Readme for the NEMO-LIM2/EnKF Sea ice Reanalysis project
--------------------------------------------------------

Author 		-- Francois Massonnet
E-mail		-- francois.massonnet@uclouvain.be
Last update	-- May 2013

Thanks to the following contributors:
P. Mathiot, M. Vancoppenolle, C. Koenig Beatty, T. Fichefet, H. Goosse, T. Lavergne

1/ Structure of the folder
--------------------------
From any browser, go to www.climate.be/seaice-reanalysis

For login and password , please contact Francois Massonnet.

http://www.climate.be/seaice-reanalysis/

			/AREA_EXTENT_VOLUME
				Amundsen_Bellingshausen_Seas.txt
				Arctic.txt
				Indian_Ocean.txt
				Pacific_Ocean.txt
				Ross_Sea.txt
				Southern_Ocean.txt
				Weddell_Sea.txt
			/DB_FILE
				db_EnKF_l2_as_err
			/GEOM
				ORCA2_mesh_mask.nc
			/SEAICE_REANALYSIS
				mean_restart_ice.EnKF_l2_as_err.PXXXXX.an.nc !! about 11 000 files
			/SCRIPTS
				compute.m 			

			README_seaice_reanalysis.txt	!! (this file)
				


1/ Short description
--------------------

An Ensemble Kalman filter has been implemented to better estimate the sea ice state of the ocean-sea ice model NEMO-LIM2. Sea ice concentration is assimilated every day/second day depending on availability. 

The following two papers describe extensively the methods, and must be acknowledged whenever the sea ice data are used.

| Massonnet, F.; Mathiot, P.; Fichefet, T.; Goosse, H.; König Beatty, C.; Vancoppenolle, M. and Lavergne, T. 
| A model reconstruction of the Antarctic sea ice thickness and volume changes over 1980-2008 using data assimilation
| Ocean Modelling, 2013, 64, 67-75

| Mathiot, P.; König Beatty, C.; Fichefet, T.; Goosse, H.; Massonnet, F. and Vancoppenolle, M. 
| Better constraints on the sea-ice state using global sea-ice data assimilation Geosci. 
| Model Dev., Copernicus Publications, 2012, 5, 1501-1515


2/ Contents of the data
-----------------------

2A/ Sea ice fields 
------------------
The folder SEAICE_REANALYSIS contains the analyzed sea ice restart files, that is, the assimilated sea ice fields at daily frequency (when observations are not available, the model forecast is considered as the analysis).

The syntax is : mean_restart_ice.EnKF_l2_as_err.PXXXXX.an.nc where XXXXX is a 5-digit number between 2 and 11248. The match between this identifier and the corresponding year, month and day is given by the file DB_FILE/db_EnKF_l2_as_err . The first column of this file is the identifier, and the last column is the date in YYYYMMDD format.

In the restart files, the main variables of interest are "hicif" (the in situ ice thickness, not averaged including open water) and "frld" (the *lead fraction* = 1 - sea ice concentration .

2B/ Mask, mesh, etc.
--------------------
The folder GEOM contains the ORCA2 grid specifications. The file "ORCA2_mesh_mask.nc" has some important variables:
	- tmaskutil, which is the land-sea mask (1 at ocean points, zero elsewhere) 
	- e1t and e2t, the grid cell edge lengths, in meter.
	- nav_lon and nav_lat, the longitude and latitude.

2C/ Sea ice area, extent and volume
-----------------------------------
Those are in the AREA_EXTENT_VOLUME directory. There are several text files with the name of a "sector":
	Amundsen_Bellingshausen_Seas.txt	[ LAT<0 , 130W < LON < 60W  ]
	Arctic.txt				[ LAT>0                     ]
	Indian_Ocean.txt			[ LAT<0 , 20E  < LON < 90E  ]
	Pacific_Ocean.txt			[ LAT<0 , 90E  < LON < 160E ]
	Ross_Sea.txt				[ LAT<0 , 160E < LON < 130W ]
	Southern_Ocean.txt			[ LAT<0                     ]
	Weddell_Sea.txt                         [ LAT<0 , 60W  < LON < 20E  ]

Each file has 7 columns
Column 1: identifier (defined as in section 2A above)
Column 2: Year
Column 3: Month
Column 4: Day
Column 5: Sea ice area [million km2] (sum of sea ice concentration * cell area)
Column 6: Sea ice extent [million km2] (sum of cell area where sea ice concentration > 15%)
Column 7: Sea ice volume [thousands km3] (sum of sea ice concentration * sea ice thickness * cell area)

Missing values are represented by a value of -9e19

The Matlab script used to generate these time series is available at SCRIPTS/compute.m