Changes In Cosmic Ray Flux Research Articles

Charging of free-falling test masses in orbit due to cosmic rays: Results from LISA Pathfinder

A comprehensive summary of the measurements made to characterize test mass charging due to the space environment during the LISA Pathfinder mission is presented. Measurements of the residual charge of the test mass after release by the grabbing and positioning mechanism, show that the initial charge of the test masses was negative after all releases, leaving the test mass with a potential in the range $-12$ mV to $-512$ mV. Variations in the neutral test mass charging rate between $21.7$ e s$^{-1}$ and $30.7$ e s$^{-1}$ were observed over the course of the 17-month science operations produced by cosmic ray flux changes including a Forbush decrease associated with a small solar energetic particle event. A dependence of the cosmic ray charging rate on the test mass potential between $-30.2$ e s$^{-1}$ V$^{-1}$ and $-40.3$ e s$^{-1}$ V$^{-1}$ was observed and this is attributed to a contribution to charging from low-energy electrons emitted from the gold surfaces of the gravitational reference sensor. Data from the on-board particle detector show a reliable correlation with the charging rate and with other environmental monitors of the cosmic ray flux. This correlation is exploited to extrapolate test mass charging rates to a 20-year period giving useful insight into the expected range of charging rate that may be observed in the LISA mission.

Barometric coefficient dependence on the geomagnetic cutoff rigidity of neutron monitors

Several studies have been showing that cosmic ray intensity variations observed at the Earth surface can be a useful tool to analyze and predict space weather and climate phenomena. However, before reach the ground level, the cosmic ray particles interact with different atmospheric atoms. This results in the generation of different secondary particles that are differently affected by atmospheric effects. For example, data from neutron monitors, which are widely used to study cosmic ray flux changes related to space phenomena, are significantly affected by atmospheric pressure changes. Thus, for a more detailed study of these instruments’ data, it is necessary to know very well how works the pressure affects secondary neutrons. In this way, we seek to understand how this effect changes according to the cosmic rays’ energy. Thus, in this work, we compare how the barometric coefficient ( β ), which quantifies the pressure effect on the cosmic ray intensity, changes with the geomagnetic cutoff rigidity ( R C ), which quantifies the minimal rigidity/energy that a primary particle needs to reach a given location in a chosen direction. To do that, we used data recorded between January 2008 to December 2016 by several neutron monitors around the globe with R C from 0.1 to 8.3 GV. We experimentally obtained β in two ways: (I) the typical one, which does not explicitly consider isotropic variations unrelated to the pressure effect; and (II) one that considers such variations by using coupling coefficients and a reference neutron monitor station. Like other works, we found that the pressure effect seems to present a logarithmic relation with the cutoff rigidity when we estimate β through the typical method used. On the other hand, we found that the pressure effect linearly decreases with the cutoff rigidity when considering an adjustment in this typical method to eliminate external isotropic variations. This linear relation appears to not change accordingly to the reference monitor chosen. These results enhance our knowledge of how the pressure effect globally acts on the cosmic ray intensity observed at ground level and, consequently, improves future analysis about global changes in the cosmic ray flux related to space weather phenomena.

May 2005 Halo CMEs and Galactic Cosmic Ray Flux Changes at Earth’s Orbit

The pressure corrected hourly data from the global network of cosmic ray detectors, measurements of the interplanetary magnetic field (IMF) intensity (B) at Earth’s orbit and its components B x , B y , B z (in the geocentric solar ecliptic coordinates) are used to conduct a comprehensive study of the galactic cosmic ray (GCR) intensity fluctuations caused by the halo coronal mass ejection of 13 May 2005. Distinct differences exist in GCR timelines recorded by neutron monitors (NMs) and multidirectional muon telescopes (MTs), the latter respond to the high rigidity portion of the GCR differential rigidity spectrum. The Forbush decrease (FD) onset in MTs is delayed (∼5 h) with respect to the onset of a geomagnetic storm sudden commencement (SSC) and a large pre-increase is present in MT data before, during, and after the SSC onset, of unknown origin. The rigidity spectrum, for a range of GCR rigidities (≤200 GV), is a power law in rigidity (R) with a negative exponent (γ=−1.05) at GCR minimum intensity, leading us to infer that the quasi-linear theory of modulation is inconsistent with observations at high rigidities (>1 GV); the results support the force field theory of modulation. At present, we do not have a comprehensive model for the FD explaining quantitatively all the observational features but we present a preliminary model listing physical processes that may contribute to a FD timeline. We explored the connections between different phases of the FD and the power spectra of IMF components but did not find a sustained relationship.

