Maximum Of Cycle Research Articles

A study on the solar coronal dynamics during the post-maxima phase of the solar cycle 24 using S-band radio signals from the Indian Mars Orbiter Mission

ABSTRACT Radio signals from India’s Mars Orbiter Mission (MOM) have been used to study turbulence in the solar plasma during the post-maximum phase of solar cycle 24. S-band (2.29 GHz) radio carrier downlink signals from MOM were received at the Indian Deep Space Network, Bangalore, and frequency residuals were spectrally analysed to obtain coronal turbulence spectra at heliocentric distances ranging between 4 and 20 R⊙, corresponding to coronal regions where the solar wind is primarily accelerated. The frequency fluctuation spectrum relates to the turbulence regime in the near-Sun region. The turbulence power spectrum (the temporal spectrum of frequency fluctuations) at smaller heliocentric distances (<10 R⊙) reveals flattening in lower-frequency regions, with a spectral index αf ∼ 0.3−0.5, which corresponds to the solar wind acceleration region. For larger heliocentric distances (>10 R⊙), the curve steepens with a spectral index αf ∼ 0.7−0.8, a value close to 2/3 and indicative of a developed Kolmogorov-type turbulence spectrum. The findings are consistent with earlier results. Plausible explanations to support the theory of coronal heating by magnetohydrodynamic waves and the acceleration of the solar wind are presented. An insight into the feeble maximum of solar cycle 24 is discussed.

Multipoint Interplanetary Coronal Mass Ejections Observed with Solar Orbiter, BepiColombo, Parker Solar Probe, Wind, and STEREO-A

Abstract We report the result of the first search for multipoint in situ and imaging observations of interplanetary coronal mass ejections (ICMEs) starting with the first Solar Orbiter (SolO) data in 2020 April–2021 April. A data exploration analysis is performed including visualizations of the magnetic-field and plasma observations made by the five spacecraft SolO, BepiColombo, Parker Solar Probe (PSP), Wind, and STEREO-A, in connection with coronagraph and heliospheric imaging observations from STEREO-A/SECCHI and SOHO/LASCO. We identify ICME events that could be unambiguously followed with the STEREO-A heliospheric imagers during their interplanetary propagation to their impact at the aforementioned spacecraft and look for events where the same ICME is seen in situ by widely separated spacecraft. We highlight two events: (1) a small streamer blowout CME on 2020 June 23 observed with a triple lineup by PSP, BepiColombo and Wind, guided by imaging with STEREO-A, and (2) the first fast CME of solar cycle 25 (≈1600 km s−1) on 2020 November 29 observed in situ by PSP and STEREO-A. These results are useful for modeling the magnetic structure of ICMEs and the interplanetary evolution and global shape of their flux ropes and shocks, and for studying the propagation of solar energetic particles. The combined data from these missions are already turning out to be a treasure trove for space-weather research and are expected to become even more valuable with an increasing number of ICME events expected during the rise and maximum of solar cycle 25.

Retrieving Pulsatility in Ultrasound Localization Microscopy

Ultrasound localization microscopy (ULM) is a vascular imaging method that provides a 10-fold improvement in resolution compared to ultrasound Doppler imaging. Because typical ULM acquisitions accumulate large numbers of synthetic microbubble (MB) trajectories over hundreds of cardiac cycles, transient hemodynamic variations such as pulsatility get averaged out. Here we introduce two independent processing methods to retrieve pulsatile flow characteristics from MB trajectories sampled at kilohertz frame rates and demonstrate their potential on a simulated dataset. The first approach follows a Lagrangian description of the flow. We filter the MB trajectories to eliminate ULM localization grid artifacts and successfully recover the pulsatility fraction <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</sub> with a root mean square error (RMSE) of 3.3%. Our second approach follows a Eulerian description of the flow. It relies on the accumulation of MB velocity estimates as observed from a stationary observer. We show that pulsatile flow gives rise to a bimodal velocity distribution with peaks indicating the maximum and minimum velocities of the cardiac cycle. In this second method, we recovered the pulsatility fraction <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</sub> by measuring the location of these distribution peaks with a RMSE of 5.2%. We evaluated the impact of the MB localization precision σ on our ability to retrieve the bimodal signature of a pulsatile flow. Together, our results demonstrate that pulsatility can be retrieved from ULM acquisitions at kilohertz frame rate and that the estimation of the pulsatility fraction improves with localization precision.

