Anthony Mark McCaffrey

We present conjugate observations of ionospheric small‐scale magnetic perturbations and GPS scintillations from the Tandem Reconnection and Cusp Electrodynamics Reconnaissance Satellites (TRACERS) and the Canadian High Arctic Ionospheric Network (CHAIN) during a storm‐time substorm on 9 August 2025 in the nightside auroral region. Rotational transverse of up to ∼1,000 nT, associated with filamentary field‐aligned currents (FACs) exceeding 150 on spatial scales of ∼1–16 km, were colocated with extreme, localized auroral scintillations ( 10 rad, 0.3) and ∼10 dB‐Hz intensity reduction. The most intense scintillations lasted ∼1.5 s and coincided with peaks in auroral electrojets, Pi2 pulsations, and enhanced dTEC (∼12 TECU). The sheet‐like morphology and spatiotemporal correlation with auroral electrojets suggest that Farley–Buneman processes likely play a dominant role in scintillation formation, with additional contributions from FAC‐driven and gradient‐drift instabilities.

The high latitude ionospheric evolution of the May 10‐11, 2024, geomagnetic storm is investigated in terms of Total Electron Content and contextualized with Incoherent Scatter Radar and ionosonde observations. Substantial plasma lifting is observed within the initial Storm Enhanced Density plume with ionospheric peak heights increasing by 150–300 km, reaching levels of up to 630 km. Scintillation is observed within the cusp during the initial expansion phase of the storm, spreading across the auroral oval thereafter. Patch transport into the polar cap produces broad regions of scintillation that are rapidly cleared from the region after a strong Interplanetary Magnetic Field reversal at 2230UT. Strong heating and composition changes result in the complete absence of the F2‐layer on the eleventh, suffocating high latitude convection from dense plasma necessary for Tongue of Ionization and patch formation, ultimately resulting in a suppression of polar cap scintillation on the eleventh.

The high latitude ionospheric evolution of the May 10-11, 2024, geomagnetic storm is investigated in terms of Total Electron Content and contextualized with Incoherent Scatter Radar and ionosonde observations. Substantial plasma lifting is observed within the initial Storm Enhanced Density plume with ionospheric peak heights increasing by 150km to 300km, reaching levels of up to 630km. Scintillation is observed within the cusp during the initial expansion phase of the storm, spreading across the auroral oval thereafter. Patch transport into the polar cap produces broad regions of scintillation that are rapidly cleared from the region after a strong Interplanetary Magnetic Field reversal at 2230UT. Strong heating and composition changes result in the complete absence of the F2-layer on the 11th, suffocating high latitude convection from dense plasma necessary for Tongue of Ionization and patch formation, ultimately resulting in a suppression of polar cap scintillation on the 11th.

The Assimilative Canadian High Arctic Ionospheric Model (A‐CHAIM) is a near‐real‐time data assimilation model of the high latitude ionosphere, incorporating measurements from many instruments, including slant Total Electron Content measurements from ground‐based Global Navigation Satellite System (GNSS) receivers. These measurements have receiver‐specific Differential Code Biases (DCB) which must be resolved to produce an absolute measurement, which are resolved simultaneously with the ionospheric state using Rao‐Blackwellized particle filtering. These DCBs are compared to published values and to DCBs determined using eight different Global Ionospheric Maps (GIM), which show small but consistent systematic differences. The potential cause of these systematic biases is investigated using multiple experimental A‐CHAIM test runs, including the effect of plasmaspheric electron content. By running tests using the GIM‐derived DCBs, it is shown that using A‐CHAIM DCBs produces the lowest overall error, and that using GIM DCBs causes an overestimation of the topside electron density which can exceed 100% when compared to in situ measurements from DMSP.

