Solar Wind Sector Research Articles

The Mansurov effect: Seasonal and solar wind sector structure dependence

We investigate the connection between the interplanetary magnetic field (IMF) By-component and polar surface pressure, also known as the Mansurov effect. The aim of the investigation is to unravel potential dependencies on specific seasons and/or solar wind sector structures, and it serves as a sequel to Edvartsen et al. (2022) [J Space Weather Space Clim 12: 11]. The mechanism for the effect includes the ability of the IMF to modulate the global electric circuit (GEC), which is theorized to impact and modulate cloud generation processes. By usage of daily ERA5 reanalysis data for geopotential height since 1968, we find no significant response confirming the current Mansurov hypothesis. However, we do find statistically significant correlations on decadal timescales in the time period March–May (MAM) in the northern hemisphere, but with an unusual timing. Similar phased anomalies are also found in the southern hemisphere for MAM, but not at a significant level. In an attempt to explain the unusual timing, heliospheric current sheet crossing events, which are highly correlated with the By-index, are used. These events result in higher statistical significance in the NH for the MAM period, but cannot fully explain the timing of the response. In general, these statistically significant correlations differ from previously reported evidence on the Mansurov effect, and suggest a revision of the Mansurov hypothesis. Our results also highlight a general feature of time-lagged cross-correlation with autocorrelated variables, where the correlation value itself is shown to be a fragile indicator of the robustness of a signal. For future studies, we suggest that the p-values obtained by modern statistical methods are considered, and not the correlation values alone.

Comment on “Identification of the IMF sector structure in near-real time by ground magnetic data” by Janzhura and Troshichev (2011)

Abstract. The only published description of the solar wind sector (SS) term used for the reference level in the post-event and real-time derivation of the Polar Cap (PC) indices, PCN (Polar Cap North) and PCS (Polar Cap South), in the version endorsed by the International Association for Geomagnetism and Aeronomy (IAGA) is found in the commented publication, Janzhura and Troshichev: Identification of the IMF sector structure in near-real time by ground magnetic data, Annales Geophysicae, 29, 1491–1500, 2011. Actually, the publication has served as a basis for the index endorsement by IAGA in 2013. However, neither the illustrations nor the results presented there have been derived by the specified near real-time method. Figures 1, 6, 7, and 8 display values derived by post-event calculations based on daily medians smoothed over 7 d centred on the day of interest. Figures 2, 3, and 4 display observed values smoothed over 7 d, while the remaining Fig. 5 displays averages over 4 months. In summary, there are strong disagreements between indications in the title, abstract, and statements in the text compared to the actual results and their illustrations.

Seasonal and Solar Wind Sector Duration Influences on the Correlation of High Latitude Clouds With Ionospheric Potential

AbstractIrradiances from long‐lived stratus‐type clouds at Alert (Canada), Summit (Greenland), and South Pole, previously measured, show correlations with the day‐to‐day input to the global atmospheric electric circuit from the solar wind, as well as with the inputs of low‐ and mid‐latitude thunderstorms and shower clouds. We analyze the measured Alert cloud irradiances, and find differences in the responses to 2, 4, or more solar wind sectors per 27‐days solar rotation. We find seasonal variations in the correlations, with sign reversal in the summer. The correlation coefficients that were found previously for all‐year, all sector types show further increases for just winter months and in addition, for just 2‐sector intervals. At high magnetic latitudes, the ionospheric potential correlates strongly with the solar wind sector structure, and determines the flow of current density (JZ) to the Earth's surface that passes through clouds and modifies space charge in them. Parameterizations of the potential distribution near the magnetic pole are used in the correlations. The daily average values depend mainly on the solar wind (interplanetary) magnetic field (IMF) BY component, with lesser influence of the solar wind speed and IMF BZ. Mechanisms by which space charge in clouds can affect cloud microphysics and cloud opacity are described and are qualitatively consistent with the correlations, but need quantitative testing.

