Moderate Storm Research Articles

Ionospheric Response to the St. Patrick's Day Space Weather Events in March 2012, 2013, and 2015 at Southern Low and Middle Latitudes

AbstractThe changes in critical frequency of the F2 layer (foF2) and foF2 deviation (ΔfoF2) have been determined for three geomagnetic storms in March of the years 2012, 2013, and 2015 at low‐latitude stations, Darwin (geomag. lat. 21.96°S) and Townsville (28.95°S), and midlatitude stations, Brisbane (36.73°S), Canberra (45.65°S), and Hobart (54.17°S). The moderate storm during 15–16 March 2012 (Dst = −87 nT) showed a decrease in foF2 at midlatitude and no effect at low‐latitude stations. For the intense storm of 17–18 March 2013 (Dst = −132 nT) and the super storm of 17–18 March 2015 (Dst = −222 nT), some middle‐ to low‐latitude stations showed a short‐duration increase in foF2, but all stations showed a long‐duration decrease in foF2 during the recovery phases with ΔfoF2% varying from 26% (Darwin) to 36.6% at Hobart for the March 2013 storm and above 40% for the March 2015 storm at all of the stations. Short‐duration (~2–4 hr) increase in foF2 seems to be associated with the prompt penetrating electric fields. Long‐duration (>6 hr) decrease in foF2 is mainly accounted to the decrease in thermospheric O/N2 density ratio because of storm‐induced high‐latitude circulation of gas with depleted O/N2 density ratio to lower latitudes and partly due to disturbance dynamo electric fields. A comparison of ionosonde given foF2 for equinoctial storms (March 2013 and 2015) with similar strength Southern Hemisphere winter storms (July 2012 and June 2015) has been made with the IRI‐2016 model foF2 for Darwin, Brisbane, and Canberra stations.

Analysis of cosmic ray dynamics and ionospheric parameters during increased solar activity and magnetic storms

Based on the ground station data, the paper investigates the dynamics of space rays and ionospheric parameters during strong and moderate magnetic storms 2018. The research was carried out applying new methods for modeling and data analysis suggested by the authors. In the course of investigation, anomalous changes in ionospheric parameters preceding and accompanying magnetic storms were detected. When they were compared with the data of cosmic rays and interplanetary magnetic field, correlation was observed. It confirms the solar nature of the detected ionospheric effects. Application of regression methods confirmed the assumption on statistically significant effect of interplanetary magnetic field parameters on ionospheric parameter dynamics during increased solar activity. The results are of interest in the tasks of space weather forecast.

Role of the external drivers in the occurrence of low-latitude ionospheric scintillation revealed by multi-scale analysis

We analyze the amplitude scintillation on L-band signals over San Miguel de Tucumán (Argentina), focusing on the multi-scale variability and speculating on the possible relationship between forcing factors from the geospace and the ionospheric response. The site is nominally located below the expected position of the southern crest of the Equatorial Ionospheric Anomaly (EIA). For this scope, we concentrate on the period 1–31 March 2011, during which one minor and one moderate storm characterize the first half of the month, while generally quiet conditions of the geospace stand for the second half. By leveraging on the Adaptive Local Iterative Filtering (ALIF) signal decomposition technique, we investigate the multi-scale properties of Global Navigation Satellite Systems (GNSS) amplitude scintillation and helio-geophysical parameters, looking for possible cause-effect mechanisms relating the former to the latter. Namely, we identify resonant modes in the Akasofu (ε) parameter as likely related to the frequency components in the time evolution found for the amplitude scintillation index, hence modulating the scintillation itself.

Intertidal boulder transport: A proposed methodology adopting Radio Frequency Identification (RFID) technology to quantify storm induced boulder mobility

