[Crater-team] Interesting Artifacts in CRaTER Data: 6-Month Periodicity in Low LET Fluxes (including a strange anti correlation)

[Jody Wilson]

There was also a 6-month periodicity in the old proton swoosh summation, 
and there's a 6-month periodicity in the SEPI components (individual 
detectors, Andrew is investigating this further) that is 
indistinguishable from a longitudinal variation.  Mark's explanation may 
be the reason for all of these - I just wanted to point out that 6-month 
periodicities have shown up before.

-Jody


On 5/17/2021 1:28 PM, de Wet, Wouter wrote:
>
> Mark,
>
> Ahh, yes that makes sense! When I cut everything below the peak the 
> 6-month periodicity in the low LET flux data all but disappears.
>
> Thanks for the quick response. It looks like I will need to cut 
> everything below roughly 0.3 keV/micron out of the analysis.
>
> Wouter
>
> *From: *Mark D Looper <mark.d.looper at aero.org>
> *Date: *Monday, May 17, 2021 at 1:11 PM
> *To: *"de Wet, Wouter" <wouter.dewet at unh.edu>, 
> "crater-team at lists.sr.unh.edu" <crater-team at lists.sr.unh.edu>
> *Subject: *Re: Interesting Artifacts in CRaTER Data: 6-Month 
> Periodicity in Low LET Fluxes (including a strange anti correlation)
>
> *Caution - External Email*
>
> If I remember correctly, that’s due to thermal noise in the lowest PHA 
> channels, which is periodic because of the differing sun exposure as 
> the orbit changes.  I will see if I can find some plots that I made 
> near the beginning of the mission which showed this.  It is why I 
> discard the lowest PHA channels and never look much below the proton 
> peak – the data are not valid down there.
>
> --Mark
>
> Mark D. Looper
> Space Sciences Department
> The Aerospace Corporation
> M/S M2-260
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> *From: *Crater-team <crater-team-bounces at lists.sr.unh.edu>
> *Date: *Monday, May 17, 2021 at 7:07 AM
> *To: *crater-team at lists.sr.unh.edu <crater-team at lists.sr.unh.edu>
> *Subject: *[Crater-team] Interesting Artifacts in CRaTER Data: 6-Month 
> Periodicity in Low LET Fluxes (including a strange anti correlation)
>
> All,
>
> While working on the final processing of the observed CRaTER Flux vs. 
> LET data, I have found an interesting artifact.
>
> I have been looking at the Flux vs. LET vs Time data for the entire 
> mission so far.
>
>   * For the smallest LET values, there seems to be a 6-month
>     periodicity in the observed flux, see the ‘wavy’ red edge in
>     Figure 1 below.
>   * When I divide everything by the flux observed in August 2009, I
>     get the flux ratio shown in Figures 2 and 3 below. When looking at
>     the flux ratio, the 6 month periodicity becomes very clear.
>   * One interesting thing I also notice is that it seems like there is
>     an anti-correlation between the flux in lowest LET bins (< 0.25
>     keV/micron) and the slightly higher LET bins  (> 0.25 keV/micron).
>
> Has anyone else observed this yet? Any thoughts about what is causing 
> this?
>
> Thanks,
>
> Wouter
>
> Figure 1: Flux vs. LET vs. Time
>
> Figure 2: Flux Ratio vs. LET vs. Time (3-Dimensioal)
>
> Figure 3: Flux Ratio vs. LET vs. Time (2-Dimensioal)
>
>
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