Short-period Variations Research Articles

Short-period variations in microphysical characteristics of aerosol nanoparticles in the dry steppe zone of southern Russia in summer

Short-period variations in microphysical characteristics of aerosol nanoparticles in the dry steppe zone of southern Russia in summer

Hybrid Method of Uncertainty Propagation for Near-Earth Conjunction Analysis

In this research, several existing semi-analytical dynamics and uncertainty propagation techniques are combined with conjunction models to achieve fast and accurate probability of collision results. Initial Gaussian uncertainty associated with two objects is split into smaller Gaussian distributions using Gaussian mixture models to achieve mixture components that will maintain linearity over longer propagation times. These mixture components are propagated forward using second-order state transition tensors that can capture the nonlinearity in the propagation accurately by taking into account the desired dynamics. The dynamic solution and these tensors are computed using the Deprit–Lie averaging approach, including transformations between mean and osculating states, which accounts for perturbations due to solar radiation pressure and J2. This simplified dynamic system allows fast and accurate propagation by combining the speed of propagation with averaged dynamics and the accuracy of short-period variation addition. Combined, these mathematical tools are used to propagate the object’s uncertainties forward. The final distributions are compared using analytical conjunction methods to compute the probability of collision, which is then compared to the Monte Carlo result to confirm the method’s validity.

On geomagnetic feld short-period variations and their application to study the geoelectric structure of the Ural region

On geomagnetic feld short-period variations and their application to study the geoelectric structure of the Ural region

Characterizing the Water Storage Variation of Kusai Lake by Constructing Time Series from Multisource Remote Sensing Data

In September 2011, Zhuonai Lake (ZL) in the northeast of Hoh Xil (HX) on the Qinghai–Tibet Plateau (QTP) broke out. The outburst event seriously changed the environmental hydraulics in this region. Due to the insufficient temporal resolution of observations, it is challenging to assess the impact of this event on short-period variations of water volumes in three lakes downstream of ZL. Combining multisource remote sensing data, we constructed long and high-temporal-resolution time series for the lake level, area, and lake water storage (LWS) of Kusai Lake (KL) to characterize the variabilities before and after the outburst. The water level, area, and LWS time series contain 1051 samples from 1990 to 2022, with uncertainties of 0.16 m, 2.5 km2, and 0.016 km3, respectively. The accuracies verified using the Database for Hydrological Time Series of Inland Waters (DAHITI) are 0.26 m, 2.64 km2, and 0.08 km3 for water level, area, and LWS, respectively. We characterized the LWS variations during the past 30 years based on the high temporal resolution LWS time series. Before the outburst, the 1-year and 3.5-year variations dominated the LWS time series, and there was no obvious semi-annual signal. After the outburst, the 3.5-year variation disappeared, and a strong semi-annual oscillation was observed. From 2012 to 2015, the periodic LWS variations in KL were disturbed by the ZL outburst and the subsequent outflow of KL led by the outburst. Regular cyclic signals have been restored since 2016, with an amplified annual fluctuation. By analysis, precipitation, evaporation, and glacier area change are excluded as driving factors of the pattern change in LWS variations of KL. It can be concluded that the altered recharge pattern of KL triggered by the outburst directly resulted in the observed changes in TWS behavior. For the first time, we identified the periodic patterns of LWS variations of KL during the past 30 years and revealed that the ZL outburst event significantly influenced these patterns. This finding contributes to the comprehensive understanding of the effects of the ZL outburst on downstream lake dynamics. Furthermore, the presented procedure for constructing long and high-resolution time series of LWS allows for monitoring and characterizing the short-period variabilities of Tibetan lakes that lack hydrological data.

