Observations of polar patches generated by solar wind Alfvén wave coupling to the dayside magnetosphere

A long series of polar patches was observed by ionosondes and an all-sky imager during a disturbed period (K_p = 7- and IMF B_z <0). The ionosondes measured electron densities of up to 9 × 10¹¹ m⁻³ in the patch center, an increase above the density minimum between patches by a factor of ≈4.5. Bands of F-region irregularities generated at the equatorward edge of the patches were tracked by HF radars. The backscatter bands were swept northward and eastward across the polar cap in a fan-like formation as the afternoon convection cell expanded due to the IMF B_y > 0. Near the north magnetic pole, an all-sky imager observed the 630-nm emission patches of a distinctly band-like shape drifting northeastward to eastward. The 630-nm emission patches were associated with the density patches and backscatter bands. The patches originated in, or near, the cusp footprint where they were formed by convection bursts (flow channel events, FCEs) structuring the solar EUV-produced photoionization and the particle-produced auroral/cusp ionization by segmenting it into elongated patches. Just equatorward of the cusp footprint Pc5 field line resonances (FLRs) were observed by magnetometers, riometers and VHF/HF radars. The AC electric field associated with the FLRs resulted in a poleward-progressing zonal flow pattern and backscatter bands. The VHF radar Doppler spectra indicated the presence of steep electron density gradients which, through the gradient drift instability, can lead to the generation of the ionospheric irregularities found in patches. The FLRs and FCEs were associated with poleward-progressing DPY currents (Hall currents modulated by the IMF B_y) and riometer absorption enhancements. The temporal and spatial characteristics of the VHF backscatter and associated riometer absorptions closely resembled those of poleward moving auroral forms (PMAFs). In the solar wind, IMP 8 observed large amplitude Alfvén waves that were correlated with Pc5 pulsations observed by the ground magnetometers, riometers and radars. It is concluded that the FLRs and FCEs that produced patches were driven by solar wind Alfvén waves coupling to the dayside magnetosphere. During a period of southward IMF the dawn-dusk electric field associated with the Alfvén waves modulated the subsolar magnetic reconnection into pulses that resulted in convection flow bursts mapping to the ionospheric footprint of the cusp.     

Long-term solar wind variations in the 20th–23rd solar activity cycles according to radio-astronomical data

We analyzed the variations of the interplanetary plasma parameters, obtained from radio astronomical observations of scintillations of cosmic radio sources during four 11-year cycles of solar activity, from 1966 to present. It is shown that the state of the interplanetary plasma permanently changes in conformity with cyclicity in the solar activity. In the studied time period, besides the 11-year variations in the velocity and scintillation index, there is also an increasing linear trend of these variables, which is presumably due to a secular 80–90-year cycle of solar activity. The observed differences between the 11-year variations and trends in the solar wind velocity and interplanetary scintillation index suggest that the 11-year and secular cycles have different origins. It is found that these trends occur in this time period in each link of the Sun-Earth system: in the solar activity indices, in the characteristics of the interplanetary medium, and practically in all characteristics of the geophysical, demographical, medical, and other Earth’s processes. From the entire set of facts we can conclude that most of the analyzed Earth’s processes are dominated not by anthropogenic factors, but by the effects of the secular cyclic processes of the solar activity.     

Effects of solar and geomagnetic activity in long-term variations in the ionospheric parameters of the auroral zone in 1963–1986

A stable linear relation between foF2 and W with a correlation coefficient of 0.68–0.96 has been revealed as a result of a joint analysis of the foF2 critical frequencies and the virtual minimal heights (h’F) obtained from the data of vertical sounding (VS) of the ionosphere at Dixon Island auroral station, Wolf numbers (W), and PC geomagnetic index from 1963 to 1986. A significant linear relation exists between foF2 and the PC index with a correlation coefficient of r = 0.18–0.67. The correlation between the PC index and W is low in winter and autumn and is r = 0.50 and 0.74 at a significance level of ss = 0.96–0.99 in spring and summer. When the correlation between PC and foF2 is analyzed, it is necessary to consider the effect of solar activity (SA) on both parameters. The multiple correlation coefficients between these parameters have been calculated with regard to the effect of W. They were R = 0.75−0.98; however, the standardized regression coefficients β _W and β _PC indicated that W and PC considerably and insignificantly affect multiple correlation with foF2, respectively, and this effect depends on the season and time of day. It has been detected that the cyclic variations in foF2 and h’F are asymmetric. The amplitudes of these parameters in cycle 20 are smaller than in cycle 21.     

