Rezy Pradipta

Interplanetary shocks and the resulting geomagnetically induced currents at the equator

Geomagnetically induced currents (GICs) caused by interplanetary shocks represent a serious space weather threat to modern technological infrastructure. The arrival of interplanetary shocks drives magnetosphere and ionosphere current systems, which then induce electric currents at ground level. The impact of these currents at high latitudes has been extensively researched, but the magnetic equator has been largely overlooked. In this paper, we investigate the potential effects of interplanetary shocks on the equatorial region and demonstrate that their magnetic signature is amplified by the equatorial electrojet. This local amplification substantially increases the regions susceptibility to GICs. Importantly, this result applies to both geomagnetic storms and quiet periods and thus represents a paradigm shift in our understanding of adverse space weather impacts on technological infrastructure.

Global equatorial plasma bubble occurrence during the 2015 St. Patrick's Day storm

An analysis of the occurrence of equatorial plasma bubbles (EPBs) around the world during the 2015 St. Patricks Day geomagnetic storm is presented. A network of 12 Global Positioning System receivers spanning from South America to Southeast Asia was used, in addition to colocated VHF receivers at three stations and four nearby ionosondes. The suppression of postsunset EPBs was observed across most longitudes over 2 days. The EPB observations were compared to calculations of the linear Rayleigh-Taylor growth rate using coupled thermosphere-ionosphere modeling, which successfully modeled the transition of favorable EPB growth from postsunset to postmidnight hours during the storm. The mechanisms behind the growth of postmidnight EPBs during this storm were investigated. While the latter stages of postmidnight EPB growth were found to be dominated by disturbance dynamo effects, the initial stages of postmidnight EPB growth close to local midnight were found to be controlled by the higher altitudes of the plasma (i.e., the gravity term). Modeling and observations revealed that during the storm the ionospheric plasma was redistributed to higher altitudes in the low-latitude region, which made the plasma more susceptible to Rayleigh-Taylor growth prior to the dominance of the disturbance dynamo in the eventual generation of postmidnight EPBs.

Geomagnetically induced currents around the world during the 17 March 2015 storm

Geomagnetically induced currents (GICs) represent a significant space weather issue for power grid and pipeline infrastructure, particularly during severe geomagnetic storms. In this study, magnetometer data collected from around the world are analyzed to investigate the GICs caused by the 2015 St. Patricks Day storm. While significant GIC activity in the high-latitude regions due to storm-time substorm activity is shown for this event, enhanced GIC activity was also measured at two equatorial stations in the American and South-East Asian sectors. This equatorial GIC activity is closely examined, and it is shown that it is present both during the arrival of the interplanetary shock at the storm sudden commencement (SSC) in South-East Asia and during the main phase of the storm ∼ 10 hours later in South America. The SSC caused magnetic field variations at the equator in South-East Asia that were twice the magnitude of those observed only a few degrees to the north, strongly indicating that the equatorial electrojet (EEJ) played a significant role. The large equatorial magnetic field variations measured in South America are also examined and the coincident solar wind data are used to investigate the causes of the sudden changes in the EEJ ∼ 10 hours into the storm. From this analysis it is concluded that sudden magnetopause current increases due to increases in the solar wind dynamic pressure, and the sudden changes in the resultant magnetospheric and ionospheric current systems, are the primary drivers of equatorial GICs.

Interhemispheric propagation and interactions of auroral traveling ionospheric disturbances near the equator

We present the results of our GPS total electron content and ionosonde observations of large-scale traveling ionospheric disturbances (LSTIDs) during the 26 September 2011 geomagnetic storm. We analyzed the propagation characteristics of these LSTIDs from the auroral zones all the way to the equatorial region and studied how the auroral LSTIDs from opposite hemispheres interact/interfere near the geomagnetic equator. We found an overall propagation speed of 700 m/s for these LSTIDs and that the resultant amplitude of the LSTID interference pattern actually far exceeded the sum of individual amplitudes of the incoming LSTIDs from the immediate vicinity of the interference zone. We suspect that this peculiar intensification of auroral LSTIDs around the geomagnetic equator is facilitated by the significantly higher ceiling/canopy of the ionospheric plasma layer there. Normally, acoustic-gravity waves (AGWs) that leak upward (and thus increase in amplitude) would find a negligible level of plasma density at the topside ionosphere. However, the tip of the equatorial fountain at the geomagnetic equator constitutes a significant amount of plasma at a topside-equivalent altitude. The combination of increased AGW amplitudes and a higher plasma density at such altitude would therefore result in higher-amplitude LSTIDs in this particular region, as demonstrated in our observations and analysis.

