Assimilation of AIRS CO 2 Observations with EnKF in a Carbon-Climate - PowerPoint PPT Presentation

Assimilation of AIRS CO 2 Observations with EnKF in a Carbon-Climate Model Junjie Liu, Inez Fung (UCB) Eugenia Kalnay, Ji-Sun Kang (UMD) Mous Chahine, Ed Olsen, Luke Chen (JPL) 1

Differ Di eren ent CO CO 2 v vertical gradient forecasts give gi ve di differ erent ent CO CO 2 f flux obs Tropical CO 2 land Vertical levels NH land obs surface ppm Stephens et al., 2007, (Science)  Numbers and characters are different transport models. => Important to have accurate vertical mixing in the model; => Accurate 4-D (x, y, z, t) CO 2 fields. 2

Meteo Met eorology gy fiel elds ds & & CO CO 2 Atmosphere Winds CO 2 Height  Offline transport models have been used.  The initialization meteorology fields are from either reanalysis products (usually 6-hourly) or off-line dynamical model;  The vertical mixing has large uncertainty;  Single realization of meteorological field. 3

Research Goals Research Goals  Generate 6-hourly 3-D (x, y, z) CO 2 fields by assimilating CO 2 and meteorological observations with full GCM 4

Carbon-Climate Model Carbon-Climate Model Community Atmospheric Model (fvCAM 3.5) (2.5x1.9x26) CO 2 , winds, q, T, Ps Fossil fuel Photosynthesis emission Ocean CO 2 flux Respiration (Takahashi et al. 2002) Ocean Land  CO 2 is transported as a tracer;  Vertical mixing is updated every 30 minutes;  Land carbon flux: 6-hourly flux from biogeochemical model. 5

Ensemble Kalman Filter (EnKF) process Ensemble Kalman Filter (EnKF) process Ensemble Ensemble analyses forecasts (initial states) Observations t=0hr t=06hr t=12hr  Forecast error changes with time;  Obtain ensemble analyses. 6

CO 2 Observation Operator • Model forecast x b is CO 2 vertical profile; • AIRS CO 2 is column-weighted Volume Mixing Ratio (vmr); => observation operator: interpolate x b to obs location & calculate model forecast column-weighted CO 2 vmr. T ( = y b x b A S ( )) ! ! ! ! avg kernel spatial interpolator " $$ $ # $$$ % model forecast "obs" model forecast obs operator 7

Assimilation experiments  Met-run: assimilate raw meteorological observations (10 6 observations ) AIRS-run: assimilate AIRS CO 2 observations in conjunction  with meteorological observations. 8

The impact of AIRS CO The impact of AIRS CO 2 assimilation assimilation on 6-hourly CO on 6-hourly CO 2 2 3D (x, y, z) fields D (x, y, z) fields Met-run AIRS-run CAM3.5 CAM3.5 (u, v, T, q, Ps) (u, v, T,q, Ps) analysis analysis analysis (CO 2 ) 6 hour forecast 6 hour forecast (u, v, T, q, Ps) CO 2 (u, v, T, q, Ps) CO 2 LETKF LETKF LETKF Observations Observations Observations (u,v,T,q,Ps) AIRS CO 2 (u,v,T,q,Ps)  AIRS-run: AIRS CO 2 +met obs; Met-run: only met obs.  The year of 2003.  Prescribed surface CO 2 flux forcing. 9

Mo More e than an 2000 2000 AI AIRS CO 2 w within 6 hours; mo more e sen ensitive e in the e mi middl ddle e tropo posph pher ere AIRS averaging kernel AIRS CO 2 at 18Z01May2003 (+/-3hour) € € o: polar region; +: mid-latitude; closed circles: the tropics. ppm  Averaging kernel: the sensitivity of AIRS CO 2 to CO 2 at each vertical level. 10

Analysi Anal ysis s cor correct ections ons to o CO CO 2 fo forecast peak at the si similar ar level evels s as as the he peak peak of of the he averagi averaging ng kernel kernels Time-averaged (10 months) absolute analysis corrections Averaging Kernel Vertical levels (hPa) o: polar region; +: mid-latitude; closed circles: the tropics. 90°S 0° 90°N  No CO 2 observations beyond 60ºS. 11

Assimilating CO 2 adjusts CO 2 vertical gradient May 2003: CO 2 (850hPa)-CO 2 (400hPa) Met-run  In the NH, CO 2 (850hPa)>CO 2 (400hPa): fossil fuel+ land carbon source;  In the SH, CO 2 (850hPa)<CO 2 (400hPa): transported from the NH. 12

Assimilating CO 2 adjusts CO 2 vertical gradient May 2003: CO 2 (850hPa)-CO 2 (400hPa) Met-run (AIRS-run)-(met-run)  In the NH, CO 2 (850hPa)>CO 2 (400hPa): fossil fuel+ land carbon source;  In the SH, CO 2 (850hPa)<CO 2 (400hPa): transported from the NH.  Require CO 2 obs in the lower troposphere to further constrain gradient. 13

In Inconsiste sistent sp t spatia tial d l distrib istributio tion b betw tween AI AIRS RS CO CO 2 a and nd oc ocean-air CO 2 f flux Annual mean AIRS CO 2 spatial anomaly (ppm) Ocean-atmosphere CO 2 flux (unit: 10 -9 kgC/m 2 /s Takahashi et al., 2002) 14

