scholarly journals Intermediate Layers responses to Geomagnetic Activity During the 2009 Deep Solar Minimum Over the Brazilian Low Latitude Sector

2021 ◽  
Author(s):  
Ângela Santos ◽  
Christiano Brum ◽  
Inez Batista ◽  
José Sobral ◽  
Mangalathayil Abdu ◽  
...  
Keyword(s):  
Geomagnetic Activity ◽  
Solar Minimum ◽  
Early Morning ◽  
Low Latitude ◽  
Seasonal Behavior ◽  
F Region ◽  
Intermediate Layers ◽  
Bottom Side ◽  
E Region ◽  
First Time

Abstract. Intermediate layers (ILs) are regions of enhanced electron density located in the ionospheric valley that extends from the peak altitude of the daytime E-region to the bottom side of the F-region. This work presents the daytime behavior of the ILs parameters (the virtual height - h’IL, and the top frequency - ftIL) over the low latitude region of Cachoeria Paulista (CP, 22.42° S; 45° W, I: −34.4°) for the deepest solar minimum of the last 500 years. In such a unique condition, this research reveals for the first time the ILs' quiet state seasonal behavior as well as its responses to moderate changes in the geomagnetic activity. The main results show that even small variations of geomagnetic activity (quantified by the planetary Kp index) are able to modify the dynamics of the ILs parameters. For the first time, it was observed that during the summer, the h’IL decrease rapidly with the increase of geomagnetic activity mainly in the early morning hours. In the following hours, a smoothed rise of the IL was found in all seasons analyzed. Regarding to frequency, it was observed that after 12:00 LT, there is a tendency of it decreased with the increase of the magnetic disturbances, being this characteristic more intense after 16:00 LT, except in the equinox, when little or no response was found during all the interval analyzed. In addition, it stands out that the annual periodicity of the ftIL was observed while the h’IL presents semiannual component.

Intermediate Layers responses to Geomagnetic Activity During the 2009 Deep Solar Minimum Over the Brazilian Low Latitude Sector

2021 ◽  
Author(s):  
Angela M Santos ◽  
C G M Brum ◽  
I S Batista ◽  
J H A Sobral ◽  
M A Abdu ◽  
...  
Keyword(s):  
Geomagnetic Activity ◽  
Solar Minimum ◽  
Low Latitude ◽  
Intermediate Layers

scholarly journals Climatology of intermediate descending layers (150 km) over the equatorial and low latitude regions of Brazil during the deep solar minimum of 2009

2019 ◽  
Author(s):  
Ângela M. Santos ◽  
Inez S. Batista ◽  
Mangalathayil A. Abdu ◽  
José H. A. Sobral ◽  
Jonas R. Souza
Keyword(s):  
Wave Propagation ◽  
Gravity Wave ◽  
Solar Minimum ◽  
Interesting Case ◽  
Time Interval ◽  
Low Latitude ◽  
Intermediate Layers ◽  
Prompt Penetration Electric Field ◽  
Latitude Region ◽  
First Time

Abstract. In this work, we report for the first time the climatology of intermediate descending layers over Brazilian equatorial and low latitudes regions during the extreme solar minimum period of 2009. The occurrence frequency of this layer is very high, being > 60 % over São Luís (2° S; 44° W, I: −5.7°) and > 90 % in Cachoeira Paulista (22.42° S; 45° W, I: −34.4°). Our results reveal that in most of the cases the intermediate layers (IL’s) appear during the day at altitudes varying from 130 to 180 km and present a descent movement that reaches the lower altitudes (~ 100 km) in a time interval of a few minutes to hours. Differently from other longitudinal sectors, the diurnal tide (24 h) can be considered as the main cause of IL’s for the low latitude region, followed by a smaller dominance of semidiurnal (12 h), terdiurnal (8 h) and quarter-diurnal (6 h) tide components. In the equatorial sector, similar behavior was found, with the exception of the semidiurnal tide, which in general does not appear to influence the IL’s dynamics (except in summer). The IL’s mean descent velocities over São Luís and Cachoeira Paulista show a day-to-day variability that may be associated with gravity waves propagation. Some peculiarities in the IL’s dynamics have been noted, such as the presence of the IL’s during the night hours, ascending IL’s, simultaneous IL’s, and descending IL’s been formed from some connection with the ionospheric F layer. Quite often, these characteristics are observed in the presence of strong signatures in the ionogram F-layer trace similar to those caused by the gravity wave propagation. We will show further that the descending intermediate layer over Brazil can be formed through a process of F1 layer base detachment. Besides that, we will present an interesting case study in which an ascending IL’s, initially detected at ~ 140 km, reached the base of F2 layer, probably due to the gravity wave propagation and/or due to the effect of the prompt penetration 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 Geomagnetic control of the <i>fo</i>F2 long-term trends

