The GLOBALVIEW-CO2, 2013 product includes a single extended data file per data record. Each file includes the extended record, the suggested relative weights assigned to each value, the reference marine boundary layer time series at the latitude of the sampling location, and extensive metadata. The Reference Marine Boundary Layer matrix, which was provided in previous releases, is no longer available. Instead, NOAA has made a more comprehensive MBL reference product available at http://www.esrl.noaa.gov/gmd/ccgg/mbl/. Statistical summaries of key features in the observations are also no longer provided. Data files are presented using the new Observation Package (ObsPack) framework. Click here to learn more about ObsPack data products including GLOBALVIEW-CO2, 2013.
EXTENDED RECORDS
The extended record file names have changed from previous updates. The new file name structure is described here.
Extended records include extensive sampling site, measurement laboratory, and data provider information. Each item in the extended record includes
- [year month day] "Weekly" synchronized time steps in Universal Coordinated Time (UTC). Each year has 48 "weekly" steps. "Synchronized" means that the synchronization period and the time steps are the same for all extended record files.
- [gv_sc] Smoothed values, S(t), extracted from a curve fitted to measurement data that have been selected for conditions where the sampled air is thought to be representative of large well-mixed air parcels. Internal and external gaps in the measurement record are denoted as default values.
- [gv_ref] The latitude reference time-series, based on marine boundary layer sites, constructed at the sine (latitude) of the measurement site. The latitude reference is defined at all time steps.
- [gv_diff] The difference climatology describes how the site differs from marine boundary layer (MBL) sites that are nearby in latitude. The difference climatology is defined at all time steps.
- [gv_wt] Scaled weights determined using the relative weighting scheme described by Masarie and Tans, [1995]. Suggest weights are computed using annual statistics. If insufficient measurements exist, suggested weights cannot be determined and are assigned a default minimum weight of one (1).
- [gv_wt_rsd] Residual standard deviation (RSD) of the measurements about the smooth curve, S(t), with annual resolution. Years with fewer than six (6) measurements are assigned default values.
- [gv_wt_num] The number of residuals per year used in the RSD determination.
The length of the files depends on the number of years in the synchronization period.
USING EXTENDED RECORDS
- Extended records are comprised of smoothed values, and interpolated and extrapolated values defined at each time step of the synchronization period. Those who wish to use extended records in their modeling application must simply add the reference MBL vector (gv_ref) to the difference climatology (gv_diff), i.e., extended record = REF + diff. Users will notice that S(t) = REF + diff wherever smoothed values (gv_sc) exist.
- You may also choose to use only the smoothed values (gv_sc) from the sites that are synchronized which will have assigned default values where there are no measurements.
USING RELATIVE WEIGHTS
- Any method used to fill spatial and temporal gaps in observational records is forced to make assumptions creating uncertainty in the resulting data product. Each extended value has an associated suggested relative weight that indicates the relative significance of each value in the extended file. All smooth values (derived directly from the actual measurements) receive a relative weight (ranging from 2 to 10) that depends on sampling density and measurement variability. All filled values (interpolated and extrapolated) receive a fixed weight of 1.
- We strongly encourage users of this data product to consider the suggested relative weights, which provide an estimate of the relative significance of each value in the extended record.
EXTENDED RECORD CAVEATS
- Occasional discontinuities at the transition between smoothed values and extrapolated values may be significant in certain modeling applications. These occur when values derived from data extension techniques (based on average behavior) join actual measurements that depart from average behavior. Discontinuities may occur at either end of the smoothed measurement record.
- Discontinuities within periods of interpolated or extrapolated values may occur when MBL measurement records begin, end, or are interrupted for long periods of time. Some discontinuities may be significant in certain modeling applications. Serious discontinuities are identified below.
- The data extension procedure requires at least 2 years of observations.
| Time step | Latitude1 | Cause |
|---|---|---|
| 1979.666667 | 10°S | ESRL sampling program at Ascension Island begins |
| 1981.062500 | 35°S | LSCE sampling program at Amsterdam Island begins |
| 1984.208333 | 5°N | ESRL sampling program at Christmas Island, Kiribati begins |
| 1987.000000 | 25°S | ESRL shipboard sampling in Pacific Ocean begins |
| 1991.229167 | 45°S | ESRL sampling program at Crozet begins |
| 2000.812500 | 20°S | ESRL shipboard sampling in Pacific Ocean suspended |
| 2001.958333 | 41°S | NIWA data from Baring Head, New Zealand become unavailable |