A localized small-scale external quality assessment (EQA) for PCR testing of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in the molecular laboratories

The aim of this study was to estimate the PCR results for SARS-CoV-2 testing in 32 participating laboratories in a localized small-scale external quality assessment (EQA) scheme. EQA samples were distributed to the participants and detected immediately on the day of delivery. Qualitative results were submitted to the EQA provider, including negative or positive results along with cycle threshold (Ct) values for different target genes. Although the variability of Ct values differed among the laboratories in the EQA, a total of 32 (100 %) participants reported correct qualitative results. The study showed that the mean loads of N or E gene were higher than those of ORF1ab in SARS-CoV-2 RNA samples. Regardless of the analyzed gene target, the mean Ct values for weak positive and positive samples varied by fewer than 1.74 and 1.91 cycles, respectively. Less than 12 % of reported Ct values for ORF1ab and N genes deviated by more than ±4 cycles (maximum: −9.92 cycles), while none deviated by more than ±4 cycles for the E gene. The current EQA program can provide a robust practical basis for follow-up planning to conduct evaluations for SARS-CoV-2 PCR testing and other novel emerging pathogens in the future.

Numerical analysis of fatigue crack growth under SuperBlock2020 load sequence

The components are usually submitted to variable amplitude loading, and it is important to understand the mechanisms explaining fatigue crack growth (FCG) rate variations. The relative importance of residual stresses and crack closure, in particular, is a controversial issue. This work studies a specific load pattern, called Super Block 2020, composed of four pairs of load blocks of different amplitude (A, B, C and D) and the same maximum load, separated by overloads. The transition from the overloads to the constant amplitude load blocks occurred alternatively from the maximum or minimum loads of the overload cycles. These patterns, called i1 and i2 for load blocks i (i = A, B, C or D), produce different residual stresses ahead of crack tip. A numerical procedure was followed to predict FCG rate in the 2024-T351 aluminium alloy, based on cumulative plastic strain. This approach includes the effects of material hardening, crack tip blunting, crack closure and partial crack closure. A significant difference was found between FCG rate and crack increments produced by i1 and i2 load blocks. The numerical predictions are according the experimental trends and crack closure was found to be the main mechanism behind FCG trends.

Variability of phytoplankton biomass and environmental drivers in a semi-enclosed coastal ecosystem (San Matías Gulf, Patagonian Continental Shelf, Argentina) using ocean color remote sensing (MODIS) and oceanographic field data: Implications for fishery resources

Annual cycles of phytoplankton biomass (using chlorophyll-a as a proxy) and seasonal patterns of environmental drivers were analyzed in a semi-enclosed coastal ecosystem (San Matías Gulf, SMG, Patagonian Continental Shelf, Argentina). Monthly climatologies (2003–2014) of satellite images of chlorophyll-a (Chla-sat), sea surface temperature (SST), photosynthetically available radiation (PAR), and euphotic depth (Z 1% ) were analyzed using Principal Component Analysis (PCA). Satellite environmental variables were evaluated together with oceanographic field data (temperature, nitrate, and chlorophyll-a). Thus, this study analyzes the Chla-sat data to describe the spatio-temporal distribution of the phytoplankton biomass in the SMG and investigates its relationship with the regional environmental drivers. Two contrasting phytoplankton annual cycles characteristic of these temperate waters were distinguished. PCA discriminated the inner and outer areas separated by a complex frontal system. The gulf's inner waters showed a bimodal phytoplankton cycle (maximums in autumn and spring) associated with the seasonal stratification of the water column in deeper areas and the consequent nitrate limitation in summer. The outer waters adjacent to the continental shelf showed unimodal cycles (maximum in autumn or spring) linked to the vertical mixing of the water column in shallow areas with moderate light intensity and nitrate availability. For both annual phytoplankton cycles, light is the main limiting factor in winter. Finally, the analyzed environmental patterns suggest that a tidal front favor feeding and spawning fishery resources in the north of the gulf. • Twelve years of chlorophyll-a MODIS data are analyzed in San Matías Gulf. • Environmental data from satellite and oceanographic cruises are investigated. • A frontal system separated two contrasting annual cycles of phytoplankton biomass. • Oceanographic features are favorable for feeding and spawning of fisheries resources.

