Solar Activity Variations Research Articles

ДОВГОТРИВАЛІ ВАРІАЦІЇ МАГНІТНОЇ АКТИВНОСТІ СОНЦЯ

The main law of the evolution of the Earth’s climate is the cyclical nature of global changes in the latter. One of the possible explanations for the cyclical nature of global climate changes is provided by the astrophysical model of fluctuations in the insolation of the Earth’s surface by solar radiation. Modern climate change is mainly associated with variations in the magnetic activity of the Sun, one of the main proxies of which are sunspots. The decrease in the number of sunspots coincides with the epochs of cooling on the Earth, while during the maximum number of sunspots warming is observed. The paper reviews cosmogenic reconstructions of long-term variations in the Sun’s magnetic activity (large minima and large maxima) during the Holocene (last 12,000 years). The accidental appearance of large minima and maxima can to some extent be reproduced by modern models of a turbulent dynamo with a stochastic drive. An important key to studying the impact of solar activity variations on the Earth’s climate is the Maunder minimum (late 17th century), during which extremely little sunspots were observed. Applying the method of analysis of rare events to these observations led researchers to conclude that the appearance of sunspots at the Maunder minimum was characterized by a weak amplitude of 22 years. The concept of continuity of magnetic cycles at this time is also confirmed by measurements of cosmogenic radionuclides in natural terrestrial archives. Therefore, today it is believed that during the Maunder minimum, the cyclic magnetic activity of the Sun did not stop, although the amplitude of the cycles was quite low. In the αΩ-dynamo model, this may be due to the fact that the magnitude of the magnetic induction of the toroidal field excited by radial differential rotation in the solar convection zone at this time did not reach the threshold value required for lifting magnetic power tubes on the solar surface (nonlinear dynamo mode). Possible physical mechanisms describing the suppression of the dynamo process at intervals when no sunspots were observed are analyzed. A scenario for explaining the north-south asymmetry of magnetic activity during the Maunder minimum is proposed. A key role in the proposed scenario is played by the special nature of the internal rotation of the Sun, revealed as a result of helioseismological experiments. The modern grand maximum of solar activity, which began in the 1940s, has ceased after solar cycle 23, and activity of the Sun seems to be returning to its normal moderate level.

The post sunset equatorial F- region zonal drift variability and its linkage with equatorial spread F onset and duration over Indian longitudes

The seasonal and solar activity variation of the post sunset F- region zonal plasma drift, at the magnetic equatorial region over Indian longitudes is analyzed using the Republic of China Satellite-1 data from January 2000 to April 2004. The post sunset F- region zonal drifts are observed to be higher in the years of high solar activity in comparison with low solar activity, while seasonally the drifts are minimum in summer with much higher values in other seasons. The seasonal and solar activity variations of zonal plasma drift are attributed to the corresponding variations in the neutral winds. The dependences of the F region peak vertical drift on the zonal plasma drift at 18.5 IST (Indian Standard Time) and the time difference of the conjugate points sunset times, are quantitatively analyzed. Further an integrated parameter (incorporating the above mentioned two independent factors), which is able to predict the peak vertical drift and growth rate of Rayleigh Taylor instability is proposed. The other major outcome of the study is the successful prediction of the Equatorial Spread F (ESF) onset time and duration using the new integrated parameter at 18.5 IST. ESF irregularities and associated scintillations adversely affect communication and navigation systems. Hence, the present methodology for the prediction of the characteristics of these nocturnal irregularities becomes relevant.

