Minimum Epoch Research Articles

Development and benchmarking of an epoch time synchronization method for distributed simulation

In this paper, a new epoch time synchronization approach for distributed simulation federates is presented. The approach allows federates in the simulation system to advance their local times at full speed while it is safe to do so. That is, the simulation moves rapidly to the minimum next epoch (interaction) event time, which is calculated using the minimum sojourn time for each federate, and then slows for federation synchronization. The proposed approach is demonstrated using a manufacturing supply chain simulation composed of four distributed federates. Experiments are executed to benchmark the proposed epoch time synchronization method against conventional conservative synchronization methods to show typical improvements for simulation operation. The experimental results reveal that the proposed approach reduces supply chain simulation execution time significantly while maintaining complete accuracy as compared with traditional conservative federation coordination approaches.

Features of the 11-year variation of galactic cosmic rays in different periods of solar magnetic cycles

Variations of galactic cosmic ray intensity have been studied based on the neutron monitors and interplanetary magnetic field experimental data for different ascending and descending epochs of solar activity. The dependence of the diffusion coefficient on the cosmic ray particles rigidity R is stronger in the maxima epoch than in the minima epoch of solar activity. For the period of 1977–1981 ( qA > 0) the diffusion coefficient for the minimum epoch is, χ min ∝ R 0.7 ± 0.04 and for the maximum χ max ∝ R 1.3 ± 0.05 ; for the period of 1987–1990 ( qA < 0), χ min ∝ R 0.8 ± 0.05 and χ max ∝ R 1.1 ± 0.04 . The exponents ν y and ν z of the power spectral density of the B y and B z components of the IMF in the region of the frequencies (10 −6– 4 × 10 −6) Hz are larger for the minimum epoch of 1987 ( ν y ≈ 2.0 and ν z ≈ 1.93) than for the maximum epoch of 1990 ( ν y ≈ 1.43 and ν z ≈ 1.27).

Hale Cyclicity of Solar Activity and Its Relation to Climate Variability

The periodicity of climatic processes along the Russian Arctic Ocean coast has been studied by analyzing the tree-ring chronologies for the regions close to the northern timberline. The wavelet analysis of annual series of conifer tree rings for the period 1458–1975 has revealed climatic oscillations with periods of 20–25 years. The amplitudes and periods of climatic oscillations in the region of Russian Arctic Ocean proved to exhibit appreciable changes. Especially strong climatic variations in comparison with the recent ones were found to occur during the Maunder minimum epoch when the period of oscillations increased from 22–23 years to 24–29 years, and oscillations with periods of 15 years appeared. After the Maunder minimum, the periods of oscillations and their amplitudes again decreased, and the 15–16-year maximum disappeared. Analysis of solar activity based on of radiocarbon (14C) concentration in annual tree rings has revealed a similar pattern in changes of periodicity before, during, and after the Maunder minimum. This suggests that quasi-bidecadal climatic oscillations and variations in solar activity can be connected with each other. A possible solar forcing of periodic climatic processes and its nonlinear influence on the atmosphere-ocean-continental system are discussed. The intense quasi-bidecadal climatic oscillations can be, in all probability, interpreted as resulting from amplification of a weak solar signal in the atmosphere-ocean system that has its own noises whose frequencies are close to the 22–23-year solar cycles.

Coronal mass ejections and eruptive prominences: Mutual spatial arrangement

The mutual spatial arrangement of coronal mass ejections and eruptive prominences on the Sun is considered. These phenomena occur on different scales and are observed at different heights above the solar surface. In spite of the presumed causal connection between them, they are often widely separated in position angle at epochs of solar minimum. This means that the motion of a prominence in the corona is not strictly radial and has an appreciable component along the surface. This behavior can be explained in a model of a filament as a magnetic flux rope in equilibrium in the coronal magnetic field. The initial trajectory of the filament is determined by the structure of the global field.

