https://vital.seals.ac.za/vital/access/manager/Index ${session.getAttribute("locale")} 5 Influence of argon ion implantation on the thermoluminescence properties of aluminium oxide https://vital.seals.ac.za/vital/access/manager/Repository/vital:50173 Wed 20 Jul 2022 09:15:38 SAST ]]> Combined spectral and stimulated luminescence study of charge trapping and recombination processes in α-Al2O3:C https://vital.seals.ac.za/vital/access/manager/Repository/vital:28235 Wed 15 Sep 2021 14:30:53 SAST ]]> Classical and quantum picture of the interior of two-dimensional black holes https://vital.seals.ac.za/vital/access/manager/Repository/vital:20531 Wed 12 May 2021 23:48:00 SAST ]]> Finite precision arithmetic in Polyphase Filterbank implementations https://vital.seals.ac.za/vital/access/manager/Repository/vital:38503 Wed 12 May 2021 23:20:29 SAST ]]> Thermoluminescence of secondary glow peaks in carbon-doped aluminium oxide https://vital.seals.ac.za/vital/access/manager/Repository/vital:5537 Wed 12 May 2021 22:37:25 SAST ]]> Comparison of A₄ neutrino mass models https://vital.seals.ac.za/vital/access/manager/Repository/vital:5554 Wed 12 May 2021 22:30:24 SAST ]]> Analysing emergent time within an isolated Universe through the application of interactions in the conditional probability approach https://vital.seals.ac.za/vital/access/manager/Repository/vital:38547 Wed 12 May 2021 20:57:26 SAST ]]> An analysis of ionospheric response to geomagnetic disturbances over South Africa and Antarctica https://vital.seals.ac.za/vital/access/manager/Repository/vital:5534 Wed 12 May 2021 20:15:43 SAST ]]> Nonlinear optical responses of phthalocyanines in the presence of nanomaterials or when embedded in polymeric materials https://vital.seals.ac.za/vital/access/manager/Repository/vital:25548 Wed 12 May 2021 20:07:23 SAST ]]> Observations of diffuse radio emission in the Perseus Galaxy Cluster https://vital.seals.ac.za/vital/access/manager/Repository/vital:38233 Wed 12 May 2021 19:59:26 SAST ]]> Thermoluminescence of annealed synthetic quartz https://vital.seals.ac.za/vital/access/manager/Repository/vital:19957 Wed 12 May 2021 19:55:06 SAST ]]> Assignment of spin and parity to states in the nucleus ¹⁹⁶T1 https://vital.seals.ac.za/vital/access/manager/Repository/vital:5558 Wed 12 May 2021 19:49:57 SAST ]]> Tomographic imaging of East African equatorial ionosphere and study of equatorial plasma bubbles https://vital.seals.ac.za/vital/access/manager/Repository/vital:28516 Wed 12 May 2021 19:46:51 SAST ]]> Modelling storm-time TEC changes using linear and non-linear techniques https://vital.seals.ac.za/vital/access/manager/Repository/vital:30762 4. The performance evaluation of MIDAS compared with ANNs to reconstruct storm-time TEC over the African low- and mid-latitude regions showed that MIDAS and ANNs provide comparable results. Their respective mean absolute error (MAE) values were 4.81 and 4.18 TECU. The ANN model was, however, found to perform 24.37 % better than MIDAS at estimating storm-time TEC for low latitudes, while MIDAS is 13.44 % more accurate than ANN for the mid-latitudes. When their performances are compared with the IRI model, both MIDAS and ANN model were found to provide more accurate storm-time TEC reconstructions for the African low- and mid-latitude regions. A comparative study of the performances of EOF, NLRA, ANN, and IRI models to estimate TEC during geomagnetic storm conditions over various latitudes showed that the ANN model is about 10 %, 26 %, and 58 % more accurate than EOF, NLRA, and IRI models, respectively, while EOF was found to perform 15 %, and 44 % better than NLRA and IRI, respectively. It was further found that the NLRA model is 25 % more accurate than the IRI model. We have also investigated for the first time, the role of meridional neutral winds (from the Horizontal Wind Model) to storm-time TEC modelling in the low latitude, northern and southern hemisphere mid-latitude regions of the African sector, based on ANN models. Statistics have shown that the inclusion of the meridional wind velocity in TEC modelling during geomagnetic storms leads to percentage improvements of about 5 % for the low latitude, 10 % and 5 % for the northern and southern hemisphere mid-latitude regions, respectively. High-latitude storm-induced winds and the inter-hemispheric blows of the meridional winds from summer to winter hemisphere have been suggested to be associated with these improvements.]]