Bubble Events Research Articles

Regional Ionospheric Super Bubble Induced by Significant Upward Plasma Drift During the 1 December 2023 Geomagnetic Storm

AbstractAn unseasonal equatorial plasma bubble (EPB) event occurred in the East/Southeast Asian sector during the geomagnetic storm on 1 December 2023, causing strong amplitude scintillations from equatorial to middle latitudes. Based on the observations from multiple instruments over a large latitudinal and longitudinal region, the spatial features of the super EPB were investigated. The EPB developed vertically at a fast rising speed ∼470 m/s over the magnetic equator and extended to a very high middle latitude more than 40°N, despite that the storm intensity was not very strong with the minimum SYM‐H index −132 nT. In the zonal direction, the super EPB covered over a specific region ∼95–140°E, where the local sunset roughly coincided with southward turning of interplanetary magnetic field (IMF) Bz component. Before the onset of the super EPB, significant upward plasma drift up to ∼110 m/s was observed over the magnetic equator, which could amplify the growth rate of Rayleigh‐Taylor instability and lead to the generation of the super EPB. The significant drift was likely caused by eastward penetration electric field (PEF) due to sharp southward turning of IMF Bz. The local time of storm onset and duration of IMF Bz southward turning during the storm main phase may partly determine the onset region and zonal coverage of the EPB.

Monitoring underwater volcano degassing using fiber-optic sensing

Continuous monitoring of volcanic gas emissions is crucial for understanding volcanic activity and potential eruptions. However, emissions of volcanic gases underwater are infrequently studied or quantified. This study explores the potential of Distributed Acoustic Sensing (DAS) technology to monitor underwater volcanic degassing. DAS converts fiber-optic cables into high-resolution vibration recording arrays, providing measurements at unprecedented spatio-temporal resolution. We conducted an experiment at Laacher See volcano in Germany, immersing a fiber-optic cable in the lake and interrogating it with a DAS system. We detected and analyzed numerous acoustic signals that we associated with bubble emissions in different lake areas. Three types of text-book bubbles exhibiting characteristic waveforms are all found from our detections, indicating different nucleation processes and bubble sizes. Using clustering algorithms, we classified bubble events into four distinct clusters based on their temporal and spectral characteristics. The temporal distribution of the events provided insights into the evolution of gas seepage patterns. This technology has the potential to revolutionize underwater degassing monitoring and provide valuable information for studying volcanic processes and estimating gas emissions. Furthermore, DAS can be applied to other applications, such as monitoring underwater carbon capture and storage operations or methane leaks associated with climate change.

Machine Learning to Forecast Financial Bubbles in Stock Markets: Evidence from Vietnam

Financial bubble prediction has been a significant area of interest in empirical finance, garnering substantial attention in the literature. This study aims to detect and forecast financial bubbles in the Vietnamese stock market from 2001 to 2021. The PSY procedure, which involves a right-tailed unit root test to identify the existence of financial bubbles, was employed to achieve this goal. Machine learning algorithms were then utilized to predict real-time financial bubble events. The results revealed the presence of financial bubbles in the Vietnamese stock market during 2006–2007 and 2017–2018. Additionally, the empirical evidence supported the superior performance of the random forest and artificial neural network algorithms over traditional statistical methods in predicting financial bubbles in the Vietnamese stock market.

Multi‐Source Perturbations in the Evolution of a Low‐Latitudinal Equatorial Plasma Bubble Event Occurred Over China

