scholarly journals Statistical correlation of spectral broadening in VLF transmitter signal and low-frequency ionospheric turbulence from observation on DEMETER satellite

2008 ◽  
Vol 8 (5) ◽  
pp. 1105-1111 ◽  
Author(s):  
A. Rozhnoi ◽  
M. Solovieva ◽  
O. Molchanov ◽  
O. Akentieva ◽  
J. J. Berthelier ◽  
...  
Keyword(s):  
Middle Latitude ◽  
Statistical Correlation ◽  
Occurrence Rate ◽  
Signal Spectrum ◽  
Ionospheric Turbulence ◽  
Low Latitude ◽  
Demeter Satellite ◽  
Ion Cyclotron ◽  
Latitude Region

Abstract. In our earlier papers we have found the effect of VLF transmitter signal depression over epicenters of the large earthquakes from observation on the French DEMETER satellite that can be considered as new method of global diagnostics of seismic influence on the ionosphere. At present paper we investigate a possibility VLF signal-ionospheric turbulence interaction using additional characteristic of VLF signal-spectrum broadening. This characteristic is important for estimation of the interaction type: linear or nonlinear scattering. Our main results are the following: – There are two zones of increased spectrum broadening, which are centered near magnetic latitudes Φ=±10° and Φ=±40°. Basing on the previous case study research and ground ionosonde registrations, probably it is evidence of nonlinear (active) scattering of VLF signal on the ionospheric turbulence. However occurrence rate of spectrum broadening in the middle-latitude area is higher than in the near-equatorial zone (~15–20% in comparison with ~100% in former area) that is probably coincides with the rate of ionospheric turbulence. – From two years statistics of observation in the selected 3 low-latitude regions and 1 middle-latitude region inside reception area of VLF signal from NWC transmitter we find a correlation of spectrum broadening neither with ion-cyclotron noise (f=150–500 Hz), which possibly means poor representation of the turbulence by the noise due to its mixture with natural ELF emission (which correlates with whistler), nor with magnetic storm activity. – We find rather evident correlation of ion-cyclotron frequency noise, VLF signal depression and weak correlation of spectrum broadening with seismicity in the middle-latitude region over Japan. But in the low-latitude regions we do not find such a correlation. Statistical decrease of VLF signal supports our previous case study results. However rather weak spectrum broadening-seismicity statistical correlation means probably that passive scattering prevails upon nonlinear (active) one.

scholarly journals Ionospheric Effects on GPS Signal in Low-Latitude Region: A Case Study Review of South East Asia and Africa

2015 ◽  
Vol 34 (3) ◽  
pp. 523 ◽  
Author(s):  
I Abba ◽  
WAWZ Abidin ◽  
T Masri ◽  
KH Ping ◽  
MS Muhammad ◽  
...  
Keyword(s):  
East Asia ◽  
South East Asia ◽  
Low Latitude ◽  
Ionospheric Effects ◽  
Latitude Region ◽  
Study Review

scholarly journals Performance of Network-Based RTK GPS in Low-Latitude Region: A Case Study in Thailand

2012 ◽  
Vol 16 (5) ◽  
pp. 95-104 ◽  
Author(s):  
Teeratat Charoenkalunyuta ◽  
Chalermchon Satirapod ◽  
Hung-Kyu Lee ◽  
Yoon-Soo Choi
Keyword(s):  
Low Latitude ◽  
Latitude Region ◽  
Rtk Gps

scholarly journals Attribution of the Principal Components of the Summertime Ozone Valley in the Upper Troposphere and Lower Stratosphere

2021 ◽  
Vol 8 ◽  
Author(s):  
Shujie Chang ◽  
Chunhua Shi ◽  
Dong Guo ◽  
Jianjun Xu
Keyword(s):  
Principal Components ◽  
Middle Latitude ◽  
Composite Analysis ◽  
Tropopause Height ◽  
The South ◽  
Low Latitude ◽  
Factors Affecting ◽  
Upper Troposphere ◽  
Latitude Region ◽  
East West

The key factors affecting the variation of the ‘ozone valley’, which appears during the boreal summer in the upper troposphere and lower stratosphere (UTLS) over the South Asian High (SAH) and its adjacent areas, have not been determined. This study has performed statistical analysis to improve the understanding of the roles of the sea surface temperature (SST), tropopause height, and the West Pacific Subtropical High (WPSH) on the ozone valley. Based on the European Center for Medium-Range Weather Forecasts Interim Re-Analysis (ERA5), Modern Era Retrospective Analysis for Research and Applications dataset version 2 (MERRA2), and the Stratospheric Water and Ozone Satellite Homogenized (SWOOSH) observation dataset, we examined the principal components of the zonal deviation of the total column ozone (TCO*) in the UTLS by applying the empirical orthogonal function (EOF), Liang-Kleeman information flow method, regression analysis, and composite analysis. The variations of the TCO* anomalies show three dominant modes, namely the east-west dipole mode in the low latitude region, the east-west tripole mode in the middle latitude region, and the south-north mode. According to the regression analysis and information flow, the three leading principal components of TCO* variations are related to the SST near Indonesia and the western Pacific Ocean in low latitudes, the tropopause height over the Iranian Plateau (IP), and the strength of the SAH over the eastern part of the Tibetan Plateau (TP), which is linked to the synchronousness between the SAH and the WPSH. For the east-west dipole mode in the low latitude region, composite analysis shows the interaction between the atmosphere and ocean causes the strengthening of the southern trough at 850 hPa and the divergence at 200 hPa, resulting in a decrease of the TCO* in the UTLS near the low latitude region around the TP. For the east-west tripole mode in the middle latitude region, the composite analysis shows obvious negative anomalies over the IP, where the TCO* reduces and the extent of the ozone valley over the IP increases with the rise of the tropopause. Comparatively, the south-north mode shows obvious positive anomalies over the TP, where the TCO* increases and the extent of the ozone valley over the TP decreases with a weak SAH. This mode is closely related to the location of the WPSH. In summary, the leading factors affecting the three dominant modes for the variations of the TCO* anomalies are SST, tropopause height, and the WPSH.