> Wed 12 May 2021 19:12:42 SAST ]]> Developing an ionospheric map for South Africa https://vital.seals.ac.za/vital/access/manager/Repository/vital:5459 Wed 12 May 2021 19:06:06 SAST ]]> Thermoluminescence of synthetic quartz annealed beyond its second phase inversion temperature https://vital.seals.ac.za/vital/access/manager/Repository/vital:25577 Wed 12 May 2021 18:51:02 SAST ]]> A feasibility study into the possibility of ionospheric propagation of low VHF (30-35 MHZ) signals between South Africa and Central Africa https://vital.seals.ac.za/vital/access/manager/Repository/vital:5465 Wed 12 May 2021 18:48:02 SAST ]]> A study of why some physic concepts in the South African Physical Science curriculum are poorly understood in order to develop a targeted action-research intervention for Newton’s second law https://vital.seals.ac.za/vital/access/manager/Repository/vital:38575 Wed 12 May 2021 18:39:05 SAST ]]> Challenges in topside ionospheric modelling over South Africa https://vital.seals.ac.za/vital/access/manager/Repository/vital:5453 Wed 12 May 2021 18:37:56 SAST ]]> Thermoluminescence characteristics of synthetic quartz https://vital.seals.ac.za/vital/access/manager/Repository/vital:5538 Wed 12 May 2021 18:18:39 SAST ]]> Statistical study of traveling ionospheric disturbances over South Africa https://vital.seals.ac.za/vital/access/manager/Repository/vital:30556 Wed 12 May 2021 17:50:57 SAST ]]> The variability and predictability of the IRI shape parameters over Grahamstown, South Africa https://vital.seals.ac.za/vital/access/manager/Repository/vital:5496 Wed 12 May 2021 17:49:23 SAST ]]> Statistical analysis of the ionospheric response during storm conditions over South Africa using ionosonde and GPS data https://vital.seals.ac.za/vital/access/manager/Repository/vital:5555 Wed 12 May 2021 17:41:38 SAST ]]> Addressing flux suppression, radio frequency interference, and selection of optimal solution intervals during radio interferometric calibration https://vital.seals.ac.za/vital/access/manager/Repository/vital:38663 Wed 12 May 2021 17:37:38 SAST ]]> Ionospheric disturbances during magnetic storms at SANAE https://vital.seals.ac.za/vital/access/manager/Repository/vital:26639 Wed 12 May 2021 17:31:19 SAST ]]> Temperature dependence of the HartRAO pointing model https://vital.seals.ac.za/vital/access/manager/Repository/vital:5491 Wed 12 May 2021 17:23:16 SAST ]]> Verification of Ionospheric tomography using MIDAS over Grahamstown, South Africa https://vital.seals.ac.za/vital/access/manager/Repository/vital:5497 Wed 12 May 2021 17:18:51 SAST ]]> A comparative polarimetric study of the 43 GHz and 86 GHz SiO masers toward the supergiant star VY CMa https://vital.seals.ac.za/vital/access/manager/Repository/vital:5454 Wed 12 May 2021 17:16:47 SAST ]]> Development of an ionospheric map for Africa https://vital.seals.ac.za/vital/access/manager/Repository/vital:5519 Wed 12 May 2021 17:12:10 SAST ]]> Reconstructing ionospheric TEC over South Africa using signals from a regional GPS network https://vital.seals.ac.za/vital/access/manager/Repository/vital:5487 Wed 12 May 2021 16:48:40 SAST ]]> Calibration and wide field imaging with PAPER: a catalogue of compact sources https://vital.seals.ac.za/vital/access/manager/Repository/vital:20285 Wed 12 May 2021 16:46:56 SAST ]]> Updating the ionospheric propagation factor, M(3000)F2, global model using the neural network technique and relevant geophysical input parameters https://vital.seals.ac.za/vital/access/manager/Repository/vital:5434 Wed 12 May 2021 16:43:54 SAST ]]> Mechanisms of luminescence in α-Al₂O₃:C : investigations using time-resolved optical stimulation and thermoluminescence techniques