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Register a new userCharacteristics and energy dependence of recurrent galactic cosmic-ray flux depressions and of a Forbush decrease with LISA Pathfinder
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Catia Grimani Prof.
Publication date
2018
fields
Physics
and research's language is
English
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Galactic cosmic-ray (GCR) energy spectra observed in the inner heliosphere are modulated by the solar activity, the solar polarity and structures of solar and interplanetary origin. A high counting rate particle detector (PD) aboard LISA Pathfinder (LPF), meant for subsystems diagnostics, was devoted to the measurement of galactic cosmic-ray and solar energetic particle integral fluxes above 70 MeV n$^{-1}$ up to 6500 counts s$^{-1}$. PD data were gathered with a sampling time of 15 s. Characteristics and energy-dependence of GCR flux recurrent depressions and of a Forbush decrease dated August 2, 2016 are reported here. The capability of interplanetary missions, carrying PDs for instrument performance purposes, in monitoring the passage of interplanetary coronal mass ejections (ICMEs) is also discussed.
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Non-recurrent short term variations of the galactic cosmic-ray (GCR) flux above 70 MeV n$^{-1}$ were observed between 2016 February 18 and 2017 July 3 aboard the European Space Agency LISA Pathfinder (LPF) mission orbiting around the Lagrange point L1 at 1.5$times$10$^6$ km from Earth. The energy dependence of three Forbush decreases (FDs) is studied and reported here. A comparison of these observations with others carried out in space down to the energy of a few tens of MeV n$^{-1}$ shows that the same GCR flux parameterization applies to events of different intensity during the main phase. FD observations in L1 with LPF and geomagnetic storm occurrence is also presented. Finally, the characteristics of GCR flux non-recurrent variations (peaks and depressions) of duration $<$ 2 days and their association with interplanetary structures are investigated. It is found that, most likely, plasma compression regions between subsequent corotating high-speed streams cause peaks, while heliospheric current sheet crossing cause the majority of the depressions.
Galactic cosmic-ray (GCR) flux short-term variations ($<$1 month) in the inner heliosphere are mainly associated with the passage of high-speed solar wind streams (HSS) and interplanetary (IP) counterparts of coronal mass ejections (ICMEs). Data gathered with a particle detector flown on board the ESA LISA Pathfinder (LPF) spacecraft, during the declining part of the solar cycle 24 (February 2016 - July 2017) around the Lagrange point L1, have allowed to study the characteristics of recurrent cosmic-ray flux modulations above 70 MeV n$^{-1}$. %These modulations are observed when the solar wind speed is $>$ 400 km s$^{-1}$ and/or the IP magnetic field intensity $>$ 10 nT. It is shown that the amplitude and evolution of individual modulations depend in a unique way on both IP plasma parameters and particle flux intensity before HSS and ICMEs transit. By comparing the LPF data with those gathered contemporaneously with the magnetic spectrometer experiment AMS-02 on board the International Space Station and with those of Earth polar neutron monitors, the GCR flux modulation was studied at different energies during recurrent short-term variations. It is also aimed to set the near real-time particle observation requirements to disentangle the role of long and short-term variations of the GCR flux to evaluate the performance of high-sensitivity instruments in space such as the future interferometers for gravitational wave detection. Finally, the association between recurrent GCR flux variation observations in L1 and weak to moderate geomagnetic activity in 2016-2017 is discussed. Short-term recurrent GCR flux variations are good proxies of recurrent geomagnetic activity when the B$_z$ component of the IP magnetic field is directed northern.
