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Context.On December 27, 2020, Solar Orbiter completed its first gravity assist manoeuvre of Venus (VGAM1). While this flyby was performed to provide the spacecraft with sufficient velocity to get closer to the Sun and observe its poles from progressively higher inclinations, the Radio and Plasma Wave (RPW) consortium, along with other operational in situ instruments, had the opportunity to perform high cadence measurements and study the plasma properties in the induced magnetosphere of Venus.Aims.In this paper, we review the main observations of the RPW instrument during VGAM1. They include the identification of a number of magnetospheric plasma wave modes, measurements of the electron number densities computed using the quasi-thermal noise spectroscopy technique and inferred from the probe-to-spacecraft potential, the observation of dust impact signatures, kinetic solitary structures, and localized structures at the bow shock, in addition to the validation of the wave normal analysis on-board from the Low Frequency Receiver.Methods.We used the data products provided by the different subsystems of RPW to study Venus’ induced magnetosphere.Results.The results include the observations of various electromagnetic and electrostatic wave modes in the induced magnetosphere of Venus: strong emissions of ∼100 Hz whistler waves are observed in addition to electrostatic ion acoustic waves, solitary structures and Langmuir waves in the magnetosheath of Venus. Moreover, based on the different levels of the wave amplitudes and the large-scale variations of the electron number densities, we could identify different regions and boundary layers at Venus.Conclusions.The RPW instrument provided unprecedented AC magnetic and electric field measurements in Venus’ induced magnetosphere for continuous frequency ranges and with high time resolution. These data allow for the conclusive identification of various plasma waves at higher frequencies than previously observed and a detailed investigation regarding the structure of the induced magnetosphere of Venus. Furthermore, noting that prior studies were mainly focused on the magnetosheath region and could only reach 10–12 Venus radii (RV) down the tail, the particular orbit geometry of Solar Orbiter’s VGAM1, allowed the first investigation of the nature of the plasma waves continuously from the bow shock to the magnetosheath, extending to ∼70RVin the far distant tail region.

We present a multi-frequency and multi-instrument study of the 20 January 2005 event. We focus mainly on the complex radio signatures and their association with the active phenomena taking place: flares, CMEs, particle acceleration and magnetic restructuring. As a variety of energetic particle accelerators and sources of radio bursts are present, in the flare-ejecta combination, we investigate their relative importance in the progress of this event. The dynamic spectra of {Artemis-IV-Wind/Waves-Hiras with 2000 MHz-20 kHz frequency coverage, were used to track the evolution of the event from the low corona to the interplanetary space; these were supplemented with SXR, HXR and gamma-ray recordings. The observations were compared with the expected radio signatures and energetic-particle populations envisaged by the {Standard Flare--CME model and the reconnection outflow termination shock model. A proper combination of these mechanisms seems to provide an adequate model for the interpretation of the observational data.

We show that the continuous wavelet transform can provide a unique decomposition of a timeseries in to 'signal-like' and 'noise-like' components: From the overall wavelet spectrum two mutually independent skeleton spectra can be extracted, allowing the separate detection and monitoring in even non-stationary timeseries of the evolution of (a) both stable but also transient, evolving periodicities, such as the output of low dimensional dynamical systems and (b) scale-invariant structures, such as discontinuities, self-similar structures or noise. An indicative application to the monthly-averaged sunspot index reveals, apart from the well-known 11-year periodicity, 3 of its harmonics, the 2-year periodicity (quasi-biennial oscillation, QBO) and several more (some of which detected previously in various solar, earth-solar connection and climate indices), here proposed being just harmonics of the QBO, in all supporting the double-cycle solar magnetic dynamo model (Benevolenskaya, 1998, 2000). The scale maximal spectrum reveals the presence of 1/f fluctuations with timescales up to 1 year in the sunspot number, indicating that the solar magnetic configurations involved in the transient solar activity phenomena with those characteristic timescales are in a self-organized-critical state (SOC), as previously proposed for the solar flare occurence (Lu and Hamilton, 1991)., Comment: 22 pages, 2 figures

