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Ulysses measurements of variations in the solar wind‐interstellar hydrogen charge exchange rate
Author(s) -
McComas D. J.,
Funsten H. O.,
Gosling J. T.,
Pryor W. R.
Publication year - 1999
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/1999gl900519
Subject(s) - heliosphere , physics , solar wind , astrophysics , hydrogen , charge exchange , ionization , population , interplanetary medium , energetic neutral atom , astronomy , polar wind , coronal mass ejection , atmospheric sciences , plasma , ion , interplanetary spaceflight , nuclear physics , demography , quantum mechanics , sociology
Charge exchange with solar wind protons is the primary ionization process for interstellar hydrogen traveling through the heliosphere. In this study we use Ulysses solar wind observations to examine and quantify variations in charge exchange. We find that these variations are largest within stream interaction regions where the charge exchange rate is tens of times larger in compressional, corotating interaction regions (CIRs) than in rarefactions. Similarly, we find enhanced charge exchange in compression regions ahead of fast CMEs. As a consequence, much of the interstellar hydrogen at low latitudes is picked up in pulses as CIRs and fast CMEs sweep past. Observations over Ulysses' first full polar orbit indicate that the charge exchange rate is higher at low than at high latitudes, and that this rate drops off more slowly than the inverse square of heliocentric distance. We believe that this is due to the growth of CIRs as they propagate out through the inner heliosphere. The variability of hydrogen charge exchange has implications for the analysis of scattered Lyman‐α observations and produces variations in the pickup rates of newly ionized interstellar hydrogen, which is a seed population for anomalous cosmic rays.