On statistical relationship of solar, geomagnetic and human activities

Data of galactic cosmic rays, solar and geomagnetic activities and solar wind parameters on the one side and car accident events (CAE) in Poland on the other have been analyzed in order to reveal the statistical relationships among them for the period of 1990–2001. Cross correlation and cross spectrum of the galactic cosmic ray intensity, the solar wind (SW) velocity, K p index of geomagnetic activity and CAE in Poland have been carried out. It is shown that in some epochs of the above-mentioned period there is found a reliable relationship between CAE and solar and geomagnetic activities parameters in the range of the different periodicities, especially, 7 days. The periodicity of 7 days revealed in the data of the CAE has the maximum on Friday without any exception for the minimum and maximum epochs of solar activity. However, the periodicity of 7 days is reliably revealed in other parameters characterizing galactic cosmic rays, SW, solar and geomagnetic activities, especially for the minimum epoch of solar activity. The periodicity of 3.5 days found in the series of CAE data more or less can be completely ascribed to the social effects, while the periodicity of 7 days can be ascribed to the social effect or/to the processes on the Sun, in the interplanetary space and in the Earth's magnetosphere and atmosphere.

Experimental and theoretical investigations of the 11-year variation of galactic cosmic rays

Data of super neutron monitors have been used to study features of the temporal changes of the energy spectrum of the galactic cosmic rays isotropic intensity variations in the various ascending and descending epochs of solar activity (1954–2000) for different solar magnetic cycles (qA > 0 and the qA < 0). Parker's transport equation is numerically solved in order to establish a relationship between the experimentally obtained and theoretically expected energy spectra of.galactic cosmic rays. It is found that the theoretical expected energy spectrum is single valued determined by the dependence of the diffusion coefficient on the rigidity of galactic cosmic rays. The temporal changes of the energy spectrum of galactic cosmic rays isotropic intensity variations from the maxima to the minima epochs of solar activity indicate the radical redistributions of the EAF's fluctuations (irregularities) from the higher frequencies to the lower frequencies. It is concluded that this radical redistributions of the DVIF's fluctuations from the maxima to the minima epochs is one of the general reasons (mechanism) of the 11-year variation of the galactic cosmic rays m 2003 COSPAR.

Imprints from the solar cycle on the helium atom and helium pickup ion distributions

Abstract. Neutral interstellar helium atoms penetrate into the solar system almost unaffected by gas–plasma interactions in the heliospheric interface region, and thus can be considered as carriers of original information on the basic parameters (like density, temperature, bulk velocity) of the Very Local Interstellar Medium (VLISM). Such information can nowadays be derived from analysis of data obtained from different experimental methods: in situ measurements of He atoms (Ulysses), observations of the solar backscattered He 584 A radiation (EUVE), in situ measurements of He + pickup ions (AMPTE, Ulysses, Wind, SOHO, ACE). In view of the current coordinated international ISSI campaign devoted to the study of the helium focusing cone structure and its evolution, we analyze expected variations of neutral He density, of He + pickup fluxes and of their phase space distributions at various phases of the solar activity cycle based on a realistic time-dependent modelling of the neutral helium and He + pickup ion distributions, which reflect solar cycle-induced variations of the photoionization rate. We show that the neutral helium density values are generally anticorrelated with the solar activity phase and in extreme cases (near the downwind axis) the maximum-to-minimum density ratio may even exceed factors of ~ 3 at 1 AU. We also demonstrate that in the upwind hemisphere (at 1 AU and beyond) the He + fluxes are correlated with the solar cycle activity, whereas on the downwind side the maximum of the expected flux up to distances of ~ 3 AU occurs around solar minimum epoch, and only further away does the correlation with solar activity become positive. Finally, we present the response of the phase space distribution spectra of He + pickup ions (in the solar wind frame) for different epochs of the solar cycle and heliocentric distances from 1 to 5 AU covering the range of Ulysses, Wind and ACE observations.Key words. Solar physics, astrophysics and astronomy (ultraviolet emissions) – Space plasma physics (ionization processes; numerical simulation studies)

Fading of light maximum and linear polarization variation in the carbon Mira R Leporis

