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December 9, 2017 - Storm Discussion (Breaking the seal on the season for many)

Baroclinic Zone

By Baroclinic Zone,
in New England

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Typhoon Tip

Typhoon Tip

Posted
Posted
2 minutes ago, OceanStWx said:

All models basically handle spurious (maybe less spurious, more poorly modeled?) data the same way. The analysis starts running, observations (think raobs, satellite, etc) come in, the analysis is corrected in the direction of observations, then the analysis is allowed to continue. This is why upper air data can be so important for getting a sense of the true strength of features.

The difference becomes in how the models handle that observational assimilation. All models can handle the 3D stuff (the atmosphere is 3D after all), but the Euro is king for a reason. The 4th dimension is time. The Euro can place the observations at the correct time anywhere in the assimilation window. The GFS for instance has to assume that all observations happen at a specific time, whether that's the beginning, middle, or end of the window. If the window is say 6 hours long, that could mean very large errors are introduced right off the bat. The sacrifice is shorten the assimilation window (less obs). So the Euro can have a longer window (more obs), and correctly place those obs in time.

Now back to waiting on the reggie.

still no RGEM?  

Huh.. i'm at work stuck in a meeting - 

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CoastalWx

CoastalWx

Posted
Posted
2 minutes ago, OceanStWx said:

All models basically handle spurious (maybe less spurious, more poorly modeled?) data the same way. The analysis starts running, observations (think raobs, satellite, etc) come in, the analysis is corrected in the direction of observations, then the analysis is allowed to continue. This is why upper air data can be so important for getting a sense of the true strength of features.

The difference becomes in how the models handle that observational assimilation. All models can handle the 3D stuff (the atmosphere is 3D after all), but the Euro is king for a reason. The 4th dimension is time. The Euro can place the observations at the correct time anywhere in the assimilation window. The GFS for instance has to assume that all observations happen at a specific time, whether that's the beginning, middle, or end of the window. If the window is say 6 hours long, that could mean very large errors are introduced right off the bat. The sacrifice is shorten the assimilation window (less obs). So the Euro can have a longer window (more obs), and correctly place those obs in time.

Now back to waiting on the reggie.

That is a great explanation for those who wondered what 4D Var is. Nice post!

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CoastalWx

CoastalWx

Posted
Posted
Just now, OceanStWx said:

I should also say, that's why the Euro only runs twice a day. Having the longer window to assimilate data is expensive as far as computing resources go.

And since it's been awhile that I completed the MetEd module, the EC is the only one that continuous ingests and corrects for observations during this assimilation window? Or does the GFS do this as well?

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OceanStWx

OceanStWx

Posted
Posted
1 minute ago, CoastalWx said:

And since it's been awhile that I completed the MetEd module, the EC is the only one that continuous ingests and corrects for observations during this assimilation window? Or does the GFS do this as well?

I think the GFS does, but like I said it has to assume they all happen at the same time. I still have to read up on what the NGGPS difference will be, if there is one (there should be).

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dendrite

dendrite

Posted
Posted
6 minutes ago, OceanStWx said:

I think the GFS does, but like I said it has to assume they all happen at the same time. I still have to read up on what the NGGPS difference will be, if there is one (there should be).

So all of these RAOBs that get launched between 00-01z are being assumed to have occurred at 00z?

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WxBlue

WxBlue

Posted
Posted
4 minutes ago, OceanStWx said:

Correct. And actually we all launch at 23z, so that way it gets into the model before 00z. 

Yep. That surprised me when I first helped out with launches for MHX office back in my volunteering days. 

Also, some room for time adjustment if there's a thunderstorm in the area. One time, SOO and I found ourselves trapped in the air station for 20 minutes with a snake because a popcorn storm erupted while we were preparing. Just things you deal with in the South.

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