The Properties and Origins of Corotating Plasmaspheric Irregularities as Revealed Through a New Tomographic Technique

Abstract

This paper describes insights into the nature of corotating plasmaspheric irregularities (CPIs) enabled by a newly developed method for range-and time-resolved tomographic images of these structures. The method is based on high-precision measurements of total electron content gradients measure toward cosmic radio sources using an interferometric radio telescope, the Very Large Array (VLA). Exploiting hundreds of hours of data from the VLA Low-band Ionosphere and Transient Experiment, we confirm that CPIs are predominantly detected at night and at L shells ∼2-4. Combining this large data set with other ionospheric, atmospheric, and space weather databases, we have established that CPI detection rates are much higher when levels of solar and geomagnetic activity are low. We also demonstrate that higher detection rates coincide with drivers of perturbations in the ionospheric electric field, including sporadic E and gravity waves. The gravity wave sources most commonly associated with CPIs are jet stream bend/shear and substorm-triggered atmospheric disturbances. We also show that simulations of the plasmaspheric impact of both gravity wave-driven electric field perturbations and polarization electric fields associated with electrobuoyancy waves/sporadic E produce results that are very similar to what is observed with the VLA.

Ionospheric Irregularities Observed During the GLEAM Survey

“…This may indicate that the polarization electric fields that are the hallmarks of electrobuoyancy waves can also play a role in driving the formation of disturbed flux tubes in the upper ionosphere/lower plasmasphere. In fact, a long‐term study of corotating plasmaspheric irregularities by Helmboldt et al (2020) has shown that this is likely the case, at least over North America. If the same phenomenon is active here, it could be that some of the disturbed flux tubes/ducts observed with MWA are driven by ionospheric electric field perturbations that occurred too far south to be directly imaged with MWA, but whose effects were seen within the topside ionosphere/lower plasmasphere over the telescope.…”

Observations of the Electrodynamical Ties Between Sporadic E and the Plasmasphere

“…While the CPI data provide good constraints on λ , V ph must be assumed. A phase speed of 20 m s −1 was assumed for similar calculations by Helmboldt et al (2020) and Helmboldt (2020) because it yielded simulated data with properties similar to those actually observed, and the same was the case for this study.…”

“…These are roughly consistent with the properties of the waves noted within SuperDARN data by Ogawa et al (2009). This is significantly larger than the apparent wavelengths typically measured for CPIs of ∼20–50 km (Helmboldt, 2020; Helmboldt et al, 2020). However, the beam spacing of the radars is such that only phase fronts with wavelengths >70 km can be resolved out to the maximum E region range of 630 km.…”

“…Data from these two arrays acquired in June 2018 were used to detect and map CPIs. The method used was described in detail by Helmboldt et al (2020) and its adaptation to compact arrays of GPS receivers is likewise reported by Helmboldt (2020). Briefly, the method works by treating CPIs as field‐aligned wavefronts that appear to move opposite the line‐of‐sight (LoS) motion.…”

“…Likewise, the CPIs could be directly tied to E S polarization electric fields. Both Helmboldt et al (2020) and Helmboldt (2020) used relatively simple models of plane wave electric field disturbances with modest amplitudes (∼0.1–1 mV m −1 ) to show that such F and/or E region phenomena could reproduce the observed CPI properties.…”