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Stening, R. J. "Modelling the low latitude F region". Journal of Atmospheric and Terrestrial Physics 54, nr 11-12 (listopad 1992): 1387–412. http://dx.doi.org/10.1016/0021-9169(92)90147-d.
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Jensen, J. W., i B. G. Fejer. "Longitudinal dependence of middle and low latitude zonal plasma drifts measured by DE-2". Annales Geophysicae 25, nr 12 (2.01.2007): 2551–59. http://dx.doi.org/10.5194/angeo-25-2551-2007.
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Abstract. We used ion drift observations from the DE-2 satellite to study for the first time the longitudinal variations of middle and low latitude F region zonal plasma drifts during quiet and disturbed conditions. The quiet-time middle latitude drifts are predominantly westward; the low latitude drifts are westward during the day and eastward at night. The daytime quiet-time drifts do not change much with longitude; the nighttime drifts have strong season dependent longitudinal variations. In the dusk-premidnight period, the equinoctial middle latitude westward drifts are smallest in the European sector and the low latitude eastward drifts are largest in the American-Pacific sector. The longitudinal variations of the late night-early morning drifts during June and December solstice are anti-correlated. During geomagnetically active times, there are large westward perturbation drifts in the late afternoon-early night sector at upper middle latitudes, and in the midnight sector at low latitudes. The largest westward disturbed drifts during equinox occur in European sector, and the smallest in the Pacific region. These results suggest that during equinox SAPS events occur most often at European longitudes. The low latitude perturbation drifts do not show significant longitudinal
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Qu, Tao, Lifeng Zhang, Yuan Wang, Xu Wang i Jiping Guan. "Seasonal Variations in the Vertical Wavenumber Spectra of Stratospheric Gravity Waves in the Asian Monsoon Region Derived from COSMIC-2 Data". Remote Sensing 14, nr 24 (14.12.2022): 6336. http://dx.doi.org/10.3390/rs14246336.
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We used the Constellation Observing System for Meteorology, Ionosphere, and Climate-2 (COSMIC-2) dry temperature profile data from December 2019 to November 2021 to study the vertical wavenumber spectra of the potential energy of stratospheric gravity waves (GWs Ep) in the Asian monsoon region (15–45°N, 70–150°E). The GW Ep decreases with increasing vertical wavenumber, and the spectral slope varies with wavenumber. The spectral slope becomes smaller over a wavenumber range of 0.1–0.45 km−1, and larger from 0.45–1 km−1, with increasing wavenumber. The energy density distribution at middle and low latitudes shows seasonal variations. Over a wavenumber range of 0.05–0.5 km−1, the energy density in winter is higher at middle latitudes than at low latitudes, and the opposite is observed in summer over a wavenumber range from 0.1 to 1 km−1. Both the spectral amplitude and characteristic wavelength exhibit band-like patterns, and the large-value bands and their centers vary significantly with the season. In winter, the middle latitude spectral amplitude is larger than that at low latitudes, and the significant large-value band-like distribution is at 40°N. In summer, the distribution is opposite, with large-value band regions over the Bay of Bengal and Indo-China Peninsula. The large-value region of the middle latitude spectral amplitude corresponds to a longer characteristic wavelength, while the large-value region of the low latitude spectral amplitude corresponds to a shorter characteristic wavelength. There is also significant seasonal variation in the distribution of spectral slopes. Over a wavenumber range of 0.1 to 0.5 km−1, the slope is smaller at middle latitudes and larger at low latitudes in winter; the opposite is observed in summer. There is a significant annual cycle of spectral amplitude at middle and low latitudes, and a 4.8 month cycle at middle latitudes.
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Dabas, R. S., R. M. Das, V. K. Vohra i C. V. Devasia. "Space weather impact on the equatorial and low latitude F-region ionosphere over India". Annales Geophysicae 24, nr 1 (7.03.2006): 97–105. http://dx.doi.org/10.5194/angeo-24-97-2006.
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Abstract. For a detailed study of the space weather impact on the equatorial and low latitude F-region, the ionospheric response features are analysed during the periods of three recent and most severe magnetic storm events of the present solar cycle which occurred in October and November 2003, and November 2004. The F-layer base height (h'F), peak height (hmF2) and critical frequency (foF2) data, from Trivandrum, an equatorial station and Delhi, a low latitude location, are examined during the three magnetic storm periods. The results of the analysis clearly shows that the height of the F-region (both h'F and hmF2), at the equator and low latitude, simultaneously increases by 200 to 300 km, in association with maximum negative excursion of Dst values around the midnight hours with a large depletion of ionization over the equator, which is followed by an ionization enhancement at low latitude during the recovery phase of the storm. At Delhi, fast variations up to 200 m/s are also observed in the F-layer vertical upward/downward velocity, calculated using Doppler shifts, associated with the maximum negative excursion of Dst. This shows that during magnetic disturbances, the equatorial ionization anomaly (EIA) expands to a much wider latitude than the normal fountain driven by the E/F-layer dynamo electric fields. It is also observed that during the main phase of the storm, at low latitude there is generally an enhancement of F-region ionization with an increase in h'F/hmF2 but in the equatorial region, the ionization collapses with a decrease in h'F/hmF2, especially after sunset hours. In addition, at the equator the normal pre-sunset hours' enhancement in h'F is considerably suppressed during storm periods. This might be due to changes in magnitude and direction of the zonal electric field affecting the upward E×B drift and hence the plasma distribution in the form of a decrease in electron density in the equatorial region and an increase in the low latitude region. In association with disturbance electric fields, the enhanced storm-induced equatorward meridional winds in the thermosphere can also further amplify the F-layer height rise at low latitudes during the post-midnight hours, as observed in two of the storm periods.
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Krishna Murthy, B. V., i S. S. Hari. "Electric fields in the low latitude F-region". Advances in Space Research 18, nr 6 (styczeń 1996): 93–98. http://dx.doi.org/10.1016/0273-1177(95)00906-x.
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Zhou, Yun-Liang, Li Wang, Chao Xiong, Hermann Lühr i Shu-Ying Ma. "The solar activity dependence of nonmigrating tides in electron density at low and middle latitudes observed by CHAMP and GRACE". Annales Geophysicae 34, nr 4 (27.04.2016): 463–72. http://dx.doi.org/10.5194/angeo-34-463-2016.
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Abstract. In this paper we use more than a decade of in situ electron density observations from CHAMP and GRACE satellites to investigate the solar activity dependence of nonmigrating tides at both low and middle latitudes. The results indicate that the longitudinal patterns of F region electron density vary with season and latitude, which are exhibiting a wavenumber 4 (WN4) pattern around September equinox at low latitudes and WN1/WN2 patterns during local summer at the southern/northern middle latitudes. These wave patterns in the F region ionosphere can clearly be seen during both solar maximum and minimum years. At low latitudes the absolute amplitudes of DE3 (contributing to the WN4 pattern) are found to be highly related to the solar activity, showing larger amplitudes during solar maximum years. Similarly a solar activity dependence can also be found for the absolute amplitudes of D0, DW2 and DE1 (contributing to the WN1 and WN2 pattern) at middle latitudes. The relative amplitudes (normalized by the zonal mean) of these nonmigrating tides at both low and middle altitudes show little dependence on solar activity. We further found a clear modulation by the quasi-biennial oscillation (QBO) of the relative DE3 amplitudes in both satellite observations, which is consistent with the QBO dependence as reported for the E region temperatures and zonal wind. It also supports the strong coupling of the low-latitude nonmigrating tidal activity between the E and F regions. However, the QBO dependence cannot be found for the relative amplitudes of the nonmigrating tides at middle latitudes, which implies that these tides are generated in situ at F region altitudes.
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Abe, Oladipo Emmanuel, Xurxo Otero Villamide, Claudia Paparini, Rodrigue Herbert Ngaya, Sandro M. Radicella i Bruno Nava. "Signature of ionospheric irregularities under different geophysical conditions on SBAS performance in the western African low-latitude region". Annales Geophysicae 35, nr 1 (3.01.2017): 1–9. http://dx.doi.org/10.5194/angeo-35-1-2017.