GPS observation of continent‐size traveling TEC pulsations at the start of geomagnetic storms

We report our experimental observation of continent-size traveling plasma disturbances using GPS measurements of total electron content (TEC) over the North American sector. These plasma disturbances occurred at the beginning of geomagnetic storms, immediately after the shock arrived, and prior to the appearance of large-scale traveling ionospheric disturbances (LSTIDs) from the auroral region. Specifically, these supersize TEC perturbations were observed when the interplanetary magnetic field Bz was oscillating between northward and southward directions. They were found to propagate zonally with a propagation speed of 2–3 km/s. We interpret these TEC pulsations as ion drift waves in the magnetosphere/plasmasphere that propagate azimuthally inside the GPS orbit.

Response of the equatorial ionosphere to the geomagnetic DP 2 current system

The response of equatorial ionosphere to the magnetospheric origin DP 2 current system fluctuations is examined using ground-based multiinstrument observations. The interaction between the solar wind and fluctuations of the interplanetary magnetic field (IMF) Bz, penetrates nearly instantaneously to the dayside equatorial region at all longitudes and modulates the electrodynamics that governs the equatorial density distributions. In this paper, using magnetometers at high and equatorial latitudes, we demonstrate that the quasiperiodic DP 2 current system penetrates to the equator and causes the dayside equatorial electrojet (EEJ) and the independently measured ionospheric drift velocity to fluctuate coherently with the high-latitude DP 2 current as well as with the IMF Bz component. At the same time, radar observations show that the ionospheric density layers move up and down, causing the density to fluctuate up and down coherently with the EEJ and IMF Bz.

Ionosonde observations of ionospheric disturbances due to the 15 February 2013 Chelyabinsk meteor explosion

We report the results of our investigations on ionospheric effects potentially caused by the 15 February 2013 Chelyabinsk meteor explosion. We used the observation data from a number of digisonde s...

Assessing the Occurrence Pattern of Large Ionospheric TEC Gradients over the Brazilian Airspace: Ionospheric Gradients over Brazilian Airspace

We investigate the occurrence pattern of equatorial plasma bubbles and the corresponding ionospheric gradients over a section of the Brazilian airspace in 2014/2015. The GPS-derived total electron content (TEC) data from a chain of receiver stations were used in this study to compute the TEC gradients along the southern crest of the equatorial ionospheric anomaly region over Brazil. Here, we present a few illustrative examples to delineate the general qualitative features of equatorial plasma bubbles in this region, and the varying degree of TEC gradient magnitudes associated with these bubbles. We also inferred the overall probability distribution function of the computed TEC gradient magnitudes in this region, which extend up to 1000 mm/km at the GPS L1 frequency. Copyright

An effective TEC data detrending method for the study of equatorial plasma bubbles and traveling ionospheric disturbances

Using a mechanical analogy of rolling a cylindrical barrel on a rough uneven surface, we developed a special method for detrending the GPS-derived total electron content (TEC) data. This method is specifically designed to recognize the presence of depletions in the TEC time series data and handle them differently from wavelike features. We also demonstrate a potential application of this technique to map the detailed geographic profile of TEC depletions over the equatorial region, using the South American sector as an example.

Solar-Powered Microwave Transmission for Remote Sensing and Communications

A solar-powered microwave transmission system is proposed for remote sensing and communications purposes. We present in this paper a proof of concept to operate solar-powered microwave transmission and an investigation of microwave interactions with atmospheric plasmas. In this conceptualized system, a solar thermophotovoltaic system is considered to produce direct current electricity, which is then used to power solid-state microwave transmitters. The results from these simulations provide insights on how to produce an economically and environmentally conscientious energy source, which can be used for remote-sensing and communication applications. However, it is expected that microwaves may interact with ionospheric plasmas, primarily in the E-region to induce large-scale fluctuations in plasma density and geomagnetic fields with threshold wave electric-field intensities of ~ 1 V/m. After we determine the instability thresholds, we can use them to set up the safe operation range of solar-powered microwave transmission.