https://vital.seals.ac.za/vital/access/manager/Repository/vital:5447 Wed 12 May 2021 16:26:41 SAST ]]> An analysis of sources and predictability of geomagnetic storms https://vital.seals.ac.za/vital/access/manager/Repository/vital:5451 Wed 12 May 2021 16:24:52 SAST ]]> A real time HF beacon monitoring station for South Africa https://vital.seals.ac.za/vital/access/manager/Repository/vital:5486 Wed 12 May 2021 16:17:43 SAST ]]> A feasibility study into total electron content prediction using neural networks https://vital.seals.ac.za/vital/access/manager/Repository/vital:5466 Wed 12 May 2021 16:16:20 SAST ]]> PyMORESANE: A Pythonic and CUDA-accelerated implementation of the MORESANE deconvolution algorithm https://vital.seals.ac.za/vital/access/manager/Repository/vital:5563 Wed 12 May 2021 16:14:42 SAST ]]> The dispersion measure in broadband data from radio pulsars https://vital.seals.ac.za/vital/access/manager/Repository/vital:29157 Wed 12 May 2021 16:10:48 SAST ]]> Automation of source-artefact classification https://vital.seals.ac.za/vital/access/manager/Repository/vital:20743 Wed 12 May 2021 16:10:45 SAST ]]> Using co-located radars and instruments to analyse ionespheric events over South Africa https://vital.seals.ac.za/vital/access/manager/Repository/vital:5493 Wed 12 May 2021 15:59:02 SAST ]]> Statistical Analysis of the Radio-Interferometric Measurement Equation, a derived adaptive weighting scheme, and applications to LOFAR-VLBI observation of the Extended Groth Strip https://vital.seals.ac.za/vital/access/manager/Repository/vital:30942 Wed 12 May 2021 15:54:37 SAST ]]> Parametrised gains for direction-dependent calibration https://vital.seals.ac.za/vital/access/manager/Repository/vital:42196 Wed 12 May 2021 14:25:43 SAST ]]> Observations of cosmic re-ionisation with the Hydrogen Epoch of Reionization Array: simulations of closure phase spectra https://vital.seals.ac.za/vital/access/manager/Repository/vital:42480 0:5 h Mpc-1. We also found that the foreground leakage is worse when edge antennas are included, as they have a more different primary beam compared to antennas at the centre of the array. The leakage magnitude is worse when bright foregrounds appear in the antenna sidelobes, as expected. Our simulations provide a useful framework to interpret observations and assess which power spectrum region is expected to be most contaminated by foreground power leakage.]]> Wed 12 May 2021 14:24:29 SAST ]]> Design patterns and software techniques for large-scale, open and reproducible data reduction https://vital.seals.ac.za/vital/access/manager/Repository/vital:42172 Wed 12 May 2021 13:59:27 SAST ]]> Third generation calibrations for Meerkat Observation of Saraswati Supercluster https://vital.seals.ac.za/vital/access/manager/Repository/vital:65374 Wed 10 Jan 2024 11:01:27 SAST ]]> Predictability of Geomagnetically Induced Currents using neural networks https://vital.seals.ac.za/vital/access/manager/Repository/vital:5483 Thu 26 Aug 2021 14:37:41 SAST ]]> On the gravitational dual to strongly coupled fluids https://vital.seals.ac.za/vital/access/manager/Repository/vital:45280 Thu 23 Jun 2022 12:03:49 SAST ]]> The EPR paradox: back from the future https://vital.seals.ac.za/vital/access/manager/Repository/vital:20338 Thu 23 Jun 2022 11:24:04 SAST ]]> Dynamics of stimulated luminescence in natural quartz: Thermoluminescence and phototransferred thermoluminescence https://vital.seals.ac.za/vital/access/manager/Repository/vital:38509 Thu 13 May 2021 15:55:13 SAST ]]> CubiCal: a fast radio interferometric calibration suite exploiting complex optimisation https://vital.seals.ac.za/vital/access/manager/Repository/vital:30711 Thu 13 May 2021 15:04:39 SAST ]]> Development of a neural network based model for predicting the occurrence of spread F within the Brazilian sector https://vital.seals.ac.za/vital/access/manager/Repository/vital:5460 Thu 13 May 2021 09:13:17 SAST ]]> Structure of the nucleus ¹¹⁴Sn using gamma-ray coincidence data https://vital.seals.ac.za/vital/access/manager/Repository/vital:5562 Thu 13 May 2021 