Search

Space weather variations can significantly affect ionospheric electron density, which can, in turn, adversely affect various navigational and communication technologies. One such phenomenon is the prompt penetration electric field. The convective electric field from a magnetospheric origin penetrates the lower ionosphere during a geomagnetic storm. The electric field penetrating the ionosphere can challenge space-based technologies. Thus, understanding the convectional electric field from higher latitudes to the low-latitudinal region during geomagnetic disturbance is critical. The ionosphere over the Indian region consists of equatorial and low latitude dynamics, such as equatorial ionization anomaly, that are highly dynamic even during the quiet days. Therefore, understanding the effects of prompt penetration electric field observed in the Equatorial Electrojet is of utmost importance over the Indian region. In the current study, two geomagnetic storms, the St. Patrick's Day storm of 17th March 2015 and another low intense storm of 8th June 2014, were chosen to understand the effects of PPEF over equatorial ionization anomaly. The ionospheric density was enhanced during the relatively less intense geomagnetic storm compared to the St. Patrick's Day storm. In these two events, large-scale ionospheric irregularities were observed from ROTI values during the local daytime hours, but no ionospheric scintillation was detected (S4 index). [ABSTRACT FROM AUTHOR]

The variation of correlation between ROTI and S 4 index is examined by using GPS L1 and L5 signals over an Indian low latitude station, Waltair (17.73° N, 83.37° E) during the period from 2015 to 2017. The effect of geomagnetic storms on the correlation between ROTI and S 4 index is the main focus of the present study. The influence of satellite elevation angle and signal frequency on the correlation between ROTI and S 4 index is also investigated during different seasons and geomagnetic conditions. The correlation is found to vary between 0.28 and 0.63 for elevation angles above 30⁰ and between 0.56 and 0.87 for the elevation angles above 50⁰. The correlation coefficient values are decreasing with solar activity from 2015 to 2017 during quiet and disturbed geomagnetic periods. From the analysis on the seasonal correlation between ROTI and S 4 index, it is found that solar activity dependent seasonal correlation is observed for both GPS L1 and L5 signals over lower elevation angle 30⁰. The correlation between ROTI and S 4 index is increasing over higher elevation angles and for lower signal frequency. [ABSTRACT FROM AUTHOR]

Ionospheric delay is of concern for trans -ionospheric radio communication, especially for the navigation systems relying on these satellite signals. Most of the ionospheric delays are estimated to a degree of first-order using dual frequency global navigation satellite system (GNSS) receivers except during irregularities and equatorial plasma bubbles. The plasma bubbles are observed as a decrease or reduction in total electron content (TEC) as a result of large-scale irregularities that are generated at the equatorial ionosphere. These plasma bubbles can be detected from TEC values visually or by using mathematical algorithms. The mathematical algorithms may have limitations based on assumptions made for the current dataset. Therefore, various machine learning (ML) techniques were tried by training them with selected TEC depletions that are verified for accuracy. From this study, the Random Forest Method (RFM) has performed well compared to other ML methods. The RFM is trained to use for the detection of TEC depletions from the Indian low-latitude region. The training accuracy obtained is 97.6%, with a minimum classification error of 0.023%. The result obtained from the confusion matrix ascertained that the proportion of positively classified cases that are truly positive that is the positive predictive value (PPV) is 96.8%. These statistical results are validated after plotting the observed TEC depletion patch obtained from the ML method. There are cases in which depletions detected by the ML method are appreciable over the mathematical algorithm. The ML technique once trained will not have inherent limitations, as there are no assumptions or threshold values needed to set as required by most of the mathematical algorithms. Thus, the results are encouraging and have scope for further improvement and advancement. [ABSTRACT FROM AUTHOR]