AbstractBoulder transport is an area of growing interest to coastal scientists as a means of improving our understanding of the complex interactions between extreme wave activity and the evolution of rocky coasts. However, our knowledge of the response of intertidal boulder deposits to contemporary storm events remains limited due to a lack of quantifiable field‐based evidence.We address this by presenting a methodology incorporating Radio Frequency Identification (RFID) tagging and Differential Global Positioning Navigation Satellite System (DGNSS) technology to monitor and accurately quantify the displacement of RFID tagged boulders resulting from storm wave activity. Based on preliminary findings we highlight the suitability of the technology and methodology to better understand the spatial and temporal response of intertidal boulders to contemporary storm events.We inserted RFID tags in 104 limestone boulders (intermediate axes from 0.27 to 2.85 m) across a range of morphogenic settings at two sites on the intertidal shore platforms at Bembridge, Isle of Wight (UK). Fifteen topographic surveys were conducted between July 2015 and May 2017 to relocate and record tagged boulder locations (tag recovery rate: 91%). The relocated boulder coordinate data from both sites identified 164 individual transport events in 63% of the tagged boulder array amounting to 184.6 m of transport, including the displacement of a boulder weighing more than 10 tonnes.Incidents of boulder quarrying and overturning during transport were also recorded, demonstrating that despite the relatively sheltered location, intertidal boulders are created and regularly transported under moderate storm conditions. This suggests that contemporary storm events have a greater propensity to mobilise boulders in the intertidal range than has previously been realised.Consequently, by documenting our methodology we provide guidance to others and promote further use of RFID technology to enable new hypotheses on boulder transport to be tested in a range of field settings and wave regimes. © 2018 John Wiley & Sons, Ltd.

Improvements and validation of the IRI UP method under moderate, strong, and severe geomagnetic storms

This work describes several important improvements made to the International Reference Ionosphere UPdate (IRI UP) method, and a careful validation of its performances under disturbed conditions. The IRI UP method has been improved developing an algorithm capable to properly filter wrongly autoscaled ionosonde data to be assimilated, avoiding the use of these in the assimilation process. Furthermore, the preliminary quality check used to choose the variogram model in the Universal Kriging method has been replaced with a new quality check routine (NQCR), based on statistical tests carried out using the variables Q1, Q2, and cR, built on variogram’s residuals. NQCR objectively identifies the best variogram model from which to get more reliable effective indices maps to be ingested in the IRI model to obtain updated foF2 and hmF2 maps. IRI UP has been applied on 30 different time intervals, between January 1, 2004, and December 31, 2016, characterized by moderate, strong, and severe geomagnetic conditions, over the European region. A statistical comparison between IRI UP and IRI at the truth sites located at Fairford (51.7°N, 1.5°W, UK) and San Vito (40.6°N, 17.8°E, Italy), for foF2 and hmF2, has been performed. From the statistical validation clearly emerges how IRI UP, for foF2, performs significantly better than IRI, for each of the 30 geomagnetic storms considered. Regarding hmF2, IRI UP performances are lower than those for foF2, although still better than IRI ones. In the light of the results achieved in this investigation, the IRI UP method represents an interesting approach to Space Weather forecast in the ionospheric domain.

Unusual Generation of Localized EPB in the Dawn Sector Triggered by a Moderate Geomagnetic Storm

AbstractAn interesting piece of observation related to the equatorial plasma bubble (EPB) that is triggered by a geomagnetic storm at dawn sector on 4–5 February 2011 is presented. The storm activity was initiated at 17 UT when interplanetary magnetic field (IMF) Bz turned southward and the Dst index started decreasing (accompanied by AE intensifications) attaining its minimum at −70 nT. The IMF Bz presented large fluctuations marked by southward/northward transitions at slow and rapid rates and eventually returning to normal in the morning of 5 February. Observations from the very high frequency radar located at Gadanki, an off‐equatorial station; an all‐sky imager located at Kolhapur, a low‐latitude station; and an ionosonde at Tirunelveli, an equatorial station, are analyzed to study the impact of this storm on the postmidnight to presunrise equatorial spread F. The results demonstrate that EPB irregularities can be generated by penetration electric field during what can be characterized as a moderate storm event. In contrast to prevailing belief, the present results show that EPB/equatorial spread F can be generated by undershielding electric field in the dawn sector, caused by an unusually delayed polarity reversal of the penetration electric field. The results further reveal oscillatory behavior in the height of F layer topside irregularities in association with IMF Bz oscillations. Observation of radar echoes from nighttime E layer irregularity structures and their Doppler velocities representing the penetration electric field polarity and intensity are also a notable finding of this paper.