Variations in the polar precipitation equatorward boundary during the interaction between the Earth’s magnetosphere and solar wind streams from isolated solar sources

The position of the auroral luminosity equatorward boundary during the interaction between the Earth’s magnetosphere and isolated solar wind streams from different solar sources has been statistically studied based on the ground and satellite observations of auroras. These studies continue the series of the works performed in order to develop the technique for predicting auroras based on the characteristics of the interplanetary medium and auroral disturbances. The dependences of the minimal position of the auroral luminosity equatorward boundary (Φ′) on the values of the azimuthal component of the interplanetary electric field (E _y ) and AL indices of magnetic activity, averaged over 6 and 24 h, are presented. The distribution limits for each type of isolated solar wind streams on the Φ′-E _y and Φ′-AL planes have been determined.     

Is climate change responsible for changing landslide activity in high mountains?

Climate change, manifested by an increase in mean, minimum, and maximum temperatures and by more intense rainstorms, is becoming more evident in many regions. An important consequence of these changes may be an increase in landslides in high mountains. More research, however, is necessary to detect changes in landslide magnitude and frequency related to contemporary climate, particularly in alpine regions hosting glaciers, permafrost, and snow. These regions not only are sensitive to changes in both temperature and precipitation, but are also areas in which landslides are ubiquitous even under a stable climate. We analyze a series of catastrophic slope failures that occurred in the mountains of Europe, the Americas, and the Caucasus since the end of the 1990s. We distinguish between rock and ice avalanches, debris flows from de‐glaciated areas, and landslides that involve dynamic interactions with glacial and river processes. Analysis of these events indicates several important controls on slope stability in high mountains, including: the non‐linear response of firn and ice to warming; three‐dimensional warming of subsurface bedrock and its relation to site geology; de‐glaciation accompanied by exposure of new sediment; and combined short‐term effects of precipitation and temperature. Based on several case studies, we propose that the following mechanisms can significantly alter landslide magnitude and frequency, and thus hazard, under warming conditions: (1) positive feedbacks acting on mass movement processes that after an initial climatic stimulus may evolve independently of climate change; (2) threshold behavior and tipping points in geomorphic systems; (3) storage of sediment and ice involving important lag‐time effects. Copyright © 2011 John Wiley & Sons, Ltd.     

Monitoring ionospheric response to auroral electrojet activity from sub-auroral to equatorial latitudes in the East Asian-Australian longitudinal sector over a solar cycle (1978–1986)

Large auroral and ionospheric databases, covering a solar cycle (1978–1986), were used to obtain a comprehensive evaluation of the auroral electrojet effect (as inferred from the auroral AE-index) on the ionospheric response in both hemispheres from sub-auroral to equatorial latitudes. The study was limited to the East Asian-Australian longitudinal sector where data are available from a chain of nine latitudinally displaced stations. Enhancement in the standard ionospheric parameter, the virtual height of the F-region (Δh′F) recorded by vertical-incidence ionosondes, was used to trace the ionospheric disturbance.Unlike the previous studies of this type, the total magnetic and ionospheric data, in hourly intervals, were used to derive the correlation coefficient r between two intrinsically different parameters: Δh′F and AE-index for the local nighttime (20–06 LT or 10–20 UT). A suitable averaging and smoothing technique was applied to the data to enhance the correlation trend between these parameters. It is evident that the height fluctuations of sub-auroral ionosphere (for stations: Yakutsk in Siberia and Hobart and Canberra in Australia) closely resemble the auroral electrojet surges, inferred from the AE-index over the solar cycle. The linear coefficient r is highly significant, being close to 0.6 for most of the time; during the years of maximum auroral activity (1981–1983) r approached 0.8. The consistently high correlation r, regardless of the season, applies only to the most poleward station used in this study, Yakutsk. The sub-auroral stations (Hobart and Canberra) positioned further equatorwards show a strong decline in the correlation coefficient r during the local summer but have high r during winter and the equinoxes. There is a general decline in r towards lower latitudes, suggesting that the response to auroral substorms is on the whole diminishing with the distance from the auroral source to the equator. There appears to be an anomalous increase in r as observed around 10° invariant latitude.These findings appear to be the first long-term proof of the symmetry of the ionospheric responses to auroral substorm activity in the northern and southern auroral ovals which is an important contribution to space climatology. It is suggested that the aurorally generated acoustic gravity waves (AGWs), manifested in the global ionosphere as large scale travelling ionospheric disturbances (LSTIDs), may contribute to the observed auroral-ionospheric phenomena.     

