Dataset Structure

You should now be more comfortable with finding datasets in the Data Library. Let us take a closer look at the information and utilities available to you when you select a dataset. You will not use these utilities in this section, but it is important to know what they do and where they are for Parts II and III. The TMA ENACTS version2 ALL monthly temperature dataset is a commonly used dataset and is the example for this section.

Select TMA ENACTS version2 ALL monthly temperature*.

There is a wealth of information about the dataset on its main page. Let us look at all of the elements from left to right (some tabs may be absent depending of the type of dataset).

Function Tabs

The function tabs has its greatest utility after the desired data variable and station(s) or region have been selected, however it is important to be aware of what options are available. Therefore, a brief explanation of these tools is offered here. (Note that the links in the example above are inactive.)

Views: The views tab take you to a selected list of options to generate an image of the selected data in a data viewer. Let us quickly go over the different types of images seen here. The colored and contoured images generally display a spatial (e.g., [X,Z], [lon,lat]) image as either colors or contours. The line graph typically illustrates a time series (e.g., [data value,T]) image. Other types of views icons will appear depending on your data selection. It is important to remember that the image in the icon is representative of the image to which the icon is linked. We will talk much more about these links and their visualization capabilities in Part III.

Select the "Expert Mode" tab.

Expert Mode: This option switches the interface into a mode that allows you to enter data-manipulating Ingrid commands directly rather than clicking on a series of pages to perform an identical task. You must not already be familiar with Ingrid at this point. These commands will be introduced throughout the tutorial.

When in Expert Mode there is a list of active datasets at the top of the page and a text window containing the command equivalent of the current page where the commands can be edited. Right now, you should see only one dataset, temperature, noted as the active dataset. Because no variable has been selected, you can see all of the possible variables listed in this location as well. Much more detail about expert mode, including specific examples, will be given in Parts II and III.

Select the "Data Selection" tab.

Data Selection: This option allows you to pick out a subset of the full dataset. Right now this option displays the available data variables that you also see on the dataset main page. In Part II, you will learn how to use this option to select data for specific locations and time periods.

Go back to the dataset main page by selecting the "Description" tab.
Select the "Data Files" tab.

Data Files: This option allows you to download the dataset in a variety of formats. You will learn much more about this option in Part III.

Go back to the dataset main page by selecting the "Description" tab.
Select the "Data Tables" link.

Data Tables: This option allows you to view the data as a table in a variety of formats. You will learn much more about this option in Part III.

The function tabs are largely used to select, manipulate, and visualize data and will therefore be covered in much greater detail in Parts II and III. Keep in mind that many of the contents of the links in the function tabs will appear signifcantly different after you have selected your data variable and station(s) or region. The goal here was just to introduce you the options available in the function tabs.

Go back to the dataset main page by selecting the "Description" tab.

The source bar, as described in the previous section, indicates to the user the location of the current dataset in the Data Library and offers the opportunity to go to any of the higher levels in the hierarchy by selecting one of the bubbles. For example, you can view other ENACTS datasets by selecting the "ENACTS" bubble and other monthly ALL version2 ENACTS datasets by selecting the "monthly" bubble.

The source bar is an extremely valuable navigation tool in the Data Library. Try using its options...

Select the "ENACTS" bubble in the source bar.

These are the other subsets of data available from ENACTS.

Go back to the temperature dataset main page (back button).

Dataset Map/Data Viewer
A dataset map will appear when the selected dataset is comprised of station data. Those datasets with gridded data will have a main page with an identical structure with the exception of this map. For example, look at the main page for the NOAA NCEP-NCAR CDAS-1 MONTHLY Diagnostic* dataset, which is a gridded dataset. You should note the options and structure of this page are identical to those of the FSOD dataset, with the exception of the dataset map.

The data viewer is an interactive interface that helps you find data for a specific location. The black dots on the map represent stations for which there is data in the dataset. The FSOD dataset primarily contains data from the United States and you can see that by the density of dots in the United States on the dataset map. You can select any of those stations by clicking on them. However, that may not be easy if the stations are as dense as they are here. Therefore, there a few options that make finding specific station(s) easier. First, you can zoom in on the map using the Zoom pull-down menu on the left side.

Select a zoom magnitude from the Zoom pull-down.
Click "Redraw".

You can also limit the map by selecting latitude and longitude values and place labels on the map to help you identify stations.

Select new lat/lon limits and click "Redraw".
Select one of the label methods in the pull-down menu on the right side. Its default says "no labels".
Click "Redraw".

These options can be combined to easily select any number of stations. There is also a "Searches" link on the dataset map that will allow you to search for stations in a number of ways. These methods will be highlighted and fully discussed in the next section.

Go back to the default dataset map by clicking on the "FSOD" link in the source bar.

Select the "outline" link. CHECK
This is one way to view the available variables within the dataset. The bracketed text with each variable indicates the grids that are associated with that variable. The idea of grids will be addressed later in this section.

Go back to the dataset main page.
If there is one, select the "dataset documentation" link.

This is the same documention that reached via the "Documentation" tab. If not specific documentation document was set up, then there is no link nor tab.

Go back to the dataset main page.

Datasets and variables
This is the same list of variables that you saw on the outline page. There is a link to each variable, as well as the abbreviated name of the variable in the dataset, and its grids (in brackets).

You may chose a variable from this list, but it is often easier to select the station(s) or region first. Right now, let us just look to see what information is available when we select a variable.

Select the tmin variable.

This is the typical information given for each variable. You are given the specific information about the grids as well as how the data are scaled, how missing values are replaced, and the units of the data.

Go back to the dataset main page.

You can think of grids as the ways in which the data are dependent. In this example, the data vary with longitude and latitude as well as with time. The information after each grid indicates the units and range of the grid. For example, the time grid has units of find data units and has data from first point through last point, which creates npts different time grid points. (Note: month is another common temporal grid unit.)

Grids vary from dataset to dataset, but there is a fundamental difference between those for station data and those for gridded data.

Select SOURCES NOAA NCDC ERSST version4* here.
This is a gridded dataset and, accordingly, it has latitude and longitude grids instead of a station grid. You can see this in the grid brackets with one of the variables as well as in the information below the Grids heading. The description of the latitude and longitude grid gives the spatial resolution of the data as well as the spatial range and number of grid points in each direction.