08:52:22 SAST ]]> Investigation into the extended capabilities of the new DPS-4D ionosonde https://vital.seals.ac.za/vital/access/manager/Repository/vital:5472 Thu 13 May 2021 08:08:05 SAST ]]> Measuring the RFI environment of the South African SKA site https://vital.seals.ac.za/vital/access/manager/Repository/vital:5474 Thu 13 May 2021 07:16:45 SAST ]]> Designing and implementing a new pulsar timer for the Hartebeesthoek Radio Astronomy Observatory https://vital.seals.ac.za/vital/access/manager/Repository/vital:5458 Thu 13 May 2021 07:10:11 SAST ]]> Long-term analysis of ionospheric response during geomagnetic storms in mid, low and equatorial latitudes https://vital.seals.ac.za/vital/access/manager/Repository/vital:28517 Thu 13 May 2021 07:06:25 SAST ]]> A VLBI study of OH masers in a proto-planetary nebula OH 0.9+1.3 https://vital.seals.ac.za/vital/access/manager/Repository/vital:5499 Thu 13 May 2021 06:26:01 SAST ]]> Multi-instrument observations of ionospheric irregularities over South Africa https://vital.seals.ac.za/vital/access/manager/Repository/vital:5476 Thu 13 May 2021 06:18:50 SAST ]]> Real-time audio spectrum analyser research, design, development and implementation using the 32 bit ARMR Cortex-M4 microcontroller https://vital.seals.ac.za/vital/access/manager/Repository/vital:25997 Thu 13 May 2021 06:12:17 SAST ]]> TiRiFiG, a graphical 3D kinematic modelling tool https://vital.seals.ac.za/vital/access/manager/Repository/vital:30558 Thu 13 May 2021 06:10:31 SAST ]]> Link between ghost artefacts, source suppression and incomplete calibration sky models https://vital.seals.ac.za/vital/access/manager/Repository/vital:5556 Thu 13 May 2021 06:07:57 SAST ]]> A Bayesian approach to tilted-ring modelling of galaxies https://vital.seals.ac.za/vital/access/manager/Repository/vital:38466 Thu 13 May 2021 05:58:42 SAST ]]> Solar cycle effects on GNSS-derived ionospheric total electron content observed over Southern Africa https://vital.seals.ac.za/vital/access/manager/Repository/vital:5489 Thu 13 May 2021 05:54:01 SAST ]]> Observing cosmic reionization with PAPER: polarized foreground simulations and all sky images https://vital.seals.ac.za/vital/access/manager/Repository/vital:29218 0.3 h Mpc -¹ We also analyzed data from the last observing season of PAPER via all-sky imaging with a view to characterize the foregrounds. We generated an all-sky catalogue of 88 sources down to a flux density of 5 Jy. Moreover, we measured both polarized point source and the Galactic diffuse emission, and used these measurements to constrain our model of polarization leakage. We find the leakage due to a population of point sources to be 12% lower than the prediction from our polarized model.]]> Thu 13 May 2021 05:43:39 SAST ]]> Observations of diffuse radio emission in the Abell 773 galaxy cluster https://vital.seals.ac.za/vital/access/manager/Repository/vital:38394 Thu 13 May 2021 05:41:52 SAST ]]> MEQSILHOUETTE: a mm-VLBI observation and signal corruption simulator https://vital.seals.ac.za/vital/access/manager/Repository/vital:25019 Thu 13 May 2021 05:32:08 SAST ]]> Modelling and investigating primary beam effects of reflector antenna arrays https://vital.seals.ac.za/vital/access/manager/Repository/vital:38635 Thu 13 May 2021 05:23:36 SAST ]]> Thermoluminescence of natural quartz https://vital.seals.ac.za/vital/access/manager/Repository/vital:5543 Thu 13 May 2021 05:21:09 SAST ]]> The SKA's the limit : on the nature of faint radio sources https://vital.seals.ac.za/vital/access/manager/Repository/vital:5504 Thu 13 May 2021 05:20:46 SAST ]]> Optimizing MIDAS III over South Africa https://vital.seals.ac.za/vital/access/manager/Repository/vital:5517 Thu 13 May 2021 05:10:35 SAST ]]> A pilot wide-field VLBI survey of the GOODS-North field https://vital.seals.ac.za/vital/access/manager/Repository/vital:30027 5x105 K and >6x1021 W Hz-1 respectively. This work demonstrates that automated post-processing pipelines for wide-field, uniform sensitivity VLBI surveys are feasible and indeed made more efficient with new software, wide-field imaging algorithms and more purpose-built source- finders. This broadens the discovery space for future wide-field surveys with upcoming arrays such as the African VLBI Network (AVN), MeerKAT and the Square Kilometre Array (SKA).]]