Polar Science Center, Applied Physics Laboratory
University of Washingon, Seattle, Washington

 
 
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Predictions of Summer Ice Conditions near Barrow Alaska

2010 Prediction Season

End of May 2010:

Here we attempt to predict the ice conditions near Barrow Alaska as listed in Table 4 of the Seasonal Outlook For North American Arctic Waters Summer 2010 prepared by the North American Ice Service in a collaboration with the Canadian Ice Service, 02 June 2010 (http://www.natice.noaa.gov/products/nais_forecasts.html ).  The parameters in this table (listed below) are various measures of the amount or duration of open water near Barrow.

The predictions are based on the output of a coupled ice-ocean model which provides us with retrospective estimates of the ice and ocean conditions in the Arctic.  The model is the PIOMAS model developed and operated by Dr. Jinlun Zhang (http://psc.apl.washington.edu/zhang/IDAO/seasonal_outlook.html).   The model uses the air temperature, winds, clouds, and precipitation from the NCEP Reanalysis to estimate maps of the ice motion, ice thickness distribution, and ocean temperatures and currents for past years, up to and including the most recent month.  The observed ice concentration is assimilated so that the model ice extent is close to the observed ice extent.  Statistical relationships between the model parameters in May (or any other month) and the various measures of the ice conditions are found from past years using a method developed by Dr. Sheldon Drobot (Drobot et al, 2006).  This relationship is then used with the current month model output to predict either the pan-Arctic ice extent or any other scalar quantity such as those listed in the Ice Service outlook.   Updates are posted at http://psc.apl.washington.edu/lindsay/prediction.html

The Alaskan ice parameters predicted here are
1. Distance from Point Barrow northward to ice edge on 10 Aug (nautical miles).
2. Distance from Point Barrow northward to ice edge 15 Sept (nautical miles).
3. Distance from Point Barrow northward to boundary of five-tenths ice concentration on 10 Aug (nautical miles).
4. Distance from Point Barrow northward to boundary of five-tenths ice concentration on 15 Sept (nautical miles).
5. Initial date entire sea route to Prudhoe Bay less than/equal to five tenths ice concentration (year day).
6. Date that combined ice concentration and thickness dictate end of prudent navigation (year day).
7. Number of days entire sea route to Prudhoe Bay ice free.
8. Number of days entire sea route to Prudhoe Bay less than/equal to five-tenths ice concentration.
9. Number of days between initial opening date and 1 Oct
10. Barnett Ice Severity Index, high numbers indicate large expanses of open water.
11. Rank of the BIS index from 1953 to 2009 (1 is the highest BIS Index, 57 the lowest)

We have determined the single most effective predictor for each of these variables for each predictor month and the amount of the variance explained by the predictor.   The candidate predictors include fields of the ice thickness (H), the ice concentration (IC), the ice extent (IX, 0 or 1 for each grid cell), the fraction of the area with open water or ice less than 0.4m (G0.4m), less than 1.0 m (G1.0m), or less than 1.9 m (G1.9m).   Table 1 lists each of the Alaskan ice parameters and for each month the percent of the variance explained and the most effective predictor.  The method uses monthly averaged model output, so for predictions using the month of May, the model is run through the end of May and the fields of the average values for each predictor variable are used to make the prediction.

Table 2 gives the prediction for each Alaskan ice parameter using May 2010 data.  Parameters for which the method predicts a 50% or greater chance of a new record value are printed in bold and the standard deviation of the regression error gives an indication of the uncertainty of the prediction.  The prediction for the amount of open water as seen in the BIS index is 1145, very close to the previous maximum of 1136 seen in 2007 or the 1103 seen last year (plot).

A set of four panels is shown for each Alaskan ice parameter.  The first is shows the observed value for the last 22 years, 1988–2009, the values of the regression fit (blue) and the predicted value for 2010 (orange) with the one-standard-deviation error bar.  The trend line and the trend prediction are also shown (black).  The three maps show the correlation between the ice parameter and the best predictor (right), the anomaly of the best predictor for May 2010 (center), and the product of the correlation and the anomaly (left).  It is the integral of the last map that makes the single predictor variable used in the regression equation.

