Nature of the sunrise effect in daily electric field variations at Kamchatka: 2. Electric field frequency variations

The power spectra of time variations in the electric field strength in the near-Earth’s atmosphere and in the geomagnetic field horizontal component, which were simultaneously observed at the Paratunka observatory (φ = 52°58.3′ N; λ = 158°14.9′ E) in September 1999, have been studied. The periods of the day (including sunrise, sunset, and night) have been considered. It has been indicated that oscillations with periods T ～ 2.0–2.5 h are present in the power spectra of these parameters during the day. The intensity of these oscillations increases noticeably and the oscillations in the band of periods T < 1 h increase simultaneously in the field strength power spectra at sunrise. The variations in the argument of the cross-spectrum of these parameters indicated that oscillations in the 2.0–2.5 h period band are caused by sources that are located above the ionospheric dynamo region; at the same time, oscillations in the 0.5–1 h period band are caused by sources in the lower atmosphere. A possible mechanism by which these oscillations are generated, related to the vortex motion of convective cells that originate at sunrise in the boundary atmospheric layer, is proposed.     

Secular variations in the geomagnetic field in St. Petersburg and the adjacent area from historical data, 1630–1930

Geomagnetic field parameters have been measured in different sites of the northwest of Russia for hundreds of years. This work presents the results of numerous measurements in St. Petersburg, as well as in the Gulf of Finland within the zone from 25° to 30°30′ E and from 59° to 61° N. The first measurements were made in the period1630–1650. For this work, archival data, provided by the Archives of the St. Petersburg Magnetic Observatory (SPbF IZMIRAN), and data from different historical records have been used. Data on the Earth’s magnetic field variations in St. Petersburg have been recorded since 1726; they were analyzed and corrected to get a uniform and complete data set. The reconstructed long-term data set of magnetic variation measurements in St. Petersburg was compared with the GUFM1 historical model. This model allows us to calculate the values of all parameters of the main magnetic field in any place on the Earth since 1590. The comparative analysis carried out by us has revealed a discrepancy between the model and measured values. This discrepancy can be caused by local secular variations in the magnetic field in the St. Petersburg region. The correction of the area-averaged secular variation makes this discrepancy insignificant.     

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.     

Geomagnetic variation peculiarities at middle latitudes of the East European Platform

The results of instrumental observations of geomagnetic variations at the Mikhnevo midlatitudinal observatory of Institute of Geosphere Dynamics of the Russian Academy of Sciences (54.9595° N; 37.7664° E) are presented and discussed. The main periodicities of the local background variations of geomagnetic field are determined. Variations of ~ 27 days have been registered, as well as periodicities with periods of ~6–9, 12–14, 60 days, and a semiannual periodicity. It has been shown that the background geomagnetic variation periodicities have a sporadic and scaling character. An alternating effect of increasing and degradation periods in geomagnetic variation intensity (the intermittency effect) is found.     

Peculiarities of the magnetic flux emerging in the equatorial solar zone

The magnetic flux longitudinal distribution in the equatorial solar zone has been studied. The magnetic synoptic maps of the Wilcox Solar Observatory (WSO) during Carrington rotations (CRs) 2052–2068 in 2007 and early 2008 have been analyzed. The longitudinal distributions of the area of the zones where the photospheric magnetic field locally enhanced have been constructed for each CR. The obtained distributions indicate that the zones are located discretely and that a clearly defined one narrow longitudinal interval with the maximum flux is present. The longitudinal position of this maximum shifted discretely by ≈130° at an interval of 5.5 ± 0.5 CRs. A longitudinal shift of the zones with an increased magnetic flux multiple of 60° was observed between the hemispheres. In addition, a time shift of ≈2.5 CRs existed between the instants when the position of maximum fluxes in different hemispheres shifted. The established peculiarities of the magnetic flux longitudinal distribution and time dynamics are interpreted as an action of supergiant convection cells. These actions result in that magnetic fields are removed from the generation region through the channels that are formed between such cells at a longitudinal interval of 120°. The average synodic rotation velocity of the considered equatorial channels, through which the magnetic flux emerges, is 13.43° day^–1.     