Astronomical control on organic matter enrichment of lacustrine mudstones in the first member of the Late Cretaceous Qingshankou Formation, the Songliao Basin, NE China

Astronomical forcing has an important effect on organic matter enrichment in marine mudstones, but this effect remains poorly constrained in lacustrine mudstones. Here, we investigate the astronomical control of organic matter enrichment in lacustrine black mudstone from the first member of the Qingshankou Formation in the Songliao Basin. Detailed mineralogical, lithological, geochemical, and cyclostratigraphic studies were carried out. The results show that there are high-frequency variations in the organic matter content in the mudstones of the Qingshankou Formation. The upper and lower sections are further divided according to the organic matter content level and the variation frequency. The organic matter content in the lower section is high, up to 6.08 wt%, with long-period variation and individual cycles around 10 m. The organic matter content in the upper section is relatively low, the highest organic matter content is only 2.91 wt%, with short-period variation and individual cycles mostly less than 5 m. Cyclostratigraphic studies indicate that significant astronomical signals are recorded in the mudstone stratigraphy. 100 kyr short eccentricity and 38 kyr obliquity strongly control the variation of organic matter content in the lower and upper sections, respectively. Organic matter enrichment has a closely synchronized phase relationship with paleoproductivity, preservation conditions, and dilution indicators. Astronomical cycles influence the depositional conditions of organic matter enrichment by controlling climate change, which eventually forces organic matter enrichment. At high values of eccentricity and obliquity, enhanced insolation, monsoon, precipitation, and river runoff caused lake expansion, increased input of terrestrial nutrients, and increased bottom water reduction conditions, which are conducive to organic matter enrichment. On the contrary, the depositional conditions for organic matter enrichment become poor.

Short-Period Variation of the Activity of Atmospheric Turbulence in the MLT Region over Langfang

In this paper, we investigate the activity of atmospheric turbulence in the MLT region and the relationship between the activity of atmospheric turbulence and atmospheric wave activity. We use data from the Langfang MF radar (39.4∘N, 116.7∘E) from July 2019 to June 2020 and NRLMSIS 2.0 to calculate the parameters of atmospheric wave activity and atmospheric turbulence energy dissipation rate (ε). Atmospheric ε is modulated by different periods at different altitudes, and while there are 12 h and 24 h periods at all altitudes, the main period is different at different altitudes. A comparison of the ε with atmospheric tide activity shows that tides have an effect on ε, and the influence of tides on ε may be different at different altitudes. The pattern of variation in ε is similar to that of the atmospheric activity of the gravity wave, with both ε and the atmospheric activity of the gravity wave showing significant semi-annual variation.

Prediction of Extremely Severe Cyclonic Storm “Fani” Using Moving Nested Domain

The prediction of extremely severe cyclonic storms has been a long-standing and challenging issue due to their short life period and large variation in intensities over a short time. In this study, we predict the track, intensity, and structure of an extremely severe cyclonic storm (ESCS) named ‘Fani,’ which developed over the Bay of Bengal region from 27 April to 4 May 2019, using the Advanced Research version of the Weather Research and Forecasting (WRF-ARW) model. Two numerical experiments were conducted using the moving nested domain method with a 3 km horizontal resolution, one with the FLUX-1 air-sea flux parameterization scheme and the other with the FLUX-2 air-sea flux parameterization scheme. The NCEP operational Global Forecast System (GFS) analysis and forecast datasets with a 25 km horizontal resolution were used to derive the initial and boundary conditions. The WRF model’s predicted track and intensity were validated with the best-fit track dataset from the India Meteorological Department (IMD), and the structure was validated with different observations. The results showed that the WRF model with the FLUX-1 air-sea parameterization scheme accurately predicted the track, landfall (position and time), and intensity (minimum sea level pressure and maximum surface wind) of the storm. The track errors on days 1 to 4 were approximately 47 km, 123 km, 96 km, and 27 km in the FLUX-1 experiment and approximately 54 km, 142 km, 152 km, and 166 km in the FLUX-2 experiment, respectively. The intensity was better predicted in the FLUX-1 experiment during the first 60 h, while it was better predicted in the FLUX-2 experiment for the remaining period. The structure, in terms of relative humidity, water vapor, maximum reflectivity, and temperature anomaly of the storm, was also discussed and compared with available satellite and Doppler Weather Radar observations.

