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 and the CSIRO Air Sampling Network available for each year studied, 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 six towers: (1) the 396m level of the LEF tower in Wisconsin; (2) the 107m level of the AMT tower in Argyle, Maine; (3) the 251m level of the WKT tower in Texas; (4) the 40m level of the tower in Fraserdale, Canada (FRD) operated by Environment Canada (EC); (5) the 30m level of the tower at Candle Lake (CDL, formerly Old Black Spruce), Canada operated by EC; and (6) the 60m level of the tower at the Atmospheric Radiation and Monitoring (ARM) program Southern Great Plains, Oklahoma site (SGP). 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-2005). 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. 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 Program | Data Preprocessing
| | ESRL discrete surface | All retained data. Multiple values from the same day and location are averaged. No sample time-of-day restriction. |
| ESRL observatories (BRW, SMO, SPO) | All baseline data. Day average using 12-16 LST. |
| ESRL observatories (MLO) | All baseline data. Day average using 00-04 LST. |
| ESRL tower sites | All valid data from highest intake. Day average using 12-16 LST. |
| EC in situ sites | All valid data from highest intake. Day average using 12-16 LST. |
| NCAR in situ sites | All valid data from highest intake where 1σ of hourly average < 1 ppm. Day average using 0-4 LST. |
| CSIRO discrete surface | All retained data. Multiple values from the same day and location are averaged. No sample time-of-day restriction. |
| LBNL in situ sites | All valid data for the period 2003-2004. Day average using 14-18 LST. |
| CarboEurope discrete surface | All retained data. Multiple values from the same day and location are averaged. No sample time-of-day restriction. |
| CarboEurope tower sites | All valid data from highest intake. Day average using 12-16 LST |
| CarboEurope altitude sites (SCH, CMN, PUY, PRS) | All valid data from highest intake. Night average using 00-04 LST |
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 1x1 degree 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 gives a summary of the observing sites used in CarbonTracker and the assimilation performance. 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 is a statistic of the posterior residuals (final modeled values - measured values). The bias is the mean of these residuals.
Table 2: Summary of observing sites used in CarbonTracker and assimilation performance.
| Site code | Lab. | Location | Lat, Lon, Elev. (m ASL) | No. Obs. Avail. | No. Obs. Used | No. Obs. Rej. | r (μmol mol-1) | Innov. χ2 | Bias (μmol mol-1) |
| ALT_01D0 | ESRL | Alert, Nunavut, Canada | 82 27'N, 62 31'W, 200.0m | 328 | 328 | 0 | +1.50 | +0.43 | +0.34 |
| ALT_06C0 | EC | Alert, Nunavut, Canada | 82 27'N, 62 31'W, 200.0m | 2213 | 2213 | 0 | +2.50 | +0.22 | +0.39 |
