Engineering topics

Ahluwalia, H. S.

Publications and source records attributed to Ahluwalia, H. S..

At least 19 records

NASA NTRS1995

The observed North-South Asymmetry of IMF spiral

We appraise the finding, reported in the literature, that a small but finite north-south asymmetry (NSA) exists in the interplanetary magnetic field (IMF) spiral at Earth's orbit. We have analyzed the data available on the Omnitape for the 1963 to 1993 period. The coverage is very uneven, ranging from less than 40% to greater than 80%. The magnitude of NSA fluctuates considerably during the period of our analysis. This is true even if one considers the period 1967 to 1982 when the coverage is greater than 50%. The values of NSA derived from 27-day averages of the hourly data points range from greater than +50 deg to less than -40 deg. If one arranges the data according to the magnetic polarity epochs of the solar polar field, the epoch averages gives the magnitude of NSA less than approximately 2 deg. This is also true, if one considers the average magnitude of NSA for the 1965 to 1993 period, when the coverage is greater than 25%. A genuine, persistent, NSA of IMF spiral is likely to affect the cosmic ray modulation, on either side of the current sheet, by introducing a corresponding change in the radial diffusion coefficient of energetic particle transport in the heliosphere. The annual mean values of the observed NSA of IMF spiral are compared with the observed off-ecliptic contributions to cosmic ray modulation.

Ahluwalia, H. S.↗

NASA NTRS1995

Long term variability of the solar wind speed

We have reviewed the solar wind data obtained over a period of more than three decades. The data coverage on the Omnitape begins on 27 November 1963 and ends on 31 December 1993, for the version used by us. The coverage is very uneven, ranging from less than 40% to greater than 80%. We find that a correlation continues to exist between the measured values of the solar wind speed (V) and the geomagnetic index Ap. For the period when the coverage is greater than or equal to 85%, the data fit the equation: V (km/s) = 11.7 A(sub p) + 260. The correlation coefficient is 0.8, at a confidence level of 99.95%. However, we find that the predicted value of V may differ from the observed value by as much as 15% for a year in which the coverage is poorer. A comparison of IMP 8 with Pioneer Venus Orbiter (PVO) data indicates that the average values at the former are systematically higher by as much as 35 km/s (approximately 8%) for an overlapping time period. Also, we draw attention to the observed three solar cycle periodicity in A(sub p) data for the 1932 to 1994 period and its implications for forecasting the parameters for solar cycle 23 as well as on the computations of the modulation parameters for cosmic rays.

Gazis, P. R.↗

NASA NTRS1995

Is coverage a factor in non-Gaussianity of IMF parameters?

Recently, Feynman and Ruzmaikin (1994) showed that IMF parameters for the 1973 to 1990 period are not log-normally distributed as previously suggested by Burlaga and King (1979) for the data obtained over a shorter time period (1963-75). They studied the first four moments, namely: mean, variance, skewness, and kurtosis. For a Gaussian distribution, moments higher than the variance should vanish. In particular, Feynman and Ruzmaikin obtained very high values of kurtosis during some periods of their analysis. We note that the coverage for IMF parameters is very uneven for the period analyzed by them, ranging from less than 40% to greater than 80%. So a question arises as to whether the amount of coverage is a factor in their analysis. We decided to test this for the B(sub z) component of IMF, since it is an effective geoactive parameter for short term disturbances. Like them, we used 1-hour averaged data available on the Omnitape. We studied the scatter plots of the annual mean values of B(sub z)(nT) and its kurtosis versus the percent coverage for the year. We obtain a correlation coefficient of 0.48 and 0.42 respectively for the 1973-90 period. The probability for a chance occurrence of these correlation coefficients for 18 pair of points is less than 8%. As a rough measure of skewness, we determined the percent asymmetry between the areas of the histograms representing the distributions of the positive and the negative values of B(sub z) and studied its correlation with the coverage for the year. This analysis yields a correlation coefficient of 0.41 When we extended the analysis for the whole period for which IMF data are available (1963-93) the corresponding correlation coefficients are 0.59, 0.14, and 0.42. Our findings will be presented and discussed

