scholarly journals Comparison of EEJ Longitudinal Variation from Satellite and Ground Measurements over Different Solar Activity Levels

Universe ◽  
2021 ◽  
Vol 7 (2) ◽  
pp. 23
Author(s):  
Wan Nur Izzaty Ismail ◽  
Nurul Shazana Abdul Hamid ◽  
Mardina Abdullah ◽  
Akimasa Yoshikawa ◽  
Teiji Uozumi ◽  
...  
Keyword(s):  
Solar Activity ◽  
Local Time ◽  
Equatorial Electrojet ◽  
Activity Level ◽  
South American ◽  
Activity Levels ◽  
Swarm Satellites ◽  
Magnetometer Data ◽  
Longitudinal Profiles ◽  
Longitudinal Variability

The longitudinal variability and local time of equatorial electrojet (EEJ) current using simultaneous data recorded by ground and satellite magnetometers at different levels of solar activity were investigated. In this study, we used data from the CHAMP and Swarm satellites to obtain EEJ current measurements around the globe. The ground data were provided by the MAGDAS, INTERMAGNET, and IIG networks. The ground observation was carried out by analyzing magnetometer data in four different sectors: the South American, Indian, African, and Southeast Asian sectors. These ground data were normalized to the dip equator to overcome the latitudinal variation of each station. The analysis for both measurements was performed using quiet day data. Both the ground and satellite data were categorized according to solar activity level; low, moderate, and high. The results revealed that, during the low solar activity, there was a good agreement between the longitudinal profiles of the EEJ measured using the satellite and the ground data. In general, strong correlations were obtained in most of the sectors where ground data were available between 11 and 13 local time (LT). Besides that, our analysis revealed that the different times of maximum EEJ appearances were seasonally dependent only at certain longitude sectors.

scholarly journals The Solar Twin Planet Search

2018 ◽  
Vol 619 ◽  
pp. A73 ◽  
Author(s):  
Diego Lorenzo-Oliveira ◽  
Fabrício C. Freitas ◽  
Jorge Meléndez ◽  
Megan Bedell ◽  
Iván Ramírez ◽  
...  
Keyword(s):  
Solar Activity ◽  
Activity Index ◽  
Open Clusters ◽  
Activity Level ◽  
Age Dating ◽  
Physical Parameters ◽  
Activity Levels ◽  
Sharp Drop ◽  
Activity Diagram ◽  
Activity Indices

Context. It is well known that the magnetic activity of solar-type stars decreases with age, but it is widely debated in the literature whether there is a smooth decline or if there is an early sharp drop until 1–2 Gyr that is followed by a relatively inactive constant phase. Aims. We revisited the activity-age relation using time-series observations of a large sample of solar twins whose precise isochronal ages and other important physical parameters have been determined. Methods. We measured the Ca II H and K activity indices using ≈9000 HARPS spectra of 82 solar twins. In addition, the average solar activity was calculated through asteroids and Moon reflection spectra using the same instrumentation. Thus, we transformed our activity indices into the S Mount Wilson scale (SMW), recalibrated the Mount Wilson absolute flux and photospheric correction equations as a function of Teff, and then computed an improved bolometric flux normalized activity index log R′HK (Teff) for the entire sample. Results. New relations between activity and the age of solar twins were derived by assessing the chromospheric age-dating limits using log R′HK (Teff). We measured an average solar activity of SMW = 0.1712 ± 0.0017 during solar magnetic cycles 23–24 covered by HARPS observations, and we also inferred an average of SMW = 0.1694 ± 0.0025 for cycles 10–24, anchored on a sunspot number correlation of S index versus. We also found a simple relation between the average and the dispersion of the activity levels of solar twins. This enabled us to predict the stellar variability effects on the age-activity diagram, and consequently, to estimate the chromospheric age uncertainties that are due to the same phenomena. The age-activity relation is still statistically significant up to ages around 6–7 Gyr, in agreement with previous works using open clusters and field stars with precise ages. Conclusions. Our research confirms that Ca II H & K lines remain a useful chromospheric evolution tracer until stars reach ages of at least 6–7 Gyr. We found evidence that for the most homogenous set of old stars, the chromospheric activity indices seem to continue to decrease after the solar age toward the end of the main sequence. Our results indicate that a significant part of the scatter observed in the age-activity relation of solar twins can be attributed to stellar cycle modulations effects. The Sun seems to have a normal activity level and variability for its age.

