#Gridded circle series

Additional geographic information also informed our interpolations. Shepard’s (1968) spatial-interpolation algorithm, modified for use over Earth’s near-spherical surface (Willmott et al., 1985), was employed to interpolate station records to each grid node. A small number of station records, obtained through personal communication, are also included (see the attached graphs of the overall number of available T and P station records each year). The gridded estimates are based primarily on observation-station records that were compiled, for the most part, from several publicly available sources such as the Global Historical Climatology Network dataset ( GHCN2) (Peterson and Vose, 1997), the Global Historical Climatology Network Monthly (GHCNM) Version 3 (GHCN3) dataset (Lawrimore et al., 2011), the Daily Global Historical Climatology Network (GHCN-Daily) archive (Menne et al., 2012), and the Global Surface Summary of Day (GSOD). The time-period covered in Version 4.01 is from 1900 through 2014. Like most previous versions of our gridded climate data sets, this data set (Version 4.01) provides point estimates of monthly average air temperature ( T, oC) and monthly total precipitation ( P, mm) across Earth’s land surfaces at the nodes of a 0.5 o by 0.5 o grid. Users should note that our gridded estimates are point estimates, even though some users have treated our data as raster (grid-cell-average) data. We note, however, that they have been used for large-scale numerical climate-model validations as well as in economic applications. Our hope is that they will be helpful in a wide array of applications. Most of the gridded climate fields produced by my colleagues and myself at the University of Delaware were not developed for a specific purpose. They were not corrected to mitigate raingage under-catch bias.

Our precipitation records are derived from 'raw' precipitation observation.

Interpolation accuracy heavily depends on the spatial coverage of the station-records networks.Our interpolators have been refined over the years with additional independent variables (in addition to latitude and longitude) such as elevation (e.g., Willmott and Matsuura, 1995) and climatological fields (e.g., Willmott et al., 1995) and these have improved the accuracy of our interpolated P and T fields. Our spatial interpolations are all spherically based and therefore do not contain map-projection biases that are all-too-common within packaged spatial-analysis software.This allows meaningful comparisons of a climate variable among areas. Our global maps are based on an equal-area map projection.Spatial analyses of grid-cell-average estimates of monthly P or T also will underestimate the spatial variability within P or T. Within gridded data sets that contain grid-cell-average estimates of monthly P or T, the grid-cell areas and, therefore, the area-averages of P or T and their interpretations vary with latitude. The meanings of our gridded P and T values, therefore, do not vary with latitude. Each of our gridded monthly values of P and T is a local point estimate at a 0.5-degree of longitude-latitude resolution.The following was contributed by Kenji Matsuura, University of Delaware, September, 2017: For more information, please read the 'Expert Guidance.' Also, the precipitation data are not corrected for rain-gauge undercatch, and the accuracy of the gridded fields depends on the station density.

Users should be aware that each value of precipitation or temperature is a local grid-point estimate, not grid-cell average or raster data. Selected averages from Legates and Willmott’s (1990a and b) long-term station averages of monthly and annual T and P also were used to help produce this new gridded archive.

#Gridded circle series

These two sets of station time series were drawn primarily from recent versions of the Global Historical Climatology Network (GHCN version 2) and the Global Surface Summary of Day (GSOD) archive. Station records that served as bases for the Terrestrial Air Temperature: 1900-2014 Gridded Monthly Time Series (Version 4.01) and Terrestrial Precipitation: 1900-2014 Gridded Monthly Time Series (Version 4.01) archives are used here to help create new gridded climatologies of monthly and annual average air temperature (T) and total precipitation (P). A series of gridded temperature and precipitation data sets.