> Thu 13 May 2021 05:08:27 SAST ]]> Empirical modelling of the solar wind influence on Pc3 pulsation activity https://vital.seals.ac.za/vital/access/manager/Repository/vital:5464 Thu 13 May 2021 05:04:36 SAST ]]> Properties of traveling ionospheric disturbances (TIDs) over the Western Cape, South Africa https://vital.seals.ac.za/vital/access/manager/Repository/vital:5557 Thu 13 May 2021 04:57:39 SAST ]]> Machine learning methods for calibrating radio interferometric data https://vital.seals.ac.za/vital/access/manager/Repository/vital:31398 Thu 13 May 2021 04:55:12 SAST ]]> Calibration and imaging with variable radio sources https://vital.seals.ac.za/vital/access/manager/Repository/vital:24721 Thu 13 May 2021 04:51:42 SAST ]]> A 150 MHz all sky survey with the Precision Array to Probe the Epoch of Reionization https://vital.seals.ac.za/vital/access/manager/Repository/vital:34556 Thu 13 May 2021 04:40:36 SAST ]]> Thermoluminescence and phototransferred phermoluminescence of synthetic quartz https://vital.seals.ac.za/vital/access/manager/Repository/vital:38472 Thu 13 May 2021 03:05:20 SAST ]]> Modelling Ionospheric vertical drifts over the African low latitude region https://vital.seals.ac.za/vital/access/manager/Repository/vital:28396 Thu 13 May 2021 02:06:20 SAST ]]> Foreground simulations for observations of the global 21-cm signal https://vital.seals.ac.za/vital/access/manager/Repository/vital:30557 Thu 13 May 2021 01:46:55 SAST ]]> Beta decay of 100/400 Zr produced in neutron-induced fission of natural uranium https://vital.seals.ac.za/vital/access/manager/Repository/vital:20353 Thu 13 May 2021 01:43:27 SAST ]]> A light-emitting-diode pulsing system for measurement of time-resolved luminescence https://vital.seals.ac.za/vital/access/manager/Repository/vital:20976 Thu 13 May 2021 01:37:18 SAST ]]> Geomagnetically induced current characteristics in southern Africa https://vital.seals.ac.za/vital/access/manager/Repository/vital:5469 Thu 13 May 2021 01:31:54 SAST ]]> Advanced radio interferometric simulation and data reduction techniques https://vital.seals.ac.za/vital/access/manager/Repository/vital:26875 Thu 13 May 2021 01:03:59 SAST ]]> A contribution to TEC modelling over Southern Africa using GPS data https://vital.seals.ac.za/vital/access/manager/Repository/vital:5456 Thu 13 May 2021 00:26:54 SAST ]]> Forecasting solar cycle 24 using neural networks https://vital.seals.ac.za/vital/access/manager/Repository/vital:5468 Thu 13 May 2021 00:24:49 SAST ]]> Variability analysis of a sample of potential southern calibration sources https://vital.seals.ac.za/vital/access/manager/Repository/vital:5495 Thu 13 May 2021 00:13:28 SAST ]]> Single station TEC modelling during storm conditions https://vital.seals.ac.za/vital/access/manager/Repository/vital:20545 Thu 13 May 2021 00:00:25 SAST ]]> Accelerated implementations of the RIME for DDE calibration and source modelling https://vital.seals.ac.za/vital/access/manager/Repository/vital:42199 Thu 13 Jul 2023 12:40:08 SAST ]]> Semantic segmentation of astronomical radio images: a computer vision approach https://vital.seals.ac.za/vital/access/manager/Repository/vital:71937 Thu 04 Apr 2024 19:33:11 SAST ]]> MeerKAT observations of three high-redshift galaxy clusters https://vital.seals.ac.za/vital/access/manager/Repository/vital:71936 6×1014 M⊙ at intermediate redshifts (0.3 < z < 0.4), providing support to their connection between mergers, which provide the necessary energy to re-accelerate particles via turbulence. Probing the redshift evolution of radio halos is an important test of the turbulent re-acceleration scenario, as fewer halos are expected at high redshift, given the same mass interval. In this thesis, we present MeerKAT observations at 1.28 GHz of three high-redshift (PSZ2G254.08- 58.45, PSZ2G255.60-46.18 and PSZ2G277.76-51.74, in the 