Twenty-two year modulation of cosmic rays associated with polarity reversal of polar magnetic field of the sun

The existence of the 22-year modulation of cosmic ray intensity is pointed out, using data of the ion chamber at Huancayo and the neutron monitors at Ottawa and Deep River for about four solar cycles. The modulation consists of two discrete states (high and low intensities), corresponding respectively to those of the polarity of the polar magnetic field of the Sun. This can be interpreted on the basis of the following hypothesis; when the polar magnetic field of the Sun is nearly parallel to the galactic magnetic field, they could easily connect with each other, so that galactic cosmic rays could intrude more easily into the heliomagnetosphere along the magnetic line of force, as compared with those in the anti-parallel state of the magnetic fields. The observed intensity difference between two states is about 4.3 ± 0.2% for neutron monitor (P_c = 1.5GV). The abnormal increase in proton (0.28–0.42 GV) and electron (0.41-3.24 GV) fluxes in the 20th solar cycle and the sudden appearance of anomalous components (He⁺, etc.) since 1972 can be also explained on the basis of the present hypothesis. The transition between the two states has a time lag behind the polarity reversal, depending on the cosmic ray rigidity, such as about 1 year for the neutron monitor (P_c = 1.5 GV) and about 3.5 years for low rigidity components (P < 1 GV). These time lags could be explained on the basis of the generalized Simpson's coasting solar wind model and the general diffusion-convection theory on some assumptions.     

Lunar occultation of Saturn: III. How big is Iapetus?

By considering both the orbital lightcurve of Iapetus and data obtained during the March 30, 1974, occultation of the satellite by the Moon, we obtain information about the brightness distribution on the bright face of Iapetus and derive an accurate value for the satellite's radius. From the observed orbital lightcurve we find that the trailing face of Iapetus must consist predominantly of a single bright material with an effective limb-darkening parameter of k = 0.62_?0.12^0.10. Given this result the occultation observations imply a radius of 718_?78⁺⁸⁷ km. If the patchy albedo model proposed by Morrison et al. represents the surface of Iapetus accurately (as far as the relative albedo distribution is concerned) then the radius of Iapetus is 724 ± 60 km. Both estimates are consistent with the radiometric radius of 835 (+50, ?75) km derived by Morrison et al. Combining our results with the value of 0.60 ± 0.14 for the normal reflectance (in V) of the material at the center of the bright face derived by Elliot et al. we find that the normal reflectance of the dark side material is 0.11_?0.03^+0.04. These values are higher than the corresponding values of 0.35 and 0.05 quoted by Morrison et al.     

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.     

Measurement of the radial density gradient of cosmic ray in the heliosphere by the GRAPES-3 experiment

A radial anisotropy in the flux of cosmic rays in heliosphere was theoretically predicted by Parker and others within the framework of the diffusion–convection mechanism. The solar wind is responsible for sweeping out the galactic cosmic rays, creating a radial density gradient within the heliosphere. This gradient coupled with the interplanetary magnetic field induces a flow of charged particles perpendicular to the ecliptic plane which was measured and correctly explained by Swinson, and is hereafter referred as ‘Swinson flow’. The large area GRAPES-3 tracking muon telescope offers a powerful probe to measure the Swinson flow and the underlying radial density gradient of the galactic cosmic rays at a relatively high rigidity of ∼100 GV. The GRAPES-3 data collected over a period of six years (2000–2005) were analyzed and the amplitude of the Swinson flow was estimated to be (0.0644 ± 0.0008)% of cosmic ray flux which was an ∼80σ effect. The phase of the maximum flow was at a sidereal time of (17.70 ± 0.05) h which was 18 min earlier than the expected value of 18 h. This small 18 min phase difference had a significance of ∼6σ indicating the inherent precision of the GRAPES-3 measurement. The radial density gradient of the galactic cosmic rays at a median rigidity of 77 GV was found to be 0.65% AU⁻¹.     

A new method for determining the helium abundance in the solar atmosphere

Recent observations of a cut-off frequency in the acoustic modes of the Sun (Claverie et al., 1981b) should help determine the mean molecular weight and, thereby, the helium abundance in the visible layers of the solar atmosphere. A first preliminary result of Y = 0.42 ± 0.04 is obtained for an assumed minimum photospheric temperature of 4400 K ± 200 K.     

