RClimate Script: Pacific Decadal Oscillation Trend

This RClimate Script lets users retrieve and plot the monthly and moving average  Pacific Decadal Oscillation (PDO) data  from the University of Washington’s JISAO website. The script retrieves the PDO data from January, 1900 until latest month available at time script is run.  The trend chart shows the JISAO PDO trend and user selected moving average period.

Brief Introduction to Pacific Decadal Oscillation (PDO)

I have read so many blog posts about the PDO’s potential role in global warming that I have decided to learn about it for myself.  While I plan to examine the PDO – ENSO – global warming relationships in future posts, readers can get a preview of my inquiry from the posts that have gotten me started.

1. First, I would read Tamino’s post  at Open Mind at this link. This is probably the best place to start if you are new to PDO.
2. Next, I would go to the data source, the JISAO site to get a complete grounding in PDO.
3. Third, I’d go to Bob Tisdale’s Misunderstandings About the PDO – Revisited post to get a clearer picture of what the PDO is and what it is not.

PDO Trend Chart

Here’s my R script based JISAO’s PDO trend by month chart  since 1900.

This chart shows the January, 1900 to March 2010 PDO trend, the 13 monthly moving average PDO, with the latest monthly value highlighted in red.

Here are the data and RClimate Script links:

• Data Link
• RClimate Script

R Script Techniques

This R script includes several tools that may be helpful for R beginners, including:

• download.file() to retrieve on-line file
• readLines() to  handle messy file with mix of documentation and data lines
• read.fwf() to handle ** characters mixed with numeric  data
• melt() to convert from wide format data set to long format
• subset() to separate positive and negative PDO series
• filter() to calculate moving average for user specified period
• abline() to add grid lines at PDO regime shift years
• legend() to provide detailed legend
• designation of last month in chart title, legend
• designation of last point in series

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