The land sea mask used in the ECMWF IFS changed with the introduction of 41R1. Figures in the table below are examples of where there have been changes (for colour meaning refer to the image titles, all are consistent). Mostly the changes were for the better, with some notable improvements over Europe†. Unfortunately however there have also been some areas of degradation, specifically in the Pacific, where some islands have unfortunately 'disappeared' due to errors in the new reference geographical dataset. All known instances of disappearing islands are included below, in rows 2-7. It is mainly HRES that is affected. Locations of these plots are also marked on the global maps on row 1. Following consultation it was decided to wait until the next cycle (41R2) before these errors are rectified. Row 8 illustrates that there have also been some significant changes in the land and sea points around Antarctica.

† Mostly the land area of Europe is larger in 41R1 than it was in 40R1 (see e.g. row 9). Interestingly, in ENS Leg A the Faeroe Islands are now represented by a (new) land point, and there are also new land points over southwest England, in leg A and leg B.


Land Point Differences between 40R1 and 41R1

Row LabelArea


ENS - Leg A

 = to day 10

ENS - Leg B

= from day 10

1GlobeLabels are included to show locations of other plots below.
2Samoa (and Niue) 

In HRES: Samoa reduced from 12 land gridpoints to 1. Niue is now a sea point.

In ENS to day 10: Samoa reduced from 2 land gridpoints to none.

3Tahiti and the Marquesas  In HRES: Main Tahiti and Marquesas islands are now just sea points.
4Chatham  In HRES: Chatham island is now just sea points.
5Micronesia  In HRES: Micronesia island is now just a sea point.
6Marion  In HRES: Marion island is now just a sea point.
7Noname  In HRES: Nameless island near Antarctica is now just a sea point (lower left of plot)
8Antarctic PeninsularThe distinction between permanent sea ice and land around Antarctica is blurred. Locally around Antarctica there are some large changes in 41R1 compared to 40R1 (not just in the area shown - more HRES examples can be seen here). Two reasons for representing some of the sea ice as land are (i) that it extends well above sea level locally, eg >50m, and (ii) its roughness (& sub-grid orography) is not uniform.
9Baltic / NW Europe
These plots illustrate the general point that over Europe as a whole there are more land points in 41R1 than in 40R1 (more green dots). Land and sea depiction in 41R1 is believed to be much more accurate in the European region.
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