1. Hey there, Guest! Join us in the Discord where it's all weather, all the time, 24/7/365. Membership applications are processed in 24hrs or less. Drop by and see how we've improved this important medium.
    Dismiss Notice

Model Spinup

Discussion in 'Advanced weather & chasing' started by Michael Wilkinson, Mar 12, 2019.

  1. Michael Wilkinson

    Joined:
    Jun 17, 2017
    Messages:
    35
    Likes Received:
    21
    In the Forecasting chapter of Tim Vasquez’s book, Storm Chasing Handbook, (p.119) there’s mention of “model spinup” time.

    I’m not sure that I understand the concept since the way I’m interpreting it makes it very counterintuitive to me.

    Here’s a quote from the book, “within a couple of hours of the model start time, model accuracy is poor due to the effects of ‘model spinup’, the temporary mathematical noise which quickly dampens after the first few hours. This can produce spurious artifacts in the model charts.”

    It sounds like that a model such as the HRRR is producing more accurate forecasts for a few hours in the future than it is for an hour in the future.

    Does that mean that the model is doing something different in obtaining an hour 4 forecast than it is an hour 1 forecast?

    Is the hour 4 forecast based on the model’s hour 3 forecast which is based on the hour 2 forecast which is based on the hour 1 forecast? If so, how does the hour 4 forecast become more accurate than hour 1?

    Where can I find a beginner level, in-depth explanation of model spin up?

    Tim’s book was published in 2009. Some resources I found online that mentioned model spin up were from 2011 and 2015. Is model spin up still a factor to consider with the newest versions of weather models?
     
  2. Paul Knightley

    Joined:
    Feb 6, 2006
    Messages:
    893
    Likes Received:
    154
    Others will be much better placed than me to comment on this, but I think it (at least partially) depends on how the model is started up - if there are no spin-up processes in the initial condition (e.g. various motions) then this might be an issue - but if the model starts with these processes already 'spun up', it eliminates it.
     
    • Informative Informative x 1
  3. Jeff Duda

    Jeff Duda Resident meteorological expert
    Staff Member

    Joined:
    Oct 7, 2008
    Messages:
    2,830
    Likes Received:
    1,182
    Model "spin-up" refers to the initiation of grid-scale circulations that are not present in the initial conditions of a model run. Nearly all high-resolution model runs are initialized from a coarser-resolution field, which means the circulations that the model grid can represent do not exist in the initial conditions. "Spin-up" refers to the process of those circulations coming into being from nothing. The larger the difference in grid spacing between the source of the initial conditions and the model resoution, the longer the 'spin-up' process takes. If you can start a model integration using initial conditions on the same scale as the model domain, then there is essentially no spin-up.

    The reason the HRRR, in particular, does not deal with "spin up" problems, is because it uses the output from a 1-hour 'pre-forecast' that does have spin-up issues as its own initial conditions. This helps alleviate the traditional-spin up problems. Other models do not do this.
     
    • Like Like x 5
    • Agree Agree x 1
    • Informative Informative x 1
    #3 Jeff Duda, Mar 14, 2019 at 1:26 AM
    Last edited: Mar 14, 2019 at 10:52 AM
  4. Tim Vasquez

    Joined:
    Dec 4, 2003
    Messages:
    3,412
    Likes Received:
    18
    One of my readers mentioned the discussion so I figured I'd take a look. I haven't been on the forum much lately due to all the data projects I have going on.

    This is a good discussion and Jeff and Paul posted some good info. I'll likely update all this in the next version of Storm Chasing Handbook, as much of the older text is about 15 years old. I'm planning on at least one more update for next winter (Storm Chasing Handbook 2020) and that may be the final edition.
     
    • Like Like x 1
  5. Steve Miller

    Steve Miller Owner
    Staff Member

    Joined:
    Jun 14, 2004
    Messages:
    1,531
    Likes Received:
    657
    Tim, I'm thrilled to know there is another version on the way! That book and your others were an important part of my early chase days.
     

Share This Page

  1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
    By continuing to use this site, you are consenting to our use of cookies.
    Dismiss Notice