scholarly journals Nonmigrating tidal signatures in the magnitude and the inter-hemispheric asymmetry of the equatorial ionization anomaly

2013 ◽  
Vol 31 (6) ◽  
pp. 1115-1130 ◽  
Author(s):  
C. Xiong ◽  
H. Lühr
Keyword(s):  
Hemispheric Asymmetry ◽  
Strong Dependence ◽  
Magnetic Activity ◽  
Planetary Waves ◽  
Leading Role ◽  
Equatorial Ionization Anomaly ◽  
June Solstice ◽  
December Solstice ◽  
Apex Height ◽  
Stationary Planetary Wave

Abstract. Based on nine years of observations from the satellites CHAMP and GRACE the tidal signatures in the magnitude and the inter-hemisphere asymmetry of the equatorial ionization anomaly (EIA) have been investigated in this study. The EIA magnitude parameters show longitudinal wavenumber 4 and 3 (WN4/WN3) patterns during the months around August and December, respectively, while for different EIA parameters the contributions of the various tidal parameters are different. For the crest-to-trough ratio (CTR) the dominating nonmigrating tidal component contributing to WN4 is DE3 during the months around August, while during the months around December solstice the stationary planetary wave, SPW3, takes a comparable role to DE2 in contributing to WN3. For the apex height index (ApexHC) of the EIA fluxtube the stationary planetary waves, SPW4/SPW3, exceed the amplitudes of DE3/DE2 taking the leading role in causing the longitudinal WN4/WN3 patterns. During the months around December solstice the SW3 tide is prominent in both CTR and ApexHC. SW3 shows a strong dependence on the solar flux level, while it is hardly dependent on magnetic activity. For the EIA inter-hemispheric asymmetry only WN1 and WN2 longitudinal patterns can be seen. During June solstice months the pattern can be explained by stationary planetary waves SPW1 and SPW2. Conversely, around December solstice months longitudinal features exhibit some local time evolution, in particular the diurnal nonmigrating tide D0 takes the leading role.

scholarly journals Simultaneous observations of the main trough using GPS imaging and the EISCAT radar

2005 ◽  
Vol 23 (3) ◽  
pp. 753-757 ◽  
Author(s):  
R. W. Meggs ◽  
C. N. Mitchell ◽  
V. S. C. Howells
Keyword(s):  
Magnetic Activity ◽  
The West ◽  
West Side ◽  
Gps Receivers ◽  
Equatorial Ionization Anomaly ◽  
Main Trough ◽  
Spread F ◽  
A Chain ◽  
Eiscat Radar ◽  
June July

Abstract. We use a digisonde at Jicamarca and a chain of GPS receivers on the west side of South America to investigate the effects of the pre-reversal enhancement (PRE) in ExB drift, the asymmetry (Ia) of equatorial ionization anomaly (EIA), and the magnetic activity (Kp) on the generation of equatorial spread F (ESF). Results show that the ESF appears frequently in summer (November, December, January, and February) and equinoctial (March, April, September, and October) months, but rarely in winter (May, June, July, and August) months. The seasonal variation in the ESF is associated with those in the PRE ExB drift and Ia. The larger ExB drift (>20m/s) and smaller |Ia| (<0.3) in summer and equinoctial months provide a preferable condition to development the ESF. Conversely, the smaller ExB drift and larger |Ia| are responsible for the lower ESF occurrence in winter months. Regarding the effects of magnetic activity, the ESF occurrence decreases with increasing Kp in the equinoctial and winter months, but not in the summer months. Furthermore, the larger and smaller ExB drifts are presented under the quiet (Kp<3) and disturbed (Kp≥3) conditions, respectively. These results indicate that the suppression in ESF and the decrease in ExB drifts are mainly caused by the decrease in the eastward electric field.

scholarly journals Vertical and longitudinal electron density structures of equatorial E- and F-regions

2011 ◽  
Vol 29 (1) ◽  
pp. 81-89 ◽  
Author(s):  
P. S. Brahmanandam ◽  
Y.-H. Chu ◽  
K.-H. Wu ◽  
H.-P. Hsia ◽  
C.-L. Su ◽  
...  
Keyword(s):  
Electron Density ◽  
Phase Relation ◽  
F Region ◽  
Good Consistency ◽  
June Solstice ◽  
December Solstice ◽  
Different Seasons ◽  
E Region ◽  
First Time ◽  
Longitudinal Structures