Ibrutinib Plus Rituximab and Venetoclax (IRV) Followed By Risk-Stratified Observation or Short Course R-Hypercvad/MTX in Young Patients with Previously Untreated Mantle Cell Lymphoma - Phase-II Window-2 Clinical Trial

Ibrutinib Plus Rituximab and Venetoclax (IRV) Followed By Risk-Stratified Observation or Short Course R-Hypercvad/MTX in Young Patients with Previously Untreated Mantle Cell Lymphoma - Phase-II Window-2 Clinical Trial

Role of rotational radial magnetic advection in possible explaining a cycle with two peaks

• Double maximum of the 11-year solar cycle. • Turbulent effects of macroscopic magnetohydrodynamics. • Negative magnetic buoyancy. • Turbulent pumping of a large-scale magnetic field. • Reconstructing of the toroidal magnetic field of the Sun. To explain the observed phenomenon of 11-year sunspot cycle with two peaks, we draw attention to the possible role of the turbulent magnetic pumping effects in the solar convection zone (SCZ) at the reconstructing of the toroidal magnetic field that generates the sunspots. Turbulent radial pumping of magnetic field has both kinetic (diamagnetism) and magnetic (vertical advection) contributions. We take into account five physical processes for the combined magnetic reconstructing in deep layers of the SCZ. They are the Ω effect near the tachocline, magnetic buoyancy of the smoothed field, macroscopic diamagnetism, rotational magnetic advection, and deep equatorward meridional circulation. It is the effect of advection with taking into account Sun's rotation that plays a key role in the proposed scenario of magnetic reconstructing. We found that reconstructing of deep toroidal field develops differently in the near-polar and equatorial domains of the SCZ. In the lower half of the near-polar domain, two downward pumping effects (diamagnetism and advection) act against magnetic buoyancy and, as a result, they neutralize magnetic buoyancy and thereby block the toroidal field near the tachocline. At the same time, in the deep layers of the equatorial domain, the rotational advection due to the latitudinal convection anisotropy changes its direction to the opposite (from downward to upward), thereby helping magnetic buoyancy. As a result, this upward magnetic pumping here contributes to the transport of the toroidal field to the solar surface. We call this transport as first upward magnetic advection surge. It ensures a transfer of the deep strong fields to the surface in the latitudes belt of sunspots. Meanwhile, a deep equatorward meridional flow transports the blocked near pole toroidal field in the tachocline from high latitudes to low ones where are favourable conditions for floating up of the magnetic field. Here this belated field is transported upward to the solar surface (the second upward magnetic advection surge). Ultimately, two time-delayed upward magnetic surges may cause on the surface in the “royal zone” the first and second peaks of the sunspots cycle.

Spotless days and geomagnetic index as the predictors of solar cycle 25

We study the sunspot activity in relation to spotless days (SLDs) during the descending phase of solar cycles 11–24 to predict the amplitude of sunspot cycle 25. For this purpose, in addition to SLD, we also consider the geomagnetic activity (aa index) during the descending phase of a given cycle. A very strong correlation of the SLD (0.68) and aa index (0.86) during the descending phase of a given cycle with the maximum amplitude of next solar cycle has been estimated. The empirical relationship led us to deduce the amplitude of cycle 25 to be 99.13± 14.97 and 104.23± 17.35 using SLD and aa index, respectively as predictors. Both the predictors provide comparable amplitude for solar cycle 25 and reveal that solar cycle 25 will be weaker than cycle 24. Further, we predict that the maximum of cycle 25 is likely to occur between February and March 2024. While the aa index has been utilized extensively in the past, this work establishes SLDs as another potential candidate for predicting the characteristics of the next cycle.

