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Assimilation of AIRS CO 2 Observations with EnKF in a Carbon-Climate Model 1 Junjie Liu 2 Eugenia Kalnay, 1 Inez Fung 3 Moustafa T. Chahine and 3 Edward T. Olsen 1 University of California, Berkeley; 2 University of Maryland; 3 Jet Propulsion Lab

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Assimilation of AIRS CO2 Observations with EnKF in a Carbon-Climate Model

1Junjie Liu

2Eugenia Kalnay, 1Inez Fung 3Moustafa T. Chahine and 3Edward T. Olsen

1University of California, Berkeley; 2University of Maryland; 3 Jet Propulsion Lab (JPL), NASA

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Big Problem: The Elusive Carbon Sink

  • Only half of the CO2

produced by human activities is remaining in the atmosphere.

  • Where are the sinks that

are absorbing about 50%

  • f the CO2 that we emit?

– Land or ocean? – Eurasia/North America?

  • How will CO2 sinks

respond to climate change?

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  • Top-down approach: CO2 concentrations->carbon flux
  • Carbon flux estimation has been constrained by limited
  • bservation coverage.

Background: Top-down Approach & Conventional CO2 Observation Coverage

NOAA/ESRL

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  • Generate CO2 vertical profiles
  • Preliminary results on surface carbon flux

estimation.

AIRS CO2 at 18Z01May2003 (+/-3hour)

AIRS averaging kernel

  • : polar region; +:

mid-latitude; closed circles: the tropics.

AIRS CO2 Observations & Research Goals

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Ensemble Kalman Filter process

  • Blue: analysis ensemble and its uncertainty; Green: background

ensemble and its uncertainty; Magenta: observation and its uncertainty; Background error changes with time;

  • Obtain ensemble analyses;

t=0hr t=06hr t=12hr

Ensemble forecasts Ensemble analyses Observations

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Carbon-Climate Model

  • Community Atmospheric Model 3.5 (CAM 3.5) coupled with

Community Land Model 3.5 (CLM 3.5)

– Finite Volume dynamical core – 2.5°x1.9° horizontal resolution, with 26 vertical levels up to 3.5hPa.

  • CO2 is transported as a tracer in CAM 3.5
  • Carbon surface fluxes:

– Fossil fuel emission (yearly average value for 2003) – Ocean C fluxes (monthly means, interpolated between months; Takahashi et al., 2002) – Land C flux (6-hourly carbon flux from CASA)

  • Initial CO2 is the spin-up after 3 years.
  • Assimilation time period: 01Jan2003-30June2003
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Quality Control: Buddy Check

Buddy check: compare each obs to the mean of the adjacent obs

Before buddy check After buddy check

The quality of the rejected obs is not necessarily bad by itself!

  • 8% of AIRS CO2 observations were deleted in this way

AIRS CO2 within 6 hours

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CO2 Observation Operator

  • Model forecast xb is CO2 vertical profile;
  • AIRS CO2 is column-weighted Volume Mixing Ratio (vmr);

=> observation operator: interpolate xb to obs location & calculate model forecast column-weighted CO2 vmr.

yb

model forecast "obs"

  • =

A

avg kernel

  • T (

S

spatial interpolator

  • bs operator
  • (

xb

model forecast

  • ))
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Analysis Increments (contour) & Observation Increments (shaded) At One Assimilation Cycle

PPM

  • Analysis increments agree with observation increments

Analysis increments: the difference between analysis and forecast; Observation increments: the difference between

  • bservation and forecast
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Time-averaged Absolute Analysis Increments

  • Obtain CO2 vertical profiles from column weighted CO2; no

AIRS CO2 observations beyond 60ºS.

  • Analysis increments peak at the similar levels of the peak of

the averaging kernels. Time-averaged absolute analysis increments Averaging Kernel

Vertical levels (hPa)

  • : polar region; +:

mid-latitude; closed circles: the tropics.