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Abstract. Rate of change of TEC (ROT) and its index (ROTI) are considered a good proxy to characterize the occurrence of ionospheric plasma irregularities like those observed after sunset at low latitudes. SBASs (satellite-based augmentation systems) are civil aviation systems that provide wide-area or regional improvement to single-frequency satellite navigation using GNSS (Global Navigation Satellite System) constellations. Plasma irregularities in the path of the GNSS signal after sunset cause severe phase fluctuations and loss of locks of the signals in GNSS receiver at low-latitude regions. ROTI is used in this paper to characterize plasma density ionospheric irregularities in central–western Africa under nominal and disturbed conditions and identified some days of irregularity inhibition. A specific low-latitude algorithm is used to emulate potential possible SBAS message using real GNSS data in the western African low-latitude region. The performance of a possible SBAS operation in the region under different ionospheric conditions is analysed. These conditions include effects of geomagnetic disturbed periods when SBAS performance appears to be enhanced due to ionospheric irregularity inhibition. The results of this paper could contribute to a feasibility assessment of a European Geostationary Navigation Overlay System-based SBAS in the sub-Saharan African region.
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Yizengaw, E., E. A. Essex i R. Birsa. "The Southern Hemisphere and equatorial region ionization response for a 22 September 1999 severe magnetic storm". Annales Geophysicae 22, nr 8 (7.09.2004): 2765–73. http://dx.doi.org/10.5194/angeo-22-2765-2004.
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Abstract. The ionospheric storm evolution process was monitored during the 22 September 1999 magnetic storm over the Australian eastern region, through measurements of the ionospheric Total Electron Content (TEC) from seven Global Positioning Systems (GPS) stations. The spatial and temporal variations of the ionosphere were analysed as a time series of TEC maps. Results of our analysis show that the main ionospheric effect of the storm under consideration are: the long lasting negative storm effect during a magnetic storm at mid-latitude regions; the strong, positive disturbances during the storm's main phase at auroral latitude regions; the effects of storm-induced equatorward directed wind causing a positive disturbance at high and mid-latitude stations with appropriate time shift between higher and lower latitudes; daytime poleward movement of depleted plasma that causes temporary suppression of the equatorial anomaly during the start of the storm recovery phase; and prompt penetration of eastward electric fields to ionospheric altitudes and the production of nearly simultaneous TEC enhancement at all latitudes. In general, we found dominant negative disturbance over mid and high latitudes and positive disturbance at low latitudes. A comparison of storm-time behaviour of TEC determined from GPS satellites, and foF2 derived from ionosondes at a range of latitudes, showed reasonable agreement between the two independent measurements.
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Kumar, Edwin A., i Sushil Kumar. "Geomagnetic Storm Effect on F2-Region Ionosphere during 2012 at Low- and Mid-Latitude-Latitude Stations in the Southern Hemisphere". Atmosphere 13, nr 3 (15.03.2022): 480. http://dx.doi.org/10.3390/atmos13030480.
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The ionospheric effects of six intense geomagnetic storms with Dst index ≤ −100 nT that occurred in 2012 were studied at a low-latitude station, Darwin (Geomagnetic coordinates, 21.96° S, 202.84° E), a low-mid-latitude station, Townsville (28.95° S, 220.72° E), and a mid-latitude station, Canberra (45.65° S, 226.30° E), in the Australian Region, by analyzing the storm–time variations in the critical frequency of the F2-region (foF2). Out of six storms, a storm of 23–24 April did not produce any ionospheric effect. The storms of 30 September–3 October (minimum Dst = −122 nT) and 7–10 October (minimum Dst = −109 nT) are presented as case studies and the same analysis was done for the other four storms. The storm of 30 September–3 October, during its main phase, produced a positive ionospheric storm at all three stations with a maximum percentage increase in foF2 (∆foF2%) of 45.3% at Canberra whereas during the recovery phase it produced a negative ionospheric storm at all three stations with a maximum ∆foF2% of −63.5% at Canberra associated with a decrease in virtual height of the F-layer (h’F). The storm of 7–10 October produced a strong long-duration negative ionospheric storm associated with an increase in h’F during its recovery phase at all three stations with a maximum ∆foF2% of −65.1% at Townsville. The negative ionospheric storms with comparatively longer duration were more pronounced in comparison to positive storms and occurred only during the recovery phase of storms. The storm main phase showed positive ionospheric storms for two storms (14–15 July and 30 September–3 October) and other three storms did not produce any ionospheric storm at the low-latitude station indicating prompt penetrating electric fields (PPEFs) associated with these storms did not propagate to the low latitude. The positive ionospheric storms during the main phase are accounted to PPEFs affecting ionospheric equatorial E × B drifts and traveling ionospheric disturbances due to joule heating at the high latitudes. The ionospheric effects during the recovery phase are accounted to the disturbance dynamo electric fields and overshielding electric field affecting E × B drifts and the storm-induced circulation from high latitudes toward low latitudes leading to changes in the natural gas composition [O/N2] ratio.
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Yamauchi, Masatoshi, Magnar G. Johnsen, Carl-Fredrik Enell, Anders Tjulin, Anna Willer i Dmitry A. Sormakov. "High-latitude crochet: solar-flare-induced magnetic disturbance independent from low-latitude crochet". Annales Geophysicae 38, nr 6 (3.11.2020): 1159–70. http://dx.doi.org/10.5194/angeo-38-1159-2020.
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Abstract. A solar-flare-induced, high-latitude (peak at 70–75∘ geographic latitude – GGlat) ionospheric current system was studied. Right after the X9.3 flare on 6 September 2017, magnetic stations at 68–77∘ GGlat near local noon detected northward geomagnetic deviations (ΔB) for more than 3 h, with peak amplitudes of >200 nT without any accompanying substorm activities. From its location, this solar flare effect, or crochet, is different from previously studied ones, namely, the subsolar crochet (seen at lower latitudes), auroral crochet (pre-requires auroral electrojet in sunlight), or cusp crochet (seen only in the cusp). The new crochet is much more intense and longer in duration than the subsolar crochet. The long duration matches with the period of high solar X-ray flux (more than M3-class flare level). Unlike the cusp crochet, the interplanetary magnetic field (IMF) BY is not the driver, with the BY values of only 0–1 nT out of a 3 nT total field. The equivalent ionospheric current flows eastward in a limited latitude range but extended at least 8 h in local time (LT), forming a zonal current region equatorward of the polar cap on the geomagnetic closed region. EISCAT radar measurements, which were conducted over the same region as the most intense ΔB, show enhancements of electron density (and hence of ion-neutral density ratio) at these altitudes (∼100 km) at which strong background ion convection (>100 m s−1) pre-existed in the direction of tidal-driven diurnal solar quiet (Sq0) flow. Therefore, this new zonal current can be related to this Sq0-like convection and the electron density enhancement, for example, by descending the E-region height. However, we have not found why the new crochet is found in a limited latitudinal range, and therefore, the mechanism is still unclear compared to the subsolar crochet that is maintained by a transient redistribution of the electron density. The signature is sometimes seen in the auroral electrojet (AE = AU − AL) index. A quick survey for X-class flares during solar cycle 23 and 24 shows clear increases in AU for about half the > X2 flares during non-substorm time, despite the unfavourable latitudinal coverage of the AE stations for detecting this new crochet. Although some of these AU increases could be the auroral crochet signature, the high-latitude crochet can be a rather common feature for X flares. We found a new type of the solar flare effect on the dayside ionospheric current at high latitudes but equatorward of the cusp during quiet periods. The effect is also seen in the AU index for nearly half of the > X2-class solar flares. A case study suggests that the new crochet is related to the Sq0 (tidal-driven part) current.
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Rozhnoi, A., M. Solovieva, O. Molchanov, O. Akentieva, J. J. Berthelier, M. Parrot, P. F. Biagi i M. Hayakawa. "Statistical correlation of spectral broadening in VLF transmitter signal and low-frequency ionospheric turbulence from observation on DEMETER satellite". Natural Hazards and Earth System Sciences 8, nr 5 (16.10.2008): 1105–11. http://dx.doi.org/10.5194/nhess-8-1105-2008.
