arXiv subjects

G. W. Bowden

Publications and source records attributed to G. W. Bowden.

3 recordsLinked to original sources

arXiv2023

Numerical Modelling and GNSS Observations of Ionospheric Depletions due to a Small-Lift Launch Vehicle

Space launches produce ionospheric disturbances which can be observed through measurements such as Global Navigation Satellite System signal delays. Here we report observations and numerical simulations of the ionospheric depletion due to a Small-Lift Launch Vehicle. The case examined was the launch of a Rocket Lab Electron at 22:30 UTC on March 22, 2021. Despite the very small launch vehicle, ground stations in the Chatham Islands measured decreases in line-of-sight total electron content for navigation satellite signals following the launch. General Circulation Model results indicated ionospheric depletions which were comparable with these measurements. Line-of-sight measurements showed a maximum decrease of $2.7$~TECU in vertical total electron content, compared with a simulated decrease of $2.6$~TECU. Advection of the exhaust plume due to its initial velocity and subsequent effects of neutral winds are identified as some remaining challenges for this form of modelling.

physics.space-ph↗

arXiv2020

Numerical simulation of ionospheric depletions resulting from rocket launches using a general circulation model

Rocket exhaust plumes have been observed to cause large-scale depletions of ionospheric plasmas ("ionospheric holes"). In the F-region, charge exchange reactions occur between O^+ ions and exhaust species such as H$_2$O, H$_2$, and CO$_2$ to form ions which then undergo rapid dissociative recombination. The Global Ionosphere-Thermosphere Model (GITM) was extended to include these chemical reactions and appropriate source terms to represent rocket exhaust plumes. The resulting model was applied to ionospheric depletions resulting from the launches of Jason-3 and FORMOSAT-5 on SpaceX Falcon 9 rockets from Vandenberg Air Force Base. Outputs from the model were compared with GNSS, ionosonde, and satellite Langmuir probe measurements. Simulation indicated that the FORMOSAT-5 launch resulted in a far larger and longer-lived ionospheric depletion than the Jason-3 launch, consistent with observations.

physics.ao-ph↗

arXiv2015

Calculation of continuum damping of Alfvén eigenmodes in 2D and 3D cases

In ideal MHD, shear Alfvén eigenmodes may experience dissipationless damping due to resonant interaction with the shear Alfvén continuum. This continuum damping can make a significant contribution to the overall growth/decay rate of shear Alfvén eigenmodes, with consequent implications for fast ion transport. One method for calculating continuum damping is to solve the MHD eigenvalue problem over a suitable contour in the complex plane, thereby satisfying the causality condition. Such an approach can be implemented in three-dimensional ideal MHD codes which use the Galerkin method. Analytic functions can be fitted to numerical data for equilibrium quantities in order to determine the value of these quantities along the complex contour. This approach requires less resolution than the established technique of calculating damping as resistivity vanishes and is thus more computationally efficient. The complex contour method has been applied to the three-dimensional finite element ideal MHD code CKA . In this paper we discuss the application of the complex contour technique to calculate the continuum damping of global modes in tokamak as well as torsatron, W7X and H1-NF stellarator cases. To the authors' knowledge these stellarator calculations represent the first calculation of continuum damping for eigenmodes in fully three-dimensional equilibria. The continuum damping of global modes in W7X and H1-NF stellarator configurations investigated is found to depend sensitively on coupling to numerous poloidal and toroidal harmonics.

physics.plasm-ph↗