Engineering topics

Lockwood, J. A.

Publications and source records attributed to Lockwood, J. A..

At least 37 records · Page 2

NASA NTRS1985

The intensity recovery of Forbush-type decreases as a function of heliocentric distance and its relationship to the 11-year variation

Recent data indicating that the solar modulation effects are propagated outward in the heliospheric cavity suggest that the 11-year cosmic ray modulation can best be described by a dynamic time dependent model. In this context an understanding of the recovery characteristics of large transient Forbush type decreases is important. This includes the typical recovery time at a fixed energy at 1 AU as well as at large heliocentric radial distances, the energy dependence of the recovery time at 1 Au, and the dependence of the time for the intensity to decrease to the minimum in the transient decreases as a function of distance. These transient decreases are characterized by their asymmetrical decrease and recovery times, generally 1 to 2 days and 3 to 10 days respectively at approx. 1 AU. Near earth these are referred to as Forbush decreases, associated witha shock or blast wave passage. At R equal to or greater than + or - 10 AU, these transient decreases may represent the combined effects of several shock waves that have merged together.

Lockwood, J. A.↗

NASA NTRS1985

Latitudinal gradients of cosmic rays and the polarity reversal of the heliospheric magnetic field: A preliminary evaluation

Within the statistical limits imposed by the currently available data and the noise inherent in the determination of the latitudinal gradient, no evidence for the expected change in the latitudinal gradient from pre-1980 to post-1980 epochs can be found. In addition, the rigidity dependence of the gradient appears to be the same in the two epochs. Thus, no evidence is found for a sensitivity of the latitudinal gradient to the polarity of the largescale heliospheric magnetic field such as has been predicted by models incorporating particle drifts.

Newkirk, G., Jr.↗

NASA NTRS1985

The cosmic ray interplanetary radial gradient from 1972 - 1985

It is now established that the solar modulation of cosmic rays is produced by turbulent magnetic fields propagated outward by the solar wind. Changes in cosmic ray intensity are not simultaneous throughout the modulation region, thus requiring time dependent theories for the cosmic ray modulation. Fundamental to an overall understanding of this observed time dependent cosmic ray modulation is the behavior of the radial intensity gradient with time and heliocentric distance over the course of a solar modulation cycle. The period from 1977 to 1985 when data are available from the cosmic ray telescopes on Pioneer (P) 10, Voyager (V) 1 and 2, and IMP 8 spacecraft is studied. Additional data from P10 and other IMP satellites for 1972 to 1977 can be used to determine the gradient at the minimum in the solar modulation cycle and as a function of heliocentric distance. All of these telescopes have thresholds for protons and helium nuclei of E 60 MeV/nucleon.

Webber, W. R.↗

NASA NTRS1985

Solar activity and modulation of the cosmic ray intensity

Since its discovery by Forbush (1954), the 11-year cycle modulation of the cosmic ray intensity has been studied extensively. Bowe and Hatton (1982) obtained a well-behaved transfer function F between the solar activity S and the cosmic ray intensity modulation Io-I. They suggested that the 11-year variation for sunspot cycle 20 can be attributed to the modulating effect of solar flare-induced shocks propagating through the heliosphere. The cosmic ray intensity in the absence of solar activity is denoted by Io, while I denotes the observed intensity. Bowe and Hatton infer that the boundary of the heliosphere is located at a distance of 70-90 AU. Since their conclusion is of great importance in understanding the mechanism of the 11-year modulation, the present investigation is concerned with a repetition of their study for two cycles, taking into account the use of a slightly modified method. The obtained results confirm the conclusions reached by Bowe and Hatton that there is a well-behaved transfer function for solar flares.

Akasofu, S.-I.↗

NASA NTRS1984

Integral radial cosmic ray gradients in the solar system from 1972 to 1982

The cosmic-ray telescope data on IMP 8, Voyagers 1 and 2, and Pioneer 10 have been used to determine the integral radial cosmic-ray intensity gradients for energies greater than 60 MeV per nucleon. When the 26 day average counting rates are time-shifted for the effects of the outward propagation speed of the solar modulation, the average integral radial gradients (Gr) are 3.0 + or - 0.35 (percent/AU) from 1975 to 1982. Gr is independent to the first order of the cosmic-ray intensity and radial heliocentric distance out to about 30 AU. After the large transient variations in the cosmic-ray intensity in mid-1982, the integral gradients returned to their original values.