Secular changes in the upper cut-off rigidity of the solar diurnal anisotropy of cosmic rays

We have calculated the upper cut-off rigidities applicable to the solar diurnal anisotropy of cosmic rays, for the period 1965–1979. Our results are consistent with those reported by others. We note that the mean values of the upper cut-off rigidities during 1975–1977 are less than 50 GV. This explains why no diurnal variation is observed by the muon detectors at Socorro (NM) at a depth of 80 m of water equivalent (MWE) for this period. The threshold (R_o) and the median primary rigidities (R_m) of response applicable to the underground vertical telescope at Socorro are 45 and 300 GV, respectively.     

Intensity variation of cosmic rays near the heliospheric current sheet

Cosmic ray intensity variations near the heliospheric current sheet—both above and below it—have been studied during 1964–1976. Superposed epoch analysis of the cosmic ray neutron monitor data with respect to sector boundaries (i.e., heliospheric current sheet crossings) has been performed. In this analysis we have used the data from neutron monitors well distributed in latitude over the Earth's surface. First, this study has been made during the two solar activity minimum periods 1964–1965 and 1975–1976, using the data from Thule (cut-off rigidity 0 GV), Deep River (cut-off rigidity 1.02 GV), Rome (cut-off rigidity 6.32 GV) and Huancayo (cut-off rigidity 13.45 GV) neutron monitors. We have also analyzed the data from Deep River, Rome and Huancayo neutron monitors, for whom we have the data for full period (1964–1976), by dividing the periods according to the changes in solar activity, interplanetary magnetic field polarity and coronal holes. All these studies have shown a negative gradient with respect to heliomagnetic latitude (current sheet). These results have been discussed in the light of theoretical and observational evidences. Suggestions have been given to overcome the discrepancy between the observational and theoretical results. Further, possible explanations for these observational results have been suggested.     

Characteristics of Two-Way Cosmic-Ray Diurnal Anisotropy

We examine the deviation of the solar diurnal anisotropy vector from the 18 LT direction during the positive state of the solar cycle by assuming two anisotropies in free space. We use two detectors characterized by two linearly independent coupling functions. The median primary rigidity of response of these detectors covers the range 16 GV R _m 331 GV. Amplitude, direction, spectrum exponent, and the upper cut-off rigidity of each anisotropy have been calculated using the least-squares method over the time interval 1968–1988. This period covers a complete solar magnetic cycle. Only one anisotropy is dominant during each magnetic state of the solar cycle. The upper cut-off rigidity at which the dominant anisotropy vanishes varies between 50–250 GV. The direction of the dominant anisotropy vector points toward the 18 LT direction during the negative state of the solar cycle and toward earlier hours than 18 LT during the positive state. The non-dominant anisotropy is characterized by very high upper cut-off rigidity and sharper energy spectral.     

Earliest high-Ti volcanism on the Moon: 40Ar-39Ar,Sm-Nd,and Rb-Sr isotopic studies of Group D basalts from the Apollo 11 landing site

Abstract High-Ti basalts from the Apollo collections span a range in age from 3.87 Ga to 3.55 Ga. The oldest of these are the common Apollo 11 Group B2 basalts which yield evidence of some of the earliest melting of the lunar mantle beneath Mare Tranquillitatis. Rare Group D high-Ti basalts from Mare Tranquillitatis have been studied in an attempt to confirm a postulated link with Group B2 basalts (Jerde et al., 1994). The initial Sr isotopic ratio of a known Group D basalt (0.69916 ± 3 at 3.85 Ga) lies at the lower end of the tight range for Group B2 basalts (⁸⁷Sr/⁸⁶Sr = 0.69920 to 0.69921). One known Group D basalt and a second postulated Group D basalt yield indistinguishable initial ?_Nd (1.2 ± 0.6 and 1.2 ± 0.3) and again lie at the lower end of the range for the Group B2 basalts from Apollo 11 (+2.0 ± 0.4 to +3.9 ± 0.6, at 3.85 Ga). A third sample has isotopic (⁸⁷Sr/⁸⁶Sr = 0.69932 ± 2; ?_Nd = 2.5 ± 0.4; at 3.59 Ga; as per Snyder et al., 1994b) and elemental characteristics similar to the Group A high-Ti basalts returned from the Apollo 11 landing site. Ages of ⁴⁰Ar-³⁹Ar have been determined for one known Group D basalt and a second postulated Group D basalt using step-heating with a continuous-wave laser. Suspected Group D basalt, 10002, 1006, yielded disturbed age spectra on two separate runs, which was probably due to ³⁹Ar recoil effects. Using the “reduced plateau age” method of Turner et al. (1978), the ages derived from this sample were 3898 ± 19 and 3894 ± 19 Ma. Three separate runs of known Group D basalt 10002, 116 yielded ⁴⁰Ar/³⁹Ar plateau ages of 3798 ± 9 Ma, 3781 ± 8 Ma, and 3805 ± 7 Ma (all errors 2σ). Furthermore, this sample has apparently suffered significant ⁴⁰Ar loss either due to solar heating or due to meteorite impact. The loss of a significant proportion of ⁴⁰Ar at such a time means that the plateau ages underestimate the “true” crystallization age of the sample. Modelling of this Ar loss yields older, “true” ages of 3837 ± 18, 3826 ± 16, and 3836 ± 14 Ma. These ages overlap the ages of Group B2 high-Ti basalts (weighted average age = 3850 ± 20 Ma; range in ages = 3.80 to 3.90 Ga). The combined evidence indicates that the Group D and B2 high-Ti basalts could be coeval and may be genetically related, possibly through increasing degrees of melting of a similar source region in the upper mantle of the Moon that formed >4.2 Ga ago. The Group D basalts were melted from the source first and contained 3–5×more trapped KREEP-like liquid than the later (by possibly only a few million years) Group B2 basalts. Furthermore, the relatively LREE- and Rb-enriched nature of these early magmas may lend credence to the idea that the decay of heat-producing elements enriched in the KREEP-like trapped liquid of upper mantle cumulates, such as K, U, and Th, could have initiated widespread lunar volcanism.     