Ahluwalia, H. S.↗

NASA NTRS1994

Cosmic ray transverse gradient for a Hale cycle

We have used neutron monitor data obtained at Deep River and Huancayo as well as the vertical underground telescope data obtained at Embudo to compute the cosmic ray transverse gradient (G(sub theta)) for the 1965 to 1990 period. The computed mean value of G(sub theta) for a given qA epoch, changes sign with the change in the solar magnetic polairty in accordance with the predictions of some contemporary hypotheses. Also, we find that the magnitude of G(sub theta) undergoes a significant time variation during a given polarity epoch. It has the largest value near the solar polar field reversal epoch boundaries, when magnetic polarity in the solar northern hemisphere is positive (qA greater than O). For each of the three solar polar field reversals, the change in the magnitude of G(sub theta) is steeper across the epoch boundaries. There is a good correlation between G(sub theta) and the tilt angle of the helisopheric neutral current sheet (HNCS). Our results are in agreement with the reported piecemeal measurements of the latitudinal gradient made by spacecrafts, at different times, at lower primary energies, at far off distances from Earth's orbit. As such, their global significace is appreciable. Even so, it is not clear yet how these findings reflect upon the drift hypothesis in its present form. However, they do affirm the important role played by the tilt angle of HNCS in the modulation processes.

Ahluwalia, H. S.↗

NASA NTRS1993

Hale cycle effects in cosmic ray east-west anisotropy and interplanetary magnetic field

We have reanalyzed diurnal anisotropy data obtained with the shielded ion chamber (IC) at Cheltenham/Fredericksburg and the neutron monitor (NM) at Swarthmore/Newark. IC data are for the 1936-1977 period and NM data are for the 1965-1988 period. We have corrected IC data for the diurnal temperature effect. Application of this correction results in a better agreement between IC and other data sets, thereby making it possible to study the long-term changes in the diurnal anisotropy using IC data. The behavior of the annual mean east-west anisotropy is studied for 53 years of observations. The period encompasses more than two solar magnetic (Hale) cycles. Its amplitude undergoes the expected 11 and 22 year variations, with the largest changes occurring near solar activity minima. Moreover, the data indicate the presence of the subsidiary maxima for the entire 53-year period, following the solar polar field reversals, during the declining phases of activity cycles when high-speed solar wind streams are present in the heliosphere. The data suggest that the amplitude of the subsidiary maximum is large when the solar polar magnetic field points toward the sun in the Northern Hemisphere, and radial anisotropy is absent.

Ahluwalia, H. S.↗

NASA NTRS1993

Atmospheric attenuation length for relativistic solar protons

We compute the mean attenuation length lambda(f) in earth's atmosphere for the protons produced in the solar flare of 29 September, 1989. We use data obtained with three pairs of neutron monitors. The detectors in the pair have very similar values of the geomagnetic vertical cutoff rigidity R(0) and overlapping asymptotic cones of acceptance but they differ in terms of the altitudes of the observing sites. We apply the Wilson et al. (1967) method to compute the values of lambda(f) for the three representative pairs which cover a range of solar proton rigidities. The computed mean values of lambda(f) are significantly larger than the consensus value of (100 +/- 5) g/sq cm reported in the literature. Also, they exhibit a linear correlation with R(0).

Ahluwalia, H. S.↗

NASA NTRS1993

The limiting primary rigidity of cosmic ray diurnal anisotropy

Our calculations of the upper cutoff primary rigidity (Rc), applicable to the solar diurnal anisotropy, have been extended to cover the declining phase of the solar activity cycle 21. The calculated values of Rc now encompass a complete solar magnetic cycle (1965-1987). We found that the values of Rc were very large for the 1982-1985 period, almost twice as large as those observed previously for the periods of maximum solar activity. The largest value occurred in 1983. Also, the value obtained at the solar activity minimum year of 1986 was about twice as large as that obtained in 1965. Our results are compared with those reported by others.

