Documentation - CT2011
Biosphere Oceans Observations Fires Fossil Fuel TM5 Nested Model Assimilation
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Observations [goto top]
1.   Introduction
The observations of CO2 mole fraction by NOAA ESRL and partner laboratories are at the heart of CarbonTracker. They inform us on changes in the carbon cycle, whether they are regular (such as the seasonal growth and decay of leaves and trees), or irregular (such as the release of tons of carbon by a wildfire). The results in CarbonTracker depend directly on the quality, amount and location of observations available, and the degree of detail at which we can monitor the carbon cycle reliably increases strongly with the density of our observing network.

2.   Detailed Description
This study uses measurements of air samples collected at surface sites in the NOAA ESRL Cooperative Global Air Sampling Network, the CSIRO Air Sampling Network and the IPEN-CQMA sampling program where available, except those flagged for analysis or sampling problems, or those thought to be influenced by local sources. The sites for which data are available thus varies each week depending on successful sampling and analysis, and each site's sampling frequency. In addition, we use in situ quasi-continuous CO2 time series from the following towers:

  • the 107m level of the AMT tower in Argyle, Maine
  • the 300m level of the BAO tower in Boulder, Colorado
  • the 396m level of the LEF tower in Park Falls, Wisconsin
  • the 305m level of the SCT tower in Beech Island, South Carolina
  • the 17m level of the SNP tower in Shenandoah National Park, Virginia
  • the 379m level of the WBI tower in West Branch, Iowa
  • the 483m level of the WGC tower in Walnut Grove, California
  • the 457m level of the WKT tower in Moody, Texas

  • the 30m level of the tower at Candle Lake (CDL, formerly Old Black Spruce), Saskatchewan, Canada operated by Environment Canada (EC);
  • the 105m level of the tower in East Trout Lake, Saskatchewan, Canada (ETL) operated by EC
  • the 40m level of the tower in Fraserdale, Ontario, Canada (FRD) operated by EC
  • the 10m level of the tower in Lac Labiche, Alberta, Canada (LLB) operated by EC

  • the 60m level of the tower at the Atmospheric Radiation and Monitoring (ARM) Carbon Project Southern Great Plains, Oklahoma site (SGP) operated by Lawrence Berkeley National Laboratory (LBNL).

Other in situ quasi-continuous CO2 time series used are from the NOAA ESRL observatories at Barrow (BRW), Mauna Loa (MLO), Samoa (SMO), and South Pole (SPO); the EC Canadian sites at Alert, Nunavut (ALT), Sable Island, Nova Scotia (SBL) and Egbert, Ontario (EGB); and the NCAR sites at Niwot Ridge, Colorado (NWR) and Storm Peak Laboratory, Colorado (SPL). Note that all of these observations are calibrated against the same world CO2 standard (WMO-X2007). Also, note that aircraft observations from the NOAA ESRL program were NOT assimilated, but used for independent assessment of the CarbonTracker results.

For most of the quasi-continuous sampling sites, we construct an afternoon daytime average mole fraction for each day from the time series, recognizing that our atmospheric transport model does not always capture the continental nighttime stability regime while daytime well-mixed conditions are better matched. At mountain-top sites (MLO, NWR, and SPL), we use an average of nighttime hours as this tends to be the most stable time period and avoids periods of upslope flows that contain local vegetative and/or anthropogenic influence. Moreover, observations at sub-daily time scales are likely to be strongly correlated and therefore add relatively little independent information to our results.

Data from the Sutro tower (STR_01P0) and the Boulder tower (BAO_01P0, BAO_01C3) are strongly influenced by local urban emissions, which CarbonTracker is unable to resolve. At these two sites, pollution events have been identified using co-located measurements of carbon monoxide. In this study, measurements thought to be affected by pollution events have been excluded. This technique is still being developed.

Also based on Transcom continuous simulations, we decided to move a set of coastal sites by one degree into the ocean to force the model sample to be more representative of the actual site conditions. These sites are labeled for reference in the complete table of sites used in CarbonTracker. Table 1 summarizes how data from the different measurement programs are preprocessed for this study.