Reconstruction of horizontal tidal current fields in a shallow water with model-oriented coastal acoustic tomography

Reciprocal acoustic transmission and coastal acoustic tomography (CAT) is a powerful tool for measuring tidal currents in shallow coastal water, especially if data assimilation is employed. In previous CAT data assimilation studies, the ensemble Kalman filter (EnKF) has been implemented to assimilate observed path-averaged velocity, but ad-hoc procedures called localization and inflation, which compensate for issues associated with using ensemble approximation, were not always implemented. In this study, EnKF is applied to assimilate the path-averaged currents obtained from a reciprocal acoustic transmission experiment conducted at Mihara-Seto in the Seto Inland Sea, Japan, with four acoustic stations in 2020 to reconstruct spatiotemporal variations of tidal currents at the observation site. We executed EnKF with several combinations of different values of the inflation, localization, and the number of ensemble members. The resulting data assimilated velocity reconstructions are compared with acoustic Doppler current profiling (ADCP) results. The results show that data assimilation with EnKF improved the velocity reproduction compared with the model prediction and that implementing covariance inflation contributed to additional improvements. The covariance localization did not improve the results in our case. The best result in terms of fractional error variance (FEV) between the ADCP velocity was obtained from the case with 980 ensemble members with a covariance inflation of 1.01; the FEV was 7.9%. The case of 98 ensemble members with a covariance inflation of 1.01 resulted in similar performance; the FEV value was 8.2%. Thus, with the covariance inflation, the number of ensemble member used in previous CAT studies are reasonable. In the study, we also clarified the reason for the high-frequency variation in the observed path-averaged currents in a preliminary experiment; the path-averaged currents had captured the spatiotemporal variation of vortex generation associated with island wakes. The reciprocal acoustic transmission with EnKF can capture short-period variation over a long period; thus, it can be used in studies of coastal physical processes with various time scales.

Variability of DMS in the East China Sea and its response to different ENSO categories

Dimethylsulfide (DMS) produced by marine phytoplankton is the most important volatile sulfur compound in ocean surface seawater and has a distinct contribution to global climate change. To assess DMS-climate feedbacks, the interannual variations in seawater DMS concentrations in the East China Sea (ECS) were examined, and their periodic characteristic patterns related to different El Niño-Southern Oscillation (ENSO) categories were discussed. Based on satellite surface seawater temperature (SST) and chlorophyll-a (Chl-a) datasets, a 23-year (1998–2020) dataset of DMS concentrations in the ECS was hindcasted by using a generalized additive mixed model (GAMM). The ENSO events from 1998 to 2020 were selected and divided into persistent, recession and transformed types according to their development process. The variability of surface seawater DMS concentration in the Yangtze River Estuary and its adjacent seas, the coast of Zhejiang and Fujian, and the coast of northern Jiangsu are more strongly influenced by ENSO events than the remainder of the ECS. Furthermore, ENSO alters the seasonal variability in DMS concentrations in the Yangtze River Estuary. The DMS concentrations of Apr-Jul were reduced (enhanced) by approximately 3.05 (0.61) nmol/L during Persistent El Niño (PEN) (Persistent La Niña (PLN)) events, which were reduced by approximately 0.51 and 1.10 nmol/L during recessionary El Niño (REN) event and recessionary La Niña (RLN) event, respectively. However, the DMS concentrations were enhanced by approximately 0.53 (1.29) nmol/L during El Niño-La Niña transition (ELT) (La Niña-El Niño transition (LET)) events. ENSO events affected the DMS concentrations in the surface seawater of the study area by influencing Chl-a and SST, where the short-period interannual variability (2–3 years) of DMS was mainly affected by SST, while the interannual variability of the long period (6 years) was mainly affected by Chl-a. The findings can be applied to the development of DMS concentration prediction methods.

