Cosmic Ray Positron Fraction Observations during the A- Magnetic Solar Minimum John Clem and Paul Evenson* * Presenter AESOP Departing Esrange, Sweden

The combination of the outward flowing solar wind and the solar rotation produces the spiral geometry of solar magnetic field lines as shown above. A+ symbol represents the case when the dipole axis projection rotation axis is positive and A- the projection is negative Reversals of the solar magnetic field occurs every 11 years. q>0 q<0 q>0 Drift Directions As the particle moves along a curved magnetic field line it experiences a centrifugal force due to the field curvature, and therefore the particle trajectory drifts perpendicular to both the centrifugal force and B. In this case, it is either toward or away from neutral current sheet depending on the charge sign and polarity. Gradients in the HCS will also cause drifts. It is important to note the resulting drift direction is charged sign dependent. 19

Illustrates how the response of electrons and nuclei to changing conditions in interplanetary space is qualitatively similar but quantitatively different. Fluxes are low when the sun is active and high when the sun is inactive, however particles with opposite sign to the polarity state reveal a narrower time profile than those with like charge-sign. The electron profile in the 1990s seems to be broader than the helium spike profile observed in the 1980s possibly due to positron component in the electron observations. 1.2GV Electrons 1.2GV Helium Time Profile of Helium and Electron observations at a rigidity of ~1.2 GV Filled Symbols Open Symbols Magnetic Polarity

AESOP instrument Schematic Drawings of the instruments. Briefly, AESOP detects electrons with plastic scintillators T1, T3 and G (anticoincidence) and the gas Cherenkov detector T2. It measures the electron energy in a leadglass (T5) calorimeter. Scintillator cup T6 also assists in particle identification and energy determination by counting the number of particles that escape the calorimeter. A permanent magnet and a spark chamber SC1,2,3 hodoscope determine the charge sign and momentum of the electron. 25

Vertical axis: Energy measured in the Pb-Glass calorimeter Horizontal: the trajectory deflection in the magnet in units of inverse rigidity. Curve represents the ideal instrument response for positrons (positive side) and electrons (negative side). The red symbols represents those events tagged as high energy protons (E>20GeV to trigger gas CK) as determined by the T3 scintillator detector. The particle ID and energy of each event is assign using a likelyhood analysis 27 AESOP 2006 flight trajectory

Solid line is the modulated (charge sign independent, i.e. no drifts) abundance as calculated by Protheroe (1982). Dashed lines are from Clem et al. (1996) for A+ (top line) and A- (bottom line). Solid symbols show data taken in the A+ state, while the open symbols represent data taken in the A- state. The world summary of observations. Compiled AESOP balloon instrument measurements and calculations of the positron abundance including the 2006 preliminary results.

Shaded rectangles represent periods of well defined magnetic polarity. The black line is a positron abundance prediction based on the analysis of Clem et al. (1996). The red line is an antiproton/proton ratio drift (steady- state) model (Bieber et al. 1999) interpolated to 1.3GV. The current sheet tilt angles used in the drift model were acquired from the Wilcox Solar Observatory database. Dashed lines represent the predicted results for future observations. The anti-protons were measured by the series of BESS flights (Asaoka et al. 2002). Time profile of positron abundance (black) and anti-proton ratio (red) at a rigidity of roughly 1.3GV.