Short-period Oscillations Research Articles

Study the variation of the pitching frequency of sounding rockets

Sounding rockets typically feature an axially symmetric design and are launched vertically to facilitate research and high-altitude atmospheric data collection. Manufacturing errors can cause axial asymmetry, leading to undesirable rocket trajectory dispersion. Sounding rockets are often designed to spin around their axis to mitigate these effects. However, axial spinning motion can resonate with short-period oscillations, creating large normal loads that may damage the rocket’s structures. This paper focuses on analyzing the variations in the pitching frequency, which may help predict the roll resonance phenomenon. In this study, the authors constructed a six-degree-of-freedom dynamic model for a sounding rocket, considering all aerodynamic problems and the variation of inertial characteristics. To determine the pitching frequency, an impulse is applied to the rocket to generate short-period oscillation. The Fourier transform is then used to analyze and obtain the frequency of the rocket while oscillating in space. The results demonstrate agreement with the theoretical model, thereby substantiating the validity of the current method. The findings of this research provide valuable recommendations for the design and manufacturing process of sounding rockets, which may help mitigate the adverse effects of motion resonance during flight.

Repetitive shock waves generated by a single long pulse underwater arc discharge

The electrohydraulic effect induced by underwater arc discharge is an efficient way to generate controllable, high-intensity shock waves. However, the development process of underwater arc discharge involves the complex coupling of plasma arc, gas bubble, and liquid medium, of which the evolution mechanism is not well understood. In this paper, the underwater arc discharge process at a millisecond pulse (>50 ms) was investigated by high-speed shadow imaging and colorimetric temperature measurement, and a simulation model of bubble pulsation was proposed to quantitatively estimate the state variation and energy transfer of the gas bubble. The results indicate that the whole arc discharge process can be categorized into three successive stages: short-period oscillation, long-period oscillation, and quasi-steady state. The vapor inside the bubble can reach a supercritical state (827 K and 140 MPa) at the minimum bubble radius. The simulation shows that the light radiation absorption and the heat conduct loss through metal electrodes are the two dominant factors influencing the pulsation of the bubble, and further analysis indicates that the dynamic evolution of the arc determines the bubble pulsation mode. Our findings demonstrate why and how repetitive electrohydraulic shock waves can be generated by a single long pulse underwater arc discharge, providing a low-cost way of shock wave generator based on an AC/DC high-voltage power source.

Short-period flow oscillation during eruptions of Onikobe geyser, NE Japan: Insights from thermal infrared observation and acoustic measurements

Geysers are episodic features with variable eruption intervals that range from minutes to years. Although many previous studies on geysers have focused on subsurface properties and processes such as plumbing geometry and recharge process, it is known that erupting fluid column exhibits short-term behaviors such as individual water jets from the vent. In the present study, we conducted observations at Onikobe geyser, NE Japan, a relatively small geyser (geysering well) erupting water up to ∼6–8 m every ∼10 min and observed the erupting fluid column using a thermal infrared camera and an acoustic sensor. We succeed in tracking the water jets by analyzing spatio-temporal temperature map obtained from the thermal infrared observation, which clearly shows the eruptions at Onikobe geyser are not completely stationary but rather a series of intermittent jets with a short period interval of <1 s. We estimate the exit velocity by fitting a ballistic model under the air drag condition of inertial resistance to the jet trajectory. The exit velocity and the averaged gas volume fraction of the erupting fluid are estimated to be ∼4–79 m/s and ∼0.93–0.96, respectively. The exit velocity is ∼30 m/s during the first bursts, then it rapidly increases to ∼50–80 m/s for ∼15 s, and then decreases to ∼20–30 m/s until ∼10 s before the eruption ends. Time series analyses of the thermal infrared and acoustic signals during an eruption indicate harmonic spectra with integer multiple peaks. The fundamental frequency showing ∼4 Hz at the beginning gradually decreases to ∼2 Hz for ∼15 s, keeps almost constant in the following 30 s, and then slightly increases near the end of the eruption. These harmonic spectra may be caused by a resonance mechanism, non-linear fluid motion, and/or subsurface two-phase flow. We discuss the case of a closed organ-pipe resonance in a subsurface crack and attribute the frequency decrease to a decrease in the water level in the crack (an increase in the length of the resonating liquid-vapor column) and/or a decrease in the gas volume fraction of the liquid-vapor mixture in the crack. Since such harmonic characteristics are observed at other geysers, further simultaneous observation of the short-period oscillations on the erupting column proposed in this study with seismic observations of harmonic tremor may provide an improved understanding of geyser subsurface phenomena.

