Changes in total electron content (TEC) during the annular solar eclipse of 15 January 2010

The solar eclipse of 15 January 2010 was an annular eclipse of the Sun with a maximum magnitude of 0.96 at 1.62°N, 69.29°E. To study the effect of this solar eclipse on the ionosphere the GPS data recorded at three different Indian stations Varanasi (Geographic latitude 25°, 16′N, longitude 82°, 59′E), Hyderabad (Geographic latitude 17°, 20′N, longitude 78°, 30′E) and Bengaluru (Geographic latitude 12°, 58′N, longitude 77°, 33′E) have been used to retrieve ionospheric total electron content (TEC). The ionospheric response to this rare event has been studied in terms of GPS-derived TEC observed at all the three Indian stations. A significant reduction in TEC reflected by all PRNs at all the three stations has been observed. The magnitude of the reduction in VTEC compared to quiet mean VTEC depends on latitude as well as longitude. The amount of reduction observed from different satellites (PRN) is different and depends on the location of the satellite from the solar eclipse path.     

Broadband electrostatic noise and low-frequency waves in the Earth’s magnetosphere

Broadband electrostatic noise (BEN) is commonly observed in different regions of the Earth’s magnetosphere, eg., auroral region, plasma sheet boundary layer, etc. The frequency of these BENs lies in the range from lower hybrid to the local electron plasma frequency and sometimes even higher. Spacecraft observations suggest that the high and low-frequency parts of BEN appear to be two different wave modes. There is a well established theory for the high-frequency part which can be explained by electrostatic solitary waves, however, low-frequency part is yet to be fully understood. The linear theory of low-frequency waves is developed in a four-component magnetized plasma consisting of three types of electrons, namely cold background electron, warm electrons, warm electron beam and ions. The electrostatic dispersion relation is solved, both analytically and numerically. For the parameters relevant to the auroral region, our analysis predict excitation of electron acoustic waves in the frequency range of 17 Hz to 2.6 kHz with transverse wavelengths in range of (1–70) km. The results from this model may be applied to explain some features of the low-frequency part of the broadband electrostatic noise observed in other regions of the magnetosphere.     

SLUCUBE: Innovative high performance nanosatellite science and technology demonstration mission

The Space Systems Research Laboratory (SSRL) at Saint Louis University is developing SLUCUBE nanosatellite as part of the space mission design program. The objective of the mission is to demonstrate space capability of high performance nanosatellite components that has been developed at SSRL for the past three years. The objective of the program is to provide extremely low-cost and rapid access to space for scientists and commercial exploitation using commercial-off-the-shelf components. SLUCUBE is a double CubeSat with dimensions 10×10×20 cm and a mass of 2 kg. This nanosatellite features suite of technology demonstration components to enlarge the capability of space mission for such class of spacecrafts. The primary mission of SLUCUBE is to test and demonstrate several enabling technologies by flying a number of university developed high performance components. This paper describes the new developed technologies by providing details of specific components developed along with the R&D efforts and laboratory facilities. A brief discussion about the student involvement and educational benefits will also be presented.     

Equatorial Ionospheric Anomaly (EIA) and comparison with IRI model during descending phase of solar activity (2005–2009)

The ionospheric variability at equatorial and low latitude region is known to be extreme as compared to mid latitude region. In this study the ionospheric total electron content (TEC), is derived by analyzing dual frequency Global Positioning System (GPS) data recorded at two stations separated by 325 km near the Indian equatorial anomaly region, Varanasi (Geog latitude 25°, 16^/ N, longitude 82°, 59^/ E, Geomagnetic latitude 16°, 08^/ N) and Kanpur (Geog latitude 26°, 18^/ N, longitude 80°, 12^/ E, Geomagnetic latitude 17°, 18^/ N). Specifically, we studied monthly, seasonal and annual variations as well as solar and geomagnetic effects on the equatorial ionospheric anomaly (EIA) during the descending phase of solar activity from 2005 to 2009. It is found that the maximum TEC (EIA) near equatorial anomaly crest yield their maximum values during the equinox months and their minimum values during the summer. Using monthly averaged peak magnitude of TEC, a clear semi-annual variation is seen with two maxima occurring in both spring and autumn. Results also showed the presence of winter anomaly or seasonal anomaly in the EIA crest throughout the period 2005–2009 only except during the deep solar minimum year 2007–2008. The correlation analysis indicate that the variation of EIA crest is more affected by solar activity compared to geomagnetic activity with maximum dependence on the solar EUV flux, which is attributed to direct link of EUV flux on the formation of ionosphere and main agent of the ionization. The statistical mean occurrence of EIA crest in TEC during the year from 2005 to 2009 is found to around 12:54 LT hour and at 21.12° N geographic latitude. The crest of EIA shifts towards lower latitudes and the rate of shift of the crest latitude during this period is found to be 0.87° N/per year. The comparison between IRI models with observation during this period has been made and comparison is poor with increasing solar activity with maximum difference during the year 2005.     