We make new applications of our previously proposed method for estimating the strain-rate tensor and vorticity vector in plasmas (concerning the local deformation and self rotation of the plasma fluid elements, respectively) solely from magnetic field time series. Here we use solar wind measurements of Ulysses spacecraft made in the outer heliosphere, on and off the ecliptic plane, during the period 1990-1998. The application results imply that the solar wind plasma is, to a good approximation, weakly incompressible , being nearly incompressible on the local magnetic field-normal plane, while expanding at maximum strain rate in the magnetic field direction. This property is theoretically expected, at least for low and intermediate beta plasmas, and supports previous arguments for two-dimensional MHD turbulence in the solar wind. In the magnetic induction equation the vorticity term is favoured, being at least an order of magnitude larger than the strain-rate term, thus explaining the magnetic field alignment of the minimum magnetic field variance and the random wandering of the magnetic field's vector tip on a sphere, both being well known, general features of the heliospheric magnetic field fluctuations. Further, the solar wind is found dominated by magnetized vortex sheet structures (MVS), on the tangential plane of which lie the, (not generally aligned) average vectors of magnetic field, vorticity and plasma velocity in the solar-corotating frame of reference. These coplanarity properties are shown to be consistent with a theoretically predicted force-free state, minimizing the total energy while conserving a generalized helicity function. The theory additionally implies that the (not directly measured by Ulysses) electric current density also lies on the MVS tangential plane, hence the MVS also constitute current sheets . The MVS spatial orientation implies that the MVS are wrapped in the form of magnetized vortex tubes with axes aligned to the average magnetic field. The vector couplings, characterizing the MVS, are found to weaken with increasing heliodistance and near the heliospheric current sheet.

It is shown that the magnetic field's local evolution in plasmas is directly affected by an interplay between the deformation (strain rate) and the self-rotation (vorticity) of the elementary plasma fluid volumes. At regions of strong strain rate, the fast local convergence or divergence of the flow causes exponential increase or decrease of the field's components, respectively. At regions of strong vorticity, faster directional than magnitude variations of the field occur, explaining the field alignment of the field minimum-variance direction and the random wandering of the field's tip on a sphere, both observed in the solar wind plasma, even in the absence of Alfven waves. We further investigate the coupling between the maximum strain-rate direction and the local magnetic field, that was previously deduced from magnetic field measurements in the outer heliosphere. Cases of long-lasting, non-Parkerian, radial heliospheric magnetic field are also shown to be periods of field-aligned strain rate. A statistical proof for this alignment is given, assuming that the small-scale field fluctuations are weakly stationary and time reversible. We further propose a generalization of the Stokesian fluid stress-strain relation to the case of one-fluid, collisionless MHD plasmas, including the effects of turbulent viscosity and magnetically induced shearing motion. For a negligible or isotropic or `field-aligned' thermal pressure tensor, the proposed `Stokesian plasma' relation implies the field alignment of the solar wind plasma strain-rate direction and leads to anisotropic stress-strain balance equations, related to those of `firehose' plasma instability. The field alignment of a principal strain-rate direction leads to simplifications in the magnetic-induction equation, especially in the case of force-free fields. For the simplified case of homogeneous, isotropic and incompressible plasma turbulence, the proposed stress-strain-rate relation implies that the velocity and magnetic field inertial range spectra should be identical, further reducing to the Kolmogorov-like k-5/3 law for scale-invariant eddy cascade at constant energy-dissipation rate.

A detailed analysis of small period (15-900 sec) magnetohydrodynamic (MHD) turbulences of the interplanetary magnetic field (IMF) has been made using Pioneer-11 high time resolution data (0.75 sec) inside a Corotating Interaction Region (CIR) at a heliocentric distance of 2.5 AU in 1973. The methods used are the hodogram analysis, the minimum variance matrix analysis and the cohenrence analysis. The minimum variance analysis gives evidence of linear polarized wave modes. Coherence analysis has shown that the field fluctuations are dominated by the magnetosonic fast modes with periods 15 sec to 15 min. However, it is also shown that some small amplitude Alfven waves are present in the trailing edge of this region with characteristic periods (15-200 sec). The observed wave modes are locally generated and possibly attributed to the scattering of Alfven waves energy into random magnetosonic waves.

We present the time distribution of a large number (7798) of Myocardial Infractions (MI) recorded at the General Hospital ‘St. Panteleimon’ of the city of Nikea (in Piraeus, Greece), during time interval 1997–2007. This data set consisted of 5160 NON‐STEACS (non‐ST) and 2638 STEACS (ST) infractions are examined along with the monthly numbers of solar flares and Coronal Mass Ejections (CMEs), solar wind parameters and the geomagnetic activity (Dst geomagnetic index and other). The mean monthly value of ST and non‐ST events is 20 and 40 respectively. The maximum monthly value of non‐ST events (72 and 73) are recorded in October 2002 and January 2003, as well as the one of ST events (32), while solar maximum, recorded in November 2002. This time interval is characterized by magnetic storms from August 2002 peaked in October 2002 and ended in February 2003. It is noticeable that August 2002 corresponds to the solar maximum of CMEs and strong solar flares monthly values. The maximum monthly value of ST events (40) is recorded in November 2005 almost simultaneously with a sudden absence of solar flares (October 2005). Increased values have been recorded during a period of extreme solar events of October–November 2003 and January–March 2005. It seems from this extensive statistical study that there is an association between the monthly values of MI and of CMEs; the non‐ST MI shows a better association with CMEs. Moreover, the MI yearly distribution is in accordance with the time distribution of magnetic storms (number and duration). The non‐ST distribution is also affected by intense magnetic storms.