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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.
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Patra, A. K., S. Sripathi, P. B. Rao i K. S. V. Subbarao. "Simultaneous VHF radar backscatter and ionosonde observations of low-latitude E region". Annales Geophysicae 23, nr 3 (30.03.2005): 773–79. http://dx.doi.org/10.5194/angeo-23-773-2005.
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Abstract. The first results of simultaneous observations made on the low-latitude field-aligned irregularities (FAI) using the MST radar located at Gadanki (13.5° N, 79.2° E, dip 12.5°) and the Es parameters using an ionosonde at a nearby station Sriharikota (13.7° N, 80.1° E, dip 12.6°) are presented. The observations show that while the height of the most intense radar echoes is below the virtual height of Es (h'Es) during daytime, it is found to be either below or above during nighttime. The strength of the FAI is better correlated with the top penetration frequency (ftEs) and the blanketing frequency (fbEs) during the night (r=0.4 in both cases) as compared to the day (r=0.35 and -0.04, respectively). Furthermore, the signal strength of FAI is reasonably correlated with (ftEs-fbEs) during daytime (r=0.59) while very poorly correlated during nighttime (r=0.18). While the radar observations in general appear to have characteristics close to that of mid-latitudes, the relationship of these with the Es parameters are poorer than that of mid-latitudes. The observations reported here, nevertheless, are quite consistent with the expectations based on the gradient drift instability mechanism.
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Aldahan, A., G. Possnert, A. El Saiy i O. Abdelghany. "Particle-bound 10Be from a low latitude arid region". Journal of Radioanalytical and Nuclear Chemistry 299, nr 3 (20.11.2013): 1709–13. http://dx.doi.org/10.1007/s10967-013-2853-8.
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Maute, Astrid, i Arthur D. Richmond. "$F$-Region Dynamo Simulations at Low and Mid-Latitude". Space Science Reviews 206, nr 1-4 (12.07.2016): 471–93. http://dx.doi.org/10.1007/s11214-016-0262-3.
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N, Dr Swathi. "Performance Evaluation of Delay Locked Loop based GPS Multipath Estimation Algorithm over Low Latitude Region". Journal of Advanced Research in Dynamical and Control Systems 12, SP7 (25.07.2020): 2395–403. http://dx.doi.org/10.5373/jardcs/v12sp7/20202368.
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Yizengaw, Endawoke. "Global Longitudinal Dependence Observation of the Neutral Wind and Ionospheric Density Distribution". International Journal of Geophysics 2012 (2012): 1–11. http://dx.doi.org/10.1155/2012/342581.
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The statistical global view of the low-latitude ionospheric density stimulates further interest in studying the strong longitudinal variability of the ionospheric density structures in low-to-equatorial latitudes. However, we are not completely certain how the electrodynamics and ion-neutral coupling proceeds at low latitudes; in particular, the longitudinal difference in the dynamics of plasma structures in the low-to-mid latitude ionosphere is not yet fully understood. Numerical studies of latent heat release in the troposphere have indicated that the lower atmosphere can indeed introduce a longitudinal dependence and variability of the low-latitude ionosphere during quiet conditions. For the first time, we present simultaneous observations of the tidally modulated global wind structure, using TIDI observations, in the E-region and the ionospheric density distribution using ground (global GPS receivers) and space-based (C/NOFS in situ density and GPS TEC on CHAMP) instruments. Our results show that the longitudinally structured zonal wind component could be responsible for the formation of wave number four pattern of the equatorial anomaly.
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Zhang, H., Y. Liu, J. Wu, T. Xu i D. Sheng. "Observations and modeling of UHF-band scintillation occurrence probability over the low-latitude region of China during the maximum activity of solar cycle 24". Annales Geophysicae 33, nr 1 (16.01.2015): 93–100. http://dx.doi.org/10.5194/angeo-33-93-2015.
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Abstract. The climatological characteristics of UHF-band scintillations over the low-latitude region of China were investigated by analyzing the observations recorded at three stations of our regional network of satellite-beacon-based scintillation monitoring in 2013. The three stations are Hainan (geographic 20.0° N, 110.3° E; geomagnetic 10.1° N, 177.4° W, dip 28.2°), Guangzhou (geographic 23.0° N, 113.0° E; geomagnetic 13.1° N, 174.8° W, dip 33.9°) and Kunming (geographic 25.6° N, 103.7° E; geomagnetic 15.7° N, 176.4° E, dip 39.0°), located at low latitudes of China. The variations of UHF-band scintillation occurrence with latitude, time and season are presented in detail to understand the morphology and climatology of ionospheric scintillations over the low-latitude region of China. An equinoctial asymmetry in the occurrences of scintillation and an obvious difference of the onset time of scintillations between Hainan and Kunming is noted in this data set. Subsequently, the ionosonde data are utilized to study the possible causes of the asymmetry between two equinoxes. The observations suggest that the mean critical frequency (foF2) at 20:00 LT (12:00 UT) in the autumnal equinoctial months (September and October) and the vernal equinoctial months (March and April) has a similar asymmetry. The ratio of the mean foF2 between two equinoxes is proportional to the ratio between the maximum scintillation occurrence in the autumnal equinox and in the vernal equinox. Therefore, this ratio can act as a proxy for the equinoctial asymmetry in the occurrences of scintillation over the low-latitude region of China, and can be used to model the equinoctial asymmetry in our empirical climatological model of scintillation occurrence probability (CMSOP). The CMSOP can provide the predictions of the occurrences of scintillation over the low-latitude region of China and was validated in this study.
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Pastor Yabar, A., M. J. Martínez González i M. Collados. "Photospheric magnetic topology of a north polar region". Astronomy & Astrophysics 635 (marzec 2020): A210. http://dx.doi.org/10.1051/0004-6361/202037480.
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Aims. We aim to characterise the magnetism of a large fraction of the north polar region close to a maximum of activity, when the polar regions are reversing their dominant polarity. Methods. We make use of full spectropolarimetric data from the CRisp Imaging Spectro-Polarimeter installed at the Swedish Solar Telescope. The data consist of a photospheric spectral line, which is used to infer the various physical parameters of different quiet Sun regions by means of the solution of the radiative transfer equation. We focus our analysis on the properties found for the north polar region and their comparison to the same analysis applied to data taken at disc centre and low-latitude quiet Sun regions for reference. We also analyse the spatial distribution of magnetic structures throughout the north polar region. Results. We find that the physical properties of the polar region (line-of-sight velocity, magnetic flux, magnetic inclination and magnetic azimuth) are compatible with those found for the quiet Sun at disc centre and are similar to the ones found at low latitudes close to the limb. Specifically, the polar region magnetism presents no specific features. The structures for which the transformation from a line-of-sight to a local reference frame was possible harbour large magnetic fluxes (>1017 Mx) and are in polarity imbalance with a dominant positive polarity, the largest ones (>1019 Mx) being located below 73° latitude.
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Pryse, S. E., R. W. Sims, J. Moen i K. Oksavik. "Ionospheric signatures of the low-latitude boundary layer under conditions of northward IMF and small clock angle". Annales Geophysicae 24, nr 8 (13.09.2006): 2169–78. http://dx.doi.org/10.5194/angeo-24-2169-2006.
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Abstract. A case study is presented that concerns the footprints of the low-latitude boundary layer in the high-latitude ionosphere. The measurements were made near local magnetic noon in summertime under conditions of Bz>0 and small clock angle. Of particular interest are particle fluxes measured in the region by the NOAA-12 satellite that revealed energetic (>30 keV) electrons, characteristic of trapped particles, together with a population of softer precipitating magnetosheath particles. The particle energy-distribution was distinct from those identifying the central plasma sheet at lower latitudes. On its poleward side the layer extended to at least the latitude of the polar cap boundary as identified in ion flows and electron densities measured by the EISCAT Svalbard radar. It is proposed that the particles of the low-latitude boundary layer occurred on newly-closed magnetic field lines, which were formed by the closure of open polar cap field by lobe reconnection in both Northern and Southern Hemispheres.