scholarly journals Longitudinal variation of equatorial electrojet and the occurrence of its counter electrojet

2017 ◽  
Vol 35 (3) ◽  
pp. 535-545 ◽  
Author(s):  
A. Babatunde Rabiu ◽  
Olanike Olufunmilayo Folarin ◽  
Teiji Uozumi ◽  
Nurul Shazana Abdul Hamid ◽  
Akimasa Yoshikawa
Keyword(s):  
Addis Ababa ◽  
Equatorial Electrojet ◽  
Seasonal Distribution ◽  
Horizontal Component ◽  
South American ◽  
The South ◽  
Counter Electrojet ◽  
Western Africa ◽  
Meridional Winds ◽  
Longitudinal Variability

Abstract. We examined the longitudinal variability of the equatorial electrojet (EEJ) and the occurrence of its counter electrojet (CEJ) using the available records of the horizontal component H of the geomagnetic field simultaneously recorded in the year 2009 (mean annual sunspot number Rz  =  3.1) along the magnetic equator in the South American, African, and Philippine sectors. Our results indicate that the EEJ undergoes variability from one longitudinal representative station to another, with the strongest EEJ of about 192.5 nT at the South American axis at Huancayo and a minimum peak of 40.7 nT at Ilorin in western Africa. Obtained longitudinal inequality in the EEJ was explicable in terms of the effects of local winds, dynamics of migratory tides, propagating diurnal tide, and meridional winds. The African stations of Ilorin and Addis Ababa registered the greatest % of CEJ occurrence. Huancayo in South America, with the strongest electrojet strength, was found to have the least occurrence of the CEJ. It is suggested that activities that support strong EEJ inhibits the occurrence of the CEJ. Percentage of occurrence of the CEJ varied with seasons across the longitudes. The order of seasonal variation of morning occurrence does not tally with the evening occurrence order at any station. A semiannual equinoctial maximum in percentage of morning occurrence of the CEJ was obtained at Huancayo and Addis Ababa. Only Addis Ababa recorded equal equinoctial maxima in percentage of evening occurrence of the CEJ. The seasonal distribution of the occurrences of the CEJ at different time regimes implies a seasonal variability of causative mechanisms responsible for the occurrence of the CEJ.

scholarly journals Solar rotational cycle in lightning activity in Japan during the 18–19th centuries

2018 ◽  
Vol 36 (2) ◽  
pp. 633-640 ◽  
Author(s):  
Hiroko Miyahara ◽  
Ryuho Kataoka ◽  
Takehiko Mikami ◽  
Masumi Zaiki ◽  
Junpei Hirano ◽  
...  
Keyword(s):  
Solar Activity ◽  
Solar Rotation ◽  
Galactic Cosmic Rays ◽  
Activity Level ◽  
Lightning Activity ◽  
Activity Levels ◽  
Rotational Period ◽  
Solar Activity Level ◽  
The Impact

Abstract. Thunderstorm and cloud activities sometimes show a 27-day period, and this has long been studied to uncover a possible important link to solar rotation. Because the 27-day variations in the solar forcing parameters such as solar ultraviolet and galactic cosmic rays become more prominent when the solar activity is high, it is expected that the signal of the 27-day period in meteorological phenomena may wax and wane according to the changes in the solar activity level. In this study, we examine in detail the intensity variations in the signal of the 27-day solar rotational period in thunder and lightning activity from the 18th to the 19th centuries based on 150-year-long records found in old diaries kept in Japan and discuss their relation with the solar activity levels. Such long records enable us to examine the signals of solar rotation at both high and low solar activity levels. We found that the signal of the solar rotational period in the thunder and lightning activity increases as the solar activity increases. In this study, we also discuss the possibility of the impact of the long-term climatological conditions on the signals of the 27-day period in thunder/lightning activities. Keywords. Meteorology and atmospheric dynamics (lightning)