Abstract. From global soundings of ionospheric electron density made with FORMOSAT 3/COSMIC satellites for September 2006–August 2009, day-night variations in vertical and longitudinal structures of the electron densities in equatorial E- and F-regions for different seasons are investigated for the first time. The results reveal that the wavenumber-3 and wavenumber-4 patterns dominated the nighttime (22:00–04:00 LT) F-region longitudinal structures in solstice and in equinox seasons, respectively. In daytime (08:00–18:00 LT) F-region, the wavenumber-4 patterns governed the longitudinal structures in the September equinox and December solstice, and wavenumber-3 in March equinox and June solstice respectively. A comparison of the daytime and nighttime longitudinal electron density structures indicates that they are approximately 180° out of phase with each other. It is believed that this out of phase relation is very likely the result of the opposite phase relation between daytime and nighttime nonmigrating diurnal tidal winds that modulate background E-region dynamo electric field at different places, leading to the day-night change in the locations of the equatorial plasma fountains that are responsible for the formation of the F-region longitudinal structures. Further, a good consistency between the locations of the density structures in the same seasons of the different years for both daytime and nighttime epochs has been noticed indicating that the source mechanism for these structures could be the same.

scholarly journals Using magnetic activity and Galactic dynamics to constrain the ages of M dwarfs

2008 ◽  
Vol 4 (S258) ◽  
pp. 327-336 ◽  
Author(s):  
Andrew A. West ◽  
Suzanne L. Hawley ◽  
John J. Bochanski ◽  
Kevin R. Covey ◽  
Adam J. Burgasser
Keyword(s):  
Spectral Type ◽  
Galactic Plane ◽  
Strong Dependence ◽  
Magnetic Activity ◽  
Sloan Digital Sky Survey ◽  
Dynamical Model ◽  
M Dwarfs ◽  
Mass Spectral ◽  
Vertical Distance ◽  
Active Stars

AbstractWe present a study of the dynamics and magnetic activity of M dwarfs using the largest spectroscopic sample of low-mass stars ever assembled. The age at which strong surface magnetic activity (as traced by Hα) ceases in M dwarfs has been inferred to have a strong dependence on mass (spectral type, surface temperature) and explains previous results showing a large increase in the fraction of active stars at later spectral types. Using spectral observations of more than 40000 M dwarfs from the Sloan Digital Sky Survey, we show that the fraction of active stars decreases as a function of vertical distance from the Galactic plane (a statistical proxy for age), and that the magnitude of this decrease changes significantly for different M spectral types. Adopting a simple dynamical model for thin disk vertical heating, we assign an age for the activity decline at each spectral type, and thus determine the activity lifetimes for M dwarfs. In addition, we derive a statistical age-activity relation for each spectral type using the dynamical model, the vertical distance from the Plane and the Hα emission line luminosity of each star (the latter of which also decreases with vertical height above the Galactic plane).

scholarly journals Diurnal, seasonal and solar cycle variation of total electron content and comparison with the IRI-2016 model at Birnin Kebbi

2019 ◽  
Author(s):  
Aghogho Ogwala ◽  
Emmanuel Olufemi Somoye ◽  
Olugbenga Ogunmudimu ◽  
Rasaq Adewemimo Adeniji-Adele ◽  
Eugene Ogheneakpobor Onori ◽  
...  
Keyword(s):  
Solar Cycle ◽  
Diurnal Variation ◽  
Total Electron Content ◽  
Electron Content ◽  
Total Electron ◽  
Equatorial Station ◽  
Solar Cycle Variation ◽  
June Solstice ◽  
December Solstice ◽  
Cycle Dependence

Abstract. Total Electron Content (TEC) is an important ionospheric parameter used to monitor possible space weather impacts on satellite to ground communication and satellite navigation system. TEC is modified in the ionosphere by changing solar Extreme Ultra-Violet (EUV) radiation, geomagnetic storms, and the atmospheric waves that propagate up from the lower atmosphere. Therefore, TEC depends on local time, latitude, longitude, season, geomagnetic conditions, solar cycle activity, and condition of the troposphere. A dual frequency GPS receiver located at an equatorial station, Birnin-Kebbi in Northern Nigeria (geographic location: 12.64° N; 4.22° E), has been used to investigate variation of TEC during the period of 2011 to 2014. We investigate the diurnal, seasonal and solar cycle dependence of observed (OBS) TEC and comparison with latest version of International Reference Ionosphere (IRI-2016) model. On a general note, diurnal variation reveals discrepancies between OBS-TEC and IRI-2016 model for all hours of the day except during the post-midnight hours. Slight post-noon peaks in the daytime maximum and post-sunset decrease and enhancement are observed in the diurnal variation of OBS-TEC of some months. On a seasonal scale, we observed that OBS-TEC values were higher in the equinoxes than the solstices only in 2012. Where as in 2011, September equinox and December solstice recorded higher magnitude followed by March equinox and lowest in June solstice. In 2013, December solstice magnitude was highest, followed by the equinoxes and lowest in June solstice. In 2014, March equinox and December solstice magnitude were higher than September equinox and June solstice magnitude. June solstice consistently recorded the lowest values for all the years. OBS-TEC is found to increase from 2011 to 2014, thus revealing solar cycle dependence.