The Tendencies of Change of the Incoming Solar Radiation to the Upper Atmosphere Boundary and Their Spatial Localization

Satellite-based measurements of the total flow of incoming solar radiation arriving at the Earth (total solar irradiance (TSI)) have been carried out since 1977. By now, a continuous series of variations of the TSI is obtained. The 11-year cycle and its amplitude in multiyear variations of solar radiation are revealed. However, two mechanisms having different physical nature are defined in regulation of the incoming solar radiation to the Earth (with the atmosphere not accounted for), and in its distribution over the Earth surface (solar climate of the Earth). One mechanism is related to the variation in solar activity. Another mechanism is defined by celestial-mechanical processes, which alter the orbit elements of the Earth (Earth–Sun distance, duration of the tropical year, etc.), the Earth rotation axis tilt, and the relevant variations in the Earth’s insolation. The performed calculations of the insolation related to the celestial-mechanical processes were used as a basis for differentiating the satellite observational data on the changes of the TSI with respect to the mechanisms of different physical nature. It was made possible to estimate the contributions of the variation in solar activity and of the celestial-mechanical processes to the total incoming solar radiation.

Long–Term Variations in Solar Differential Rotation and Sunspot Activity, II: Differential Rotation Around the Maxima and Minima of Solar Cycles 12 – 24

Studies of variations in the solar differential rotation are important for understanding the underlying mechanism of solar cycle and other variations of solar activity. We analyzed the sunspot-group daily data that were reported by Greenwich Photoheliographic Results (GPR) during the period 1874 – 1976 and Debrecen Photoheliographic Data (DPD) during the period 1977 – 2017. We determined the equatorial rotation rate [ $A$ ] and the latitude gradient [ $B$ ] components of the solar differential rotation by fitting the data in each of the 3-year moving time intervals (3-year MTIs) successively shifted by one year during the period 1874 – 2017 to the standard law of differential rotation. The values of $A$ and $B$ around the years of maxima and minima of Solar Cycles 12 – 24 are obtained from the 3-year MTIs series of $A$ and $B$ and studied the long-term cycle-to-cycle modulations in these coefficients. Here we have used the epochs of the maxima and minima of the Solar Cycles 12 – 24 that were recently determined from the revised Version-2 international sunspot-number series. We find that there exits a considerably significant secular decreasing-trend in $A$ around the maxima of solar cycles. There exist no secular trends in both $A$ and $B$ around the minima of solar cycles. The secular trend in $B$ around the maxima of solar cycles is also found to be statistically insignificant. We fitted a cosine function to the values of $A$ , and also to those of $B$ , after removing the corresponding linear trends. The cosine-fits suggest that there exist ≈54-year (≈94-year) and ≈82-year (≈79-year) periodicities in $A$ ( $B$ ) around the maxima and minima of solar cycles, respectively. The amplitude of the cosine-profile of $A$ ( $B$ ) around the minima of solar cycles is about 41% (65%) larger than that of $A$ ( $B$ ) around the maxima. In addition, the cosine profiles of $A$ and $B$ suggest a large (up to $180^{\circ }$ ) phase difference between the long-term variations of $A$ , and also between those of $B$ , around maxima and minima of solar cycles. Implications of all these results are discussed briefly.

Periods of Extremely High Rates of the Production of Cosmogenic 14C and Temperature Variation According to Data on the 40Ar Content in the Ice Layers for the Last 4000 Years

The possible application of temperature reconstructions based on measurement of the 40Ar concentration in ice layers of the Greenland ice sheet to study past solar activity with radiocarbon data is considered. The rate of 14С production and the heliosphere modulation potential from the 2nd millennium B.C. to the middle of the 18th century A.D. is reconstructed with allowance for the Earth’s climate variation. The temperature reconstruction based on the 40Ar content in the annual ice layers of Greenland revealed two global minima of solar activity with duration of ~200 years during the cold Sub-Atlantic period, which lasted on the Earth from 900 B.C. to 300 B.C. This suggests that solar-activity variation can influence climate change.

Solar Activity Predictability Horizons

The chaotic component in solar-activity variations, the limited amount of observational statistics, and the use of proxy data impose limitations on long-term predictions. This study uses the well-known reconstructions of total solar irradiance (TSI) from optical observations (from 1610 AD) and cosmogenic radioisotopes (from 7362 BC) to estimate the maximum Lyapunov exponent for 11-year and secular cycles. This is done with the classical algorithm described by Wolf et al. (1985). The maximum Lyapunov exponents turned out to be positive in both cases, thus confirming the presence of the chaotic component in time series. We then estimate the predictability horizon Tp with the well-known error for each reconstruction. It turned out that the predictability horizon is on average 10 ≤ Tp ≤ 22 years for 11-year cycles and on average 40 ≤ Tp ≤ 60 years for secular cycles.