The heliocentric radial gradient in cosmic ray density and the ‘swinson’ sidereal time variation

The sidereal time variation reported by Swinson depends on the existence of a heliocentric radial gradient of cosmic ray density in the rigidity range ? 100 GV and appears because of the inclination of the axis of rotation of the Earth to the normal to the ecliptic plane. It is sensitive to the polarity of the interplanetary magnetic field. Meson detectors on the surface of the Earth near the equator and at shallow underground depths can be used to measure this effect.In this paper results obtained at Makerere on the Earth's surface and at Kilembe (50 m.w.e.) in Uganda, East Africa, are compared with data previously reported by Swinson from Chacaltaya (25 m.w.e.) and Embudo (40 m.w.e.).From the relationship between the sidereal time variation and the heliocentric radial gradient it is concluded that the data are consistent with a local radial gradient of ($\text{(41 ± 8)}\text{P)}\text{\% A.U.}{}^{\mathrm{?1}}$ in the rigidity range 15 < P ? 100 GV during 1967–1971, a period including the most recent solar maximum. This estimate is consistent with modulation theory and the prevailing power spectrum in the interplanetary magnetic field.The Swinson effect is not appreciable at depths of more than 50 m.w.e. underground.     

HD molecular lines in an absorption system at redshift z=2.3377

Having analyzed the spectrum of the quasar PKS 1232+0.82 taken by Petitjean et al. (2000), we identified HD molecular lines in an absorption system at redshift z=2.3377. We estimated the column density of HD molecules in this system, N(HD) = (1?4) × 10¹⁴cm^?2. The excitation temperature of the first rotational level J=1 relative to the ground state J=0 is T _ex=70 ± 7 K. As far as we know, this is the first detection of HD molecules at high redshift.     

Heliospheric Modulation of Galactic Cosmic Rays During Solar Cycle 23

Galactic cosmic rays (GCRs) encounter an outward-moving solar wind with cyclic magnetic-field fluctuation and turbulence. This causes convection and diffusion in the heliosphere. The GCR counts from the ground-based neutron monitor stations show intensity changes that are anti-correlated with the sunspot numbers with a lag of a few months. GCRs experience various types of modulation from different solar activity features and influence space weather and the terrestrial climate. In this work, we investigate certain aspects of the GCR modulation at low cut-off rigidity (R _c≈1 GV) in relation to some solar and geomagnetic indices for the entire solar cycle 23 (1996?–?2008). We separately study the GCR modulation during the ascending phase of cycle 23 including its maximum (1996?–?2002) and the descending phase including its minimum (2003?–?2008). We find that during the descending phase, the GCR recoveries are much faster than those of the solar parameters with negative time-lag. The results are discussed in light of modulation models, including drift effects and previous results.     

The quenching of OH1 in the atmosphere

The intensity distribution of the OH Meinel bands in the airglow has been derived from the minor constituent profiles of Moreels et al. (1977). It has been shown that there is good agreement between the observed and calculated intensity distribution for excitation through the hydrogen-ozone reaction and quenching of the excited state by reaction with atomic oxygen and through vibrational relaxation. The rate constants for vibrational relaxation have been derived and are found to be vibrational level dependent; for the ν = 7 level, the peak value, the rate constant is 5.8 × 10^?12cm³s^?1.     

