[Crater-team] Albedo from slopes; Carmageddon in the Pacific

[Mark D Looper]

Hello—

                A landslide Monday took out the main highway from this side of the island to downtown, and as a result traffic on the remaining routes is awful.  Unfortunately, it is no longer feasible for my wife to take both kids to school, and so I am losing half a working day on the road taking one of them in the morning and picking them both up.  (I know people have worse commutes in L.A., but still…)  We hope this will revert to normal next week, but today I may not make it back in time to dial in to the telecon, though I’ll try.

                Partly as a result of losing such a big chunk of yesterday, I didn’t quite finish a brief PPTX I wanted to send reporting the results of my calculations of albedo from sloping surfaces.  I attach a couple of figures that will go into it when I finish it later today; these are my usual energy-angle plots for proton albedo produced by all GCRs (solar minimum spectra) from a dry FAN surface.  One is a repeat of the results from a horizontal target surface; the other shows what you get when you (1) tilt the simulation by 15 degrees, (2) discard albedo particles coming out below horizontal or due to primary GCRs coming in from below horizontal in the new coordinate system, and (3) average over all azimuths around the new vertical.  Implicitly, this amounts to the assumptions that the target surface has 15 degrees of slope everywhere, in random azimuths, and that the individual patches that slope in the same azimuthal direction are small compared to the sensor FOV and large compared to the size of the contained GCR showers (about 1 meter, from previous work).

You can see that the strong hardening and intensification of the spectrum near the limb in the 0 degree (horizontal) baseline plot is lost because most of those particles are cut out by step (2) above – only a band going across the slope is left with grazing GCRs coming in and near-horizontal albedo coming out.  The near-vertical albedo (left side of the plot) has a similar distribution but is diluted by the discarding of some primary GCRs, and past the 75 degree zenith angle where the line of sight starts to run into the ground you see the lower, more isotropic fluxes from the more vertical directions in the baseline simulation being averaged over the azimuths that are nearer to horizontal in the tilted simulation.  I have produced, but not quite yet collected into a plot, comparisons of damp (10 cm of 10% H) vs. dry albedo in the same energy/angle bands I showed earlier (Geant4 meeting, AGU meeting), for a range of tilts from 0 to 30 degrees; I will send this out in a PPTX later today.  I expect that steeper slopes will make everything resemble the near-vertical direction from the original level simulations.

Hope to talk to you on the telecon, but not taking bets—
--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
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