Analysis and Attribution of Climate Change in the Upper Atmosphere From 1950 to 2015 Simulated by WACCM‐X

AbstractMonitoring climatic changes in the thermosphere and ionosphere and understanding their causes is important for practical purposes. To support this effort and facilitate comparisons between observations and model results, a long transient simulation with the Whole Atmosphere Community Climate Model eXtension (WACCM‐X) from 1950 to 2015 was conducted. This simulation used realistic variations in solar and geomagnetic activity, main magnetic field changes, and trace gas emissions, including CO2, thereby including all known drivers of upper atmosphere climate change. Analysis of the full 1950–2015 interval with a standard multilinear regression approach demonstrated difficulties in removing solar cycle effects sufficiently to obtain reliable trends. Results improved when an (F10.7a)2 was included in the regression model, in addition to terms for F10.7a, KP, and the trend itself. Comparisons with previous studies and analysis of spatial variations in trend estimates confirmed that the increase in CO2 concentration is the main driver of trends in thermosphere temperature and density, but at high (magnetic) latitudes effects of main magnetic field changes play a role as well, especially in the Northern Hemisphere. Spatial patterns of trends in hmF2, NmF2, and total electron content indicate a superposition of CO2 and geomagnetic field effects, with the latter dominating trends in the region of ∼50–20°N, ∼60°W to 20°E. Additional model experiments to investigate the indirect dynamical effects of climate change in the lower atmosphere (<50 km) on the upper atmosphere (>100 km) suggested that these effects are small and insignificant. However, current model limitations could mean that these effects are underestimated.

Radiocarbon Data from the Late 18th Century as a Reflection of Solar Activity Variation, Natural Climate Change, and Anthropogenic Activity

The data on the content of the 14C cosmogenic isotope in the natural archives make it possible to study the solar activity (SA) in the past centuries and millennia. However, the 14C content in the natural archives is influenced not only by the intensity of incoming galactic cosmic rays (GCRs), which are modulated by the interplanetary magnetic field and vary according to SA variations; changes in the geomagnetic field and in the Earth’s climate also affect radiocarbon data. In particular, climate variation leads to the redistribution of radiocarbon between natural reservoirs. In the 19th century, increased anthropogenic activity was also reflected in radiocarbon data. This article presents the results of the reconstruction of the rate of 14C production under the influence of GCRs with allowance for the above factors. It is shown that the rate of radiocarbon release from the deep ocean into the surface layer and the atmosphere has increased since the second quarter of the 19th century. Apparently, this process is natural.

A solar activity correction term for the IRI topside electron density model

In situ measurements by the Low Earth Orbital (LEO) satellites, such as CHAMP, GRACE, and C/NOFS satellites have shown that the International Reference Ionosphere (IRI) model has shortcomings in describing the solar activity variation of the topside electron density. In particular IRI overestimates the measured densities in the topside ionosphere during the very low solar activity reached during the last solar minimum (2008–2009). We have used Alouette and ISIS topside sounder data and CHAMP, GRACE, as well as Swarm in situ measurements to deduce a correction term for the IRI electron density topside model that more accurately describes the variation with solar activity. We have used a linear variation with the solar index PF10.7 and described the latitudinal and altitudinal variation of the regression parameters A0 and A1 (intercept and slope). We find good agreement between the regression parameters deduced from the topside sounder and from the CHAMP and GRACE observations. Swarm results show the same latitudinal structure as the other data sets, however, a scaling factor is needed to obtain agreement of the absolute values. The new model was evaluated with Alouette and ISIS topside sounder, as well as LEO satellites in situ data showing a significant improvement over the current IRI model.