Statistical investigation of decayless oscillations in small-scale coronal loops observed by Solar Orbiter/EUI

Decayless kink oscillations are omnipresent in the solar atmosphere, and they are a viable candidate for coronal heating. Although there have been extensive studies of decayless oscillations in coronal loops with lengths of a few hundred megameters, the properties of these oscillations in small-scale (∼10 mm) loops are yet to be explored. In this study, we present the properties of decayless oscillations in small loops embedded in the quiet corona and coronal holes. We use high-resolution observations from the Extreme Ultraviolet Imager on board Solar Orbiter with pixel scales of 210 km and a cadence of 5 s or better. We analysed 42 oscillations in coronal loops with loop lengths varying between 3 to 23 mm. The average displacement amplitude is found to be 134 km. The oscillations period has a range of 28 to 272 s, and the velocity amplitudes range from 2.1 to 16.4 km s−1. The variation in the loop length with the period does not indicate a significant correlation. The wave mode of these waves is uncertain, and standing waves are one possibility. Our results for the coronal seismology and energy flux estimates were obtained considering standing modes. The observed kink speeds are lower than those observed in active region coronal loops. We obtain an average magnetic field value of 2.1 G. We estimated the energy flux with a broad range of 0.6–313 W m−2. Moreover, we note that short-period decayless oscillations are not prevalent in the quiet Sun and coronal holes. Our study suggests that decayless oscillations in small-scale coronal loops are unlikely to provide enough energy to heat the quiet Sun and accelerate solar wind in coronal holes.

Absolute properties of the oscillating eclipsing Algol XZ Ursae Majoris

Abstract It is known from archival TESS data that the semi-detached Algol system XZ Ursae Majoris (UMa) is one of the candidate binary stars exhibiting short-period oscillations. We secured new high-resolution spectroscopic observations for the program target to better understand its binary and pulsation properties. From the echelle spectra, the radial velocities (RVs) of the eclipsing pair were derived, and the atmosphere parameters of the primary component were measured to be vAsin i = 80 ± 7 km s−1, Teff, A = 7940 ± 120 K, and [M/H] = −0.15 ± 0.20. The combined solution of our double-lined RVs and the TESS data provides robust physical parameters for XZ UMa with mass and radius measurement precision of better than 2%. The outside-eclipse residuals from a mean light curve in the 0.002 phase bin were used for multifrequency analyses, and we extracted 32 significant frequencies (22 in &amp;lt;5.0 d−1 and 10 in 39–52 d−1). The low frequencies may be mostly aliasing sidelobes, while six of the high frequencies may be pulsation signals arising from the detached primary located inside the δ Sct domain. Their periods, pulsation constants, and pulsational–orbital-period ratios indicate that the mass-accreting primary star is a δ Sct pulsator and, hence, XZ UMa is an oscillating eclipsing Algol.

On the existence of ‘Maia variables’