The Assimilative Canadian High Arctic Ionospheric Model (A-CHAIM) is a data assimilation model of the high latitude ionosphere, incorporating measurements from many instruments, including slant Total Electron Content measurements from ground-based Global Navigation Satellite System (GNSS) receivers. These measurements have receiver-specific Differential Code Biases (DCB) which must be resolved to produce an absolute measurement, which are resolved along with the ionospheric state using Rao-Blackwellized particle filtering. These DCBs are compared to published values and to DCBs determined using 8 different Global Ionospheric Maps (GIM), which show small but consistent systematic differences. The potential cause of these systematic biases is investigated using multiple experimental A-CHAIM test runs, including the effect of plasmaspheric electron content. By running tests using the GIM-derived DCBs, it is shown that using A-CHAIM DCBs produces the lowest overall error, and that using GIM DCBs causes an overestimation of the topside electron density which can exceed 100% when compared to in-situ measurements from DMSP.

The Assimilative Canadian High Arctic Ionospheric Model (A‐CHAIM) is an operational ionospheric data assimilation model that provides a 3D representation of the high latitude ionosphere in Near‐Real‐Time (NRT). A‐CHAIM uses low‐latency observations of slant Total Electron Content (sTEC) from ground‐based Global Navigation Satellite System (GNSS) receivers, ionosondes, and vertical TEC from the JASON‐3 altimeter satellite to produce an updated electron density model above 45° geomagnetic latitude. A‐CHAIM is the first operational use of a particle filter data assimilation for space environment modeling, to account for the nonlinear nature of sTEC observations. The large number (>10⁴) of simultaneous observations creates significant problems with particle weight degeneracy, which is addressed by combining measurements to form new composite observables. The performance of A‐CHAIM is assessed by comparing the model outputs to unassimilated ionosonde observations, as well as to in‐situ electron density observations from the SWARM and DMSP satellites. During moderately disturbed conditions from 21 September 2021 through 29 September 2021, A‐CHAIM demonstrates a 40%–50% reduction in error relative to the background model in the F2‐layer critical frequency (foF2) at midlatitude and auroral reference stations, and little change at higher latitudes. The height of the F2‐layer (hmF2) shows a small 5%–15% improvement at all latitudes. In the topside, A‐CHAIM demonstrates a 15%–20% reduction in error for the Swarm satellites, and a 23%–28% reduction in error for the DMSP satellites. The reduction in error is distributed evenly over the assimilation region, including in data‐sparse regions.

In this study, we use measurements from over 4,735 globally distributed Global Navigation Satellite System receivers to track the progression of traveling ionospheric disturbances (TIDs) associated with the 15 January 2022 Hunga Tonga‐Hunga Ha'apai submarine volcanic eruption. We identify two distinct Large Scale traveling ionospheric disturbances (LSTIDs) and several subsequent Medium Scale traveling ionospheric disturbances (MSTIDs) that propagate radially outward from the eruption site. Within 3,000 km of epicenter, LSTIDs of >1,600 km wavelengths are initially observed propagating at speeds of ∼950 and ∼555 ms⁻¹, before substantial slowing to ∼600 and ∼390 ms⁻¹, respectively. MSTIDs with speeds of 200–400 ms⁻¹ are observed for 6 hrs following eruption, the first of which comprises the dominant global ionospheric response and coincides with the atmospheric surface pressure disturbance associated with the eruption. These are the first results demonstrating the global impact of the Tonga eruption on the ionospheric state.

In this study, we use measurements from over 4,735 globally distributed Global Navigation Satellite System (GNSS) receivers to track the progression of travelling ionospheric disturbances (TIDs) associated with the 15 January 2022 Hunga Tonga-Hunga Ha’apai submarine volcanic eruption. We identify two distinct Large Scale TIDs (LSTIDs) and several subsequent Medium Scale TIDs (MSTIDs) that propagate radially outward from the eruption site. Within 3000 km of epicenter, LSTIDs of >1600 km and ~1350 km wavelengths are initially observed propagating at speeds of ~950 ms-1 and ~555 ms-1, before substantial slowing to ~600 ms-1 and ~390 ms-1, respectively. MSTIDs with speeds of 200-400 ms-1 are observed for six hours following eruption, the first of which comprises the dominant global ionospheric response and coincides with the atmospheric surface pressure disturbance associated with the eruption. These are the first results demonstrating the global impact of the Tonga eruption on the ionospheric state.