Case study: NavIC Performance Observation on Low Latitude Region

2021 ◽  
Author(s):  
Darshna D. Jagiwala ◽  
Shweta N. Shah ◽  
Mehul V. Desai
Keyword(s):  
Low Latitude ◽  
Latitude Region

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

2019 ◽  
Vol 37 (6) ◽  
pp. 1005-1024 ◽  
Author(s):  
Ângela Machado dos Santos ◽  
Inez Staciarini Batista ◽  
Mangalathayil Ali Abdu ◽  
José Humberto Andrade Sobral ◽  
Jonas Rodrigues de Souza ◽  
...  
Keyword(s):  
Wave Propagation ◽  
Gravity Wave ◽  
Solar Minimum ◽  
Interesting Case ◽  
Time Interval ◽  
Low Latitude ◽  
Prompt Penetration Electric Field ◽  
Latitude Region ◽  
First Time

Abstract. In this work, we have performed a study for the first time on the climatology of the intermediate descending layers (ILs) over Brazilian equatorial and low-latitude regions during the extreme solar minimum period of 2009. The result of this study shows that the occurrence frequency of the ILs is very high, being > 60 % over São Luís (2∘ S, 44∘ W; inclination: −3.8∘) and > 90 % in Cachoeira Paulista (22.42∘ S, 45∘ W; inclination: −33.5∘). In most cases the ILs occur during the day at altitudes varying from 130 to 180 km and they may descend to lower altitudes (∼100 km) in a time interval of a few minutes to hours. The main driving force for the ILs at the low-latitude region, may be considered to be the diurnal tide (24 h) followed in smaller dominance by the semidiurnal (12 h), terdiurnal (8 h) and quarter-diurnal (6 h) components. In the magnetic equatorial sector, similar behavior was seen, with the exception of the semidiurnal tide, which in general does not appear to have influenced the IL's dynamics (except in summer). Additionally, the IL mean descent velocity over São Luís and Cachoeira Paulista shows a day-to-day variability that may be associated with a wave-like perturbation with a periodicity of some days. Some peculiarities in the IL dynamics were noted, such as the presence of the ILs during the night hours. Ascending and descending ILs appeared to have been formed from some connection with the ionospheric F layer. Quite often, these characteristics are observed in the presence of strong signatures of the gravity wave propagation as suggested by the F layer traces in the ionogram. The descending intermediate layer over Brazil appears to have been formed through a process of F1 layer base detachment. An interesting case study showed that an ascending ILs, initially detected at ∼130 km, reached the base of the F2 layer, due probably to the gravity wave propagation and/or the effect of a prompt penetration electric field.

scholarly journals Investigation of Low Latitude Spread-F Triggered by Nighttime Medium-Scale Traveling Ionospheric Disturbance

2021 ◽  
Vol 13 (5) ◽  
pp. 945
Author(s):  
Zhongxin Deng ◽  
Rui Wang ◽  
Yi Liu ◽  
Tong Xu ◽  
Zhuangkai Wang ◽  
...  
Keyword(s):  
Ionospheric Disturbance ◽  
Phase Speed ◽  
Morphological Processing ◽  
Wave Number ◽  
Occurrence Rate ◽  
Electron Content ◽  
Low Latitude ◽  
Total Electron ◽  
Medium Scale ◽  
Spread F

In the current study, we investigated the mechanism of medium-scale traveling ionospheric disturbance (MSTID) triggering spread-F in the low latitude ionosphere using ionosonde observation and Global Navigation Satellite System-Total Electron Content (GNSS-TEC) measurement. We use a series of morphological processing techniques applied to ionograms to retrieve the O-wave traces automatically. The maximum entropy method (MEM) was also utilized to obtain the propagation parameters of MSTID. Although it is widely acknowledged that MSTID is normally accompanied by polarization electric fields which can trigger Rayleigh–Taylor (RT) instability and consequently excite spread-F, our statistical analysis of 13 months of MSTID and spread-F occurrence showed that there is an inverse seasonal occurrence rate between MSTID and spread-F. Thus, we assert that only MSTID with certain properties can trigger spread-F occurrence. We also note that the MSTID at night has a high possibility to trigger spread-F. We assume that this tendency is consistent with the fact that the polarization electric field caused by MSTID is generally the main source of post-midnight F-layer instability. Moreover, after thorough investigation over the azimuth, phase speed, main frequency, and wave number over the South America region, we found that the spread-F has a tendency to be triggered by nighttime MSTID, which is generally characterized by larger ΔTEC amplitudes.

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