The Polar Cap (PC) Index: Invalid Index Series and a Different Approach

AbstractThe Polar Cap (PC) indices are derived from the magnetic variations generated by the transpolar convection of magnetospheric plasma and embedded magnetic fields driven by the interaction with the solar wind. The PC indices are potentially very useful for space weather monitoring and forecasts and for related research. However, this study suggests that the PC index series in the near‐real‐time and final versions endorsed by the International Association for Geomagnetism and Aeronomy (IAGA) are invalid and unreliable. Both versions include solar wind sector (SWS) effects in the calculation of the reference levels from which magnetic disturbances are measured. The SWS effects are caused by current systems in the dayside Cusp region related to the Y‐component, BY, of the interplanetary magnetic field (IMF). However, the IAGA‐endorsed handling of SWS effects may generate unfounded PC index changes of up to 4 mV/m at the nightside away from the Cusp. For the real‐time PCN and PCS indices, the cubic spline‐based reference level construction may cause additional unjustified index excursions of more than 3 mV/m with respect to the corresponding final index values. Noting that PC index values above 2 mV/m indicate geomagnetic storm conditions, such unjustified contributions invalidate the PC index series and prove the IAGA‐endorsed derivation methods erroneous. Alternative derivation methods are shown to provide more consistent index reference levels for both final and real‐time PC indices, to reduce their unfounded excursions, and to significantly increase their reliability.

Evolution of Renewable Energy in India: Wind and Solar

Being among the most populated country with one of the fastest growing economies in the world, the country is met with ever-increasing fossil fuel consumption. The use of fossil fuels for energy is threatening India with emission pollutants, the import burden of crude oil and natural gas, and coal resource extinction. Clean energies have long been thought to reduce or eliminate a country’s dependence on fossil fuels for electricity generation. In the past decade, India has made major additions to its renewable energy capacity, especially with respect to solar and wind, which represent a major proportion of renewable generation in the country. This paper analyzes the government policies, programs, and incentives to enhance and develop the solar–wind sector in India, alongside potential limitations and solutions. It also reviews the development of “offshore wind,” which is slated to be added to the energy mix of the country over the coming decade.

A critical note on the IAGA-endorsed Polar Cap index procedure: effects of solar wind sector structure and reverse polar convection

Abstract. The International Association of Geomagnetism and Aeronomy (IAGA) has recently endorsed a new Polar Cap (PC) index version to supersede the previous seven different versions of the PCN (North) index and the five different PCS (South) index versions. However, the new PC index has some adverse features which should be known and taken into account by users of the index. It uses in its derivation procedure an "effective" quiet day level (QDC) composed of a "basic" QDC and an added solar wind sector term related to the azimuthal component (By) of the interplanetary magnetic field (IMF). The added IMF By-related terms may introduce unjustified contributions to the PC index of more than 2 index units (mV m−1). Furthermore, cases of reverse convection during strong northward IMF Bz (NBZ) conditions included in the database for calculation of index coefficients can cause unjustified index enhancements of 0.5–1 mV m−1 during calm conditions, reduction of index values by more than 20 % during disturbed conditions, and inconsistencies between index coefficients and index values for the northern and southern polar caps. The aim here is to specify these adverse features and quantify their effects, and to suggest alternative steps for future modifications of the index procedure.

Statistical analysis of thermospheric density response to solar wind sector structure

AbstractThe global averaged thermospheric mass density data during 1967–2007 are analyzed to investigate thermospheric response to solar wind sector structure. Well‐defined solar wind sectors have polarities of interplanetary magnetic field (IMF) toward (+Bx, −By) or away (−Bx, +By) from the Sun for multiple days. In March, thermospheric mass densities increase from the away to toward polarities, with a maximum density perturbation of ~23% at 400 km with respect to the 11 day averages; they decline from the toward to away polarities, and the maximum reduction at 400 km can reach 12%, which is associated with a weakened heating effect of the geomagnetic activity. In September, thermospheric densities respond in an opposite way to the same sector structure as compared with the March results. In solstice seasons, thermospheric density variations in response to solar wind sector structure are typically smaller than 10% relative to the 11 day averages. Besides the seasonal dependence, relative density changes tend to become greater at higher altitude and lower solar activity. However, during solar minimum the density variations at 550 km are not substantially larger than those at 400 km due to the possible descending of the transition altitude between helium and atomic oxygen. Moreover, the corotating interaction region (CIR) has a high probability to occur around the sector boundary. Consequently, the CIR effects account for one third of the density enhancement at 400 km during ineffective‐effective sectors, whereas the density reduction associated with effective‐ineffective sectors can be impaired by about 50%, which is independent of altitude.