The role of the global electric circuit in solar and internal forcing of clouds and climate

Reports of a variety of short-term meteorological responses to changes in the global electric circuit associated with a set of disparate inputs are analyzed. The meteorological responses consist of changes in cloud cover, atmospheric temperature, pressure, or dynamics. All of these are found to be responding to changes in a key linking agent, that of the downward current density, J z , that flows from the ionosphere through the troposphere to the surface (ocean and land). As it flows through layer clouds, J z generates space charge in conductivity gradients at the upper and lower boundaries, and this electrical charge is capable of affecting the microphysical interactions between droplets and both ice-forming nuclei and condensation nuclei. Four short-term inputs to the global circuit are due to solar activity and consist of (1) Forbush decreases of the galactic cosmic ray flux; (2) solar energetic particle events; (3) relativistic electron precipitation changes; and (4) polar cap ionospheric convection potential changes. One input that is internal to the global circuit consists of (5) global ionospheric potential changes due to changes in the current output of the highly electrified clouds (mainly deep convective clouds at low latitudes) that act as generators for the circuit. The observed short-term meteorological responses to these five inputs are of small amplitude but high statistical significance for repeated J z changes of order 5% for low latitudes increasing to 25–30% at high latitudes. On the timescales of multidecadal solar minima, such as the Maunder minimum, changes in tropospheric dynamics and climate related to J z are also larger at high latitudes, and correlate with the lower energy component (∼1 GeV) of the cosmic ray flux increasing by as much as a factor of two relative to present values. Also, there are comparable cosmic ray flux changes and climate responses on millennial timescales. The persistence of the longer-term J z changes for many decades to many centuries would produce an integrated effect on climate that could dominate over short-term weather and climate variations, and explain the observed correlations. Thus, we propose that mechanisms responding to J z are a candidate for explanations of sun–weather–climate correlations on multidecadal to millenial timescales, as well as on the day-to-day timescales analyzed here.

Are there connections between the Earth's magnetic field and climate?

Understanding climate change is an active topic of research. Much of the observed increase in global surface temperature over the past 150 years occurred prior to the 1940s and after the 1980s. The main causes invoked are solar variability, changes in atmospheric greenhouse gas content or sulfur due to natural or anthropogenic action, or internal variability of the coupled ocean–atmosphere system. Magnetism has seldom been invoked, and evidence for connections between climate and magnetic field variations have received little attention. We review evidence for correlations which could suggest such (causal or non-causal) connections at various time scales (recent secular variation ∼ 10–100 yr, historical and archeomagnetic change ∼ 100–5000 yr, and excursions and reversals ∼ 10 3–10 6 yr), and attempt to suggest mechanisms. Evidence for correlations, which invoke Milankovic forcing in the core, either directly or through changes in ice distribution and moments of inertia of the Earth, is still tenuous. Correlation between decadal changes in amplitude of geomagnetic variations of external origin, solar irradiance and global temperature is stronger. It suggests that solar irradiance could have been a major forcing function of climate until the mid-1980s, when “anomalous” warming becomes apparent. The most intriguing feature may be the recently proposed archeomagnetic jerks, i.e. fairly abrupt (∼ 100 yr long) geomagnetic field variations found at irregular intervals over the past few millennia, using the archeological record from Europe to the Middle East. These seem to correlate with significant climatic events in the eastern North Atlantic region. A proposed mechanism involves variations in the geometry of the geomagnetic field (f.i. tilt of the dipole to lower latitudes), resulting in enhanced cosmic-ray induced nucleation of clouds. No forcing factor, be it changes in CO 2 concentration in the atmosphere or changes in cosmic ray flux modulated by solar activity and geomagnetism, or possibly other factors, can at present be neglected or shown to be the overwhelming single driver of climate change in past centuries. Intensive data acquisition is required to further probe indications that the Earth's and Sun's magnetic fields may have significant bearing on climate change at certain time scales.