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Chen, Yiding, Libo Liu, Huijun Le, Hui Zhang i Ruilong Zhang. "Responding trends of ionospheric F2-layer to weaker geomagnetic activities". Journal of Space Weather and Space Climate 12 (2022): 6. http://dx.doi.org/10.1051/swsc/2022005.
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Geomagnetic activities frequently occur in varying degrees. Strong geomagnetic activities, which have been widely investigated, occur occasionally; they can cause distinguishable and significant disturbances in the ionosphere. Weaker geomagnetic activities frequently appear, whereas their effects are generally difficult to be distinguished from complex ionospheric variations. Weaker geomagnetic activities play important roles in ionospheric day-to-day variability thus should deserve further attention. In this study, long-term (longer than one solar cycle) measurements of the F2-layer critical frequency (foF2) were collected to statistically investigate ionospheric responses to weaker geomagnetic activities (Ap < 60). The responding trends of low- to high-latitude foF2 to increasing geomagnetic activity are presented for the first time; they are statistically evident. Both increasing and decreasing trends can occur, depending on latitudes and seasons. The trend gradually transits from high-latitude decreasing trends to equatorial increasing trends with decreasing latitude, and this transition is seasonally dependent. As a result, the trend has a seasonal difference at mid-latitudes. The responding trend is generally more distinct at higher latitudes and in the equatorial region than at mid-latitudes, and the responding intensity is largest at higher latitudes. Although theoretically, geomagnetic activities can disturb the ionosphere through multiple mechanisms, the morphology of the trend suggests that the frequent weaker geomagnetic activities modulate the high- to low-latitude ionosphere mainly through disturbing high-latitude thermospheric composition and further altering the thermospheric background circulation.
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Pitout, F., P. T. Newell i S. C. Buchert. "Simultaneous high- and low-latitude reconnection: ESR and DMSP observations". Annales Geophysicae 20, nr 9 (30.09.2002): 1311–20. http://dx.doi.org/10.5194/angeo-20-1311-2002.
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Abstract. We present EISCAT Svalbard Radar and DMSP observations of a double cusp during an interval of predominantly northward IMF on 26 November 2000. In the cusp region, the ESR dish, pointing northward, recorded sun-ward ionospheric flow at high latitudes (above 82° GL), indicating reconnection occuring in the magnetospheric lobe. Meanwhile, the same dish also recorded bursts of poleward flow, indicative of bursty reconnection at the subsolar magnetopause. Within this time interval, the DMSP F13 satellite passed in the close vicinity of the Svalbard archipelago. The particle measurement on board exhibited a double cusp structure in which two oppositely oriented ion dispersions are recorded. We interpret this set of data in terms of simultaneous merging at low- and high-latitude magnetopause. We discuss the conditions for which such simultaneous high-latitude and low-latitude reconnection can be anticipated. We also discuss the consequences of the presence of two X-lines in the dayside polar ionosphere.Key words. Magnetospheric physics (solar wind-magnetosphere interactions) – Ionosphere (polar ionosphere; plasma convection)
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Haitaamar, Zineddine, Abdulrahman Sulaiman, Sidi Ahmed Bendoukha i Diogo Rodrigues. "Lower Inclination Orbit Concept for Direct-Communication-To-Satellite Internet-Of-Things Using Lean Satellite Standard in Near-Equatorial Regions". Applied Sciences 13, nr 9 (4.05.2023): 5654. http://dx.doi.org/10.3390/app13095654.
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This research proposes a low-inclined orbit concept and design for the Internet-of-Things (IoT) using lean satellite standards in near-equatorial regions. The study aims to evaluate the coverage of various inclination angles at various latitudes and inclination angles in order to determine the most suitable satellite design for providing IoT coverage in these regions. The main methods applied in the study included analyzing the coverage performance of different inclination angles, the link budget analysis using simulations and the definition of the mission criteria. The results of the study show that the overall coverage performance decreases with an increase in the inclination angle. Satellites with lower inclination angles have ground tracks that are more closely aligned with the equator, while satellites with higher inclination angles have ground tracks that are inclined further toward the poles. In addition, the results show that the fraction of orbits with coverage (expressed as a percentage) declines with increasing latitude. Based on these findings, a low-inclined orbit of 24° provides the best coverage for IoT in near-equatorial regions within ±20 and 26° latitude, with a peak coverage of 27% at 24° latitude and a minimum coverage of 10% in the region spanning from 0° to ±27° latitude. This design offers more coverage time and a shorter revisit time to the selected regions for communication missions.
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Tatsuta, K., Y. Hobara, S. Pal i M. Balikhin. "Sub-ionospheric VLF signal anomaly due to geomagnetic storms: a statistical study". Annales Geophysicae 33, nr 11 (30.11.2015): 1457–67. http://dx.doi.org/10.5194/angeo-33-1457-2015.
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Abstract. We investigate quantitatively the effect of geomagnetic storms on the sub-ionospheric VLF/LF (Very Low Frequency/Low Frequency) propagations for different latitudes based on 2-year nighttime data from Japanese VLF/LF observation network. Three statistical parameters such as average signal amplitude, variability of the signal amplitude, and nighttime fluctuation were calculated daily for 2 years for 16–21 independent VLF/LF transmitter–receiver propagation paths consisting of three transmitters and seven receiving stations. These propagation paths are suitable to simultaneously study high-latitude, low-mid-latitude and mid-latitude D/E-region ionospheric properties. We found that these three statistical parameters indicate significant anomalies exceeding at least 2 times of their standard deviation from the mean value during the geomagnetic storm time period in the high-latitude paths with an occurrence rate of anomaly between 40 and 50 % presumably due to the auroral energetic electron precipitation. The mid-latitude and low-mid-latitude paths have a smaller influence from the geomagnetic activity because of a lower occurrence rate of anomalies even during the geomagnetically active time period (from 20 to 30 %). The anomalies except geomagnetic storm periods may be caused by atmospheric and/or lithospheric origins. The statistical occurrence rates of ionospheric anomalies for different latitudinal paths during geomagnetic storm and non-storm time periods are basic and important information not only to identify the space weather effects toward the lower ionosphere depending on the latitudes but also to separate various external physical causes of lower ionospheric disturbances.
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Venkatesham, K., i Rajesh Singh. "Extreme Space-Weather Effect on D-Region Ionosphere in Indian Low Latitude Region". Current Science 114, nr 09 (10.05.2018): 1923. http://dx.doi.org/10.18520/cs/v114/i09/1923-1926.
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Cui, Suzhen, Yun Li, Le Liu, Qianhong Wang i Feizhou Chen. "Changes in astaxanthin and fatty acid concentrations during the developmental process in the calanoid Arctodiaptomus walterianus in an alpine lake at low latitudes". Journal of Plankton Research 43, nr 2 (marzec 2021): 314–24. http://dx.doi.org/10.1093/plankt/fbab019.
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Abstract Astaxanthin is ubiquitous in calanoid copepods in high latitude or altitude regions and is well studied. However, the dynamics of astaxanthin in calanoids at low latitudes are less studied. We collected samples during the ice-free season from Lake Mubanghai, an alpine lake located in a low-latitude and high-altitude region, and analyzed astaxanthin content changes among different developmental stages in Arctodiaptomus walterianus. The total astaxanthin content in A. walterianus varied from 1.66 to 4.49 μg/mg dry weight and was highest in October, the month with the lowest temperature among the three sampling dates. Both free astaxanthin and astaxanthin esters content per biomass and the ratio of free astaxanthin increased from the nauplius to adult stage, and astaxanthin esters dominated in total astaxanthin in all developmental stages. The concentrations of polyunsaturated fatty acids were low in seston but were the main fatty acids in the calanoid. The total fatty acid concentration was positively correlated with the concentrations of total astaxanthin, free astaxanthin and astaxanthin esters in the calanoid. These results suggested that astaxanthin may be beneficial to the accumulation of fatty acids. This strategy may benefit calanoids in adaptation to high mountain environments at low latitudes.