The preprocessed data used in CarbonTracker are freely available for download. Preprocessed data are not the original measurement data. Users are encouraged to review the literature and contact the measurement labs directly for details about and access to the actual observations.

Table 1: Summary of CarbonTracker data preprocessing.
Measurement ProgramData Preprocessing
ESRL discrete surfaceAll valid1 data. Multiple values from the same day and location are averaged. No sample time-of-day restriction (see exception below).
ESRL discrete towerAll valid1 data. Multiple values from the same day and location are averaged. Only samples collected between 12-16 LST are considered.
ESRL observatories (BRW, SMO, SPO)All valid1 data. Day average using 12-16 LST.
ESRL observatories (MLO)All valid1 data. Day average using 0-4 LST.
ESRL tower sitesAll valid data from highest intake. Day average using 12-16 LST.
EC in situ sitesAll valid data from highest intake. Day average using 12-16 LST.
NCAR in situ sitesAll valid data from highest intake where 1σ of hourly average < 1 ppm. Day average using 0-4 LST.
CSIRO discrete surfaceAll valid1 data. Multiple values from the same day and location are averaged. No sample time-of-day restriction.
IPEN discrete surfaceAll valid1 data. Multiple values from the same day and location are averaged. No sample time-of-day restriction.
LBNL in situ siteAll valid data for the period 2003-2010. Day average using 14-18 LST.
1In this context "Valid Data" means the observation is thought to be free of sampling and analytical problems and has not been locally influenced.

We apply a further selection criterion during the assimilation to exclude non-marine boundary layer (MBL) observations that are very poorly forecasted in our framework. We use the so-called model-data mismatch in this process, which is the random error ascribed to each observation to account for measurement errors as well as modeling errors of that observation. We interpret an observed-minus-forecasted (OmF) mole fraction that exceeds 3 times the prescribed model-data mismatch as an indicator that our modeling framework fails. This can happen for instance when an air sample is representative of local exchange not captured well by our 1° x 1° fluxes, when local meteorological conditions are not captured by our offline transport fields, but also when large-scale CO2 exchange is suddenly changed (e.g. fires, pests, droughts) to an extent that can not be accommodated by our flux modules. This last situation would imply an important change in the carbon cycle and has to be recognized by the researchers when analyzing the results. In accordance with the 3-sigma rejection criterion, ~2% of the observations are discarded through this mechanism in our assimilations.

Table 2 (below) gives a summary of the observing sites used in CarbonTracker, and the performace of the assimilation scheme at each site. These diagnostics are useful for evaluating how well CarbonTracker does in simulating observed CO2.

