A statistical study of the performance of the Hakamada-Akasofu-Fry version 2 numerical model in predicting solar shock arrival times at Earth during different phases of solar cycle 23

The performance of the Hakamada Akasofu-Fry, version 2 (HAFv.2) numerical model, which provides predictions of solar shock arrival times at Earth, was subjected to a statistical study to investigate those solar/interplanetary circumstances under which the model performed well/poorly during key phases (rise/maximum/decay) of solar cycle 23. In addition to analyzing elements of the overall data set (584 selected events) associated with particular cycle phases, subsets were formed such that those events making up a particular sub-set showed common characteristics. The statistical significance of the results obtained using the various sets/subsets was generally very low and these results were not significant as compared with the hit by chance rate (50%). This implies a low level of confidence in the predictions of the model with no compelling result encouraging its use. However, the data suggested that the success rates of HAFv.2 were higher when the background solar wind speed at the time of shock initiation was relatively fast. Thus, in scenarios where the background solar wind speed is elevated and the calculated success rate significantly exceeds the rate by chance, the forecasts could provide potential value to the customer. With the composite statistics available for solar cycle 23, the calculated success rate at high solar wind speed, although clearly above 50%, was indicative rather than conclusive. The RMS error estimated for shock arrival times for every cycle phase and for the composite sample was in each case significantly better than would be expected for a random data set. Also, the parameter "Probability of Detection, yes" (PODy) which presents the Proportion of Yes observations that were correctly forecast (i.e. the ratio between the shocks correctly predicted and all the shocks observed), yielded values for the rise/maximum/decay phases of the cycle and using the composite sample of 0.85, 0.64, 0.79 and 0.77, respectively. The statistical results obtained through detailed analysis of the available data provided insights into how changing circumstances on the Sun and in interplanetary space can affect the performance of the model. Since shock arrival predictions are widely utilized in making commercially significant decisions re. protecting space assets, the present detailed archival studies can be useful in future operational decision making during solar cycle 24. It would be of added value in this context to use Briggs-Rupert methodology to estimate the cost to an operator of acting on an incorrect forecast

Quiet time fluxes and radial gradients of low-energy protons in the inner and outer heliosphere

Radial variations of low-energy (~1-8 MeV) quiet-time fluxes of protons are examined at distances of 20-85 AU during low solar activity periods using Voyager 1-2 data and compared with Ulysses fluxes at 1-5 AU as well as IMP-8 and SOHO at Earth and Helios between 0.3 and 1 AU. To obtain nearly background-free fluxes, the data are based on a careful pulse-height analysis. Except for high solar activity periods, contaminated with solar particles, all fluxes are very low, of the order of, and below 10^(-5) /(cm^2 s sr MeV). The Ulysses fluxes seem to be the lowest, whereas Helios and Voyager fluxes are nearly at the same level. The radial variation in 1-8 MeV suggests a negative gradient from 0.5 to about 2 AU that gradually turns positive beyond 2 AU. Whereas the true variation is difficult to infer between 5 and 17 AU due to solar contribution, from 30 to about 60 AU it exhibits a wide plateau, beyond which a slight increasing tendency is observed. At energies above ~6 MeV a clear contribution of anomalous hydrogen is observed

Dependence of decay rates of SEP events on characteristics of interplanetary medium and on radial distance

The shape of the particle flux decline in solar energetic particle (SEP) events is of particular importance in understanding the propagation of energetic particles in the interplanetary medium. The majority offew-MeV particle events exhibit exponential declines indicating the importance of adiabatic deceleration and convection transport. Then value of the decay time 't depends on the differential spectral index y, solar wind speed, and on the distance from the Sun. By analyzing the dependence of ' on enviromnental plasma parameters we showed earlier that ' tends to decrease with the increase of both solar wind speed and magnetic field strength. Comparing simultaneous observations at various radial distances (at IMP, ACE, Helios, and ffiysses) we find that whereas high-energy (tens of MeVs) proton profiles sometimes are surprisingly identical at different radii, MeV protons in the same events have significantly longer decays at farther locations than near 1 AU. This is incompatible both with pure diffusive particle propagation and with trapping between converging magnetic field lines near the Sun and at the front of traveling shock, but qualitatively supports convection transport and adiabatic deceleration. Using a simple numerical model including diffusion and adiabatic cooling the time profiles are calculated and compared with observations

Arrival times of Flare/Halo CME associated shocks at the Earth: comparison of the predictions of three numerical models with these observations