Interplanetary magnetic field structure at Saturn inferred from nanodust measurements during the 2013 aurora campaign

Interactions between the solar wind and planetary magnetospheres provide important diagnostic information about the magnetospheric dynamics. The lack of monitoring of upstream solar wind conditions at the outer planets, however, restrains the overall scientific output. Here we apply a new method, using Cassini nanodust stream measurements, to derive the interplanetary magnetic field structure during the 2013 Saturn aurora campaign. Due to the complex dynamical interactions with the interplanetary magnetic field, a fraction of fast nanodust particles emerging from the Saturnian system is sent back into the magnetosphere and can be detected by a spacecraft located within. The time-dependent directionality caused by the variable interplanetary magnetic field enable these particles to probe the solar wind structure remotely. Information about the arrival time of solar wind compression regions (coupled with the heliospheric current sheet crossings) as well as the field direction associated with the solar wind sector structure can be inferred. Here we present a tentative identification of the interplanetary magnetic field sector structure based on Cassini nanodust and radio emission measurements during the 2013 Saturn aurora campaign. Our results show that, the interplanetary magnetic field near Saturn during 2013-080 to 176 was consistent with a two-sector structure. The intensifications of aurora and the radio emission on 2013-095, 112 and 140 coincide with the IMF sector boundaries, indicating that the encounter of the compressed solar wind is the main cause of the observed activities.

Comments on quiet daily variation derivation in "Identification of the IMF sector structure in near-real time by ground magnetic data" by Janzhura and Troshichev (2011)

Abstract. The description presented in the paper of the relations of the solar wind sector structure to the derivation of the quiet daily variation (QDC) in polar magnetic recordings used for calculation of polar cap (PC) indices is found to be unclear and not properly justified. The presented example on inclusion of a solar sector term in an actual QDC series is found to be questionable even on the authors' premises.

Interstellar He+ ring‐beam distributions: Observations and implications

We report systematic measurements of the distribution of the incident angle of interstellar pickup He+ ions as observed by STEREO/Plasma and Supra‐Thermal Ion Composition (PLASTIC). We have organized these observations according to the angle spanned by the Interplanetary Magnetic Field (IMF), , and the bulk solar wind velocity, . Our measurements show clear evidence of a relatively local injection of He+ pickup ions into the solar wind, which are then seen as a ring distribution perpendicular to . Changes of the spectral shape and a reduced flux of interstellar He+ during radial IMF configuration, as observed by, e.g., Ulysses/Solar Wind Ion Composition Spectrometer (SWICS), SOHO/Charge Time‐Of‐Flight (CTOF), Active Magnetospheric Particle Tracer Explorers/SUprathermaL Energy Ionic Charge Analyzer (SULEICA), have generally been attributed to inefficient scattering across 90° pitch‐angle. Our observations of the pitch‐angle distribution of interstellar He+ suggest that these changes are instead a result of locally injected pickup ions that escape detection for IMF configuration in which the Solar Wind Sector of PLASTIC, as well as SWICS, CTOF, and SULEICA, are not sensitive to the measurement of the locally injected pickup ion ring.

Determination of the quiet daily geomagnetic variations for polar regions

A novel procedure to derive the daily varying quiet level for polar geomagnetic data is presented. Recorded data from selected quiet intervals are weighted and superposed to form the basis for an estimate of the quiet daily curve (QDC) for the variation in each of the recorded components on any selected day. The quiet daily variation is controlled by the level of solar UV and X-ray emissions, and parameters in the solar wind in combination with the actual season and the location of the observatory. The procedure uses the variability in the recorded geomagnetic data rather than international magnetic indices like Kp to determine the quiet intervals in accordance with the concept proposed by Janzhura and Troshichev (2008). A special problem for the estimation of the QDC in polar regions is the influence from the solar wind sector structure acting particularly through the azimuthal component, IMF By, of the interplanetary magnetic field. In the superposition of recordings to estimate the QDC for any given day, the present procedure uses weighting functions to give preference to intervals with quietest conditions, closest to the day in question, exposed to the same face of the sun, and within the same sector of the solar wind. The effects of control parameters for the selection of quiet intervals and smoothing of the initial QDC values are carefully controlled. The procedure is fully automated and delivers quality control parameters in addition to the QDC values. It is considered a further step forward in the processing of geomagnetic data to derive reliable and reproducible QDCs for the difficult high-latitude regions.