Lockwood, J. A.↗

NASA NTRS1984

Comparison of the solar cosmic ray events on May 7, 1978, and November 22, 1977

Neutron monitor data from the IMP 7 and 8 satellites are used in the present analysis of the cosmic ray events of Nov. 22, 1977, and May 7, 1978, in order to determine the energy spectra of the solar protons from 50 MeV to 10 GeV, together with pitch angle distributions, intensity-time profiles, and anisotropy-time profiles. The solar proton energy spectra obtained agree with the overlapping energy range when the pitch angle distribution is taken into account, and it is noted that the energy spectra covering three decades of energy and eight of intensity, together with their time variations, were very similar for the two events. The May 1978 event is important for the study of solar particle acceleration and their subsequent injection into the interplanetary medium. Although the solar proton propagation of the November 1977 event was diffusive, the solar particle injection was also time-extended and energy-dependent.

Debrunner, H.↗

NASA NTRS1984

Observations of the dynamics of the cosmic ray modulation

New measurements of the outward propagation of the cosmic ray modulation and large transient decreases at a radial distance of 10-30 AU from the earth are reported. Also, new observations of the hysteresis effect in the 11-year modulation are presented for two solar cycles, and an attempt is made to reproduce the long-term modulation at earth from the observed transient or Forbush decreases. The results indicate that steady-state, spherically symmetric models of the heliosphere are not capable of explaining the 11-year variation. A time-dependent solution to the cosmic ray transport equation is required to describe the solar cosmic ray modulation.

Webber, W. R.↗

NASA NTRS1981

A study of the long-term variation and radial gradient of cosmic rays out to 23 AU

It is shown by an examination of Pioneer, Voyager and IMP spacecraft cosmic ray long-term modulation data, for the case of E greater than 60 MeV in the period 1972-1980, that (1) long-term modulation effects are propagated outward radially from the sun with a typical speed of 350-500 km/sec; (2) the average integral radial gradient over the period, between 2 and 23 AU, is 2.85 + or - 0.5% AU, and (3) the boundary of the heliocentric modulation region in the ecliptic plane, as derived from simple conventional modulation theory, is greater than 65 AU. It is concluded that the weak dependence of the average gradient upon cosmic ray intensity may be used to estimate the location of the boundary in a standard modulation model.

Webber, W. R.↗

NASA NTRS1981

Observations of gamma radiation between 0.4 MeV and 7 MeV at balloon altitudes using a Compton telescope

Balloon-borne measurements of the atmospheric and diffuse gamma-ray flux in the energy range 0.4-7.0 MeV with a Compton telescope, which included pulse-shape discrimination of the first scattering detector and a time-of-flight system between the first and second detector elements, are reported. Comparison of the diffuse cosmic gamma-ray flux to the atmospheric gamma rays indicates that 0.2-5.0 MeV is the optimum energy range for measurements made at the top of the earth's atmosphere. The measured total atmospheric gamma-ray flux between zero and 40 deg has an energy spectrum that agrees with the calculations of Ling (1975). Observations indicate that the ratio of the diffuse to atmospheric gamma ray fluxes at 3.5 g/sq cm is a maximum, about 1.0, between 0.7 and 3.0 MeV.

Lockwood, J. A.↗

NASA NTRS1981

Cosmic ray gradients in the heliosphere and particle drifts

K-coronameter, solar wind, and neutron monitor data are used to estimate the latitudinal gradient of protons of approximately 5 GeV in the heliosphere at 1 AU during 1965 and 1975. The reversal of sign of the gradient between 1965 and 1975 and the strong positive latitudinal gradient in 1975 predicted by models in which drifts are dominant are not observed.

Newkirk, G., Jr.↗

NASA NTRS1980

A study of the effects of Forbush decreases and the 11-year variation of cosmic rays out to approximately 16 AU

In this study the onset of the new solar modulation cycle in late 1977 has been observed out to 16 AU. 27-day average cosmic-ray data (E greater than 60 MeV) from Pioneers 10, 11 and IMP 8 for the period for 1973-1978, normalized to the ground-based neutron monitor rates, have been used. Observations indicate that the long-term modulation effects propagate outward radially at 200-300 Km/sec. Forbush decreases, in contrast, are local phenomena and the associated time delays between their occurrence at earth and out to a few AU are much shorter. The data yield a radial gradient of 2-3% per AU.

Lockwood, J. A.↗

NASA NTRS1975

Comparisons of ground-based monitor data with Pioneers 8, 9, 10 and 11 observations in 1968-1974

The paper examines ground-based neutron monitor data and the counting rates in different energy channels on the Pioneer 8, 9, 10 and 11 spacecraft to determine the scale size of the transient cosmic-ray variations (Forbush decreases) and the relationship of these variations to changes in the interplanetary magnetic field. Since the Pioneer spacecraft sampled the inner modulating region extensively, the spatial extent of Forbush decreases (Fd's) can be determined. In some cases the Fd modulating region was co-rotating and in others radially expanding. The azimuthal extent of the Fd region was variable but was typically about 45 deg in extent. These observations will be interpreted in terms of models proposed for Fds.

