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

Tue May 18 08:01:56 EDT 2021

Mark,

Thanks for putting those plots together.  The amplitude of that oscillation
in temperature is larger than I remembered.  Certainly large enough that I
could believe it was causing the low-LET effect seen in the spectrogram you
provided.

Tony

---------------------------------------------------------------------

Anthony Case

Astrophysicist

High Energy Astrophysics Division (HEAD/SSXG)

Center for Astrophysics | Harvard & Smithsonian

Cell: (617) 304 0768

60 Garden Street | MS 58 | Cambridge, MA 02138

On Mon, May 17, 2021 at 11:48 PM Mark D Looper <mark.d.looper at aero.org>
wrote:

> Hello—
>
>
>
>                 I attach a text file and two plots.  The text file
> day_temp.txt is stripped out of the level 2 housekeeping files; there are
> five flight temperatures reported there at a nominal cadence of 16 seconds,
> and this file contains a daily average of each.  The temperature labels at
> the top of the file are as in CRaTER L0-L1-L2 Products--2009-01-29.docx
> from before launch.  In addition to the year, day, and five temperatures, I
> include the number of measurements in the day’s file (nominally 5400); I
> also include the standard deviation of each of the temperatures from the
> mean of each day.
>
>
>
> There is a sinusoidal pattern to the individual measurements in most days,
> which presumably correlates with the orbit; the sigma values will give you
> an idea of its amplitude.  There may be an interplay between spacecraft
> attitude (exposure to the sun’s heat) and altitude (exposure to heat from
> the Moon), but I didn’t take time to examine that.  Clearly something like
> this would correlate with latitude, and could mask or falsify other
> variations; that’s part of why I’ve been meaning for years to do background
> correction on a cadence of much less than one orbit, both for albedo
> looking down and for GCRs (searching for directionality) looking up.  I’ll
> get to it, one of these days…
>
>
>
>                 As for the plots, day_temp.png simply plots the daily
> averages of the five temperatures from the text file.  d6cutratio.png is
> from my Fall 2014 AGU talk; it shows the ratio of the daily D6 LET spectra
> for D2D4D6 triples with the average early in the mission.  You can see the
> 6-month cycle Wouter pointed out, and also the anticorrelation between the
> lowest and near-lowest channels.  That’s part of why (besides statistics at
> higher LET values) I summed up spectra for six months in Figure 6 of our
> 2020 paper in Space Weather.
>
>
>
> Hope this helps—
>
> --Mark
>
>
>
> Mark D. Looper
> Space Sciences Department
> The Aerospace Corporation
> M/S M2-260
> P.O. Box 92957
> Los Angeles, CA 90009-2957
> Mobile: 310-529-3406
> Voicemail: 310-336-6302
>
> Publications: https://www.loopers.org/curvitae.html
>
>
>
> *From: *Justin Kasper <jckasper at umich.edu>
> *Date: *Monday, May 17, 2021 at 12:22 PM
> *To: *Anthony Case <tonycase at cfa.harvard.edu>
> *Cc: *Jody Wilson <jkwilson at guero.sr.unh.edu>,
> crater-team at lists.sr.unh.edu <crater-team at lists.sr.unh.edu>, Mark D
> Looper <mark.d.looper at aero.org>, de Wet, Wouter <wouter.dewet at unh.edu>
> *Subject: *Re: [Crater-team] Interesting Artifacts in CRaTER Data:
> 6-Month Periodicity in Low LET Fluxes (including a strange anti correlation)
>
> Back in the day I think we looked and the correlation with temperature
> seemed the strongest explanation.  There’s temperature in the housekeeping
> data.
>
> On Monday, May 17, 2021, Anthony Case <tonycase at cfa.harvard.edu> wrote:
>
> I concur with the previous statements about this likely being thermal.  At
> least that's what we decided last time we discovered this feature.
>
> Does anybody have an easy way to plot temperature(s) over the course of
> the entire mission?  That'd be a nice confirmation.
>
>
>
> Tony
>
>
>
> *---------------------------------------------------------------------*
>
> *Anthony Case*
>
> *Astrophysicist*
>
> High Energy Astrophysics Division (HEAD/SSXG)
>
> *Center for Astrophysics | Harvard & Smithsonian*
>
> Cell: (617) 304 0768
>
> 60 Garden Street
> <https://www.google.com/maps/search/60+Garden+Street?entry=gmail&source=g>
> | MS 58 | Cambridge, MA 02138
>
>
>
>
>
> On Mon, May 17, 2021 at 1:43 PM Jody Wilson <jkwilson at guero.sr.unh.edu>
> wrote:
>
> 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> <mark.d.looper at aero.org>
> *Date: *Monday, May 17, 2021 at 1:11 PM
> *To: *"de Wet, Wouter" <wouter.dewet at unh.edu> <wouter.dewet at unh.edu>,
> "crater-team at lists.sr.unh.edu" <crater-team at lists.sr.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
> P.O. Box 92957
> Los Angeles, CA 90009-2957
> Mobile: 310-529-3406
> Voicemail: 310-336-6302
>
> Publications: https://www.loopers.org/curvitae.html
> <https://nam12.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.loopers.org%2Fcurvitae.html&data=04%7C01%7Cwouter.dewet%40unh.edu%7Cb92713dc10334b5bc51308d91956d196%7Cd6241893512d46dc8d2bbe47e25f5666%7C0%7C0%7C637568683036598949%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=PrZiSAJ%2FSvnA8ZFavlyyMNgB8tdb%2BGMi7Bm469KVmqo%3D&reserved=0>
>
>
>
> *From: *Crater-team <crater-team-bounces at lists.sr.unh.edu>
> <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>
> <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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