AbstractIn this paper, multi‐source perturbations during the evolution of an equatorial plasma bubble (EPB) event at low latitudes in China are studied by means of multi‐ground‐based instruments, including an all‐sky airglow imager, a very high frequency (VHF) radar and eight digisondes. We found that EPB event initially evolved from bottom perturbations (∼600 km scale) seeded by atmospheric gravity waves in a form of large‐scale wave‐like structure, accompanying smaller‐scale perturbations (∼150 km scale) mostly by collision‐shear instability (CSI); once formed, those seed perturbations further evolved into the ionospheric topside by the plasma instability. Observed and analyzed are two different instabilities: one is the Rayleigh‐Taylor instability (RTI) driven by a prereversal enhancement of the zonal electric field (PRE) occurred near sunset; the other is an equatorward wind‐induced secondary E × B gradient drift instability (GDI) around midnight. Accompanying the PRE‐induced RTI are freshly‐generated depletions with larger poleward (upward) velocities. The PRE‐driven RTI could elevate the bottom perturbations directly to form fast‐moving depletions/structures at the ionospheric topside. The E × B GDI was trigged by a vertical upward plasma jet caused by a seasonal equatorward wind in regions as far as 10°N (20°N) from the geomagnetic (geographic) equator. This equatorward wind‐induced E × B GDI continuously forced topside structures of those drifting‐type EPB depletions to extend poleward more slowly, resulting in active 3.2‐m irregularities around midnight. Besides, we present evidence that a westward polarization electric field generated in an adjacent trough region of the faster‐growing cluster‐type depletions inhibited the neighboring slower‐growing cluster‐type depletions.

Formulating MCoVaR to Quantify Joint Transmissions of Systemic Risk across Crypto and Non-Crypto Markets: A Multivariate Copula Approach

Evidence that cryptocurrencies exhibit speculative bubble behavior is well documented. This evidence could trigger global financial instability leading to systemic risk. It is therefore crucial to quantify systemic risk and investigate its transmission mechanism across crypto markets and other global financial markets. We can accomplish this using the so-called multivariate conditional value-at-risk (MCoVaR), which measures the tail risk of a targeted asset from each market conditional on a set of multiple assets being jointly in distress and on a set of the remaining assets being jointly in their median states. In this paper, we aimed to find its analytic formulas by considering multivariate copulas, which allow for the separation of margins and dependence structures in modeling the returns of the aforementioned assets. Compared to multivariate normal and Student’s t benchmark models and a multivariate Johnson’s SU model, the copula-based models with non-normal margins produced a MCoVaR forecast with superior conditional coverage and backtesting performances. Using a corresponding Delta MCoVaR, we found the crypto assets to be potential sources of systemic risk jointly transmitted within the crypto markets and towards the S&P 500, oil, and gold, which was more apparent during the COVID-19 period encompassing the recent 2021 crypto bubble event.

Air–water properties of unsteady breaking bores part 1: Novel Eulerian and Lagrangian velocity measurements using intrusive and non-intrusive techniques

Transient motion, turbulence and bubble dynamics make any velocity quantification extremely difficult in unsteady gas–liquid flows. In the present study, novel Eulerian and Lagrangian techniques of velocimetry were developed, using both intrusive and non-intrusive measurements. The selected unsteady gas–liquid flow was a breaking bore, featured with a transient motion, air entrainment and coherent structures. Intrusively, Eulerian probe measurements resulted to the development of a single bubble event detection (SBED) technique in unsteady air–water flows. Non-intrusively, the motion of air–water pattern was detected using a novel particle tracking velocimetry (PTV). Both velocities obtained using SBED and PTV techniques were validated against the established optical flow (OF) results, achieving consistent velocity data among the three techniques. The filtering criteria of the SBED and PTV techniques were discussed, showing the best options in the breaking bore. It is concluded that the most robust velocity measurements in gas–liquid flow are achieved with consistent velocity data between the SBED, PTV and OF techniques.

The Green Stock Market Bubble

One may contend that there are some clear similarities between the market for sustainable assets now and the situation of tech stocks right before the collapse of the dot-com bubble. In fact, before 2000, the risk of the new technology was primarily idiosyncratic because of the limited scale of production and the low likelihood of a widespread adoption. Subsequently, with an increasing probability of adoption, also, the old economy was affected by the new technology and, hence, the wealth of the representative agent. As a result, systematic risk increased, which depressed stock prices, because it pushed up the discount rates in the new and old economies. Similarly, given the high probability of a large-scale adoption of the new “green technology,” it is likely that there is not only a bubble forming in green energy stocks, but the boom is affecting the stock market as a whole. I apply a recently developed recursive testing procedure and dating algorithm that is useful in detecting multiple bubble events. Using S&P 500 stock market data, price-dividend ratios, I identify the well-known historical speculative bubbles and find an explosive movement in today’s market starting in June 2021, which can be associated with the new “green technology.” I find that an explosive movement in green stocks started roughly a year before it was migrating to the whole stock market. I argue that this is a good bubble because it will enable businesses to invest cheaply in green energy, hastening the transition away from fossil fuels and assisting in the fight against climate change.

