How do newly rescued pressure observations help reconstruct the weather?

The pressure observations that are being rescued will have a large demonstrable effect on our knowledge of past weather.

In the graphic below, the left hand side always shows our current estimates of the locations of the isobars (lines of equal pressure) for 9am on 26th February 1903. There are 80 different sets of lines, each of which are considered equally likely given the information currently available. There is not much agreement over western Europe, so it looks very messy!

The animation on the right hand side shows how confident we become when individual observations (red dots) are added one by one. Starting in southern Europe the isobars gradually begin to become better defined until a much clearer picture emerges when all 55 newly rescued observations have been added.

We will be repeating this process for the whole 1900-1910 period that we are rescuing data for so that we can see the improvements in detail. This will demonstrate the value of this data for answering interesting science questions about how the circulation of the atmosphere varies over time.

An analogy is that we currently have blurred ‘polaroid’ pictures of the weather at this time, but gradually we are sharpening the image. As we add observations the picture becomes more like a digital photo.

[Very technical details: this animation uses all 80 members from v3 of the 20th Century Reanalysis and an offline version of the Ensemble Kalman Filter to assimilate the new observations.]

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