Documentation

This page contains the documentation for the CRU TS 2.1 data-set, and comprises:

Data
The CRU TS 2.1 data-set is now available online: http://www.cru.uea.ac.uk/cru/data/hrg/cru_ts_2.10 (see read_me.txt)

NOTE: Users of WET and VAP parameters should see the NEW_read_me_vap_wet.txt file.

Full range of data-sets
If you have arrived at this page from a different website (without the red frame), you may be interested in the wider range of high-resolution climate grids available here. There is a table detailing the full range of data-sets. For example, there are 16 GCM-based scenarios for the 21st century on the same 0.5 degree grid (TYN SC 2.0).


Updates

23rd January 2004
A new version of the gridded data-set has been released, labelled CRU TS 2.1. The new version:

  • extends the period covered to 1901-2002;
  • extends the number of variables included to nine: daily mean, minimum and maximum temperature, diurnal temperature range, precipitation, wet day frequency, frost day frequency, vapour pressure and cloud cover;
  • is based on a complete revision of the underlying station databases and an improved methodology.
The new method is described in the paper cited below. The data-set should be referred to as CRU TS 2.1 and cited as:
Mitchell, T.D., 2004: An improved method of constructing a database of monthly climate observations and associated high resolution grids. About to be submitted.

4th August 2003
The reference for CRU TS 2.0 has been updated to: Mitchell, T.D., Carter, T.R., Jones, P.D., Hulme,M., New, M., 2003: A comprehensive set of high-resolution grids of monthly climate for Europe and the globe: the observed record (1901-2000) and 16 scenarios (2001-2100). Journal of Climate: submitted.

13th May 2003
An elevations file for the 0.5 degree grid used here is now available. This file also implicitly describes the land-sea mask, since only land boxes are given elevations. The file format is the same as that of the data files.

9th May 2003
The country-by-country summaries of recent climate have been updated to 2000, based on CRU TS 2.0. See the TYN CY 1.1 data-set.

2nd May 2003
A new software page gives users the opportunity to share software for manipulating these climate grids, and reinvent the wheel less frequently!

1st May 2003
The issue of using CRU TS 2.0 for time-series analysis has been addressed more explicitly and fully. A separate page discusses time-series analysis, and additional station files have been released that record the number of stations within range of a grid-box.

25th February 2003
Download procedure for CRU TS 2.0 eased by providing an alternative set of files for each variable. Rather than just a single file for each variable, each variable is also now broken down into 10-year periods.

4th February 2003
Data-set publicly released, as version 2.02.


Introduction
The CRU TS 2.1 data-set comprises 1224 monthly grids of observed climate, for the period 1901-2002, and covering the global land surface at 0.5 degree resolution. There are nine climate variables available: daily mean, minimum and maximum temperature, diurnal temperature range, precipitation, wet day frequency, frost day frequency, vapour pressure and cloud cover.

It was New et al (2000) who were responsible for the original high-resolution (0.5 degree) climate grids (CRU TS 1.0) and an update to 1998 (CRU TS 1.1). Mitchell et al (2004) revised these grids and updated them to 2000 (CRU TS 2.0). See the table for more details of those data-sets. This data-set revises and extends those data-sets. The grids have been recalculated for 1901-2002, following a complete revision of the underlying station databases and using an improved method. Users should not mix these grids with previous grids.


Guidance
The primary purpose for which this data-set was constructed was to provide environmental modellers with some of the inputs they require to run their models. This purpose governed the choices that were made during the construction of the data-set. The methodology we used affects how the data-set should be used. The issues involved in using CRU TS 2.1 for time-series analysis are addressed more explicitly and fully; this guidance was originally given for CRU TS 2.0, but it applies equally to CRU TS 2.1. We recommend that all users who intend to examine climate change using this data-set should consider the issues carefully before beginning their work.

The companion data-set TYN SC 2.0 may be used to extend the period available from 2000 to 2100, through 16 climate change scenarios.


Data Structure
At present, the data-set is only available in the form of large ASCII files, compressed to a total of 1.1 GB. They are designed for use on a Unix system, not in Excel! You will need the file format details. There is also a software page. Each variable is supplied separately. The data for each variable may be downloaded as a single file, or in 10-year files. The table below gives compressed sizes of the whole-period files (in MB, not KB!). The 10-year files are approximately a tenth of these sizes. When uncompressed, the 102-year files are over 400 MB, and the 10-year files are over 40 MB.

variable single file (.Z)
cloud cover 126.2
DTR 94.2
frost days 98.8
precipitation 144.5
daily minimum temperature 123.7
daily mean temperature 124.5
daily maximum temperature 124.8
vapour pressure 104.1
wet days 148.2

Additional station files record the number of stations within range of a grid-box. These files have been released to help with any time-series analysis.

An elevations file for the 0.5 degree grid used here is available. This file also implicitly describes the land-sea mask, since only land boxes are given elevations. The file format is the same as that of the data files.


Ownership
The creator of this data set (Dr. T. D. Mitchell) retains full ownership rights over it. The data set may be freely used for non-commerical scientific and educational purposes, provided it is described as CRU TS 2.1 and attributed to:

Mitchell, T.D., 2004: An improved method of constructing a database of monthly climate observations and associated high resolution grids. About to be submitted.


Disclaimer
The author of this data-set cannot bear any responsibility for the consequences of using it, which are entirely the responsibility of the user. It is inevitable that a data-set of this size will contain some errors and inconsistencies. However, these have been kept to a minimum and when they are identified they are corrected when resources permit. Updates to this data-set will be notified on this web page and by email to registered users.


Further Information

  • See the FAQ.
  • The information available for the previous version of this data-set (CRU TS 2.0) may be of interest.
  • If you have arrived at this page from a different website (without the red frame), you may be interested in the wider range of high-resolution climate grids available here. There is a table detailing the full range of data-sets.