Reconstructing IJIS Arctic Sea Ice Extent Data

[Mallow]

Hi, all!

Today, I decided I wanted a reconstructed ice extent dataset that approximated the IJIS data, but went further back in time than 2002. To do this, I got Northern Hemisphere sea ice data from the following site:

http://arctic.atmos....cecon.1901-2005

(Located at the "Cryosphere Today" website)

Data from the above site is valid for the last day of the given month. The methods of calculating sea ice are different between IJIS and UIUC (Cryosphere Today). So, I took a linear fit between overlapping data from IJIS and UIUC. The fit looked like this:

I then used the fit to come up with an IJIS estimate for every day there was UIUC data available. I formatted the data in four different ways.

1. For all times available (monthly for times when only UIUC was available, daily otherwise), use actual IJIS data if available, otherwise use UIUC-based IJIS estimates.

2. For times when UIUC data was available (monthly), use only UIUC-based IJIS estimates.

3. For all last-days-of-the-month, use actual IJIS data if available, otherwise use UIUC-based IJIS estimates.

4. For all last-days-of-the-month, use only UIUC-based IJIS estimates.

The four datasets are listed below in the same order.

method1.txt

method2.txt

method3.txt

method4.txt

Using the dataset from method 3, I calculated 30-year means and trends, both monthly, and annually. The middle date of the 30-year period was the end of the month on 2/1995.

The mean annual sea ice over the 30 year period is 11.0132 million sq km. The mean annual trend in sea ice over the 30 year period is -0.0427 million sq km per year. The annual standard deviation is 0.1840 million sq km.

The following is a list of 30-year mean sea ice values with trends removed, by month (first is for Jan 31st, last is for Dec 31st), in millions of square km:

13.8905250243917
14.2033479489308
14.1399103142203
13.3287860888654
11.8984447780809
9.80956260202981
7.48683752596019
6.38390868009679
6.89897648309496
9.63126479137632
11.4241721890414
13.0624898151056

The following is a list of 30-year trends in sea ice by month (first is for Jan 31st, last is for Dec 31st), in millions of square km:

-0.0314935436591402
-0.0174512929255636
-0.0247658587046857
-0.0341329535149007
-0.0396565435075318
-0.0356464888463229
-0.0403727759584093
-0.0617475871408971
-0.0749980513125176
-0.0493941506005346
-0.0586116078042656
-0.0445433994333738

In other words, on average, sea ice on December 31st has decreased by 0.0445 million sq km per year.

Finally, the following is a list of standard deviations based on the last 30 years of data by month (first is for Jan 31st, last is for Dec 31st), in millions of square km:

0.279604371753973
0.254891638303691
0.254151574986798
0.284259498148183
0.246127786573951
0.355280411991971
0.336662348824347
0.350317624005304
0.551612126615030
0.389464676410573
0.340701945086469
0.243034019014646

I will be using this as background info soon in a sea-ice-forecasting contest.