International audienceThe arrival times at L1 of eleven travelling shocks associated both with X-ray flaring and with halo CMEs recorded aboard SOHO/LASCO have been considered. Close to the Sun the velocities of these events were estimated using either Type II radio records or CME speeds. Close to the Earth the shocks were detected in the data of various solar wind plasma, interplanetary magnetic field (IMF) and energetic particle experiments aboard SOHO, ACE, WIND, INTERBALL-1 and IMP-8. The real-time shock arrival predictions of three numerical models, namely the Shock Time of Arrival Model (STOA), the Interplanetary Shock Propagation Model (ISPM) and the Hakamada-Akasofu-Fry Solar Wind Model (HAFv.2) were tested against these observations. This is the first time that energetic protons (tens of keV to a few MeV) have been used to complement plasma and IMF data in validating shock propagation models. The models were all generally successful in predicting shock arrivals. STOA provided the smallest values of the "predicted minus measured" arrival times and displayed a typical predictive precision better than about 8 h. The ratio of the calculated standard deviation of the transit times to Earth to the standard deviation of the measurements was estimated for each model (treating interacting events as composite shocks) and these ratios turned out to be 0.60, 1.15 and 1.02 for STOA, ISPM and HAFv.2, respectively. If an event in the sample for which the shock velocity was not well known is omitted from consideration, these ratios become 0.36, 0.76 and 0.81, respectively. Larger statistical samples should now be tested. The ratio of the in situ shock velocity and the "Sun to L1" transit velocity (Vsh /Vtr) was in the range of 0.7?0.9 for individual, non-interacting, shock events. HAFv.2 uniquely provided information on those changes in the COBpoint (the moving Connection point on the shock along the IMF to the OBserver) which directly influenced energetic particle rise times. This model also illustrated the non-uniform upstream conditions through which the various shocks propagated; furthermore it simulated shock deformation on a scale of fractions of an AU. On the spatial scale (300 RE ), where near-Earth spacecraft are located, the passing shocks, in conformity with the models, were found to be locally planar. The shocks also showed tilting relative to the Sun-Earth line, probably reflecting the inherent directionality associated with their solar origin. Key words. Interplanetary physics (energetic particles; interplanetary shocks; solar wind plasma

Solar and heliospheric sources of suprathermal and energetic particle populations

Objectives and some preliminary findings of an ongoing international team project carried out at ISSI, Bern will be presented. Suprathermal and energetic particle s in interplanetary space have a multitude of origins, i.e. acceleration and propagation hi stories. Solar flares, coronal mass ejections (CMEs), co-rotating interaction regions (CIRs), the heliospheric termination shock, planetary bow shocks and magnetospheres have all been recognized as energetic particle sources. Less energetic (suprathermal) particles of solar origin and pick-up ions have also a vital role both in their own right and as seeds of energetic particles accelerated in interplanetary disturbances. The relative contributions of various particle populations vary with energy and with the phase of the solar cycle. Particular attention will be given in our project to quiet periods and to large events. While quiet-time fluxes are expected to shed light on some base-line features of coronal and interplanetary acceleration processes, relatively large events dominate bot h the long-term fluence levels and the statistical properties of cumulative fluence plots. The importance of energetic and suprathermal particles that mostly cannot escape into interplanetary space, but contribute to co ronal heating and possibly also to solar wind composition, will also be discussed. B. Sripathi Acharya, Sunil Gupta, P. Jagadeesan, Atul Jain, S. Karthikeyan, Samuel Morris, and Suresh Tonwa

SERENA:Particle Instrument Suite for Determining the Sun-Mercury Interaction from BepiColombo

International audienceThe ESA-JAXA BepiColombo mission to Mercury will provide simultaneous measurements from two spacecraft, offering an unprecedented opportunity to investigate magnetospheric and exospheric particle dynamics at Mercury as well as their interactions with solar wind, solar radiation, and interplanetary dust. The particle instrument suite SERENA (Search for Exospheric Refilling and Emitted Natural Abundances) is flying in space on-board the BepiColombo Mercury Planetary Orbiter (MPO) and is the only instrument for ion and neutral particle detection aboard the MPO. It comprises four independent sensors: ELENA for neutral particle flow detection, Strofio for neutral gas detection, PICAM for planetary ions observations, and MIPA, mostly for solar wind ion measurements. SERENA is managed by a System Control Unit located inside the ELENA box. In the present paper the scientific goals of this suite are described, and then the four units are detailed, as well as their major features and calibration results. Finally, the SERENA operational activities are shown during the orbital path around Mercury, with also some reference to the activities planned during the long cruise phase

Correction to: SERENA: Particle Instrument Suite for Determining the Sun-Mercury Interaction from BepiColombo

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