Dynamics of a geomagnetic storm on 7–10 September 2015 as observed by TWINS and simulated by CIMI

Abstract. For the first time, direct comparisons of the equatorial ion partial pressure and pitch angle anisotropy observed by TWINS and simulated by CIMI are presented. The TWINS ENA images are from a 4-day period, 7–10 September 2015. The simulations use both the empirical Weimer 2K and the self-consistent RCM electric potentials. There are two moderate storms in succession during this period. In most cases, we find that the general features of the ring current in the inner magnetosphere obtained from the observations and the simulations are similar. Nevertheless, we do also see consistent contrasts between the simulations and observations. The simulated partial pressure peaks are often inside the observed peaks and more toward dusk than the measured values. There are also cases in which the measured equatorial ion partial pressure shows multiple peaks that are not seen in the simulations. This occurs during a period of intense AE index. The CIMI simulations consistently show regions of parallel anisotropy spanning the night side between approximately 6 and 8 RE, whereas the parallel anisotropy is seen in the observations only during the main phase of the first storm. The evidence from the unique global view provided by the TWINS observations strongly suggests that there are features in the ring current partial pressure distributions that can be best explained by enhanced electric shielding and/or spatially localized, short-duration injections.

Modeling the Midlatitude Ionosphere Storm‐Enhanced Density Distribution With a Data Assimilation Model

AbstractThe Utah State University Global Assimilation of Ionospheric Measurements‐Gauss Markov model has been used to investigate the distribution of ionospheric plasma during storm times over the continental United States. Storm periods dramatically increase the effects of space weather on the ionosphere and upper atmosphere, leading to impacts on over‐the‐horizon radars, Global Positioning System location determination, spacecraft charging, power grid overloads, and disruption of the Federal Aviation Administration Wide Area Augmentation System to name a few. Four storm periods were investigated where strong storm‐enhanced densities (SEDs) were present: two strong, October 2003 and November 2003, and two moderate, August 2010 and August 2011. It was found that a fundamental difference in the SED formation exists between the strong and moderate storms. For the strong storms, the SED was formed from the plasma in the northern equatorial anomaly crest, with the plasma in the SED channel lifting the closer it came to the high latitudes. For the moderate storms, the SED appeared to be unconnected to the northern anomaly crest but was rather produced locally in the SED channel, along with no corresponding increase in layer height associated with the SED evident in the model.

Localized Increment and Decrement in the Total Electron Content of the Ionosphere as a Response to the April 20, 2018, Geomagnetic Storm

A moderate geomagnetic storm occurred on April 20, 2018. Using vertical total electron content (VTEC) maps provided by the Center for Orbit Determination in Europe, ionospheric responses to the geomagnetic storm could be identified in generated two-dimensional differential VTEC maps. During the day of the storm the enhancement of the equatorial ionization anomaly (EIA), product of the super-fountain effect was identified. A localized TEC enhancement (LTE) was also observed to the south of the EIA on April 20, 2018. It was also possible to visualize this LTE in a longitudinal section of the EIA as a third crest. The maximum increment of VTEC for the LTE was 204%. This LTE is quite unique because it happened during the expected solar cycle 24 and 25 minimum, and according to a previous study no LTE observation could be done for the last solar two-cycle minimum. The origin of the observed LTE is suggested to be partly product of the super-fountain effect. Finally, a localized TEC decrement (LTD) was observed towards the end of the day, April 20, 2018. Because this LTD consisted in the disappearance of the northern and southern crests of the EIA and this occurred during the recovery phase of the geomagnetic storm, it can be suggested that the LTD origin is due to the westward disturbance electric field. This mechanism was put forward by a past study that also analyzed the responses to a geomagnetic storm (the 2015 St. Patrick’s day storm), being one of the responses the inhibition of both crests of the EIA.

How Different Are the Solar Wind‐Interplanetary Conditions and the Consequent Geomagnetic Activity During the Ascending and Early Descending Phases of the Solar Cycles 23 and 24?