| AMT_01C3 | ESRL | Argyle, Maine, United States | 45 2'N, 68 41'W, 50.0m | 1323 | 1279 | 44 | +3.00 | +1.16 | +0.93 |
| ASC_01D0 | ESRL | Ascension Island, United Kingdom | 7 55'S, 14 25'W, 54.0m | 589 | 589 | 0 | +0.75 | +0.95 | -0.24 |
| ASK_01D0 | ESRL | Assekrem, Algeria | 23 11'N, 5 25'E, 2728.0m | 309 | 309 | 0 | +1.50 | +0.40 | +0.22 |
| AZR_01D0 | ESRL | Terceira Island, Azores, Portugal | 38 46'N, 27 23'W, 40.0m | 213 | 210 | 3 | +1.50 | +1.04 | +0.51 |
| BAL_01D0 | ESRL | Baltic Sea, Poland | 55 21'N, 17 13'E, 3.0m | 555 | 555 | 0 | +7.50 | +0.34 | -0.85 |
| BGU_11D0 | LSCE | Begur, Spain | 41 50'N, 3 20'E, 30.0m | 219 | 204 | 15 | +2.50 | +1.34 | +0.58 |
| BIK0300_45C9 | MPI-BGC | Bialystok, Poland | 53 13'N, 23 1'E, 180.0m | 434 | 428 | 6 | +3.00 | +1.09 | +1.19 |
| BKT_01D0 | ESRL | Bukit Kototabang, Indonesia | 0 12'S, 100 19'E, 864.5m | 139 | 139 | 0 | +7.50 | +0.75 | +5.42 |
| Site code | Lab. | Location | Lat, Lon, Elev. (m ASL) | No. Obs. Avail. | No. Obs. Used | No. Obs. Rej. | r (μmol mol-1) | Innov. χ2 | Bias (μmol mol-1) |
| BME_01D0 | ESRL | St. Davids Head, Bermuda, United Kingdom | 32 22'N, 64 39'W, 30.0m | 180 | 170 | 10 | +1.50 | +1.28 | +0.60 |
| BMW_01D0 | ESRL | Tudor Hill, Bermuda, United Kingdom | 32 16'N, 64 53'W, 30.0m | 212 | 210 | 2 | +1.50 | +1.10 | +0.46 |
| BRW_01C0 | ESRL | Barrow, Alaska, United States | 71 19'N, 156 36'W, 11.0m | 1913 | 1912 | 1 | +2.50 | +0.31 | +0.62 |
| BRW_01D0 | ESRL | Barrow, Alaska, United States | 71 19'N, 156 36'W, 11.0m | 315 | 314 | 1 | +1.50 | +0.77 | +0.62 |
| BSC_01D0 | ESRL | Black Sea, Constanta, Romania | 44 10'N, 28 41'E, 3.0m | 246 | 243 | 3 | +7.50 | +1.04 | -3.23 |
| BZH_11D0 | LSCE | Portsall, France | 48 35'N, 4 40'W, 20.0m | 4 | 4 | 0 | +2.50 | +0.27 | -0.43 |
| CBA_01D0 | ESRL | Cold Bay, Alaska, United States | 55 12'N, 162 43'W, 25.0m | 598 | 563 | 35 | +1.50 | +1.27 | -0.21 |
| CBW0200_52C3 | ECN | Cabauw, Netherlands | 51 58'N, 4 55'E, 20.0m | 1536 | 1517 | 19 | +7.50 | +0.71 | -0.52 |
| CDL_06C3 | EC | Candle Lake, Saskatchewan, Canada | 53 59'N, 105 7'W, 628.0m | 1698 | 1688 | 10 | +3.00 | +0.84 | +1.35 |
| CGO_01D0 | ESRL | Cape Grim, Tasmania, Australia | 40 41'S, 144 41'E, 94.0m | 269 | 269 | 0 | +1.50 | +0.07 | -0.18 |
| Site code | Lab. | Location | Lat, Lon, Elev. (m ASL) | No. Obs. Avail. | No. Obs. Used | No. Obs. Rej. | r (μmol mol-1) | Innov. χ2 | Bias (μmol mol-1) |
| CHR_01D0 | ESRL | Christmas Island, Republic of Kiribati | 1 42'N, 157 10'W, 3.0m | 270 | 270 | 0 | +0.75 | +1.57 | -0.80 |
| CMN_17C0 | IMS | Mt. Cimone Station, Italy | 44 11'N, 10 42'E, 2165.0m | 1469 | 1463 | 6 | +3.00 | +0.67 | +0.60 |
| CRZ_01D0 | ESRL | Crozet Island, France | 46 27'S, 51 51'E, 120.0m | 245 | 245 | 0 | +0.75 | +0.29 | -0.24 |
| EIC_01D0 | ESRL | Easter Island, Chile | 27 9'S, 109 27'W, 50.0m | 151 | 151 | 0 | +7.50 | +0.02 | +0.60 |