The STEREO/PLASTIC response to solar wind ions (Flight measurements and models)

The Plasma and Supra-Thermal Ion Composition (PLASTIC) instrument is one of four experiment packages on board of the two identical STEREO spacecraft A and B, which were successfully launched from Cape Canaveral on 26 October 2006. During the two years of the nominal STEREO mission, PLASTIC is providing us with the plasma characteristics of protons, alpha particles, and heavy ions. PLASTIC will also provide key diagnostic measurements in the form of the mass and charge state composition of heavy ions. Three measurements (E/qk, time of flight, ESSD) from the pulse height raw data are used to characterize the solar wind ions from the solar wind sector, and part of the suprathermal particles from the wide-angle partition with respect to mass, atomic number and charge state. In this paper, we present a new method for flight data analysis based on simulations of the PLASTIC response to solar wind ions. We present the response of the entrance system / energy analyzer in an analytical form. Based on stopping power theory, we use an analytical expression for the energy loss of the ions when they pass through a thin carbon foil. This allows us to model analytically the response of the time of flight mass spectrometer to solar wind ions. Thus we present a new version of the analytical response of the solid state detectors to solar wind ions. Various important parameters needed for our models were derived, based on calibration data and on the first flight measurements obtained from STEREO-A. We used information from each measured event that is registered in full resolution in the Pulse Height Analysis words and we derived a new algorithm for the analysis of both existing and future data sets of a similar nature which was tested and works well. This algorithm allows us to obtain, for each measured event, the mass, atomic number and charge state in the correct physical units. Finally, an important criterion was developed for filtering our Fe raw flight data set from the pulse height data without discriminating charge states.

Spatial variation of the pickup-proton-injection rate into the ACR regime at the 3D-heliospheric termination shock

Context. Anomalous cosmic rays are thought to be generated from pick-up ions that undergo Fermi-1 acceleration in the region close to the solar wind termination shock. This selective acceleration process depends on the efficiency at which upstream pick-up ions are injected into the first reflection mode, from where acceleration into higher energy anomalous cosmic rays starts. Aims. The injection efficiency is highly sensitive to the local inclination of the upstream magnetic field with respect to the shock normal. We determine the probability of pick-up ions being reflected at the shock depending on the magnetic inclination angle, which varies characteristically with latitude and longitude. This reflection is the relevant initial step in the acceleration of pickup ions to anomalous cosmic rays. Methods. We point out that the most dramatic change in the magnetic tilt angle occurs whenever two consecutive solar wind sector structures with different magnetic polarities, pass over the shock. We treat this effect by modeling the 3D- variation of the injection efficiency and start from calculations of the pick up ion reflection probability as function of the magnetic tilt angle. We first derive the magnetic tilt angle as function of latitude and longitude, representing the 3D-shape of the termination shock by a triaxial or prolate ellipsoid adaptable for conditions of different solar cycles, respectively. This allows us to semi-analytically express the 3D-variation of the injection efficiency and rate over a solar cycle. Results. We find a substantial variation in the injection efficiency by 5 orders of magnitude when passing from the upwind parts to the flanks of the termination shock or from low to high latitudes (except at the poles). Folding this with the normalized pickup ion density gives a normalized injection rate which increases from 0% to 30% from upwind to crosswind directions and analogously decreases from crosswind into downwind direction. The maximal value of the injection rate highly depends on the underlying sector structure of the heliospheric magnetic field. During solar minimum there is almost no injection in high latitudes, except at the pole itself, while the injection rate is everywhere fairly good during solar maximum. Conclusions. Our model indicates that the injection into the anomalous cosmic ray acceleration mainly takes place in crosswind directions e.g. in the flanks of the termination shock.