In this paper we study the solar wind parameters during the 23rd solar cycle and the possible correlation between them. Those parameters’ data, which are Alfven Mach number, plasma beta, flow speed, proton density and temperature, dynamic pressure, average magnetic field, Bx and By, has been taken from OMNI 2. The first part of this project is about analysis and correlation of the data, using Pearson’s product moment correlation coefficient and Spearman Rank Correlation Coefficient, during the 11 years of the 23rd cycle. The second part is about Wavelet analysis on those parameters during the 21st, 22nd, 23rd solar cycles in comparison with them. We found that each parameter has different behavior in every cycle and certain periodicities that appear constantly.

We investigate the relationship of metric type III radio bursts obtained with radio spectrograph ARTEMIS IV (20–650 MHz) in Thermopylae, to GOES SXR/Ha and SOHO/LASCO CMEs within the period of intense activity 20 October to 5 November 2003. Our sample consists of 123 type III radio bursts, 115 SXR Flares (mostly C—type) and 12 CMEs. 69% of type III bursts are coincident in time with SXR Flares, while the rest 31% were detected between successive SXR flux maxima and though not always in the same active region as the SXR Flare, thereby labeled as SXR Less. The lack of SXR enhancement in SXR less type III bursts was probably the result of increased SXR background which prevented detection. It is found also, that 62% of the Flares are associated with type III radio bursts. Furthermore, we study the characteristic type III parameters i.e. start frequency, frequency band and duration as well as the SXR Flare parameters i.e. Flux, Duration, Apparent Area, rise time, decay time and their ratio. Finally, we tried to investigate any characteristic variation occurred because of the different morphology of the three major active regions, 484, 486 and 488 of that period.

Pioneer 11 magnetic field data at 20 AU are analysed by the computational method of Moussas, Quenby, and Webb (1975), Moussas and Quenby (1978), and Moussas, Quenby, and Valdes-Galicia (1982a, b) to obtain the parallel mean free path λ ∥, and the diffusion coefficient parallel to the magnetic field line K ∥. This method is the most appropriate for the mean free path calculation at large heliodistances since the alternative method which is based on fitting of energetic particle intensities cannot be easily and accurately be used because the association of energetic particles with their parent flares is not precise. The results show that the mean free path has values between 0.85 and 0.98 AU, linearly increasing with energy according to λ∥(Tkinetic) = ∧ + MT, where Λ = 0.846 AU and M = 4.44 × 10 −5 AU MeV−1 for energies between 10 MeV and 3 GeV for protons. These values of the parallel mean free path are much larger than the values estimated by previous studies up to 6 AU. The diffusion coefficient dependence upon energy follows a relation which simply reflects an almost constant mean free path and a linear dependence on the velocity of the particle, so that at 20 AU heliodistance K ∥(T kin) = K ∥, 1 MeV(T kin)T kinetic α, with α = 1/2. The distance dependence of the parallel diffusion mean free path follows a power law, λ ∥(R) = λ ∥, 1 AU R λ , where λ is 1 ± 0.1. While the parallel diffusion coefficient obeys a power-law relation with heliodistance R, K ∥ (R, T kin) = K ∥, 1 AU(T kin)R β , with β = 1 ± 0.1. The radial diffusion coefficient of cosmic rays is not expected to strongly depend upon the parallel diffusion coefficient because the nominal magnetic field at these large heliodistances (20 AU) is almost perpendicular to the radial direction and the contribution of the diffusion coefficient perpendicular to the magnetic field is expected to play a dominant role. However, the actual garden hose angle varies drastically and for long time periods and hence the contribution of the diffusion parallel to the field may continue to be important for the small scale structure of intensity gradients.

The KEP/EPAC instrument, on board Ulysses spacecraft, measures directional intensities of interplanetary energetic protons and ions. We analyze Compton‐Getting corrected data received from the beginning of the year 1991 to the end of 2000 and we also perform statistical analysis for the observed angle between first‐order anisotropy of particle distribution and interplanetary magnetic field. The results show that the energetic particle’s anisotropy is mostly in the direction perpendicular to the magnetic field, indicating a diffusion across the magnetic field lines. A strong correlation is found between the perpendicular to the magnetic field streaming of protons and ions, in the energy range of MeV, and the solar wind velocity. This correlation is simply interpreted in terms cross‐field particle diffussion in the presence of an ambient plasma density gradient.