2000 ◽  
Vol 18 (6) ◽  
pp. 653-665 ◽  
Author(s):  
A. V. Mikhailov ◽  
D. Marin
Keyword(s):  
Geomagnetic Activity ◽  
Early Morning ◽  
Lower Latitude ◽  
Ionospheric Disturbances ◽  
Trend Magnitude ◽  
Layer Parameter ◽  
Long Term Trends ◽  
First Time ◽  
Further Development

Abstract. Further development of the method proposed by Danilov and Mikhailov is presented. The method is applied to reveal the foF2 long-term trends on 30 Northern Hemisphere ionosonde stations. Most of them show significant foF2 trends. A pronounced dependence of trend magnitude on geomagnetic (invariant) latitude is confirmed. Periods of negative/positive foF2 trends corresponding to the periods of long-term increasing/decreasing geomagnetic activity are revealed for the first time. Pronounced diurnal variations of the foF2 trend magnitude are found. Strong positive foF2 trends in the post-midnight-early-morning LT sector and strong negative trends during daytime hours are found on the sub-auroral stations for the period with increasing geomagnetic activity. On the contrary middle and lower latitude stations demonstrate negative trends in the early-morning LT sector and small negative or positive trends during daytime hours for the same period. All the morphological features revealed of the foF2 trends may be explained in the framework of contemporary F2-region storm mechanisms. This newly proposed F2-layer geomagnetic storm concept casts serious doubts on the hypothesis relating the F2-layer parameter long-term trends to the thermosphere cooling due to the greenhouse effect.Key words: Ionosphere (ionosphere-atmosphere interactions; ionospheric disturbances)

scholarly journals Relationships between pre-sunset electrojet strength, pre-reversal enhancement and equatorial spread-F onset

2010 ◽  
Vol 28 (2) ◽  
pp. 449-454 ◽  
Author(s):  
J. Uemoto ◽  
T. Maruyama ◽  
S. Saito ◽  
M. Ishii ◽  
R. Yoshimura
Keyword(s):  
Electric Field ◽  
Equatorial Electrojet ◽  
Layer Height ◽  
Equatorial Spread F ◽  
Magnetic Latitude ◽  
F Region ◽  
Spread F ◽  
Bottom Side ◽  
E Region ◽  
Height Increase

Abstract. The virtual height of the bottom side F-region (h'F) and equatorial spread-F (ESF) onsets at Chumphon (10.7° N, 99.4° E; 3.3° N magnetic latitude) were compared with the behaviour of equatorial electrojet (EEJ) ground strength at Phuket (8.1° N, 98.3° E; 0.1° N magnetic latitude) during the period from November 2007 to October 2008. Increase in the F-layer height and ESF onsets during the evening hours were well connected with the EEJ ground strength before sunset, namely, both the height increase and ESF onsets were suppressed when the integrated EEJ ground strength for the period from 1 to 2 h prior to sunset was negative. The finding suggests observationally that the pre-sunset E-region dynamo current and/or electric field are related to the F-region dynamics and ESF onsets around sunset.

scholarly journals Night-time F-region and daytime E-region ionospheric drifts measured at Udaipur during solar flares

2002 ◽  
Vol 20 (11) ◽  
pp. 1837-1842 ◽  
Author(s):  
B. M. Vyas ◽  
R. Pandey
Keyword(s):  
Electric Fields ◽  
Solar Flares ◽  
Night Time ◽  
Low Latitude ◽  
F Region ◽  
Reflection Height ◽  
E Region ◽  
Electric Fields And Currents ◽  
East West ◽  
Ionospheric Drifts

Abstract. Ionospheric drifts measured at a low latitude station, Udaipur (Geomag. Lat. 14.5° N), in the night-time F-region and daytime E-region during solar flares have been studied. The night-time observations, which correspond to the F-region drifts, were carried out on five different nights. The daytime observation corresponding to the E-region drifts is only for one day. It is found that the apparent drift during the solar flare period is reduced considerably, in the daytime E-region as well as in the night-time F-region. The East-West and North-South components of the apparent drift speed are also similarly affected. For the daytime E-region drifts during a flare, increased ionization and subsequent reduction of reflection height is proposed to be the cause of reduced drift speeds. For the night-time F-region drifts, a reduced electric field at the F-region heights resulting from coupling of sunlit and dark hemispheres has been proposed to be the possible cause.Key words. Ionosphere (electric fields and currents; ionospheric disturbances)

scholarly journals Comparative investigations of equatorial electrodynamics and low-to-mid latitude coupling of the thermosphere-ionosphere system

2006 ◽  
Vol 24 (2) ◽  
pp. 503-513 ◽  
Author(s):  
M. J. Colerico ◽  
M. Mendillo ◽  
C. G. Fesen ◽  
J. Meriwether
Keyword(s):  
General Circulation ◽  
Large Scale ◽  
Circulation Model ◽  
Upper Atmosphere ◽  
Low Latitude ◽  
Brightness Wave ◽  
F Region ◽  
Fabry Perot ◽  
Low Latitudes ◽  
First Time

