Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “FORBUSH DECREASE”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1995

Heliospheric 2-3 kHz radio emissions and their relationship to large Forbush decreases

Two intense heliospheric 2-3 kHz radio emission events have been observed by Voyagers 1 and 2, the first in 1983-84 and the second in 1992-93. These radio emission events occurred about 400 days after large Forbush decreases in mid-1982 and mid-1991. Since Forbush decreases are indicative of a strong interplanetary shock propagating outward through the heliosphere, this temporal relationship provides strong evidence that the radio emissions are triggered by the interaction of a shock with one of the outer boundaries of the heliosphere. From the travel time and the known speed of the shock, the distance to the interaction region can be estimated and is well beyond 100 AU. At this great distance the plasma frequency at the terminal shock (100 to 200 Hz) is believed to be too small to explain the observed emission frequencies, which extend up to 3.6 kHz. For this reason, we have proposed that the interaction takes place at or near the heliopause, where remote sensing measurements show that the plasma frequency is in a suitable range (approximately 3 kHz) for explaining the radio emission. From the travel time and shock propagation speed, the radial distance to the heliopause has been calculated for various candidate solar events. After taking into account the likely deceleration of the shock, the heliopause is estimated to be in the range from about 110 to 160 AU.

Gurnett, D. A.↗
NASA NTRS1989

Electron density profiles in the background of LF absorption during Forbush-decrease and PSE

Based on the simulation of different Forbush decrease and particle precipitation effects in the D region, electron density profiles in the mid-latitudes the ionospheric absorption of low frequency (LF) radio waves was determined. The absorption variations at different frequenceis are strongly affected by the shape of the electron density profile. A structure appears which sometimes resembles the letter S (in a sloping form). Both the height (around 70 to 72 km) and the depth of the local minimum in the electron density contribute to the computed absorption changes of various degree at different frequencies. In this way several observed special absorption events can be interpreted.

Satori, G.↗
NASA NTRS1993

Balloon observations of Galactic cosmic ray helium before and during a Forbush decrease

The energy spectrum of Galactic cosmic ray helium was measured in two different balloon experiments launched four days apart from Canada: SMILI-I on Sept 1, 1989 and MASS on Sept 5, 1989. A slow Forbush decrease began on Sept 4, 1989 and had not reached its maximum at the time of the MASS flight. Comparison of the balloon measurements shows a fractional decrease of 0.37 to 0.15 in the Helium flux between 200 and 450 MeV/nucleon (1.2-2.0 GV). The rigidity dependence is analyzed in two models and found to be steeper than previous observations. Interplanetary particle data and ground-based Neutron Monitor results are consistent with the balloon observations. Probable sources for this Forbush decrease are discussed.

Clem, J. M.↗
NASA NTRS1973

Variations of three-dimensional anisotropy of cosmic rays during Forbush decreases.

Variations of three-dimensional anisotropy of cosmic rays during Forbush decreases are examined by a spherical harmonic method and by constructing successive isointensity contour maps in the solar ecliptic coordinate system. The east-west and north-south anisotropies are studied statistically and for several individual events; the data are based on cosmic ray records from about 24 stations for the 3-year period from 1966 to 1968. For the individual events, the high anisotropies of about 4% are examined in terms of the convective, diffusive and density gradient components of the differential streaming as well as the interplanetary magnetic field and solar wind. In each case, vector gradients are derived that lead to the observed anisotropies, and the magnitude of these gradients is typically 10-20 times that of the quiet time interplanetary gradient.

Yoshida, S.↗
DOE OSTI2017

A Numerical Study of Forbush Decreases with a 3D Cosmic-Ray Modulation Model Based on an SDE Approach

Based on the reduced diffusion mechanism for producing Forbush decreases (Fds) in the heliosphere, we constructed a three-dimensional (3D) diffusion barrier, and by incorporating it into a stochastic differential equation (SDE) based time-dependent, cosmic-ray transport model, a 3D numerical model for simulating Fds is built and applied to a period of relatively quiet solar activity. This SDE model generally corroborates previous Fd simulations concerning the effects of the solar magnetic polarity, the tilt angle of the heliospheric current sheet (HCS), and cosmic-ray particle energy. Because the modulation processes in this 3D model are multi-directional, the barrier’s geometrical features affect the intensity profiles of Fds differently. We find that both the latitudinal and longitudinal extent of the barrier have relatively fewer effects on these profiles than its radial extent and the level of decreased diffusion inside the disturbance. We find, with the 3D approach, that the HCS rotational motion causes the relative location from the observation point to the HCS to vary, so that a periodic pattern appears in the cosmic-ray intensity at the observing location. Correspondingly, the magnitude and recovery time of an Fd change, and the recovering intensity profile contains oscillation as well. Investigating the Fd magnitude variation with heliocentric radial distance, we find that the magnitude decreases overall and, additionally, that the Fd magnitude exhibits an oscillating pattern as the radial distance increases, which coincides well with the wavy profile of the HCS under quiet solar modulation conditions.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Quantitative understanding of Forbush decrease drivers based on shock-only and CME-only models using global signature of February 14, 1978 event

