Dr. Gary Webb

RESEARCH SCIENTIST II, CSPAR

Biography

Gary Webb obtained his Ph.D. in physics from the University of Tasmania, Australia, in 1976, on the subject of: Steady State Cosmic Ray Propagation in Interplanetary Space, which was supervised by Dr. K.B. Fenton (University of Tasmania) and co-supervised by Dr. L.J. Gleeson (Monash University, Melbourne, Vic. Australia). After his Ph. D. he took up a position as Research Assistant with L.J. Gleeson, and K.C. Westfold, followed by a position as Lecturer in Mathematics at UNITECH. Lae, Papua New Guinea (1977,1979). In (1980,1981) he took up a postdoc. position with Prof. W.I. Axford (Max Planck Institute for Aeronomy, Katlenburg-Lindau, FRG), (1980,1981) followed by a second postdoc. position with Prof. H.J. Volk at Max Planck Institute for Nuclear Physics (Heidelberg, FRG) for the period (1983,1984) to work on the problem of the acceleration of cosmic rays by the first order Fermi mechanism at astrophysical shocks (e.g. at heliospheric shocks, such as the Solar Wind termination shock, and also at supernova remnant shocks). From (1984-2002) Dr. Webb continued these investigations in a research associate position under Dr. J. R. Jokipii at the Lunar and Planetary Laboratory at the University of Arizona, Tucson Arizona. In 2002, he took up a research postdoc. position with G.P. Zank at the Institute for Geophysics and Planetary Physics (IGPP) at the University of California, Riverside (2002-2008), followed by a research scientist position with G.P. Zank at CSPAR, The University of Alabama in Huntsville, (2008-present).

Some highlights of Dr. Webb’s research are listed below. Dr. Webb was the first to derive transport equations for cosmic rays in relativistic flows (e.g. as in relativistic radio-jets; and for both special relativistic and general relativistic flows). This includes the pitch angle dependent focused transport equation in (1985), and also diffusive transport equations in which the momentum space distribution function is assumed to be near isotropic in the fluid frame (Webb (1989)). Analytical solutions of the diffusive transport equation, illustrating cosmic ray acceleration due to cosmic ray viscosity in relativistic radio-jet shear flows were obtained (Webb, 1990; Webb et al, 2018,2019,2020), which predict the power law spectral index of the accelerated particles depending on the speed of the jet, the fluid shear and other physical parameters.

In the period (2005)-(2020), Dr. Webb developed Lagrangian and Hamiltonian action principles for magnetohydrodynamics (MHD). The Lagrangian map, allows one to relate Lagrangian and Eulerian formulations of the equations. Both local, nonlocal and topological conservation laws for MHD and fluid dynamics were obtained . The Lagrangian map is a group of transformations from Lagrange label space to Eulerian position and time space. The Eulerian momentum equation then arises as an Euler-Poincare equation (i.e. a group constrained variational principle). Non-canonical Hamiltonian equations using non-canonical Poisson brackets and Casimirs give other formulations of the equations (see e.g. Morrison 1982, Holm and Kupershmidt 1983; Webb 2018, Magnetohydrodynamics and Fluid Dynamics: Action Principles and Conservation Laws, Lecture Notes in Physics, Volume 946, Springer Verlag). Multi-symplectic formulations of MHD were also obtained.

Dr. Webb has authored or co-authored more than 160 major publications in refereed journals, and more than 90 conference papers, and two textbooks (Brio, M., Zakharian, A.R. and Webb, G.M., 2010, Numerical Time Dependent Partial Differential Equations for Scientists and Engineers, Math. in Science and Engineering Series, 123, Elsevier Press; Amsterdam; Webb, G. M. 2018, Lecture Notes in Physics, 946, Springer).

Dr. Webb is a member of the Solar Probe Mission to the Sun along with other members of CSPAR and Marshall space Flight Center (MSFC), who have been recognized by a NASA exceptional scientific achievement award.


Education

  • Ph. D. in Physics, University of Tasmania, Australia, 1976
  • B.Sc. Hons., University of Tasmanian, 1971
  • B. Sc. University of Tasmania, Australia, 1967-1970

Select Publications

  • Webb, G.M., 1985, Relativistic transport theory for cosmic rays, ApJ. 296, 319-330; erratum 1987, ApJ., 321, 606.
  • Webb, G.M. 1989, The diffusion approximation and transport theory for cosmic rays in relativistic flows, ApJ., 340, 1112.
  • Webb, G.M., Barghouty, A.F., Hu, Q. and le Roux, J.A. 2018, Particle acceleration due to cosmic ray viscosity and fluid shear in astrophysical jets, ApJ, 885:31 (23pp).
  • Webb, G.M., Mostafavi, P., Al-Nussirat, S., Barghouty, A.F., Li, G., le Roux, J.A., and Zank, G.P. 2020, Cosmic ray acceleration in radio-jet shear flows: scattering inside and outside the jet, ApJ, 894:95 (25pp).
  • Webb, G.M., Dasgupta, B., McKenzie, J.F., Hu, Q., and Zank, G.P. 2014, Local and nonlocal advected invariants and helicities in magnetohydrodynamics, I: Lie dragging approach, J. Phys. A, Math. and Theoret., 47, 095501 (33pp).
  • Webb, G.M., and Anco, S.C. 2017, On magnetohydrodynamic gauge theory, J. Phys. A, Math. and Theoret., 50, 25501 (34 pp).
  • Webb, G.M., Hu, Q., Dasgupta, B. and Zank, G.P. 2010, Homotopy formulas for the magnetic vector potential and magnetic helicity: the Parker spiral interplanetary magnetic field and magnetic flux ropes, J. Geophys. Res., Space physics, 115, A10112, Correction J. Geophys. Res. 116, A11102 (2011).