More than softer-when-brighter: The X-ray powerlaw spectral variability in NGC 4051

The powerlaw X-ray spectra of active galactic nuclei at moderate to high accretion rates normally appear softer when they brighten, for which the underlying mechanisms are yet unclear. Utilizing XMM-Newton observations and excluding photons $<$ 2 keV to avoid contamination from the soft excess, in this work we scrutinize the powerlaw spectral variability of NCG 4051 from two new aspects. We first find that a best-fit "softer-when-brighter" relation is statistically insufficient to explain the observed spectral variabilities, and intervals deviated from the empirical relation are clearly visible in the light curve of 2 -- 4 keV/4 -- 10 keV count rate ratio. The deviations are seen not only between but also within individual XMM-Newton exposures, consistent with random variations of the corona geometry or inner structure (with timescales as short as $\sim$ 1 ks), in addition to those behind the smooth "softer-when-brighter" trend. We further find the "softer-when-brighter" trend gradually weakens with the decreasing timescale (from $\sim$ 100 ks down to 0.5 ks). These findings indicate that the powerlaw spectral slope is not solely determined by its brightness. We propose a two-tier geometry, including flares/nano-flares on top of the inner disc and an embedding extended corona (heated by the flares, in analogy to solar corona) to explain the observations together with other observational clues in literature. Rapid spectral variabilities could be due to individual flares/nano-flares, while slow ones are driven by the variations in the global activity of inner disc region (akin to the variation of solar activity, but not the accretion rate) accompanied with heating/cooling and inflation/contraction of the extended corona.

Estimation of frequency and duration of ionospheric disturbances over Turkey with IONOLAB-FFT algorithm

One of the more common methods of observation of variability of the Earth’s ionosphere is based on total electron content (TEC) estimated from ground-based dual-frequency Global Positioning System (GPS) receivers. Variations in solar, geomagnetic and seismic activity cause depletions or enhancements in the ionospheric electron concentrations that can be detected as disturbances. Some of these disturbances have wave-like characteristics, where frequency of oscillation can be used to identify and classify the disturbance. In this study, the frequency of such periodic disturbances is estimated using a fast Fourier transform (FFT)-based method, namely IONOLAB-FFT, in the spectral domain. IONOLAB-FFT, which was initially developed to be used on slant TEC (STEC), is modified to be applied to TEC in the local zenith direction of the receiver. The algorithm is tested using literature data on disturbances generated by a geomagnetic activity, a solar flare, a medium-scale traveling ionospheric disturbance (MSTID), a large-scale TID (LSTID) and an earthquake. An accordance with these known disturbances is observed in running IONOLAB-FFT, and the main frequencies and durations of the disturbances are estimated. IONOLAB-FFT method is applied to TEC computed from Turkish Permanent GPS Network (TNPGN-Active) which lies in mid-latitude region to detect the any wave-like oscillations, sudden disturbances and other irregularities during December, March, June and September months for 2010, 2011 and 2012 years. It is observed that a large number of the estimated frequencies are accumulated between 0.08 and 0.14 MHz corresponding to periods of 3.5 h to 2 h. The significant frequencies are grouped less than 0.28 MHz. A large number of the durations of the oscillations are between 425 and 550 min in 2010, 300 and 550 min in 2011 and 350 and 400 min in 2012. The longest duration (around 800 min: 13.33 h) is observed in December months, and the shortest duration (around 2 h) is observed in September months.

A Comprehensive Approach for Estimating Collective and Average Effective Doses of Galactic Cosmic Radiation Received by Pilots.

