AMS 2014 Monitoring the South Atlantic Anomaly with Photometric Particle Hit Noise in Low 11th Conference Poster 317 R. Schaefer1, L. Paxton1, Giuseppe Romeo1, Christina Selby2, Brian Wolven1, Syau-Yun Hsieh1 1Johns Hopkins University Applied Physics Laboratory, Laurel, MD, United States 2Rose-Hulman Institute, Terre Haute, IN, United States http://ssusi.jhuapl.edu

The South Atlantic Anomaly (SAA) A New Model of the SAA Monitoring the Intensity and Position of

The SAA is a region where the , and hence the inner radiation Filtered, binned data averaged of the year 2006 displays the well known shape of the SAA the SAA Radiation belt dips to its lowest point over the Earth. in Low Earth Orbit flying through this region are bombarded with the energetic particles trapped in the SAA Drift in Time inner radiation belt, causing problems with electronics and instruments. Counts per second from the UV 428 nm nadir photometer Magnetic field contours at instrument, binned and Like the rest of the Topex geomagnetic field, the SAA altitude (1340 filtered over the course km). of the year, provides a also moves with time. We map of the intensity of have determined the drift the particle radiation in rate by plotting the location the South Atlantic of the fitted centroid rate Anomaly. year by year. This fit is Binned into 2o x 2o bins made to our spherical harmonic expansion for The unsymmetric magnetic field A plot of the locations of electronics problems (latitude x longitude) causes the inner radiation belt to dip (Single Event Upsets - squares) on the Topex/ 2006 with the position and lower over the South Atlantic (figure Poseidon , most of which occur in the overall intensity are free from Wikipedia) South Atlantic Anomaly region parameters. Particle hits in the polar regions are also seen during geomagnetic storms – we have filtered them out with a geographical data cut (purple box) for this work

UV Photometric Instruments and SAA geographic data filtering box These storm related Particle Hits polar region MeV Work Westward drift Northward drift Year range Measurement energy particle fluxes (deg/year) (deg/year) altitude (km) Table comparing are important for Badhwar (1997) 0.28 0.08 1974-1995 393 & 438 km drift rates found Fuerst et al. (2009) 0.29 N.A. 1996-2006 592 SAA understanding storm here to values in The SSUSI instrument dynamics and for Cassadio & Arino 0.35 0.12 1992-2010 800 (2011) previous work consists of a scanning monitoring spacecraft This work 0.31 +/- 0.04 0.18 +/- 0.06 2004-2011 850 imaging spectrograph charging rates. Our (uses 2-d microchannel next effort will be to plates) and 3 nadir better model the SAA Intensity Variations and Solar Cycle pointing photometers. Sub-auroral MeV particles GUVI consists of only distribution and Variations in overall intensity of the SAA year by year l the scanning imaging variability of these polar max Total Power = C2 spectrograph. All UV MeV particles. ∑ l photometers on these l=0 --- Sunspot number instruments are Later years are affected by particle hits The model intensity can be where satellite orbit Modeling the SAA shape determined orbit by orbit limits amount of for every SAA passage. useable data Orbital Parameters The SAA induced count rate is modeled with a spherical The solar zenith angle filter harmonic expansion for each year of data SSUSI (Spectial Sensor Ultraviolet severely restricts data in later years Spectrographic Imager) flies on DMSP lmax +l F16, F17, F18, and soon F19 spacecraft SAA(ϑ,φ)= C Y (ϑ,φ) ∑ ∑ lm lm Solar cycle variations DMSP ~ 99 degrees l=0 m=−l consistent with CRAND Re DMSP Orbital Altitude ~ 850 km 2 lmax +l 2 lmax theory. SAA(ϑ,φ) sinϑdϑdφ = C = C2 ∫ ∑ ∑ lm ∑ l GUVI (Global UltraViolet Imager) flies on l=0 m=−l l=0 NASA’s TIMED mission 2 +l 2 C = ∑ C Total integrated squared counts TIMED Orbital Inclination ~ 74 degrees l lm TIMED Orbital Altitude ~ 630 km m=−l over the entire area of the SAA SAA Shorter Term Intensity Variations Angular Power Spectra Relatively Constant Over Time Taking each year from 2006-2008 and subtracting the mean gives us the plot below. We see a “two-humped” pattern reminiscent of the Russel McPherron effect, but the not quite Energy Sensitivity of SSUSI Nadir Photometers consistent – one peak appears near the September equinox, but the other occurs in mid The SAA angular (northern hemisphere) winter. power spectra are The response of photomultiplier instruments to hits from relatively constant up energetic charged particle radiation is well studied (e.g., Sunshades to a normalization Johnson, 1973 and Gavrilov, et al, 1995). It was noted that the photometer pulse rate is proportional to the the Equinoxes energetic particle hit rate for charged particles of energy ∼ 1 MeV or greater. Phototubes are surrounded by metal. The housing is 1/16 inch thick aluminum. Most paths between the phototube and outer space pass through two layers of aluminum, so 1/8 inch aluminum is roughly the amount of metal between the phototube and empty space. Charged particles with low energies cannot pass through 1/8 inch aluminum. The energies of particles that can Some sub-auroral Phototubes are mounted penetrate this amount of metal: horizontally in the white particle noise affects the fit of coefficients l=1-3 instrument box below the • Protons (Ep>25 MeV) sunshades. • Electrons (Ee>1.5 MeV)

SAA Visualization Monitoring Tool Based on Model Performance Orbit by Orbit SSUSI photometer noise data provides daily monitoring of the state of the SAA over a many years. Used in conjunction with the SAA model, we can provide detailed monitoring and even SAA Model and SSUSI Near-Realtime Data forecasting of the location and intensity of the particle fluxes in the SAA. Example orbital pass from 2006 The prototype Widget at right Example orbital pass References from 2008 was developed • Badhwar, G. 1997, Drift Rate of the South Atlantic Anomaly, Jour. Geophys. Res., 102, 2343-2349. as a Space • Casadio, S., and Arino, O. 2011, Monitoring the South Atlantic Anomaly using ATSR instrument series, Advances in Space Research, 48, 1056-1066. doi:10.1016/j.asr.2011.05.014. Stiuational • Fuerst, F., Wilms, J., Rothschild, R. E., Pottschmidt, K., Smith, D. M., Lingenfelter, R. 2009, Temporal Variations of Awareness tool strength and location of the South Atlantic Anomaly as measured by RXTE, Earth Planet. Sci. Lett., 281, 125-133. for the Air Force • Gavrilov, V., Kuleshov, S., Rusinov, V., Ulyanov, A., Umashev, A., 1995 Sensitivity of Photomultipliers to Protons and Gammas, CMS Technical Note 95 145, November 15, 1995. Weather Agency. • Hess, W. N., 1959 Van Allen Protons from Cosmic-Ray Neutron Leakage, Phys. Rev. Lett., 3, 11. It uses SSUSI This model of the SAA accurately predicts (up to an overall normaliztion) the intensity of the • Johnson, S. M., 1973, Radiation effects on multiplier phototubes, IEEE Trans. Nucl. Sci., 20, 1, 113-124. photometer data particle hits in the SSUSI instrument given the satellite track and a fit to the SAA positional drift • Singer, S. F. 1958, Trapped albedo theory of the radiation belt, Phys. Rev. Lett., 1, 181-183. rate • Vernov, S. N., Gorchakov, E. V., Shavrin, P. I., and Sharvina, K. N. 1967, Radiation Belts in the Region of the South to update the Atlantic using ATSR instrument series, Space Science Reviews, 7, 490-533. intensity of the ! SAA.