Observation of daytime aurora

The fractal properties of geomagnetic northward component data (H-component) in the equatorial region during various phases of solar activity over Southeast Asia were investigated and then quantified using the parameter of the Hurst exponent (H). This study began with the identification of existence of spectral peaks and scaling properties in international quiet day H-component data which were measured during three levels of solar activity: low, intermediate, and high. Then, various cases of quiet and disturbed days during different solar activity levels were analyzed using the method that performed the best in the preceding part. In all the years analyzed, multifractal scaling and spectral peaks exist, signifying that the data have fractal properties and that there are external factors driving the fluctuations of geomagnetic activity other than solar activity. The analysis of various cases of quiet and disturbed days generally showed that quiet days had anti-persistence tendencies (H < 0.5) while disturbed days had persistence tendencies (H > 0.5)—generally a higher level of Hurst exponent compared to quiet days. As for long-term quiet day H-component data, it had a Hurst exponent value that was near H ≃ 0.50, while the long-term disturbed day H-component data showed higher values than that of the quiet day.

The paper deals with an analysis of the behaviour of sporadic E on disturbed days and quiet days during the IGY period. Data from Wilkes (geomag. lat. 77·9°S), Halley Bay (geomag. lat. 65·8°S), Hobart (geomag. lat. 52°S), Townsville (geomag. lat. 28·5°S) and Kodaikanal (geomag. lat. 0·6°N) representing the very high latitude, the auroral, the high latitude temperate, low latitude temperate and the equatorial zones have been considered. The analysis has shown that at station near the pole and high latitude temperate station the occurrence is less on disturbed days than on quiet days, whereas at the auroral station is more on disturbed days than on quiet days. At the low latitude temperate station and at equatorial station no such clear indication is found. The distribution of the frequency of disappearance of Es indicate that lower frequencies of disappearance tend to occur more at temperate and high latitude zones and higher frequencies at the equatorial zone. On disturbed days, the occurrence of Es over the whole range of frequencies is less than on quiet days at very high latitude and high latitude temperate station, whereas at the auroral station the position is reversed. At low latitude stations, no clear indication is observed. The cumulative distribution of Es shows that the Phillips Rule (Phillips, 1947) is applicable above the most probable value of the occurrence of fEs for both quiet and disturbed days individually. The diurnal and seasonal variation of fEs are described.

Geomagnetic quiet days and magnetic storms are naturally believed to be due to very different solar wind conditions. In this study we however demonstrate that the long‐term variation of geomagnetic quiet and disturbed days are surprisingly similar. By the use of daily averages of the geomagnetic index aa we examine the activity level of the most quiet and most disturbed days separately through 130 years from 1868 to 1998. We find that the linear correlation between the average level of activity at the 5 most quiet days pr year and the yearly average is 0.8. For the 5 most disturbed days it is 0.7. The results indicate that the long‐term increase is due to an increase in the background solar wind parameters, rather than in the number of solar wind disturbances.

The global positioning system (GPS) signal that is transmitted from satellite to receiver will be disturbed and degraded in the atmosphere layers due to many factors affecting the signal quality, especially in the ionosphere layer which is an ionised layer in upper atmosphere. Ionospheric scintillation and Total Electron Content (TEC) depletions are the most famous factors that can cause serious effects on GPS signal. This research investigates and analyses the measurement of the ionospheric amplitude scintillation and TEC depletions at quiet and disturbed day. The other parameters involved on this study are the carrier-to-noise (C/No) ratio, and rate of change of TEC (ROT). Data from GISTM receiver at UKM station for minimum solar cycle event were analysed on 5 April 2010 (quiet day) and 7 January 2010 (disturbed day); whereas, data from GISTM for maximum solar cycle event were analysed on 7 October 2015 (quiet day) and 2 June 2015 (disturbed day). The solar cycle event affected on the GPS signal especially when this event increased, so the analysis of ionospheric scintillation during maximum solar cycle event was compared with minimum solar cycle event to investigate the differences between these solar cycle events. The ionospheric scintillation and TEC variations are affected by solar cycle. Results showed that the ionospheric scintillation and TEC variations increased during maximum solar cycle event.

A plasma is a medium containing a large number of charged particle interactions. For this reason, it is common and appropriate to examine the plasma in terms of kinetic theory. In this context, the collision dynamics of the ‘O+ + N2 → NO+ + N’ reaction for geomagnetically quiet day (04/09/2017) and disturbed day (08/09/2017) were calculated for ionospheric altitudes with the help of kinetic theory. As a result of the calculation, it was seen that the mean free path values were less on the disturbed day, as expected. The total collisions number was seen to reach maximum at the height of hmF2 on both quiet and disturbed days, and the disturbed day values were greater. It was seen that the collision frequency decreased exponentially with altitude.

