David R. Themens

David R. Themens
University of Birmingham · School of Electronic, Electrical and Computer Engineering

Ph.D. Physics

About

60
Publications
17,647
Reads
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568
Citations
Introduction
I currently work as a Lecturer in the School of Engineering at the University of Birmingham, Birmingham, UK. I am also an Adjunct at UNB. My research focuses on Space Plasma and Radio Physics of the ionosphere. I am currently working on the development of empirical and data assimilation models of the ionosphere for use at high latitudes: The Empirical Canadian High Arctic Ionospheric Model (E-CHAIM) and Assimilation CHAIM (A-CHAIM). I also do work examining ionosphere-atmosphere coupling.
Additional affiliations
January 2021 - present
University of New Brunswick
Position
  • Adjunct Professor
September 2020 - present
University of Birmingham
Position
  • Lecturer
March 2020 - October 2020
University of New Brunswick
Position
  • Research Scientist

Publications

Publications (60)
Article
Full-text available
While modern GPS receiver differential code bias estimation techniques have become highly refined, they still demonstrate unphysical behavior, namely notable solar cycle variability. This study investigates the nature of these seasonal and solar cycle bias variabilities in the polar cap region using single station bias estimation methods. It is sho...
Article
Full-text available
Monthly median values of ionospheric peak height (hmF2) and density (NmF2), derived from ionosonde measurements at four Canadian High Arctic Ionospheric Network (CHAIN) stations situated within the Polar Cap and Auroral Oval, are used to evaluate the performance of the IRI 2007 empirical ionospheric model during the recent solar minimum between 200...
Article
Full-text available
Total Electron Content (TEC) measurements from ten dual-frequency GPS receivers in the Canadian High Arctic Ionospheric Network (CHAIN) are used to evaluate the performance of IRI-2007 within the Canadian sector. Throughout the region, we see systematic underestimation of daytime TEC, particularly at solar maximum, where summer and equinox RMS erro...
Article
Full-text available
Global Positioning System (GPS) total electron content (TEC) measurements, although highly precise, are often rendered inaccurate due to satellite and receiver differential code biases (DCBs). Calculated satellite DCB values are now available from a variety of sources, but receiver DCBs generally remain an undertaking of receiver operators and proc...
Article
Full-text available
The ability of different ground-based measurement strategies for constraining thermodynamic variables in the troposphere, particularly at the mesoscale, is investigated. First, a preliminary assessment of the capability of pure-vertical sounders for constraining temperature and water vapor fields in clear-sky conditions to current accuracy requirem...
Article
Full-text available
Observations made using the LOw Frequency ARray (LOFAR) between 10:15 and 11:48 UT on the 15th of September 2018 over a bandwidth of approximately 25-65 MHz contain discrete pseudo-periodic features of ionospheric origin. These features occur with a period of approximately ten minutes and collectively last roughly an hour. They are strongly frequen...
Preprint
Full-text available
An examination of the performance of the near-real-time ionospheric assimilation A-CHAIM, using manually scaled ionosondes and in-situ electron density measurements from the DMSP and Swarm satellites.
Article
Full-text available
Plain Language Summary The Sporadic‐E layer (Es layer) is a globally common phenomenon, which is comprehensively and unceasingly studied in decades by using the observation measurements and numerical simulations. The remarkable agreements on the characteristics and generation mechanisms of Es layer at middle latitudes have then been almost achieved...
Preprint
During minor to moderate geomagnetic storms, caused by corotating interaction regions at the leading edge of high-speed streams, solar wind Alfvén waves modulated the magnetic reconnection at the dayside magnetopause. The Resolute Bay Incoherent Scatter Radars (RISR-C and RISR-N), measuring plasma parameters in the cusp and polar cap, observed iono...
Article
Full-text available
Plain Language Summary The 2022 Tonga oceanic volcanic eruption and resulting tsunami was an incredibly impulsive and high energy event. Such events can generate strong pressure waves in the atmosphere that can propagate up into the Earth's ionosphere and modulate the plasma therein. Using every available Global Navigation Satellite System (GNSS) r...