0.42 ≲ z ≲ 0.46 range) clusters, with masses M500 ≳ 6.2 × 1014 M⊙, selected for their disturbed dynamical state – inferred from existing X-ray observations. Our observations reached rms noise values between 20 and 23.5 μJy beam−1, with ∼ 4′′ angular resolution. No evidence of diffuse emission is found at ii full resolution. Low-resolution (∼ 30′′) images achieved rms noise levels of 30-50 μJy beam−1, amongst the deepest observations of high-redshift targets. One radio halo was detected in the least massive cluster PSZ2G254.08-58.45 extending over ∼ 500 kpc, with a 1.20 } 0.08 mJy integrated flux density. We placed a ∼1 mJy upper limit at 95% confidence level on the radio halo flux density for the other two targets. The radio-halo detection is consistent with the recent P1.4 GHz − M500 correlation from Cuciti et al. (2021b), while the upper limit on PSZ2G255.60-46.18 is consistent with being on the correlation. On the other hand, the upper limit on PSZ2G277.76-51.74 places the radio halo well below the correlation. Recently a 1.5 GHz survey (Giovannini et al., 2020) detected a slightly higher fraction of radio halos in clusters in the same redshift range, with power and size typically higher than what we found in our observations. Both observations are, however, not inconsistent with each other. Our results, although with limited statistics, do not disfavour the current scenario of radiohalo formation based on the turbulent re-acceleration model.]]> Thu 04 Apr 2024 19:25:15 SAST ]]> M3: Mining Mini-Halos with MeerKAT https://vital.seals.ac.za/vital/access/manager/Repository/vital:72181 Sun 21 Apr 2024 13:42:47 SAST ]]> An investigation of traveling ionospheric disturbances (TIDs) in the SANAE HF radar data https://vital.seals.ac.za/vital/access/manager/Repository/vital:49986 Sun 09 Oct 2022 17:48:47 SAST ]]> A statistical study of travelling ionospheric disturbances over the African-European and American sectors https://vital.seals.ac.za/vital/access/manager/Repository/vital:71956 4 and Dst_ -50 nT was used as a criterion for geomagnetic disturbed conditions, while the four geomagnetically quiet days were selected each month based on Kp < 3. Observations of TIDs are made using Global Navigational Satellite Systems (GNSS) total electron content derived data. During quiet conditions, seven and two transhemispheric TIDs were identified over the African-European and American sectors, respectively. The observed TIDs originated from the wintertime hemisphere and propagated into the summertime hemisphere. The horizontal velocity, periods, and horizontal wavelengths of TIDs are in range of cH = 120-274 m/s, 48-80 min and _H = 379-1104 km, respectively. These quiet-time equatorward TIDs have been associated with tertiary gravity waves (GWs) from the dissipation of secondary GWs which are in turn generated from the dissipation of mountain waves (MWs) as a result of excited orographic forcing. The poleward TIDs during geomagnetically quiet conditions over the African and American sectors occur mainly during local daytime. Poleward TIDs were observed mostly in the African-European sector than the American sector. Their horizontal propagation velocities and periods range between 129-280 m/s and 39-70 min over African-European and American sectors. Although the mechanisms responsible for launching quiet-time poleward TIDs have not been established in this study, lower atmospheric processes such as convection systems, sudden stratospheric warming and cold weather fronts may have a role in their generation. During geomagnetic storms in the African sector, almost all poleward TIDs (with the exception of two cases) during the main phase were large-scale with horizontal velocities and periods ranging from 250-503 m/s and 30 min to 2 hours. During recovery phase, poleward TIDs fall under the category of medium scale. In the American sector, the majority of poleward TIDs occurred during the storm's main phase, as opposed to the African-European sector, which experienced a significant number of poleward TIDs during the recovery phase. The periods and horizontal velocities of TIDs range from 45 min-1.5 h and 180-296 m/s during main phase. During the recovery phase, the horizontal velocity and period range from 177-271 m/s and 40-1.5 h, respectively. Overall, it has been shown that statistically, changes in equatorial electrodynamics related to enhanced eastward electric _eld and hence increased equatorial electrojet (vertical E_B drift) correlates highly with the reported poleward TIDs.]]