Active longitudes in the period of overlap of 11-year cycles

It is shown that “active longitudes” for the sunspots of old and new cycles manifest themselves approximately in the same longitudinal intervals and remain for several 11-year cycles. To be more accurate, they vanish in some cycles but then appear again at the same longitudinal intervals in the other cycles. The entire period is characterized by a total of four active longitudes. The old-cycle sunspots observed at low equatorial latitudes in the Northern and Southern Hemispheres are characterized by a shift by ≈180°, which indicates antipodality of the active longitudes in the Northern and Southern Hemispheres. In the case of highlatitude sunspots (new-cycle sunspots), the best correlation is observed for the shift of ≈90°. There is supposedly a dependence of the rotation speed of active longitudes on the secular cycle.     

Unique variations of the total electron content in the preparation period of Haitian earthquake (M7.9) on January 12, 2010

Variations of the total electron content according to the index IONEX IGS in the period of preparation of the earthquake in Haiti (M7.9) on January 12, 2010, are considered. The situation is exceptional owing to the unique position of the island of Haiti relative to the structure of the ionosphere over the Caribbean Sea: the ionospheric region over Haiti is in the trough formed by the northern slope of the equatorial anomaly and additional maximum formed at latitudes of approximately 30° N within this longitudinal interval. Distortion of the shape of the equatorial anomaly, total decrease in the electron content in the equatorial anomaly a few days prior to the earthquake, increase in the electron concentration directly over the earthquake epicenter a few days prior to the earthquake, increase in the additional maximum at latitudes of ∼30° N, and formation of an additional maximum in the Southern Hemisphere in the region conjugated to the additional maximum in the Northern Hemisphere in the periods of its intensification are observed. The configuration of the equatorial anomaly is restored after the earthquake.     

Cenozoic latitudinal shift of the Hawaiian hotspot and its implications for true polar wander

Pacific plate equatorial sediment facies provide estimates of the northward motion of the Pacific plate that are independent of paleomagnetic data and hotspot tracks. Analyses of equatorial sediment facies consistently indicate less northward motion than analyses of the dated volcanic edifices of the Hawaiian-Emperor chain. The discrepancy is largest 60–70 Ma B.P.; the 60- to 70-Ma equatorial sediment facies data agree with recent paleomagnetic results from deep-sea drilling on Suiko seamount [1] and from a northern Pacific piston core [2]. Equatorial sediment facies data and paleomagnetic data, combined with K-Ar age dates along the Emperor chain [3], indicate a position of the spin axis at 65 Ma B.P. of 82°N, 205°E in the reference frame in which the Pacific Ocean hotspots are fixed. This pole agrees well with the position of the spin axis in the reference frame in which the Atlantic Ocean hotspots and the Indian Ocean hotspots are fixed [4,5], supporting the joint hypotheses that (1) the Pacific Ocean hotspots are fixed with respect to the hotspots in other oceans, (2) the hotspots have shifted coherently with respect to the spin axis, and (3) the time average of the earth's magnetic field 65 Ma B.P. was an axial geocentric dipole. Global Neogene paleomagnetic data suggest that a shift of the mantle relative to the spin axis has been occurring during the Neogene in the same direction as the shift between 65 Ma B.P. and the present. All data are consistent with a model in which the hotspots (and by inference the mantle) have shifted with respect to the spin axis about a fixed Euler pole at a constant rate of rotation for the last 65 Ma.     

Local time and longitude dependence of the equatorial electrojet magnetic effects

An empirical model of the equatorial electrojet (EEJ), including local time and longitude dependence, has been constructed based on the surface magnetic data recorded at 26 stations located in six different longitude sectors that were set up or augmented during the international equatorial electrojet year (IEEY). The model reproduces the characteristic signatures of the EEJ-associated horizontal and vertical magnetic components at ground level. The model-predicted variations at the orbit of the POGS satellite are generally in good agreement with the onboard magnetic signatures, although strong discrepancies are also often seen. The nature of the differences suggests that the global scale magnetospheric or field-aligned current systems may sometimes dominate the satellite data. The nature of the longitudinal inequalities in the EEJ strength indicates that the equatorial electrojet is strongest in South America (80°–100°W) and weakest in the Indian sector (75°E) with a secondary minimum and a maximum centered, respectively, in the Atlantic Ocean (30°W) and in western Africa (10°E). The EEJ strength is shown to be inversely correlated with the main field intensity along the dip-equator.     