Variability of ionospheric parameters by the Swarm satellites for different solar activity

2020 ◽  
Author(s):  
Daria Kotova ◽  
Yaqi Jin ◽  
Wojciech Miloch
Keyword(s):  
Solar Activity ◽  
Spatial Scales ◽  
Activity Level ◽  
Plasma Parameters ◽  
Solar Activity Level ◽  
Ionospheric Variability ◽  
Swarm Satellites ◽  
Swarm Mission ◽  
Northern And Southern Hemispheres

<p>The use of satellite data allows us to study the variability of ionospheric plasma parameters globally without references to ground stations or receivers in different regions of the Earth. The Swarm mission, which was launched in 2014 and is still operational, allows us to investigate the effects of decreasing solar activity on the ionospheric variability. In our study we use the Swarm in-situ measurements of the electron density and derived parameters. This dataset provides characteristics of the plasma variability along the orbit and gives information on plasma density structures in the ionosphere in terms of their amplitudes, gradients and spatial scales. We analyze the variability of these parameters in the contexts of the northern and southern hemispheres, specific latitudinal regions, and the solar activity level. Understanding of the distribution of such parameters in the context of the solar activity level and selected ionospheric regions can have implications for the development of new satellite instruments and for the accuracy of GNSS precise positioning.</p>

scholarly journals A climatology of the F-layer equivalent winds derived from ionosonde measurements over two decades along the 120°-150°E sector

2004 ◽  
Vol 22 (8) ◽  
pp. 2785-2796 ◽  
Author(s):  
X. Luan ◽  
L. Liu ◽  
W. Wan ◽  
J. Lei ◽  
T. Yu
Keyword(s):  
Solar Activity ◽  
Local Time ◽  
Solar Maximum ◽  
Equatorial Region ◽  
Latitudinal Gradients ◽  
Local Times ◽  
Approximate Symmetry ◽  
Activity Levels ◽  
Relative Contribution ◽  
Latitudinal Dependence

Abstract. The vertical equivalent winds (VEWs) at the F-layer are analyzed along the 120°-150°E longitude sector with an emphasis on their latitudinal dependence. The VEWs are derived from the monthly median data of fourteen ionosonde stations over two decades. The results show that the VEWs have considerable dependences on the magnetic latitude with an approximate symmetry about the magnetic equator. They are mostly controlled by the electric field drifts in the magnetic equatorial region, and shift to be mostly contributed by neutral winds at mid-latitudes. The relative contribution of the two dynamic factors is regulated by the magnetic dip in addition to their own magnitudes. The VEWs generally have opposite directions and different magnitudes between lower and higher latitudes. At solar minimum, the magnitudes of VEWs are only between -20 and 20m/s at lower latitudes, while at higher latitudes they tend to increase with latitudes, typically having magnitudes between 20-40m/s. At solar maximum, the VEWs are reduced by about 10-20m/s in magnitudes during some local times at higher latitudes. A tidal analysis reveals that the relative importance of major tidal components is also different between lower and higher latitudes. The VEWs also depend on local time, season and solar activity. At higher latitudes, the nighttime VEWs have larger magnitude during post-midnight hours and so do the daytime ones before midday. The VEWs tend to have an inverse relationship with solar activity not only at night, but also by day, which is different from the meridional winds predicted by the HWM93 model. The latitudinal dependence of VEWs has two prevailing trends: one is a maximum at the highest latitudes (as far as the latitudes concerned in the present work); the other is a mid-latitude maximum. These two latitudinal trends are mostly dependent on season, while they depend relatively weakly on local time and solar activity. The latitudinal gradients of VEWs also show a tendency of a mid-latitude maximum, except that there are much stronger latitudinal gradients at southern higher mid-latitudes in some seasons. The gradients during daytime are much smaller at solar maximum than minimum, whereas they are generally comparable at night under both solar activity levels.