> Sat 06 Apr 2024 13:06:52 SAST ]]> The development of an ionospheric storm-time index for the South African region https://vital.seals.ac.za/vital/access/manager/Repository/vital:42937 4. The modeling methods used in the study were artificial neural network (ANN), linear regression (LR) and polynomial functions. The approach taken was to first test the modeling techniques on a single station before expanding the study to cover the regional aspect. The single station modeling was developed based on ionosonde data over Grahamstown. The inputs for the model which related to seasonal variation, diurnal variation, geomagnetic activity and solar activity were considered. For the geomagnetic activity, three indices namely; the symmetric disturbance in the horizontal component of the Earth’s magnetic field (SYM − H), the Auroral Electrojet (AE) index and local geomagnetic index A, were included as inputs. The performance of a single station model revealed that, of the three geomagnetic indices, SYM − H index has the largest contribution of 41% and 54% based on ANN and LR techniques respectively. The average correlation coefficients (R) for both ANN and LR models was 0.8, when validated during the selected storms falling within the period of model development. When validated using storms that fall outside the period of model development, the model gave R values of 0.6 and 0.5 for ANN and LR respectively. In addition, the GPS total electron content (TEC) derived measurements were used to estimate foF2 data. This is because there are more GPS receivers than ionosonde locations and the utilisation of this data increases the spatial coverage of the regional model. The estimation of foF2 from GPS TEC was done at GPS-ionosonde co-locations using polynomial functions. The average R values of 0.69 and 0.65 were obtained between actual and derived _foF2 over the co-locations and other GPS stations respectively. Validation of GPS TEC derived foF2 with RO data over regions out of ionospheric pierce points coverage with respect to ionosonde locations gave R greater than 0.9 for the selected storm period of 4-8 August 2011. The regional storm-time model was then developed based on the ANN technique using the four South African ionosonde stations. The maximum and minimum R values of 0.6 and 0.5 were obtained over ionosonde and GPS locations respectively. This model forms the basis towards the regional ionospheric storm-time index.]]> Mon 31 May 2021 15:12:57 SAST ]]> Dynamics of charge movement in ∞-Al2O3:C,Mg using thermoluminescence phototransferred and optically stimulated luminescence https://vital.seals.ac.za/vital/access/manager/Repository/vital:57237 Mon 24 Oct 2022 14:52:01 SAST ]]> Night-time gravity waves detected with multi-frequency airglow imager https://vital.seals.ac.za/vital/access/manager/Repository/vital:42931 Mon 17 May 2021 13:00:31 SAST ]]> Neutral Atomic Hydrogen in Gravitationally Lensed Systems https://vital.seals.ac.za/vital/access/manager/Repository/vital:45263 Mon 15 Nov 2021 14:52:54 SAST ]]> Neutral winds and tides over South Africa https://vital.seals.ac.za/vital/access/manager/Repository/vital:49993 Mon 10 Oct 2022 08:47:40 SAST ]]> Behaviour of quiet time ionospheric disturbances at African equatorial and midlatitude regions https://vital.seals.ac.za/vital/access/manager/Repository/vital:28228 Fri 17 Sep 2021 14:51:46 SAST ]]> Data compression, field of interest shaping and fast algorithms for direction-dependent deconvolution in radio interferometry https://vital.seals.ac.za/vital/access/manager/Repository/vital:21089 Fri 07 Jul 2023 06:30:13 SAST ]]>