Effects of the geomagnetic field time–varying components compensation as evidenced by heart rate variability of healthy males.

Evolutionarily, a human organism is adapted to the natural geomagnetic environment and its slight alterations. However, during geomagnetic storms (GMSs), the strength of the geomagnetic field (GMF) sharply increased hundreds of times and can pose a serious threat to people. We examine the effects of controlled compensation in the time-varying components of the GMF, using a specially created experimental setup with electrically shielding solutions, providing an electromagnetically quiet environment. The measurement of heart rate variability (HRV) on 25 healthy young male volunteers was carried out in the laboratory using the experimental setup at different levels of outdoor geomagnetic activity (GMA). The geomagnetic K-index was used to characterize the magnitude of GMSs; volunteers were tested during quiet magnetic days (K = 1–3), days with K = 4, and days with GMSs (K ≥ 5) in the period of solar cycle maximum. During quiet magnetic days, the comparison between HRV baseline values with values measured under GMF time-varying components compensation mode (CM) did not reveal any changes. On days with K = 4 some HRV indices shifted from their initial values, but it was statistically not significant. However, on days with GMSs statistically significant changes in SDNN* (p = 0.033) and LF* (p = 0.011) indices of HRV were observed in the GMS CM compared to their baseline values. The experiments showed that GMSs cause a sensitive reaction of the heart rate regulatory mechanism, the effect of which can be canceled in the GMS CM. The efficiency of the used technology is supported by the results of this study. * SDNN (Standard Deviation Normal to Normal R-R of cardiointervals), LF (Low frequency spectral band of cardiointervals).

Seasonal Modulation of Submesoscale Kinetic Energy in the Upper Ocean of the Northeastern South China Sea

AbstractAlthough submesoscale processes are revealed to have a strong seasonality in many regions of global ocean, their seasonal modulation in the northeastern South China Sea (NESCS) remains unexplored by observations. In this study, approaches to diagnose submesoscale kinetic energy (KE) and its conversion terms using data from a single mooring are proposed and validated. Based on these approaches, seasonal modulation of submesoscale KE in the NESCS is for the first time investigated using 8.7‐year‐long moored velocity and temperature data between August 2010 and April 2019. It is found that the monthly climatology of submesoscale KE shows an asymmetric annual cycle with a steep peak between December and February but a flat trough between April and October. The maximum and minimum of this annual cycle occur in January and May, respectively. Although the submesoscale KE rapidly decreases with depth, its seasonality is still evident at 300 m, which is far beneath the mixed layer. Statistical analysis suggests that the overall seasonality of submesoscale KE is shaped by mixed‐layer depth while its steep peak in winter is modulated by mesoscale strain rate. It therefore suggests that the combination of mixed‐layer instability and strain‐induced frontogenesis determines the detailed annual cycle of submesoscale KE. Energetics analysis demonstrates that submesoscales obtain their KE from the release of available potential energy but lose a small portion of its KE through inverse cascade. This submesoscale inverse KE cascade may play an important role in modulating the temporal variation of mesoscale KE in winter.