Table 2. Summary of Observational Sites Used in CarbonTracker. Model-data-mismatch ("r") is a value assigned to a given site that is meant to quantify our expected ability to simulate observations there. This value is principally determined from the limitations of the atmospheric transport model. It is part of the standard deviation used to interpret the difference between a simulation first guess ("Hx") of an observation and the actual measured value ("z"). The other component, HPHT, is a measure of the ability of the ensemble Kalman filter to improve its simulated value for this observation by adjusting fluxes. These elements together form the innovation χ statistic for the site: χ = (z-Hx)/√(HPHT+r2). The innovation χ2 reported above is the mean of all squared χ values for a given site. An average χ2 below 1.0 indicates that the √(HPHT+r2) values are too large. Conversely, values above 1.0 mean that this standard deviation is underestimated. The bias and SE columns are statistics of the posterior residuals (final modeled values - measured values). The bias is the mean of these residuals; the SE is the standard error of those residuals.
Site code Lab. Location Latitude Longitude Elev. (m ASL) No. Obs. Avail. No. Obs. Used No. Obs. Rej. r (μmol mol-1) Innov. χ2 Bias (μmol mol-1) SE (μmol mol-1)
ABP_01D0 ESRL Arembepe, Bahia, Brazil 12.77°S 38.17°W 1 102 102 0 2.50 0.06 -0.50 0.53
ABP_26D0 IPEN Arembepe, Bahia, Brazil 12.77°S 38.17°W 1 101 101 0 2.50 0.11 -0.63 0.68
ALT_01D0 ESRL Alert, Nunavut, Canada 82.45°N 62.51°W 200 530 530 0 1.50 0.53 0.29 0.90
ALT_06C0_14LST EC Alert, Nunavut, Canada 82.45°N 62.51°W 200 3652 3652 0 2.50 0.23 0.29 0.99
AMT_01C3_14LST ESRL Argyle, Maine, United States 45.03°N 68.68°W 50 2272 2218 54 3.00 0.93 0.55 3.22
AMT_01P0 ESRL Argyle, Maine, United States 45.03°N 68.68°W 50 325 310 15 3.00 1.23 0.85 3.52
ASC_01D0 ESRL Ascension Island, United Kingdom 7.97°S 14.40°W 74 915 915 0 0.75 0.82 -0.01 0.58
ASK_01D0 ESRL Assekrem, Algeria 23.18°N 5.42°E 2728 480 480 0 1.50 0.34 0.13 0.92
AZR_01D0 ESRL Terceira Island, Azores, Portugal 38.77°N 27.38°W 40 333 329 4 1.50 1.11 0.62 1.46
BAL_01D0 ESRL Baltic Sea, Poland 55.35°N 17.22°E 3 929 929 0 7.50 0.26 -1.09 3.90
BAO_01C3_14LST ESRL Boulder Atmospheric Observatory, Colorado, United States 40.05°N 105.00°W 1584 964 952 12 3.00 1.00 -0.98 2.70
Site code Lab. Location Latitude Longitude Elev. (m ASL) No. Obs. Avail. No. Obs. Used No. Obs. Rej. r (μmol mol-1) Innov. χ2 Bias (μmol mol-1) SE (μmol mol-1)
BAO_01P0 ESRL Boulder Atmospheric Observatory, Colorado, United States 40.05°N 105.00°W 1584 720 694 26 3.00 1.36 -0.97 3.42
BHD_01D0 ESRL Baring Head Station, New Zealand 41.41°S 174.87°E 85 142 142 0 1.50 0.28 0.20 0.74
BKT_01D0 ESRL Bukit Kototabang, Indonesia 0.20°S 100.32°E 864 247 247 0 7.50 0.63 4.55 3.62
BME_01D0 ESRL St. Davids Head, Bermuda, United Kingdom 32.37°N 64.65°W 30 236 225 11 1.50 1.57 0.69 1.83