Effect of auroral electrojets and solar wind parameters on variations in the intensity of low-latitude geomagnetic disturbances and Dst during the extremely large magnetic storm of November 20–21, 2003

The effect of auroral electrojets on the variations in the low-latitude geomagnetic disturbances and Dst during a strong magnetic storm of November 20–21, 2003, with Dst ≈ ?472 nT has been studied based on the global magnetic observations. It has been indicated that the magnetospheric storm expansive phase with Δt ≈ 1–2 h results in positive low-latitude disturbances (ΔH) of the same duration and with an amplitude of ～ 1–2 h results in positive low-latitude disturbances (ΔH) of the same duration and with an amplitude of ～ 30–100 nT in the premidnight-dawn sector. A growth of negative low-latitude ΔH values and Dst is mainly caused by regular convection electrojets with Δt ≥ 10 h, the centers of which shift to latitudes of ～ 50°–55° during the storm development. It has been established that the maximal low-latitude values of the field ΔH component at 1800–2400 MLT are observed when the auroral luminosity equatorward boundary shifts maximally southward during an increase in the negative values of the IMF B _z component. It has been assumed that, during this storm, a magnetic field depression at low latitudes was mainly caused by an enhancement of the partially-ring current which closes through field-aligned currents into the ionosphere at the equatorward boundary of the auroral luminosity zone.     

Effect of magnetic storms in variations in the atmospheric electric field at midlatitudes

The observations of the variations in the vertical component of the atmospheric electric field (E _z ) at Swider midlatitude Poland observatory (geomagnetic latitude 47.8°) under the conditions of fair weather during 14 magnetic storms have been analyzed. The effect of the magnetic storm main phase in the daytime midlatitude variations in E _z in the absence of local geomagnetic disturbances has been detected for the first time. Considerable (～100–300 V m^?1) decreases in the electric field strength (E _z ) at Swider observatory were observed in daytime simultaneously with the substorm onset in the nighttime sector of auroral latitudes (College observatory). The detected effects indicate that an intensification of the interplanetary electric field during the magnetic storm main phase, the development of magnetospheric substorms, and precipitation of energetic electrons into the nighttime auroral ionosphere can result in considerable disturbances in the midlatitude atmospheric electric field.     

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.     

Unusual spatial-temporal dynamics of geomagnetic disturbances during the main phase of the extremely strong magnetic storm of November 7–8, 2004

The spatial dynamics of geomagnetic variations and pulsations, auroras, and riometer absorption during the development of the main phase of the extremely strong magnetic storm of November 7–8, 2004, has been studied. It has been indicated that intense disturbances were observed in the early morning sector of auroral latitudes rather than in the nighttime sector, as usually takes place during magnetic storms. The unusual spatial dynamics was revealed at the beginning of the storm main phase. A rapid poleward expansion of disturbances from geomagnetic latitudes of 65°–66° to 74°–75° and the development of the so-called polar cap substorm with a negative bay amplitude of up to 2500 nT, accompanied by precipitation of energetic electrons (riometer absorption) and generation of Pi2–Pi3 pulsations, were observed when IMF B _z was about ?45 nT. The geomagnetic activity maximum subsequently sharply shifted equatorward to 60°–61°. The spatial dynamics of the westward electrojet, Pi2–Pi3 geomagnetic pulsations, and riometer absorption was similar, which can indicate that the source of these phenomena is common.     

Burst regimes of long-period irregular pulsations at frequencies of 2.0–6.0 mHz and substorm activity in the nightside magnetosphere

The results of studying the simultaneous observations of burst regimes of long-period irregular pulsations at frequencies of 2.0–6.0 mHz (the series of ipcl bursts) in the region of the dayside polar cusp and magnetic field disturbances in the nightside auroral oval are presented. The data on the magnetic field at Mirny (MIR, Φ = 76.93°; Λ = 122.92°) and Yellowknife (YKC, Φ = 69.94°; Λ = 294.38°) antipodal observatories as well as the AE index values (http://www.cetp.ipsl.fr/~isgi/homepag1.htm) have been used in an analysis. It has been found out that 87% (group I) and 13% (group II) of events were registered against a back-ground of substorm activity and a quiet nightside magnetosphere, respectively. It has been revealed that several morphological characteristics of the group-I and -II ipcl bursts differ depending on the conditions in the nightside magnetosphere. It has been indicated that the intervals between peaks and the amplitudes of ipcl bursts of both types are distributed according to the exponential and power laws. The results indicate that magnetospheric plasma turbulence develops in the region where burst regimes are formed. It is assumed that the substorm processes in the magnetotail manifest themselves in plasma turbulence in the dayside cusp.     