Modeling the partial ring current effect in a disturbed magnetosphere

The mathematical model of the magnetic field of the partial ring current has been proposed. This current is considered as a pair of spatial current circuits in the Northern and Southern hemispheres, either of which includes two ring zones, in the geomagnetic equator plane and ionosphere, and two zones of the field-aligned current, flowing along the geomagnetic dipole field lines and joining ring fragments of the circuit. The model parameters are: colatitude of the eastward electrojet, longitudinal shift relative to the Sun-Earth axis, circuit half-angle, and the total current flowing in the circuit. The Biot-Savart-Laplace law has been used to calculate the magnetic field of the current circuit. The magnetic field of the partial ring current has been calculated under the conditions typical of a strong magnetic storm. The technique for calculating the partial ring current intensity, using the Asym-H geomagnetic index, has been proposed.     

Longitudinal statistics of plasma bubbles observed as He+ density depletions at altitudes of the topside ionosphere

This work presents a new examination of the hypothesis regarding the equatorial origin of low He⁺ density plasma depletions (or subtroughs). For this purpose, we have conducted a detailed comparative analysis of longitudinal variations in the occurrence probabilities of subtroughs in both hemispheres and variations in the occurrence probabilities of equatorial F-region irregularities (EFIs), equatorial spread F (RFS and ESF), and equatorial plasma bubbles (EPBs). Taking into consideration the seasonal dependence and some peculiarities of magnetic field variations in different hemispheres, a conclusion has been reached regarding the similarity between longitudinal statistical occurrences of subtroughs and equatorial ionospheric F-region irregularities. In addition, another piece of evidence in favor of the similarity of the nature of the above-mentioned phenomena has been obtained. We have got a confirmation once again that low He⁺ density depletions (or subtroughs) can be rightfully considered as equatorial plasma “bubbles,” which can be observed at altitudes of the topside ionosphere as depletions in the He⁺ density.     

Diurnal and Longitudinal Variations of the Structure of an Equatorial Anomaly During Equinoxes According to Intercosmos-19 Satellite Data

Longitudinal and local time variations in the structure of the equatorial anomaly under high solar activity in the equinox are considered according to the Intercosmos-19 topside sounding data. It is shown that the anomaly begins to form at 0800 LT, when the southern crest is formed. The development of the equatorial anomaly is associated with well-known variations in the equatorial ionosphere: a change in the direction of the electric field from the west to the east, which causes vertical plasma drift W (directed upward) and the fountain effect. At 1000 LT, both anomaly crests appear, but they become completely symmetrical only by 1400 LT. The average position of the crests increases from I = 20° at 1000 LT to I = 28° at 1400 LT. The position of the crests is quite strong, sometimes up to 15°, varies with longitude. The foF2 value above the equator and the equatorial anomaly intensity (EAI) at 1200–1400 LT vary with the longitude according to changes in the vertical plasma drift velocity W. At this time, four harmonics are observed in the longitudinal variations of W, foF2, and EAI. The equatorial anomaly intensity increases to the maximum 1.5–2 h after the evening burst in the vertical plasma drift velocity. Longitudinal variations of foF2 for 2000–2200 LT are also associated with corresponding variations in the vertical plasma drift velocity. The equatorial anomaly intensity decreases after the maximum at 2000 LT and the crests decrease in size and shift towards the equator, but the anomaly is well developed at midnight. On the contrary, after midnight, foF2 maxima in the region of the anomaly crests are farther from the equator, but this is obviously associated with the action of the neutral wind. At 0200 LT, in contrast to the morning hours, only the northern crest of the anomaly is clearly pronounced. Thus, in the case of high solar activity during the equinoxes, a well-defined equatorial anomaly is observed from 1000 to 2400 LT. It reaches the maximum at 2000 LT.     