Polarimetry of R Lep obtained over the years 1991-2002 is presented. During this period the star underwent an episode of fading of the brightness at light maximum, after an interval of about 35 yr. An analysis of the data shows that the percentage linear polarization increased as the fading progressed, attained a maximum of slightly over 3 per cent in the V band close to the epoch of minimum, and remained more or less at the same level during and well after the recovery to normal brightness. The polarization, apparently, originated from the circumstellar envelope above the region where the dust that caused the fading in the star condensed. The physical mechanism that causes the rather large polarization during fadings is perhaps selective extinction by aligned foreground grains produced by the passage of shocks through the circumstellar envelope. The small-amplitude, short-term fluctuations in polarization observed in R Lep, which appear to be superposed on the fading-related large-amplitude variation, are probably pulsation-related and arise from the inner zones of the circumstellar envelope.

Time series analysis of V511 Lyrae photometry

Our time series analysis of sixteen BV light curves of the chromospherically active binary V511 Lyr confirmed the $2\fd7$ rotation period uniquely. The seasonal periodicity changes of 3.8% indicated the presence of detectable surface differential rotation. The significant $2\fd67455$ periodicity in the light curve minimum epochs suggested that the strongest starspot formation in V511 Lyr was concentrated on one stable active longitude.

Solar cycle variation of outer belt electron dose at low-Earth orbit

The solar cycle dependence of dose rates in the low-altitude horns of the outer zone electron belt is examined using data from TSX5/CEASE (solar maximum epoch) and APEX/PASP+ (solar minimum epoch). It is found, after normalizing the dose rates to account for the different shielding geometries, that the ratio of PASP to CEASE dose rates is /spl sim/4 for L>4. This is contrary to the equal dose rates predicted by the NASA AE8MIN and AE8MAX models.

Brightness of the Coronal Green Line and Prediction for Activity Cycles 23 and 24

Cyclic variations of the mean semi-annual intensities Iλ of the coronal green line λ530.3 nm are compared with the mean semi-annual variations of the Wolf numbers W during the period of 1943–1999 (activity cycles 18–23). The values of Iλ in the equatorial zone proved to correlate much better with the Wolf numbers in a following cycle than in a given one (the correlation coefficient r is 0.86 and 0.755, respectively). Such increase of the correlation coefficient with a shift by one cycle differs in different phases of the cycle, being the largest at the ascending branch. The regularities revealed make it possible to predict the behaviour of W in the following cycle on the basis of intensities of the coronal green line in the preceding cycle. We predict the maximum semi-annual W in cycle 23 to be 110–122 and the epoch of minimum between cycles 23 and 24 to take place at 2006–2007. A slow increase of Iλ in the current cycle 23 permits us to forecast a low-Wolf-number cycle 24 with the maximum W∼50 at 2010–2011. A scheme is proposed on the permanent transformation of the coronal magnetic fields of different scales explaining the found phenomenon.

On galactic cosmic ray flux decrease near solar minima and Imf intensity

We have analyzed the annual mean hourly rate data obtained with a variety of detectors located at the global sites as well as at the balloon altitudes, for the sunspot number (SSN) cycles 20, 21, 22. A systematic decrease is observed in all of them near the solar minimum epochs, for the period 1965 to 1987. The median rigidity of response (Rm) for these detectors, to the galactic cosmic ray (GCR) spectrum, lies in the range: 3GV &lt; Rm &lt; 67 GV. The observed decrease in GCR flux corresponds to an observed increase in the baselevel of the interplanetary magnetic field (IMF) intensity (B) during the same time period; no increase is observed in SSN minimum levels during this interval. The available data for GCR (1937 to 1998) and B (1963 to 1998) are reviewed. We argue that the cause of the observed GCR flux decrease (increase in the residual modulation) must be located in the heliosphere and not in the local interstellar medium.

