What is reanalysis?

What is reanalysis?
It is today more vital than ever that we have long and reliable historical records of the Earth's climate.
But measurements are not uniformly spread across the world, meaning there are overlapping data in some areas and gaps in others. In addition, older datasets tend to be less complete than recent records.
In the new animation of the Copernicus Climate Change Service (C3S) you can learn more about how reanalysis can solve this problem.

[@stexecutor1]

Very simple and clear explanation of the reanalysis concept. Good animations. I really like the jigsaw analogy.

[@StarpathNav]

Excellent. Thanks. For sailors studying past sailing routes or winning routes in races, it is the reanalysis data we need for that. Not the actual maps or forecasts from the time of the event. ECMWF does have these reanalyzed maps available in grib format, but there may be a charge for the data.

[@MeOuda]

Astonishingly clear explanation!

[@pabloborgesdeamorim7615]

Awesome! I love the metaphor with the puzzle! Very didatic.

[@nazimurrashidchowdhury2843]

Beautiful stuff. Thanks.

[@nicolemontenegro3294]

Muchas gracias!!!

[@Rainstorm121]

Thanks for this explanation. By the way, what actually do you refer to when you use the term 'composite" anomaly of the reanalysis?

[@Saptisunil]

Heyy ! How can i do the aggregate data like max, min and mean in cdsapi ?? Please help me and thanks in advance

[@UKSCIENCEORG]

Slightly misleading as the process involves 'creating data' which does not actually exist. It is a prediction of missing data values. I presented a paper in the late 90s that revealed the numerous issues with ERA-15 at resolving 750hpa circulation patterns - then ERA-40 was wheeled out. It is not a perfect representation of historical conditions and this should be made clearer for the sake of honesty.