Abstract There are different classes of pulsating stars in the H-R diagram. While many of those classes are undisputed, some remain a mystery such as the objects historically called ‘Maia variables’. Whereas the presence of such a class was suggested seven decades ago, no pulsational driving mechanism is known that could excite short-period oscillations in these late B to early A-type stars. Alternative hypotheses that would render the reports of variability of those stars erroneous have been proposed such as incorrect effective temperatures, binarity or rapid rotation, but no certain conclusions have been reached yet. Therefore, the existence of these variables as a homogeneous class of pulsating star is still under discussion. Meanwhile, many new candidates of these variables have been claimed especially by using photometric observations of space telescopes. In this study, we examined 31 objects that are alleged members of this hypothetical group and carried out detailed spectroscopic and photometric analyses to test the proposed hypotheses for their cause of variability. The $T_\textrm{eff}$ , $\log g$ , $v \sin i$ , and chemical abundances of the targets were determined and the TESS photometric data were examined. As a result, we found that most of these targets are located inside the $\delta$ Scuti, $\beta$ Cephei, or SPB star instability strips, a few show evidence for binarity and others for rapid rotation. We give arguments that none of the apparently rapid pulsations in our targets is caused by a star outside any known instability strip. By extrapolation, we argue that most stars proposed as pulsators outside well-established instability domains are misclassified. Hence there is no sufficient evidence justifying the existence of a class of pulsating stars formerly known as the ‘Maia variables’.

Flight Dynamic Characteristics of Wide-Body Aircraft with Wind Gust and Turbulence

In this research, a wide-body aircraft was analyzed with critical monitoring of its states, a function of several control inputs (wind gust, turbulence, and microburst). The aerodynamic and stability coefficients of a Boeing 747-200 were obtained from previously published works and 6- DOF equations were formulated. Simulations were conducted for various control inputs to determine the aircraft’s free response, as well as the forced response. In order to understand the nature of the atmosphere, three different models were incorporated, including (i) the Dryden Model, (ii) wind gust, and (iii) microburst. The aircraft was found to be stable in the longitudinal and lateral flight modes, with trim conditions agreeing with published data. For a vertical wind gust of −10 ft/s, the AoA and pitch rate were observed to oscillate sinusoidally and became stable with new trim conditions. These states were found to regain trim conditions once the gust was removed. In the case of 3D gust, it was found that the longitudinal modes achieved a new trim condition through Phugoid oscillations, whereas the lateral modes underwent short-period oscillations. For the case of turbulence, random fluctuations were observed for trim conditions with no unstable behavior. When considering the microburst case, it was found that the aircraft initially gained altitude in the region of the headwind; this was followed by a sharp descent under the influence of a vertical velocity component.

Storm Franz: Societal and energy impacts in northwest Europe on 11–12 January 2007

Abstract. January 2007 was a bad storm month for much of central and northern Europe with a series of extratropical cyclones bringing high winds and precipitation to highly populated areas between Ireland and Russia. Although Storm Kyrill on 18–19 January 2007 was the most serious for its infrastructure damage and insurance costs, Storm Franz from the preceding week on 11–12 January 2007 was actually more serious for its maritime impacts in western Europe. This contribution takes a closer look at Storm Franz with an overview of its wind field and its impact on energy infrastructure, transportation networks and building damage. Maritime casualties are reviewed with respect to met-ocean conditions. The storm was notable for a series of wave-related accidents off southeast Ireland, the English Channel, and German Bight. An analysis is carried out on water level recorders around the North Sea to assess the storm surge and short period oscillations that may reveal harbour seiches or meteotsunamis. The results are compared with wave recorders, which had a fairly good coverage across the North Sea in 2007. The issue of wave damage to offshore infrastructure was highlighted in events associated with Storm Britta on 31 October–1 November 2006. Offshore wind energy in northwest Europe was in a growth phase during this time, and there were questions about the extreme met-ocean conditions that could be expected in the 20 year lifetime of an offshore wind turbine.