Longitudinal variation of the pickup-proton-injection efficiency and rate at the heliospheric termination shock

Context. Pickup ions are considered to be the seed population of the anomalous cosmic rays. The acceleration of the pickup ions at the solar wind termination shock depends on the efficiency with which they are injected into the first reflection mode, from where acceleration into high energy anomalous cosmic rays begins. In this letter, we study the longitudinal variation of this efficiency. Aims. We consider the specific MHD conditions at the longitudinal position of the termination shock, which are highly sensitive to the local inclination angle between the magnetic field and the shock normal. We determine the probability for pickup-ions to become reflected which depends on how the inclination angle varies with longitude. This is the first and relevant step in the acceleration of pickup ions to anomalous cosmic rays. Methods. The most dramatic change in the magnetic tilt angle occurs in the current sheet between two consecutive solar wind sector structures of different polarity, when they pass over the shock. We consider this effect by modeling the longitudinal variation in the injection efficiency. Starting from calculations of the pickup-ion reflectance probability as a function of the magnetic tilt angle with respect to the normal, we find an analytic expression for the injection efficiency: to do this we need the magnetic tilt angle as a function of longitude, which we obtain from an analytic representation of the termination shock shape. This enables us to determine the longitudinal dependence of the injection efficiency. Results. We find that a substantial variation in the injection efficiency of a factor of 3 occurs when passing from the upwind part to the flanks of the termination shock. Folding this with the longitudinal dependence of the pickup ion density gives an analytic expression the injection rate which varieis by a factor of 2 between up- and ecliptical crosswind direction and a factor of 5 between cross- and downwind direction. Conclusions. Our model indicates that injection into the anomalous cosmic ray acceleration predominantly occurs in the ecliptical crosswind direction e.g. in the flanks of the termination shock.

The magnetic field draping direction at Mars from April 1999 through August 2004

Using more than five years of data from the magnetometer and electron reflectometer (MAG/ER) on Mars Global Surveyor (MGS), we derive the draping direction of the magnetic field above a given latitude band in the northern hemisphere. The draping direction varies on timescales associated with the orbital period of Mars and with the solar rotation period. We find that there is a strongly preferred draping direction when Mars is in one solar wind sector, but the opposite direction is not preferred as strongly for the other solar wind sector. This asymmetry occurs at or below the magnetic pileup boundary (MPB), is observed preferentially on field lines that connect to the collisional ionosphere, and is independent of planetary longitude. The observations could be explained by a hemispherical asymmetry in the access of field lines to the low-altitude ionosphere, or possibly from global modification of the low-altitude solar wind interaction by crustal magnetic fields. We show that the draping direction affects both the penetration of sheath plasma to 400 km altitudes on the martian dayside and the radial component of the magnetic field on the planetary night side.

Distribution of energetic oxygen events in the tail region — A view from HEP-LD/GEOTAIL

The periodic passage of a high-speed solar wind sector and the related corotating interaction region (CIR) in January and February 1994 resulted in two well-defined periods of sustained geoactivity. During this time interval GEOTAIL happened to be in quasi-elliptical orbits with apogees at about x = −90 R E and with orbital periods close to the solar rotation of 27 days. These orbits provided consecutive radial cuts through the magnetosphere from a mid-tail position (x = −90 R E ) to the dayside magnetopause. The energetic particle spectrometer HEP-LD onboard GEOTAIL was used to identify oxygen bursts with beam-like angular distributions. A significant majority of these beams were moving in a tailward direction. All of these events are closely related to substorm activity. The formation of near-Earth neutral lines (NENLs) are a possible source for particle acceleration. Low charge states of the oxygen ions are strong evidence for an ionospheric origin. The main focus of this study is to provide a coarse picture of oxygen events and their distribution in the regions of geospace visited by GEOTAIL in the time interval of interest. Details are obviously beyond the scope of this report.

Solar Wind Modulation of the Global Electric Circuit and Apparent Effects on Cloud Microphysics, Latent Heat Release, and Tropospheric Dynamics.

