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

Mon May 17 23:48:22 EDT 2021

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<mailto: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

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On Mon, May 17, 2021 at 1:43 PM Jody Wilson <jkwilson at guero.sr.unh.edu<mailto: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><mailto:mark.d.looper at aero.org>
Date: Monday, May 17, 2021 at 1:11 PM
To: "de Wet, Wouter" <wouter.dewet at unh.edu><mailto:wouter.dewet at unh.edu>, "crater-team at lists.sr.unh.edu"<mailto:crater-team at lists.sr.unh.edu> <crater-team at lists.sr.unh.edu><mailto: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><mailto: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<mailto:crater-team at lists.sr.unh.edu> <crater-team at lists.sr.unh.edu><mailto: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
[cid:image001.png at 01D74B44.C7E37170]

Figure 2: Flux Ratio vs. LET vs. Time (3-Dimensioal)

[cid:image002.png at 01D74B44.C7E37170]

Figure 3: Flux Ratio vs. LET vs. Time (2-Dimensioal)
[cid:image003.png at 01D74B44.C7E37170]

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