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Patra, A. K., i N. Venkateswara Rao. "Low-latitude valley region irregularities studied using the Gadanki radar". Journal of Geophysical Research: Space Physics 112, A3 (marzec 2007): n/a. http://dx.doi.org/10.1029/2006ja011857.
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Liu, Tong, Zhibin Yu, Zonghua Ding, Wenfeng Nie i Guochang Xu. "Observation of Ionospheric Gravity Waves Introduced by Thunderstorms in Low Latitudes China by GNSS". Remote Sensing 13, nr 20 (15.10.2021): 4131. http://dx.doi.org/10.3390/rs13204131.
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The disturbances of the ionosphere caused by thunderstorms or lightning events in the troposphere have an impact on global navigation satellite system (GNSS) signals. Gravity waves (GWs) triggered by thunderstorms are one of the main factors that drive short-period Travelling Ionospheric Disturbances (TIDs). At mid-latitudes, ionospheric GWs can be detected by GNSS signals. However, at low latitudes, the multi-variability of the ionosphere leads to difficulties in identifying GWs induced by thunderstorms through GNSS data. Though disturbances of the ionosphere during low-latitude thunderstorms have been investigated, the explicit GW observation by GNSS and its propagation pattern are still unclear. In this paper, GWs with periods from 6 to 20 min are extracted from band-pass filtered GNSS carrier phase observations without cycle-slips, and 0.2–0.8 Total Electron Content Unit (TECU) magnitude perturbations are observed when the trajectories of ionospheric pierce points fall into the perturbed region. The propagation speed of 102.6–141.3 m/s and the direction of the propagation indicate that the GWs are propagating upward from a certain thunderstorm at lower atmosphere. The composite results of disturbance magnitude, period, and propagation velocity indicate that GWs initiated by thunderstorms and propagated from the troposphere to the ionosphere are observed by GNSS for the first time in the low-latitude region.
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Nemecek, Z., A. Fedorov, J. Safrankova i G. Zastenker. "Structure of the low-latitude magnetopause: MAGION-4 observations". Annales Geophysicae 15, nr 5 (31.05.1997): 553–61. http://dx.doi.org/10.1007/s00585-997-0553-9.
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Abstract. The aims of this paper are (1) briefly to describe the plasma devices onboard the MAGION-4 satellite, launched on 3 August 1995, of the INTERBALL project, and (2) to discuss first observations made near the magnetopause region. During the presented boundary crossings the MAGION-4 observed quasi-periodic pulses of magnetosheath-like plasma in a region of low plasma density. This region is located just earthwards of the magnetopause and is populated by a plasma which, except for the density, has the same parameters as in the magnetosheath. Deeper in the magnetosphere, the encounter of a layer of hot electrons and high-energy ions was interpreted as low-latitude boundary layer.
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Zhang, D. H., W. Zhang, Q. Li, L. Q. Shi, Y. Q. Hao i Z. Xiao. "Accuracy analysis of the GPS instrumental bias estimated from observations in middle and low latitudes". Annales Geophysicae 28, nr 8 (25.08.2010): 1571–80. http://dx.doi.org/10.5194/angeo-28-1571-2010.
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Abstract. With one bias estimation method, the latitude-related error distribution of instrumental biases estimated from the GPS observations in Chinese middle and low latitude region in 2004 is analyzed statistically. It is found that the error of GPS instrumental biases estimated under the assumption of a quiet ionosphere has an increasing tendency with the latitude decreasing. Besides the asymmetrical distribution of the plasmaspheric electron content, the obvious spatial gradient of the ionospheric total electron content (TEC) along the meridional line that related to the Equatorial Ionospheric Anomaly (EIA) is also considered to be responsible for this error increasing. The RMS of satellite instrumental biases estimated from mid-latitude GPS observations in 2004 is around 1 TECU (1 TECU = 1016/m2), and the RMS of the receiver's is around 2 TECU. Nevertheless, the RMS of satellite instrumental biases estimated from GPS observations near the EIA region is around 2 TECU, and the RMS of the receiver's is around 3–4 TECU. The results demonstrate that the accuracy of the instrumental bias estimated using ionospheric condition is related to the receiver's latitude with which ionosphere behaves a little differently. For the study of ionospheric morphology using the TEC derived from GPS data, in particular for the study of the weak ionospheric disturbance during some special geo-related natural hazards, such as the earthquake and severe meteorological disasters, the difference in the TEC accuracy over different latitude regions should be paid much attention.
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Li, Yaoguo, Misac Nabighian i Douglas W. Oldenburg. "Using an equivalent source with positivity for low-latitude reduction to the pole without striation". GEOPHYSICS 79, nr 6 (1.11.2014): J81—J90. http://dx.doi.org/10.1190/geo2014-0134.1.
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We present a reformulation of reduction to the pole (RTP) of magnetic data at low latitudes and the equator using equivalent sources. The proposed method addresses both the theoretical difficulty of low-latitude instability and the practical issue of computational cost. We prove that a positive equivalent source exists when the magnetic data are produced by normal induced magnetization, and we show that the positivity is sufficient to overcome the low-latitude instability in the space domain. We further apply a regularization term directly to the recovered RTP field to improve the solution. The use of equivalent source also naturally enables the processing of data acquired on uneven surface. The result is a practical algorithm that is effective at the equatorial region and can process large-scale data sets with uneven observation heights.
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Shen, Linlin, Haiyan Deng, Ganglong Zhang, Anqi Ma i Xiaoyong Mo. "Effect of Climate Change on the Potentially Suitable Distribution Pattern of Castanopsis hystrix Miq. in China". Plants 12, nr 4 (6.02.2023): 717. http://dx.doi.org/10.3390/plants12040717.
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Climate warming poses a great threat to ecosystems worldwide, which significantly affects the geographical distribution and suitable growth area of species. Taking Castanopsis hystrix Miq. as the research object, the potentially suitable cultivation regions under present and future climatic emission scenarios in China were predicted based on the MaxEnt model with 360 effective individual distributions and eight environmental variables. The min temperature of coldest month (bio6), precipitation of driest month (bio14), and precipitation of warmest quarter (bio18) are three leading factors affecting the geographical distribution area of C. hystrix Miq. The suitable cultivation regions of C. hystrix Miq. range from 18°–34° N, 89°–122° E in central and southern China and cover an area of 261.95 × 104 km2. The spatial pattern of C. hystrix Miq. will migrate to the southern region of low latitudes with a decreasing suitable area when in ssp1-2.6, and to the southwestern region of low latitudes or expand to the northeast region at high latitudes in ssp5-8.5, with an increasing suitable area; no significant change on the spatial pattern in ssp2-2.4. For ssp1-2.6 or ssp2-4.5 climate scenarios, the southern region of high latitudes will be appropriate for introducing and cultivating C. hystrix Miq., and the cultivation area will increase. For ssp5-8.5, its cultivation will increase and expand to the northeast of high-latitude areas slightly.
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Liu, Wenxuan, Hu Wang, Hongyang Ma, Yingyan Cheng, Pengyuan Li, Bo Li i Yingying Ren. "Analysis of Regional Satellite Clock Bias Characteristics Based on BeiDou System". Remote Sensing 14, nr 23 (29.11.2022): 6047. http://dx.doi.org/10.3390/rs14236047.