scholarly journals Dusk-to-nighttime enhancement of mid-latitude <i>Nm</i>F2 in local summer: inter-hemispheric asymmetry and solar activity dependence

2015 ◽  
Vol 33 (6) ◽  
pp. 711-718 ◽  
Author(s):  
Y. Chen ◽  
L. Liu ◽  
H. Le ◽  
W. Wan ◽  
H. Zhang
Keyword(s):  
Solar Activity ◽  
Southern Hemisphere ◽  
Northern Hemisphere ◽  
Peak Height ◽  
Activity Level ◽  
High Solar Activity ◽  
Activity Levels ◽  
Solar Activity Level ◽  
Latitudinal Dependence ◽  
The Difference

Abstract. In this paper ionosonde observations in the East Asia–Australia sector were collected to investigate dusk-to-nighttime enhancement of mid-latitude summer NmF2 (maximum electron density of the F2 layer) within the framework of NmF2 diurnal variation. NmF2 were normalized to two solar activity levels to investigate the dependence of the dusk-to-nighttime enhancement on solar activity. The dusk-to-nighttime enhancement of NmF2 is more evident at Northern Hemisphere stations than at Southern Hemisphere stations, with a remarkable latitudinal dependence. The dusk-to-nighttime enhancement shows both increasing and declining trends with solar activity increasing, which is somewhat different from previous conclusions. The difference in the dusk-to-nighttime enhancement between Southern Hemisphere and Northern Hemisphere stations is possibly related to the offset of the geomagnetic axis from the geographic axis. hmF2 (peak height of the F2 layer) diurnal variations show that daytime hmF2 begins to increase much earlier at low solar activity level than at high solar activity level at northern Akita and Wakkanai stations where the dusk-to-nighttime enhancement is more prominent at low solar activity level than at high solar activity level. That implies neutral wind phase is possibly also important for nighttime enhancement.

scholarly journals Identifying equatorial ionospheric irregularities using in situ ion drifts

2014 ◽  
Vol 32 (4) ◽  
pp. 421-429 ◽  
Author(s):  
R. A. Stoneback ◽  
R. A. Heelis
Keyword(s):  
Solar Activity ◽  
Local Time ◽  
Density Perturbation ◽  
Equatorial Ionosphere ◽  
Morlet Wavelet ◽  
Ionospheric Irregularity ◽  
Activity Levels ◽  
Late Night ◽  
Ion Drifts

Abstract. Previous climatological investigations of ionospheric irregularity occurrence in the equatorial ionosphere have utilized in situ measurements of plasma density to identify the presence of an irregularity. Here we use the Morlet wavelet and C/NOFS to isolate perturbations in meridional ion drifts and generate irregularity occurrence maps as a function of local time, longitude, season, and solar activity. For the low solar activity levels in 2008, the distributions identified by velocity perturbations follow normalized density perturbation (ΔN/N) maps with large occurrences after midnight into dawn over all longitudes. The velocity and normalized density occurrence maps contract in both local time and longitude with increasing solar activity. By 2011 irregularities are confined to particular longitudes expected by alignment and a few hours of local time after sunset. The variation in the occurrence of the late night irregularities with solar activity is consistent with the presence of gravity wave seeding.

scholarly journals Later sleep timing predicts accelerated summer weight gain among elementary school children: a prospective observational study

2021 ◽  
Vol 18 (1) ◽  
Author(s):  
Jennette P. Moreno ◽  
Javad Razjouyan ◽  
Houston Lester ◽  
Hafza Dadabhoy ◽  
Mona Amirmazaheri ◽  
...  
Keyword(s):  
Physical Activity ◽  
Observational Study ◽  
Sleep Duration ◽  
Obesity Prevention ◽  
Prospective Observational Study ◽  
Light Exposure ◽  
Activity Level ◽  
Activity Levels ◽  
School Year ◽  
Children’S Sleep

