Even–odd cycle parity in complexity of hemispheric sunspot activity

We have used the Lempel–Ziv measure to describe the complexity in sunspot activity during the solar cycles 18–23. In particular, we examined the time series of daily sunspot numbers in the northern and southern hemispheres in each of the six cycles and calculated the Lempel–Ziv complexity (LZC) value for each time series. Our results indicate that in the even cycles, the LZC values of the sunspot numbers in the two hemispheres are very close to each other, whereas in the odd cycles they differ significantly between the two hemispheres. We also find that within each hemisphere the LZC varies from cycle to cycle. This even–odd cycle parity reflects the variations in inter-hemispheric strengths of the solar magnetic field leading to different temporal distributions of sunspots in the two hemispheres. The degree of complexity may influence the predictability of sunspot activity in the two hemispheres during the various cycles. Although the physical implication of the results is not clear, these results may stimulate new ideas into modeling the complex dynamics of the solar dynamo.     

Development of simultaneous imaging polarimeter for asteroids

We are currently developing a polarimeter to study surface physical properties of asteroids. To enhance polarimetric accuracy and observational efficiency, we newly devised the polarimeter whose measurements can provide the two Stokes parameters Q and U, simultaneously. The test-observations of the prototype polarimeter have been carried out in December 2003 and January 2004, mounted on the 101 cm telescope at Bisei Astronomical Observatory, Okayama, Japan. In the observations, unpolarized and polarized standard stars were observed to measure an instrumental polarization and its uncertainty. As a result, an instrumental polarization of 5.06 ± 0.18% has been measured.     

Ozone mini-hole observation over the Balkan Peninsula in March 2005

Areas with dimensions of 1000–3000 km in which the total ozone content (TOC) decreases fast are called ozone mini-holes. They are generated mainly dynamically in two ways, either by poor-ozone air mass transport from the tropics to higher latitudes by planetary wave activity or, they are connected with strong adiabatic uplifting of the tropopause height. An ozone mini-hole, generated by the second mechanism, was observed over the Balkan Peninsula on 19/21 March 2005. In the middle of March, the polar vortex was strongly disturbed by Rossby waves, reaching up to the lower stratosphere. Warming episodes over a geographical area, covering the Barents Sea and the Polar Sea north from Central Siberia, displaced a polar vortex fragment extremely southwards. However, the vorticity was weak and the stratospheric temperatures did not reach low values, providing conditions for ozone chemical destruction via heterogenic reactions. At the same time, a Rossby wave ridge was located below the European polar fragment. In the period from 13 to 19 March, the thermal tropopause over Sofia was uplifted almost by 3 km. Ozone distributions observed by the SCIAMACHY instrument on 18–21 March show a fast TOC decrease westwards from Ireland, which was moving eastwards during the next days, increasing the area in which the ozone content decreased. On 20/21 March low ozone content was observed above the Stara Zagora (42°N, 25°E) ground-based station by means of the GASCOD instrument, using DOAS technique. The TOMS Earth probe instrument detected 237 DU over Sofia. This is a record low March value from the beginning of the TOMS instrument measurements in 1978. In March/April the ozone distribution was characterized by its mean annual maximum of 360 DU at 42°N.     

Statistical properties of the most powerful solar and heliospheric disturbances

We present and discuss here the first version of a data base of extreme solar and heliospheric events. The data base contains now 87 extreme events mostly since 1940. An event is classified as extreme if one of the three critical parameters passed a lower limit. The critical parameters were the X-ray flux (parameter R), solar proton flux (parameter S) and geomagnetic disturbance level (parameter G). We find that the five strongest extreme events based on four variables (X-rays SEP, Dst, Ap) are completely separate except for the October 2003 event which is one the five most extreme events according to SEP, Dst and Ap. This underlines the special character of the October 2003 event, making it unique within 35 years. We also find that the events based on R and G are rather separate, indicating that the location of even extreme flares on the solar disk is important for geomagnetic effects. We also find that S = 3 events are not extreme in the same sense as R > 3 and G > 3 events, while S = 5 events are missing so far. This suggests that it might be useful to rescale the classification of SEP fluxes.     

Ionospheric precursors observed at low latitudes around the time of koyna earthquake

On December 11, 1967 at 05:21 LT, an immense earthquake of magnitude 6.7 struck Koyna, the Indian province of Maharashtra. Its epicenter was located at geographic latitude 17.37°N and longitude 73.75°E with depth of about 3 km. Ground based measurements show variation in the critical frequency of ionospheric F2 layer (foF2) before and after the shock. In the present study the behavior of F2-region of ionosphere has been examined over the equatorial and low latitudinal region ionosphere during the month of December 1967 around the time of Koyna earthquake. For this purpose, the ionospheric data collected with the help of ground-based ionosondes installed at Hyderabad (located close to the earthquake epicenter) Ahmedabad, Trichirapulli, Kodaikanal and Trivendrum have been utilized. The upper and lower bound of Interquartile range (IRQ) are constructed to monitor the variations in foF2 other than day-to-day and diurnal pattern for finding the seismo-ionospheric precursors. Some anomalous electron density variations are observed between post midnight hours to local pre-noon hours at each station. These anomalies are strongly time dependent and appeared a couple of days before the main shock. The period considered in this study comes under the quiet geomagnetic conditions. Hence, the observed anomalies (which are more than the usual day-to-day variability) over all stations are likely to be associated with this imminent earthquake. The possible mechanism to explain these anomalies is the effect of seismogenic electric field generated just above the surface of earth within the earthquake preparation zone well before the earthquake due to emission of radioactive particles and then propagated upward, which perturbs the F-region ionosphere.     