Table 1.  Percent variance explained and best predictor for each parameter using model data from the end of each month, May to August, using data from 1988 to 2009.

      Ice Parameter     Apr    May    Jun    Jul    Aug

   ice_dist_10Aug   0.71   0.72   0.77   0.77   0.70   R2
                  G1.0m     IC     IC     IC     IC   Predictor

  ice_dist_15Sep   0.83   0.81   0.82   0.83   0.86
                  G1.0m  G1.0m     IC     IC     IC

    ice_05_10Aug   0.82   0.79   0.75   0.72   0.72
                  G1.0m  G0.4m  G0.4m  G0.4m  G0.4m

    ice_05_15Sep   0.76   0.72   0.80   0.81   0.85
                  G1.0m  G1.0m     IC     IC     IC

      date_start   0.62   0.64   0.68   0.58   0.54
                  G1.0m     IC     IC     IC  G1.0m

        date_end   0.40   0.34   0.62   0.50   0.40
                  G1.0m  G1.0m     IC     IC     IC

  Ndays_ice_free   0.50   0.60   0.70   0.57   0.53
                  G1.0m     IC     IC     IC  G1.9m

    Ndays_ice_05   0.49   0.58   0.75   0.59   0.47
                  G1.0m     IC     IC     IC  G1.9m

Ndays_start_1oct   0.62   0.63   0.67   0.58   0.53
                  G1.0m     IC     IC     IC  G1.0m

       BSI_Index   0.81   0.78   0.84   0.86   0.89
                  G1.0m  G1.0m     IC     IC     IC

            Rank   0.70   0.69   0.69   0.70   0.70
                  G1.9m  G1.9m  G1.9m  G1.9m  G1.0m

Table 2.  Predictions using data from the end of May 2010. Parameters for which the method predicts a 50% or greater chance of a new record value are printed in bold.

   Ice Parameter Prediction Error
  ice_dist_10Aug   151.4    23.0
  ice_dist_15Sep   419.8    52.6
    ice_05_10Aug   215.2    26.7
    ice_05_15Sep   480.0    69.2
      date_start   184.0     7.4   (3 July)
        date_end   297.8     9.0   (25 October)
  Ndays_ice_free    93.6    13.9
    Ndays_ice_05   114.1    15.1  
Ndays_start_1oct    89.8     7.5   (3 July)
       BIS_Index  1145.0   131.8
            Rank    -1.0     8.5

References

Drobot, S. D., J. A. Maslanik, and C. F. Fowler (2006), A long-range forecast of Arctic summer sea-ice minimum extent, Geophys. Res. Lett., 33, L10501, doi:10.1029/2006GL026216

Lindsay, R. W., J. Zhang, A. J. Schweiger, and M. A. Steele, 2008a: Seasonal predictions of ice extent in the Arctic Ocean, J. Geophys. Res., 113, C02023, doi:10.1029/2007JC004259.


Figures

Distance to ice edge, 10 August

:all_elements_2010:end_of_may-01-ice_dist_10Aug.png

Distance to ice edge, 15 September

:all_elements_2010:end_of_may-02-ice_dist_15Sep.png

Distance to 0.5 ice, 10 August

:all_elements_2010:end_of_may-03-ice_05_10Aug.png

Distance to 0.5 ice, 15 September

:all_elements_2010:end_of_may-04-ice_05_15Sep.png

Start Date

:all_elements_2010:end_of_may-06-date_end.png

End date

:all_elements_2010:end_of_may-07-Ndays_ice_free.png

N days ice free

:all_elements_2010:end_of_may-08-Ndays_ice_05.png

N days with ice concentration less than 0.5

:all_elements_2010:end_of_may-09-Ndays_start_1oct.png

Start date as Ndays before 1 Oct

:all_elements_2010:end_of_may-10-Obs_Indx.png

Barnett Ice Severity Index

:all_elements_2010:end_of_may-00-RANK.png

Rank

:all_elements_2010:end_of_may-00-RANK.png