BMW_01D0 ESRL Tudor Hill, Bermuda, United Kingdom 32.27°N 64.88°W 30 347 344 3 1.50 0.87 0.59 1.28
BRW_01C0_14LST ESRL Barrow, Alaska, United States 71.32°N 156.61°W 11 2975 2973 2 2.50 0.23 0.07 1.04
BRW_01D0 ESRL Barrow, Alaska, United States 71.32°N 156.61°W 11 499 497 2 1.50 0.55 -0.01 1.05
BSC_01D0 ESRL Black Sea, Constanta, Romania 44.17°N 28.68°E 3 399 386 13 7.50 1.18 -5.28 7.32
CBA_01D0 ESRL Cold Bay, Alaska, United States 55.21°N 162.72°W 21 736 702 34 1.50 1.59 -0.15 1.83
CDL_06C0_14LST EC Candle Lake, Saskatchewan, Canada 53.99°N 105.12°W 600 2509 2494 15 3.00 0.59 0.24 2.15
CFA_02D0 CSIRO Cape Ferguson, Queensland, Australia 19.28°S 147.06°E 2 205 205 0 2.50 0.24 -0.44 1.09
Site code Lab. Location Latitude Longitude Elev. (m ASL) No. Obs. Avail. No. Obs. Used No. Obs. Rej. r (μmol mol-1) Innov. χ2 Bias (μmol mol-1) SE (μmol mol-1)
CGO_01D0 ESRL Cape Grim, Tasmania, Australia 40.68°S 144.69°E 94 404 404 0 0.75 0.16 0.07 0.28
CGO_02D0 CSIRO Cape Grim, Tasmania, Australia 40.68°S 144.69°E 94 404 404 0 0.75 0.16 0.03 0.27
CHR_01D0 ESRL Christmas Island, Republic of Kiribati 1.70°N 157.17°W 3 419 419 0 0.75 0.65 -0.38 0.47
CRZ_01D0 ESRL Crozet Island, France 46.45°S 51.85°E 120 402 402 0 0.75 0.19 0.01 0.27
CYA_02D0 CSIRO Casey, Antarctica, Australia 66.28°S 110.52°E 51 200 200 0 0.75 0.30 -0.21 0.27
EGB_06C0_14LST EC Egbert, Ontario, Canada 44.23°N 79.78°W 251 1959 1845 114 3.00 1.80 0.29 4.30
EIC_01D0 ESRL Easter Island, Chile 27.15°S 109.45°W 50 288 288 0 7.50 0.03 0.87 0.93
ETL_06C0_14LST EC East Trout Lake, Saskatchewan, Canada 54.35°N 104.98°W 492 1865 1857 8 3.00 0.57 0.13 2.01
FSD_06C0_14LST EC Fraserdale, Canada 49.88°N 81.57°W 210 3605 3579 26 3.00 0.56 0.19 2.57
GMI_01D0 ESRL Mariana Islands, Guam 13.43°N 144.78°E 3 723 723 0 1.50 0.37 -0.03 0.90
HBA_01D0 ESRL Halley Station, Antarctica, United Kingdom 75.58°S 26.50°W 30 486 486 0 0.75 0.15 -0.02 0.20
Site code Lab. Location Latitude Longitude Elev. (m ASL) No. Obs. Avail. No. Obs. Used No. Obs. Rej. r (μmol mol-1) Innov. χ2 Bias (μmol mol-1) SE (μmol mol-1)
HPB_01D0 ESRL Hohenpeissenberg, Germany 47.80°N 11.01°E 985 210 206 4 7.50 0.74 2.70 5.83
HUN_01D0 ESRL Hegyhatsal, Hungary 46.95°N 16.65°E 248 510 509 1 7.50 0.35 -0.12 4.37
ICE_01D0 ESRL Storhofdi, Vestmannaeyjar, Iceland 63.40°N 20.29°W 118 486 482 4 1.50 0.55 -0.02 1.07
KEY_01D0 ESRL Key Biscayne, Florida, United States 25.67°N 80.16°W 3 347 346 1 2.50 0.26 0.20 1.40
KUM_01D0 ESRL Cape Kumukahi, Hawaii, United States 19.52°N 154.82°W 3 638 638 0 1.50 0.34 -0.02 0.95
KZD_01D0 ESRL Sary Taukum, Kazakhstan 44.06°N 76.82°E 601 441 438 3 2.50 0.63 0.49 3.21
KZM_01D0 ESRL Plateau Assy, Kazakhstan 43.25°N 77.88°E 2519 393 388 5 2.50 0.94 0.55 2.28
LEF_01C3_14LST ESRL Park Falls, Wisconsin, United States 45.95°N 90.27°W 472 3489 3412 77 3.00 0.87 0.25 2.85
LEF_01P0 ESRL Park Falls, Wisconsin, United States 45.95°N 90.27°W 472 1350 1296 54 3.00 1.28 0.39 3.29