Analysis of the eastern Adriatic sea level extremes

Aim: To examine the frequency, strength, and driving mech-anisms of the eastern Adriatic sea level extremes.Methods: In 2017, a tide-gauge station, and a meteorological station have been installed at Stari Grad (Hvar Island, east-ern middle Adriatic Sea). Three years of sea level and at-mospheric measurements were analysed. Ten strongest ep-isodes of the following extreme types were extracted from sea level data: positive long-period (T &amp;gt;210 min) extremes; negative long-period (T &amp;gt;210 min) extremes; short-period (T &amp;lt; 210) extremes. Long-period extremes were defined as situations when sea level surpasses (is lower than) 99.7 (i.e., 2) percentile of residual long-period sea level height, and short-period extremes as situations when 2.5-h variance of short-period sea level oscillations is higher than 99.4 per-centile of total variance of short-period series. Types of sea level extremes were subsequently associated to characteris-tic atmospheric situations.Results: Positive long-period extremes commonly appeared during the presence of low-pressure atmospheric systems over the Adriatic – such system were accompanied with strong SE winds. Negative long-period extremes were as-sociated with presence of high atmospheric pressure fields over the Adriatic Sea, either with strong NE winds, or calm weather. Appearance of short-period sea level extremes corresponded to either low atmospheric pressure fields and strong SE wind, or normal/high pressure fields and calm weather/no winds over the Adriatic. A strong seasonal sig-nal was detected, with the positive long-period extremes occurring mostly during November to February, and the negative long-period extremes occurring during January to February. The short-period extremes appeared throughout the year, but strongest events appeared during May to July.Conclusion: Results show that Stari Grad is a flood-prone lo-cation, both when it comes to positive long-period extremes and to short-period extremes. Furthermore, long-period and short-period extremes occasionally occur simultane-ously in Stari Grad, pointing to a previously unknown added hazard level

Experimental investigation of bubble dynamics and flow patterns during flow boiling in high aspect ratio microchannels with the effect of flow orientation

Multiphase flow and boiling phase-change within microchannels are of paramount importance to thermal management and electronics cooling, among others. The present experimental study investigated the bubble dynamics and flow patterns during flow boiling in a high aspect ratio microchannel at different channel orientations. Hydrofluoroether (HFE−7000) was used as the working fluid within a transparent glass microchannel with a width-to-height aspect ratio of 10 and a hydraulic diameter of 909 μm. A tantalum layer coating was applied to the channel, allowing visual observation to be conducted whilst imposing uniform heating along the channel. Under horizontal and vertical upward flow, the mass fluxes were varied between 14 kg m−2 s−1 and 42 kg m−2 s−1 for Reynolds numbers between 28.4 and 85.2, while the heat fluxes were set from 2.8 kW m−2 to 18.7 kW m−2. The results show that single bubble growth can be divided into three stages, namely: bubble-free growth, partially confined bubble growth, and fully confined growth. The effects of mass flux and heat flux on bubble behaviour and transition points between the defined stages are discussed. Equally important, the channel orientation influences the bubble behaviour in terms of bubble evolution, bubble shape, and bubble nose velocity, with no significant differences observed for the flow patterns when comparing horizontal and vertical upward cases. The comparison of the present work with previous flow pattern map results from the literature shows that earlier flow pattern transition models cannot accurately predict the observed flow patterns in the present configuration. Two types of instabilities are observed, which are associated with the dominant flow pattern during flow boiling and hence a function of the mass flux to heat flux ratio. The first type of instability, high amplitude and long period oscillation, is found during slug flow which is characterised by the presence of bubble rapid expansion along the channel. In addition, a second instability ensues when churn and annular flow create short period oscillations due to the high number of nucleation events, bubble coalescence, and the breakage of liquid slug or liquid film.

A Statistical Study of Short-period Decayless Oscillations of Coronal Loops in an Active Region

Coronal loop oscillations are common phenomena in the solar corona, which are often classified as decaying and decayless oscillations. Using the high-resolution observation measured by the Extreme Ultraviolet Imager (EUI) on board the Solar Orbiter, we statistically investigate small-scale transverse oscillations with short periods (<200 s) of coronal loops in an active region (AR), i.e., NOAA AR 12965. A total of 111 coronal loops are identified in EUI 174 Å images, and they all reveal transverse oscillations without any significant decaying, regarded as decayless oscillations. Oscillatory periods are measured from ∼11 to ∼185 s, with a median period of 40 s. Thus, they are also termed short-period oscillations. The corresponding loop lengths are measured from ∼10.5 to ∼30.2 Mm, and a strong dependence of oscillatory periods on loop lengths is established, indicating that the short-period oscillations are standing kink-mode waves in nature. Based on the coronal seismology, kink speeds are measured to be ∼330–1910 km s−1, and magnetic field strengths in coronal loops are estimated to be ∼4.1–25.2 G, while the energy flux carried by decayless kink oscillations lies in the range from roughly 7 to 9220 W m−2. Our estimations suggest that the wave energy carried by short-period decayless kink oscillations cannot support the coronal heating in the AR.