AbstractThe current work investigates the possible solar wind‐interplanetary (SW‐IP) drivers of geomagnetic storms during the longest period (ascending to early descending phases) of the ongoing solar cycle (24). We present a comparative analysis between the two consecutive solar cycles (SCs) 23 and 24. Both the cycles exhibited dual peak feature as observed in the smoothed sunspot numbers SSNsmoothed. For both the cycles, second peak in the SSNsmoothed is higher than the first one as exhibited in the revised SSNsmoothed version. During the entire interval between the ascending to early descending phases (December 2008 to December 2016) of SC‐24, the southward directed Bz and the dawn‐dusk electric field (Ey) were consistently weaker as compared to that during similar interval of SC‐23 (May 1996 to July 2004). The geomagnetic field response represented by Dst index concurrently exhibited similar variation patterns during both the periods. A striking reduction in the intense storm occurrence rate by ∼75% was observed during the considered period of the current solar cycle in comparison to the previous cycle. However, moderate storm occurrence was reduced only by 32% in SC‐24 as compared to SC‐23, which could be attributed to the dominance of corotating interaction regions during SC‐24. No significant difference is found between the intense storm rates around the vernal and autumnal equinoxes in cycle 24, whereas distinct autumnal equinoctial dominance is evident for cycle 23. Further, within each cycle, there is no significant difference in the moderate storm rates around vernal and autumnal equinoxes.

The role of meteorological tsunamis on beach erosion in the buenos aires coast: some numerical experiments

ABSTRACTMeteorological tsunamis (meteotsunamis) are very similar to ordinary tsunamis but are produced by atmospheric processes. In this work, some numerical experiments are performed using XBeach numerical model investigate the role of moderate meteorological tsunamis on a sandy beach. The model was forced using tide, a moderate storm surge event, wave height data series and a meteorological tsunami event recorded in the Buenos Aires coast, Argentina. Several numerical experiments were carried out considering different time lags between the peak level of the meteotsunami event and the highest sea level (storm surge and tide). In these experiments, the volumes of moved sand were quite similar, although different erosion patterns on the beach were appreciated. Numerical experiments presented in this work constitute the first indication that the occurrence of regular meteotsunamis during moderate storm conditions could change the erosion pattern on sandy beaches in the coast of Buenos Aires.

Hurricane storm surge in Volusia County, Florida: evidence of a tipping point for infrastructure damage.

Storm surge often is the most destructive consequence of hurricanes and tropical storms, causing significant economic damage and loss of life. Many coastal communities that are located in high-risk areas vis-à-vis hurricanes and tropical storms are prepared for moderate (between six and eight feet) storm surges. Such preparation, though, is not commensurate with more severe, but less frequent, storm surges (greater than eight feet). These gaps in preparedness have serious implications for community resilience. This paper explores elements of the vulnerability and resilience of coastal communities during major storm surge events, drawing on Volusia County, Florida, United States, as a case study. It simulates the impacts of five hurricanes (Categories I-V) and their associated storm surges on local infrastructure systems, populations, and access to resources. The results suggest that Volusia County is subject to a 'tipping point' , where surge damage from Category IV storms is significantly greater than that from Category III and lower hurricanes.

Observations and Modeling of Increased Nitric Oxide in the Antarctic Polar Middle Atmosphere Associated With Geomagnetic Storm‐Driven Energetic Electron Precipitation

AbstractNitric oxide (NO) produced in the polar middle and upper atmosphere by energetic particle precipitation depletes ozone in the mesosphere and, following vertical transport in the winter polar vortex, in the stratosphere. Medium‐energy electron (MEE) ionization by 30–1,000 keV electrons during geomagnetic storms may have a significant role in mesospheric NO production. However, questions remain about the relative importance of direct NO production by MEE at altitudes ~60–90 km versus indirect NO originating from auroral ionization above 90 km. We investigate potential drivers of NO variability in the southern‐hemisphere mesosphere and lower thermosphere during 2013–2014. Contrasting geomagnetic activity occurred during the two austral winters, with more numerous moderate storms in the 2013 winter. Ground‐based millimeter‐wave observations of NO from Halley, Antarctica, are compared with measurements by the Solar Occultation For Ice Experiment (SOFIE) spaceborne spectrometer. NO partial columns over the altitude range 65–140 km from the two observational data sets show large day‐to‐day variability and significant disagreement, with Halley values on average 49% higher than the corresponding SOFIE data. SOFIE NO number densities, zonally averaged over geomagnetic latitudes −59° to −65°, are up to 3 × 108/cm3 higher in the winter of 2013 compared to 2014. Comparisons with a new version of the Whole Atmosphere Community Climate Model, which includes detailed D‐region ion chemistry (WACCM‐SIC) and MEE ionization rates, show that the model underestimates NO in the winter lower mesosphere whereas thermospheric abundances are too high. This indicates the need to further improve and verify WACCM‐SIC with respect to MEE ionization, thermospheric NO chemistry, and vertical transport.