Geomagnetic pulsations and magnetic disturbances during the initial phase of a strong magnetic storm of May 15, 2005

A very strong magnetic storm of May 15, 2005, was caused by an interplanetary magnetic cloud that approached the Earths’ orbit. The sheath region of this cloud was characterized by a high solar wind density (～25–30 cm^?3) and velocity (～850 km/s) and strong variations (to ～20 nT) in the interplanetary magnetic field (IMF). It has been indicated that an atypical bay-like geomagnetic disturbance was observed during the initial phase of this storm in a large longitudinal region at high latitudes: from the morning to evening sectors of the geomagnetic local time. Increasing in amplitude, the magnetic bay rapidly propagated to the polar cap latitudes up to the geomagnetic pole. An analysis of the global space-temporal dynamics of geomagnetic pulsations in the frequency band 1–6 mHz indicated that most intense oscillations were observed in the morning sector in the region of the equivalent ionospheric current at latitudes of about 72°–76°. The wavelet structure of magnetic pulsations in the polar cap and fluctuations in IMF was generally similar to the maximum at frequencies lower than 4 mHz. This can indicate that waves directly penetrated into the polar cap from the solar wind.     

Experimental errors of measurements of vertical geomagnetic gradients in the stratosphere

The errors of measurements of vertical geomagnetic gradients at altitudes of 20–40 km, using a balloon magnetic gradiometer with a 6-km-long measuring base oriented along gravity, have been studied in the work. The errors related to the deviation of the measuring base position relative to the vertical have been studied during the real balloon flight with the help of the navigation GPS receivers. The deviations of the measuring base within 5°, which can sometimes reach 15°, have been obtained. This results in a decrease in the magnetic gradient measurement accuracy due to the errors introduced in the specification of the normal magnetic field used to detect magnetic anomalies. To eliminate this error, a GPS receiver was built in each magnetometer in order to observe magnetometers during synchronous measurements and to correct the measurements for the normal magnetic field. It has been indicated that the effect of deviations of the measuring base position on the results is not more than 2% of the measured value at such organization of a gradiometer.     

Model simulation of the equatorial electrojet in the Peruvian and Philippine sectors

Between 100 and 120 km height at the Earth's magnetic equator, the equatorial electrojet (EEJ) flows as an enhanced eastward current in the daytime E region ionosphere, which can induce a magnetic perturbation on the ground. Calculating the difference between the horizontal components of magnetic perturbation (H) at magnetometers near the equator and about 6–9° away from the equator, ΔH, provides us with information about the strength of the EEJ. The NCAR Thermosphere–Ionosphere–Electrodynamics General Circulation Model (TIE-GCM) is capable of simulating the EEJ current and its magnetic perturbation on the ground. The simulated diurnal, seasonal (March equinox, June solstice, December solstice), and solar activity (F_10.7=80, 140 and 200 units) variations of ΔH in the Peruvian (76°W) and Philippine (121°E) sectors, and the relation of ΔH to the ionospheric vertical drift velocity, are presented in this paper. Results show the diurnal, seasonal and solar activity variations are captured well by the model. Agreements between simulated and observed magnitudes of ΔH and its linear relationship to vertical drift are improved by modifying the standard daytime E region photoionization in the TIE-GCM in order to better simulate observed E region electron densities.     

Standing MHD wave structure in the magnetosphere analyzed using the method of correlation functions of amplitude and phase fluctuations

The method of correlation functions of signal amplitude and phase fluctuations (CFAF) was used to process fluctuations that were numerically obtained for different standing MHD waves in a flat rectangular resonator. It has been established that the CFAF dependences on the average fluctuation phase shift (τ) always look like a periodic peak train. The interval between two adjacent peaks depends on the first harmonic frequency of one of the possible one-dimensional resonator standing waves and is determined using the universal formula. In the proposed method, processing results in measured values of this frequency. In addition, the CFAF method was for the first time used to process magnetic field variations in a range of periods from 0.5 to 6.0 s. The distribution functions of the first harmonic periods have been experimentally obtained for Borok (Φ = 53.9°, Λ = 114.3°) and Mondy (Φ = 46.7°, Λ = 173.6°) observation stations. It was established that all of the characteristic values of these periods completely correspond to the periods of known standing MHD waves in the plasmasphere and at its boundary.     