Evolution of the solar wind transition region over the epoch of solar activity minimum

Occultation studies of near-Sun plasmas at radial distances of 10 to 40 solar radii from the Sun, by using several natural sources simultaneously, result in large-scale patterns, radio maps of the solar wind flow. Large radio telescopes of the P.N.Lebedev Physical Institute, Pushino, were used. The 1995–1997 experiments showed that the evolution of the transition region geometry is very close to that of the optical corona. Correlations between the solar wind flow structure and magnetic field data were studied. It emphasizes the fundamental role of the magnetic fields at all stages of the solar wind acceleration, from subsonic flow close to the Sun up to supersonic streams far in the interplanetery space.

Impact of rapid urban growth on heat and moisture islands in Pune City, India

The detailed horizontal structure of the heat and moisture islands of the Pune city is investigated. Changing shapes and intensities of warm and cool pockets and development of cliffs and plateaus at minimum temperature epoch are elucidated and also compared with similar aspects for Pune city documented in earlier studies. Dry and wet bulb temperature data obtained by whirling psychrometers in a mobile survey conducted in April 1997 formed the base of analysis. In total 9,9 routes were devised for moving observations to give data for 170 locations within the city region. Results indicate that at night, the core of the city appears as both heat and moisture islands whereas at the time of sunrise as heat and dry islands. Morphological variations in hill slope include barren, vegetated and residential area induced cool katabatic airflow of varying intensity as there has been formation of a cool pool in the first case, linearity in the main heat island in downwind direction in the second case and development of secondary warm pockets in the last one. Situated in a basin-like topography, the city experiences stronger influence of katabatic winds rather than the thermal circulation systems arising from spatial inhomogeneity in thermal and moisture patterns.

Paleoastrophysics: Progress and prospects

Results of highly accurate measurements of the radiocarbon concentration in the annual growth rings of trees over the last 400 years are presented. The temporal behavior of the intensity of galactic cosmic rays is reconstructed for the first time for the periods before, during, and after a deep and extended solar activity minimum — the Maunder minimum (1645–1715). It was established that even during the epoch of a deep solar minimum, the intensity of the galactic cosmic rays experienced solar modulation. The time profile of the generation of high-energy gamma radiation from the supernova explosion of 1006 is established. It is shown that processes of particle acceleration and generation of high-energy gamma rays take place with a three-year delay relative to the onset of the optical flare. The time profile of the generation of solar cosmic rays was obtained for the first time over the last thirty cycles of solar activity by precision measurements of the nitrate content in the polar ice cap. It is shown that solar flares accompanied by the generation of cosmic rays occur during the growth and decay phase of solar activity (measured by the Wolf numbers). Research prospects in the field of experimental paleoastrophysics are discussed.

Use of Kp index of geomagnetic activity in the forecast of solar activity

It is well established that geomagnetic activity in the declining phase of a solar cycle is a useful precursor of the amplitude of the solar activity in the next cycle. In the present analysis, we show that the frequency of occurrence of Kp index with values (0–1) representing geomagnetic calm and with values between 4 and 7 representing moderate geomagnetic disturbances in the declining phase of a solar cycle is linearly related to the sunspot maximum of the next cycle. Highest correlations are obtained when the frequencies are averaged over three years preceding the solar minimum epochs. We also show that the frequency of occurrence of consecutive 4 or 6 intervals of Kp with the same magnitude (0–1 or 4–5) is also equally reliable as a predictor of the ensuing solar maximum. The rate of increase of sunspot number to the solar maximum and its subsequent rate of decline to the next minimum can also be predicted reliably with these frequencies. Based on the observations for 1993–1996, we expect the coming solar maximum to be associated with an annual mean sunspot number of about 140, with a rate of ascent of 35/year and a decline rate of about 25/year.

STRUCTURE OF THE HELIOSPHERIC CURRENT SHEET DERIVED FOR THE INTERVAL 1915 -1916

Hα observations of solar large-scale fields were used to reconstruct the heliosphere structure for the time interval of 1915–1996. A special method of polar correction was developed. The expansion coefficients in Legendre polynomials were calculated. An atlas of the heliosphere structure was compiled. ‘Inferred’ strength of the polar and equatorial field in 1915–1996 years was calculated. Cyclic variations of the polar field and the number of polar plages were compared to show a satisfactory agreement. The q parameter, characterizing the divergence of the polar plumes in the epochs of the solar minimum, was calculated and its quasi-periodic behaviour with a period of the order of 70 years was revealed. Our calculations were tentatively compared with the interplanetary magnetic field structure.