The Acceleration of Ultrarelativistic Electrons During a Small to Moderate Storm of 21 April 2017

AbstractThe ultrarelativistic electrons (E > ~3 MeV) in the outer radiation belt received limited attention in the past due to sparse measurements. Nowadays, the Van Allen Probes measurements of ultrarelativistic electrons with high energy resolution provide an unprecedented opportunity to study the dynamics of this population. In this study, using data from the Van Allen Probes, we report significant flux enhancements of ultrarelativistic electrons with energies up to 7.7 MeV during a small to moderate geomagnetic storm. The underlying physical mechanisms are investigated by analyzing and simulating the evolution of electron phase space density. The results suggest that during this storm, the acceleration mechanism for ultrarelativistic electrons in the outer belt is energy‐dependent: local acceleration plays the most important role in the flux enhancements of ~3–5 MeV electrons, while inward radial diffusion is the main acceleration mechanism for ~7 MeV electrons at the center of the outer radiation belt.

Variations in the Geomagnetic Cutoff Rigidity during the Magnetic Storm in March 2015

Variations in the planetary system of the geomagnetic cutoff rigidity during the moderate geomagnetic storm in March 2015 are calculated on the basis of data from cosmic-ray measurements at the world network of stations. The distance to the subsolar point and the radius of the ring current are calculated on the basis of the axisymmetric restricted Earth’smagnetosphere model that takes into account currents at the magnetopause and the ring current. The contribution of the ring current to variations in the geomagnetic cutoff rigidity and to the disturbance storm time (Dst) index is also determined within this model.

Composition of 1–128 keV Magnetospheric ENAs

AbstractThe Two Wide‐angle Imaging Neutral‐atom Spectrometers (TWINS) mission has observed the inner magnetosphere since 2008. TWINS flies energetic neutral atom (ENA) cameras aboard two spacecraft in separate Molniya orbits. TWINS images the ENA emissions from the inner magnetosphere across a broad range of energies (1 to 128 keV for H, 16 to 128 keV for O, and higher energies for total ENAs). This allows TWINS to observe the evolution, on minute timescales, of the trapped and precipitating particles that dominate storm time dynamics. Presented here are ENA observations over this broad energy range of the large storm of 17 March 2015 (Dst < −223)—the St. Patrick's Day storm. The ENA observations are presented with a 15‐min cadence for improved counting statistics. During the St. Patrick's Day storm the flux of ENAs and the concentration of O+/H+ increased significantly during the main phase. The concentration increased to a value of 1.0 for the 16 keV ions, and the temperature in the inner magnetosphere dropped during the time between the prestorm phase and the main phase. Comparing the results from this storm to a moderate storm on 22 July 2009, and a collection of nine other large storms, we find that the most energetic O+ ions in the ring current occur before the peak of the storm.

Low‐Altitude Observations of Recurrent Short‐Lived keV Ion Microinjections Inside the Diffuse Auroral Zone

AbstractThe AMBRE experiment onboard the ocean topography mapper JASON‐3 aims at measuring the spacecraft potential as well as auroral particle precipitation using two top‐hat analyzers for electrons and ions in the 20 eV–28 keV energy range. The JASON‐3 spacecraft has a nearly circular orbit at an altitude of 1,336 km with an inclination of 66°, at times probing the equatorward part of the auroral oval in a nearly tangential manner upon leaving the outer radiation belt. In this region of space, during periods of enhanced geomagnetic activity with small or moderate storms, AMBRE detected recurrent “microinjections” of ions with energies in the 200 eV–28 keV range and which exhibit clear time‐of‐flight dispersion. Ray tracing using single trajectory computations suggests that these ions are launched from a source located in the 8,000–12,000 km altitudinal range and subsequently propagate downward toward the ionosphere. Such observations of quasiperiodic dispersed downflowing ions are new, and we argue that these structures could be produced by ion‐wave interactions at midaltitudes.