Acoustic response in the transition region to transverse oscillations in a solar coronal loop

Context. Magnetohydrodynamic (MHD) waves play an important role in the dynamics and heating of the solar corona. Transverse (Alfvénic) oscillations of loops commonly occur in response to solar eruptions and are mostly studied in isolation. However, acoustic coupling has been shown to be readily observable in the form of propagating intensity variations at the loop footpoints. Aims. We extend the modelling of wave coupling between a transverse loop oscillation and slow magnetoacoustic waves in a structured loop to include a lower atmosphere. Methods. We achieve this with combined analytical modelling and fully non-linear MHD simulations. Results. Transverse loop oscillations result in the excitation of propagating slow waves from the top of the transition region and the lower boundary. The rate of excitation for the upward propagating waves at the lower boundary is smaller than for waves at the top of the transition region due to the reduced local sound speed. Additionally, slow waves are found to propagate downwards from the transition region, which reflect at the lower boundary and interfere with the upward propagating waves. Resonances are present in the normal mode analysis but these do not appear in the simulations. Due to the presence of the transition region, additional longitudinal harmonics lead to a narrower slow wave profile. The slow wave field is anti-symmetric in the direction of wave polarisation, which highlights the importance that the loop orientation has on the observability of these waves. The ponderomotive effect must be accounted for when interpreting intensity oscillations. Evidence is found for an additional short-period oscillation, which is likely a hybrid mode.

Mars 2020 Perseverance Rover Studies of the Martian Atmosphere Over Jezero From Pressure Measurements.

The pressure sensors on Mars rover Perseverance measure the pressure field in the Jezero crater on regular hourly basis starting in sol 15 after landing. The present study extends up to sol 460 encompassing the range of solar longitudes from L s ∼13°-241° (Martian Year (MY) 36). The data show the changing daily pressure cycle, the sol-to-sol seasonal evolution of the mean pressure field driven by the CO2 sublimation and deposition cycle at the poles, the characterization of up to six components of the atmospheric tides and their relationship to dust content in the atmosphere. They also show the presence of wave disturbances with periods 2-5 sols, exploring their baroclinic nature, short period oscillations (mainly at night-time) in the range 8-24min that we interpret as internal gravity waves, transient pressure drops with duration ∼1-150s produced by vortices, and rapid turbulent fluctuations. We also analyze the effects on pressure measurements produced by a regional dust storm over Jezero at L s ∼155°.

Study of Neptune dayside magnetosheath fluctuations during Voyager-2 flyby

Turbulence in the outer planetary magnetospheres has been relatively less studied than in the Earth’s magnetosphere, especially for the ice giants which have been visited only by the Voyager-2 spacecraft so far. The aim of this work is to study the turbulence in Neptune’s dayside magnetosheath. Voyager-2 magnetometer 3-s averaged magnetic field data were analyzed with several data analysis techniques. It was found that most of the magnetosheath magnetic field is aligned in the BT direction. The BR-component spectrum showed the predominance of short-period (5minutes) oscillations, while the BT- and BN- components showed the occurrence of longer-period (20–50minutes) oscillations. The Fourier spectrum of the magnetic field showed a breakpoint near 0.00165Hz. The lower frequency portion showed index (absolute values) smaller than 1.0. The higher frequency portion showed a much steeper spectrum, with power law values varying from about 2.0 to 2.4. The statistical kurtosis parameters for BR and BN are higher than 3 in almost all scales, while the BT component (main field direction) has a more Gaussian or sub-Gaussian behavior, specially in scales higher than 20minutes. The kurtosis is very high at the low frequency spectral power of 40minutes for the BN-component, indicating asymmetric or non-Gaussian magnetic field distribution in the magnetosheath. The multifractal spectrum is well spread in the magnetosheath revealing a rich and dynamic activity in this region. Overall, the Neptune’s magnetosheath is found to have a strong turbulence activity that is comparable to that of other planetary magnetosheaths.