| FIK_11D0 | LSCE | Finokalia, Greece | 35 19'N, 25 40'E, 130.0m | 24 | 22 | 2 | +1.50 | +2.04 | +0.28 |
| FRD_06C3 | EC | Fraserdale, Canada | 49 53'N, 81 34'W, 210.0m | 2230 | 2193 | 37 | +3.00 | +0.79 | +0.47 |
| GMI_01D0 | ESRL | Mariana Islands, Guam | 13 26'N, 144 47'E, 1.0m | 475 | 475 | 0 | +1.50 | +0.37 | -0.05 |
| HBA_01D0 | ESRL | Halley Station, Antarctica, United Kingdom | 75 35'S, 26 30'W, 30.0m | 317 | 317 | 0 | +0.75 | +0.26 | -0.32 |
| HUN0115_35C3 | HMS | Hegyhatsal, Hungary | 46 57'N, 16 39'E, 248.0m | 1797 | 1722 | 75 | +3.00 | +1.39 | +0.15 |
| HUN_01D0 | ESRL | Hegyhatsal, Hungary | 46 57'N, 16 39'E, 248.0m | 314 | 313 | 1 | +7.50 | +0.41 | +0.45 |
| Site code | Lab. | Location | Lat, Lon, Elev. (m ASL) | No. Obs. Avail. | No. Obs. Used | No. Obs. Rej. | r (μmol mol-1) | Innov. χ2 | Bias (μmol mol-1) |
| ICE_01D0 | ESRL | Storhofdi, Vestmannaeyjar, Iceland | 63 20'N, 20 17'W, 118.0m | 307 | 306 | 1 | +1.50 | +0.38 | +0.08 |
| IZO_01D0 | ESRL | Tenerife, Canary Islands, Spain | 28 18'N, 16 29'W, 2360.0m | 254 | 253 | 1 | +1.50 | +1.31 | +1.18 |
| JFJ_49D0 | UB | Jungfraujoch, Switzerland | 46 33'N, 7 59'E, 3580.0m | 154 | 144 | 10 | +1.50 | +1.27 | -0.00 |
| KAS_53C0 | UKRAK/AGH | Kasprowy Wierch, Poland | 49 13'N, 19 59'E, 1987.0m | 1526 | 1515 | 11 | +7.50 | +0.66 | +0.07 |
| KEY_01D0 | ESRL | Key Biscayne, Florida, United States | 25 40'N, 80 12'W, 3.0m | 214 | 214 | 0 | +2.50 | +0.33 | -0.06 |
| KUM_01D0 | ESRL | Cape Kumukahi, Hawaii, United States | 19 31'N, 154 49'W, 3.0m | 303 | 303 | 0 | +1.50 | +0.41 | +0.11 |
| KZD_01D0 | ESRL | Sary Taukum, Kazakhstan | 44 27'N, 75 34'E, 412.0m | 315 | 313 | 2 | +2.50 | +1.34 | +2.70 |
| KZM_01D0 | ESRL | Plateau Assy, Kazakhstan | 43 15'N, 77 53'E, 2519.0m | 278 | 277 | 1 | +2.50 | +1.22 | +0.49 |
| LMP_28D0 | ENEA | Lampedusa, Italy | 35 31'N, 12 37'E, 70.0m | 221 | 220 | 1 | +2.50 | +0.88 | -0.61 |
| LMP_28C9 | ENEA | Lampedusa, Italy | 35 31'N, 12 37'E, 70.0m | 637 | 626 | 11 | +3.00 | +0.89 | -0.54 |
| Site code | Lab. | Location | Lat, Lon, Elev. (m ASL) | No. Obs. Avail. | No. Obs. Used | No. Obs. Rej. | r (μmol mol-1) | Innov. χ2 | Bias (μmol mol-1) |
| LEF_01C3 | ESRL | Park Falls, Wisconsin, United States | 45 56'N, 90 16'W, 472.0m | 2123 | 2089 | 34 | +3.00 | +0.98 | +0.70 |
| LMU0079_47C3 | BU | La Muela, Spain | 41 35'N, 1 50'E, 611.0m | 364 | 362 | 2 | +3.00 | +1.23 | +0.89 |
| LPO_11D0 | LSCE | Ile Grande, France | 48 35'N, 3 35'E, 20.0m | 90 | 85 | 5 | +2.50 | +1.43 | +0.99 |
| LUT0060_44C3 | CIO-RUG | Lutjewad, Netherlands | 53 21'N, 6 20'E, 60.0m | 644 | 595 | 49 | +3.00 | +1.17 | -0.35 |
| MHD_01D0 | ESRL | Mace Head, Ireland | 53 19'N, 9 53'W, 25.0m | 252 | 251 | 1 | +2.50 | +0.24 | +0.20 |
| MHD_11C0 | LSCE | Mace Head, Ireland | 53 19'N, 9 53'W, 25.0m | 2045 | 2011 | 34 | +3.00 | +0.41 | +0.04 |
| MID_01D0 | ESRL | Sand Island, Midway, United States | 28 13'N, 177 23'W, 3.7m | 310 | 309 | 1 | +1.50 | +0.75 | +0.59 |