Equatorial Plasma Bubbles Observed at Dawn and After Sunrise Over South America During the 2015 St. Patrick's Day Storm

AbstractThis paper presents an analysis of Equatorial Plasma Bubble (EPB) events that occurred during pre‐ and post‐sunrise hours in the South America sector on 18 March 2015, when the St. Patrick's Day geomagnetic storm was in the recovery phase. The data from a set of multi‐diagnostic instruments, including Global Navigation Satellite Systems (GNSS) receivers, L‐band GNSS ionospheric scintillation monitors, ionosondes, and a Fabry‐Perot interferometer, are analyzed. Strong L‐band amplitude scintillation was observed with spread‐F and total electron content (TEC) fluctuations at times when the electron density and tTEC were minimum with respect to their diurnal variations. The EPBs remained observed for about 3:30 hr after sunrise on the east coast of the South American continent. The daytime ionospheric irregularities show a longitudinal dependency between the west and east coasts, separated by about 3,600 km. Our analysis of the observations suggests that a Disturbance Dynamo Electric Field effect caused by storm‐time wind perturbations might have triggered the Rayleigh‐Taylor instability near local dawn on the east and west coasts of the South American continent. The effects of ambient ionosphere‐thermosphere conditions on the evolution of irregularities are assessed to understand the longitudinal differences. The assessment includes the effect of the E region that appears in the morning hours and the effects of geomagnetic declination and tilting the solar‐terminator.

Strong Ionospheric Spatial Gradient Events Induced by Signal Propagation Paths Aligned With Equatorial Plasma Bubbles

Low-latitude ionospheric behavior directly interferes with a wide range of applications dependent on signals and information from satellites. The most severe and variable events are plasma bubbles and ionospheric scintillation. During plasma bubble events, large and steep plasma density gradients may intersect transionospheric signal from satellites, especially around the equatorial anomaly region. Large ionospheric spatial gradients (or decorrelations) are a critical component of ionospheric threat models for global navigation satellite systems augmentation systems; however, the models cannot assimilate abrupt changes in ionospheric behavior. In this article, an investigation of the relationship between plasma depletions, the occurrence of scintillation, and strong ionospheric spatial decorrelation events was conducted. The results indicate that strong scintillations occur when large gradients are verified. Additionally, the most critical ionospheric spatial gradients were verified mostly under certain conditions: when satellite signals are aligned with the plasma bubble propagation along geomagnetic field lines. Therefore, even though amplitude scintillation may degrade communications, the critical gradient events seem to be related to a particular configuration of satellite signal across the ionosphere. Thus, it is recommended that ionospheric threat models for augmentation systems in low-latitude regions consider this alignment aspect.

Study of the equatorial and low-latitude total electron content response to plasma bubbles during solar cycle 24–25 over the Brazilian region using a Disturbance Ionosphere indeX

Abstract. This work uses the Disturbance Ionosphere indeX (DIX) to evaluate the ionospheric responses to equatorial plasma bubble (EPB) events from 2013 to 2020 over the Brazilian equatorial and low latitudes. We have compared the DIX variations during EPBs to ionosonde and All-Sky Imager data, aiming to evaluate the physical characteristics of these events. Our results show that the DIX was able to detect EPB-related TEC disturbances in terms of their intensity and occurrence times. Thus, the EPB-related DIX responses agreed with the ionosphere behavior before, during, and after the studied cases. Finally, we found that the magnitude of those disturbances followed most of the trends of solar activity, meaning that the EPB-related total electron content variations tend to be higher (lower) in high (low) solar activity.