Energetic particle (0.1 to 100 MeV protons) acceleration is studied by using high resolution interplanetary magnetic field and plasma measurements at 1 AU (HEOS-2) and at ∼5 AU (Pioneer 10). Energy changes of a particle population are followed by computing test particle trajectories and the energy changes through the particle interaction with the time varying magnetic field. The results show that considerable particle acceleration takes place throughout the interplanetary medium, both in the corotating interaction regions (CIR) (5 AU), and in quiet regions (1 AU). Although shocks may contribute to acceleration we suggest statistical acceleration within the CIRs is sufficient to explain most energetic particle observations (e.g., McDonaldet al., 1975; Barnes and Simpson, 1976). The first and second order statistical acceleration coefficients which include transit time damping and Alfven resonance interactions, are found to be well represented byD T ≈8.5×10−6 T 0.5 MeV s−1 andD TT ≈4×10−6 T 1.5 MeV2 s−1 at 5 AU. By comparison, Fisk's estimates (1976), based on quasi-linear theory for transit-time damping, gaveD TT ≈5×10−7 T MeV2 s−1 at 1 AU.

Crank-Nicholson solutions are obtained to the time-dependent Fokker-Planck equation for propagation in the interplanetary medium following a point in time injection of energetic solar particles and including the acceleration terms $$\frac{\partial }{{\partial T}}\left( {D_{TT} \frac{{\partial U}}{{\partial T}}} \right) - \frac{\partial }{{\partial T}}\left( {\frac{{D_{TT} U}}{{2T}}} \right)$$ . The diffusion coefficient in kinetic energyDTT is allowed to be either independent of radial distance,R(AU), or follow the lawDTT=D0T2R02/(A2+R2) in either case with the 1 AU value ofDTT at 10 MeV ranging between 10−4 (MeV)2 s−1 and zero. The spatial diffusion mean free path at the Earth's orbit is fixed at λ‖ AU at 10 MeV according to numerical estimates made by Moussas and Quenby. However, a variety ofR dependences are allowed. Reasonable agreement with experimental data out to 4 AU is obtained with the above values ofDTT and the spatial diffusion coefficientKr=K0R−2 forR«1 andKr=K0R0.4 forR»1 AU. It is only in the decay phases of prompt events as seen at 2–4 AU that significant differences in the temporal behaviour of the events can be distinguished, depending on the value ofDTT chosen within the above range. Experimental determination of the decay constant is difficult.

An analysis of the interplanetary medium structure is made during STIP 1. (September–October, 1975). Using a simple extrapolation method a reconstruction of the stream lines is made which shows that the interplanetary space during this time period was very quiet. Such a behaviour is expected because this interval is close to the minimum of the solar cycle activity.

A realistic model of the interplanetary magnetic field (IMF) is constructed based on measurements taken by Pioneer 10 magnetometer at 5 AU. Energetic particle (0.1–100 MeV) propagation in this field is studied by a computer simulation of its motion in order to calculateK ⊥, the perpendicular diffusion coefficient, and 〈V D 〉 the average drift velocity of an ensemble of particles. Determinations ofK ⊥ lie in the range 3×1019–8×1020 cm2 s−1 for the energies considered and they show that perpendicular diffusion may be an important process at these heliodistances when compared with parallel diffusion results obtained by similar techniques, contrary to what was previously thought. Drift velocity calculations are very close to predictions of guiding centre theory (within 30%) suggesting that this theory can be applied in the IMF. This result shows that gradient and curvature drifts can be present even in a highly perturbed field and thus they can have some influence in cosmic ray modulation.

A numerical simulation of energetic particle motion in the interplanetary medium is carried out using HEOS-2 magnetometer data in order to computeD(μ), the pitch angle diffusion coefficient, where μ is cosine of pitch angle defined with respect to the local field. WhileD(μ) exceeds that given by quasi-linear theory near 90° pitch angle, it is significantly less at higher values of μ, leading to a parallel transport coefficient in good accord with that given by experimental studies of solar proton propagation. In particular, α∥=0.031 AU at a particle magnetic rigidity of 455 MV, while experimental results range from 0.05 to 0.07 AU (+100%, −50%) in this rigidity region. Furthermore, observed approximately μ-dependent solar proton pitch angle distributions are consistent with the computed findingD(μ)/(1 −μ2)2 ~ constant.