Generation of a burst of geomagnetic pulsations in the 1–3 Hz frequency range in the daytime sector as a result of dramatic increases in the solar wind dynamic pressure

The spatio-temporal evolution of geomagnetic pulsation bursts at frequencies of 1–3 Hz, observed at the Mondy (MLT ≈ 1200; M_lat = 46.8°; L = 2.16) and Borok (MLT ≈ 0820; M_lat = 54.0°; L = 2.94) midlatitude observatories and Lovozero auroral observatory (MLT ≈ 0820; M_lat = 64.2°; L = 5.36), has been studied. The considered bursts were registered in daytime sector of the magnetosphere after sudden impulses (SIs) caused by dramatic increases in the solar wind dynamic pressure and registered on board the WIND satellite. The SI onset time corresponds to the Sc* time shown in the Geomagnetic Indices Bulletin. The possible relationship between the excitation of these bursts and the variations in the particle partial density in the range of energies 0.03–45 keV per unit charge has been studied. The bursts were registered on board the LANL geosynchronous satellites. A comparison of the particle partial density variations measured on the satellites and the variation temperature anisotropy (A = T_⊥/T_‖ − 1) with the variations in the pulsation burst amplitude on the ground indicated that the partial density maximum and the minimum (A ≤ 0) of the electron temperature anisotropy index in the vicinity of local noon coincide in time with the pulsation generation instant. A comparison of the electron partial density variations on the LANL-1994 and LANL-97A geosynchronous satellites spaced in longitude and the spatio-temporal variations in the development of bursts make it possible to assume that 1–3 Hz geomagnetic pulsations are excited in the vicinity of local noon and subsequently propagate along the ionospheric waveguide.     

A study of phase-steepened Alfvén waves in a high-speed stream at 0.29 AU

This work performs a search of phase-steepened Alfvén waves under a priori ideal conditions: a high-speed solar wind stream observed in one of the closest approaches to the Sun by any spacecraft (Helios 2). Five potential candidates were initially found following procedures established in earlier work. The observed cases exhibited arc-like or elliptical polarizations, and the rotational discontinuities that formed the abrupt wave edges were found at either the leading or the trailing part. The consideration of some additional specific parameters (mainly related to the relative orientation between mean magnetic field, wave and discontinuity) has been suggested here for an ultimate and proper identification of this kind of phenomenon. After the inclusion of these calculations in our analysis, even fewer cases than the five originals remain. It is suggested that optimum conditions for the detection rather than just for the existence of these events have to be reconsidered.     

Response of currents in Earth’s and Saturn’s dayside magnetopause to a sudden change in the solar wind density

When the effect of a solar wind dynamic pressure pulse on the magnetospheric and ionospheric dynamics is studied, it is usually difficult to detect the effect of a sudden change in the density against the background of the other varying solar wind parameters, which often play a most pronounced role. Cases in which the solar wind plasma density gradient dominated in the dynamics of the different parameters of an interplanetary medium and its magnetic field are considered in this work. Variations in the Earth’s dayside magnetopause current caused by a change in the solar wind ion density are presented for two such cases (February 11 and January 11, 1997) based on the method developed by us previously. Variations in the dayside magnetopause current for collisions of the magnetosphere with corotating interacting flows in January 2004, studied in detail by us previously, are also presented for Saturn. The estimates are comparable with the current values in the transitional three-dimensional current systems of Saturn that were previously calculated by us.     

Periodic Restructuring of Auroral Arcs as an Indicator of Alfvén Resonance in the Region of Substorm Onset

Using optical data from observatories of the Polar Geophysical Institutes, as well all-sky TV observations at Canadian stations of ground support for the THEMIS satellite mission, we clarify whether Alfvén resonance should necessarily be present in the region of subsequent substorm onset. If this is true, the diversion of magnetospheric cross-tail current to the ionosphere, which leads to substorm onset, may be due to resonant Alfvén (or flapping) oscillations that increase in duration. This possibility is believed to indicate optically the presence of Alfvén resonance via periodic restructuring of the preonset auroral arc 3–15 min before onset at T ₀ . At the latitudes of the observatories included in this study, auroral restructuring occurs as repetitive poleward excursions of the preonset arc (the periods of excursions are 1–3 min) and can be readily explained by the theory of Alfvén resonance. It is shown that this feature, while typically observed in strong substorm events, may be lacking for weaker substorms. As proved by conjugate satellite observations, the lack of auroral restructuring in the latter case may result from the weakness of the involved Alfvén resonance, which is still present but not accompanied by large field-aligned currents sufficient for visualization in the ionosphere of the apparent propagation of oscillation phase across the resonance layer.     

Standing Alfvén waves with m ≫ 1 in an axisymmetric magnetosphere excited by a stochastic source

In the framework of an axisymmetric magnetospheric model, we have constructed a theory for broad-band standing Alfvén waves with large azimuthal wave number m 1 excited by a stochastic source. External currents in the ionosphere are taken as the oscillation source. The source with statistical properties of –white noise is considered at length. It is shown that such a source drives oscillations which also have the –white noise properties. The spectrum of such oscillations for each harmonic of standing Alfvén waves has two maxima: near the poloidal and toroidal eigenfre-quencies of the magnetic shell of the observation. In the case of a small attenuation in the ionosphere the maximum near the toroidal frequency is dominated, and the oscillations are nearly toroidally polarized. With a large attenuation, a maximum is dominant near the poloidal frequency, and the oscillations are nearly poloidally polarized.     