This study proposes a feasible and comprehensive approach for estimating collective and average effective doses of galactic cosmic radiation received by pilots on the basis of data in publicly available civil aviation annual statistical reports. Large uncertainties are associated with the estimation of these quantities because the radiation environment at aviation altitudes is complex, and a large number of flights operated by various air carriers is involved. A best estimate can be obtained through this approach because it considers all passenger, cargo, and charter flights operated during a long period of time instead of subjectively selecting some representative flights for dose evaluation. The approach becomes feasible and practical with the aid of a special feature called automatic batch analysis in the NTHU Flight Dose Calculator. There are two international airlines in Taiwan: China Airlines and EVA Air. As a demonstration, the collective effective dose received by the 2,513 pilots from the two airlines in 2018 was estimated to be 4,947 person-mSv, and the average effective dose per pilot was 1.97 mSv. These estimates were considered representative because they were based on all 151,526 flight segments operated that year. The assessment of the annual effective doses received by pilots in Taiwan from 2006 to 2018 was performed. The results varied in the range of 1.70-2.97 mSv because of variations in solar activity and operational flight routes. A regression model that can effectively reproduce the derived average effective dose rates on board aircraft was obtained for future application in aircrew dosimetry.

Thermal effects of nonlinear acoustic-gravity waves propagating at thermospheric temperatures matching high and low solar activity

Numerical high-resolution modeling of nonlinear acoustic-gravity waves (AGWs) generated at the Earth's surface and propagating to the thermosphere shows that wave characteristics are depending on modifications in the mean density, temperature, molecular dissipation and composition due to variations of solar activity (SA). Amplitudes of temperature wave perturbations are generally larger at high SA at altitudes above 150 km, due to larger mean temperature and smaller molecular heat conductivity. Increasing kinematic coefficients of molecular heat conduction and viscosity result in stronger decreasing AGW amplitudes at altitudes larger 150 km at low SA. Dissipating AGWs generally produce heating at altitudes below 120 km. At larger heights, AGWs generally heat the thermosphere at low SA and cool it at high SA. Wave enthalpy fluxes are mainly upwards below 120 km altitude and downwards above 150 km at high SA, where they may have directions opposite to the upward wave energy fluxes. Downward wave enthalpy fluxes correspond to AGW cooling the upper atmosphere at high SA. Nonlinear dissipating AGWs may produce upward and downward transport of atmospheric mass. These mass flows may produce adiabatic heat influxes in the upper atmosphere. Mainly positive residual wave-induced mass flows at altitudes higher 150 km may contribute to the wave cooling of the upper atmosphere. Wave breaking and interactions between waves and the mean flow in the nonlinear model are stronger at higher amplitudes of AGW excitation at the ground, which lead to bigger energy losses for larger-amplitude waves. At high SA, resulting effects in the thermosphere depend on the balance between, on one hand, increases in wave amplitudes, caused by weaker molecular dissipation and smaller transfer of the wave energy to the wave-induced jet flows, and, on the other hand, decreases in the amplitudes due to higher density and larger AGW reflection. The thermal effects of waves in the upper atmosphere may depend on competitions between heating due to dissipation of the upward wave energy flux and cooling due to divergence of the downward wave entropy (or potential enthalpy) flux. At high SA, larger mean temperatures and larger temperature perturbations might increase magnitudes of downward wave entropy fluxes, which may result in more frequent downward wave enthalpy fluxes and wave cooling of the upper atmosphere.

Recursive Integer Sequences, Detected in Solar-Cycle Periodicities Measured in Numbers of Rigid Rotations of the Sun

Consecutive integers in the recursive number sequences, the Fibonacci sequence (Fn) and the Lucas sequence (Ln), are detected in the lengths of solar-activity variations from ≈ 1 yr to ≈ 12 yr, measured in rigid rotations of the Sun at the helioseismologically determined frequency in the radiative zone, $433 \pm 3$ nHz. One rotation is denoted by the symbol $\Omega $ . Firstly, in the new international sunspot-number record (Ri) the most frequent (modal) sunspot-cycle length, which is also the period defined by autocorrelation for the recurrence of sunspot cycles, has been $144 \pm \approx 2~\Omega $ ( $\mbox{F}_{12} = 144$ ). The most frequent length for a descending leg of the cycle has been 89 ± 2 $\Omega $ (F $_{11} = 89$ ), and for an ascending leg 55 ± 1 $\Omega $ (F $_{10} = 55$ ). Secondly, there is some observational evidence of Ri spectral peaks at the consecutive Ln numbers of $\Omega $ : 18 $\Omega $ (≈ 1.3 yr), 29 $\Omega $ (≈ 2.1 yr), 47 $\Omega $ (≈ 3.4 yr), and 76 $\Omega $ (≈ 5.6 yr), which are harmonics of the 144 $\Omega $ period divided by the first four F $_{{n}} > 1$ : 2, 3, 5, and 8. The numbers of $\Omega $ : 144, 89, and 55 may be kinematical thresholds in the dynamo process starting at sunspot maximum, when the poles change polarity and the process is re-set. The ratio of two consecutive Fn or Ln converges to $\frac{1+ \sqrt{5}}{2}$ , hence it is suggested that this proportion plays a role in solar behavior over time, described numerically. The length ratio $\frac{1+ \sqrt{5}}{2}$ also is characteristic of fivefold symmetry in space. Since the icosahedral group is the link between numerical and spatial expressions of fivefold symmetry, it is proposed that the presence of icosahedral symmetry in the large-scale geometry of the Sun could also be tested.