The solar wind modulation of the energy distribution and flux of galactic cosmic rays causes 11 year cycles in the latitude distribution of air-earth current density in the global electric circuit. Similar changes occur with solar activity on the day to day time scale. At least 3 independent data sets correlate changes in tropospheric winds and vorticity with measured and modelled changes in air-earth current density in the troposphere. These are (1) the decadal oscillations in winter in the North Atlantic region, with period averaging 11 ± 2 years over the last 120 years, and which appear to have been phase locked to the solar cycle except for a period of generally low solar activity prior to 1925; (2) the decrease in 500 mbar Vorticity Area Index (VAI) in winter at times of Forbush decreases of cosmic ray flux; and (3) decreases of 500 mbar VAI in winter at times of solar wind magnetic sector boundary passages, when volcanic aerosols from Agung and El Chicon were in the global stratosphere, together with solar wind sector modulated relativistic electron precipitation. One possible physical mechanism connecting changes in air-earth current density with changes in tropospheric dynamics is via the accumulation of electrostatic charge at cloud tops affecting the microphysics of ice nucleation and precipitation, with consequences for latent heat release and the intensification of winter cyclones.

Response of the equatorial ionosphere to solar magnetic sector crossing

A superposed epoch analysis has been carried out of h′F values at Kodaikanal (10°14′N, 77°28′E, dip 3.0°N) pertaining to years of high sunspot activity using solar wind sector boundary passages past the earth as key days. It is found that there is a reduction in h′F values at 2000 LT 1 or 2 days after the sector boundary crossing. The amplitude of this effect which is noticed with both (+, −) and (−, +) sector boundary crossings is higher in equinoxes than in solstices. The response of the equatorial F region to sector boundary crossing seems to originate from perturbations of the equatorial east–west electric field in the post-sunset period associated with the enhancement in geomagnetic activity in the wake of sector boundary crossing.

Influence of solar sector boundaries on ionospheric variability

A latitudinal network of total electron content (TEC) observations has been used to assess the contributions to day‐to‐day F region variability associated with a wide variety of solar‐terrestrial phenomena. Recent discussions of a proposed “sun‐weather coupling” effect related to solar wind sector boundary (SB) crossings prompted a systematic search to document any upper atmospheric components of such a linkage. TEC data from several North American sites close to the 70°W meridian (Narssarssuaq, Greenland (L = 5); Goose Bay, Labrador (L = 4); Sagamore Hill, Massachusetts (L = 3); and the Kennedy Space Center, Florida (L = 2) were examined during the years 1973–1975. Average daytime (0900–1700 LT) TEC values were compared with a 27‐day mean centered on the day of an SB crossing. The resultant percentage deviations were examined for sector polarity (plus to minus versus minus to plus) effects and for overall latitudinal patterns during a period of ±5 days from the SB crossings. Average results for the entire data set show peak excursions well within the ±20–25% deviations associated with day‐to‐day variability. There is, however, a remarkable consistency in the coherence of the small amplitude latitudinal patterns. At middle to high latitudes (L = 3–5), the TEC variations show an ordered transition from enhancements to depletions following an SB crossing. At lower latitudes (L = 2), the opposite pattern of depletions to enhancements occurs. An identical analysis for geomagnetic activity variations (using the planetary index Ap) reveals the well‐known pattern of a transition from relatively quiet to relatively disturbed activity as a sector is crossed. A merging of these two results suggests that the manifestation in the F region of SB crossings is nothing more than a small‐scale version of the average “geomagnetic/ionospheric storm effect” that is well documented over the L = 2–5 range. The latitudinal patterns for ΔTEC, and their seasonal variations, are consistent with the morphology of O/N2 variations during geomagnetic disturbances and southward IMF effects during equinoctial versus solstice periods.

Interplanetary gas. XXVIII - A study of the three-dimensional properties of interplanetary sector boundaries using disconnection events in cometary plasma tails

Studies of the solar wind on the basis of cometary plasma tail observations are considered. Niedner and Brandt (1978, 1979) have concluded that the plasma tail frequently disconnects from the cometary head, and that these disconnection events (DEs) are produced by magnetic reconnection at sector boundary passages. They proposed that the disconnections are a natural combination of Alfven's model and the solar-wind sector structure first discovered by Wilcox and Ness (1965). The DEs can be utilized as probes of interplanetary sector structure. Correlations between DEs and sector boundaries observed at earth are considered, and sector boundary properties deduced from DEs are discussed. Attention is given to a review of the warped sheet model, the latitude extent of sector structure, the sector boundary tilt, and specific sources of error in the tilt angles derived from DEs.