Model "Spin up"

[TheTrials]

This was brought up in the NYC thread (post below) and would love an explanation about model spin up and why the NAM seems to be prone to it and how the other models deal with it or are affected by it. The OP has mentioned this before. Articles and/or explanation is appreciated. Thank you.

http://www.americanwx.com/bb/index.php/topic/27434-signals-for-heavy-rain-late-next-week/page__view__findpost__p__1036624

[ohleary]

This was brought up in the NYC thread (post below) and would love an explanation about model spin up and why the NAM seems to be prone to it and how the other models deal with it or are affected by it. The OP has mentioned this before. Articles and/or explanation is appreciated. Thank you.

http://www.americanw...ost__p__1036624

The NAM (like the other major models) has a warm start with data assimilation, which should pretty much wipe out any spin up issues. Spin up is mainly an issue with a model that has a cold start, i.e. initialized with another more coarse model run with no data assimilation. From the MetEd site (need a login to access the "How Mesoscale Models Work" module):

"The spin-up problem depends on whether the model had a “warm start” or “cold start.” In a warm start, the model uses a data assimilation system to incorporate data, such as surface observations and soundings, over a long time to help create the analysis. The data assimilation system merges observations with the model run in such a way as to preserve the ongoing circulation. This way, the resulting analysis will not exactly match surface observations, but will reflect an ongoing evolution of conditions just prior to the analysis."

[Amped]

It's cause of the Eddy Flux Convergence.

[SBUWX23]

I guess things have changed more than I was taught. Lovely graduate school professors dont even know anything. Sorry for any confusion I may have caused and thanks for clearing things up

[TheTrials]

The NAM (like the other major models) has a warm start with data assimilation, which should pretty much wipe out any spin up issues. Spin up is mainly an issue with a model that has a cold start, i.e. initialized with another more coarse model run with no data assimilation. From the MetEd site (need a login to access the "How Mesoscale Models Work" module):

"The spin-up problem depends on whether the model had a “warm start” or “cold start.” In a warm start, the model uses a data assimilation system to incorporate data, such as surface observations and soundings, over a long time to help create the analysis. The data assimilation system merges observations with the model run in such a way as to preserve the ongoing circulation. This way, the resulting analysis will not exactly match surface observations, but will reflect an ongoing evolution of conditions just prior to the analysis."

Thank you.

I guess things have changed more than I was taught. Lovely graduate school professors dont even know anything. Sorry for any confusion I may have caused and thanks for clearing things up

You did everyone a great service by bringing this up since I am sure you weren't the only one who was up to date on this matter.