All will be assimilated

Weather from a scout run of the 20th Century reanalysis, using the US oldWeather observations.


The observations we are recovering will have many uses, but one is clear – they will be assimilated into collective reconstructions of historical weather (reanalyses). We’ve done this already with the original set of Royal Navy ships, and now we are starting to use the US Arctic ship observations in the same way. Leading the way, again, is the 20th Century reanalysis (we are working on nineteenth century records at the moment, but it’s too late to change the name now); the video above shows a new reconstruction of the weather for 1880 and 1881, and stars three of our ships (red dots) Jeannette, Corwin, and Rodgers. As well as the wind (vectors), temperature (colours), sea-ice, rain (black shading), and observations used (dots), it shows grey fog masking the areas where the reconstruction is still very uncertain (because there are no observations there – yet).

The improvement from our new observations can be seen clearly in the gaps in the fog surrounding each red dot, but the effect can be seen even more starkly if we follow one ship:

Observations from the arctic voyage of the USS Jeannette.


The map shows the route of the ship and the sea-ice for the period. The graph shows sea-level pressure, and near-surface air temperature, as observed by the ship (red dots), as reconstructed by 20CR version 2c (not using the ship’s observations: light grey band), and as reconstructed by a scout version of 20CR assimilating the Jeannette’s pressure observations (dark grey band – starts in Nov. 1879). Small yellow dots mark the other observations available to the reanalyses. The narrowing of the band indicates a reduction in our uncertainty about the weather – an increase in the value of the reconstruction.

So far we’ve only captured those three ships, but we’ll get to the rest – their observations and historical distinctiveness will be added to our reconstructions. Resistance is futile.

4 responses to “All will be assimilated”

  1. Kathy Wendolkowski says :

    Resistance is futile…

  2. Craig says :

    If I understand correctly, there is a substantial reduction in the uncertainty of the air pressure but very little for the air temperature. Why is that?

    • Philip says :

      We treat pressure and temperature differently in this reanalysis: pressure is assimilated – so we force the modelled weather as close to the observed pressures as possible within the physical constraints of the model. We don’t do this with the temperatures, so they are only improved as a side-effect of improving the pressure.

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  1. Voyage of the Jeannette | Daily Zooniverse - June 5, 2015

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