The characteristic variations of postnoon bite-out in foF2 were studied by using f-plots obtained at Karachi (gcog. coord. 24.95°N, 67.14°E; mag. dip 36°N) from March 1976 to February 1978. It has been found that the % occurrence of bite-out was minimum in June and maximum in February. The development of bite-out during magnetically quiet and disturbed days was also studied. The % occurrence of bite-out was found to be greater during magnetically quiet days but the depression of foF2 was larger during magnetically disturbed days.

The morphology of prompt penetration effects (PP) in the Equatorial Electrojet (EEJ) at Vencode (VEN, Geomagnetic latitude 0.29ºN) was studied using 5-min samples of EEJ and interplanetary Ey component data from 2011 to 2015. In contrast to previous studies that mainly focused on storm-time PP events, our study investigated the characteristics of PP effects on EEJ during both quiet and disturbed periods. Our findings reaffirm earlier reports of high PP efficiency during local noon for both quiet and disturbed days. Moreover, PP amplitudes were greater when IMF-Bz was oriented northward compared to southward, indicating the presence of overshielding effects even during quiet conditions. Additionally, we examined seasonal variations in PP amplitudes and observed weaker PP during the solstice compared to the equinox. Furthermore, our study analysed the equatorial counter electrojet (CEJ) caused by PP events associated with northward-turning IMF-Bz. We report 15% of CEJs at VEN associated with PP effects; a few PP events were observed while the equatorial electric field at VEN was already westward (i.e. PP within CEJ), indicating the combined effects of magnetospheric and ionospheric perturbations. Identifying CEJs caused by PP during quiet days helps to differentiate between magnetospheric and ionospheric mechanisms/processes. Additionally, we investigated the spatial variability in PP amplitudes at closely spaced sites, utilizing one year of concurrent data from Minicoy (MNC, Geomagnetic latitude 0.19ºN), VEN, and Campbell Bay (CBY, Geomagnetic latitude 0.29ºN) situated at geographic longitudes 72º, 77º and 93º, respectively. Our results showed significant differences in PP amplitudes between VEN-CBY and MNC-CBY, separated by 15º and 20º longitude, respectively. Observations from the three equatorial sites demonstrated a longitudinal trend, with PP amplitudes increasing westward towards MNC, inverse to the amplitudes of EEJ.Graphical

Some characteristics of the F2 layer of the ionosphere over Madras (Geographic lat. 13°05'N., Geomag. lat. 03°05'N.) for the period February 1959 to January 1960 are studied in this paper. Data for both quiet and disturbed days have been analysed.Diurnal variation of the F2 layer critical frequency for different months are described. The total electron content in a vertical column of unit cross-section below the level of maximum ionization has been calculated, on the assumption of parabolic distribution, for different times of the day and for different seasons. The diurnal variation of total electron content is smoother than that of maximum electron density for both quiet and disturbed days. The ‘bite-out’ effect observed in the diurnal variation of electron density is removed in the variation of the total electron content. The day-time values of electron density and total electron content are generally higher on disturbed days than on quiet days.Temperatures for the different seasons have been obtained from the values of scale height. The values of temperature on disturbed days are generally somewhat less than on quiet days.Scale height appears to increase when the height of maximum electron density increases.

Satellite Radio Navigation System (SRNS) is a satellite navigation system which provides autonomous geo-spatial positioning with global coverage. Among the several SRNS available across the world, one among them is Navigation with Indian Constellation (NavIC) developed and operated by ISRO. The performance evaluation of this new Indian system is very much needed. Hence, this work discusses about the performance accuracy. In this paper, NavIC receiver position parameters evaluated i.e 2DRMS, 3DRMS CEP, SEP, and Geometric Dilution of Precision (GDOP) for NavIC System. The quiet day (18-06-2019) and disturbed day (14-06-2019) are considered for the analysis over the Hyderabad station, India(17.40°N, 78.51° E). The real time NavIC data is acquired for ISRO IGS receiver. The NavIC receiver is operated in Hybrid mode(L5 and S1).The results obtained from this study indicate that for Hybrid mode of operation) position values are better for quiet day than that of the disturbed day.

Regional catalogues of the ionospherically disturbed and quiet days are developed on the basis of the analysis of vertical-incidence sounding data over European area during 1964-1990. This paper presents the results obtained by comparing and combining two regional catalogues of the ionospheric disturbed and quiet days into one definitive catalogue recommended for implementation in the PRIME oriented and other studies. According to the criteria applied to the F region peak parameters, only 10 to 20% days per year manifest quietness of acceptable level. Comparison of ionospherically quiet days with geomagnetically quiet periods during 1976-1988 shows coincidence of quiet days in both fields not more than 30% of times considered. Conventional practice of analysis of the ionosphere state by comparing it with the geomagnetic conditions should be forerun by specification of the proper ionospheric quiet and disturbed periods.