Evidence for large century time-scale changes in solar activity in the past 32 Kyr, based on in-situ cosmogenic 14C in ice at Summit, Greenland

We present results of estimates of cosmic ray flux in Greenland at the Summit (3200 m.a.s.l, 72.6°N, 38.5°W), during the past 32 Kyr. We derive these estimates based on concentrations of in-situ cosmogenic 14C produced in ice crystals. Based on the secular equilibrium concentration of in-situ produced 14C in quartz in terrestrial rocks, we find that on century time-scales, the cosmic ray production rate of 14C at the Summit was close to its estimated long-term average production rate, except during 3 periods: (i) during 8500–9500 yr B.P. and 27,000–32,000 yr B.P, when the production rate was higher by about a factor of 2, and (ii) during 12,000–16,000 yr B.P, when the production rate was lower by a factor of ∼ 1.5. The observed variation in cosmic ray flux at the polar site is best attributed to changes in solar activity resulting in variable modulation of terrestrial cosmic ray flux. Changes in the geomagnetic field in the past do not affect the cosmic ray flux at polar latitudes. Likewise, climate changes do not affect the in-situ 14C record in ice. During the first two epochs, the solar activity must have been very low, as during Maunder Minimum (virtually no sunspots), resulting in essentially no modulation of the cosmic ray flux by the solar plasma. During the low cosmic ray flux epoch, 12,000–16,000 yr B.P., the observed decrease in cosmic ray flux corresponds to high solar activity as seen in 1958 ( sun-spot number ∼ 190). We discuss the proxy evidence from tree ring and sediment based records of atmospheric 14C/ 12C ratios during the three epochs. These records have been used as a measure of changes in cosmic ray flux, and solar activity in the past. However, since they are also appreciably affected by climatic changes, a comparison of the two records is potentially valuable for delineating the nature of past changes in solar activity, and large-scale ocean circulation and air–sea exchange.

On the relationship of cosmic ray flux and precipitation

This paper evaluates whether there is empirical evidence to support the hypothesis that solar variability is linked to the Earth's climate through the modulation of atmospheric precipitation processes. Using global data from 1979–1999, we find evidence of a statistically strong relationship between cosmic ray flux (CRF), precipitation (P) and precipitation efficiency (PE) over ocean surfaces at mid to high latitudes. Both P and PE are shown to vary by 7–9% during the solar cycle of the 1980s over the latitude band 45–90°S. Alternative explanations of the variation in these atmospheric parameters by changes in tropospheric aerosol content and ENSO show poorer statistical relationships with P and PE. Variations in P and PE potentially caused by changes in CRF have implications for the understanding of cloud and water vapour feedbacks.

Apparent tropospheric response to MeV‐GeV particle flux variations: A connection via electrofreezing of supercooled water in high‐level clouds?

The ionization production by MeV‐GeV particles (mostly galactic cosmic rays) in the lower atmosphere has‐well defined variations on a day‐to‐day time scale related to solar activity, and on the decadal time scale related to the sunspot cycle. New results based on an analysis of 33 years of northern hemisphere meteorological data show clear correlations of winter cyclone intensity (measured as the changes in the area in which vorticity is above a certain threshold) with day‐to‐day changes in the cosmic ray flux. Similar correlations are also present between winter cyclone intensity, the related storm track latitude shifts, and cosmic ray flux changes on the decadal time scale. These point to a mechanism in which atmospheric electrical processes affect tropospheric thermodynamics, with a requirement for energy amplification by a factor of about 107 and a time scale of hours. A process is hypothesized in which ionization affects the nucleation and/or growth rate of ice crystals in high‐level clouds by enhancing the rate of freezing of thermodynamically unstable supercooled water droplets which are known to be present at the tops of high clouds. The electrofreezing increases the flux of ice crystals that can glaciate midlevel clouds. In warm core winter cyclones the consequent release of latent heat intensifies convection and extracts energy from the baroclinic instability to further intensify the cyclone. As a result, the general circulation in winter is affected in a way consistent with observed variations on the interannual/decadal time scale. The effects on particle concentration and size distributions in high‐level clouds may also influence circulation via radiative forcing.