skip to main content


Title: A Bottomside Parameterization for the Empirical Canadian High Arctic Ionospheric Model
Abstract

In this study, we present a bottomside model representation to be used by the Empirical Canadian High Arctic Ionospheric Model (E‐CHAIM). This model features a new approach to modeling the bottomside electron density; namely, instead of modelling electron density directly, E‐CHAIM models the altitude profile of the scale thickness of a single bottomside layer. In this approach, the curvature in the bottomside associated with theEregion andF1 layer is represented in the scale thickness domain as a peak function centered at the layer peak altitude. The use of this approach ensures the production of explicitly doubly differentiable bottomside electron density profiles and directly avoids issues known to exist within current standards, such as the International Reference Ionosphere (IRI), which has discontinuities in space, time, and in the vertical electron density gradient. In terms of performance, after removing the impacts ofhmF2 andNmF2, the new E‐CHAIM profile function generally performs comparably to the IRI, with bottomside TEC from both models within 2.0 TECU (1 TECU = 1016 e/m3) of observations. More specifically, the E‐CHAIM bottomside is demonstrated to outperform the IRI bottomside function in theFregion during low solar activity periods with respect to incoherent scatter radar observations. At high latitudes, E‐CHAIM tends to outperform the IRI during winter months by between 10% and 40% ofNmF2 while being outperformed by the IRI by between 10% and 25% ofNmF2 during summer periods, mainly during the daytime at high solar activity.

 
more » « less
NSF-PAR ID:
10461166
Author(s) / Creator(s):
 ;  ;  ;  ;  
Publisher / Repository:
DOI PREFIX: 10.1029
Date Published:
Journal Name:
Radio Science
Volume:
54
Issue:
5
ISSN:
0048-6604
Page Range / eLocation ID:
p. 397-414
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. Abstract

    Competing theories exist for the generation mechanism of auroral medium‐frequency burst (MFB). In an effort to constrain MFB source heights, this study analyzes 33 events in which MFB and auroral 2fceroar co‐occurred at Sondrestrom, Greenland. Using measurements from an array of receiving antennas, direction‐of‐arrival calculations indicate that in a given co‐occurrence, the elevation angle of MFB typically is higher than that of roar. Ray tracing is used to determine source heights of the MFB signals. Density profiles are obtained from the International Reference Ionosphere (IRI) and shifted in magnitude until each event's roar signals originate at heights where the frequency‐matching condition for 2fceroar generation is satisfied. This shifting method is validated using density measurements from the Sondrestrom incoherent scatter radar (ISR) facility for the two events with available ISR data. After shifting, ray tracing demonstrates that in 25 of the 33 events, burst originates at a height of about 200 km, lower than the typical altitude of peak electron density. However, ISR measurements show that the density profile is enhanced at low altitudes while MFB is observed, peaking in theEregion rather than theFregion. This finding implies that the MFB sources at 200 km are on the topside of the density peak, in a region of downward pointing density gradient, in qualitative agreement with the mechanism of MFB generation by Langmuir waves in the topside ionosphere. These results also suggest a new method of estimating density in the polar cap using roar signals to calibrate IRI profiles.

     
    more » « less
  2. Abstract

    We present a new high‐resolution empirical model for the ionospheric total electron content (TEC). TEC data are obtained from the global navigation satellite system (GNSS) receivers with a 1° × 1° spatial resolution and 5‐min temporal resolution. The linear regression model is developed at 45°N, 0°E for the years 2000–2019 with 30‐min temporal resolution, unprecedented for typical empirical ionospheric models. The model describes dependency of TEC on solar flux, season, geomagnetic activity, and local time. Parameters describing solar and geomagnetic activity are evaluated. In particular, several options for solar flux input to the model are compared, including the 10.7 cm solar radio flux (F10.7), the Mg II core‐to‐wing ratio, and formulations of the solar extreme ultraviolet flux (EUV). Ultimately, the extreme ultraviolet flux presented by the Flare Irradiance Spectral Model, integrated from 0.05 to 105.05 nm, best represents the solar flux input to the model. TEC time delays to this solar parameter on the order of several days as well as seasonal modulation of the solar flux terms are included. TheAp3index and its history are used to reflect the influence of geomagnetic activity. The root mean squared error of the model (relative to the mean TEC observed in the 30‐min window) is 1.9539 TECu. A validation of this model for the first 3 months of 2020 shows excellent agreement with data. The new model shows significant improvement over the International Reference Ionosphere 2016 (IRI‐2016) when the two are compared during 2008 and 2012.