A Quantitative Assessment of LIDAR Data Accuracy

Airborne laser scanning sensors are impressive in their ability to collect a large number of topographic points in three dimensions in a very short time thus providing a high-resolution depiction of complex objects in the scanned areas. The quality of any final product naturally depends on the original data and the methods of generating it. Thus, the quality of the data should be evaluated before assessing any of its products. In this research, a detailed evaluation of a LIDAR system is presented, and the quality of the LIDAR data is quantified. This area has been under-emphasized in much of the published work on the applications of airborne laser scanning data. The evaluation is done by field surveying. The results address both the planimetric and the height accuracy of the LIDAR data. The average discrepancy of the LIDAR elevations from the surveyed study area is 0.12 m. In general, the RMSE of the horizontal offsets is approximately 0.50 m. Both relative and absolute height discrepancies of the LIDAR data have two components of variation. The first component is a random short-period variation while the second component has a less significant frequency and depends on the biases in the geo-positioning system.

СИНОПТИЧЕСКАЯ СОСТАВЛЯЮЩАЯ МЕТЕОРОЛОГИЧЕСКИХ ЭЛЕМЕНТОВ НАД ЮЖНОЙ ЧАСТЬЮ БАЛТИЙСКОГО МОРЯ

Based on field observations of air temperature Ta, relative humidity f (dew point temperature Td or water vapor elasticity ea), atmospheric pressure at sea level P0 and wind speed W at stations Arkona, Darss Sill and Fehmarn-Belt of the MARNET monitoring network of the German Oceanographic Datacentre for 2002–2020 with a discreteness of 1 hour, as well as on the offshore ice-resistant stationary platform of OOO LUKOIL – Kaliningradmorneft (D6) for 2004–2020 with a discreteness of 1 hour, estimates of the contributions of the short-term (consisting of irregular intradiurnal, regular daily variation, synoptic component) and long-term (consisting of irregular intra-annual, regular seasonal variation and inter-annual component) variability into the total temporal variability of the initial series of these meteorological elements. The influence of the location of the station and the nature of the meteorological element itself on the structures of the time series of meteorological elements in the southern part of the Baltic is shown. This confirms the stability of the conclusion obtained by many researchers of the temporal variability of hydrometeorological parameters for various zones and regions of the World Ocean. In this case, the relative (specific) contribution of synoptic variability for W, P0 and f is predominant for the entire initial series (47.6÷76.1%), and for Ta, Td and ea only for short-period variability (8.1÷17.7%). The intra-annual and inter-annual variability of the specific contribution of the synoptic component Ta, Td, f, ea, P0 and W are considered. Thus, the maximum contribution of the intra-annual synoptic variability is timed to September–November, and the minimum is noted in January–February. The annual range of the contribution of intra-annual synoptic variability for most stations varies from 12–38% for W and P0 to 36–38% for Ta.

On the perspectives for separating the radio flux variations of the nucleus and the jet of active galactic based on data from monitoring programs and VLBI observations

The subject and purpose of the work: the possibility of separating the spectral flux densities of the active core and the jet of sources (3C 120, 3C 273, 3C 345, 3C 454.3, 3C 446, Bl Lac, CTA 102, OJ 287, OT 081) is considered. The data of long-term monitoring of changes in the integral flux of extragalactic radio sources performed on the 26-meter telescope of the University of Michigan UMRAO (1969–2012) at frequencies of 14.5, 8, 4.8 GHz are used. Also, data on the core flux and images of active galactic nuclei at a frequency of 15–15.4 GHz VLBA monitoring MOJAVE are used. The subject of this work is to separate the jet flow from the integral flux from the source, as well as to compile the catalog of the quasi-periods of variability of nuclei and jets separately. Methods and methodology: Fourier-periodogram analysis is used to distinguish long-term and short-period variability of nuclei and jets of extragalactic sources. Autocorrelation calculations were carried out in order to confirm the periods of variability. Results: conclusions were made about the applicability of the described method for separating the jet flux, and a catalog of long-term and short-period variability of radio emission fluxes from nuclei and jets for the investigated radio sources was compiled.