Non-Value-Added Tax to improve market fairness and quality

The promotion of both market fairness and efficiency has long been a goal of securities market regulators worldwide. Accelerated digital disruption and abusive trading behaviors, such as the GameStop mania, prompt regulatory changes. It is unclear how this “democratization” of trading power affects market fairness as economies cope with pandemic-driven shifts in basic systems. Excessive speculation and market manipulation undermine the quality of financial markets in the sense that they cause volatility and increase the pain of bubble and crash events. Thereby, they weaken public confidence in financial markets to fulfill their roles in proper capital allocation to irrigate the real economy and generate value for society. While previous studies have mostly focused on market efficiency, our study proposes a tool to improve market fairness, even under periods of stress. To encourage value generation and improve market quality, we advance a graduated Non-Value-Added Tax that we implement in an agent-based model that can realistically capture the properties of real-world financial markets. A profitable transaction is taxed at a higher rate if it does not enhance the efficiency measured by deviation from fundamentals. When an agent locks in profit not supported by fundamentals but driven by trend-following strategies, the generated profit is taxed at various rates under the Non-Value-Added Tax regime. Unlike existing financial transaction taxes, the non-value-added tax is levied on profit rather than on price or volume. We show that the proposed tax encourages profitable trades that add value to the market and discourages valueless profit-making. It significantly curtails volatility and prevents the occurrence of extreme market events, such as bubbles and crashes.

DETECTING ASSET PRICE BUBBLES DURING THE COVID-19 CRISIS AND ITS IMPLICATIONS: EVIDENCE FROM THE STOCK AND OIL MARKET

This study investigates whether the COVID-19 pandemic has caused asset price bubbles in the stock and oil markets in the United States and Malaysia. More specifically, the study seeks to detect the onset and end of possible speculative bubbles and their causes in these markets. It also examines the existence of a contagion effect between the stock and oil markets during the Covid-19 pandemic. To achieve these objectives, the study used the Generalized SADF (GSADF) developed by Phillips et al. (2015) in order to check for existence of bubbles within the time frame from January 1, 2020, to April 24,2020. This technique allows one to look for the occurrence of multiple bubbles during the sample period with great precision. The findings showed that five out of the six equities, including the oil price indices had multiple bubbles. Evidence was also obtained which linked the explosive activity episodes between the crude oil market and the US stock markets from the start and end point of each bubble event. These findings add not only to the literature on the existence of bubbles in the financial and energy markets during the initial outbreak of COVID-19, but also to the significance of the negative impact of pandemics on bubble contagion effects under extreme market conditions.

Long-lasting stagnant equatorial plasma bubble event and the related scintillation over the Brazilian region

Diverse studies about equatorial plasma bubble structures and their relation with ionospheric scintillation have been performed in the last decades. Among many findings, the investigations usually reported dominant plasma bubble eastward velocity with a magnitude of few tens of m/s and larger amplitude scintillation for transionospheric signals aligned with these depleted structures. However, an uncommon long-lasting event with negligible average zonal drift prevailing for hundreds of minutes was registered over the Brazilian region, allowing a case study of the scintillation pattern under this particular condition. Data from ionosondes, all-sky imager (6300 Å filter), geostationary satellites and Global Navigation Satellite System were used here, covering the eastern portion of the Brazilian ionosphere. The results show that the scintillation was less intense than in other nights around the event, suggesting that larger plasma density gradients and sequential bubble structures seem to cause more severe scintillation scenario than the alignment condition alone, even though the last also contributes to worsen the scintillation effects. Regarding the stagnant bubble pattern, the results suggest prevailing E region Hall conductivity and equatorward wind as potential agents.

Surface Treatment of Glass Vials for Lyophilization: Implications for Vacuum-Induced Surface Freezing

Freeze-drying is commonly used to increase the shelf-life of pharmaceuticals and biopharmaceuticals. Freezing represents a crucial phase in the freeze-drying process, as it determines both cycle efficiency and product quality. For this reason, different strategies have been developed to allow for a better control of freezing, among them, the so-called vacuum-induced surface freezing (VISF), which makes it possible to trigger nucleation at the same time in all the vials being processed. We studied the effect of different vial types, characterized by the presence of hydrophilic (sulfate treatment) or hydrophobic (siliconization and TopLyo Si–O–C–H layer) inner coatings, on the application of VISF. We observed that hydrophobic coatings promoted boiling and blow-up phenomena, resulting in unacceptable aesthetic defects in the final product. In contrast, hydrophilic coatings increased the risk of fogging (i.e., the undesired creeping of the product upward along the inner vial surface). We also found that the addition of a surfactant (Tween 80) to the formulation suppressed boiling in hydrophobic-coated vials, but it enhanced the formation of bubbles. This undesired bubbling events induced by the surfactant could, however, be eliminated by a degassing step prior to the application of VISF. Overall, the combination of degasification and surfactant addition seems to be a promising strategy for the successful induction of nucleation by VISF in hydrophobic vials.