| MKN_01D0 | ESRL | Mt. Kenya, Kenya | 0 3'S, 37 18'E, 3897.0m | 75 | 75 | 0 | +2.50 | +1.09 | +1.77 |
| MLO_01C0 | ESRL | Mauna Loa, Hawaii, United States | 19 32'N, 155 35'W, 3397.0m | 1038 | 1038 | 0 | +0.75 | +0.65 | +0.16 |
| MLO_01D0 | ESRL | Mauna Loa, Hawaii, United States | 19 32'N, 155 35'W, 3397.0m | 361 | 361 | 0 | +1.50 | +0.24 | +0.09 |
| Site code | Lab. | Location | Lat, Lon, Elev. (m ASL) | No. Obs. Avail. | No. Obs. Used | No. Obs. Rej. | r (μmol mol-1) | Innov. χ2 | Bias (μmol mol-1) |
| NMB_01D0 | ESRL | Gobabeb, Namibia | 23 35'S, 15 2'E, 456.0m | 34 | 34 | 0 | +2.50 | +0.18 | -0.35 |
| NWR_01D0 | ESRL | Niwot Ridge, Colorado, United States | 40 3'N, 105 35'W, 3523.0m | 305 | 303 | 2 | +1.50 | +0.92 | +0.44 |
| NWR_03C3 | NCAR | Niwot Ridge, Colorado, United States | 40 3'N, 105 35'W, 3523.0m | 648 | 648 | 0 | +3.00 | +0.26 | -0.34 |
| OBN_01D0 | ESRL | Obninsk, Russia | 55 7'N, 36 36'E, 183.0m | 107 | 106 | 1 | +7.50 | +0.57 | +1.59 |
| OXK_01D0 | ESRL | Ochsenkopf, Germany | 50 4'N, 11 48'E, 1193.0m | 80 | 71 | 9 | +2.50 | +1.31 | +0.34 |
| PAL_01D0 | ESRL | Pallas-Sammaltunturi, GAW Station, Finland | 67 58'N, 24 7'E, 560.0m | 235 | 232 | 3 | +2.50 | +0.69 | +0.53 |
| PAL_30C0 | FMI | Pallas-Sammaltunturi, GAW Station, Finland | 67 58'N, 24 7'E, 560.0m | 2424 | 2422 | 2 | +3.00 | +0.45 | +0.65 |
| PDM_11D0 | LSCE | Pic du Midi, France | 43 4'N, 0 9'E, 2877.0m | 171 | 160 | 11 | +1.50 | +0.90 | -0.03 |
| POC_01D1 | ESRL | Pacific Ocean, N/A | 99 59'S, 999 59'W, 10.0m | 1599 | 1599 | 0 | +7.50 | +0.03 | -0.02 |
| PRS_21C0 | CESI RICE | Plateau Rosa, Italy | 45 56'N, 7 42'E, 3480.0m | 1708 | 1704 | 4 | +3.00 | +0.35 | +0.50 |
| Site code | Lab. | Location | Lat, Lon, Elev. (m ASL) | No. Obs. Avail. | No. Obs. Used | No. Obs. Rej. | r (μmol mol-1) | Innov. χ2 | Bias (μmol mol-1) |
| PSA_01D0 | ESRL | Palmer Station, Antarctica, United States | 64 55'S, 64 0'W, 10.0m | 326 | 326 | 0 | +0.75 | +0.53 | -0.47 |
| PTA_01D0 | ESRL | Point Arena, California, United States | 38 57'N, 123 44'W, 17.0m | 233 | 233 | 0 | +7.50 | +0.32 | -1.63 |
| PUY_11C0 | LSCE | Puy de Dome, France | 45 45'N, 3 0'E, 1465.0m | 1542 | 1517 | 25 | +3.00 | +1.02 | +0.46 |
| RPB_01D0 | ESRL | Ragged Point, Barbados | 13 10'N, 59 26'W, 45.0m | 325 | 325 | 0 | +1.50 | +0.63 | +0.09 |
| SBL_06C3 | EC | Sable Island, Nova Scotia, Canada | 43 56'N, 60 1'W, 5.0m | 1477 | 1456 | 21 | +3.00 | +0.64 | -0.06 |
| SCH_23C0 | UBA/UHEI- | Schauinsland, Germany | 47 55'N, 7 55'E, 1205.0m | 2090 | 2061 | 29 | +3.00 | +0.86 | -0.40 |
| SEY_01D0 | ESRL | Mahe Island, Seychelles | 4 40'S, 55 10'E, 3.0m | 309 | 309 | 0 | +0.75 | +1.02 | -0.18 |
| SGP_01D0 | ESRL | Southern Great Plains, Oklahoma, United States | 36 48'N, 97 30'W, 314.0m | 574 | 554 | 20 | +2.50 | +1.20 | +0.87 |
| SHM_01D0 | ESRL | Shemya Island, Alaska, United States | 52 43'N, 174 6'E, 40.0m | 245 | 243 | 2 | +2.50 | +0.87 | +0.29 |