This paper describes the unfolding of the solar modulated galactic cosmic ray H and He nuclei spectra beyond ~105 AU in the heliosheath. Between 2008.0 and 2012.3 when Voyager 1 went from about 105 to 120.5 AU the spectral intensities of these two components between about 30 and 500 MeV/nuc unfolded (increased) in a manner consistent with an average modulation potential decrease ~5 MV per AU as described by a Parker like cosmic ray transport in the heliosphere where the overall modulation is described by a modulation potential in MV. Between 120.5 and 121.7 AU, however, as a result of two sudden intensity increases starting on May 8th and August 25th, 2012, this modulation potential decreased by ~80 MV and spectra resembling possible local interstellar spectra for H and He were revealed. Considering these spectra to be the local interstellar spectra would imply that almost 1/3 of the total modulation potential of about 270 MV required to explain the spectra of these components observed at the Earth must occur in just a 1 AU radial interval in the outer heliosheath. As a result about ~80% of the total modulation potential observed at the Earth at this time occurs in the heliosheath itself. The remaining 20% of the total modulation occurs inside the heliospheric termination shock. The details of these intensity changes and their description by a simple modulation model are discussed.
The Latin American Giant Observatory (LAGO) is a distributed cosmic ray observatory that spans over Latin America in a wide range of latitudes and altitudes. One of the main goals of LAGO is to study atmospheric radiation and space weather through the measurement of the secondary particles from cosmic ray flux at ground level using Water Cherenkov Detectors (WCD). Thus, due to differences in the local geomagnetic rigidity cut-off affecting the low energy cosmic rays impinging on the atmosphere and the well-known relation between altitude and the development of the extended atmospheric showers, different secondary particle fluxes are expected at each LAGO site. It is therefore crucial for our objectives to be able to determine the expected flux of secondary particles at any place in the World and for any geomagnetic or atmospheric conditions. To characterize the response of a particular LAGO site we developed ARTI, a complete framework intended to simulate the WCD signals produced by the interaction of the secondary inside the detector. ARTI comprises a simulation sequence by integrating three different simulation tools: a) Magnetocosmics, to account for the geomagnetic field effects on the primary flux; b) CORSIKA, to simulate the atmospheric showers originated on the complete flux of cosmic rays and, thus, to estimate the expected flux of secondary particle at the site; and c) Geant4, for simulating the LAGO detectors response to this secondary flux. In this work, we show the usage of the ARTI framework by calculating the expected flux of signals at eight LAGO sites, covering a wide range of altitudes and rigidity cut-offs to emphasize the capabilities of the LAGO network spanning over Latin America. These results show that we are able to estimate the response of any water Cherenkov detector located at any place in the World, even under evolving atmospheric and geomagnetic conditions.
The Solar System contains a population of dust and small particles originating from asteroids, comets, and other bodies. These particles have been studied using a number of techniques ranging from in-situ satellite detectors to analysis of lunar microcraters to ground-based observations of zodiacal light. In this paper, we describe an approach for using the LISA Pathfinder (LPF) mission as an instrument to detect and characterize the dynamics of dust particles in the vicinity of Earth-Sun L1. Launching in late 2015, LPF is a dedicated technology demonstrator mission that will validate several key technologies for a future space-based gravitational-wave observatory. The primary science instrument aboard LPF is a precision accelerometer which we show will be capable of sensing discrete momentum impulses as small as $4times 10^{-8},textrm{N}cdottextrm{s}$. We then estimate the rate of such impulses resulting from impacts of micrometeoroids based on standard models of the micrometeoroid environment in the inner solar system. We find that LPF may detect dozens to hundreds of individual events corresponding to impacts of particles with masses $> 10^{-9},$g during LPFs roughly six-month science operations phase in a $5times 10^5,textrm{km}$ by $8times 10^5,textrm{km}$ Lissajous orbit around L1. In addition, we estimate the ability of LPF to characterize individual impacts by measuring quantities such as total momentum transferred, direction of impact, and location of impact on the spacecraft. Information on flux and direction provided by LPF may provide insight as to the nature and origin of the individual impact and help constrain models of the interplanetary dust complex in general. Additionally, this direct in-situ measurement of micrometeoroid impacts will be valuable to designers of future spacecraft targeting the environment around L1.
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