PIOMAS Verification

Below is the PIOMAS forecast vs. actual. Red represents areas where they over-predicted melt. Green is the opposite. Their forecast error is 20%, compared to my 7%.


It is not terribly surprising that they are also claiming a record low volume.

About stevengoddard

Just having fun
This entry was posted in Uncategorized. Bookmark the permalink.

5 Responses to PIOMAS Verification

  1. Peter Ellis says:

    I’m not sure where you’re taking that PIOMAS picture from, but it doesn’t seem to match their current model run (visible here http://psc.apl.washington.edu/zhang/IDAO/seasonal_outlook.html ). I suspect you’re using the previous model run from the start of July (or possibly even the June run), rather than the current one initialised at the start of August. Note that both the July and August runs gave the same prediction for a minimum ice extent of 4.8 million sq km, as submitted to SEARCH by Zhang (rather than the 4.0 prediction submitted by Lindsay & Zhang).

    Looking at the detailed description of both methodologies in the June report, it is clear that the Zhang prediction (4.8) is the one that actually uses the PIOMAS model to generate the forecast. To make the prediction, they run the PIOMAS model forwards, using average data for atmospheric forcing, as reported both to SEARCH and on the PIOMAS home page. Why have you excluded it from your bullseye chart and retained only the Lindsay/Zhang one?

    In contrast, the Lindsay/Zhang prediction does not use the PIOMAS model to generate the forecast. Rather, this forecast was initialised at prediction date using the *current* daily PIOMAS estimates of ice thickness, and a linear regression fitted using various parameters (i.e. percentage of ice of each thickness category). It doesn’t actually make use of the PIOMAS model at all except to estimate the starting thickness of the ice, so it’s wrong of you to claim it’s representative of the PIOMAS model predictions.

    As to whether the PIOMAS prediction of 4.8 million or your prediction of 5.1 million is more accurate, only time will tell. IJIS extent is currently at 5,034,219 and dropping by 50k per day. NSIDC extent is lower than IJIS.

    • Neven says:

      That’s an excellent summary, Peter Ellis. I covered the Lindsay and Zhang predictions on my blog a few months ago.

      Let me quote their caveats again:

      The exact thickness of the ice in spring that might survive depends on the location and on the air temperatures and cloud cover during the summer, both of which are not possible to predict more than a week or so into the future. Also, the ice extent is strongly dependent on the winds, as we saw in the summer of 2007. It is not possible to accurately predict the strength and direction of the winds months in advance. Depending on the air pressure patterns, the winds may or may not herd the remaining ice to one side of the basin, thus reducing the extent. What we do know is that the reduced ice thickness of recent years will lead to much more variability in the fall ice area and extent because the open water created during the summer is more sensitive to the initial ice conditions and the amount of melt. We still have a lot to learn about seasonal ice prediction.

      And Zhang:

      The purpose of the seasonal predictions of arctic sea ice is for scientific research and education only. There are many uncertainties with the predictions and the results must be viewed with caution.

    • Since I am comparing accuracy against my early forecasts, it seems only fair to use their early forecast.

    • Amino says:

      Where are the complaints over PIOMAS updating their forecast that should be voiced and loudly as those over Steven Goddard? And if PIOMAS is going to be justified then those who were less off than PIOMAS should be justified also.

      Please try to deal evenhandedly. People can see when it is otherwise.

  2. Peter,

    I am normally assuming that readers are current with what I have already written about PIOMAS. It is seems pretty clear that you aren’t.

    In April, I critiqued their seasonal outlook.

    The computer model (PIOMAS) is predicting that 3+ year old ice (which is probably in excess of 10 feet thick) is going to melt by early August

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s