Article
Full-text available
Ionogram data from the Global Ionospheric Radio Observatory (GIRO), processed with Automatic Real-Time Ionogram Scaler With True Height (ARTIST), is provided with confidence scores to guide users on the reliability of the data set. Here we use manually processed data to assess the extent to which these confidence scores have value and to provide us...
Article
Full-text available
High Frequency (HF) radio propagation, and applications such as Over-The-Horizon Radar (OTHR), is sensitive to ionospheric disturbances caused by space weather. Improved ionospheric modelling and monitoring techniques for the high-latitude and polar regions supports high quality OTHR long-range surveillance. One such ionospheric disturbance is Spor...
Article
Full-text available
Over‐the‐horizon radar (OTHR) systems operating in the high‐frequency (HF) band (3–30 MHz) are unique in their ability to detect targets at extreme ranges, offering cost‐effective large‐area surveillance. Due to their reliance on the reflective nature of the ionosphere in this band, OTHR systems are extremely sensitive to ionospheric conditions and...
Article
Full-text available
Here, we assess to what extent the Empirical Canadian High Arctic Ionospheric Model (E‐CHAIM) can reproduce the climatological variations of vertical Total Electron Content (vTEC) in the Canadian sector. Within the auroral oval and polar cap, E‐CHAIM is found to exhibit Root Mean Square (RMS) errors in vTEC as low 0.4 TECU during solar minimum summ...
Article
Full-text available
The Empirical Canadian High Artic Ionospheric Model (E‐CHAIM) provides the four‐dimensional ionosphere electron density at northern high latitudes (>50° geomagnetic latitude). Despite its emergence as the most reliable model for high‐latitude ionosphere density, there remain significant deficiencies in E‐CHAIM's representation of the lower ionosphe...
Presentation
Full-text available
Presentation on "Improving the NeQuick topside model through COSMIC/FORMOSAT-3 Radio Occultation data" given at the URSI GASS 2021 in Rome.
Article
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A Global Positioning System (GPS) network in the polar cap, along with ionosonde and SuperDARN radar measurements, are used to study GPS signal amplitude and phase scintillation associated with a polar cap patch. The patch was formed due to a north-to-south transition of the interplanetary magnetic field (IMF Bz). The patch moved antisunward with a...
Article
Full-text available
The Sporadic-E (Es) layer is an often observed phenomenon at the high-latitude; however, our understanding of the polar cap Es layer is severely limited due to the scarce number of measure-ments. Here, the first comprehensive study of the polar cap Es layer associated with Global Posi-tioning System (GPS) Total Electron Content (TEC) variations and...
Article
Full-text available
The construction of the background covariance matrix is an important component of ionospheric data assimilation algorithms, such as Ionospheric Data Assimilation Four‐Dimensional (IDA4D). It is a matrix that describes the correlations between all the grid points in the model domain and determines the transition from the data‐driven to model‐driven...
Article
Full-text available
The ensemble Kalman filter is a widely used technique across the many radio science domain areas. Despite this, conventional descriptions of Kalman filters can, at times, be somewhat opaque and difficult to conceptualize, making them difficult to approach for many users. This article presents a visualization of the underlying mathematical equations...
Article
Full-text available
Measurements of the electron density at the F region peak by the Canadian Advanced Digital Ionosonde (CADI) and the Resolute Incoherent Scatter Radar (RISR) are used to assess the quality of peak electron density estimates made from elevation angle measurements by the Super Dual Auroral Radar Network (SuperDARN) high-frequency radar at Rankin Inlet...
Conference Paper
This study examines the role of traveling planetary waves in producing day-to-day variability of the ionosphere. Traveling planetary waves in the middle atmosphere, especially those having periods around 6, 10, 16 days, are generally regarded as the manifestation of atmospheric normal modes. A sudden stratospheric warming (SSW) is sometimes accompa...
Technical Report
Full-text available
Final Report for the ESA VERA project. Project details can be found here at: https://www.gfz-potsdam.de/en/section/geomagnetism/projects/vera-vertical-coupling-in-earths-atmosphere-at-mid-and-high-latitudes/