Penetration of Pc5 geomagnetic pulsations to unusually low latitudes during the recovery phase of a superstrong magnetic storm of October 31, 2003

Based on the data of the ground observations, the global distributions of the Pc5 geomagnetic pulsation amplitudes during the recovery phase of the superstorm of October 31, 2003, have been mapped, and an unusually deep penetration of these pulsations into the inner magnetosphere has been found out. Thus, two more zones with identical dynamic spectra and oscillation amplitudes from the polar to equatorial latitudes have been detected in the postnoon sector simultaneously with morning classical Pc5 pulsations in the narrow (～63°–68° CGM) latitudinal band extended along longitude. The higher-latitude zone as if continues the morning band, and the lower-latitude zone is characterized by the maximal intensity at latitudes of ～50°–57° CGM. The oscillation amplitudes are of the same order of magnitude in both zones. The zones are spatially separated by a very narrow latitudinal amplitude minimum and by a change in the phase and sense of rotation of the wave polarization vector. The pulsation spectra in the morning and daytime sectors are different, which indicates that the nature of the morning and postnoon oscillations is different.     

Comparative characteristics of ion and electron precipitation in the dawn and dusk sectors

Characteristics of ion and electron precipitations in the dawn and dusk sectors are investigated by DMSP F6 and F7 satellite observations. It is shown that in the dusk sector the positions of electron and ion precipitation boundaries are nearly coincident for all levels of magnetic activity; however the latitudinal distribution of energy fluxes indicates that the positions of electron and ion precipitation maxima are spatially separated. Maximum energy fluxes of ions is observed at the equatorial precipitation boundary, while those of electrons at the poleward one. In the dawn sector, the electron precipitation region is 3°–4° wider than that of ions. The isotropy boundary in the dusk sector is located in the region of diffuse precipitation (DAZ) near its poleward boundary for all levels of magnetic activity, while in the dawn sector it falls in the region of structured precipitations (AOP). Electron precipitations are dominating in the dawn sector. Here in the region of diffuse precipitation (DAZ), the ion energy fluxes Fi make less than 5% as compared to the electron energy flux Fe. In the region of structured precipitations (AOP), the portion of Fi decreases with increasing magnetic activity from ~10–20% for AL ≈ -100 nT to <5% for AL ≈ -1000 nT. As for the dusk sector, in the AOP region, electron precipitations are dominating as well, while in the DAZ region the ion energy fluxes are significant. In the 1500–1800 MLT sector, the ratio Fi/Fe increases from ~0.7 to ~3.0 with AL changing from -100 nT to -1000 nT.     

POLAR spacecraft observations of helium ion angular anisotropy in the Earth’s radiation belts

New observations of energetic helium ion fluxes in the Earth’s radiation belts have been obtained with the CAMMICE/HIT instrument on the ISTP/GGS POLAR spacecraft during the extended geomagnetically low activity period April through October 1996. POLAR executes a high inclination trajectory that crosses over both polar cap regions and passes over the geomagnetic equator in the heart of the radiation belts. The latter attribute makes possible direct observations of nearly the full equatorial helium ion pitch angle distributions in the heart of the Earth’s radiation belt region. Additionally, the spacecraft often re-encounters the same geomagnetic flux tube at a substantially off-equatorial location within a few tens of minutes prior to or after the equatorial crossing. This makes both the equatorial pitch angle distribution and an expanded view of the local off-equatorial pitch angle distribution observable. The orbit of POLAR also permitted observations to be made in conjugate magnetic local time sectors over the course of the same day, and this afforded direct comparison of observations on diametrically opposite locations in the Earth’s radiation belt region at closely spaced times. Results from four helium ion data channels covering ion kinetic energies from 520 to 8200 KeV show that the distributions display trapped particle characteristics with angular flux peaks for equatorially mirroring particles as one might reasonably expect. However, the helium ion pitch angle distributions generally flattened out for equatorial pitch angles below about 45°. Significant and systematic helium ion anisotropy difference at conjugate magnetic local time were also observed, and we report quiet time azimuthal variations of the anisotropy index.     