| SIS_02D0 | CSIRO | Shetland Islands, Scotland | 60 17'N, 1 17'W, 30.0m | 189 | 184 | 5 | +1.50 | +1.14 | +0.58 |
| Site code | Lab. | Location | Lat, Lon, Elev. (m ASL) | No. Obs. Avail. | No. Obs. Used | No. Obs. Rej. | r (μmol mol-1) | Innov. χ2 | Bias (μmol mol-1) |
| SMO_01C0 | ESRL | Tutuila, American Samoa | 14 14'S, 170 34'W, 42.0m | 2243 | 2243 | 0 | +0.75 | +0.66 | -0.14 |
| SMO_01D0 | ESRL | Tutuila, American Samoa | 14 14'S, 170 34'W, 42.0m | 364 | 364 | 0 | +1.50 | +0.15 | -0.17 |
| SPL_03C3 | NCAR | Storm Peak Lab, United States | 40 27'N, 106 44'W, 3210.0m | 714 | 714 | 0 | +3.00 | +0.45 | -0.97 |
| SPO_01C0 | ESRL | South Pole, Antarctica, United States | 89 59'S, 24 48'W, 2810.0m | 2384 | 2384 | 0 | +0.75 | +0.23 | -0.24 |
| SPO_01D0 | ESRL | South Pole, Antarctica, United States | 89 59'S, 24 48'W, 2810.0m | 337 | 337 | 0 | +1.50 | +0.04 | -0.17 |
| STM_01D0 | ESRL | Ocean Station M, Norway | 66 0'N, 2 0'E, 0.0m | 587 | 587 | 0 | +1.50 | +0.64 | +0.44 |
| SUM_01D0 | ESRL | Summit, Greenland | 72 35'N, 38 29'W, 3238.0m | 258 | 258 | 0 | +1.50 | +0.52 | +0.45 |
| SYO_01D0 | ESRL | Syowa Station, Antarctica, Japan | 69 0'S, 39 35'E, 11.0m | 162 | 162 | 0 | +0.75 | +0.47 | -0.48 |
| TAP_01D0 | ESRL | Tae-ahn Peninsula, Republic of Korea | 36 44'N, 126 8'E, 20.0m | 235 | 233 | 2 | +7.50 | +0.67 | +2.41 |
| TDF_01D0 | ESRL | Tierra Del Fuego, Ushuaia, Argentina | 54 52'S, 68 29'W, 20.0m | 83 | 83 | 0 | +0.75 | +0.45 | -0.28 |
| Site code | Lab. | Location | Lat, Lon, Elev. (m ASL) | No. Obs. Avail. | No. Obs. Used | No. Obs. Rej. | r (μmol mol-1) | Innov. χ2 | Bias (μmol mol-1) |
| THD_01D0 | ESRL | Trinidad Head, California, United States | 41 3'N, 124 9'W, 107.0m | 232 | 200 | 32 | +2.50 | +1.36 | -1.40 |
| UTA_01D0 | ESRL | Wendover, Utah, United States | 39 54'N, 113 43'W, 1320.0m | 293 | 293 | 0 | +2.50 | +1.01 | +2.01 |
| UUM_01D0 | ESRL | Ulaan Uul, Mongolia | 44 27'N, 111 6'E, 914.0m | 320 | 317 | 3 | +2.50 | +0.89 | +0.21 |
| WES_23C0 | UBA/UHEI- | Westerland, Germany | 54 56'N, 8 0'E, 12.0m | 774 | 774 | 0 | +7.50 | +0.42 | -0.22 |
| WIS_01D0 | ESRL | Sede Boker, Negev Desert, Israel | 31 8'N, 34 53'E, 400.0m | 336 | 336 | 0 | +2.50 | +0.76 | +0.58 |
| WKT_01C3 | ESRL | Moody, Texas, United States | 31 19'N, 97 20'W, 251.0m | 1169 | 1159 | 10 | +3.00 | +0.85 | +0.50 |
| WLG_01D0 | ESRL | Mt. Waliguan, Peoples Republic of China | 36 17'N, 100 54'E, 3810.0m | 229 | 222 | 7 | +1.50 | +1.15 | -0.01 |
| ZEP_01D0 | ESRL | Ny-Alesund, Svalbard, Norway and Sweden | 78 54'N, 11 53'E, 475.0m | 351 | 350 | 1 | +1.50 | +0.81 | +0.89 |
| ZEP_31C0 | ITM | Ny-Alesund, Svalbard, Norway and Sweden | 78 54'N, 11 53'E, 475.0m | 1231 | 1231 | 0 | +2.50 | +0.32 | +0.83 |
| All | | Weigthed sum of all observations | | 59019 | 58396 | 623 | | +0.66 | +0.25 |
3. Further Reading
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