Solar wind Alfvénicity during solar cycle 23 and 24

Context.Alfvénic fluctuations are ubiquitous features observed in solar wind, especially in the inner heliosphere. However, strong Alfvénic fluctuations are recovered in the near-Earth solar wind too, mainly in fast streams, but also in some cases in slow wind intervals, as highlighted in recent studies.Aims.The present study focuses on a statistical comparison between different phases of solar cycles 23 and 24 with regard to the Alfvénic content of solar wind fluctuations. Particular attention is devoted to the Alfvénic slow solar wind, in relation to the solar wind composition and other parameters.Methods.Two-dimensional histograms of the solar wind speed versus the normalized cross-helicity have been used to feature the Alfvénic character of solar wind turbulence on each phase of the solar cycles considered. Moreover, we characterize the different phases of solar cycles by also using composition data. Finally, case studies are discussed to better highlight the similarities and differences between the two solar maxima, which more clearly show a predominance of Alfvénic slow solar wind.Results.The statistical analysis highlights similarities between two solar cycles and confirms that the Alfvénic slow wind is more frequently observed during the maximum of solar activity. The two representative time intervals, containing samples of this solar wind regime, show similar characteristics, with a particular reference to the spectral analysis.Conclusions.This study has important implications for future observations by Parker Solar Probe and Solar Orbiter, devoted to the study of the inner heliosphere inside Mercury’s orbit. In fact, both missions will operate up to the maximum of solar cycle 25 which is fast approaching. These unprecedented measurements will then provide insights into the origin and evolution of the Alfvénic solar wind close to the region where it is generated and accelerated.

A Study of Variations in Correlation Between Rotation Residual and Meridional Velocity of Sunspot Groups

We analyzed the combined 142 years sunspot-group data from Greenwich Photoheliograpic Results (GPR) and Debrecen Photoheliographic Data (DPD) and determined the yearly mean residual rotation rate and the meridional velocity of sunspot groups in different 5-degree latitude intervals. The residual rotation rate is found to be -120 m/s to 80 m/s. In a large number of solar cycles the rotation is to some extent weaker during maxima than that of during minima. There exist alternate bands of equatorward and poleward merdional motions. The equatorward motion is dominant mostly around the maxima of solar cycles with velocity 8-12 m/s, whereas the poleward motion is dominant mostly around the minima but with a relatively weak velocity, only 4-6 m/s. This analysis suggests the existence of equatorward migrating alternate bands of slower and faster than average rotation within the activity belt and no clear equatorward or poleward migrating bands of meridional motions. A statistically significant anticorrelation exists between the meridional motion and residual rotation. The corresponding linear-least-squares best-fit is found to be reasonably good (slope, -0.028 + or - 0.008, is about 3.5 times larger than its standard deviation). The significant negative value of the slope indicates the existence of a strong angular momentum transport toward equator. The slope leads sunspot number (SN) by about 4 and 9 years. The Morlet wavelet spectrum of the slope suggests the existence of approximate 11-year periodicity in the slope almost throughout the data window, but it was very weak during 1920-1940.Overall the results suggest there exits a strong relationship between the slope and amount of activity during a solar cycle. However, no relationship is found between the slope and strength of activity on a long-time scale (longer than 11-year period).

Combining white light and UV Lyman-α coronagraphic images to determine the solar wind speed

Context. The availability of multi-channel coronagraphic images in different wavelength intervals acquired from the space will provide a new view of the solar corona, allowing us to investigate the 2D distribution and time evolution of many plasma physical parameters, such as plasma density, temperature, and outflow speed. Aims. This work focuses on the combination of white light (WL) and UV (Lyα) coronagraphic images to demonstrate the capability of measuring the solar wind speed in the inner corona directly with the ratio of these two images (a technique called the quick inversion method), thus avoiding having to account for the line-of-sight (LOS) integration effects in the inversion of data. Methods. After a derivation of the theoretical basis and illustration of the main hypotheses in the quick inversion method, the data inversion technique is tested first with 1D radial analytic profiles and then with 3D numerical MHD simulations in order to show the effects of variabilities related to different phases of the solar activity cycle and the complex LOS distribution of plasma parameters. The same technique is also applied to average WL and UV images obtained from real data acquired by the SOHO UVCS and LASCO instruments around the minimum and maximum of the solar activity cycle. Results. Comparisons between input and output velocities show a good agreement overall, demonstrating that this method, which allowed us to infer the solar wind speed with the WL-to-UV image ratio, can be complementary to more complex techniques requiring the full LOS integration. The analysis described here also allowed us to quantify the possible errors in the outflow speed, and to identify the coronal regions where the quick inversion method performs at the best. The quick inversion applied to real UVCS and LASCO data also allowed us to reconstruct the typical bimodal distribution of fast and slow wind at solar minimum, and to derive a more complex picture around the solar maximum. Conclusions. The application of the technique shown here will be very important for the future analyses of data acquired with multi-channel WL and UV (Lyα) coronagraphs, such as Metis on board the Solar Orbiter, LST on board ASO-S, and any other future WL and UV Lyα multi-channel coronagraphs.