scholarly journals Statistical analysis of low-latitude spread F observed over Puer, China, during 2015–2016

2019 ◽  
Vol 71 (1) ◽  
Author(s):  
Ting Lan ◽  
Chunhua Jiang ◽  
Guobin Yang ◽  
Yuannong Zhang ◽  
Jing Liu ◽  
...  
Keyword(s):  
Statistical Analysis ◽  
Magnetic Activity ◽  
Ionospheric Disturbances ◽  
Low Latitude ◽  
Equatorial Ionization Anomaly ◽  
Spread F ◽  
Latitude Region ◽  
Range Spread ◽  
Activity Dependence ◽  
Maximum Occurrence

AbstractStatistical analysis of spread F (SF), recorded at Puer (PUR, 22.7° N, 101.05° E, Dip Latitude 12.9° N) during 2015–2016, was carried out to reveal its characteristics at the northern equatorial ionization anomaly. In our study, SF was categorized into four types, frequency spread F (FSF), range spread F (RSF), mix spread F (MSF) and strong range spread F (SSF). The statistical results presented that FSF and MSF were dominant over Puer. Most types of SF appeared mostly in summer months, except the maximum occurrence of SSF in equinox months. Moreover, observations of SF events also showed that the solar activity and magnetic activity dependence of SF varied with seasons. Compared with observations at other region, the present results suggest that medium-scale traveling ionospheric disturbances (MSTIDs) may play a key role in generation of SF in low-latitude region.

scholarly journals Investigation of Solstice Horizon Interactions at Chacoan Monumental Architecture

2017 ◽  
Vol 21 (1 and 2) ◽  
pp. 151-171
Author(s):  
Andrew M. Munro ◽  
Tony Hull ◽  
J. McKim Malville ◽  
F. Joan Mathien ◽  
Cherilynn Morrow
Keyword(s):  
Field Research ◽  
Chaco Canyon ◽  
Severe Drought ◽  
Religious Revival ◽  
Monumental Architecture ◽  
Sacred Landscape ◽  
June Solstice ◽  
Park Service ◽  
December Solstice ◽  
Cardinal Directions

Multiple monumental structures built during the ninth through the twelfth centuries CE at Chaco Canyon, NM, are in locations where solstice sunrise or sunset visually interacts with horizon foresights. We report on the results of field survey and photo-confirmation of seven solstice foresight interactions at Chacoan Great Houses. These include two ‘Early Bonito phase’ (850–1040 CE) sites. A June solstice sunset (JSSS) horizon foresight is visible from Pueblo Bonito, including early (ninth century) portions of the structure. December solstice sunrise (DSSR) interacts with a foresight visible from Hungo Pavi kiva A. We also confirm solstice horizon foresights at five additional ‘Late Bonito phase’ (1100– 1140 CE) Great Houses. These include DSSR at Kin Sabe, DSSR at the Peñasco Blanco McElmo unit, DSSR at the proposed Chetro Ketl McElmo unit (west room block), December solstice sunset (DSSS) at Hillside Ruin, and June solstice sunrise (JSSR) at Rabbit Ruin. Hillside Ruin, the Chetro Ketl McElmo unit, and Rabbit Ruin also participate in inter-site alignments to the cardinal directions. Integration of this data with previous temporal analyses further highlights contrasting cultural intent between periods. A minority of Early and Classic Bonito phase Great Houses (850–1100 CE) are known to have been built at solstice foresight observing locations. During the Late Bonito phase, ten of thirteen (77%) newly built Great Houses are at such locations. Six of thirteen (46%) participate in inter-site alignments to the cardinal directions. Three of thirteen (23%) participate in both the inter-site cardinal alignment and solstitial foresight traditions. This provides direct evidence of common social intent and the growing importance of solar events for Late Bonito phase people at Chaco. These structures may indicate an interest in theophanies, i.e., conjoining the sacred sun at solstice with the cardinal directions and prominent features of the sacred landscape. They bolster the argument for either centralized leadership by an astronomically adept Late Bonito elite, or a religious revival among the Chacoan people after the severe drought of the 1090s CE. Under the terms of a U.S. National Park Service field research permit, some locationspecific site data has been deliberately withheld in this document, as required by the U.S. Archaeological Resources Protection Act of 1979.