• Study of Ionospheric scintillations indices S4 and ROTI in Indian region. • Relation between ROTI & S4 is useful for standard GNSS receivers to estimate S4. • Correlation of ROTI & S4 is better than 0.6, yet an estimate of S4 is unreliable. • Using obtained relation, a range of S4 values can be estimated from ROTI value. Ionospheric irregularities cause fluctuations (scintillations) in received satellite signal strength, degrading communication and navigation signals. The scintillation strength depends on the scale sizes of the irregularities and the frequency of the radio signal. The parameter S4 index describes the scintillation strength derived from the amplitude of high rate received signal sampled at 50 Hz, usually from special GNSS receivers. Most GNSS receivers have a lower data sampling rate, so an alternate parameter, Rate of Change of TEC Index (ROTI), is derived from the total electron content (TEC) sampled at 30 s. Here, the correlation between ROTI and S4 is performed for the Indian ionospheric region, with different elevation mask angles and ROTI calculated over different averaging intervals. An estimate of the S4 value from ROTI is unreliable even though the correlation between them is better than 0.6. Different elevation mask angles and ROTI with varying averaging intervals do not significantly affect the correlation between S4 and ROTI. Further, the correlation and occurrence percentages of S4 corresponding to ROTI are analyzed. An 80% confidence range is obtained to correlate the observed ROTI with the corresponding S4 index. These probability estimates of S4 values derived from ROTI values also vary with latitude. This relation between ROTI and S4 will be beneficial in using standard GNSS receivers for the studies of ionospheric scintillations. [ABSTRACT FROM AUTHOR]

Abstract: Ionospheric storms represent large global disturbances of the ionospheric F-region electron density in response to geomagnetic storms. This study investigates the ionospheric response during a minor geomagnetic storm that occurred on 13–15 September 2004. In particular, we use total electron content (TEC) measurements (rate of TEC change, ROT) to examine the presence of ionospheric irregularities over four low-latitude stations in the African sector, a region that has been less studied. Ionospheric irregularities are known to cause fading and phase fluctuation of L-band radio navigation signals such as those used by the Global Navigation Satellite Systems (GNSS), and are a common feature in the equatorial and low-latitude ionosphere. In the present study, the storm began with a sudden commencement at approximately 20:00UT on 13 September, while the peak of the main phase occurred on 14 September with an SYM-H index value around −59nT. On 13 September, the storm did not appear to hinder the development of irregularities as they were observed over all the stations. In contrast, irregularities were rarely observed at two of the 4 stations under study and were absent over the other two stations on 14 September. The DSMP F15 satellite post-sunset flight over the African region observed deep density depletions on 13 September that can be associated with the presence of ionospheric plasma bubble irregularities. Furthermore, an analysis of (horizontal geomagnetic component corrected for ring current effects) shows that there was a strong positive perturbation observed in the post-sunset hours on 13 September, which suggests the presence of an eastward penetration electric field, while a negative perturbation of , which is associated with the equatorial counter-electrojet, was observed on 14 September. [Copyright &y& Elsevier]

Forecasting Indian Summer Monsoon Rainfall (ISMR) is a formidable task due to its intricate variability. This study harnesses the power of machine learning (ML) to decipher the chaotic trajectory within ISMR, drawing inspiration from ML's success in predicting analogous systems. By utilizing ERA-interim data, the method dissects ISMR's chaotic nature through correlation dimension-based techniques. Employing the Lorenz-96 model on daily rainfall data, trained with an Echo State Network (ESN), the technique discerns patterns within a span of 1 model time slightly trailing its performance in other systems. This discrepancy could stem from the intricacies of observational data and the training process involving 500 initial conditions. Notably, this method achieves accuracy in slightly over 50% of cases. Despite its current limitations, this approach exhibits promise in shedding light on the chaotic behaviour enforced in ISMR. As a result, it contributes to the advancement of monsoon forecasting techniques. [ABSTRACT FROM AUTHOR]