Longitudinal variations in the daytime low-latitude ionosphere according to the data of topside sounding from the intercosmos-19 satellite

Using the data of the topside ionosphere sounding from the Intercosmos-19 satellite, longitudinal variations in foF2 at low latitudes at the daytime hours are considered. It is obtained that these variations in particular days in the majority of cases have a regular wave-like character with periods of about 75°–100° in longitude and amplitudes on the average of 2–4 MHz. In other words, along the valley and crests of the equatorial anomaly, a structure with four maximums and four minimums which have a tendency to be located near certain longitudes (the same in all seasons) is observed. The variations in foF2 along the crests of the equatorial anomaly are usually in anti-phase to variations along its valley. Comparing the characteristics of this wavelike structure at the daytime and nighttime hours, we obtained that the average positions of its extremes at the nighttime hours are shifted eastwards by 10°–50° relative to the daytime extremes. As a cause of formation of such a structure, high harmonics of atmospheric tides are assumed which, uplifting from below to heights of the E region, via the electric currents in this region influence the longitudinal structure of the electrodynamic plasma drift over the equator and by that impact the structure of the entire daytime low-latitude ionosphere.     

The ionospheric F2-region at low geomagnetic latitudes during the geomagnetic storms of 22–26 April 1990: Comparison of observed and modeled response

A comparison between the modeled NmF2 and hmF2 and NmF2 and hmF2, which were observed by the Kokubunji, Okinawa, Manila, Vanimo, and Darwin ionospheric sounders and by the middle and upper (MU) atmosphere radar, have been used to study the time-dependent response of the low-latitude ionosphere to geomagnetic forcing during a time series of geomagnetic storms from 22 to 26 April 1990. The reasonable agreement between the model results and data requires the modified equatorial meridional E×B plasma drift, the modified HWM90 wind, and the modified NRLMSISE-00 neutral densities. We found that changes in a flux of plasma into the nighttime equatorial F2-region from higher L-shells to lower L-shells caused by the meridional component of the E×B plasma drift lead to enhancements in NmF2 close to the geomagnetic equator. The equatorward wind-induced plasma drift along magnetic field lines, which cross the Earth equatorward of about 20° geomagnetic latitude in the northern hemisphere and about −19° geomagnetic latitude in the southern hemisphere, contributes to the maintenance of the F2-layer close to the geomagnetic equator. The nighttime weakening of the equatorial zonal electric field (in comparison with that produced by the empirical model of Fejer and Scherliess [Fejer, B.G., Scherliess, L., 1997. Empirical models of storm time equatorial zonal electric fields. J. Geophys. Res. 102, 24047–24056] or Scherliess and Fejer [Scherliess, L., Fejer, B.G., 1999. Radar and satellite global equatorial F region vertical drift model. J. Geophys. Res. 104, 6829–6842) in combination with corrected equatorward nighttime wind-induced plasma drift along magnetic field lines in the both geomagnetic hemispheres are found to be the physical mechanism of the nighttime NmF2 enhancement formation close to the geomagnetic equator over Manila during 22–26 April 1990. The model crest-to-trough ratios of the equatorial anomaly are used to study the relative role of the main mechanisms of the equatorial anomaly suppression for the 22–26 April 1990 geomagnetic storms. During the most part of the studied time period, a total contribution from geomagnetic storm disturbances in the neutral temperature and densities to the equatorial anomaly changes is less than that from meridional neutral winds and variations in the E×B plasma drift. It is shown that the latitudinal positions of the crests are determined by the E×B drift velocity and the neutral wind velocity.     

Role of the solar main magnetic dipole field in the solar-tropospheric relations. Part II. Dependence on the types of solar sources

Two criteria have previously been reported for efficient solar-tropospheric relations through corpuscular channels: the appropriate Sun-Earth attitude (equinoxes) and the mutual orientations of the terrestrial and solar main magnetic dipole fields. The effect also depends on the geographical position. The present paper reports a further criterion. The solar-meteorological correlations also depend on the solar origin of the given corpuscular impact: disturbances originating from the polar and equatorial regions release opposite behaviours. We conclude that the solar-meteorological relations can only be described by taking into account the specific spatial situations and polarity distributions.     