English

The study deals with determining ionosphere parameter at low latitudes during the maximum of solar cycle 22 on quiet days. It uses Thermosphere-Ionosphere-Electrodynamics General Circulation Model (TIEGCM) to carry out Total Electron Content (TEC) parameter in the ionosphere region. TEC time variability on summer and winter highlights a seasonal anomaly, a phenomenon observed since 1965 and which appears while radiations coming from the sun are more intensive in summer than in winter under low latitudes. A mathematical approach integrating the time values of TEC parameter is developed to calculate TEC total value during all the season. The study shows that the seasonal anomaly phenomenon is not observed at every time between summer and winter. Comparison of the rate of electrons production matches with solar radiation intensity between summer and winter during a short period. Apparition of winter anomaly phenomenon shows that ultraviolet and X-rays emitted from the Sun are not the only causes of ionization of particles in ionosphere. Other chemical or physical phenomena also contribute to enhance the concentration of electrons in the atmosphere. The estimation of the rate of TEC production in ionosphere F2-layer enables a comparison of summer and winter behavior in ionosphere layer. The study offers a good knowledge of winter anomaly phenomenon. &nbsp; Key words: Total electron content, thermosphere-ionosphere-electrodynamics general circulation model, winter anomaly, maximum of solar cycle, quiet day.

Status of CAS global ionospheric maps after the maximum of solar cycle 24

As a new Ionosphere Associate Analysis Center (IAAC) of the International GNSS Service (IGS), Chinese Academy of Sciences (CAS) started the routine computation of the real-time, rapid, and final Global Ionospheric Maps (GIMs) in 2015. The method for the generation of CAS rapid and final GIMs and recent updates are presented in the paper. The quality of CAS post-processed GIMs is assessed during 2015–2018 after the maximum of solar cycle 24. To perform an independent and fair assessment, Jason-2/3 Vertical Total Electron Contents (VTEC) are first used as the references over the ocean. GPS differential Slant TECs (dSTEC) generated from 55 Multi-GNSS Experimental (MGEX) stations of the IGS are also employed, which provides a complementing way to evaluate the ability of electron content models to reproduce the spatial and temporal gradients in the ionosphere. During the test period, Jet Propulsion Laboratory (JPL) GIMs present significantly positive deviations compared to the Jason VTEC and GPS dSTEC. Technical University of Catalonia (UPC) rapid GIM UQRG exhibits the best performance in both Jason VTEC and GPS dSTEC analysis. The CAS GIMs show comparable performance with the results of the first four IAACs of the IGS. As expected, the poor performance of all GIMs is in equatorial regions and the high latitudes of the southern hemisphere. The consideration of generating multi-layer or three-dimensional ionospheric maps is emphasized to mitigate the inadequacy of ionospheric single-layer assumption in the presence of pronounced latitudinal gradients. The use of ionospheric observations from the new GNSS constellations and other space- or ground-based observation techniques is also suggested in the generation of future GIMs, given the sparse GPS/GLONASS stations in the southern hemisphere.

Solar activity global minimum and genogeographic features of the COVID-19 pandemic

The relationship between space weather and influenza pandemics of the 19th and 21st centuries and the COVID-19 pandemic is considered. All influenza epidemics of the 19-21 centuries developed only at the extremes of solar activity, and the difference in the number of infectious diseases in Russia in the minimum and maximum of 11-year SA cycles is more than 25 million people. The COVID-19 pandemic took start at the minimums of the 11-year and quasi-secular solar cycle. Weather factors and characteristics of the population genetic composition in each country can accelerate the development of a local epidemic, as well as increase its severity and mortality rate. Mortality by country during the COVID-19 pandemic varies by more than 5-8 times. This haplogroup is characterized by the rapid development of an epidemic with low mortality and a large number of asymptomatic patients. Genetic variations explain differences in the strength of leukocyte antigens immune responses. The article investigated the DNA oxidative damage degree as a molecular predictor of exogenous disorders to expose to UV radiation and magnetic field different frequencies. The greatest number of DNA damage was observed in the age groups over 60 and under 20.