Standing Alfvén waves with m ≫ 1 in an axisymmetric magnetosphere excited by a non-stationary source

As a continuation of our earlier paper, we consider here the case of the excitation of standing Alfvén waves by a source of the type of sudden impulse. It is shown that, following excitation by such a source, a given magnetic shell will exhibit oscillations with a variable frequency which increases from the shells poloidal to toroidal frequency. Simultaneously, the oscillations will also switch over from poloidally (radially) to toroidally (azimuthally) polarized. With a reasonably large attenuation, only the start of this process, the stage of poloidal oscillations, will be observed in the ionosphere.     

Effect of the ponderomotive force caused by Alfvén waves on a background plasma in the dayside magnetosphere

The effect of the ponderomotive force on the background plasma modification near magnetic holes, which form at the dayside magnetospheric boundary under the action of the solar wind, has been studied. It was shown that this effect results in a substantial increase in a nonlinear plasma density disturbance. The dependence of the ponderomotive force on the magnetospheric parameters (the magnetic longitude, distance from the Earth’s surface, ratio of the wave frequency to the proton gyrofrequency, and ionospheric ion cyclotron wave amplitude) has been studied. Nonlinear plasma density disturbances will be maximal in the region of magnetic holes, which are located in the dayside magnetosphere at λ ~ 0°?30° geomagnetic longitudes (λ = 0° corresponds to noon), where the effect of the solar wind pressure is maximal. A similar effect is also observed in the dependence of a nonlinear plasma density disturbance on other magnetospheric parameters.     

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.     

Geomagnetic activity as a possible cause of changes in the middle atmosphere and troposphere; observations made in Prague in the years 1932–1987

Summary A possible relation between the 10-day, 1-month, and 2-month geomagnetic as well as solar activity, characterized by Kp and Wolf's number R, and temperatures measured at the Prague-Klementinum meteorological station in January–February of the years 1932–1987 was sought. It was found that:1) Kp correlates with the temperature in Prague better than Wolf's number R.2) If the QBO phase is taken into account, the correlations improve.3) Even if the correlations improves with increasing length of the subintervals into which the individual winter periods (January-February) were derived, their statistical significance declines.     

Powerful solar radio bursts as a global and free tool for testing satellite broadband radio systems,including GPS–GLONASS–GALILEO

We investigated failures in the global positioning system (GPS) performance produced by solar radio bursts with unprecedented radio flux density during the X6.5 and X3.4 solar flares on 6 and 13 December 2006, respectively. The effect of these events on GPS was compared to that of the X17.2 solar flare of 28 October 2003. Significant experimental evidence was found that high-precision GPS positioning on the Earth's entire sunlit side was partially disrupted for more than 10–15 min on 6 and 13 December 2006. The high level of phase slips and count omissions resulted from the wideband solar radio noise emission. Our results provide serious grounds for revising the role of space weather factors in the functioning of modern satellite systems and for considering these factors more carefully in practice. Similar failures in the operation of satellite navigation systems (GPS, GLONASS, and GALILEO) can be fatal for operating safety systems as a whole and lead to great financial losses. Another important conclusion of our investigation concerns the continuous calibrated monitoring of the level of the solar radio emission flux. This monitoring involved a large number of solar radio spectrographs and allowed us to estimate the solar radio noise level in the range of the GPS–GLONASS–GALILEO frequencies.     

Benthic macroinvertebrate field sampling effort required to produce a sample adequate for the assessment of rivers and streams of Neuquén Province,Argentina

This multi-year pilot study evaluated a proposed field method for its effectiveness in the collection of a benthic macroinvertebrate sample adequate for use in the condition assessment of streams and rivers in the Neuquén Province, Argentina. A total of 13 sites, distributed across three rivers, were sampled. At each site, benthic macroinvertebrates were collected at 11 transects. Each sample was processed independently in the field and laboratory. Based on a literature review and resource considerations, the collection of 300 organisms (minimum) at each site was determined to be necessary to support a robust condition assessment, and therefore, selected as the criterion for judging the adequacy of the method. This targeted number of organisms was collected at all sites, at a minimum, when collections from all 11 transects were combined. Subsequent bootstrapping analysis of data was used to estimate whether collecting at fewer transects would reach the minimum target number of organisms for all sites. In a subset of sites, the total number of organisms frequently fell below the target when fewer than 11 transects collections were combined.Site conditions where <300 organisms might be collected are discussed. These preliminary results suggest that the proposed field method results in a sample that is adequate for robust condition assessment of the rivers and streams of interest. When data become available from a broader range of sites, the adequacy of the field method should be reassessed.