LLB_06C0_14LST EC Lac La Biche, Alberta, Canada 54.95°N 112.45°W 540 1225 1172 53 3.00 1.66 0.19 3.76
LMP_01D0 ESRL Lampedusa, Italy 35.52°N 12.62°E 45 200 193 7 1.50 1.38 0.64 1.45
Site code Lab. Location Latitude Longitude Elev. (m ASL) No. Obs. Avail. No. Obs. Used No. Obs. Rej. r (μmol mol-1) Innov. χ2 Bias (μmol mol-1) SE (μmol mol-1)
MAA_02D0 CSIRO Mawson Station, Antarctica, Australia 67.62°S 62.87°E 32 206 206 0 0.75 0.26 -0.17 0.26
MHD_01D0 ESRL Mace Head, County Galway, Ireland 53.33°N 9.90°W 5 407 407 0 2.50 0.18 0.09 1.06
MID_01D0 ESRL Sand Island, Midway, United States 28.21°N 177.38°W 4 497 496 1 1.50 0.61 0.52 1.12
MKN_01D0 ESRL Mt. Kenya, Kenya 0.05°S 37.30°E 3897 134 134 0 2.50 1.12 1.85 1.89
MLO_01C0_02LST ESRL Mauna Loa, Hawaii, United States 19.54°N 155.58°W 3397 3342 3342 0 0.75 0.76 0.18 0.63
MLO_01D0 ESRL Mauna Loa, Hawaii, United States 19.54°N 155.58°W 3397 566 566 0 1.50 0.22 0.13 0.68
MQA_02D0 CSIRO Macquarie Island, Australia 54.48°S 158.97°E 12 265 265 0 0.75 0.28 0.05 0.33
NMB_01D0 ESRL Gobabeb, Namibia 23.58°S 15.03°E 456 161 161 0 2.50 0.14 0.04 0.91
NWR_01D0 ESRL Niwot Ridge, Colorado, United States 40.05°N 105.58°W 3523 495 491 4 1.50 0.66 0.40 1.38
NWR_03C0_02LST NCAR Niwot Ridge, Colorado, United States 40.05°N 105.58°W 3523 1550 1549 1 3.00 0.25 -0.36 1.32
OBN_01D0 ESRL Obninsk, Russia 55.11°N 36.60°E 183 155 151 4 7.50 0.97 -1.16 8.26
Site code Lab. Location Latitude Longitude Elev. (m ASL) No. Obs. Avail. No. Obs. Used No. Obs. Rej. r (μmol mol-1) Innov. χ2 Bias (μmol mol-1) SE (μmol mol-1)
OXK_01D0 ESRL Ochsenkopf, Germany 50.03°N 11.80°E 1022 163 148 15 2.50 2.09 -0.31 3.62
PAL_01D0 ESRL Pallas-Sammaltunturi, GAW Station, Finland 67.97°N 24.12°E 560 373 372 1 2.50 0.56 -0.12 1.89
POC_01D1 ESRL Pacific Ocean, N/A 0.39°S 132.32°W 10 2043 2042 1 0.75 0.78 -0.01 0.63
PSA_01D0 ESRL Palmer Station, Antarctica, United States 64.92°S 64.00°W 10 529 529 0 0.75 0.26 -0.09 0.27
PTA_01D0 ESRL Point Arena, California, United States 38.95°N 123.74°W 17 381 381 0 7.50 0.43 -2.75 4.06
RPB_01D0 ESRL Ragged Point, Barbados 13.17°N 59.43°W 45 499 499 0 1.50 0.47 0.21 1.09
SCT_01C3_14LST ESRL Beech Island, South Carolina, United States 33.41°N 81.83°W 115 675 667 8 3.00 1.00 0.08 2.94
SEY_01D0 ESRL Mahe Island, Seychelles 4.67°S 55.17°E 3 481 481 0 0.75 1.07 0.06 0.72
SGP_01D0 ESRL Southern Great Plains, Oklahoma, United States 36.80°N 97.50°W 314 407 388 19 2.50 1.42 -0.54 3.06
SGP_64C3_16LST LBNL Southern Great Plains, Oklahoma, United States 36.80°N 97.50°W 314 2625 2565 60 3.00 1.08 0.07 3.23
SHM_01D0 ESRL Shemya Island, Alaska, United States 52.72°N 174.10°E 40 383 383 0 2.50 0.72 -0.03 2.01
Site code Lab. Location Latitude Longitude Elev. (m ASL) No. Obs. Avail. No. Obs. Used No. Obs. Rej. r (μmol mol-1) Innov. χ2 Bias (μmol mol-1) SE (μmol mol-1)
SIS_02D0 CSIRO Shetland Islands, Scotland 60.17°N 1.17°W 30 88 88 0 2.50 0.41 0.74 1.31