Long‐term observations of VHF scintillation and total electron content near the crest of the equatorial anomaly in the Indian longitude zone

Ionospheric VHF scintillation (SI ≥ 3 dB and saturated level) and total electron content (TEC) data obtained at Calcutta (subionospheric 21°N, 92.7°E geographic, 27°N dip) and ionosonde data at Kodaikanal ( 10.2°N, 77.5°E geographic, 3.5°N dip) for the period 1977‐1990 have been analysed to show the importance of electrodynamic drift near the magnetic equator in controlling nighttime ionospheric F region ionization and irregularities in the equatorial region. Such long‐term observations extending over a period of more than 13 years are possibly being reported for the first time from a location situated near the equatorial anomaly crest. Frequent and intense VHF scintillations near the equatorial anomaly crest during equinoctial and December solstice months around solar maximum years, have been identified with the equatorial F region irregularities. Simultaneous measurement of TEC at the same location shows that during solar maximum years the high F region ambient ionization is sustained for several hours in the postsunset period, often showing secondary enhancements during equinoctial months. Under solar minimum epoch, when scintillation is sparse, TEC in the above period shows a rapid decrease. At Kodaikanal, situated near the magnetic equator, during the equinoctial and December solstice months of solar maximum years, h/F values rise by more than 100 km in about an hour around sunset. These features are seldom observed during solar minimum epoch. A causative connection among h/F variation near the magnetic equator and the maintenance of high ambient ionization and occurrence of scintillation near the anomaly crest is established. Further, scintillation occurrence during the May‐July months shows a remarkable hysteresis effect with solar activity level.

The Sun's total irradiance: Cycles, trends and related climate change uncertainties since 1976

A composite record of the Sun's total irradiance compiled from measurements made by five independent space‐based radiometers since 1978 exhibits a prominent 11‐year cycle with similar levels during 1986 and 1996, the two most recent minimum epochs of solar activity. This finding contradicts recent assertions of a 0.04% irradiance increase from the 1986 to 1996 solar minima and suggests that solar radiative output trends contributed little of the 0.2°C increase in the global mean surface temperature in the past decade. Nor does our 18‐year composite irradiance record support a recent upward irradiance trend inferred from solar cycle length, a parameter used to imply a close linkage in the present century between solar variability and climate change.

The Search for Rotational Modulation of T Tauri Stars in the Ophiuchus Dark Clouds

We report some results of a long-term photometric program called ROTOR being carried out at Maidanak Observatory in the Republic of Uzbekistan. The goal of the program is to search for periodic components in the light of T Tauri stars (TTSs), Herbig Ae/Be stars (HAEBEs), FU Orionis stars, and related objects. In this paper we analyze results obtained for TTSs in the vicinity of the ρ Oph dark clouds obtained between 1986 and 1993. Our sample includes 6 weak-emission TTSs (WTTSs) and 11 classical TTSs (CTTSs). All of the WTTSs investigated have significant photometric periods that are attributed to spottedness of the stellar photospheres. Two of them, SR 9 and SR 12, maintained stable periods and phases during the entire span of observation. The periods are between 1 and 4 days, except for SR 9, which has a period of 6.53 days; its relatively large Hα equivalent width (for a WTTS) also suggests it may be a transition object between the WTTSs and CTTSs. Among the CTTSs in our sample, we found only three stars with definite periods, two of which were longer than 8 days. Generally speaking, therefore, our observations are in accordance with the canonical view of WTTSs and CTTSs, in which stars with more active accretion disks spin slower due to disk locking and show greater irregular variations due to accretion hot spots. The exception is V895 Sco (Haro 1-1), which seems to be a typical CTTS with a rotation period of less than 4 days. The stability of the periods and epochs of minima of some or most WTTSs is noted and discussed.