role of baroclinic transport on seasonal rectifier effect
DESCRIPTION
Role of Baroclinic Transport on Seasonal Rectifier Effect. Misa Ishizawa 1,2 , Douglas Chan 1 , Kaz Higuchi 1 , Shamil Maksyutov 3 and Jing Chen 2 1 Atmospheric Science and Technology Directorate, Environment Canada 2 University of Toronto, Canada - PowerPoint PPT PresentationTRANSCRIPT
Role of Baroclinic Transport on Seasonal Rectifier Effect
Misa Ishizawa1,2, Douglas Chan1, Kaz Higuchi1, Shamil Maksyutov3 and Jing Chen2
1 Atmospheric Science and Technology Directorate, Environment Canada 2 University of Toronto, Canada3 National Institute for Environmental Studies, Japan
Fig 3 from Gurney et al., (Tellus, 2003, T3L2 Experiment)
The annual mean north-south CO2 gradient as a result of the covariance of the transport and the neutral biospheric fluxes.
Seasonal Rectifier Effect
In CO2 flux inversion estimate, background CO2 field is an important factor, especially one produced by the biospheric fluxes.
Rectifier Effect - Impact on CO2 Inversion -
Large Carbon Sink Required in Northern High and Mid Latitudesto balance the carbon budget with observations
Fig 1 from Denning et al., (Tellus, 1999)
Rectifier EffectBiosphere
Observations
Required Sink
Annual mean: Accumulation of CO2 near the ground
Dilution of photosynthesis signal through deep mixing
Transport of low-CO2 air into upper troposphere
Summer
Deep PBLMixing
Low CO2
Concentration
Photosynthesis
StrongConvection
Accumulation of respiration signal near the surface
Elevated CO2 in lower troposphere
Autumn
Shallow PBLMixing
High CO2
Concentration
Decomposition
Weak Cumulus Convection
One Suggested Mechanism: Seasonal covariation of PBL and NEP fluxes (Denning).
(From S. Denning)
A Rectifier Mechanism
• with less difference between Fraserdale(50ºN) and Alert in winter than in summer
• with more synoptic variability in winter than in summer
Another Rectifier Mechanism?observational evidence
Continuous CO2 measurements
at Alert (82ºN) 400
390
380
370
360
350
340
200520042003200220012000
Alert Fraserdale
2.5
2.0
1.5
1.0
0.5
0.0
CO
2 fo
r A
lert
[pp
m]
5
4
3
2
1
0
CO
2 for Fraserdale [ppm
]
J F M A M J J A S O N D
Alert Fraserdale
Mean deviations of obs to fitted curves
Another Rectifier Mechanism?
• Motivation: – In the extra-tropics, north-south sensible heat and
humidity transports are dominated by the baroclinic meridional circulations.
– Meridional transport by LSE (Large Scale Eddies or Synoptic Systems) ~dT/dy. dT/dy has seasonal variations.
• Potential Mechanism of Rectifier Effect: – Seasonal variation of baroclinic meridional transport
has covariance with NEP fluxes?
Summer : T=~25
Wnter : T=~50
Annual : T=~35
Horizontal Temperature Gradient : T
Eq NP
Relationship between LSE and TFrom 2-D diffusive transport by Stone (1974)
LSE is a function of T
Large Seasonal Variation of T Seasonal Variation of LSE
Another Rectifier MechanismWhy Baroclinic Process (Large Scale Eddies)?
Vertical Cross-SectionWinter (DJF)Summer (JJA)
More CO2 air transported to Northern High Latitudes
Weaker transport results in stronger CO2 gradient from mid-latitude to the pole
Winter (DJF)
Annual mean
Summer (JJA)
Simulated Fossil Fuel-CO2 with constant PBL
Seasonality of Meridional Transport7
6
5
4
3
2
1
0
CO
2 [p
pn]
-50 0 50
500
400
300
200
100
0
FF
Em
ission [TgC
/grid/yr]
Summer• Equator-Pole T~(30-5)=25• Weak Meridional Transport (of
photosynthesis signals to the polar region)
Winter• Equator-Pole T~(30-(-20))=50• Strong Meridional Transport (of
respiration signals to the polar region)
NET RESULT: In winter, higher CO2 concentration in polar region, hence ‘RECTIFIER EFFECT’
NPEQNPEQ
5°C
30°C 30°C
-20°C
T=~25 T=~50
Low CO2High CO2
Another Rectifier Mechanism Baroclinic Process and NEP in Northern Hemisphere
• To study the effect horizontal transport has on the CO2 distribution
• To study the effect PBL variation has on the CO2 distribution
LocallyInteraction between atmospheric transport/mixing and biospheric CO2 flux
GloballyNorth-South atmospheric CO2 gradient
Biosphere
Atmosphere
CO2
Horizontal Transport
Vertical Mixing
CO2 flux
Objectives
• Transport Model– NIES Transport Model – NCEP Reanalysis– PBL monthly
• Surface Fluxes– Biospheric Flux (annually balanced monthly mean NEP
from Biome-BGC)
• Model Integration– 10 years’ (1990-1999) integration: – First two years for spinup, – Averaged over year 3 to year 10
Method
• Reference
• Case 1 : Constant PBL No Rectifier ?– Fix the PBL annually
• Case 2 : PBL Shifted Negative Rectifier ?– Shift the PBL seasonality by 6 months
• Case 3 : Constant PBL & CO2 Flux Shifted ??– Fix the PBL annually– Shift the CO2 biospheric fluxes by 6 months
Test Proposed Mechanisms
NIES model with Biome-BGC has mean gradient of ~3-4 ppm
Reference Rectifier
4
3
2
1
0
CO
2 [p
pm]
-90 -60 -30 0 30 60 90
Latitude [degree]
Annual mean PBL
Case 1: Constant PBL
• Fix the PBL height annually, no seasonal variation.• PBL varies spatially but not temporally.• NEP normal.• No PBL-NEP covariation• Covariation of the meridional transport and NEP
Seasonal variation of PBL has ~30% effect on the north-south CO2 gradient.