The role of energetic particle precipitation in the formation of thermospheric tides is investigated. Using the Global Self-consistent Model of the Thermosphere, Ionosphere, and Protonosphere (GSM TIP) and two models of energetic particle precipitation, APM (Auroral Precipitation Model) and AIMOS 2.0.-AISstorm (Atmospheric Ionization Module Osnabrück 2.0—Atmospheric Ionization during Substorms), we performed simulations for the period 3–12 September 2017. This period covers both geomagnetically quiet days and the storm of 7–8 September. The analysis shows that migrating tides diurnal wave (DW) and semidiurnal wave (SW) prevail on quiet days for both versions of the simulations. On the day of maximum storm development on 8 September and the day after—9 September, the nonmigrating components of tidal waves, mainly DW0 and SW0, are intensified. There are also increasing differences in the spatial structure of tides between the two versions of simulations, especially between diurnal and semidiurnal tides at 154 km. On the disturbance days, the amplitudes of diurnal and semidiurnal tides at 154 km in the APM version are markedly greater than the corresponding values in the AIMOS version. Thus, it should be noted that the integral characteristics of the ionization function from precipitations are more important for the formation of DW and SW than its spatial structure or the features of temporal variations. A comparison of the total electron content (TEC) maps for the two versions of the simulation showed that the AIMOS version nicely reproduces the experimental data for a quiet time. The APM version is less accurate for quiet time but simulates the quantitative increase to disturbed conditions at high and middle latitudes better. For model reproduction of observed TEC variations at low and equatorial latitudes, it is not enough to consider the thermospheric source of thermospheric tides. In this case, the role of atmosphere–ionosphere coupling is very important.

Unprecedented 4D spatiotemporal infant regional cerebral blood flow framework and region-specific physiology–function coupling across infancy were elucidated, highlighting strong physiology–function coupling specifically at the default-mode network to meet extraneuronal metabolic demand for network emergence.

The red and green forbidden coronal iron lines, [Fe X] λ6374 and [Fe XIV] λ5303, have been detected along an arc on the north rim of the supernova remnant IC 443 that positionally correspond well with the soft X-ray emission there. The data have been carefully corrected for Paschen continuum contamination. Maximum surface brightnesses are 17% of sky (the red line) and 6% of sky (the green line). A shell-like structure is revealed by the iron line surface brightness, suggesting that in a restricted part of the north rim the shock may be encountering a smooth part of the interstellar medium.

The green (5577 \AA) and red-doublet (6300, 6364 \AA) lines are prompt emissions of metastable oxygen atoms in the $^1$S and $^1$D states, respectively, that have been observed in several comets. The value of intensity ratio of green to red-doublet (G/R ratio) of 0.1 has been used as a benchmark to identify the parent molecule of oxygen lines as H$_2$O. A coupled chemistry-emission model is developed to study the production and loss mechanisms of O($^1$S) and O($^1$D) atoms and the generation of red and green lines in the coma of C/1996 B2 Hyakutake. The G/R ratio depends not only on photochemistry, but also on the projected area observed for cometary coma, which is a function of the dimension of the slit used and geocentric distance of the comet. Calculations show that the contribution of photodissociation of H$_2$O to the green (red) line emission is 30 to 70% (60 to 90%), while CO$_2$ and CO are the next potential sources contributing 25 to 50% ($<$5%). The ratio of the photo-production rate of O($^1$S) to O($^1$D) would be around 0.03 ($\pm$ 0.01) if H$_2$O is the main source of oxygen lines, whereas it is $\sim$0.6 if the parent is CO$_2$. Our calculations suggest that the yield of O($^1$S) production in the photodissociation of H$_2$O cannot be larger than 1%. The model calculated radial brightness profiles of the red and green lines and G/R ratios are in good agreement with the observations made on comet Hyakutake in March 1996.

The vertical flux of O+ in the F region has been obtained from incoherent scatter radar measurements at Millstone Hill. The paper reports an investigation of the altitude variation of the flux during two 24‐hour periods in March taken a year apart. We find that except for a brief period around sunrise the flux is always directed downwards at altitudes below 500 km and its magnitude seems governed simply by the competing processes of production, loss, and diffusion. On the quiet day above 535 km the flux is directed upward in the afternoon when the electron density is not changing with time. This upward flux reached a peak value of ∼108 ions cm−2 sec−1 near 700 km altitude and then decreased at higher altitudes. This decrease is attributed to charge exchange with hydrogen. During the night on this day there is evidence for a downward flux of 3 × 107 O+ ions cm−2 sec−1 from the protonosphere. Additional H+ ions may be diffusing through the 1000‐km level and contributing to the maintenance of the nighttime F layer, but they would not be detected in our observations. On the disturbed day there is no evidence of a flux of ionization into the protonosphere except at sunrise. We suggest that this change is brought about by a large reduction in the abundance of neutral hydrogen, resulting from increased escape either via the polar wind or from the heating of the atmosphere in the vicinity of the auroral zones. Thus, it is suggested that the abundance of neutral hydrogen at the base of the exosphere is reduced at high latitudes during magnetic storms.