The Compatibility of Flare Temperatures Observed with AIA,GOES, and RHESSI

We test the compatibility and biases of multi-thermal flare DEM (differential emission measure) peak temperatures determined with AIA with those determined by GOES and RHESSI using the isothermal assumption. In a set of 149 M- and X-class flares observed during the first two years of the SDO mission, AIA finds DEM peak temperatures at the time of the peak GOES 1?–?8 Å flux to have an average of T _p=12.0±2.9 MK and Gaussian DEM widths of log₁₀(σ _T )=0.50±0.13. From GOES observations of the same 149 events, a mean temperature of T _p=15.6±2.4 MK is inferred, which is systematically higher by a factor of T _GOES/T _AIA=1.4±0.4. We demonstrate that this discrepancy results from the isothermal assumption in the inversion of the GOES filter ratio. From isothermal fits to photon spectra at energies of ?≈6?–?12 keV of 61 of these events, RHESSI finds the temperature to be higher still by a factor of T _RHESSI/T _AIA=1.9±1.0. We find that this is partly a consequence of the isothermal assumption. However, RHESSI is not sensitive to the low-temperature range of the DEM peak, and thus RHESSI samples only the high-temperature tail of the DEM function. This can also contribute to the discrepancy between AIA and RHESSI temperatures. The higher flare temperatures found by GOES and RHESSI imply correspondingly lower emission measures. We conclude that self-consistent flare DEM temperatures and emission measures require simultaneous fitting of EUV (AIA) and soft X-ray (GOES and RHESSI) fluxes.     

High dispersion observations of Venus during 1972: The CO2 band at 7820Å

Forty-seven well exposed photographic plates of Venus which show the spectrum of the carbon dioxide band at 7820Å were obtained at Table Mountain Observatory in September and October 1972. These spectra showed a semiregular four-day variation in the CO₂ abundance over the disk of the planet (Young et al., 1974). We also find evidence for temporal variations in the rotational temperature of this band and temperature variations over the disk. The two quantities, CO₂ abundance and temperature, do not show any obvious relationship; however, an increase in the temperature usually is accompanied by a decrease in the abundance of CO₂. The average temperature, found from a curve-of-growth analysis assuming a constant CO₂ line width, is 249±1.4K (one standard deviation). This temperature is noticeably higher than the rotational temperature of 242±2K found for this same band in 1967 (Schorn et al., 1969) and of 242±1.2K in 1968–1969 (Young et al., 1971).     

Relative flow of H+ and O+ ions in the topside ionosphere at mid-latitudes

Theoretical results on the daily variation of O⁺ and H⁺ field-aligned velocities in the topside ionosphere are presented. The results are for an L = 3 magnetic field tube under sunspot minimum conditions at equinox. They come from calculations of time-dependent O⁺ and H⁺ continuity and momentum balance in a magnetic field tube which extends from the lower F2 region to the equatorial plane (Murphy et al., 1976).There are occasions when ion counterstreaming occurs, with the O⁺ velocity upward and H⁺ velocity downward. The conditions causing this counterstreaming are described: the H⁺ layer is descending whilst O⁺ is supplied from below either to increase the O⁺ concentration at fixed heights or to replace O⁺ ions lost by charge exchange with neutral H. It is suggested that the results of observations at Arecibo by Vickrey et al. (1976) of O⁺ and H⁺ concentrations and counterstreaming velocities are significantly affected by $\text{E}\text{×}\text{B}$ drift.     

Oblateness,radius, and mean stratospheric temperature of Neptune from the 1985 August 20 occultation

The occultation of a bright (K∼6) infrared star by Neptune revealed a central flash at two stations and provided accurate measurements of the limb position at these and several additional stations. We have fitted this data ensemble with a general model of an oblate atmosphere to deduce the oblateness e and equatorial radius a₀ of Neptune at the 1-μbar pressure level, and the position angle p_n of the projected spin axis. The results are e=0.0209±0.0014, a₀=25269±10 km, p_n=20.1°±1°. Parameters derived from fitting to the limb data alone are in excellent agreement with parameters derived from fitting to central flash data alone (E. Lellouch, W.B. Hubbard, B. Sicardy, F. Vilas, and P. Bouchet, 1986, Nature 324, 227–231), and the principal remaining source of uncertainty appears to be the Neptune-centered declination of the Earth at the time of occultation. As an alternative to the methane absorption model proposed by Lellouch et al., we explain an observed reduction in the central flash intensity by a decrease in temperature from 150 to 135°K as the pressure rises from 1 to 400 μbar. Implications of the oblateness results for Neptune interior models are briefly discussed.     

