8 research outputs found
Geoeffectiveness of Coronal Mass Ejections in the SOHO era
The main objective of the study is to determine the probability distributions
of the geomagnetic Dst index as a function of the coronal mass ejection (CME)
and solar flare parameters for the purpose of establishing a probabilistic
forecast tool for the geomagnetic storm intensity. Several CME and flare
parameters as well as the effect of successive-CME occurrence in changing the
probability for a certain range of Dst index values, were examined. The results
confirm some of already known relationships between remotely-observed
properties of solar eruptive events and geomagnetic storms, namely the
importance of initial CME speed, apparent width, source position, and the
associated solar flare class. In this paper we quantify these relationships in
a form to be used for space weather forecasting in future. The results of the
statistical study are employed to construct an empirical statistical model for
predicting the probability of the geomagnetic storm intensity based on remote
solar observations of CMEs and flares
How the area of solar coronal holes affects the properties of high-speed solar wind streams near Earth : An analytical model
Since the 1970s it has been empirically known that the area of solar coronal holes affects the properties of high-speed solar wind streams (HSSs) at Earth. We derive a simple analytical model for the propagation of HSSs from the Sun to Earth and thereby show how the area of coronal holes and the size of their boundary regions affect the HSS velocity, temperature, and density near Earth. We assume that velocity, temperature, and density profiles form across the HSS cross section close to the Sun and that these spatial profiles translate into corresponding temporal profiles in a given radial direction due to the solar rotation. These temporal distributions drive the stream interface to the preceding slow solar wind plasma and disperse with distance from the Sun. The HSS properties at 1 AU are then given by all HSS plasma parcels launched from the Sun that did not run into the stream interface at Earth distance. We show that the velocity plateau region of HSSs as seen at 1 AU, if apparent, originates from the center region of the HSS close to the Sun, whereas the velocity tail at 1 AU originates from the trailing boundary region. Small HSSs can be described to entirely consist of boundary region plasma, which intrinsically results in smaller peak velocities. The peak velocity of HSSs at Earth further depends on the longitudinal width of the HSS close to the Sun. The shorter the longitudinal width of an HSS close to the Sun, the more of its "fastest" HSS plasma parcels from the HSS core and trailing boundary region have impinged upon the stream interface with the preceding slow solar wind, and the smaller is the peak velocity of the HSS at Earth. As the longitudinal width is statistically correlated to the area of coronal holes, this also explains the well-known empirical relationship between coronal hole areas and HSS peak velocities. Further, the temperature and density of HSS plasma parcels at Earth depend on their radial expansion from the Sun to Earth. The radial expansion is determined by the velocity gradient across the HSS boundary region close to the Sun and gives the velocity-temperature and density-temperature relationships at Earth their specific shape. When considering a large number of HSSs, the assumed correlation between the HSS velocities and temperatures close to the Sun degrades only slightly up to 1 AU, but the correlation between the velocities and densities is strongly disrupted up to 1 AU due to the radial expansion. Finally, we show how the number of particles of the piled-up slow solar wind in the stream interaction region depends on the velocities and densities of the HSS and preceding slow solar wind plasma.Peer reviewe
Multiple Satellite Analysis of the Earth’s Thermosphere and Interplanetary Magnetic Field Variations due to ICME/CIR Events During 2003–2015
We present a refined statistical analysis based on interplanetary coronal
mass ejections as well as co-rotating interaction regions for the time period
2003-2015 to estimate the impact of different solar wind types on the
geomagnetic activity and the neutral density in the Earth's thermosphere. For
the time-based delimitation of the events, we rely on the catalog maintained by
Richardson and Cane and the CIR-lists provided by S. Vennerstroem and Jian et
al. [2011]. These archives are based on in-situ measurements from the ACE
and/or the Wind spacecraft. On this basis, we thoroughly investigated 196
Earth-directed ICME and 195 CIR events. To verify the impact on the Earth's
thermosphere we determined neutral mass densities by using accelerometer
measurements collected by the low-Earth orbiting satellites GRACE and CHAMP.
Subsequently, the atmospheric densities are related to characteristic ICME
parameters. In this process a new calibration method has been examined. Since
increased solar activity may lead to a decrease of the satellites orbital
altitude we additionally assessed the orbital decay for each of the events and
satellites. The influence of CIR events is in the same range of magnitude as
the majority of the ICMEs (186 out of 196). Even though, the extended
investigation period between 2011 and 2015 has a lack of extreme solar events
the combined analysis reveals comparable correlation coefficients between the
neutral densities and the various ICME and geomagnetic parameters (mostly >
0.85). The evaluation of orbit decay rates at different altitudes revealed a
high dependency on the satellite actual altitude.Comment: accepted for publication in JGR-Space Physic
Farside explorer: Unique science from a mission to the farside of the moon
Farside Explorer is a proposed Cosmic Vision medium-size mission to the farside of theMoon consisting of two landers and an instrumented relay satellite. The farside of the Moon is a unique scientific platform in that it is shielded from terrestrial radio-frequency interference, it recorded the primary differentiation and evolution of the Moon, it can be continuously monitored from the Earth–Moon L2 Lagrange point, and there is a complete lack of reflected solar illumination from the Earth. Farside Explorer will exploit these properties and make the first radio-astronomy measurements from the most radio-quiet region of near-Earth space, determine the internal structure and thermal evolution of the Moon, from crust to core, and quantify impact hazards in near-Earth space by the measurement of flashes generated by impact events. The Farside Explorer flight system includes two identical solarpowered landers and a science/telecommunications relay satellite to be placed in a halo orbit about the Earth–Moon L2 Lagrange point. One lander would explore the largest and oldest recognized impact basin in the Solar System—the South Pole–Aitken basin—and the other would investigate the primordial highlands crust. Radio astronomy, geophysical, and geochemical instruments would be deployed on the surface, and the relay satellite would continuously monitor the surface for impact events.Space EngineeringAerospace Engineerin