Measuring the precise photometric period of the intermediate polar 1RXS J230645.0+550816 (1SWXRT J230642.7+550817) based on extensive photometry

Recently, Halpern et al. discovered an oscillation with a period of 464 s in the cataclysmic variable 1RXS J230645.0+550816. I conducted extensive photometric observations of this object to clarify the coherence of this oscillation and to measure the oscillation period with high precision. Observations were obtained over 22 nights in 2018 and 2019. The total duration of observations was 110 hr. The oscillation was revealed in each long night of observations and was coherent throughout all my observations covering 15 months. Due to the large coverage of observations, I determined the oscillation period with high precision, which was 464.45600+\-0.00010 s. The oscillation semi-amplitude was large and showed changes from 41.8+\-1.5 mmag in 2018 to 48.6+\-1.8 mmag in 2019. The oscillation pulse profile was symmetrical with a noticeably wider minimum compared to the maximum and showed no noticeable changes during 2018 and 2019. The high precision of the oscillation period allowed me to derive an oscillation ephemeris with a long validity of 70 years. This ephemeris can be used for future studies of oscillation period changes. Although short-period X-ray oscillations have not yet been detected in 1RXS J230645.0+550816, the intermediate polar nature of this object is very probable due to the high degree of coherence of the 464-s oscillation.

Regionality of short and long period oscillators in the suprachiasmatic nucleus and their manner of synchronization.

In mammals, the center of the circadian clock is located in the suprachiasmatic nucleus (SCN) of the hypothalamus. Many studies have suggested that there are multiple regions generating different circadian periods within the SCN, but the exact localization of the regions has not been elucidated. In this study, using a transgenic rat carrying a destabilized luciferase reporter gene driven by a regulatory element of Per2 gene (Per2::dLuc), we investigated the regional variation of period lengths in horizontal slices of the SCN. We revealed a distinct caudal medial region (short period region, SPR) and a rostro-lateral region (long period region, LPR) that generate circadian rhythms with periods shorter than and longer than 24 hours, respectively. We also found that the core region of the SCN marked by dense VIP (vasoactive intestinal peptide) mRNA-expressing neurons covered a part of LPR, and that the shell region of the SCN contains both SPR and the rest of the LPR. Furthermore, we observed how synchronization is achieved between regions generating distinct circadian periods in the SCN. We found that the longer circadian rhythm of the rostral region appears to entrain the circadian rhythm in the caudal region. Our findings clarify the localization of regionality of circadian periods and the mechanism by which the integrated circadian rhythm is formed in the SCN.

Two-spacecraft detection of short-period decayless kink oscillations of solar coronal loops

ABSTRACT Decayless kink oscillations of an ensemble of loops are captured simultaneously by the High Resolution Imager (HRI) of the Extreme Ultraviolet Imager (EUI) and the Atmospheric Imaging Assembly (AIA) from 22:58 ut on 2021 November 5 to 00:27 ut on 2021 November 6. Oscillations are analysed by processing image sequences taken by the two instruments with a motion magnification technique. The analysed loops are around 51 Mm in length, and oscillate with short periods of 1–3 min (1.6 min in average) and displacement amplitudes of 24–83 km. The signals recorded by AIA are delayed by 66 s as compared to HRI, which coincides with the light traveltime difference from the Sun to each instrument. After correction of this time difference, the cross-correlation coefficient between the signals from the two data varies from 0.82 to 0.97, indicating that they are well consistent. This work confirms that HRI sees the same oscillations as AIA, which is the necessary first step before proceeding to the detection of shorter time-scales by EUI. In addition, our results indicate the robustness of the dejittering procedure in the study of kink oscillations with HRI.