H I distribution in the region of the supernova remnant G78.2+2.1

Based on RATAN-600 21-cm line observations with an angular resolution of 2.4′ over a wide range of radial velocities, we analyze the neutral-hydrogen distribution in the region of the SNR G78.2+2.1. In addition to an H I shell at low radial velocities immediately surrounding the radio remnant, we detected an extended expanding H I shell, ≈3° in diameter, at a radial velocity of ?25 km s^?1, which closely coincides in coordinates and angular sizes with the outer X-ray shell discovered by Lozinskaya et al. (2000). The Hα emission studied by these authors in the SNR region also has a secondary peak at radial velocities from ?45 to ?20 km s^?1. Since the radial velocities of these two objects differ significantly, their distances can be assumed to differ as well; i.e., a chance projection of two distinct objects is observed.     

Aluminum‐26 in H4 chondrites: Implications for its production and its usefulness as a fine‐scale chronometer for early solar system events

Abstract— In order to investigate whether or not ²⁶Al can be used as a fine‐scale chronometer for early solar system events we measured, with an ion microprobe, Mg isotopes and Al/Mg ratios in separated plagioclase, olivine, and pyroxene crystals from the H4 chondrites Ste Marguerite (SM), Forest Vale (FV), Beaver Creek and Quenggouk and compared the results with the canonical ²⁶Al/²⁷Al ratio for calcium‐aluminum‐rich inclusions (CAIs). For SM and FV, Pb/Pb and Mn‐Cr ages have previously been determined (Göpel et al., 1994; Polnau et al., 2000; Polnau and Lugmair, 2001). Plagioclase grains from these two meteorites show clear excesses of ²⁶Mg. The ²⁶Al/²⁷Al ratios inferred from these excesses and from isotopically normal Mg in pyroxene and olivine are (2.87 ± 0.64) × 10^?7 for SM and (1.52 ± 0.52) × 10^?7 for FV. The differences between these ratios and the ratio of 5 times 10^?5 in CAIs indicate time differences of 5.4 ± 0.1 Ma and 6.1 ± 0.2 Ma for SM and FV, respectively. These differences are in agreement with the absolute Pb/Pb ages for CAIs and SM and FV phosphates but there are large discrepancies between the U‐Pb and Mn‐Cr system for the relative ages for CAIs, SM and FV. For example, Mn‐Cr ages of carbonates from Kaidun are older than the Pb/Pb age of CAIs. However, even if we require that CAIs are older than these carbonates, the time difference between this “adjusted” CAI age and the Mn‐Cr ages of SM and FV require that ²⁶ Al was widely distributed in the early solar system at the time of CAI formation and was not mostly present in CAIs, a feature of the X‐wind model proposed by Shu and collaborators (Gounelle et al., 2001; Shu et al., 2001). From this we conclude that there was enough ²⁶Al to melt small planetary bodies as long as they formed within 2 Ma of CAIs, and that ²⁶Al can serve as a fine‐scale chronometer for early solar system events.     

The 7 and 25 June 1985 Neptune occultations: Constraints on the putative Neptune “arc”

Stellar occultations by Neptune on 7 and 25 June 1985 were observed in the K band from Sutherland (SAAO) to search for conforming evidence of the ring-like “arc” reported by Hubbard et al. (W.B. Hubbard, A. Brahic, B. Sicardy, L.-R. Elicer, F. Roques, and F. Vilas (1986). Nature 319, 636–640). A binary star was occulted on 7 June 1985, and since both components were occulted by the planet, their relative positions could be precisely determined. A single sharp dip, of high signal-to-noise ratio, was observed in the post-emersion occultation trace. If this feature were caused by material near Neptune, its corresponding projected equatorial plane radius is either 62,600 ± 160 km or 63,760 ± 120 km, depending on which of the binary star pair was occulted. The equatorial radius, width, and optical depth of the 7 June feature are similar to those described by Hubbard et al. The absence of a corresponding post-emersion dip due to the occultation of the companion star suggests that the ring-like material is discontinuous over a scale of several thousand kilometers in ring circumference. No ring-like features were observed during pre-immersion. The 25 June 1985 occultation was also successfully observed, including atmospheric occultation profiles for both immersion and emersion. No evidence for ring-like material was found in the region probed by this occultation during post-emersion, which included the entire range of equatorial radii over which “arc” events have been previously reported.