Wavelet analysis of the long-term activity of V833 Tau

ABSTRACT The bulk of available stellar activity observations is frequently checked for the manifestation of signs in comparison with the known characteristic of solar magnetic modulation. The problem is that stellar activity records are usually an order of magnitude shorter than available observations of solar activity variation. Therefore, the resolved time-scales of stellar activity are insufficient to decide reliably that a cyclic variation for a particular star is similar to the well-known 11-yr sunspot cycles. As a result, recent studies report several stars with double or multiple cycles which serve to challenge the underlying theoretical understanding. This is why a consistent method to separate ‘true’ cycles from stochastic variations is required. In this paper, we suggest that a conservative method, based on the best practice of wavelet analysis previously applied to the study of solar activity, for studying and interpreting the longest available stellar activity record – photometric monitoring of V833 Tau for more than 100 yr. We find that the observed variations of V833 Tau with time-scales of 2–50 yr should be comparable with the known quasi-periodic solar mid-term variations, whereas the true cycle of V833 Tau, if it exists, should be of about a century or even longer. We argue that this conclusion does not contradict the expectations from the stellar dynamo theory.

Effects of solar activity on production rates of short‐lived cosmogenic radionuclides

AbstractThe solar activity can be quantified by solar modulation parameter Φ that affects the heliospheric magnetic field. This activity influences the intensity of the galactic cosmic ray (GCR) particle flux within the solar system, and consequently, the differential primary particle spectra depend on the solar modulation parameter Φ (MeV). The modulation parameter Φ shows spatial and temporal variations (Leya and Masarik 2009). Some of the solar activity variations are cyclic and result in measurable effects as for example the 11‐year solar cycle. Variations in solar activity only induce small effects on the production of long‐lived cosmogenic radionuclides. This is due to the fact that activities measured in meteorites usually correspond to saturation values and represent long‐term average values. Long‐lived radionuclides often require millions of years of irradiation by GCR to reach saturation and therefore activity cycles average out. In contrast, one can expect strongly pronounced variations for saturation values caused by primary flux intensity variations, if short‐lived radionuclides with half‐lives ranging from days to a few years are investigated. Short‐lived cosmogenic nuclides were the subject of many experimental and theoretical investigations (e.g., Evans et al. 1982; Spergel et al. 1986; Neumann et al. 1997; Komura et al. 2002; Laubenstein et al. 2012). The aim of this work is to develop formulae for calculating production rates of radionuclides with short half‐life, taking into account temporal variations in the primary cosmic ray intensity. The developed formulae were applied to the Kosice and Chelyabinsk meteorites. The results for the Košice meteorite were already published (Povinec et al. 2015). Here, we give a full explanation of underlying model.