Episodes of relative global warming

Solar activity is regulated by the solar dynamo. The dynamo is a non-linear interplay between the equatorial and polar magnetic field components. So far, in Sun–climate studies, only the equatorial component has been considered as a possible driver of tropospheric temperature variations. We show that, next to this, there is a significant contribution of the polar component. Based on direct observations of proxy data for the two main solar magnetic fields components since 1844, we derive an empirical relation between tropospheric temperature variation and those of the solar equatorial and polar activities. When applying that relation to the period 1610–1995, we find some quasi-regular episodes of residual temperature increases and decreases, with semi-amplitudes up to ～0.3 °C. The present period of global warming is one of them.     

Geometric properties of the coronal neutral surface

The interrelation between the density inhomogeneity and the magnetic field configuration in the solar corona has been studied. The situation of consistency with the regular cellular magnetic field organization, established by the authors based on polarization data, and helmet-shaped coronal structures has been analyzed. Consistency was found when coronal helmets appeared as projections on the plane of the sky of dense layer folds. It turned out that a dense layer on a regularly deformed neutral surface on a scale of 60° generates coronal shapes typical of solar activity minimum epochs. Threby, a weighty argument for the Molodenskii hypothesis that a dense layer is formed on the neutral surface has been obtained and it has been determined that one can find the 3D geometry of the coronal neutral surface based on modeling the visible shape of coronal helmets. The study of this geometry based on the observed coronal structures in the epoch of minimum and low solar activity indicated that the neutral surface longitudinal deformation scale remains stable and the surface latitudinal amplitude at the corona base reaches 50°–70° latitudes and tends to increase with increasing solar activity. This amplitude decreases as a power function with a variable index close to ?1 with increasing distance from the Sun. In addition, a 10° small-scale deformation of the studied surface with a predominant latitudinal flexure direction has been revealed.     

Dynamics of the ionospheric electric currents and auroral luminosity boundaries during strong magnetic storms

The regularities in the southward drift of the ionospheric current centers and luminosity boundaries during strong magnetic storms of November 2003 and 2004 (with Dst ≈ ?400 and ?470 nT, respectively) are studied based on the global geomagnetic observations and TV measurements of auroras. It has been indicated that the eastward and westward electrojets in the dayside and nightside sectors simultaneously shift equatorward to minimal latitudes of Φ _min ^° ～53°–55°. It has been obtained that the Φ _min ^° latitude decreases with increasing negative values of Dst, IMF B _z component, and westward electric field strength in the solar wind. The dependence of the electrojet equatorward shift velocity (V _av) on the rate of IMF B _z variations (ΔB _z /Δt) has been determined. It is assumed that the electrojet dynamics along the meridian is caused by a change in the structure of the magnetosphere and electric fields in the solar wind and the Earth’s magnetosphere.     

Variation of Wave Velocity and Porosity of Sandstone after High Temperature Heating

This paper reports the variations of mass, porosity, and wave velocity of sandstone after high temperature heating. The range of temperature to which the sandstone specimens have been exposed is 25–850°C, in a heating furnace. It has been shown that below 300°C, porosity and wave velocity change very little. Above 300°C, there is a rapid increase in porosity, but the wave velocity decreases significantly. The results of thermo gravimetric analysis (TGA), differential scanning calorimetry (DSC) and mercury intrusion porosimetry (MIP) suggest that a series of changes occurred between 400 and 600°C in sandstone could be responsible for the different patterns of variation in porosity and wave velocity.     

Plasmaspheric electron content (PEC) over low latitude regions around the magnetic equator in the Indian sector during different geophysical conditions

The variation of plasmaspheric electron content (PEC) is an important parameter for studying the effects of space weather events in the low latitude ionosphere. In the present study, the vertical TEC (VTEC) measurements obtained from co-located dual-frequency Global Positioning System (GPS) and Coherent Radio Beacon Experiment (CRABEX) systems have been used. The daytime PEC variations under different geophysical conditions have been estimated (around the magnetic equator) over the Indian sector, for the first time. The first observations of the nighttime PEC variations over the Indian sector are also estimated from the simultaneous measurements of Faraday rotation, differential Doppler and modulation phase delay made using the CRABEX system on-board the Indian geostationary satellite GSAT2. The study shows that the PEC varies over a range of 10–22% (of the total electron content (TEC)) during daytime of magnetically quiet period. There is an increase in PEC with latitude during magnetically quiet period. During a magnetically disturbed period of 9 November 2004, the PEC increased to ∼30% of the TEC over the magnetic equatorial location of Trivandrum (8.5°N, 76.9°E, dip 0.5°N), while at Bangalore (13°N, 78°E, dip 10°N) it showed a large depletion. The implications of the new observations are discussed.