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With the continuous development of the Global Navigation Satellite System (GNSS), the calculation theory and strategy of the global Satellite Clock Bias (SCB) tends to be mature. However, in some eventualities with restricted conditions, the calculation and application of the global SCB are limited; hence, the application of regional SCB is derived. This paper focuses on the quality of regional SCB products in different regions, calculates three groups of regional SCB products, and analyzes their properties and application effects. We expand the double-differenced assessment method for SCB and extend satellite clock accuracy assessment to regional satellite clock products. Additionally, the Regional Effect Bias (REB) is introduced to analyze the influence of the relative position of satellite geometry on the SCB products due to the regional effects. The conclusions are as follows: (1) In low-latitude regions, SCB products have a high degree of completeness and a large number of satellite observations, which is conducive to expanding the positioning application range of regional SCB; (2) the low-latitude regions SCB will be affected by ionospheric activity, and the accuracy will be slightly lower than that of satellite clocks deviation in mid-latitudes; (3) in this paper, the REB in this area is in the level of 10−7. The experiment displays the result that the values of REB in low-latitude areas are larger, leading to fluctuated Precise Point Position (PPP) results. However, there are fewer stations in the mid-latitude regions, which will also affect the accuracy of PPP; (4) the accuracy of the positioning results of the regional satellite clock deviation in the Chinese region is higher than that of the global clock.
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Wang, Ren, Jingxiang Gao, Yifei Yao, Peng Sun i Moufeng Wan. "Assessment of the Algorithm for Single Frequency Precise Point Positioning at Different Latitudes and with Distinct Magnetic Storm Conditions". Applied Sciences 10, nr 7 (26.03.2020): 2268. http://dx.doi.org/10.3390/app10072268.
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This paper analyzes the convergence time and the root mean square (RMS) error of single frequency (SF) precise point positioning (PPP) in the ionospheric-constrained (TIC1) and troposphere- and ionospheric-constrained (TIC2) conditions, when the stations are at a low latitude, mid-latitude, and high latitude area during the period of a magnetic storm (MS) and a non-magnetic storm (NMS). In this paper, 375 IGS (international global navigation satellite system (GNSS) service) stations were selected from all over the world for 30 days in September 2017. The 24 hour daily observations were split for each station into 8 data sets of 3 hours each, so that a total of 90,000 tests were carried out. After statistical analysis, it was concluded that: during the MS period, the percentage of TIC2 shortened compared to the TIC1 convergence time, and it was by at least 3.9%, 3.0%, and 9.3% when the station was at global, low latitude, and high latitude areas, respectively. According to the statistical analysis, during the NMS period the convergence time was shortened about at least 12.8%, 11.0%, and 30.0% with respect to the stations in the MS period at global, low, and high latitude areas, respectively. If the station was located in the mid-latitude region, the convergence time was not shortened in some modes. The ionospheric activity in the mid-latitude region was less than that in the low-latitude region, while there were more stations in the mid-latitude region, and the precision of the global ionospheric maps (GIMs) and zenith tropospheric delay (ZTD) products were also slightly higher. Overall, TIC1 and TIC2 have a greater impact on convergence time, but have less impact on positioning accuracy, and only have a greater impact in different environments during the MS and NMS periods.
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Yang, Yu, Dayong Wen i Jie Cao. "Linkage of the Circumglobal Teleconnection and the Interannual Variability of Early Spring Diabatic Heating over Low-Latitude Highlands in Southeast Asia". Journal of Climate 36, nr 10 (15.05.2023): 3217–29. http://dx.doi.org/10.1175/jcli-d-22-0659.1.
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Abstract This study explores the linkage of the circumglobal teleconnection (CGT) on the variability of early spring diabatic heating over the Southeast Asian low-latitude highlands (SEALLH) using ERA5 data. The early spring diabatic heating over the SEALLH shows significant interannual variability with a quasi-3-yr period. Anomalies in the advection of the early spring diabatic heating in the troposphere over the SEALLH associated with CGT are mainly responsible for the interannual variability of early spring diabatic heating over the SEALLH. When CGT is in phase with an anomalous cyclone over the eastern midlatitude North Atlantic, an anomalous cyclone usually dominates the west SEALLH throughout the troposphere. Stronger-than-normal southerly winds located on the east flank of the anomalous cyclone in the lower–upper troposphere transport more high-enthalpy air mass from lower latitudes to the SEALLH and then result in stronger-than-normal early spring diabatic heating over the SEALLH. When CGT is in phase with an anomalous anticyclone over the eastern North Atlantic, the opposite conditions occur, and weaker-than-normal early spring diabatic heating is observed over the SEALLH. Such significant correlation between CGT and early spring diabatic heating over the SEALLH can persist from winter to early summer. The key physical processes revealed in the observational analysis are mostly confirmed by the historical simulation performed with the EC-EARTH3 model. Significance Statement The low-latitude highlands in Southeast Asia are one of the earliest diabatic heating sources in the Asian summer monsoon region. Variability of diabatic heating over the low-latitude highlands in Southeast Asia significantly regulates the weather and climate over the Asian summer monsoon region. However, the interannual variability of early spring diabatic heating over the low-latitude highlands in Southeast Asia remains unclear. This study determines that the circumglobal teleconnection links with the interannual variability of early spring diabatic heating over the low-latitude highlands in Southeast Asia via modulating the local advection process from the previous winter. These results build a bridge connecting the anomalous signals occurring in the upper reaches of the low-latitude highlands in Southeast Asia with the weather and climate in the local and lower reaches of the low-latitude highlands in Southeast Asia.
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Dmitriev, A., i H. C. Yeh. "Storm-time ionization enhancements at the topside low-latitude ionosphere". Annales Geophysicae 26, nr 4 (13.05.2008): 867–76. http://dx.doi.org/10.5194/angeo-26-867-2008.
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Abstract. Ion density enhancements at the topside low-latitude ionosphere during a Bastille storm on 15–16 July 2000 and Halloween storms on 29–31 October 2003 were studied using data from ROCSAT-1/IPEI experiment. Prominent ion density enhancements demonstrate similar temporal dynamics both in the sunlit and in the nightside hemispheres. The ion density increases dramatically (up to two orders of magnitude) during the main phase of the geomagnetic storms and reaches peak values at the storm maximum. The density enhancements are mostly localized in the region of a South Atlantic Anomaly (SAA), which is characterized by very intense fluxes of energetic particles. The dynamics of near-Earth radiation was studied using SAMPEX/LEICA data on >0.6 MeV electrons and >0.8 MeV protons at around 600 km altitude. During the magnetic storms the energetic particle fluxes in the SAA region and in its vicinity increase more than three orders of magnitude. The location of increased fluxes overlaps well with the regions of ion density enhancements. Two mechanisms were considered to be responsible for the generation of storm-time ion density enhancements: prompt penetration of the interplanetary electric field and abundant ionization of the ionosphere by enhanced precipitation of energetic particles from the radiation belt.
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Zhu, Tao, i Jing Yang. "Two Types of Mid-High-Latitude Low-Frequency Intraseasonal Oscillations near the Ural Mountains during Boreal Summer". Journal of Climate 34, nr 11 (czerwiec 2021): 4279–96. http://dx.doi.org/10.1175/jcli-d-20-0589.1.
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AbstractTwo types of mid-high-latitude low-frequency intraseasonal oscillations (LF-ISOs), featuring eastward and westward propagation, have been identified over the Eurasian continent in the past 37 summers (1982–2018). The eastward and westward propagating modes commonly have a dominant periodicity of 30–50 days near the Ural Mountains (UM) but have different origins and evolutions. The eastward propagating LF-ISO initiates over eastern North America, migrates northeastward across northeastern North America–western North Atlantic, central North Atlantic, western Europe, and the UM, then propagates southeastward to northwestern and eastern China, which is the Atlantic-Eurasian continental mode. In contrast, the westward propagating mode is quasi-circumpolar, initiating over the East Siberian Sea and moving southwestward across the UM and northern Europe and eventually reaching Greenland and the Canadian Arctic Archipelago. These two mid-high-latitude LF-ISOs are accompanied by significant tropical intraseasonal variations with evident tropical–extratropical interactions. Meanwhile, these two LF-ISOs have different decadal preferences before and after 2000, which are ascribed to the decadal change of both intraseasonal efficient kinetic energy obtained from the mean flow over their genesis region and their background flow associated with the North Atlantic Oscillation/Arctic Oscillation decadal change. This study deepens the understanding of subseasonal variations for mid-high latitudes and subseasonal prediction sources for low-latitude regions.