Advanced magnetic survey system and method for detailed magnetic field mapping near the sea bottom using an autonomous underwater vehicle

Marine magnetic field surveys conducted near the sea bottom are useful in producing images of the oceanic crust in order to ascertain its volcanic eruption history, active hydrothermal systems, and hydrothermal deposit evolution. An autonomous underwater vehicle (AUV) can carry out self-controlled survey operations while maintaining a stable vehicle attitude at low altitudes above the seafloor. As a result of these benefits, AUVs have attracted attention for various missions. The total magnetic field intensity is generally used for subsurface magnetization images. Recently, vector magnetic anomaly analysis has been considered to be extremely effective for high-accuracy estimation of subsurface magnetization structures. However, correcting for the anomalous magnetic field produced by the vehicle body is one of the difficulties that hinders vector magnetic anomaly analysis. Therefore, we developed a magnetometer system designed for the AUV URASHIMA with a renewed navigation data distribution system. Experimental observation was carried out around a submarine mud volcano with a small magnetic anomaly off Tanegashima Island. The results show that correction for the magnetic field of the vehicle because of the attitude, especially for changes in pitch, is essential for near-bottom magnetic surveys using AUVs. Based on these results, we proposed a suitable data acquisition method to remove the pitching effects of the vehicle for figure-eight turns. Next, practical observation was carried out in the hydrothermal area, and the proposed correction method for magnetic data reduced the pitch variation effect. These results indicate that the correction for the magnetic field of the vehicle based using attitude data, especially for pitching variations, is required in order to obtain high-quality magnetic anomaly data using AUVs. However, a short-period variation of approximately 10 nT caused by abrupt pitch changes remains.

Linear time-varying state transition matrix for spacecraft relative dynamics on highly elliptical orbits

Space exploration is a topic of great interest in the space community and worldwide. For instance, the race to the Lunar surface now includes not only government agencies, but also commercial entities and organizations. Such missions will require robotic spacecraft to perform formation flying, rendezvous and docking to reduce costs of the overall mission and establish space stations within Lunar orbits. Therefore, an accurate and computationally efficient dynamics model, to be used within a spacecraft’s guidance, navigation and control system, to calculate and control the desired relative motion will be required. This paper presents a new, linear time-varying, solution to spacecraft relative motion on Lunar orbits that includes solar radiation pressure, third-body, and J2 perturbations. The solution is obtained by using Hamiltonian dynamics in combination with the Peano–Baker solution for linear time-varying systems, which allows for the inclusion of short and long periodic variations of each perturbation within the dynamical model. The solution resulted in a 75% decrease in computational time when compared to a numerical simulator with the same perturbing effects.

SEAFLOOR POSITIONING MODEL FOR SIMULTANEOUS ESTIMATION OF SOUND VELOCITY

Abstract. The spatial and temporal change of sound speed has a significant impact on the accuracy of GNSS-A underwater positioning. However, it is hard to collect enough data to cover all the spatial and temporal changes of sound velocity. We built an acoustic ranging model that included the sound velocity component, and then we looked at how the model could be used for three-dimensional seabed location and undersea crust monitoring. Meanwhile, B-spline curves are used to construct a sound velocity model that encompasses temporal variation as well as two-dimensional spatial gradients. The method was utilized to assess the simulated data and the in-situ data collected in July 2019, respectively. Simulation results show that the root mean square of the horizontal coordinates solved by the ranging model is less than 10 cm, and the model may meet the demands of subsea crust monitoring under certain situations. In the real data experiment, the square root of variance of the coordinate was better than 10 cm. The sound velocity model findings indicated that the variance of sound velocity in the experimental marine region was less than 1m/s, with clear daily patterns and short-period variations. The algorithm does not need the sound velocity profile information and can save the measurement time of the sound velocity profile.