The spatio-temporal variations in ionospheric vertical total electron content (TEC) data, which often reflect their scale invariant properties, can well be studied with multifractal analysis. We discuss the multifractal behaviour of TEC recorded at a total of 27 stations confined to a narrow longitude band (35°W-80°W) spanning from equator to high-latitude regions (30°S to 80°N) (geographic coordinates) during solar minimum (2008) and solar maximum (2014), using multifractal detrended fluctuation analysis (MFDFA). MFDFA provides an understanding of the multifractal scaling behaviour of a signal using the multifractal singularity spectra and the generalised Hurst exponents as diagnostic tools. The objectives of this study are to (i) understand the latitudinal dependence of the multifractal behaviour of TEC, (ii) compare the multifractal behaviour of TEC corresponding to the well-known 27-day variation (solar rotation period) and its harmonics and the 1-day (solar diurnal) periodicities, during 2008 and 2014 and (iii) understand the lunar tidal influence on TEC. Results indicate that except for the 1-day period, the TEC at all other periods shows a higher degree of multifractality during solar maximum compared to solar minimum. Further, irrespective of the solar activity, the degree of mutifractality in general decreases with increase in period for all latitude zones for periods of 27-day and its harmonics. However, the 1-day period exhibits monofractal behaviour regardless of the solar activity. The influence of semi-lunar tidal effects (having a periodicity of about 14.5 days) as a function of latitude is clearly seen in the 13.5-day periodicity (i.e., the 2nd harmonic of 27-day variation) of TEC. It manifests in the form of decreasing differences in the widths of the multifractal singularity spectra corresponding to the years 2008 and 2014, with increase in latitude. Results are discussed in the light of these observations. [ABSTRACT FROM AUTHOR]

• Latitudinal distribution in OI 630.0 nm dayglow emissions presented. • The effects of the equatorial electrodynamics on dayglow emission show small variations with magnetic latitudes. • Dayglow emission rates respond to meridional winds positively near to dip equator and negatively away from equator. Earth's upper atmosphere over low latitudes is influenced by the equatorial electrodynamics. Its influence can also be modulated by the thermospheric winds. The effect of these two forces on the thermospheric neutral behaviour in the daytime can be investigated by measuring the variations in the OI 630.0 nm dayglow emission rates as these serve as effective tracers of the altitude region of their origin. The capability to measure dayglow emissions over a large field-of-view presents a unique opportunity to investigate the upper atmospheric behaviour over large spatial extents. Diurnal measurements of OI 630.0 nm dayglow emission rates have been carried out from two different locations in India using multi-wavelength imaging echelle spectrographs, MISE, which, together cover a spatial range from 5 ° -18 ° magnetic latitude. These investigations have been carried out during January-February 2020 (winter season) when solar flux variation was nearly negligible (varied only by 4 solar flux unit from 68–72 solar flux unit). Therefore, latitudinal variations in the daily averaged oxygen dayglow emission intensities have been analyzed to assess their response to the variations in the strength of the equatorial electrodynamics and the meridional winds. The results reveal that these forces show varying effects with the poleward meridional wind contributing to an enhancement in the OI 630.0 nm dayglow emission rates closer to the magnetic equator and a decrement as one moves away from the equator. The equatorial electric field effect, however, continues to be equally effective in the low-latitudes region under consideration. [ABSTRACT FROM AUTHOR]

• Quiet time seasonal trend in TEC is not seen during disturbed periods of low solar activity. • TEC difference between disturbed and quiet time periods is higher during the moderate solar activity. • The correlation of day maximum TEC with F 10.7 is found to be reduced during disturbed periods. The present study is focused to understand the geomagnetic storm effects on the short- and long-term variations of ionospheric Total Electron Content (TEC) over the equatorial and low latitude sectors. GPS-TEC observations over a near equatorial station Bangalore and low latitude stations Waltair and Hyderabad during the declining phase of the 24th solar cycle (2015–2019) is analysed. The TEC variations during quiet and disturbed conditions are individually analysed to understand the geomagnetic storm effects on the diurnal, seasonal and solar activity variations. The seasonal variations of disturbed time TEC are following the quiet time trend with equinoctial maximum and summer minimum in the moderate solar activity periods. But, during low solar activity periods, the seasonal dependence of disturbed time TEC is different than that of quiet time. The difference in TEC during disturbed and quiet times is higher during moderate solar activity than that of low solar activity conditions. The TEC difference between disturbed and quiet periods is found to be maximum during summer months of moderate solar activity periods. Further, correlation analysis between F 10.7 cm solar flux and TEC during quiet and disturbed conditions is carried out for three different locations. It is found that the correlation between TEC and F 10.7 cm solar flux is higher during quiet time compared to that during disturbed periods with more correlation at the equator than at low latitudes. [ABSTRACT FROM AUTHOR]