Abstract Objectives and background Social demands of the school-year and summer environment may affect children’s sleep patterns and circadian rhythms during these periods. The current study examined differences in children’s sleep and circadian-related behaviors during the school-year and summer and explored the association between sleep and circadian parameters and change in body mass index (BMI) during these time periods. Methods This was a prospective observational study with 119 children ages 5 to 8 years with three sequential BMI assessments: early school-year (fall), late school-year (spring), and beginning of the following school-year in Houston, Texas, USA. Sleep midpoint, sleep duration, variability of sleep midpoint, physical activity, and light exposure were estimated using wrist-worn accelerometry during the school-year (fall) and summer. To examine the effect of sleep parameters, physical activity level, and light exposure on change in BMI, growth curve modeling was conducted controlling for age, race, sex, and chronotype. Results Children’s sleep midpoint shifted later by an average of 1.5 h during summer compared to the school-year. After controlling for covariates, later sleep midpoints predicted larger increases in BMI during summer, (γ = .0004, p = .03), but not during the school-year. Sleep duration, sleep midpoint variability, physical activity levels, and sedentary behavior were not associated with change in BMI during the school-year or summer. Females tended to increase their BMI at a faster rate during summer compared to males, γ = .06, p = .049. Greater amounts of outdoor light exposure (γ = −.01, p = .02) predicted smaller increases in school-year BMI. Conclusions Obesity prevention interventions may need to target different behaviors depending on whether children are in or out of school. Promotion of outdoor time during the school-year and earlier sleep times during the summer may be effective obesity prevention strategies during these respective times.

scholarly journals Choroidal Thickness and Volume Modifications Induced by Aerobic Exercise in Healthy Young Adults

2020 ◽  
Author(s):  
Gema Insa-Sánchez ◽  
Lorena Fuentes-Broto ◽  
Alberto Cobos ◽  
Elvira Orduna Hospital ◽  
Francisco Segura ◽  
...  
Keyword(s):  
Physical Activity ◽  
Young Adults ◽  
Physical Exercise ◽  
Choroidal Thickness ◽  
Activity Level ◽  
Enhanced Depth Imaging ◽  
Activity Levels ◽  
Imaging Protocol ◽  
Post Exercise ◽  
Physical Activity Levels

<b><i>Introduction:</i></b> Our aim was to evaluate the changes in choroidal thickness (CT) and volume (CV) following aerobic physical exercise in healthy young adults. <b><i>Methods:</i></b> This study included 72 eyes from healthy volunteers between 22 and 37 years old. Using the International Physical Activity Questionnaire, total physical activity was computed. Measurements using an autorefractometer, ocular biometry, and spectral-domain optical coherence tomography using the Enhanced Depth Imaging protocol were taken. OCT was performed as a baseline measurement and after performing 10 min of dynamic physical exercise (3 and 10 min post-exercise). The choroidal layer was manually segmented, and the CT and CV in different areas from the Early Treatment Diabetic Retinopathy Study grid were obtained. <b><i>Results:</i></b> In healthy adults, at 3 min post-exercise, CT was higher in the subfoveal, the 3-mm nasal, and the 6-mm superior areas. Between 3 and 10 min post-exercise, the CT was reduced in all areas, and in some areas, the values were even smaller than the baseline measurements. The CV values showed changes after exercise similar to those of thickness. The total CV recovery after exercise was related to sex and physical activity level. <b><i>Conclusion:</i></b> Individuals with higher physical activity habits had greater CV at rest than those with lower physical activity levels. During exercise, healthy young people adjust CT and CV. At 3 min post-exercise, CT and CV increase. Women and individuals with greater physical activity levels reduce their total CV more than others during recovery.

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