Tropi Tr opical cal AI AIRS RS CO CO 2 r relates to ci circulation and and aver averagi aging ng ker kernel nel Annual mean AIRS CO 2 spatial anomaly (ppm) Ocean-atmosphere CO 2 flux (unit: 10 -9 kgC/m 2 /s Takahashi et al., 2002) 15

As Assimi milat ating g AI AIRS RS CO CO 2 i improves spatial pat patter ern Annual mean AIRS CO 2 spatial anomaly (ppm) CO 2 spatial anomaly at AIRS CO 2 space from met-run Annual mean CO 2 correction from assimilating AIRS CO 2 16

Co Consisten ent CO CO 2 d distribution and we weather pat patter ern 500hPa geopotential height (contour) and CO 2 from AIRS-run (shaded) Single time (12Z27Feb2003) Time average over Feb 2003 ppm  Simultaneous assimilation of meteorology variables and CO 2 generates CO 2 distribution consistent with weather pattern 17

CO 2 a CO analysis spread ran ranges ges from 0. 0.4ppm 4ppm to o 2ppm 2ppm at at 400hPa 400hPa 400hPa monthly mean Average num of CO 2 observations at (September) CO 2 spread each grid box within 6 hours ppm  Analysis ensemble spread is related to observation coverage, forecast error and observation error;  Larger spread over high latitudes, and over land;  Smaller spread over tropical ocean is due to observation coverage 18 and propagation through forecast.

Column Co mn-integ egrat ated ed CO CO 2 —Se Sep AIRS-run - AIRS AIRS AIRS Met-run - AIRS -run Met- run ppm ppm 19

Column Co mn-integ egrat ated ed CO CO 2 —Oc Oct AIRS-run - AIRS AIRS AIRS Met-run - AIRS -run Met- run ppm ppm 20

Co Column mn-integ egrat ated ed CO CO 2 —No Nov AIRS-run - AIRS AIRS AIRS Met-run - AIRS -run Met- run ppm 20 days with no AIRS ppm 21 CO2

Assi Assimilat ating ng AI AIRS RS CO CO 2 2 im improves surface CO CO 2 s seasonal c l cycle le a and th the N- N-S gradient Surface obs: black; Met-run: red: AIRS-run: blue Mean NH CO2 concentration at 8 The N-S gradient based on 16 surface stations surface stations Surface data is from Met-run has similar NH CO2 NOAA/ESRL website concentration and the N-S gradient 22

Assimilat Assi ating ng AI AIRS RS CO CO 2 2 im improves CO 2 state esti state estimate ate Molokai Island Briggsdale, US Cook Islands 8.5km Height (km) Met-run: no CO2 obs AIRS-run: assimilate CO2 1km rms error (ppm) Verified against independent aircraft CO 2 observations  CO 2 from the AIRS-run can be about 1 ppm more accurate than those from the met-run. 23

Prel Prelimi minary nary resul results s on on surf surface ace carbon flux carbon ux est estimat mation on by by assi assimi milat ating ng AI AIRS RS CO2 CO2 24

The impact of AIRS CO The impact of AIRS CO 2 assimilation assimilation on surface CO on surface CO 2 flux flux CAM3.5 (CO 2 Cflux) (u, v, T, Ps) analysis analysis 6 hour forecast (u, v, T, q, Ps) (CO 2 ) LETKF LETKF Observations AIRS CO 2 and conventional CO 2 (u,v,T,q,Ps) observations LETKF: Local Ensemble Transform Kalman Filter (Hunt et al., 2007) • The carbon flux analysis acts as boundary forcing for the forecast of next time step. • Four and a half months assimilation cycles (01Jan2003-10May2003). 25

Carbon Flux An Car Anal alysis:Dat Data a As Assim (l (left) Car Carbon Flux (CAS CASA A (lan and)+Tak akah ahas ashi (ocean cean))(right) January 2003 10 -8 kg/m 2 /s • AIRS has the most impact over the tropical land • Stronger source in the NH winter • Stronger sink in the tropics and SH subtropics • Noisy over ocean compared to Takahashi 26

Carbon Flux An Car Anal alysis:Dat Data a As Assim (l (left) Car Carbon Flux (CAS CASA A (lan and)+Tak akah ahas ashi (ocean cean))(right) February 2003 10 -8 kg/m 2 /s • Stronger source in the NH winter • Stronger sink in the tropics and SH subtropics • Noisy over ocean compared to Takahashi 27

Car Carbon Flux An Anal alysis:Dat Data a As Assim (l (left) Carbon Flux (CAS Car CASA A (lan and)+Tak akah ahas ashi (ocean cean))(right) March 2003 10 -8 kg/m 2 /s • Little change 28

Car Carbon Flux An Anal alysis:Dat Data a As Assim (l (left) Car Carbon Flux (CAS CASA A (lan and)+Tak akah ahas ashi (ocean cean))(right) April 2003 10 -8 kg/m 2 /s • Little change 29

Car Carbon Flux An Anal alysis:Dat Data a As Assim (l (left) Car Carbon Flux (CAS CASA A (lan and)+Tak akah ahas ashi (ocean cean))(right) May 2003 10 -8 kg/m 2 /s • As in the OSSEs, the surface fluxes appear initially to be reasonable and then they “get stuck”. 30

Monthly average AIRS CO Monthly average AIRS CO 2 does not does not change hange much much over the tropical land from January to May ver the tropical land from January to May Mar Jan April Feb 31