     
    more » « less
  3. Abstract

    E‐region models have traditionally underestimated the ionospheric electron density. We believe that this deficiency can be remedied by using high‐resolution photoabsorption and photoionization cross sections in the models. Deep dips in the cross sections allow solar radiation to penetrate deeper into the E‐region producing additional ionization. To validate our concept, we perform a study of model electron density profiles (EDPs) calculated using the Atmospheric Ultraviolet Radiance Integrated Code (AURIC; D. Strickland et al., 1999,https://doi.org/10.1016/s0022-4073(98)00098-3) in the E‐region of the terrestrial ionosphere. We compare AURIC model outputs using new high‐resolution photoionization and photoabsorption cross sections, and solar spectral irradiances during low solar activity with incoherent scatter radar (ISR) measurements from the Arecibo and Millstone Hills observatories, Constellation Observing System for Meteorology Ionosphere and Climate (COSMIC‐1) observations, and outputs from empirical models (IRI‐2016 and FIRI‐2018). AURIC results utilizing the new high‐resolution cross sections reveal a significant difference to model outputs calculated with the low‐resolution cross sections currently used. Analysis of AURIC EDPs using the new high‐resolution data indicate fair agreement with ISR measurements obtained at various times at Arecibo but very good agreement with Millstone Hills ISR observations from ∼96–140 km. However, discrepancies in the altitude of the E‐region peak persist. High‐resolution AURIC calculations are in agreement with COSMIC‐1 observations and IRI‐2016 model outputs between ∼105 and 140 km while FIRI‐2018 outputs underestimate the EDP in this region. Overall, AURIC modeling shows increased E‐region electron densities when utilizing high‐resolution cross sections and high‐resolution solar irradiances, and are likely to be the key to resolving the long standing data‐model discrepancies.

     
    more » « less
  4. Abstract

    This paper investigates the local and global ionospheric responses to the 2022 Tonga volcano eruption, using ground‐based Global Navigation Satellite System total electron content (TEC), Swarm in situ plasma density measurements, the Ionospheric Connection Explorer (ICON) Ion Velocity Meter (IVM) data, and ionosonde measurements. The main results are as follows: (a) A significant local ionospheric hole of more than 10 TECU depletion was observed near the epicenter ∼45 min after the eruption, comprising of several cascading TEC decreases and quasi‐periodic oscillations. Such a deep local plasma hole was also observed by space‐borne in situ measurements, with an estimated horizontal radius of 10–15° and persisted for more than 10 hr in ICON‐IVM ion density profiles until local sunrise. (b) Pronounced post‐volcanic evening equatorial plasma bubbles (EPBs) were continuously observed across the wide Asia‐Oceania area after the arrival of volcano‐induced waves; these caused aNedecrease of 2–3 orders of magnitude at Swarm/ICON altitude between 450 and 575 km, covered wide longitudinal ranges of more than 140°, and lasted around 12 hr. (c) Various acoustic‐gravity wave modes due to volcano eruption were observed by accurate Beidou geostationary orbit (GEO) TEC, and the huge ionospheric hole was mainly caused by intense shock‐acoustic impulses. TEC rate of change index revealed globally propagating ionospheric disturbances at a prevailing Lamb‐wave mode of ∼315 m/s; the large‐scale EPBs could be seeded by acoustic‐gravity resonance and coupling to less‐damped Lamb waves, under a favorable condition of volcano‐induced enhancement of dusktime plasma upward E×B drift and postsunset rise of the equatorial ionospheric F‐layer.

     
    more » « less
  5. Abstract

    Profiles of the electron number density in the ionosphere are observed at the Arecibo Radio Observatory in Puerto Rico on a regular basis. Here, we report on recent observations showing anomalous irregularities in the density profiles at altitudes >~300 km. The irregularities occurred during a period of “mid-latitude spreadF,” a space-weather phenomenon relatively common at middle latitudes in summer months characterized by instability and electron density irregularities in the bottomside of the ionosphericFlayer. Remarkably, electron density irregularities extended well above the layer, through the ionization peak and into the topside which is regarded as being stable. Neither the neutral atmosphere nor the ionosphere is thought to be able to support turbulence locally at this altitude. A numerical simulation is used to illustrate how a combination of atmospheric and plasma dynamics driven at lower altitudes could explain the phenomenon.

     
    more » « less