Asymmetric spreading across the Juan de Fuca and Gorda rises as obtained from a detailed magnetic survey

Marine magnetic data collected along 37 east-west lines off the Washington and Oregon coast between 42°N and 48°N westward to 144°W have been interpreted. Our interpretation shows that decrease in the offsets of the anomalies across the Surveyor fracture zone and the presence of undisturbed north-south lineations east of it are the result of continuous asymmetric spreading along the Surveyor fracture zone. The survey has delineated the extension of the Blanco fracture zone north-westward to about 133°W. Movement along the Blanco fracture zone was initiated about 15 million years ago. The undisturbed north-south trend of the magnetic anomalies between latitudes 42°N and 48°N and longitudes 133°W and 136°W is interpreted as the interval (22 to 15 my) during which the Juan de Fuca and Gorda rises were one continuous structure. West of 137° the Surveyor, Sedna and three minor fracture zones are mapped.     

Effects of planetary waves in parameters of the midlatitude sporadic <Emphasis Type="Italic">E</Emphasis> layer

The spatial structure of the planetary waves in the frequency parameters of the sporadic E layer have been studied based on an analysis of the 30-year series of the ionospheric data for the midlatitude region of the Northern Hemisphere, which made it possible to observe the planetary waves with zonal wavenumbers 1, 2, and 3. The characteristic periods of existence have been revealed for these waves, and the seasonal distributions of these periods have been constructed. These waves can be considered among quasistationary formations according to their character; i.e., these waves are stationary or slowly move during long time intervals but can abruptly change the initial phase during 1–2 days. Two clearly defined zones between 30°–60° E and 210°–240° E have been detected as a result of an analysis of the longitudinal belts where an abrupt change in the initial phases of these waves is most frequent.     

Reconstruction of a Hundred Years Series of Solar Filaments from Daily Observational Data

The preliminary results of solar filaments distinguished in daily H-alpha observations at Kodaikanal (1912–2002) are presented. To mark the boundaries of solar filaments, methods based on automated procedures of marking low-contrast objects on the solar disk, as well as editing of the marked boundaries in a semiautomated manner, were developed. The characteristics of solar filaments were analyzed. Latitudinal diagrams of filaments number in 15–23 activity cycles were constructed. As is shown, one maximum in the filament latitudinal distribution may be clearly distinguished during activity cycles in both hemispheres. This maximum is located slightly higher (θ ~ 25°–30°) than the sunspot distribution maximum (θ ~ 14°–17°). However, there are no other local maxima related to the zonal structure of the large-scale magnetic field (Makarov and Sivaraman, 1989).     

Relation between the photospheric magnetic field and phases of a 22-year solar cycle

Strong magnetic fields at latitudes of ±40° are studied on the basis of synoptic maps of the photospheric magnetic field from the Kitt Peak Observatory (1976–2003). The time variations and imbalance between positive and negative magnetic fluxes are studied for the Southern and Northern hemispheres. A change in the imbalance between fluxes of leading/following sunspots with a 22-year magnetic cycle is shown. The imbalance sign coincides with the sign of the global magnetic field in the Northern/Southern solar hemispheres, respectively.     

Diurnal variations of the total electron content under quiet helio-geomagnetic conditions

The morphology of averaged diurnal variations of total electron content (TEC) under quiet helio-geomagnetic conditions for all latitudinal bands and various longitudes has been studied using Global Ionospheric Maps (GIMs) datasets. The diurnal TEC variation maximum is generally registered at 14–15 LT. The maximum is 38±5, 14±2, 10±2 TECU (TECU is generally accepted TEC unit) at the equatorial, middle and high latitudes. The nighttime TEC minimum is within 5–7 TECU regardless of a season, latitude and longitude. At the equatorial latitudes TEC exhibits the most significant daily/season variations and the asymmetry of its behavior in the hemispheres near the equinox. Abnormal diurnal TEC variations (evening maximum, near-noon minimum) are observed at middle and high latitudes in summer due to atmospheric wind effects. The comparison of the averaged diurnal TEC variations with the behavior of the ionospheric F2-layer critical frequency indicated that GIMs describe daily/annual TEC variations reasonably well.     