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Aashiq Hussain Bhat, Bilal Ahmad Ganaie, T K Ramkumar, Manzoor A Malik i P Pavan Chaitanya. "Westward Drift of Ionospheric Plasma Irregularities over a Low to Mid-latitude Transition Region in Indian Sector". Annals of Geophysics 64, nr 4 (16.11.2021): PA437. http://dx.doi.org/10.4401/ag-8510.
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We report the observation of plasma depletions/plumes in the F region ionosphere over a low to middle latitude transition region in the Indian sector. The observation of these plasma depletions is based on the data obtained in May 2019 through the all-sky airglow CCD imager installed in the campus of University of Kashmir, Srinagar (34.12 °N, 74.83 °E, magnetic latitude 25.91 °N). The depletions on the two consecutive nights of 05 and 06 May 2019 are aligned along the North-South (N-S) direction and drift westward. Several depletion bands along with some enhancement bands are seen in the 630-nm airglow images throughout the two nights. The observed structures show certain characteristics similar to Medium Scale Traveling Ionospheric Disturbances (MSTIDs) but these airglow features are not completely periodic. Further, in the observed depletion bands some East-West asymmetries are observed along with the structured tree-like branches of the airglow depletions. Some depletion bands even bifurcate leading to the inference that the structures are signatures of plasma irregularities rather than the usual MSTIDs observed in low-mid latitude transition region. The westward drift of the depletions especially during geomagnetic quiet times over this region makes this study significant since it offers a possible evidence that shows extension of spread F irregularities from the mid latitude region to the low-mid latitude transition region. In this paper, we point out some possible mechanisms related to the occurrence of plasma depletions at this region and their westward movement during geomagnetic quiet times.
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Arkani‐Hamed, J. "Differential reduction‐to‐the‐pole of regional magnetic anomalies". GEOPHYSICS 53, nr 12 (grudzień 1988): 1592–600. http://dx.doi.org/10.1190/1.1442441.
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I present a differential reduction‐to‐the‐pole technique that reduces regional scale magnetic anomalies to the geomagnetic pole, while taking into account the variations in the direction of the geomagnetic field and that of the magnetization of the crust over the region. The technique is developed in the spectral frequency domain as an inverse problem solved iteratively using a perturbation method. I regard the variations in the directions as finite perturbations about the mean values of the directions over the region and evaluate the nonlinear coupling terms due to these perturbations in the space domain at each iteration before transforming them into the spectral frequency domain. The technique is applied to the magnetic anomalies of three semiinfinite prisms, which are inductively magnetized and located at high, mid, and low latitudes in a region where the inclination of the ambient field changes from 10 to 90 degrees and its declination changes from −30 to +30 degrees. The differential reduction to the pole shifts the positive anomaly of the low‐latitude prism toward the north more than it shifts that of the mid‐latitude prism, which in turn is shifted northward more than that of the high‐latitude prism. The reduction also suppresses the negative lobes to the north of the mid and low‐latitude prisms and moves the positive anomalies to points directly over the prisms. I also apply the technique to the marine magnetic anomalies off the east coast of Canada. The positive magnetic anomalies in the southern part of the area are displaced northward by about 30 km, whereas those in the northern part are not moved significantly.
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Singh, A. K., i R. P. Singh. "Observations and Modelling of Nocturnal Ionospheric Irregularities in Low Latitude Region." Journal of geomagnetism and geoelectricity 49, nr 9 (1997): 1115–29. http://dx.doi.org/10.5636/jgg.49.1115.
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Raghunath, Swapna, i D. Venkata Ratnam. "Maximum–Minimum Eigen Detector for Ionospheric Irregularities Over Low-Latitude Region". IEEE Geoscience and Remote Sensing Letters 14, nr 6 (czerwiec 2017): 901–5. http://dx.doi.org/10.1109/lgrs.2017.2687079.
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Ngwira, Chigomezyo M., Gopi K. Seemala i John Bosco Habarulema. "Simultaneous observations of ionospheric irregularities in the African low-latitude region". Journal of Atmospheric and Solar-Terrestrial Physics 97 (maj 2013): 50–57. http://dx.doi.org/10.1016/j.jastp.2013.02.014.
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Adebesin, B. O., J. O. Adeniyi, I. A. Adimula i B. W. Reinisch. "Low latitude nighttime ionospheric vertical E×B drifts at African region". Advances in Space Research 52, nr 12 (grudzień 2013): 2226–37. http://dx.doi.org/10.1016/j.asr.2013.09.033.
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Li, Jianfeng, Yongqian Wang, Shiqi Yang i Fang Wang. "Characteristics of Low-Latitude Ionosphere Activity and Deterioration of TEC Model during the 7–9 September 2017 Magnetic Storm". Atmosphere 13, nr 9 (26.08.2022): 1365. http://dx.doi.org/10.3390/atmos13091365.
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Under the influence of space weather, abnormal disturbances in the ionosphere will distort the ionosphere model seriously and affect the global navigation satellite system negatively. This study analyzes the ionospheric activity characteristics and the ionospheric model performance in low latitude during a strong geomagnetic storm from 7 to 9 September 2017. The research goals are to determine the abnormal behavior of the ionosphere during the geomagnetic storm and to refine the ionosphere model in the low latitude. In the experiment, the vertical total electron content (VTEC) peak value at low latitudes caused by this geomagnetic storm was significantly higher than that on the geomagnetic quiet day, and the VTEC peak value increased by approximately 75%. In the main phase of the geomagnetic storm, the degree of VTEC variation with longitude is significantly higher than that of the geomagnetic quiet day. The VTEC variation trend in the northern hemisphere is more severe than that in the southern hemisphere. In the region where VTEC decreases with longitude, the VTEC in the northern hemisphere is higher than that in the southern hemisphere on the same longitude at low latitudes, and this phenomenon is not significantly affected by the geomagnetic disturbance of the recovery phase. During the geomagnetic storm, the daily minimum value of VTEC at different latitudes was basically the same, approximately 5 TECU, indicating that the nighttime VTEC of the ionosphere in low latitudes was weakly affected by latitude and geomagnetic storms. Geomagnetic disturbances during geomagnetic storms will lead to anomalous features of the “Fountain effect” in the ionosphere at low latitudes. In addition, this geomagnetic storm event caused the accuracy of spherical harmonics (SH), polynomial, and ICE models to decrease by 7.12%, 27.87%, and 48.56%, respectively, and caused serious distortion, which is negative VTEC values fitted by the polynomial model.
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Wu, Wei Li. "Study on Magnetic Materials with Numerical Calculation of Geoelectromagnetic Field in Middle-Low Latitude Region". Advanced Materials Research 738 (sierpień 2013): 303–6. http://dx.doi.org/10.4028/www.scientific.net/amr.738.303.
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This paper expounds mechanism of the interact between the vary ionosphere currents and the Earth as a magnetic materials during magnetic storms which create the geoelectromagnetic fields on the Earths surface. Cauchy Distribution model of ionosphere currents above the middle-low latitude area is built for calculation of the fields. In order to predict and evaluate the levels of GIC flowing in technology systems,Complex Image Method (CIM) is applied to calculate geo-electric-magnetic fields on the Earths surface of the middle-low latitude. To test veracity,we compare calculation of the electromagnetic field by Complex Image Method and data measured practically. The good accuracy of CIM here is obtained. i.e,CIM can perform well in Middle-Low latitude area.
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Husin, A., Suraina, AY Putra i H. Rasidi. "A model of the deviation between IRI-2016 and ionospheric TEC observation based on GISTM at low latitude Indonesia region". Journal of Physics: Conference Series 2214, nr 1 (1.02.2022): 012023. http://dx.doi.org/10.1088/1742-6596/2214/1/012023.