Lockwood, J. A.↗

NASA NTRS1974

Solar flare proton rigidity spectra deduced from cosmic ray neutron monitor observations

The solar flare proton rigidity spectra for several flares occurring between 1967 and 1972 have been deduced from the ground level cosmic ray neutron monitor observations. To obtain consistent agreement for all the ground level events (GLEs) analyzed, the specific yield functions of Lockwood and Webber (1967) must be reduced slightly below P = 1.6 GV. The typical spectral indices of solar cosmic rays deduced for GLEs vary from 4 to 6 if the differential spectrum is represented by KP to the minus gamma power. Only occasionally is the spectrum as steep as 8 or 9. The observed spectral index is independent of the magnitude of the integral solar proton flux above 1 GV.

Lockwood, J. A.↗

NASA NTRS1974

High energy neutrons at balloon altitudes

The flux and energy spectrum of fast neutrons (3 to 20 MeV) has been measured near the top of the atmosphere with an organic liquid scintillator. The omnidirectional neutron energy spectrum from 3 to 20 MeV at 3.5 g/sq cm over Palestine, Texas can be described by a power law with an energy dependent spectral index which varies from 1.8 (plus or minus .2) between 1 and 10 MeV to 0.3 (plus or minus .3) between 15 and 20 MeV. From 20 to 50 MeV, a neutron spectrum independence of E is consistent with our data.

Klumpar, D. M.↗

NASA NTRS1974

The phase lag effect in the cosmic ray modulation during solar cycle twenty

In this analysis of the phase-lag effect we utilize more extensive primary proton and helium spectral data from balloon studies of the University of New Hampshire group, from the Pioneer 8 and 9 spacecraft, and from ground-level monitors during 1965-72. If the rigidity dependence of the diffusion coefficient at earth did not change from 1968-72, then the data imply the nonseparability of the radial and rigidity parts of the diffusion coefficient.

Lockwood, J. A.↗

NASA NTRS1973

Energy spectrum and flux of 3- to 20-Mev neutrons and 1- to 10-Mev gamma rays in the atmosphere

An experiment is described which was designed to measure the neutron and gamma ray energy spectrums and fluxes in the energy intervals 3 to 20 MeV and 1 to 10 MeV, respectively. In addition, from the 3 to 20-MeV proton recoil spectrums it is possible to infer the shape of the neutron energy spectrum from 20 to 50 MeV. The detecting system utilized a separate charged particle rejection scheme and a two-parameter display system for the output from the pulse shape discrimination which separated gamma rays from neutrons (n). Two long-duration flights were made with this detector in 1970 at Palestine, Tex. (P sub c = 4.6 Gv) and at Ft. Churchill, Canada (P sub c = 0.3 Gv).

Klumpar, D. M.↗

NASA NTRS1973

Measurements of the atmospheric neutron leakage rate

The atmospheric neutron leakage rate in the energy range from 0.01 to 10,000,000 eV has been measured as a function of latitude, altitude, and time with a neutron detector on board the Ogo 6 satellite. The latitude dependence of the neutron leakage is in reasonable agreement with that predicted by Lingenfelter (1963) and Light et al. (1973) if the neutron energy spectrum has the shape calculated by Newkirk (1963). The change in the neutron latitude dependence with the cosmic ray modulation agrees with the predictions of Lingenfelter and Light et al. For several solar proton events enhancements were observed in the neutron counting rates at lambda greater than or equal to 70 deg. Such events, however, provide an insignificant injection of protons at E less than or equal to 20 MeV into the radiation belts. An isotropic angular distribution of the neutron leakage in the energy range from 0.1 keV to 10 MeV best fits the observed altitude dependence of the neutron leakage flux.

Lockwood, J. A.↗

NASA NTRS1973

Neutron measurements in space.

The experimental measurements of the neutron flux and energy spectrum in space since 1964 are reviewed and related to the theoretical predictions. A discussion of the neutron sources is presented. The difficulties associated with neutron measurements of both the atmospheric neutron leakage flux and solar neutrons are included. Particular emphasis is placed upon the neutron leakage flux and energy measurements at energies greater than about 1 MeV. The possibilities of CRAND as a source for the energetic trapped protons are discussed in light of recent measurements of the 10- to 100-MeV neutron flux. The current status of the solar neutron flux observations is also presented. An attempt is made to interpret and discuss recent neutron measurements. In order to understand these results, the theoretical predictions of the neutron fluxes and energy spectra from possible neutron sources are briefly presented.

Lockwood, J. A.↗