[Crater-team] Another six months of D5/D6 LET spectrum tracking

[Mark D Looper]

Hello—

                With FY21 over, and with it the scramble to finish projects whose funding turned into a pumpkin at midnight last Thursday, I can start returning my focus to CRaTER.  The first thing I wanted to do is add another six-month extension to the GCR LET spectrum time history that we published in Space Weather last year; I attach one image with the full D5/D6 spectra, another with the spectra blown up in the H/He region to show the (subtle) changes more readily, and a third extending the plot of dose rate that we showed in the paper’s appendix.  As a reminder, the last period in the full peer-reviewed paper was 2019248-2020066, which showed intensity about 4% above the already record-setting intensity (per Mewaldt et al.) in 2009259-2010066, which is the red curve in the spectra plots.  For the cover image on the Space Weather issue, we added 2020066-2020248, shown in blue on the plots; this was 6% above the start of the mission and (as seen in the dose plot) was the peak during the past solar minimum.  Since then the intensity has been declining, but the new black curve for 2021066-2021248 is still slightly above the red one from the start of the mission.  (The green curve for 2014066-2014248 is the lowest intensity measured, from the last solar maximum.)

                For quite some time I have been meaning to pull out a clean triples proton measurement from the quiet-time GCR “swoosh” with three-detector consistency checks; unfortunately, there is only a very narrow energy window between the tip of the swoosh and where it runs into the scruff near the origin of a two-detector crossplot.  However, there’s a decent span of energies along the helium swoosh before it runs into the proton track, so I had also begun to define cuts to select that out; and, looking at the D135 high-Z crossplots, there are clear swooshes for many elements, albeit with more or less poor statistics.  Still, using Geant4 simulations to calculate effective geometry factors (i.e., accounting for particles lost to fragmentation in the stack), I think we can pull out clean time series for quite a few elements over an entire solar cycle with minimal background (during quiet times – I still haven’t done much to figure out the SEP problems).  These will cover energies for each species that are near or below the GCR peak, i.e., that both have significant intensity and are strongly modulated by solar activity.  My main focus still needs to be on pulling together that long-delayed paper on the effects of H/H2O on albedo; however, this may be of value in the “mission support” part of our ESM5 proposal, as (in particular) I think we go to higher energies than ACE CRIS/SIS for the lighter elements, albeit with less sensitivity.

Talk to you Wednesday—
--Mark Looper

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
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