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Abstract The diurnal variation pattern of total electron content(TEC) from the International Recurrence Ionosphere (IRI-2016) model is generally is good agreement with observational data at all latitudes. However, at low latitudes the IRI TEC is not as accurate as in midlatitudes. Some reports showed that the IRI-2016 TEC model at the maximum and minimum solar activities at low latitudes tends to be underestimate. In this paper, TEC from GISTM (GPS Ionospheric Scintillation and TEC Monitoring) that is installed at Pontianak station (0.03° S;109.33°E geomagnetic latitude 9.7°S ) used for validation and evaluation of IRI-2016 TEC model over the low latitude Indonesian sector. Data from the 2012 - 2014 period representing solar maximum and data from 2018 representing solar minimum, were used in this study. We also developed VTEC deviation (ΔTEC) model by using multiple linear regression and tested the model by using data 2019. Results show that IRI-2016 generally reproduces the diurnal variations pattern but underestimates the observation data for many hours each day especially during maximum solar activity 2012-20114. The highest deviation in the equinoctial months and lowest during the June and December solstice. The deviation (ΔTEC) model showed good agreement with observation data on January and December but not for other months especially on equinox months. Testing of the VTEC deviation model using 2019 data did not show significant improvement compared to the IRI-2016 itself, which generally produces good TEC prediction in most of the months except for equinox months.
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Bhuyan, P. K., P. K. Kakoty i S. B. Singh. "Theoretical simulation of O<sup>+</sup> and H<sup>+</sup> densities in the Indian low latitude F-region and comparison with observations". Annales Geophysicae 20, nr 12 (31.12.2002): 1959–66. http://dx.doi.org/10.5194/angeo-20-1959-2002.
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Abstract. The O+ and H+ ion density distributions in the Indian low latitude F-region, within ± 15° magnetic latitudes, are simulated using a time dependent model developed on the basis of solution of the plasma continuity equation. The simulated ion densities for solar minimum June and December solstices are then compared with ionosonde observations from the period 1959–1979 and measurements made by the Indian SROSS C2 satellite during 1995–1996 at an altitude of ~ 500 km. The simulated O+ density has a minimum around pre-sunrise hours and a maximum during noontime. H+ density is higher at nighttime and lower during the day. The simulations reproduced the well-known equatorial ionization anomaly (EIA) observed in electron density at the peak of the F2-region in the Indian low latitude sector during solar minimum. In situ measurement of O+ density by the SROSS C2, however, showed a single peak of ionization around the equator.Key words. Ionosphere (equatorial ionosphere; modeling and forecasting)
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Rama Rao, P. V. S., S. Gopi Krishna, K. Niranjan i D. S. V. V. D. Prasad. "Temporal and spatial variations in TEC using simultaneous measurements from the Indian GPS network of receivers during the low solar activity period of 2004–2005". Annales Geophysicae 24, nr 12 (21.12.2006): 3279–92. http://dx.doi.org/10.5194/angeo-24-3279-2006.
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Abstract. With the recent increase in the satellite-based navigation applications, the ionospheric total electron content (TEC) and the L-band scintillation measurements have gained significant importance. In this paper we present the temporal and spatial variations in TEC derived from the simultaneous and continuous measurements made, for the first time, using the Indian GPS network of 18 receivers located from the equator to the northern crest of the equatorial ionization anomaly (EIA) region and beyond, covering a geomagnetic latitude range of 1° S to 24° N, using a 16-month period of data for the low sunspot activity (LSSA) years of March 2004 to June 2005. The diurnal variation in TEC at the EIA region shows its steep increase and reaches its maximum value between 13:00 and 16:00 LT, while at the equator the peak is broad and occurs around 16:00 LT. A short-lived day minimum occurs between 05:00 to 06:00 LT at all the stations from the equator to the EIA crest region. Beyond the crest region the day maximum values decrease with the increase in latitude, while the day minimum in TEC is flat during most of the nighttime hours, i.e. from 22:00 to 06:00 LT, a feature similar to that observed in the mid-latitudes. Further, the diurnal variation in TEC show a minimum to maximum variation of about 5 to 50 TEC units, respectively, at the equator and about 5 to 90 TEC units at the EIA crest region, which correspond to range delay variations of about 1 to 8 m at the equator to about 1 to 15 m at the crest region, at the GPS L1 frequency of 1.575 GHz. The day-to-day variability is also significant at all the stations, particularly during the daytime hours, with maximum variations at the EIA crest regions. Further, similar variations are also noticed in the corresponding equatorial electrojet (EEJ) strength, which is known to be one of the major contributors for the observed day-to-day variability in TEC. The seasonal variation in TEC maximizes during the equinox months followed by winter and is minimum during the summer months, a feature similar to that observed in the integrated equatorial electrojet (IEEJ) strength for the corresponding seasons. In the Indian sector, the EIA crest is found to occur in the latitude zone of 15° to 25° N geographic latitudes (5° to 15° N geomagnetic latitudes). The EIA also maximizes during equinoxes followed by winter and is not significant in the summer months in the LSSA period, 2004–2005. These studies also reveal that both the location of the EIA crest and its peak value in TEC are linearly related to the IEEJ strength and increase with the increase in IEEJ.
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Nagar, Anju. "Day-to-Day Variability of Low Latitude F-Region Ionosphere During Low Solar Activity". International Journal of Astrophysics and Space Science 3, nr 3 (2015): 30. http://dx.doi.org/10.11648/j.ijass.20150303.12.
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Simpson, Isla R., Michael Blackburn i Joanna D. Haigh. "A Mechanism for the Effect of Tropospheric Jet Structure on the Annular Mode–Like Response to Stratospheric Forcing". Journal of the Atmospheric Sciences 69, nr 7 (1.07.2012): 2152–70. http://dx.doi.org/10.1175/jas-d-11-0188.1.
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Abstract For many climate forcings the dominant response of the extratropical circulation is a latitudinal shift of the tropospheric midlatitude jets. The magnitude of this response appears to depend on climatological jet latitude in general circulation models (GCMs): lower-latitude jets exhibit a larger shift. The reason for this latitude dependence is investigated for a particular forcing, heating of the equatorial stratosphere, which shifts the jet poleward. Spinup ensembles with a simplified GCM are used to examine the evolution of the response for five different jet structures. These differ in the latitude of the eddy-driven jet but have similar subtropical zonal winds. It is found that lower-latitude jets exhibit a larger response due to stronger tropospheric eddy–mean flow feedbacks. A dominant feedback responsible for enhancing the poleward shift is an enhanced equatorward refraction of the eddies, resulting in an increased momentum flux, poleward of the low-latitude critical line. The sensitivity of feedback strength to jet structure is associated with differences in the coherence of this behavior across the spectrum of eddy phase speeds. In the configurations used, the higher-latitude jets have a wider range of critical latitude locations. This reduces the coherence of the momentum flux anomalies associated with different phase speeds, with low phase speeds opposing the effect of high phase speeds. This suggests that, for a given subtropical zonal wind strength, the latitude of the eddy-driven jet affects the feedback through its influence on the width of the region of westerly winds and the range of critical latitudes on the equatorward flank of the jet.
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Priyal, Muthu, Jagdev Singh, Belur Ravindra i G. Sindhuja. "Temporal and Latitudinal Variations in Ca-K Plage and Network Area: An Implication for Meridional Flows". Astrophysical Journal 944, nr 2 (1.02.2023): 218. http://dx.doi.org/10.3847/1538-4357/acaf60.
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Abstract The Ca-K spectroheliograms obtained at the Kodaikanal observatory are used to generate a uniform time series using the equal-contrast technique for studying the long- and short-term variations in the solar chromosphere. The percentages of plage, enhanced network, and active and quiet network areas at various latitudes is compared with the activity at 35° latitude and also with the sunspot number for the period of 1907–1984. The values of the phase differences indicate that the activity begins at ∼45° latitude and shifts progressively to a lower latitude at a speed of ∼9.4 m s−1 . The shift speed slows down gradually and reaches ∼3 m s−1 at ∼5° latitude. No phase difference between the variations of Ca-K activity at 55°, 65°, and 75° latitude belts implies that changes in the activity are happening simultaneously. The analysis shows that the activity at polar latitude belts is anticorrelated with the sunspot number. This study indicates that a multicell meridional flow pattern could exist in the latitude direction. One type of cell could transport the magnetic elements from mid- to low-latitude belts through meridional flows, and the other cell type could be operating in the polar region.