Rare observation of daytime whistlers at very low latitude (L = 1.08)

The source region and propagation mechanism of low latitude whistlers (Geomag. lat. <30°) have puzzled scientific community for last many decades. In view of recent reports, there is consensus on the source region of low latitude whistlers in the vicinity of the conjugate point. But the plausible conditions of ionospheric medium through which they travel are still uncertain. In addition to that, the whistlers in daytime are never observed at geomagnetic latitudes less than 20°. Here, for the first time, we present a rare observations of whistlers during sunlit hours from a very low-latitude station Allahabad (Geomag. Lat: 16.79°N, L = 1.08) in India on 04 February 2011. More than 90 whistlers are recorded during 1200–1300 UT during which the whole propagation path from lightning source region to whistler observation site is under sunlit. The favorable factors that facilitated the whistlers prior to the sunset are investigated in terms of source lightning characteristics, geomagnetic and background ionospheric medium conditions. The whistler activity period was found to be geomagnetically quiet. However, a significant suppression in ionospheric total electron content (TEC) compared to its quiet day average is found. This shows that background ionospheric conditions may play a key role in low latitude whistler propagation. This study reveals that whistlers can occur under sunlit hours at latitudes as low as L = 1.08 when the source lightning and ionospheric medium characteristics are optimally favorable.     

A morphological study of GPS-TEC data at Agra and their comparison with the IRI model

The temporal and seasonal variations of Total Electron Content (TEC) are studied at Agra (Geographic Lat. 27.17°N, Long. 78.89°E, Dip: 41.4°), India, which is in the equatorial anomaly region, for a period of 12 months from 01 January to 31 December, 2007 using a Global Positioning System (GPS) receiver. The mean TEC values show a minimum at 0500 h LT (LT = UT + 5.5 h) and a peak value at about 1400 h LT. The lowest TEC values are observed in winter whereas largest values are observed in equinox and summer. Anomalous variations are found during the period of magnetic disturbances. These results are compared with the TEC derived from IRI-2007 using three different options of topside electron density, NeQuick, IRI01-corr, and IRI-2001. A good agreement is found between the TEC obtained at Agra and those derived from IRI models.     

External plasma flow and related geomagnetic phenomena

Considering a three layered configuration of boundary layer bounded by compressible magnetosheath and magnetospheric plasma, the dispersion equation for K-H instability has been derived. In the presence of finite compressibility normal components of wave vectors are non-zero implying propagation normal to the boundary layer. The growth rate for the magnetopause or M-mode is greater than the inner magnetospheric or I-mode surface waves. However, for certain orientations of magnetosheath magnetic field $\text{ωiIΩiM}$ and the corresponding phase and group velocities are significant. The amplitude ratio of displacement vectors at the magnetospheric and magnetosheath interfaces is greater for the I-mode than that for the M-mode. These situations are capable of exciting I-mode waves which may transport energy to the inner magnetosphere resulting in field line resonances and generation of micropulsations. The sense of polarization of M-mode and I-mode are the same in the magnetospheric region.     

The electrical environment of the Earth’s atmosphere: A review

The study of the electrical environment of the Earth’s atmosphere has rapidly advanced during the past century. Great strides have been made towards the understanding of lightning and thunderstorms and in relating them to the global electric circuit. The electromagnetic fields and currents connect different parts of the Earth’s environment, and any type of perturbation in one region affects another region. Starting from the traditional views in which the electrodynamics of one region has been studied in isolation from the neighboring regions, the modern theory of the global electrical circuit has been discussed briefly. Interconnection and electrodynamic coupling of various regions of the Earth’s environment can be easily studied by using the global electric circuit model. Deficiencies in the model and the possibility of improvement in it have been suggested. Application of the global electric circuit model to the understanding of the Earth’s changes of climate has been indicated.This revised version was published online in July 2005 with a corrected cover date.     

Asymptotically decoupled discontinuous control of systems andnonlinear aircraft maneuver

The question of control of a class of nonlinear systems that can be decoupled by state-variable feedback is considered. Based on variable-structure system theory, a discontinuous control law is derived that accomplishes asymptotic decoupled output trajectory-following in the presence of uncertainty in the system. In the closed-loop system, the trajectories are attracted toward a chosen hypersurface in the state space and then slide along it. During the sliding phase the motion is insensitive to parameter variations. Based on this result, a control law for asymptotically decoupled control of roll angle, angle of attack, and sideslip in rapid, nonlinear maneuvers is derived. Simulation results are presented to show that large, simultaneous lateral and longitudinal maneuvers can be performed in spite of uncertainty in the stability derivatives