Ahluwalia, H. S.↗

NASA NTRS1993

Cosmic ray diurnal anisotropy for a solar magnetic cycle

Cosmic ray diurnal anisotropy at high primary rigidities is extended for the 1980-1987 period. The computed values of the limiting primary rigidity for the period vary over the range 30 GV to 200 GV. For the previously studied 1965-1980 period, the mean value of the amplitude of the anisotropy is 0.5 percent. The amplitude of the diurnal anisotropy for 1965 and 1986-1987 is about 20 percent smaller. Very large amplitudes of diurnal variation are observed during the 1982-1985 period, at all primary rigidities. The value of the coupled variable lambda(parallel) x G(r) found to remain constant at about 1 percent for qA less than zero solar magnetic polarity epochs, independent of the primary rigidity. Its value is significantly lower for qA greater than zero epochs.

Ahluwalia, H. S.↗

NASA NTRS1992

Cosmic ray modulation near the onset and maximum phases of solar activity cycle 22

Using data obtained with neutron monitors we study the cosmic-ray modulation of the five-year developmental phase of solar activity cycle (SAC) 22. The main characteristics of the observed modulation are compared with those of cycle 19. The similarities and differences between the two cycles are noted. The data indicate that the amplitude of the observed modulation is larger at higher and lower primary rigidities than that for cycle 19, which still remains the most active cycle. The lowest ever monthly-mean counting rates were obtained in June 1991. Even so, based upon our prior experience, we expect the recovery of the cosmic ray intensity in SAC 22 to follow the pattern observed for cycles 20 and 18, rather than that for cycle 19.

Ahluwalia, H. S.↗

NASA NTRS1992

A correlation between IMF and the limiting primary rigidity for the cosmic ray diurnal anisotropy

A plausible explanation is provided for the existence of the subsidiary maximum in the annual mean cosmic ray diurnal anisotropy, observed during the declining phase (1982-85) of the solar activity cycle 21. For this period, the values of the limiting primary rigidity (Rc), applicable to the steady state diurnal anisotropy, are quite large. Also, the annual mean magnitudes (B) of the interplanetary magnetic field (IMF) are very high. The data for Rc and B are reviewed for 1964-1987 period. A correlation is found to exist between the two parameters.

Ahluwalia, H. S.↗

NASA NTRS1989

The onset of the solar active cycle 22

There is a great deal of interest in being able to predict the main characteristics of a solar activity cycle (SAC). One would like to know, for instance, how large the amplitude (R sub m) of a cycle is likely to be, i.e., the annual mean of the sunspot numbers at the maximum of SAC. Also, how long a cycle is likely to last, i.e., its period. It would also be interesting to be able to predict the details, like how steep the ascending phase of a cycle is likely to be. Questions like these are of practical importance to NASA in planning the launch schedule for the low altitude, expensive spacecrafts like the Hubble Space Telescope, the Space Station, etc. Also, one has to choose a proper orbit, so that once launched the threat of an atmospheric drag on the spacecraft is properly taken into account. Cosmic ray data seem to indicate that solar activity cycle 22 will surpass SAC 21 in activity. The value of R sub m for SAC 22 may approach that of SAC 19. It would be interesting to see whether this prediction is borne out. Researchers are greatly encouraged to proceed with the development of a comprehensive prediction model which includes information provided by cosmic ray data.

Ahluwalia, H. S.↗

NASA NTRS1988

The regimes of the east-west and the radial anisotropies of cosmic rays in the heliosphere

Observations dating back to 1957 are used to show that there are two distinct physical states of the heliosphere. From 1957-1970 the diurnal anisotropy consisted of the azimuthal component only. This period is defined as the regime of the east-west anisotropy. The period 1971-1979 is characterized by the appearance of a radial anisotropy which attained a maximum amplitude in 1976, when the solar activity was minimum. It is suggested that there is an inverse correlation between the amplitude of the radial anisotropy and solar activity. The physical state of the heliosphere is very stable during the regime of east-west anisotropy and extremely dynamic during the radial anisotropy regime. It is suggested that the heliosphere switches from one physical state to another following the onset of the solar polar field reversal.