We have studied the Forbush decrease (FD) event that occurred on February 14, 1978 using 43 neutron monitor observatories to understand the global signature of FD. We have studied rigidity dependence of shock amplitude and total FD amplitude. We have found almost the same power law index for both shock phase amplitude and total FD amplitude. Local time variation of shock phase amplitude and maximum depression time of FD have been investigated which indicate possible effect of shock/CME orientation. We have analyzed rigidity dependence of time constants of two phase recovery. Time constants of slow component of recovery phase show rigidity dependence and imply possible effect of diffusion. Solar wind speed was observed to be well correlated with slow component of FD recovery phase. This indicates solar wind speed as possible driver of recovery phase. To investigate the contribution of interplanetary drivers, shock and CME in FD, we have used shock-only and CME-only models. We have applied these models separately to shock phase and main phase amplitudes respectively. This confirms presently accepted physical scenario that the first step of FD is due to propagating shock barrier and second step is due to flux rope of CME/magnetic cloud.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS1985

The flare origin of Forbush decreases not associated with solar flares on the visible hemisphere of the Sun

Investigations have shown that Forbush decreases (Fds) are produced by the propagation into the interplanetary space of a strong perturbation originating from a solar flare (Sf) accompanied by Type IV radioemission. As the front of the perturbation propagates into the interplanetary space, the region in which the galactic cosmic rays are modulated (Fd-modulated region) rotates westward with the Sun and is generally included between two boundary streams; therefore the Fds not associated with observed type IV Sfs (N.Ass.Fds) are likely to be produced by type IV Sfs occurred on the Sun's backside: these vents can be observed when the Earth crosses the corotating Western boundary of the modulated region.

Iucci, N.↗
NASA NTRS1975

Causes of Forbush decreases and other cosmic ray variations

The relationship between neutron monitor variations and the intensity variations of the interplanetary magnetic field is studied by using Deep River data and Imp series satellite data. In over 80% of the cases studied in 1968, identifiable depressions of the cosmic ray intensity are associated with magnetic field enhancements of several hours duration and intensity above 10 gamma. Conversely, almost every magnetic field enhancement has an identifiable effect (though not necessarily a marked depression) on the cosmic ray intensity. Perpendicular gradient drifts are suggested as one possible mechanism producing the individual decreases, and some ideas on the recovery processes are presented. Long-lasting Forbush decreases are found to be the consequence of the action of several successive magnetic field enhancements. Evidence is presented that indicates that most of these enhancements are caused by the steepening of streams in interplanetary space.

Barouch, E.↗
NASA NTRS1985

Drift and Forbush decreases

Evidence is presented that the drift effect on the modulation of galactic cosmic rays can be seen on Forbush decreases observed by the Deep River and Hermanus neutron monitors.

Moraal, H.↗
NASA NTRS1985

Rigidity spectrum of Forbush decrease

Using data from neutron monitors and muon telescopes at surface and underground stations, the average rigidity spectrum of Forbush decreases (Fds) during the period of 1978-1982 were obtained. Thirty eight Ed-events are classified into two groups Hard Fd and Soft Fd according to size of Fd at Sakashita station. It is found that a spectral form of fractional-power type (P to the-gamma sub 1 (P+P sub c) to the -gamma sub2) is more suitable for the present purpose than that of power-exponential type or of power type with an upper limiting rigidity. The best fitted spectrum of fractional-power type is expressed by gamma sub1 = 0.37, gamma sub2 = 0.89 and P subc = 10 GV for Hard Fd and gamma sub1 = 0.77, gamma sub2 = 1.02 and P sub c - 14GV for Soft Fd.

Sakakibara, S.↗
NASA NTRS2013

Study on 2012 March 7 Solar Particle Event and Forbush Decrease with the PAMELA Experiment

The PAMELA (Payload for Antimatter Matter Exploration and Light-nuclei Astro-physics) spaceborne experiment was launched on 15 June 2006 and has been continuously collecting data since then. The apparatus measures electrons, positrons, protons, anti-protons and heavier nuclei from about 100 megaelectronvolts to several hundreds of gigaelectronvolts. The on-board instrumentation is built around a permanent magnet with a silicon microstrip tracker, providing charge and track detection information. During solar maximum conditions of solar cycle 24, PAMELA has been providing key information about solar energetic particles (SEPs) and their influence at Earth. We discuss here the recent 2012 March 7 SEP event with a brief comment on the subsequent Forbush decrease, registered by PAMELA. This event was also observed by Fermi/LAT (Large Area Telescope) exhibiting unprecedented time-extended gamma-ray emission (greater than 100 megaelectronvolts) lasting nearly 20 hours. We compare the derived accelerated ion population at the Sun with the ion population measured in space by PAMELA and discuss the implications for particle acceleration.

Forbush Decrease↗