Investigation of the Gradient Drift Instability as a Cause of Density Irregularities in Subauroral Polarization Streams. Issue 5 (2nd May 2021)

• Record Type: Journal Article
• Authors: Rathod, C.; Srinivasan, B.; Scales, W.; Kunduri, B.
• Is Part Of: Journal of geophysical research. Volume 126:Issue 5(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-05-02
• Subjects: Gradient drift instability (GDI) -- ionospheric irregularities -- Kelvin‐Helmholtz instability (KHI) -- modeling -- subauroral polarization streams (SAPS) -- SuperDARN; Magnetospheric physics -- Periodicals; Space environment -- Periodicals; Cosmic physics -- Periodicals; Planets -- Atmospheres -- Periodicals; Heliosphere (Astrophysics) -- Periodicals; Geophysics -- Periodicals; 523.01
• DOI: 10.1029/2020JA029027
• Languages: English
• ISSNs: 2169-9380

Abstract

Abstract: Density irregularities have been observed in subauroral polarization streams (SAPS). One hypothesis of the cause of this ionospheric turbulence, based on the background morphology, is the gradient drift instability (GDI). This work models the GDI using a two‐dimensional electrostatic fluid model to determine if it is a viable cause of turbulence generation in SAPS. A statistical study of different velocity profiles, based on SuperDARN radar and Global Positioning System total electron content data, is used to prescribe parameters in the numerical model. The parameter space of different SAPS profiles is explored to study the effect on GDI development. As the velocity shear is initialized closer to the unstable density gradient, the GDI becomes increasingly damped. For these cases, the density and electric potential turbulence cascades obtained from the numerical model follow power laws of about −5/3 or −2, which is in agreement with observational data. If the region of sheared velocity overlaps the density gradient, the GDI becomes stabilized. The latitudinal location of maximum GDI growth depends on the density profile, the velocity profile, and the neutral wind direction. Using velocity profiles with regions of low velocity shear can cause instabilities that grow inside SAPS which have turbulence cascades with different behavior. In all parameter regimes considered, the GDI turbulence is precluded from extending through regions of velocity shear. Turbulence is generated for a variety of SAPS relevant conditions; therefore, the GDI has been shown to be a viable candidate for generating ionospheric irregularities in SAPS. Plain Language Summary: Turbulence in the ionosphere is important to understand because it can negatively impact radio communication signals such as Global Positioning System (GPS) signals. For example, when GPS signals travel through a turbulent region in the ionosphere, a device's position estimates become less accurate. This work helps scientists understand how turbulence is generated in the ionosphere by simulating a phenomenon called subauroral polarization streams (SAPS). SAPS are a region in the ionosphere of large westward velocity, in which turbulence has been observed. The SAPS velocity is a function of latitude. A particular phenomenon called the gradient drift instability (a plasma instability) is hypothesized to be a possible cause of the observed turbulence. This study tests this hypothesis in order to understand the generation of turbulence under different velocity profiles observed in SAPS. Findings suggest that if turbulence occurs outside (or inside) of the velocity region, then it stays outside (or inside) of the velocity region. Turbulence generated in the simulations agrees with turbulence observed in real world data, which suggests that this hypothesis could be correct. Furthermore, the location of the turbulence in latitude is found to be determined by the density, velocity, and neutral wind direction. Key Points: The gradient drift instability (GDI) can cause density irregularities in subauroral polarization streams at the poleward (equatorward) density gradient with an equatorward (poleward) neutral wind The location of maximum GDI growth is a function of the density profile, velocity profile, and neutral wind direction Density irregularities cannot extend into sheared velocity regions