Case 1: Constant PBL
4
3
2
1
0C
O2
[ppm
]
-90 -60 -30 0 30 60 90Latitude
Case1 Reference
W
S
W
S
W
S
W
S
700mb
Surface
Zonal Mean CO2
Zonal Mean Biospheric Fluxes
Summer
Winter
Transport N-S Gradient
Weak/Slow Small
Strong/Fast Large
In annual mean, positive CO2 anomaly in N-S Gradient
Differential CO2 transport between Summer and Winter
Covariation of Meridional Transport and CO2 fluxes
Case 1: Constant PBL
Mid NP Mid
700mb
Low CO2 High CO2
NPSurface
Summer Winter Tsummer< Twinter
vcsummer < vcwinter
In Winter, High CO2 is transported to polar region from mid latitudes along isentropic surface faster than in summer
Case 1: Constant PBL Faster Northward Transport in Winter
EQ NPMidZonal-mean cross section of equivalent potential temperature
• Shift the PBL seasonality by 6 months• Seasonal covariation of PBL and
NEP.
Reduction of rectifier effect (Negative amplification), but still North-South CO2 gradient (high CO2 in North)
PBL effect is locally strong.
Away from Lands, PBL effect is not so significant.
Case 2: PBL Shifted
4
3
2
1
0
-90 -60 -30 0 30 60 90
Case 2 (180E) Reference
4
3
2
1
0
-90 -60 -30 0 30 60 90
Case 2 (zonal mean) Reference
- Opposite North-South CO2 Gradient, but weaker
- Strong winter North-South transport with low CO2 signal resulting in negative Rectifier Effect
Case 3:Constant PBL& CO2 Flux Shifted• Fix the PBL height annually, no seasonal variation.• Shift the NEP seasonality by 6 months.• No PBL-NEP covariation• Seasonal Covariation of the meridional transport and NEP
4
3
2
1
0
-1C
O2
[ppm
]
-90 -60 -30 0 30 60 90Latitude
Case 3 Reference
• Seasonal variation of PBL acts as an amplification mechanism, it has ~30% effect on the north-south CO2 gradient.
• The seasonal covariation of the meridional transport and CO2 flux appears to be the dominant factor in the annual mean north-south CO2 gradient (seasonal rectifier effect).
The effects of seasonal PBL variation (or vertical mixing) and seasonal variation of meridional transport on the mean annual north-south CO2 gradient were examined.
Summary
• Seasonal variation of meridional atmospheric transport can be understood in terms of the seasonal variation of the meridional temperature gradient (baroclinic forcing). The dominant baroclinic atmospheric processes are cyclones and anticyclones (synoptic processes).
North-South CO2 Gradient
CO2 fluxMeridional Transport
Vertical Mixing
Rectifier Effect
• To improve the simulation of the rectifier effect for CO2 inversion, the results of this study suggest improving the simulation of synoptic scale transport processes in transport models.
• The results also showed that PBL and CO2 covariations have stronger effects near the source regions, this is an important factor if continental sites are used in the CO2 inversion. However, synoptic processes are also important factors for the atmospheric PBL dynamics (PBL tends to be higher in the cyclonic low pressure area than under the stronger subsidence in the anticyclonic high pressure area, synoptic variations are as large as seasonal variations).
• Synoptic processes also affect the CO2 fluxes through temperature, humidity, precipitation and radiation; hence the CO2 flux and atmospheric transport covariation.
• These indicate the importance of the proper simulation of the synoptic coupling between the atmosphere and biosphere in CO2 inversion.
Impact on CO2 inversion