Useful Information and FAQ for the
Google Earth Interface to CRU TS (v4.04 onwards)

1. The purpose of this interface

This new version of the Google Earth interface to the CRU TS dataset allows the Mean Temperature, Precipitation, Diurnal Temperature Range and Vapour Pressure variables of that dataset to be investigated spatially. Both gridded data and original observations may be retrieved. To access the dataset in its original form, please follow links from the HRG page: http://www.cru.uea.ac.uk/cru/data/hrg/

2. Getting started

Because of the high spatial resolution of the dataset, the initial view displays 5°x5° 'blocks'. Each of these contains up to 100 0.5° x 0.5° land gridcells, which are revealed by clicking on a block, and following the link then displayed. Individual gridcells may now be clicked on to reveal data series for the four variables, along with the option to show contributing stations. These can in turn be clicked on to investigate station observations.

3. How do I get back to the map after clicking on a plot or data link?

If you follow a link to a cell or station data file, or to an enlarged plot, it may not be ovious how to return. However, there is a 'Return to Google Earth' button, top left of the window. Sadly this does not return you to the 'balloon' that was open, just to the position you were in.

4. What do the different station markers mean?

The station markers - 'paddles' in Google Earth - are colour- coded: red for temperature, blue for precipitation, orange for diurnal temperature range, and green for vapour pressure. A plain paddle indicates that the station is dormant; a star on the paddle shows that the station is current, ie, has data for the latest reporting period. For vapour pressure, a secondary variable, there are also synthetic stations derived from temperaure and diurnal temperature range. These are indicated with a black dot instead of a star. A legend is incorporated into the cell information popups.

5. I have clicked a lot and the map is crowded?

This can be a problem, especially now we have four variables to investigate! Fortunately, Google Earth lets you control what is displayed. If you examine the information bar (usually to the left of the map area), you will see a section called 'Places' that includes references to each item you've clicked. You can turn any of these off (and on again) using the checkboxes. You may also wish to turn off various mapping objects from the Primary Database in the 'Layers' section, such as Borders and Labels, Places and Roads.

6. Can cells be combined to calculate spatial means?

Yes, but not by Google Earth! If you wish to calculate spatial means, then there are several possibilities: If your area is a country, please look at the CRU CY dataset (http://www.cru.uea.ac.uk/cru/data/hrg/) If your area consists of just a few gridcells, you could download each cell series and then average them (using Microsoft Excel, or similar). Remember that if you are in mid- to high-latitudes then you should take account of different cell areas. For more complicated areas, you could investigate KNMI's Climate Explorer, which includes the CRU TS dataset: http://climexp.knmi.nl/

7. Why are some cell plots just flat lines?

Because of the fundamental attribute of the CRU TS dataset - that there are no missing values for any months and any land cells - there must be an approach for cells with no observing stations nearby (this is explained in Harris, et al., 2020). In brief, any cells that have no observations within the CDD (correlation decay distance) of the variable in question, (1200km for mean temperature, 450km for precipitation), will instead be influenced by the underlying 1961-1990 climatology (which is spatially complete). In extreme cases, a cell will use the climatology for the whole run. An annual mean from years where every January is the same, every February, etc., will have the same mean value every year. Hence the flat line.

8. Why are some station plots empty?

The data plots are annual means. These can only be calculated if all 12 monthly values are present. When one or more monthly normals cannot be calculated, the result is that no annual mean series can be plotted. The data for the other months will still be used in the interpolation, and can be accessed by clicking on the 'Data' link as usual.

9. What does 'Show nearby (or contributing) stations' actually mean?

The gridding mechanism for CRU TS is angular-distance weighting. This allows logging of the actual stations contributing to each cell. Google Earth does not currently offer a mechanism by which this could be explored on a per-datum basis; however, clicking on the link will highlight all stations used in interpolations to that cell over the entire timespan.

10. Some station clusters seem anomalous or inappropriate?

The Google Earth interface is a great way to find information, and that includes potential bugs! Please first check that we don't already know about this - see the blog here.

11. How to cite?

Please cite Harris, I., Osborn, T.J., Jones, P. & Lister, D.H. Version 4 of the CRU TS monthly high-resolution gridded multivariate climate dataset. Sci Data 7, 109 (2020). https://rdcu.be/b3nUI

Last updated: May 2020, Ian Harris

Licence These datasets are made available under the Open Government Licence. You are free to use this dataset but you must acknowledge the source of the information. Please use the attribution Climatic Research Unit (University of East Anglia) and Met Office. If it is appropriate to give citations and/or website links, then please also cite the relevant publication (see data table above) and/or provide a link to this website.