On the behavior of thermospheric O1D 630.0 nm dayglow emission during counter electrojet events

This study presents the response of thermospheric O1D 630.0 nm dayglow emission to the variability associated with equatorial Counter Electrojet (CEJ) events. The analysis based on the data from a meridian scanning Dayglow Photometer, Digital Ionosonde and Proton Precession Magnetometer over Trivandrum (8.5°N, 77°E, 0.5°dip lat.), indicates that the O1D 630.0 nm emission behave distinctly different during the CEJ events compared to that on normal days. It has been observed that O1D 630.0 nm emission shows enhancement during the negative excursion of the ΔH, followed by an unusual depletion during the peak CEJ time. The observed variability was found to be more pronounced in a latitudinal region of ±3° centered at around the dip equator. In addition, the emission intensities also exhibit the presence of enhanced short period oscillations of periodicity 20–30 min during the CEJ events. Analysis of the data from the collocated ionosonde revealed that the F-region electron density showed enhancement during the early phase of the CEJ and a decrease during the peak CEJ. Further, the simulation studies using a Quasi 2 dimensional ionospheric model showed that the modified plasma fountain during the CEJ can alter the plasma density at the emission centroid. The study reveals a strong dynamical coupling between the E and F-region of the dip equatorial ionosphere.

Results of comparison of fast variations of geomagnetic field and ionospheric scintillations of 3C 144 radio source in the area of Odessa geomagnetic anomaly

From November 2017 to May 2019 at the Astronomical Observatory of Odessa I.I. Mechnikov National University, the variational component of the geomagnetic field was monitored to study short-periodic geomagnetic variations in the central part of the Odessa regional magnetic anomaly. The measurements were carried out using a LEMI-008 precision fluxgate magnetometer with a sampling rate of 1 Hz. The aim of this work is to compare the manifestation of short-periodic geomagnetic oscillations (which in some cases coincided with periods of geomagnetic pulsations) and ionospheric scintillations of the 3C 144 radio source (Taurus A) according to the data of URAN-4 low-frequency phased antenna array at frequencies of 20 and 25 MHz. The data obtained were processed on a daily basis using the method of continuous wavelet transform, as well as band-pass filtering based on Fourier transform, to select individual frequency bands containing irregular and quasi-harmonic variations in the geomagnetic field and radio flux density. The analysis of results of the observations, during geomagnetic disturbances, storms and in calm conditions, is carried out. The data from long-term monitoring of variational component of the geomagnetic field in the most interesting, central part of the Odessa magnetic anomaly, where such studies have not been conducted before, have been obtained. Observations of various manifestations of ionospheric scintillations were carried out both during magnetic storms and during a calm geomagnetic field. It is shown that during storms, main scintillation time scale of the 3C 144 radio source is 1–3 minutes. Ionospheric scintillations occasionally show a quasiperiodic structure.

Behaviors of type-I instabilities in natural circulation with a heating channel under ocean conditions

Characteristics of two-phase natural circulation and density wave instability with a single-heating channel under ocean conditions were studied by using PNCMC PROGRAM (Program for Natural Circulation under Motion Condition). The superposition laws of oscillations of both mass flow rate and density wave caused by ocean conditions are found, and the corresponding stability boundaries of the natural circulation system are also proposed here. The use of a simplified mathematical description of fluid flow to describe the additional motions with waves reduces the difficulty of analysis. Specifically speaking, based on the study of stability boundary in vertical condition, first of all, it was found that inclined ocean condition can weaken the ability of natural circulation and can move down stability boundary of natural circulation, and the greater the inclination angle, the greater the amount of going-down. Secondly, the stability boundary of the system moves up in heaving circumstances, and the smaller the period, the greater the amount of going-up. Thirdly, the amplitude of rolling plays an important role in the rolling situation. In the case of rolling with large amplitude, the period of flow complex oscillation is clear, which is half the rolling period. However, in the case of rolling with a short period, the period of flow complex oscillation is ambiguous, the oscillation frequency of density wave under vertical condition is preserved in the flow complex oscillation. The stability boundary of natural circulation is moved down by rolling with a short period, where the frequency of flow complex oscillation was equal to that of density wave oscillation under vertical conditions. In contrast, the stability boundary of natural circulation is moved up by rolling with a long period, where the short-period local oscillation appears in the process of flow complex oscillation. Finally, the oscillation superpositions of rolling and heaving motion will result in a complex long-period oscillation with motion amplitudes being important.