Pc1 geomagnetic pulsations, equivalent to electromagnetic ion cyclotron waves in the magnetosphere, display a specific amplitude modulation, though the region of the modulation remains an open issue. To classify whether the amplitude modulation has a magnetospheric or ionospheric origin, an isolated proton aurora (IPA), which is a proxy of Pc1 wave‐particle interactions, is compared with the associated Pc1 waves for a geomagnetic conjugate pair, Halley Research Base in Antarctica and Nain in Canada. The temporal variation of an IPA shows a higher correlation coefficient (0.88) with Pc1 waves in the same hemisphere than that in the opposite hemisphere. This conjugate observation reveals that the classic cyclotron resonance is insufficient to determine the amplitude modulation. We suggest that direct wave radiation from the ionospheric current by IPA should also contribute to the amplitude modulation. Plain Language Summary: The amplitude of electromagnetic ion cyclotron (EMIC) waves in the magnetosphere, which are observed as Pc1 waves on the ground, is an important parameter for characterizing the loss of energetic particles. The generation region of EMIC waves is well understood as being the magnetic equator, but the amplitude modulation region is not well‐established due to wide horizontal Pc1 wave propagation in ionospheric ducts. Here we compare the properties of Pc1 waves and isolated proton precipitation from an ideal geomagnetic conjugate observation at Halley Research Base in Antarctica and Nain in Canada. By visualizing the cyclotron resonance region in the magnetosphere as an isolated proton aurora (IPA), the ambiguity of the horizontal propagation effects of Pc1 waves in the ionosphere is ideally removed. The observed IPA in the northern hemisphere has remarkable similarities with Pc1 waves in the same northern hemisphere, but not the southern hemisphere, providing evidence that the temporal variations of wave amplitude can be characterized by an ionospheric current induced in the IPA, and cannot be described only by a classical cyclotron resonance mechanism at the magnetic equator. Therefore, this study suggests that an IPA ionospheric current contributes to temporal modulations of Pc1 waves on the ground. Key Points: Similarities and differences of magnetic conjugacy between Pc1 waves and isolated proton precipitation are reportedThe proton aurora shows a strong similarity with Pc1 waves in the same hemisphere, not characterized by classical cyclotron resonanceThis study suggests the importance of ionosphere for Pc1 waves by an ionospheric current modulation of an isolated proton aurora [ABSTRACT FROM AUTHOR]

The aim of the present study is to investigate the response of ionospheric total electron content (TEC), Global Positioning System (GPS) and Global Navigation Satellite System (GLONASS) scintillations during 17 March 2015 St. Patrick's Day geomagnetic storm over Visakhapatnam, which is popularly known as Waltair (WALT) in the literature. GPS TEC observations obtained from five IGS stations (SGOC, IISC, HYDE, LCK4 and LHAZ) and WALT during the storm have been compared. The TEC derived from GPS, GLONASS constellations and CODE global ionosphere TEC map (GIM) over WALT has also been compared. Positive storm effect during the main phase of the storm and negative storm effect during the recovery phase of the storm were observed over the said stations. The variation of northern equatorial ionisation anomaly TEC (CODE GIM TEC maps) in response to the St. Patrick's Day storm over four Indian longitudes ( 75 ∘ E , 80 ∘ E , 85 ∘ E and 90 ∘ E ) has also been presented. Strong amplitude and phase scintillations were observed in the L-band signals of GPS and GLONASS constellations over WALT. Twelve satellite (Pseudo Random Noise) PRNs of GPS L1 and nine PRNs of each GLONASS L1 and L2-band signals were affected by strong amplitude and phase scintillation. The peak amplitude scintillation index (S4) obtained from the effected PRNs of GPS L1 signal and GLONASS L1-band signals over WALT range from 0.36 to 0.74 and 0.36 to 0.76, respectively. Strong fluctuations in rate of TEC index are noted over the said stations. This enhanced scintillation activity is mainly due to the main phase of the storm falls in the evening sector over the Indian region. [ABSTRACT FROM AUTHOR]