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The Impact of AIRS CO2 Assimilation

CAM3.5

LETKF Observations (u,v,T,q,Ps) analysis (u, v, T, q, Ps) (CO2) LETKF Observations AIRS CO2 analysis (CO2) LETKF: Local Ensemble Transform Kalman Filter (Hunt et al., 2007)

  • Assimilate meteorological observations along with AIRS CO2

CAM3.5

LETKF 6 hour forecast (u, v, T, q, Ps) Observations (u,v,T,q,Ps) analysis (u, v, T,q, Ps) (CO2) 6 hour forecast (u, v, T, q, Ps)

Meteor-run AIRS-run

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Verified Against Independent Aircraft CO2

  • Grey: meteor-run; black: AIRS-run.
  • CO2 vertical profiles from the AIRS-run can be about 1 ppm

more accurate that those from the meteor-run. Height (m)

1km 8.5km ppm Meteor-run AIRS-run Briggsdale, US Estevan Point Molokai Island Cook Island

Time average of all the cases between 01Jan2003-30June2003

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  • Ensemble CO2 analyses (

Ensemble CO2 analyses (grey shaded rey shaded) bracket aircraft racket aircraft obs bs

Molokai Island, Hawaii. May 11, 2003 Estevan point, British Columbia, Feb 27, 2003

  • Meteor-run: CO2 tracer transported by 64-

member ensemble meteorological analyses generated every 6hr

  • AIRS-run: CO2

assimilated along with meteorological obs.

Analysis ensemble spread along with the mean state

  • bs
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Preliminary results on surface carbon flux estimation by assimilating AIRS CO2

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The impact of AIRS CO2 assimilation

CAM3.5

LETKF Observations (u,v,T,q,Ps) analysis (u, v, T, Ps) (CO2) LETKF AIRS CO2 and conventional CO2

  • bservations

analysis (CO2 Cflux) LETKF: Local Ensemble Transform Kalman Filter (Hunt et al., 2007)

  • The carbon flux analysis acts as boundary forcing for the forecast
  • f next time step.
  • Three-month assimilation cycles (01Jan2003-31March2003).

6 hour forecast (u, v, T, q, Ps)

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Carbon Flux Analysis:Data Assim (left) Carbon Flux (CASA (land)+Takahashi (ocean)(right) February 2003

(unit: 10-8 kg/m2/s):

  • Stronger source in the NH winter
  • Stronger sink in the tropics and SH subtropics
  • Noisy over ocean compared to Takahashi
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Carbon Flux Analysis:AIRS CO2 Data Assim (left) Carbon Flux (CASA (land)+Takahashi (ocean)(right) February 2003

(unit: 10-8 kg/m2/s):

  • Stronger source in the NH winter
  • Stronger sink in the tropics and SH subtropics
  • Noisy over ocean compared to Takahashi
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Carbon flux analysis (left) and carbon flux (CASA+Takahashi)(right) (unit: 10-8 kg/m2/s): Mar March 2003

  • Stronger source in the NH winter
  • Stronger sink in the tropics and SH subtropics
  • Noisy over ocean compared to Takahashi
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RMSE Difference Between CO2 Analyses From Carbon Flux Analysis and those from Fixed Carbon Flux

Unit: ppm

Black: NH; Red: SH; Blue: Tropics

RMS against AIRS CO2

  • Negative: carbon flux analysis is more accurate than fixed carbon flux

when verified against AIRS CO2.

  • Stronger fluxes drive CO2 to better agreement with AIRS

CO2!

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Summary and Future Directions

  • Assimilation of CO2 observations have improved the CO2

vertical profiles;

  • The ensemble analyses encompasses the aircraft CO2

vertical profiles.

  • The preliminary surface carbon flux estimation from

assimilating AIRS CO2 and conventional CO2 observations are encouraging!  Extend surface carbon flux estimation, and seek more solid validation of carbon flux analysis.

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Relationship Between Analysis Ensemble Spread and Observation Coverage

  • Analysis ensemble spread is anti-correlated with the the CO2
  • bservation coverage

CO2 analysis ensemble spread at observation space Average number of AIRS CO2

  • bservations within 6-hour

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