Article
Full-text available
Temporal and spatial changes of GPS total electron content (TEC) and phase variation, called phase scintillation, during auroral substorms and breakups are investigated in the context of horizontal equivalent ionospheric currents and estimated vertical current amplitudes derived from ground magnetometer network using the spherical elementary curren...
Article
The lack of reliable global E-region electron density or conductivity measurements has hampered a detailed and quantitative understanding of the E-region electrodynamic processes. The characterization of the global E-region ionospheric irregularities as a function of local time, longitude, and season remains a great challenge. In this study, we eva...
Article
Full-text available
The analytical description of the topside ionosphere included in the NeQuick model is studied in detail. First, the modeled scale height behavior is analyzed at infinity and for the lowest part of the topside region; in the latter case, the analysis is done through an expansion in Taylor series near the F2-layer peak. Moreover, the significant infl...
Article
Full-text available
The Empirical Canadian High Arctic Ionospheric Model (E‐CHAIM) is a new empirical 3‐D electron density model intended as an alternative to the use of conventional standards, such as the International Reference Ionosphere (IRI), at high latitudes (above 50°N). In this study, we have manually scaled a year of data from two Canadian High Arctic Ionosp...
Article
Full-text available
An exceptionally strong stationary planetary wave with Zonal Wavenumber 1 led to a sudden stratospheric warming (SSW) in the Southern Hemisphere in September 2019. Ionospheric data from ESA's Swarm satellite constellation mission show prominent 6‐day variations in the dayside low‐latitude region at this time, which can be attributed to forcing from...
Article
Full-text available
Plain Language Summary During the August 2017 “Great American Eclipse,” the Global Positioning System‐receiver‐based instrument on board the CASSIOPE (also known as Swarm‐E) satellite detected significant disturbances in the terrestrial ionosphere at multiple distributed locations above the United States. Previous research on solar eclipses has poi...
Article
Full-text available
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 botto...
Article
Full-text available
The Linear Vary-Chap function has received increased attention in describing the topside ionosphere due to its good performance for predicting and extrapolating radio-occultation (RO) electron density ionospheric profiles. The systematic increase in the scale height is consistent with first principles corresponding to the increase in the electron t...
Article
Full-text available
The Empirical Canadian High Arctic Ionospheric Model (E-CHAIM) is a new empirical model of high latitude ionospheric electron density. While the introductory studies regarding E-CHAIM include validations, E-CHAIM’s topside model was notably excluded from independent validation using datasets not included in the model fitting. In this study, we unde...
Article
Operation of over-the-horizon radars comprising the Super Dual Auroral Radar Network (SuperDARN) relies on strong ionospheric refraction of high-frequency (HF, f = 10–15 MHz) radiowaves such that in order to provide reliable coverage of a given geographic location, the working frequency has to be optimized with respect to the ionospheric conditions...
Article
Full-text available
In this study, we present a topside model representation to be used by the Empirical Canadian High Arctic Ionospheric Model (E-CHAIM). In the process of this, we also present a comprehensive evaluation of the NeQuick's, and by extension the International Reference Ionosphere (IRI)'s, topside electron density model for mid and high latitudes in the...
Article
Full-text available
This paper presents validation of ionospheric Global Positioning System (GPS) radio occultation (RO) measurements of the GPS Attitude, Positioning, and Profiling Experiment occultation receiver (GAP-O). GAP is one of eight instruments comprising the Enhanced Polar Outflow Probe (e-POP) instrument suite onboard the Cascade Smallsat and Ionospheric P...
Article
Full-text available
An examination of the high latitude performance of the bottomside and topside F-layer parameterizations of the NeQuick electron density model is presented using measurements from high latitude ionosonde and Incoherent Scatter Radar (ISR) facilities. For the bottomside, we present a comparison between modeled and measured B2Bot thickness parameter....