Space weather in the 11-year solar cycle and cardio-sensitivity of volunteers in the middle latitudes

There has been studied a cardio-sensitivity of volunteers of the middle latitudes to geomagnetic activity and to the variety of the parameters of the solar wind, Bz-components of interplanetary magnetic field, solar radiation with a wave length of 10.7 cm and meteo parameters in the minimum of the 24th 11-year solar cycle. The cardio-sensitivity to geomagnetic activity has been revealed only among 9.1% of the volunteers, which is significantly lower than in the maximum of the 11-year solar cycle (42% of the volunteers). The myocard of the cardio-nonsensitive volunteers to geomagnetic activity has been also non-sensitive to the other studied factors of the space and the earth weather. Thus, in the volunteers of the middle latitudes the period of the 11-year solar cycle determines the degree of synchronization of the myocard state and change of the geomagnetic activity.

MODELING CRITICAL FREQUENCY OF IONOSPHERE D-LAYER AT MINIMUM AND MAXIMUM OF THE SOLAR CYCLE 22WITH IRI-2016

One of the interests of the study of the ionosphere lies in its importance for the transmission of radio waves in telecommunications. The ionospherebehaves as an obstacle to the passage of waves. Thus, the signals of short wavelengths are reflected by the F layer or the upper part of the sublayer E, while theD-layeris the seat of the reflection of low-frequencywaves. The presentstudyinvestigates the temporal variability of the criticalfrequency of the D-layer (for) using the 2016 version of the International Reference Ionosphere (IRI) model under quiet day conditions during at maximum and minimum phase of solar cycle 22. The workisconductedat the Ouagadougou station, located in West Africa. The methodology of the workadopted for the determination of the parameter foDisbased on the calculation of the monthlyhourlyaverages of this variable obtainedwith the help of the model during the monthsthatcharacterize the seasons. The resultsobtained for the parameter for as a function of time during the minimum and maximum of the solar cycle 22 have been presented. The seasonal and temporal variations of the criticalfrequency of the ionosphereD-layer show that the foD values are lower during a minimum of the solar cycle and present maximum values at the Zenith (1200 TL) at a minimum and maximum. Theseresultsalsorevealthatthisparameter varies with time, season, and geographical position. The results of thisstudy show a criticalfrequencybelow 1 MHz during both phases of the solar cycle.

The extreme space weather events in October 1788

Abstract Solar eruptions launch interplanetary coronal mass ejections (ICMEs) and cause geomagnetic storms and equatorial extension of the auroral oval. Their rare and unique nature has made analyses of historical events extremely important to increase their data availability. In this study, we analyzed the space weather event of 1788 October, which was characterized with simultaneous auroral observations. We extended archival surveys and confirmed the auroral visibilities down to Barcelona (46.0° MLAT) on October 21/22 as well as Mizuhara (27.5° MLAT) and Rome (44.8° MLAT) on October 22/23. The end of auroral reports overlapped with a reported declination disturbance at Mannheim, indicating a ΔD amplitude of ≥1.15°. Two positive excursions of ΔD were recorded, lasting for several tens of minutes. Upward field-aligned currents could have flowed poleward of Mannheim associated with substorms. We identified the equatorial boundary of the auroral oval down to 46.5° ILAT in the European sector and approximately ≤41.6° ILAT in the Japanese sector. This is compared with the reported equatorial auroral boundaries during extreme storms. The long storm sequence indicates the arrival of multiple ICMEs, thereby enhancing solar activity at that time. This sequence is indeed contextualized immediately after the maximum of Solar Cycle 4. Because sunspot observations are extremely scarce around 1788, it is challenging to identify the source active region. This in turn makes these auroral records valuable for the analyses of long-term solar activity before the onset of the Dalton Minimum.