Probing the Halo Gas Distribution in the Inner Galaxy with Fermi Bubble Observations

Abstract The hot halo gas distribution in the inner Milky Way (MW) contains key fossil records of the past energetic feedback processes in the galactic center. Here, we adopt a variety of spherical and disk-like MW halo gas models as initial conditions in a series of simulations to investigate the formation of the Fermi bubbles in the jet-shock scenario. The simulation results are compared directly with relevant X-ray and gamma-ray observations of the Fermi bubbles to constrain the halo gas distribution in the inner Galaxy before the Fermi bubble event. Our best-fit gas density distribution can be described by a power law in radius n e(r) = 0.01(r/1 kpc)−1.5 cm−3. Our study cannot determine if there is an inner density core, which if exists, should be very small with size r c ≲ 0.5 kpc. When extrapolating to large radii r ∼ 50–90 kpc, our derived density distribution lies appreciably below the recently estimated gas densities from ram pressure stripping calculations, suggesting that the halo gas density profile either flattens out or has one or more discontinuities within 10 ≲ r ≲ 50 kpc. Some of these discontinuities may be related to the eROSITA bubbles, and our derived gas density profile may correspond to the hot gas distribution in the inner eROSITA bubbles about 5 Myr ago.

Measuring gambling activity in options market

PurposeThis paper investigates how the gambling measure captures market bubble events, and how it predicts stock return and option return.Design/methodology/approachThis paper proposes a gambling activity measure by jointly considering open interest and moneyness of out-of-the-money (OTM) individual equity call options.FindingsThe new measure, CallMoney, captures excessive optimism during the dot-com bubble, the oil price bubble and the pre-GFC stock market bubble. CallMoney robustly and negatively predicts both OTM and at-the-money call option returns cross-sectionally. The option return predictability of CallMoney is stronger when stock price is further from its 52-weeks high, capital gains overhang is lower, and when information uncertainty of the underlying stock is higher. CallMoney also robustly and negatively predicts cross-sectional stock returns.Originality/valueThe gambling measure has the advantages of being economically intuitive, model-free, easy to measure. The measure performs more robustly than existing lottery measures with respect to option and stock return predictability and more reliably captures the overpricing of options and stocks. The work helps understanding the gambling related anomalies in equity option returns and stock returns.

On the Generation of an Unseasonal EPB Over South East Asia

AbstractAn unseasonal equatorial plasma bubble (EPB) event over South‐East Asia was observed on July 22, 2014 that has not been studied before. An investigation into this event is presented with the 26th July, 2014 as a comparison, non‐bubble day. The 22nd July EPB event occurred in the late post‐sunset sector and was associated with a small upward plasma drift. This event was highlighted using a new filter on the SCINDA S4 data. Ionosonde data show that sporadic E was present during the growth period for the EPB event. Modeling results from Thermosphere‐Ionosphere Electrodynamics (TEC) Global Circulation Model were used to conduct a numerical experiment investigating the direct effect of sporadic E on the linear R‐T growth rate. It was shown that sporadic E located in the correct latitude and local time can increase the linear growth rate. The seeding conditions were investigated using TEC data from Patumwan, Thailand. Wave‐like structures were observed for both days of interest, with larger amplitudes on 22nd July compared with the 26th July. Finally, simulations using the high‐resolution model PBMOD showed that for forcing from above conditions similar to the days of interest, EPBs would form in the presence of large seed perturbations. Therefore, it is likely that this unseasonal event was caused by large seed perturbations in TEC.