SMO_01C0_14LST ESRL Tutuila, American Samoa 14.25°S 170.56°W 42 3446 3446 0 0.75 0.49 0.16 0.50
SMO_01D0 ESRL Tutuila, American Samoa 14.25°S 170.56°W 42 559 559 0 1.50 0.12 0.10 0.52
SNP_01C3_02LST ESRL Shenandoah National Park, United States 38.62°N 78.35°W 1008 716 696 20 3.00 1.13 -0.40 3.14
SPL_03C0_02LST NCAR Storm Peak Laboratory (Desert Research Institute), United States 40.45°N 106.73°W 3210 1543 1540 3 3.00 0.44 -0.52 1.75
SPO_01C0_14LST ESRL South Pole, Antarctica, United States 89.98°S 24.80°W 2810 3882 3882 0 0.75 0.09 0.03 0.19
SPO_01D0 ESRL South Pole, Antarctica, United States 89.98°S 24.80°W 2810 533 533 0 1.50 0.02 0.09 0.20
STM_01D0 ESRL Ocean Station M, Norway 66.00°N 2.00°E 0 850 847 3 1.50 0.55 0.18 1.06
STR_01P0 ESRL Sutro Tower, San Francisco, California, United States 37.76°N 122.45°W 254 642 632 10 3.00 0.64 0.08 2.55
SUM_01D0 ESRL Summit, Greenland 72.58°N 38.48°W 3238 430 430 0 1.50 0.43 0.32 0.90
SYO_01D0 ESRL Syowa Station, Antarctica, Japan 69.00°S 39.58°E 11 255 255 0 0.75 0.22 -0.14 0.24
Site code Lab. Location Latitude Longitude Elev. (m ASL) No. Obs. Avail. No. Obs. Used No. Obs. Rej. r (μmol mol-1) Innov. χ2 Bias (μmol mol-1) SE (μmol mol-1)
TAP_01D0 ESRL Tae-ahn Peninsula, Republic of Korea 36.73°N 126.13°E 20 383 383 0 7.50 0.40 0.60 4.33
TDF_01D0 ESRL Tierra Del Fuego, Ushuaia, Argentina 54.87°S 68.48°W 20 192 192 0 0.75 0.44 -0.19 0.40
THD_01D0 ESRL Trinidad Head, California, United States 41.05°N 124.15°W 107 369 324 45 2.50 3.25 -2.39 3.83
UTA_01D0 ESRL Wendover, Utah, United States 39.90°N 113.72°W 1320 472 471 1 2.50 0.39 0.45 1.82
UUM_01D0 ESRL Ulaan Uul, Mongolia 44.45°N 111.10°E 914 509 501 8 2.50 0.81 -0.21 2.60
WBI_01C3_14LST ESRL West Branch, Iowa, United States 41.72°N 91.35°W 242 1197 1134 63 3.00 1.81 0.37 3.77
WBI_01P0 ESRL West Branch, Iowa, United States 41.72°N 91.35°W 242 862 795 67 3.00 2.07 0.22 4.18
WGC_01C3_14LST ESRL Walnut Grove, California, United States 38.27°N 121.49°W 0 1091 1021 70 3.00 1.68 -0.10 4.29
WGC_01P0 ESRL Walnut Grove, California, United States 38.27°N 121.49°W 0 891 748 143 3.00 3.67 -0.67 6.51
WIS_01D0 ESRL WIS Station, Negev Desert, Israel 31.13°N 34.88°E 400 540 537 3 2.50 0.61 0.03 1.94
WKT_01C3_14LST ESRL Moody, Texas, United States 31.31°N 97.33°W 251 2117 2100 17 3.00 0.65 0.14 2.29
Site code Lab. Location Latitude Longitude Elev. (m ASL) No. Obs. Avail. No. Obs. Used No. Obs. Rej. r (μmol mol-1) Innov. χ2 Bias (μmol mol-1) SE (μmol mol-1)
WKT_01P0 ESRL Moody, Texas, United States 31.31°N 97.33°W 251 993 979 14 3.00 0.94 -0.10 2.85
WLG_01D0 ESRL Mt. Waliguan, Peoples Republic of China 36.29°N 100.90°E 3810 427 413 14 1.50 1.12 0.13 1.91
WSA_06C0_14LST EC Sable Island, Nova Scotia, Canada 49.93°N 60.02°W 5 2358 2259 99 3.00 1.17 0.17 4.12
ZEP_01D0 ESRL Ny-Alesund, Svalbard, Norway and Sweden 78.90°N 11.88°E 475 568 566 2 1.50 0.96 0.55 1.22
All-site summary - - - 85153 83910 1243 - 0.73 0.06 2.70