An Improved Next Generation Gravity Mission

There is an opportunity to make a major reduction in the acceleration noise level for the first Next Generation Gravity Mission by replacing the accelerometers used on the GRACE Follow-On Mission by a highly simplified version of the Gravitational Reference Sensors flown very successfully on the LISA Pathfinder mission of ESA. The reduced measurement noise level can make possible much-improved measurements of the short-period and short-wavelength variations in the geopotential. This would be particularly from the along-track analysis of the results, which can permit repeat measurements about half a day apart along ground tracks within 200 km of each other over a substantial part of the globe. Such a mission would permit considerably improved testing of geophysical models for the geopotential variations due to changes in the Earth’s mass distribution.

Ground-based VLF wave intensity variations investigated by the principal component analysis

Very low frequency wave intensity variations measured by the Kannuslehto station, Finland in the frequency range 0–12 kHz between 2016 and 2020 are analyzed by the principal component analysis (PCA). As the analyzed ground-based measurements are basically continuous, the length of individual basis vectors entering into PCA is fundamentally arbitrary. To better characterize both long- and short-period variations, two PCAs with different lengths of the basis vectors are eventually performed. Specifically, either daily frequency–time spectrograms or individual frequency spectra are chosen as the PCA basis vectors. Analysis of the first three principal components shows substantial variations of the wave intensity due to seasonal and local time effects. Intensity variations related to the geomagnetic activity characterized by Kp and AE indices and standard deviation of the magnetic field magnitude are less significant. Moreover, PCA allows one to distinguish between nighttime and daytime Kannuslehto variations and study them independently. Solar and geomagnetic activity effects on the daytime and nighttime measurements are discussed. Wave intensity variations related to substorm occurrence are also analyzed.Graphic

New Clues to the Evolution of Dwarf Carbon Stars From Their Variability and X-Ray Emission

Abstract As main-sequence stars with C > O, dwarf carbon (dC) stars are never born alone but inherit carbon-enriched material from a former asymptotic giant branch (AGB) companion. In contrast to M dwarfs in post-mass-transfer binaries, C2 and/or CN molecular bands allow dCs to be identified with modest-resolution optical spectroscopy, even after the AGB remnant has cooled beyond detectability. Accretion of substantial material from the AGB stars should spin up the dCs, potentially causing a rejuvenation of activity detectable in X-rays. Indeed, a few dozen dCs have recently been found to have photometric variability with periods under a day. However, most of those are likely post-common-envelope binaries, spin–orbit locked by tidal forces, rather than solely spun-up by accretion. Here, we study the X-ray properties of a sample of the five nearest-known dCs with Chandra. Two are detected in X-rays, the only two for which we also detected short-period photometric variability. We suggest that the coronal activity detected so far in dCs is attributable to rapid rotation due to tidal locking in short binary orbits after a common-envelope phase, late in the thermally pulsing (TP) phase of the former C-AGB primary (TP-AGB).

Сигналы ртути подземных вод Култукского полигона во время подготовки и реализации Байкало-Хубсугульской сейсмической активизации 2020–2021 гг.

From 5-year monitoring of groundwater in the Kultuk area, long-period (about 2.5 years) and short-period (months) variations in mercury concentration have been established. Long-period variations are associated with the preparation and implementation of the Baikal-Khubsugul seismic reactivation; short-period ones – directly with earthquakes. Mercury concentrations was low in groundwater in 2015, when seismogenic deformations developed in a state of crustal compression, and generally increased to 2020–2021, when seismogenic deformations occurred under extention. The course of the seismic process was reflected in a successive change in mercury/redox potential rеlationship in groundwater. It is proposed that the anomalous behavior of mercury during seismic activity resulted in increasing its concentration in the sedimentary layers of the second half of the 18th century through the present.

Short-period variability of hydrophysical fields and processes in the Fourth Kuril Strait according to expedition studies

Short-period variability of hydrophysical fields and processes in the Fourth Kuril Strait according to expedition studies