Ahluwalia, H. S.↗

NASA NTRS1988

Is there a twenty year wave in the diurnal anisotropy of cosmic rays?

Data obtained with the Deep River neutron monitor and the underground vertical muon telescope at Embudo for the period 1965-1979 are analyzed. The data show that for 1957-1970 the diurnal anisotropy is unidirectional. During 1971-1979, the diurnal anisotropy consists of two components. One is in the east-west direction and the other is the radial component, with direction along 12:00 LT. The latter attains a maximum amplitude in 1976. No evidence is found for the existence of the twenty year wave in the diurnal anisotropy of cosmic rays.

Ahluwalia, H. S.↗

NASA NTRS1988

The geomagnetic field - An explanation for the microturbulence in coaxial gun plasmas

The complexity introduced by the geomagnetic field in several regions of a coaxial gun plasma device is described. It is shown that the annihilation of the swept-up geomagnetic flux, trapped within the highly compressed turbulent plasma, provides an explanation for varied performance and experimental results. The results indicate that the device should be aligned along the direction of the local geomagnetic field or enclosed in a mu-metal shield.

Mather, J. W.↗

NASA NTRS1987

A survey of the cosmic ray diurnal variation during 1973-1979. I - Persistence of solar diurnal variation. II - Application of diffusion-convection model to diurnal anisotropy data

An analysis of data obtained with the vertical underground muon telescope at Embudo, NM shows that the solar diurnal variation in cosmic ray intensity is a persistent phenomenon over the 1973-1979 period. Assuming that the daily fluctuations in the amplitude and phase of the diurnal variation are random perturbations about the mean vector, the relative magnitude of the random component is determined. In the second part, the Diffusion-Convection model of cosmic ray transport is applied to high rigidity particles detected at the earth in order to deduce the behavior of the heliospheric transport parameters between 1973 and 1979. It is suggested that the diurnal variation observed at Embudo during 1979 may require a contribution from the charged particle drifts.

Riker, J. F.↗

NASA NTRS1985

Upper cut-off rigidity for corotation anisotropy during solar activity cycles 20 and 21

At the Eleventh International Conference on Cosmic Rays in 1969, the results of a study of the solar diurnal variations of solar rays observed during the ascending phase of solar activity cycle twenty was discussed. The diurnal variation, observed underground during 1965-68 period, and results from an extraterrestrial anisotropy having a continuously increasing upper cut-off rigidity R sub c were reported. However, the coupling functions applicable to underground telescopes were controversial then. This situation has improved now. Those results wsere re-examined and extended to cover the period 1965-78. The coupling functions given by Murakami et al. for underground muons and those given by Lockwood and Weber for neutron monitors were used showed that a great deal of care should be exercised in the value of R sub c was calculated. Although numerical values of R sub c are a little different, the trend for 1965-68 period remains unchanged. Highest value of R sub c occur in 1970 and the lowest value occurs in 1976.

Ahluwalia, H. S.↗

NASA NTRS1985

Solar wind velocity and daily variation of cosmic rays

Recently parameters applicable to the solar wind and the interplanetary magnetic field (IMF) have become much better defined. Superior quality of data bases that are now available, particularly for post-1971 period, make it possible to believe the long-term trends in the data. These data are correlated with the secular changes observed in the diurnal variation parameters obtained from neutron monitor data at Deep River and underground muon telescope data at Embudo (30 MEW) and Socorro (82 MWE). The annual mean amplitudes appear to have large values during the epochs of high speed solar wind streams. Results are discussed.

Ahluwalia, H. S.↗

NASA NTRS1985

Diurnal anisotropy during solar activity cycle twenty and diffusion-convection model

Underground muon telescope data obtained at Embudo and Neutron monitor data obtained at Deep River are divided into two sets; one covers the ascending phase of the cycle (1965-70) and the other covers the descending phase (1971-76). The amplitude of diurnal anisotropy calculated from the data does not agree with the value predicted by the simplified version of the Diffusion-Convection Model (DCM); the discrepancy is worse for neutron data.

Ahluwalia, H. S.↗