Interplanetary Weather Indices

The main CREME programs (those that output energy spectra, LET spectra, or upset rates) require further information: First, the cosmic ray flux subroutines require the date, the range of nuclear charges considered, and an "interplanetary weather index". The date (in years) tells where one should be in the solar cycle. The weather index M picks which of several sources and solar conditions to use in calculating the cosmic ray flux near the earth. A weather index of M=1 gives our best approximation to the galactic cosmic ray flux at the given date. This flux is included in all other "weather conditions", except for 3. This value (M=3) gives worst-case galactic cosmic ray fluxes that allow uncertainties in flux data and solar activity. These fluxes are so severe that they have only a 10% chance of being exceeded by actual fluxes at any moment. When M=2, the anomalous component, assumed fully ionized, is added to galactic cosmic rays. When M=4, a singly-ionized "anomalous component is assumed. The singly-ionized particles are affected differently than fully-ionized particles by geomagnetic cutoff. When this weather condition is chosen, the "geomagnetic cutoff and trapped protons" option must be chosen as well.

Weather indexes from 5 through 12 add solar flare particles to the galactic cosmic rays:

• M=5: peak ordinary flare flux and mean composition
• M=6: peak ordinary flare flux and worst-case composition
• M=7: peak 10% worst-case flare flux and mean composition
• M=8: peak 10% worst-case flare flux and worst-case composition
• M=9: peak Aug. 4, 1972, flare flux and mean composition
• M=10: peak Aug. 4, 1972, flare flux and worst-case composition
• M=11: peak composite worst-case flare flux and mean composition
• M=12: peak composite worst-case flare flux and worst-case composition

The four flare options--ordinary, 10% worst-case, Aug. 1972, and composite-describe different flares. The "peak" flux is the maximum flux resulting from the flare. "Mean" and "worst-case" composition describe flares with normal and worst-case (high) ratios, respectively, of heavy ion fluxes to proton fluxes. See Appendix 1 for details on all of these cases.

The thickness of shielding surrounding the device must be entered in the runs of the main programs. Shielding thickness is entered as the thickness equivalent in inches of aluminum, which the programs convert into g/cm². Shielding of other materials can be approximated by the equivalent thickness of aluminum; i.e., corresponding to the same thickness in mass per unit area.

Another option of the main programs is whether to account for the geomagnetic cutoff and trapped protons. This decision should be made based on the spacecraft's orbit: calculations for low orbits should include these effects, while high orbits (near geosynchronous and beyond) need not. The CREME programs do not compute trapped proton fluxes; these must be entered using the auxiliary program STASS.