http://hdl.handle.net/20.500.14342/39 Sat, 02 May 2026 11:09:48 GMT 2026-05-02T11:09:48Z http://hdl.handle.net/20.500.14342/5927 Climatology of the spread F over Roquetes, Spain: Impact of the medium scale traveling ionospheric disturbances Paul, Krishnendu Sekhar; Haralambous, Haris; Altadill Felip, David; Segarra, Antoni; Navas-Portella, Víctor; de Paula Vila, Víctor Understanding the long-term variability of nighttime Spread F (SF) and its drivers is crucial for improving the knowledge of ionospheric disturbances, which impact radio communication, GNSS positioning, and space weather forecasting. This study exploits the long-term ionogram dataset from the EB040 ionosonde in Spain (1955–2022) to investigate the climatology of nighttime SF and its dependence on solar activity. We analyze the diurnal, seasonal, and solar-cycle variability of both Range Spread F (RSF) and Frequency Spread F (FSF). The results reveal a strong inverse relationship between SF occurrence and solar activity, with SF maxima during solar minima. SF is confirmed as a predominantly nighttime phenomenon in western European mid-latitudes, primarily occurring between 20:00 and 05:00 UT, peaking near the solstices, with higher occurrence in June–July than in December–January, and with RSF accounting for 69% of SF events. Complementary analysis using GNSS-derived detrended Total Electron Content (d-TEC) and Rate of TEC index (ROTI) maps (2012–2016) quantifies the connection with Medium-Scale Traveling Ionospheric Disturbances (MSTIDs). Approximately 85% of SF occurrences at EB040 coincide with MSTID activity, with correlation coefficients above 0.96 between their onset times. MSTID activity exhibits the same seasonal pattern as SF, peaking at the solstices—particularly in June–July—and displaying the same inverse dependence on solar activity. Furthermore, 62% of RSF events at EB040 are associated with strong ROTI activity, especially during summer, and 83% of RSF events lasting over two hours correspond to strong ROTI activity. Overall, these findings highlight MSTIDs as the dominant electrodynamic driver of mid-latitude SF and underline the seasonal and solar activity dependencies of SF variability, providing new constraints for understanding ionospheric dynamics. Fri, 21 Nov 2025 00:00:00 GMT http://hdl.handle.net/20.500.14342/5927 2025-11-21T00:00:00Z http://hdl.handle.net/20.500.14342/5905 Long‐Term Homogeneity of the SSC Series Curto, Juan José; Segarra, Antoni; Torta, Joan Miquel; Marsal, Santiago; Chambodut, Aude; Qvick, Timo; Mursula, Kalevi Geomagnetic storms produce global variations in the geomagnetic field that are measured at magnetic observatories. Roughly one half of magnetic storms are preceded by sudden increases in the horizontal component of the magnetic field world‐wide. These increases, called storm sudden commencements (SSC), produce geomagnetically induced currents and cause other space weather disturbances whose study is paramount due to the technological dependence of our society. SSC event lists date back to 1868 and provide invaluable information about interplanetary conditions over centennial time scales. Since 1975, the Service of Rapid Magnetic Variations has been responsible for the maintenance and consistency of the SSC list. Here we will review the significant changes in the definition and methods of SSC detection that have been introduced over time and will analyze and discuss whether those changes have affected the homogeneity of the SSC series. Alerted by the greatly reduced number of SSCs in solar cycle 24, we have reanalyzed SSC occurrence in the period 2006–2017. As a result, we found a 26% increase in the number of SSCs, which motivates a change in the adopted SSC definition but leaves the SSC level exceptionally low during this period. We completed the study by examining the relation and dependency of SSCs with solar sunspot numbers and the temporal variation of the horizontal magnetic field. Wed, 01 Jan 2025 00:00:00 GMT http://hdl.handle.net/20.500.14342/5905 2025-01-01T00:00:00Z http://hdl.handle.net/20.500.14342/5512 The Lehtinen–Pirjola method modified for efficient modelling of geomagnetically induced currents in multiple voltage levels of a power network Pirjola, Risto; Boteler, David; Tuck, Loughlin; Marsal, Santiago The need for accurate assessment of the geomagnetic hazard to power systems is driving a requirement to model geomagnetically induced currents (GIC) in multiple voltage levels of a power network. The Lehtinen–Pirjola method for modelling GIC is widely used but was developed when the main aim was to model GIC in only the highest voltage level of a power network. Here we present a modification to the Lehtinen–Pirjola (LP) method designed to provide an efficient method for modelling GIC in multiple voltage levels. The LP method calculates the GIC flow to ground from each node. However, with a network involving multiple voltage levels, many of the nodes are ungrounded, i.e. have infinite resistance to ground, which is numerically inconvenient. The new modified Lehtinen–Pirjola (LPm) method replaces the earthing impedance matrix [Ze] with the corresponding earthing admittance matrix [Ye] in which the ungrounded nodes havezeroadmittance to ground. This is combined with the network admittance matrix [Yn] to give a combined matrix ([Yn] [Ye]), which is a sparse symmetric positive definite matrix allowing efficient techniques, such as Cholesky decomposition, to be used to provide the nodal voltages. The nodal voltages are then used to calculate the GIC in the transformer windings and the transmission lines of the power network. The LPm method with Cholesky decomposition also provides an efficient method for calculating GICatmultiple timesteps. Finally, the paper shows how software for the LP method can be easily converted to the LPm method andprovides examples of calculations using the LPm method. Wed, 20 Apr 2022 00:00:00 GMT http://hdl.handle.net/20.500.14342/5512 2022-04-20T00:00:00Z http://hdl.handle.net/20.500.14342/5495 Geomagnetically induced currents in a power grid of northeastern Spain Torta, Joan Miquel; Serrano, Lluís; Regué, Joan Ramon; Sánchez, Albert Miquel; Roldán, Elionor Using the geomagnetic records of Ebro geomagnetic observatory and taking the plane wave assumption for the external current source and a homogeneous Earth conductivity, a prediction of the effects of the geomagnetic activity on the Catalonian (northeastern Spain) power transmission system has been developed. Although the area is located at midlatitudes, determination of the geoelectric field on the occasion of the largest geomagnetic storms during the last solar cycles indicates amplitudes that are higher than those recorded in southern Africa, where some transformer failures on large transmission systems have been reported. A DC network model of the grid has been constructed, and the geomagnetically induced current (GIC) flows in the power network have been calculated for such extreme events using the electric field at Ebro as a regional proxy. In addition, GICs have been measured at one transformer neutral earthing of the power grid, so that there the accuracy of the model has been assessed. Although the agreement is quite satisfactory, results indicate that better knowledge of the ground conductivity structure is needed. This represents the first attempt to study and measure GICs in southern European power grids, a region considered to have low GIC-risk up to the present. Thu, 07 Jun 2012 00:00:00 GMT http://hdl.handle.net/20.500.14342/5495 2012-06-07T00:00:00Z