Estimating Surface/Subsurface Sediment Mixing in Karst Settings Using 7Be Isotopes

AbstractThis study shows that the cosmogenic radionuclide beryllium‐7 can be used to track sediment movement through caves. The activities of beryllium‐7 and cesium‐137 were measured in two different karst settings at both surface and subsurface sites before and after storm runoff events. At one site, 7Be‐enriched sediment was detected up to 1.5 km along a stream conduit after a moderate storm event; however, the activity of 137Cs was too variable to show a meaningful pattern. The percentages of surface sediment that was found ranged from 0 to 52% along the entire 3 km cave stream and from 33 to 52% along the upper 1.5 km. At the other site, as much as 96% of the sediment initially discharged at the spring during a storm event was fresh surface material that had traveled into and through the cave stream. Moreover, during the 4 day runoff event, approximately 23% of the total suspended sediment flux was estimated to originate from surface erosion with 78% being reworked sediment from within the cave. The data in this study show that cosmogenic radionuclides with multiyear half‐lives are too long‐lived to track sediment origins in the caves; whereas, 7Be with a 53.2 day half‐life, can be used to track movement of sediment along cave streams.

Spectral characteristic of geomagnetically induced current during geomagnetic storms by wavelet techniques

An EMF (electromagnetic field) is induced over an incremental area when magnetized plasma from sun interacts with the Earth's magnetic field. This phenomenon delivers a Geomagnetically Induced Current (GIC) or induces geo-electric field at the Earth's surface and in the ground. GIC and horizontal component of geomagnetic field have been studied with respect to various geomagnetic events. Particularly, we have studied four events. The first one is geomagnetically quiet period (5 October 2003), the second one is weak storm (21 October 2003), the third one is moderate storm (14 October 2003) and the last one is an intense storm (30 October 2003). By comparing the development of GIC during geomagnetic storms, we found that intense geomagnetic storms show higher development on GIC magnitude. The GIC during storm events is several times greater than that during the quiet day. AE index shows more activity in the event of 30th October than other events and GIC is also more in this event. This can be accounted to the greater geomagnetic disturbance in this case. The power ranges of higher intensity are seen at various time scales on different events. We have analysed GIC signal associated with four geomagnetic storms and found distinct periodicities at the time when H component highly perturbed. The characteristic of GIC signal demonstrates high variability with time without presence of continuous periodicities. Discrete wavelet transform (DWT) analysis reveals that whenever the geomagnetic field is perturbed, there will be high possibility of detecting GIC. The singularities present in GIC signal are due to the peak value of electrical currents system in the ionosphere and magnetosphere, and corresponding high fluctuations in H component. In this work, we explore the remarkable ability of wavelets to highlight the singularities associated with discontinuities present in the GIC.

Gold in the hills: patterns of placer gold accumulation under dynamic tectonic and climatic conditions

Formation of placer accumulations in fluvial environments requires 103–106 or even greater times concentration of heavy minerals. For this to occur, regular sediment supply from erosion of adjacent topography is required, the river should remain within a single course for an extended period of time and the material must be reworked such that a high proportion of the sediment is removed while a high proportion of the heavy minerals remains. We use numerical modeling, constrained by observations of circum-Pacific placer gold deposits, to explore processes occurring in evolving river systems in dynamic tectonic environments. A fluvial erosion/transport model is used to determine the mobility of placer gold under variable uplift rate, storm intensity, and rock mass strength conditions. Gold concentration is calculated from hydraulic and bedload grain size conditions. Model results suggest that optimal gold concentration occurs in river channels that frequently approach a threshold between detachment-limited and transport-limited hydraulic conditions. Such a condition enables the accumulation of gold particles within the framework of a residual gravel lag. An increase in transport capacity, which can be triggered by faster uplift rates, more resistant bedrock, or higher intensity storm events, will strip all bedload from the channel. Conversely, a reduction in transport capacity, triggered by a reduction in uplift rate, bedrock resistance, or storm intensity, will lead to a greater accumulation of a majority of sediments and a net decrease in gold concentration. For our model parameter range, the optimal conditions for placer gold concentration are met by 103 times difference in strength between bedrock and fault, uplift rates between 1 and 5 mm a−1, and moderate storm intensities. Fault damage networks are shown to be a critical factor for high Au concentrations and should be a target for exploration.