15 research outputs found
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Evidence from galactic cosmic rays that the sun has likely entered a secular minimum in solar activity
Since the beginning of the space age, the Sun has been in a multi-cycle period of elevated activity (secular maximum). This secular maximum is the longest in the last 9300 years. Since the end of solar cycle 21 (SC21), however, the Sun has shown a decline in overall activity, which has remarkably increased the fluxes of galactic cosmic rays (GCRs). Here, we investigate the correlation between the modulation of GCRs, the heliospheric magnetic field, and solar wind speed for the last 24 solar cycles to find trends that can potentially be used to predict future solar activity. Specifically, we develop a tool for predicting future magnetic field intensity, based on the hysteresis in the GCR variation, during the last phases of the current cycle. This method estimates that SC25 will be as weak as or weaker than SC24. This would mean that the Sun has likely entered a secular minimum, which, according to historical records, should last for another two cycles (SC25 and SC26)
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Galactic cosmic radiation in the interplanetary space through a modern secular minimum
Recent solar conditions indicate a persistent decline in solar activity—possibly similar to thepast solar grand minima. During such periods of low solar activity, the fluxes of galactic cosmic rays(GCRs) increase remarkably, presenting a hazard for long-term crewed space missions. We used data fromthe Cosmic Ray Telescope for the Effects of Radiation (CRaTER) on the Lunar Reconnaissance Orbiter(LRO) to examine the correlation between the heliospheric magnetic field, solar wind speed, and solarmodulation potential of the GCRs through Cycle 24. We used this correlation to project observations frompast secular solar minima, including the Dalton minimum (1790–1830) and the Gleissberg minimum(1890–1920), into the next cycle. For the case of conditions similar to the Dalton (or Gleissberg) minimum,the heliospheric magnetic field could drop to 3.61 (or 4.06) nT, leading to a dose rate increase of75% (or34%). We showed that accounting for a floor in the modulation potential, invoked by the Badhwar-O'Neill2014 model, moderates the projected radiation levels in Cycle 25. We used these results to determine themost conservative permissible mission duration (PMD,290.4+37.7−35.9and 204.3+26.6−25.2days for 45-year-old maleand female astronauts, respectively) based on a 3% risk of exposure-induced death (REID) at the upper95% confidence interval in interplanetary space
EXPERIMENTAL INVESTIGATION OF WETTABILITY EFFECT AND DRAINAGE RATE ON TERTIARY OIL RECOVERY FROM FRACTURED MEDIA
Radiation Pressure from Interstellar Hydrogen Observed by IBEX through Solar Cycle 24
As the Sun moves through the local interstellar medium (LISM), neutral atoms travel through the heliosphere and can be detected by IBEX. We consider interstellar neutral (ISN) hydrogen atoms with a drifting Maxwellian distribution function in the LISM that travel on almost hyperbolic trajectories to the inner heliosphere. They are subject to solar gravity and radiation pressure, as well as ionization processes. For ISN H, the radiation pressure, which exerts an effective force comparable to gravitation, decelerates individual atoms and shifts the longitude of their observed peak relative to that of ISN He. We used the peak longitude of the observed flux in the lowest energy channel of IBEX-Lo to investigate how radiation pressure shifts the ISN H signal over almost an entire solar cycle (2009–2018). Thus, we have created a new methodology to determine the Lyα effective radiation pressure from IBEX ISN H data. The resulting effective ratio of the solar radiation pressure and gravitation (μeff=1.074±0.038), averaged over cycle 24, appears to agree within the uncertainties with simulations based on total irradiance observations7 while being higher by ∼21%. Our analysis indicates an increase of μeff with solar activity, albeit with substantial uncertainties. Further study of IBEX H response functions and future Interstellar Mapping and Acceleration Probe data should provide significant reduction of the uncertainties and improvements in our understanding of the effects of radiation pressure on ISN atoms