Article
Full-text available
We present here the Empirical Canadian High Arctic Ionospheric Model (E-CHAIM) quiet NmF2, perturbation NmF2, and quiet hmF2 models. These models provide peak ionospheric characteristics for a domain above 50°N geomagnetic latitude. Model fitting is undertaken using all available ionosonde and radio occultation electron density data, constituting a...
Article
Full-text available
Based on in situ and ground-based observations, a new type of “polar cap hot patch” has been identified that is different from the classical polar cap enhanced density structure (cold patches). Comparing with the classical polar cap patches, which are transported from the dayside sunlit region with dense and cold plasma, the polar cap hot patches a...
Article
Full-text available
A Neural Network (NN) model has been developed for the critical frequency of the F2 layer (foF2) at Resolute (74.70∘ N, 265.10∘ E) using data obtained from the Space Physics Interactive Data Resource, SPIDR (no longer available), for the period between 1975 - 1995. This model is a first step towards addressing the discrepancies of the International...
Article
Full-text available
The Global Positioning System (GPS) is a valuable tool in the measurement and monitoring of ionospheric total electron content (TEC). To obtain accurate GPS-derived TEC, satellite and receiver hardware biases, known as differential code biases (DCBs), must be estimated and removed. The Center for Orbit Determination in Europe (CODE) provides monthl...
Article
Full-text available
This article presents the results of an ion temperature climatology study that examined ionospheric measurements from the European Incoherent SCATter (EISCAT) Svalbard Radar (ESR: 78.2° N, 16.0° E) and the Poker Flat Incoherent Scatter Radar (PFISR: 65.1° N, 212.6° E) during the year-long campaign of the International Polar Year (IPY) from March 20...
Article
Full-text available
The Maximum Usable Frequency for a 3000 km range circuit (MUF(3000)F2), computed from ionosonde measurements at Resolute (74.75°N, 265.00°E) and Pond Inlet (72.69°N, 282.04°E), has been compared with values obtained from the Ionospheric Communications Enhanced Profile Analysis and Circuit (ICEPAC) prediction program, Voice of America Coverage Analy...
Conference Paper
The problem of receiver Differential Code Biases (DCBs) in the use of GPS measurements of ionospheric Total Electron Content (TEC) has been a constant concern amongst network operators and data users since the advent of the use of GPS measurements for ionospheric monitoring. While modern methods have become highly refined, they still demonstrate un...
Article
Joint observations of the Rankin Inlet (RKN) and Inuvik (INV) Super Dual Auroral Radra Network (SuperDARN) HF radars and Resolute Bay (RB) Canadian Advanced Digital Ionosonde (CADI) are used to assess the electron density at the F region peak and the electric field magnitude as factors affecting echo detection over RB. We demonstrate that the radar...
Article
F region echo occurrence rates for the Polar Dual Auroral Radar Network (PolarDARN) HF radars at Inuvik (INV), Rankin Inlet (RKN) and Clyde River (CLY) are compared for observations in 2013. The CLY radar shows somewhat smaller echo occurrence rates consistent with its more poleward geographic and geomagnetic location. For all three radars, the win...
Thesis
Full-text available
The initialization of water vapour and temperature fields has long been a concern in mesoscale weather forecasting, where small errors in these fields often produce significant errors in the model characterization of mesoscale processes, such as convective initiation. In order to address this issue, a scanning “Mesoscale” Microwave Radiometer has b...

Questions

Question (1)
Question
I have been developing models of the ionosphere for some time, but recently, I've been asked "What constitutes sufficiently accurate foF2?" The URSI standard for foF2 scaling from an ionogram is 5d, where d is the frequency resolution of the ionosonde in the vicinity of foF2. Others have mentioned accuracy standards ranging between 0.5 MHz and 1.0MHz. My question is, is there a consensus within the field on the generally required accuracy of foF2? If it is application-specific, what are the necessary accuracy levels for these various applications?
In any responses, please provide references to support your point of view.
I look forward to an interesting and productive discussion.

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