Fluxes of low-energy particles in quiet periods of solar activity and the <Emphasis Type="Italic">MgII</Emphasis> index

Low fluxes of protons with energies 0.3–10 MeV were studied during 21–23 solar cycles as a function of the MgII index using the data of the instruments CPME, EIS (IMP8), and EPHIN (SOHO). It has been shown that a) during quiet time of solar activity the fluxes of protons (background protons) have a positive correlation with the MgII index value throughout the solar cycle, b) specific features of variations of the MgII index during the solar minima of 1986–1987 and 1996–1997 can be considered, as well as variations of background fluxes of low energy charged particles, to be manifestations of the 22-year magnetic cycle of the Sun, and c) periods of the lowest value of the MgII index are also characterized by the smaller values of the ratio of intensities of protons and helium nuclei than in other quiet periods. A hypothesis is put forward that acceleration in a multitude of weak solar flares is one of the sources of background fluxes of low energy particles in the interplanetary space.     

The effect of climber transit on the space elevator dynamics

The space elevator offers an alternate and efficient method for space travel. It will have two main components. The first component is the tether (or the ribbon), which extends from the Earth to an equatorial satellite at an altitude beyond the geostationary orbit, and is fixed to a base on the surface of the Earth at its lower end. The second component is the climber, which scales the ribbon, transporting payloads to space. An important issue for effective operation of the space elevator will be to understand its dynamics. This paper attempts to develop a realistic and yet simple planar model for this purpose. The basic response of the ribbon to climber transit is determined. Both analytical and numerical results are presented. Specific climbing procedures are devised based on these results so as to minimize the adverse effects of climber transit on the ribbon.     

A Diagnostic Tree Approach for Fault Cause Identification in the Attitude Control Subsystem of Satellites

Space and Earth observation programs demand stringent guarantees ensuring smooth and reliable operations of space vehicles and satellites. Due to unforeseen circumstances and naturally occurring faults, it is desired that a fault-diagnosis system be capable of detecting, isolating, identifying, or classifying faults in the system. Unfortunately, none of the existing fault-diagnosis methodologies alone can meet all the requirements of an ideal fault- diagnosis system due to the variety of fault types, their severity, and handling mechanisms. However, it is possible to overcome these shortcomings through the integration of different existing fault-diagnosis methodologies. In this paper, a novel learning-based, diagnostic-tree approach is proposed which complements and strengthens existing efficient fault detection mechanisms with an additional ability to classify different types of faults to effectively determine potential fault causes in a subsystem of a satellite. This extra capability serves as a semiautomatic diagnostic decision support aid to expert human operators at ground stations and enables them to determine fault causes and to take quick and efficient recovery/reconfiguration actions. The developed diagnosis/analysis procedure exploits a qualitative technique denoted as diagnostic tree (DX-tree) analysis as a diagnostic tool for fault cause analysis in the attitude control subsystem (ACS) of a satellite. DX-trees constructed by our proposed machine-learning-based automatic tree synthesis algorithm are demonstrated to be able to determine both known and unforeseen combinations of events leading to different fault scenarios generated through synthetic attitude control subsystem data of a satellite. Though the immediate application of our proposed approach would be at ground stations, the proposed technique has potential for being integrated with causal model-based diagnosis and recovery techniques for future autonomous space vehicle missions.     

High Range Resolution Profiles as Motion-Invariant Features for Moving Ground Targets Identification in SAR-Based Automatic Target Recognition

A quantitative model analysis is presented to justify the extraction of high range resolution (HRR) profiles from synthetic aperture radar (SAR) images as motion-invariant features for identifying moving ground targets. A comparative study is conducted to assess the effectiveness in the identification process between using HRR profiles and SAR images as target signatures. The results indicate that HRR profiles are just as viable as SAR image for identification. Furthermore, a score-level multi-look fusion identification method has been investigated. It is found that a correct accurate identification rate of greater than 99 percent, a low false alarm rate, and a high level of identification confidence can be achieved, providing very robust performance.     

On the variabilities of the Total Electron Content (TEC) over the Indian low latitude sector

The Total Electron Content (TEC) from four locations in the Indian sector namely, Trivandrum (8.47°N, 76.91°E, Geomag.0.63°S, 0.3° dip), Waltair (17.7° N, 83.3°E, Geomag. 6.4°N, 20° dip), Bhopal (23.28°N, 77.34°E, Geomag.14.26°N, 33.2° dip), and Delhi (28.58°N, 77.21°E, Geomag.19.2°N, 43.4° dip) during a low sunspot year of 2004 are used to study the variabilities of the TEC. The day time TEC values are higher over Waltair and Bhopal compared to those at Trivandrum and Delhi. Considerable day-to-day variations in the diurnal values of TEC are observed at the anomaly crest locations. The observed GPS-TEC has been compared with the IRI-2007 model derived TEC considering three different options (IRI-2001, IRI-2001 corrected and Ne-Quick) available in the model for the topside electron density. The TEC derived with Ne-Quick and IRI-01 corrected options show better agreement with GPS-TEC while the TEC from IRI-01 method shows larger deviations. From the correlation analysis carried out between TEC value at 1300 h LT and solar indices parameters namely sunspot number (SSN), F10.7 and EUV, it is observed that the correlation is more during equinoctial months and less during summer months. The correlation coefficients observed over the anomaly locations, Bhopal and Delhi are lower compared to those at Trivandrum and Waltair.