Assimilative real-time models of HF absorption at high latitudes

Improved real-time HF communications frequency management is required for aircraft on trans-polar routes. Polar cap absorption (PCA) models have therefore been adapted to assimilate real-time measurements of zenithal cosmic radio noise absorption (~ 30 MHz) from a large network of online riometers in Canada and Finland. Two types of PCA model have been developed and improvements to model accuracy following optimisation are quantified. Real-time optimisation is performed by age-weighting riometer measurements in a non-linear regression. This reduces root-mean-square errors (RMSE) from 2-3 dB to less than 1 dB and mean errors to within ±0.2 dB over a wide latitude range. This paper extends previous work by further optimising the models’ dependences on solar-zenith angle to account for differences in the ionospheric response at sunrise and sunset (the Twilight Anomaly). Two models of the rigidity cutoff latitudes are compared and one is optimised in real time by regression to riometer measurements. Whilst measurements from the NASA POES satellites may provide a direct measurement of the rigidity cut-off, it is observed that proton flux measurements from POES often need correcting for relativistic electron contamination for several hours at the start of a PCA event. An optimised real-time absorption model will be integrated into HF ray-tracing propagation predictions relating to measurements of HF signal strengths on a network of HF transmitters and receivers in the high northern latitudes

Developments in an HF Nowcasting Model for Trans-Polar Airline Routes

HF communications can be difficult in the polar regions since they are strongly influenced by space weather events. Airline communications within the polar regions rely on HF communications and improved nowcasting and forecasting techniques in support of this are now required. Previous work has demonstrated that ray tracing through a realistic, historical ionosphere provides signal coverage in good agreement with measurements. This paper presents an approach to providing a real-time ionospheric model by assimilating TEC measurements and validates it against observations from ionosondes

Developments in HF Propagation Predictions to Support Communications with Aircraft on Trans-polar Routes

Commercial airlines began operations over polar routes in 1999 with a small number of proving flights. By 2014 the number had increased to in excess of 12,000 flights per year, and further increases are expected. For safe operations, the aircraft have to be able to communicate with air traffic control centres at all times. This is achieved by VHF links whilst within range of the widespread network of ground stations, and by HF radio in remote areas such as the Polar regions, the North Atlantic and Pacific where VHF ground infrastructure does not exist. Furthermore, the Russian side of the pole only has HF capability. This has created a demand for improved HF nowcasting and forecasting procedures to support the polar operations, which are the subject of this paper

Progress towards a propagation prediction service for HF communications with aircraft on trans-polar routes

Commercial airlines began operations over polar routes in 1999 with a small number of proving flights. By 2014 the number had increased to in excess of 12,000 flights per year, and further increases are expected. For safe operations, the aircraft have to be able to communicate with air traffic control centres at all times. This is achieved by VHF links whilst within range of the widespread network of ground stations, and is by HF radio in remote areas such as the Polar regions, the North Atlantic and Pacific where VHF ground infrastructure does not exist. Furthermore, the Russian side of the pole only has HF capability. Researchers at the University of Leicester and at Lancaster University have developed various models (outlined below) that can be employed in HF radio propagation predictions. It is anticipated that these models will form the basis of an HF forecasting and nowcasting service for the airline industry. Propagation coverage predictions make use of numerical ray tracing to estimate the ray paths through a model ionosphere. Initially, a background ionospheric model is produced, which is then perturbed to include the various ionospheric features prevalent at high latitudes (in particular patches, arcs, auroral zone irregularities and the mid-latitude trough) that significantly affect the propagation of the radio signals. The approach that we are currently adopting is to start with the IRI and to perturb this based on measurements made near to the time and area of interest to form the basis of the background ionospheric model. This is then further perturbed to include features such as the convecting patches, the parameters of which may also be informed by measurements. A significant problem is the high variability of the high latitude ionosphere, and the relative scarcity of real-time measurements over the region. Real time measurements that we will use as the basis for perturbing the IRI include ionosonde soundings from, e.g. the GIRO database, and TEC measurements from the IGS network. Real-time modelling of HF radiowave absorption in the D-region ionosphere is also included. The geostationary GOES satellites provide real-time information on X-ray flux (causing shortwave fadeout during solar flares) and the flux of precipitating energetic protons which correlates strongly with Polar Cap Absorption (PCA). Real-time solar wind and interplanetary magnetic field measurements from the ACE or DSCOVR spacecraft provide geomagnetic index estimates used to model the location of both auroral absorption (on a probabilistic basis) and the proton rigidity cutoff boundary that defines the latitudinal extent of PCA during solar proton events (SPE). Empirical climatological models have been uniquely adapted to assimilate recent measurements of cosmic noise absorption (at 30 MHz) from a large array of riometers in Canada and Scandinavia. The model parameters are continuously optimised and updated to account for regional and temporal variations in ionospheric composition (and hence HF absorption rate (dB/km)) that can change significantly during the course of an SPE, for example. Real-time optimisation during SPE can also improve estimates of the proton rigidity cutoff and improve the modelled ionospheric response function absorption vs. zenith angle) at twilight

Beyond local Nash equilibria for adversarial networks

Save for some special cases, current training methods for Generative Adversarial Networks (GANs) are at best guaranteed to converge to a ‘local Nash equilibrium’ (LNE). Such LNEs, however, can be arbitrarily far from an actual Nash equilibrium (NE), which implies that there are no guarantees on the quality of the found generator or classifier. This paper proposes to model GANs explicitly as finite games in mixed strategies, thereby ensuring that every LNE is an NE. We use the Parallel Nash Memory as a solution method, which is proven to monotonically converge to a resource-bounded Nash equilibrium. We empirically demonstrate that our method is less prone to typical GAN problems such as mode collapse and produces solutions that are less exploitable than those produced by GANs and MGANs

GPS phase scintillation and proxy index at high latitudes during a moderate geomagnetic storm

The amplitude and phase scintillation indices are customarily obtained by specialised GPS Ionospheric Scintillation and TEC Monitors (GISTMs) from L1 signal recorded at the rate of 50 Hz. The scintillation indices S[subscript 4] and σ[subscript Φ] are stored in real time from an array of high-rate scintillation receivers of the Canadian High Arctic Ionospheric Network (CHAIN). Ionospheric phase scintillation was observed at high latitudes during a moderate geomagnetic storm (Dst = −61 nT) that was caused by a moderate solar wind plasma stream compounded with the impact of two coronal mass ejections. The most intense phase scintillation (σ[subscript Φ] ~ 1 rad) occurred in the cusp and the polar cap where it was co-located with a strong ionospheric convection, an extended tongue of ionisation and dense polar cap patches that were observed with ionosondes and HF radars. At sub-auroral latitudes, a sub-auroral polarisation stream that was observed by mid-latitude radars was associated with weak scintillation (defined arbitrarily as σ[subscript Φ] 0.1 rad and DPR > 2 mm s[superscript −1], both mapped as a function of magnetic latitude and magnetic local time, are very similar.National Science Foundation (U.S.) (Grant ATM-0856093

High-Latitude GPS TEC Changes Associated With a Sudden Magnetospheric Compression

第2回極域科学シンポジウム/第35回極域宙空圏シンポジウム 11月15日（火） 国立極地研究所 2階大会議