scholarly journals Reference values for biochemical analytes in feral sheep from Socorro Island, Revillagigedo Archipelago, Mexico

2020 ◽  
Vol 72 (6) ◽  
pp. 2036-2044
Author(s):  
I.E. Arias ◽  
R.O.F. Prado ◽  
M.L.J. García ◽  
B.J.L. Zepeda ◽  
C.A.C. García
Keyword(s):  
Reference Values ◽  
Reference Range ◽  
Sodium Ion ◽  
Domestic Sheep ◽  
Data Set ◽  
Mean Values ◽  
June Solstice ◽  
December Solstice ◽  
Socorro Island ◽  
Revillagigedo Archipelago

ABSTRACT To establish reference values for biochemical analytes related to freshwater shortage adaptation, a total of 376 blood samples were collected from feral sheep at Socorro Island, Revillagigedo Archipelago. Year-round variation was assessed by sampling at the beginning of each season defined by the March equinox, June solstice, September equinox, and December solstice. The resulting data set was analyzed using Gaussian distribution and descriptive statistics. Confidence intervals of 95% were established. Analysis of variance was used to compare the mean values of each season. Total cholesterol, triglycerides, urea, albumin, total protein, sodium ion, anion gap, creatine kinase, arginine vasopressin, and aldosterone showed concentrations above the reference range for domestic sheep. Triglycerides, urea, albumin, sodium ion, and aldosterone showed concentrations within the reference range for domestic goats. Most biochemical analytes showed differences (P<0.05) between seasons, with the highest values occurring during winter, and the lowest during spring. Results could help improve the accuracy of metabolic profiles used as a tool for evaluating dehydration indicators, and to describe the physiological mechanisms employed by feral sheep to cope with seasonal availability of freshwater.

scholarly journals Studying the variability in the diurnal and seasonal variations in GPS total electron content over Nigeria

2017 ◽  
Vol 35 (3) ◽  
pp. 701-710 ◽  
Author(s):  
Victor Adetayo Eyelade ◽  
Adekola Olajide Adewale ◽  
Andrew Ovie Akala ◽  
Olawale Segun Bolaji ◽  
A. Babatunde Rabiu
Keyword(s):  
Seasonal Variation ◽  
Total Electron Content ◽  
Seasonal Variations ◽  
Gps Data ◽  
Electron Content ◽  
Total Electron ◽  
Gps Tec ◽  
June Solstice ◽  
December Solstice ◽  
Annual Distribution

Abstract. The study of diurnal and seasonal variations in total electron content (TEC) over Nigeria has been prompted by the recent increase in the number of GPS continuously operating reference stations (CORSs) across Nigeria as well as the reduced costs of microcomputing. The GPS data engaged in this study were recorded in the year 2012 at nine stations in Nigeria located between geomagnetic latitudes – 4.33 and 0.72° N. The GPS data were used to derive GPS TEC, which was analysed for diurnal and seasonal variations. The results obtained were used to produce local GPS TEC maps and bar charts. The derived GPS TEC across all the stations demonstrates consistent minimum diurnal variations during the pre-sunrise hours 04:00 to 06:00 LT, increases with sharp gradient during the sunrise period (∼ 07:00 to 09:00 LT), attains postnoon maximum at about 14:00 LT, and then falls to a minimum just before sunset. Generally, daytime variations are found to be greater than nighttime variations, which range between 0 and 5 TECU. The seasonal variation depicts a semi-annual distribution with higher values (∼ 25–30 TECU) around equinoxes and lower values (∼ 20–25 TECU) around solstices. The December Solstice magnitude is slightly higher than the June Solstice magnitude at all stations, while March Equinox magnitude is also slightly higher than September Equinox magnitude at all stations. Thus, the seasonal variation shows an asymmetry in equinoxes and solstices, with the month of October displaying the highest values of GPS TEC across the latitudes.

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