Retracted and replaced: A modelling study of hyporheic exchange pattern and the sequence,size, and spacing of stream bedforms in mountain stream networks,Oregon, USA

This article has been retracted and replaced. See Retraction and Replacement Notice DOI: 10.1002/hyp.6350 Studies of hyporheic exchange flows have identified physical features of channels that control exchange flow at the channel unit scale, namely slope breaks in the longitudinal profile of streams that generate subsurface head distributions. We recently completed a field study that suggested channel unit spacing in stream longitudinal profiles can be used to predict the spacing between zones of upwelling (flux of hyporheic water into the stream) and downwelling (flux of stream water into the hyporheic zone) in the beds of mountain streams. Here, we use two‐dimensional groundwater flow and particle tracking models to simulate vertical and longitudinal hyporheic exchange along the longitudinal axis of stream flow in second‐, third‐, and fourth‐order mountain stream reaches. Modelling allowed us to (1) represent visually the effect that the shape of the longitudinal profile has on the flow net beneath streambeds; (2) isolate channel unit sequence and spacing as individual factors controlling the depth that stream water penetrates the hyporheic zone and the length of upwelling and downwelling zones; (3) evaluate the degree to which the effects of regular patterns in bedform size and sequence are masked by irregularities in real streams. We simulated hyporheic exchange in two sets of idealized stream reaches and one set of observed stream reaches. Idealized profiles were constructed using regression equations relating channel form to basin area. The size and length of channel units (step size, pool length, etc.) increased with increasing stream order. Simulations of hyporheic exchange flows in these reaches suggested that upwelling lengths increased (from 2·7 m to 7·6 m), and downwelling lengths increased (from 2·9 m to 6·0 m) with increase in stream order from second to fourth order. Step spacing in the idealized reaches increased from 5·3 m to 13·7 m as stream size increased from second to fourth order. Simulated upwelling lengths increased from 4·3 m in second‐order streams to 9·7 m in fourth‐order streams with a POOL–RIFFLE–STEP channel unit sequence, and increased from 2·5 m to 6·1 m from second‐ to fourth‐order streams with a POOL–STEP–RIFFLE channel unit sequence. Downwelling lengths also increased with stream order in these idealized channels. Our results suggest that channel unit spacing, size, and sequence are all important in determining hyporheic exchange patterns of upwelling and downwelling. Though irregularities in the size and spacing of bedforms caused flow nets to be much more complex in surveyed stream reaches than in idealized stream reaches, similar trends emerged relating the average geomorphic wavelength to the average hyporheic wavelength in both surveyed and idealized reaches. Copyright © 2005 John Wiley & Sons, Ltd.     

Statistical study of anomalous nighttime maximums in the <Emphasis Type="Italic">NmF</Emphasis> 2 diurnal variations in the region of appearance of the equatorial anomaly northern crest

The occurrence probabilities of the first and second anomalous nighttime local maximums in the diurnal variations in the electron density at a maximum of the ionospheric F ₂ layer (NmF2) in the region where the crest (hump) of the equatorial anomaly originates in the northern geographic hemisphere have been studied using the data of the stations for vertical sounding of the ionosphere (Paramaribo, Dakar, Quagadougou, Ahmedabad, Delhi, Calcutta, Chongoing, Guangzhou, Taipei, Chung-Li, Okinawa, Yamagawa, Panama, and Bogota) from 1957 to 2004. It has been demonstrated that the anomalous nighttime NmF2 maximums are least frequently formed at ～53° geomagnetic longitude. The calculations have indicated that the studied probabilities are independent of solar activity. Geomagnetic activity weakly affects the rate of occurrence of the first nighttime NmF2 maximum at geomagnetic longitudes of approximately 140° to 358°. At geomagnetic longitudes of approximately 16° to 70° (i.e., in the longitudinal zone of a decreased occurrence frequency of anomalous nighttime maximums), the occurrence probability of the first anomalous nighttime NmF2 maximum under geomagnetically quiet conditions is pronouncedly lower than under geomagnetically disturbed conditions. The dependence of the occurrence probabilities of the first and second anomalous nighttime NmF2 maximums on the month number in a year has been studied.