NIGHTTIME TEC VARIATION ANALYSIS OF KLOBUCHAR MODEL BASED ON IGS DATA IN CHINA

Abstract. In order to further study the variation characteristics of the nighttime ionospheric accuracy of the Klobuchar model and the correlation between the nighttime ionospheric accuracy of the Klobuchar model and solar activity intensity. In this paper, a method for comparative analysis on solar activity intensity in the high, medium and low solar activity years has been proposed. The GIM provided by the IGS Center from 2008 to 2018 are treated as reference values to analyze the nighttime accuracy of the Klobuchar model for annual, seasonal, and monthly changes in high solar activity, medium solar activity and low solar activity. The results are: (1) The nighttime accuracy of the Klobuchar model is best in the medium solar activity, followed in the low solar activity and the worst in the high solar activity. (2) The Bias and RMS of the Klobuchar model at nighttime had obviously semi-annual and seasonal variations in high and medium solar activity. (3) The nighttime accuracy of the Klobuchar model did not vary with Bias and RMS changes at nighttime.

Time of evening zonal drift reversal in F- region and its implications for post sunset ionosphere

The study analyses the delayed occurrence of the F- region ionospheric manifestations like peak vertical drift and Equatorial Spread F onset in summer solstice of low solar activity years, using the ionosonde data at the magnetic equatorial station Trivandrum (8.5° N, 76.9° E) and Republic of China Satellite-1 data. The analysis reveals the unambiguous role of the time of ionospheric F- region zonal plasma drift/wind reversal in modifying the above-mentioned phenomena. The direct control of equatorial Spread F onset by the F- region drift/wind reversal is clearly established on a day-to-day basis in summer season. The role of the time of zonal wind/drift reversal in modulating the ESF onset is examined quantitatively by exploring its effect on the growth rate of Rayleigh - Taylor instability. Further, the study brings out the solar activity variation of the time of F- region zonal plasma drift/wind reversal for all seasons. The results highlight the need to have systematic neutral wind measurements to better address the enigmatic and multi-dimensional problem of equatorial Spread F day-to-day variability.

Effect of a magnetic pulse on orientation behavior in rainbow trout (Oncorhynchus mykiss)

Magnetoreception remains one of the most enigmatic of animal senses. Rainbow trout (Oncorhynchus mykiss) represent an ideal species to study this sense, as magnetoreception based upon microscopic particles of magnetite is suspected to play an important role in their orientation and navigation. Here we found that compared with controls, a magnetic pulse (a treatment commonly used to demonstrate magnetite-based magnetoreception) can induce orientation behavior in juvenile rainbow trout on a specific experimental day. Multiple circular-linear regression also indicated that this effect could at least be partially explained by daily variation in solar electromagnetic activity (i.e., sunspot count and disturbance storm time index). These results are consistent with magnetite-based magnetoreception in rainbow trout and suggest that 1) solar activity may impact magnetic orientation and 2) researchers should be cognizant of its potential consequences on studies of magnetoreception.

Records of Auroras in Arabic Historical Sources: Additional List and Preliminary Analysis

Few studies have collected and analyzed the astronomical events recorded in Arabic literature. In this paper, we present some additional events reported in four Arabic historical sources that could be classified as an aurora. These observations occurred from 9th to 20th century and cover a large geographic area: North Africa, Arabian-Peninsula and Middle-East. Some of them were observed at very low geomagnetic latitude, such as the event seen in Yemen in AD 1919 that can be considered as one of the lowest latitude auroras ever documented by Arabic scholars. In the same Yemenite source, the author describes a twilight phenomenon of 1883 October 03–November 01 which can be considered as an atmospheric-optical phenomenon arising from the major explosive eruptions of Krakatoa in 1883 August 26–27. We also noticed that one of the events which was seen for 7 days coincide probably with the prolonged manifestation of auroras of 1870 September 24–25. Including published records, we compiled a so far most complete catalog of potential auroral candidates in the Arabic sources. This data set can be used in order to study the solar activity variations and magnetic storms in the historical past. One of the interesting auroras was seen in Mecca ($\sim17^{\circ}$ MLAT) in 1872 February 04. This event is further evidence for the equatorward extension of auroral display and the planetary consequences of the great geomagnetic storm of 1872. Finally, it should be underlined that no aurora observations were recorded during the Maunder minimum (MM).