278 research outputs found
Space storm measurements of the July 2005 solar extreme events from the low corona to the Earth
The Athens Neutron Monitor Data Processing (ANMODAP) Center recorded an
unusual Forbush decrease with a sharp enhancement of cosmic ray intensity right
after the main phase of the Forbush decrease on 16 July 2005, followed by a
second decrease within less than 12 h. This exceptional event is neither a
ground level enhancement nor a geomagnetic effect in cosmic rays. It rather
appears as the effect of a special structure of interplanetary disturbances
originating from a group of coronal mass ejections (CMEs) in the 13-14 July
2005 period. The initiation of the CMEs was accompanied by type IV radio bursts
and intense solar flares (SFs) on the west solar limb (AR 786); this group of
energetic phenomena appears under the label of Solar Extreme Events of July
2005. We study the characteristics of these events using combined data from
Earth (the ARTEMIS IV radioheliograph, the Athens Neutron Monitor (ANMODAP)),
space (WIND/WAVES) and data archives. We propose an interpretation of the
unusual Forbush profile in terms of a magnetic structure and a succession of
interplanetary shocks interacting with the magnetosphere.Comment: Advances in Space Research, Volume 43, Issue 4, p. 600-60
Welcoming for NMDB@Athens conference
Prof. H. Mavromichalaki on behalf of the organizing committee welcomes everyone to the 'NMDB@Athens' conference. The obituaries for Dr. Evgenia Eroshenko and Prof. Lev Dorman who recently passed away are following
Study of the longitudinal expansion velocity of the substorm current wedge
International audienceIn this work we examine simultaneous observations from the two geosynchronous satellites GOES-5 and GOES-6 located at 282°E and 265°E respectively, and from middle and low latitude ground observatories located within 250°E and 294°E geographic longitude, during isolated substorms of moderate activity. The spatial distribution of our observation points allows us to make a detailed study of the azimuthal expansion of the substorm current wedge. The data analysis shows evidence that the substorm initiation and development mechanism include the cross-tail current diversion/ disruption, the substorm current wedge formation and the azimuthal expansion of the inner plasma sheet. The triggering mechanism is initially confined in a longitudinally narrow sector, estimated to be less than 15° and located very close to local midnight to the east or to the west. The current disruption region expands both eastward and westward in the magnetotail, so that the location of major field-aligned currents flowing into the ionosphere shifts successively eastward, and the location of the currents flowing out of the ionosphere shifts successively westward. Evidence was found that the perturbation travels toward the west with velocities greater than those expanding the wedge eastward. The drastic decrease of the velocity with the azimuthal distance from the location of the disturbance initiation, i.e., the onset sector, indicates that the energy release is a very localized phenomenon. Finally, the transient D perturbation observed by the geosynchronous satellites suggests that the field-aligned currents forming the wedge have a longitudunally limited extent
Cosmic radiation exposure of aviators for solar cycles 23 and 24
Assessing the radiation exposure of aviators and frequent flyers requires the study of the cosmic ray showers
inside the Earth’s atmosphere. DYASTIMA / DYASTIMA-R is a Geant4 based software application, implemented
by the Athens Cosmic Ray Group which allows the study of the evolving secondary particles cascades inside the
atmosphere, as well as radiation dosimetry calculations (ambient dose equivalent rate) at different atmosphe -
ric altitudes, geographic coordinates and magnetic cut-off rigidity. Results for various scenarios, as calculated
by DYASTIMA/DYASTIMA-R, are provided as a federated product through the European Space Agency Space
Situational Awareness of the Space Radiation Service Centre Network, while the DYASTIMA software is provi-
ded through the Athens Neutron Monitor Station (A.Ne.Mo.S.) portal. Initial results for the assessment of the
radiation exposure during the last Solar Cycles 23 and 24 are presented in this work, covering the most usual
flying altitudes. The results indicate the dependence of the dose rate on the magnetic cut-off rigidity threshold,
with higher dose rates at high geographic latitudes, as well as the anti-correlation of cosmic ray intensity with
the solar activity, as higher dose rates are observed during solar minimum conditions
Precursory signals of Forbush decreases with and without shock wave
Many previous studies have shown that before the beginning of a Forbush Decrease (FD) of the cosmic ray intensity, a
precursor signal can be observed. All these surveys were focused on FDs that are associated with a sudden storm com-
mencement (SSC). In this work we demonstrate that precursors could also be observed in events without a SSC that is
determined by an abrupt increase of the interplanetary magnetic field. The type of precursory signals and their diversity
among the events are the main purpose of this study. We try to figure out similarities and differences on the signals and
the associated events from both categories in the last fifty years, from 1969 to 2019, using the same selection criteria
of the under investigation FDs. Simultaneously the orientation of the upcoming solar disturbances in comparison to the
way they configure the increase of the interplanetary magnetic field and create these signals are discussed
- …