 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
1. Tracer initialized to 1 only above the 2PVU tropopause Gray (2006)
χ= 1 at PV > 2 (PVU)
χ= 0 at PV < 2 (PVU)χ at PV < 2 : ST 1 – χ at PV > 2 : TS
2. Tracer advection for 24 hours without source/sink
3. Compare with the tropopause at final time
Vertical distribution (20N-90N, Jan)Vertical distribution (20N-90N, Jan)
• 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)
Strat. Trop. Trop. Strat. Net
TL9
59TL95
TL95
9
TL95
TL9
59T
L95
TL959 TL95
Exchange in the lower levelsExchange 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.
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Horizontal Horizontal Distribution (Jan)Distribution (Jan)
• TS transport around the subtropical jet over Eurasia
• ST transport in northern winter around the storm tracks at lower altitude
StratosphereTroposphere TroposphereStratosphere
200-350hPa
400-700hPa
JulyJuly
Strat. Trop. Trop. Strat. Net
TL9
59
TL95
TL9
59
TL95
150-200hPa
250-450hPa
• 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
TL9
59TL
95
Contributions of the PV nonconservative termsContributions of the PV nonconservative terms
will move to the stratosphere in Δt
pg
p
Qfg
Dt
DPV
QfDt
DPV
fPV
z
)()(
)(1
)(1
)(1
F
Fζ
ζ
•Shortwave Radiation•Longwave Radiation•Heat release by Large-scale condensation•Heat release by Convection•(Diffusion)
•Gravity-wave drag•Convective momentum transport•(Diffusion)
22 of area PVt
Dt
DPV
t
Dt
DPVPV 22 of area
will move to the troposphere in Δt
• A nonconservative process has to work for transport across PV surface
--- stored as monthly-averaged data (except for diffusion)
Contribution by Longwave (300hPa, Jan)Contribution by Longwave (300hPa, Jan)
22 of area PVtDt
DPV
LW
p
Qfg
Dt
DPV LW
LW
)(
p
QLW
Contributions of the PV nonconservative termsContributions 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
SummarySummary• 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 !