Abstract. The thermospheric midnight temperature maximum (MTM) is a highly variable, but persistent, large scale neutral temperature enhancement which occurs at low latitudes. Its occurrence can impact many fundamental upper atmospheric parameters such as pressure, density, neutral winds, neutral density, and F-region plasma. Although the MTM has been the focus of several investigations employing various instrumentation including photometers, satellites, and Fabry-Perot interferometers, limited knowledge exists regarding the latitude extent of its influence on the upper atmosphere. This is largely due to observational limitations which confined the collective geographic range to latitudes within ±23°. This paper investigates the MTM's latitudinal extent through all-sky imaging observations of its 6300Å airglow signature referred to by Colerico et al. (1996) as the midnight brightness wave (MBW). The combined field of view of three Southern Hemisphere imaging systems located at Arequipa, Peru, and Tucuman and El Leoncito, Argentina, for the first time extends the contiguous latitudinal range of imager observations to 8° S-39° S in the American sector. Our results highlight the propagation of MBW events through the combined fields of view past 39° S latitude, providing the first evidence that the MTM's effect on the upper atmosphere extends into mid-latitudes. The observations presented here are compared with modeled 6300Å emissions calculated using the NCAR thermosphere-ionosphere-electrodynamic general circulation model (TIEGCM) in conjunction with an airglow code. We report that at this time TIEGCM is unable to simulate an MBW event due to the model's inability to reproduce an MTM of the same magnitude and occurrence time as those observed via FPI measurements made from Arequipa. This work also investigates the origins of an additional low latitude airglow feature referred to by Colerico et al. (1996) as the pre-midnight brightness wave (PMBW) and described as an enhancement in 6300Å emission which occurs typically between 20:00-22:00 LT and exhibits equatorward propagation. We present the first successful simulation of a PMBW event using the TIEGCM and the airglow code. We find that the PMBW's origin is electro-dynamical in nature, resulting from the expected evening decay of the inter-tropical arcs.

scholarly journals Some evidence of ground power enhancements at frequencies of global magnetospheric modes at low latitude

1997 ◽  
Vol 15 (1) ◽  
pp. 17-23 ◽  
Author(s):  
P. Francia ◽  
U. Villante
Keyword(s):  
Geomagnetic Field ◽  
Solar Minimum ◽  
Spectral Characteristics ◽  
Power Spectra ◽  
Low Frequency ◽  
Separate Analysis ◽  
Low Latitude ◽  
F Region ◽  
The Earth ◽  
Global Modes

Abstract. A statistical analysis of the power spectra of the geomagnetic field components H and D for periods ranging between 3 min and 1 h was conducted at a low-latitude observatory (L'Aquila, L=1.6) at the minimum and maximum of the solar cycle. For both components, during daytime intervals, we found evidence of power enhancements at frequencies predicted for global modes of the Earth\\'s magnetosphere and occasionally observed at auroral latitudes in the F-region drift velocities (approximately at 1.3, 1.9, 2.6, and 3.4 mHz). Nighttime observations reveal a relative low frequency H enhancement associated with the bay occurrence together with a peak in the H/D power ratio which sharply emerges at 1.2 mHz in the premidnight sector. The strong similarity between solar minimum and maximum suggests that these modes can be considered permanent magnetospheric features. A separate analysis on a two-month interval shows that the observed spectral characteristics are amplified by conditions of high-velocity solar wind.

Near real time plasma irregularity monitoring by FORMOSAT-7/COSMIC-2

2020 ◽  
Author(s):  
ShihPing Chen ◽  
Charles C. Lin ◽  
Rajesh Panthalingal Krishnanunni ◽  
Richard Eastes ◽  
Jong-Min Choi
Keyword(s):  
Real Time ◽  
Global Scale ◽  
Plasma Bubble ◽  
Low Latitude ◽  
Plasma Irregularities ◽  
Ion Drift ◽  
F Region ◽  
Low Latitudes ◽  
Bottom Side

&lt;p&gt;The near real-time global plasma bubble map is constructed by utilizing the FORMOSAT-7/COSMIC-2(F7/C2) radio occultation(RO) scintillation observations in low latitudes. Several tools investigating plasma bubbles like the rate of TEC index(ROTI), Range-Time-Intensity(RTI) diagrams of the Jicamarca Unattended Long-term Investigations of the Ionosphere and Atmosphere(JULIA), and the Global-scale Observations of the Limb and Disk(GOLD) 135.6nm airglow observations are provided validating the RO scintillations. Result shows that the F7/C2 scintillation is sensitive detecting plasma irregularities, especially for the bottom side of these bubbles, which can be used to investigating nighttime vertical plasma drifts in low latitudinal F-region. The hourly quick look of the low latitude plasma bubble occurrence and vertical ion drift around the globe is significant to the space weather monitoring.&lt;/p&gt;

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