Case study of an Equatorial Plasma Bubble Event investigated by multiple ground-based instruments at low latitudes over China

Observational evidence is insufficient to understand how equatorial plasma bubbles (EPBs) form over low latitudes. The mechanism of plasma-density enhancement (formation of “plasma blobs”) at low latitudes is in dispute. In this paper, we use data from multiple ground-based instruments (one all-sky airglow imager, five digisondes, and one Fabry–Perot interferometer) to investigate the evolution of an EPB event that occurred at low latitudes over China on the night of 06 December 2015 (06-Dec-2015). We provide observational evidence that an enhanced equatorward wind most likely induced by a substorm could have initiated the Rayleigh–Taylor instability (RTI) that destabilized several EPB depletions in an upwelling region of a large-scale wave-like structure (LSWS) in the bottomside ionosphere. Those EPB depletions were forced to surge poleward, from nearly 10° to 19° magnetic latitude, two hours before midnight. Smaller-scale bifurcations evolved rapidly from tips of airglow depletions by a secondary E × B instability when the aforementioned substorm-induced southwestward wind blew through. During the growth phase of the EPB depletions, a westward polarization electric field inside the LSWS is likely to have compressed plasma downward, inducing the two airglow-type blobs observed in the bottomside ionosphere, by a mechanism of LSWS-blob connection that we propose. We also provide observational evidence of brightness airglow depletions. We find that an enhanced poleward wind associated with a passing-by brightness wave (BW) is likely to have transported plasma to fill the airglow depletions, which finally evolved into brightness airglow structures. This study investigates the physical processes accompanied by the EPB event and those two-airglow blobs observed at low-latitudes over China.

Forecasting Financial Crashes: A Dynamic Risk Management Approach

Since 2009, stock markets have resided in a long bull market regime. Passive investment strategies have succeeded during this low-volatility growth period. From 2018 on, however, there was a transition into a more volatile market environment interspersed by corrections increasing in amplitude and frequency. This calls for more adaptive dynamic risk management strategies, as opposed to static buy-and-hold strategies. To hedge against market drawdowns, the greatest source of risk that should accurately be estimated is crash risk. This article applies the Log-Periodic Power Law Singularity (LPPLS) model of endogenous asset price bubbles to monitor crash risk. The model is calibrated to 15 years market history for five relevant equity country indices. Particular emphasis is put on the US S&P 500 Composite Index and the recent market history of the year 2020. The results show that relevant historical bubble events, including the Corona crash, could be detected with the model and derived indicators. Many of these events were predicted in advance in monthly reports by the Financial Crisis Observatory (FCO) at ETH Zurich. The Corona crash, as the most recent event of interest, is discussed in further detail. Our conclusion is that unsustainable price dynamics leading to an unstable bubble, fuelled by quantitative easing and other policies, already existed well before the pandemic started. Thus, the bubble bursting in February 2020 as a reaction to the Corona pandemic was of endogenous nature and burst in response to the exogenous Corona crisis, which was predictable to some degree based on the endogenous price dynamics. Following the crash, a fast recovery of the price to pre-crisis levels ensued in the following months. This lets us conclude that, as long as the underlying origins and the macroeconomic environment that created this bubble do not change, the bubble will continue to grow and potentially spread to other sectors. This may cause even more hectic market behaviour, overreaction and volatile corrections in the future.

A robust and accurate technique for Lagrangian tracking of bubbles and detecting fragmentation and coalescence

A technique for Lagrangian tracking of bubbles and detecting their time-evolution behaviors is presented. Five possible behaviors are considered: formation, extinction, continuity, binary fragmentation, and binary coalescence. The technique is based on establishing a network of mappings between bubbles identified at adjacent time instants. The mappings are determined by selecting the minimum from a set of pseudo-distance errors, which are themselves based on constraints imposed on bubble position, velocity, and volume between adjacent time instants. The technique is validated through numerical inspection of the pseudo-distance errors and visual verification of over 16,000 bubble events identified in a simulated breaking wave. The accuracies for continuity, binary fragmentation, and binary coalescence are estimated to be 99.5%, 90%, and 95%, respectively, when the analysis is limited to bubbles of sizes of at least two grid lengths. The effects of varying pseudo-distance error parameters and time resolution are also investigated. The technique robustly tracks bubbles and the occurrence of binary fragmentation and binary coalescence in a breaking wave when these processes occur away from the complex air–water interface structures and bubbles are of comparable scale. Detecting the fragmentation and coalescence of large-scale and complex air–water interfaces remains an outstanding problem.