CLIVAR VACS African Climate Atlas

This page describes the material relating to Part I and Part II of the Atlas.

Data

Observed climate data on the 0.5 degree grid is from the New et al. (1999) and New et al. (2000) climatology.  Rainfall data on the 2.5 x 3.75 grid is the Hulme (1994) data set.

The 0.5 degree data are described in New, M., M. Hulme and P. Jones, 1999: Representing twentieth-century space-time climate variability. Part I: Development of a 1961-90 mean monthly terrestrial climatology. J. Climate, 12, 829-856.

Statistics

Mean and standard deviation are available.

Mean Period

Normals from 1931-1960 and also from 1961-1990 are available.

Period

Defines the month or season to be used. For all months or all seasons, select the 'Plot Year' button at the page end.

Domain

The latitude and longitudes for the domain options are shown below:

Plot Type

Contour colour shading

Recommended for 0.5 resolution data. Data gaps result when the spatial extent of missing grid boxes is large (e.g. Hulme precipitation at 2.5 x 3.75 latitude-longitude resolution).

Grid Fill colour shading

Recommended for Hulme precipitation at 2.5 x 3.75 latitude-longitude resolution.

Black and White contours

Recommended for the smaller spatial domains.

Scale Bar

Free: the scale bar varies between the months so that details of the range of data in a single plot can be shown.

Fixed: the scale bar is fixed between the months so that different months can be compared.

File Format

The figures were generated in GrADS using the gxeps command to generate Encapsulated PostScript (eps) files. Raster images in PNG format were generated from the eps images using Ghostscript using a density of 72x72 dpi. The quality is highest in the eps files, eps being a vector format. The files can be downloaded using the "Download Image" button.

Rasterisation process

The PNG image has been generated by Ghostscript using the options: "-q -dBATCH -dNOPAUSE -dSAFER -r72 -dEPSCrop -sDEVICE=png16m". Ghostscript 7.06 or later is necessary to use -dEPSCrop. Note that antialiasing rendering (option "-dGraphicsAlphaBits=4") generates some spurious lines and is better omitted. Other packages such as ImageMagick may use it implicitly and must be configured to disable it.

Translating Encapsulated PostScript

The "compressed Encapsulated PostScript" format is to be used to generate images in other format. It can be uncompressed using gzip (http://www.gzip.org). Translations to raster formats can be achieved using ImageMagick's convert command (http://www.imagemagick.org). Translation to vector formats can be achieved using pstoedit (http://www.pstoedit.net/pstoedit). Additionally, any image manipulation package should import it happily.

Scale Plot Size

Gives the width of the screen in percentage used to display the image. If disabled, the images are rendered with their real size.