Introduction Lab

The purpose of this lab is to familiarize you with Ingrid and Excel, software which you will use in the labs.

I. Ingrid

For our labs, we will look at various types of data, available from the IRI/LDEO Climate Data Library. We will do this using Ingrid, which is a user interface which allows one to access and manipulate data. This exercise will introduce you to the basics of Ingrid.

We will look at daily surface temperature data from the NCEP/NCAR Reanalysis Project. The reanalysis provides daily data on a regular longitude-latitude-height grid. We will learn more about this data set in future labs.

Open the following link to access daily surface data http://iridl.ldeo.columbia.edu/SOURCES/.NOAA/.NCEP-NCAR/.CDAS-1/.DAILY/.Diagnostic/.surface/ (Note that you just opened a new browser window. Please move that browser aside so you can continue to access it later).

You will see a list of available variables, listed in red. Scroll down to "Temperature" and click on it. You will see information on the time and space grids. For example, longitude varies from 0 to 1.875W by intervals of 1.875, with 192 points in longitude.

You will also see a line of small figures, to the right of "Views". Clicking any one of these will create a corresponding plot. Click on the colored box just to the right of "Views", to create a 2 dimensional (latitude by longitude) plot.

The plot that appears is not necessarily the most optimal, but it can be easily manipulated to look better. We will do this by entering relevant values or choosing options in the drop boxes. most is self evident.

  1. Plotting

    Look at the latest available date's surface temperature map, by changing the date at the top and clicking redraw. The redraw button is the first one on the left with the circular arrow. Try to change the date by clicking on the button above the map or directly entering dates in the text box (e.g. 4 Jul 1958).

    Also do the following:

    1. Using the drop-down menus below, improve the figure by choosing colors|contours , drawing coasts.
    2. Flip to a southern hemisphere view by changing the N and S on the latitude boxes and clicking redraw. then go back to northern view.
    3. Limit to the North America region by entering the corresponding latitude and longitude values and clicking redraw.

    Note: the latitude, longitude and time ranges of the data set are shown in the upper right of the screen. These represent the ranges available for viewing, but do not always correspond to what you choose to see on the map. This will become clear after you have gone over the "Data Selection" section below

  2. Averaging

    To average you need to go back to the data set- click "entire dataset".

    1. Plot August mean temperature. We first need to select the time period we want. Do this by clicking "Data Selection". Then enter the date range of 1-31 August 2004 in the appropriate format, click "Restrict Ranges". To return to the main page click "Stop Selecting". Now you are ready to average. Do this by clicking "Filters". There are many options. Average options are over 1, 2 or 3 dimensions. For 1 dimension you have a choice between X (longitude), Y (latitude), T (time). You want a time average (click "T"). Ingrid will compute the average and return you to the main data page. Now click the plotting button, and again arrange the plot to have contours|colors and coasts.
    2. Click on "Entire Dataset" once again. Select the dates starting Jan 1 2004 to the last date available. Now take a global average. This is done from Filters, by clicking the "XY" option of averaging. Note that you now have only line plot options (why?). Plot a daily time series of the area average. Note the large scale seasonal variation along with shorter time scale variability.

II. Excel.

We will plot Solar radiation as a function of Latitude (we will learn all about this in the class, for now you just have to understand how to make a plot). The solar radiation has a latitude dependence as follows: I=Io cos(X). Where I is the radiation at any location, Io = 1367 W/m2, and x = latitude at that location.

Launch EXCEL. Save the workbook to the desktop and give it a recognizable name. In the first worksheet label the first column "latitude." In the following rows, enter the numbers "-90" to "90" in increments of 2.5. The easiest way to do this is to type "-90" in the second row of the first column (the first row will contain the label "latitude"). Then click on the third row of the first column (this is cell A3) and type the following expression into the formula bar at the top of the window: =A2+2.5 and hit enter. The number "-87.5" should appear in cell A3. Then copy the contents of cell A3 and paste it into the remaining rows until you have latitudes up to 90. There should be 74 rows in total. These numbers will represent the latitudes of the earth from the south pole to the north pole.

Label the second column "cos(lat)." This column will contain the cosine of the latitude values you entered earlier. However, Excel finds the cosine of an angle in radians, so you will need to convert your latitudes from degrees to radians before you find the cosines. These can be combined into one step by clicking on cell B2 and typing this expression into the formula bar: =cos(radians(A2)). Alternately, you can click on cell B2 and then use the "Paste Function" button or the "Paste Function" option on the "Insert" pull-down menu to convert the latitude from degrees to radians and then find the cosine. When you have a formula that works properly, convert the remaining latitudes to radians and find their cosines by copying the formula into the corresponding cells in that column. Finally, calculate the incoming solar flux at equinox for each latitude. Give the column an appropriate label, such as "flux at equinox (W/m2)." Recall that I = I0cos(x) where I0 = 1367 W/m2 and x = latitude. Use the "Paste Function" button to calculate the product of cos(lat) and 1367, or type the following directly into the formula bar: =product(B2,1367). Copy this formula into the cells for the remaining latitudes.

Create an Excel scatter plot showing the equinox top-of-atmosphere (TOA) radiation values versus latitude. Do this by highlighting the column containing latitudes and, while holding down the control key (on a PC) or the apple key (on a Mac), highlighting the column containing the TOA fluxes. With both columns selected, click on the "Chart Wizard" button, select "XY scatter" and continue. Be sure to include units and labels on the axes!

Updated January 23, 2006
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