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Professor of Physics & Astronomy, PhD, 1960, Gujarat University, India.

A Brief Description of Research Interests:

  1. Time Variations of Galactic Cosmic Radiation Intensity.
  2. Current research focuses on issues related to understanding the observed variations of galactic cosmic rays (GCRs), at earth's orbit, on time scales ranging from less than one hour to several decades. This work includes a study of the solar daily variations of cosmic rays, transient effects (Forbush decreases, ground level enhancements, etc), as well as the isotropic modulations of GCR intensity (11- and 22-year modulations). The observations obtained at global sites with a variety of detectors are analyzed; these include neutron monitors (NMs), shielded ion chambers (ICs), muon telescopes (MTs) located underground, as well as at sea level and mountain sites. Also, data obtained with detectors carried on board balloons and a variety of spacecrafts are looked at. The data are correlated with changes in solar activity and solar wind parameters, such as its velocity (V) and the embedded turbulent magnetic field intensity (B). A variety of GCR streaming patterns in the heliosphere contribute to observed anisotropies on the spinning earth. This is an exciting time for heliospheric physics, now that the Ulysses spacecraft has been making in situ measurements at off-ecliptic helio-latitudes since 1992 and Voyagers 1 and 2 are near the edge of the heliosphere. A concerted effort is underway to determine the rigidity dependence of the diffusion coefficients and charged particle gradients in the 3-D heliosphere.

    Selected Publications
    • Measurements of Transverse Cosmic Ray Particle Density Gradients at High Rigidities in the Ulysses Era. J. Geophys. Res., 101, 13549, 1996. .

    • Transverse Cosmic Ray Gradients in the Heliosphere and the Solar Diurnal Anisotropy. J. Geophys. Res., 102, 17433, 1997. Coauthor: L.I. Dorman.

    • Galactic Cosmic Ray Transport in the Heliosphere: Diffusive Anisotropy 1965-1994, Adv. Space Res., 23, 475, 1999. Solicited Contributed Paper, 32nd COSPAR Scientific Assembly, Nagoya, Japan. Coauthors: S.S. Xue and M.M. Fikani.

    • Galactic cosmic ray diurnal modulation, interplanetary magnetic field intensity and the planetary index Ap, Geophys. Res. Lett., 27, 617, 2000. (Highlighted Paper)

    • Solar wind and galactic cosmic ray modulation, Geophys. Res. Lett., 30(3), 1133, doi: 10.1029/2002GL016017, 2003.

    • Cycle 20 solar wind modulation of galactic cosmic rays: Understanding the challenge, J. Geophys. Res., 110, A 10106, doi:10.1029/2005JA011106, 2005.

    • Gnevyshev Gap, Forbush Decreases, ICMEs/SSCs and Solar Wind Electric Field: Relationships, Adv. Space Res., 35, 2119, 2005. Coauthor: Y. Kamide.

    • Cosmic ray detector response to transient solar modulation: Forbush decreases, J. Geophys. Res., 112, A08105, doi:10.1029/2006 JA0111958, 2007.

  3. Solar Cosmic Rays

    There is a continuing interest in the processes that lead to the productions of energetic particles and electromagnetic emissions in the solar atmosphere following a large solar flare. Data obtained with satellites and ground-based detectors are analyzed for this purpose. The intent is to acquire insights as to how energy is built up and released at the flare site on the sun.

  4. Sample Publication
    • Atmospheric Attenuation Length for Relativistic Solar Protons. Geophys. Res. Lett., 20, 995, 1993. Coauthor: S.S. Xue.

  5. Solar Activity Cycle Forecast
  6. Our efforts to understand observed correlations between solar and geophysical activity and GCR time variations led to the discovery of a three-cycle quasi-periodicity in Ap index and GCR flux. We also showed that Ap minima are linearly correlated with the max SSNs of new cycles, leading to our forecast that cycle 23 will be moderate; it came true. We are now ready to forecast cycle 24 activity.

    Selected Publications
    • The Predicted Size of Cycle 23 Based on the Inferred Three Cycle Quasi-periodicity of the Planetary Index Ap, J. Geophys. Res., 103, 12103, 1998.

    • The Development of Solar Cycle 23 (Reply to Wilson and Hathaway's Comment), J. Geophys. Res., 104, 2559, 1999.

    • Solar Cycle 23 Prediction Update, Adv. Space Res., 26, 187, 2000.

    • A meandering path to solar activity forecast for cycle 23, Solar Wind Ten, American Inst.Phys.Conf. Proc. 679. Eds. M. Velli, R. Bruno, and F. Malra, p. 176, 2003.

  7. Plasma Physics
  8. A state-of-the-art sequence of courses in plasma physics are offered by the Departments of Physics & Astronomy, Chemical & Nuclear Engineering, and Electrical & Computer Engineering, on a rotating basis. This inter-departmental program provides challenging opportunities for the students to undergo research experience in the study of the laboratory as well as space plasmas.

    Sample Publications
    • The Geomagnetic Field--An Explanation for the Microturbulence in Coaxial Gun Plasmas. IEEE Transactions on Plasma Science, 16, 56, 1988. Coauthor: J. W. Mather.

    • Solar Wind and Its Coronal Origins. Solar Interior and Atmosphere, Univ. of Arizona Press, Tucson, AZ. Eds. A.N. Cox, W.C. Livingston, and M.S. Mathews, p.1087, 1991. Invited Review Paper. Coauthors: G.L. Withbroe and W.C. Feldman.

    • Measurements of Microwave Transmission Through a Decaying Plasma Column. IEEE Trans. Plasma Sci., 22, 47, 1994. Coauthor: Kyle J. Hendricks.

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