[OpenMadrigal-developers] F10.7 Multiday average proposal

[Shunrong Zhang]

If we totally redefine Fbar to be for the last 81 days, that is fine; 
but I think what Phil suggested was "for any day less than 40 days in 
the past, we  calculate FBAR as an average over the most recent 81 days. 
" That sounds to me that you still use the old definition for any day 
greater than day 40 days in the past. I wanted to say that there should 
not be two definitions for one parameter. From modeling point of view, I 
agree with John that "ending with the day of interest will tend to give 
a somewhat better prediction". That was why I suggested my option (2) 
for a new F107 index that is an average over the past 81 days and is 
always available.

Shunrong


John Holt wrote:
> Phil's suggestion seems reasonable. In the context of a model, the
> definition of F10.7bar as a centered average is an absurdity,
> obviously. In the "old" days we always used the 81 days ending with the
> day of interest, but at some point it apparently became more common to
> forget causality and use a centered average (I have seen 27 days, 54
> days, 81 days 90 days and one year) and a variety of filter functions
> causal and not.  Unfortunately, in my view, causal filters fell out of
> favor.  Had they not, we would not have had this problem and would have
> been consistent with the laws of physics as well, which is no small
> thing. I suspect, by the way, that using the 81 days ending with the
> day of interest will tend to give a somewhat better prediction than
> using a centered average, even though the model was computed using a
> centered average.
>
> John
>
> ________________________________________________________________________
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> | John M. Holt                         tel:   781-981-5625             |
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> | MIT Haystack Observatory             email: jmh at haystack.mit.edu     |
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>> Date: Fri, 20 Oct 2006 11:53:15 -0400
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>> Phil Erickson has suggested we modify out definition of the F10.7 
>> Multiday average (FBAR).  Right now this is an 81 day average, where the 
>> 81 days the center day, 40 days in the past, and 40 days in the future.  
>> The problem with this definition is that this parameter is never 
>> available for any day less than 40 days in the past.  For example, since 
>> MSIS uses FBAR as an input, this means that MSIS also cannot be run for 
>> any day less than 40 days in the past. 
>>
>> Phil has suggested that for any day less than 40 days in the past, we 
>> calculate FBAR as an average over the most recent 81 days.  From the 
>> Madrigal point-of-view, this means that every time we reload geophysical 
>> data, the FBAR values for the latest 40 days might change slightly.  At 
>> present, FBAR is not loaded into Madrigal for days less than 40 days ago.
>>
>> We would document this FBAR definition on the Madrigal help pages.  Any 
>> thoughts?
>>
>> Bill Rideout
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-- 

_____________________________________________________________
 Shunrong Zhang  (shunrong at haystack.mit.edu)
 http://www.haystack.mit.edu/~shunrong/
 MIT Haystack Observatory, Route 40, Westford, MA 01886, USA
 Phone: 781-981-5725 FAX: 781-981-5766