A new perspective and explanation for the formation of plasmaspheric shoulder structures

Over the hours of 05:00–09:00 UT on 8 June 2001, the extreme ultraviolet (EUV) instrument on board the IMAGE satellite observed a shoulder-like formation in the morning sector and a post-noon plume-like structure. The plasmapause formation is simulated using the test particle model (TPM), based on a drift motion theory, which reproduces various plasmapause structures and evolution of the shoulder feature. The analysis indicates that the shoulder is created by sharp reduction and spatial non-uniformity in the dawn–dusk convection electric field intensity. The TPM-modeled event is found to develop an initial pre-dawn asymmetric bulge that becomes a shoulder as a result of increased “corotation” rate with an increasing L-shell that is preceded by localized outward convection. The shoulder structure rotates sunward and develops into a single- or double-plume structure during an active time period in simulation.

Assessment of the current distribution, dispersal trends and impacts of invasive species in Bana - Nui Chua Nature Reserve, Vietnam

Invasive species threaten the biodiversity and the function of ecosystems. Drone image, satellite images, and image analysis software were used to create the map of invasive distribution and the potential spreading of invasive plants. 13 most invasive plants were identified with 11 species listed as invasive species in Southeast Asia and 5 of them in the 100 world’s invasive species by IUCN. Three species Merremia boisiana (Gagn.) van Ooststr., Ipomoea eberhardtii Gagn, and Mimosa pigra were identified as the species with high-ranking impacts on biodiversity and ecosystem biodiversity in Ba Na - Nui Chua Nature Reserve (BNNR). Ipomoea eberhardtii Gagn shows the highest spreading rate at 0.65 ± 0.06 ha/month, followed by Merremia boisiana (Gagn.) van Ooststr) and Mimosa pigra at 0.12 ± 0.01 ha/month and 0.01 ± 0.001 ha/month respectively. Fresh biomass of Ipomoea eberhardtii Gagn; Merremia boisiana (Gagn.); Mimosa pigra and Sphagnetola trilobata (L.) Pruski in BNNR are 15.67; 14.9; 8.1 and 6.8 ton/ha. The database of invasive plant distribution and potential spreading will be used to monitor strategies and invasive weeds management in BNNR.

Geomagnetic method for automatic diagnostics of auroral oval boundaries in two hemispheres of Earth

The ground-based automatic method for determining auroral oval (AO) boundaries developed by the authors [Lunyushkin, Penskikh, 2019] has been modified and expanded to the Southern Hemisphere. Input data of the method contains large-scale distributions of the equivalent current function and field-aligned current density calculated in the polar ionospheres of two hemispheres in a uniform ionospheric conductance approximation based on the magnetogram inversion technique and the geomagnetic database of the world network of stations of the SuperMAG project. The software implementation of the method processes large volumes of time series of input data and produces coordinates of the main boundaries of AO in both hemi- spheres: the boundaries of the ionospheric convection reversal, the AO polar and equatorial boundaries, the lines of maximum density of field-aligned currents and auroral electrojets. The automatic method reduces the processing time for a given amount of data by 2–3 orders of magnitude (up to minutes and hours) compared to the manual method, which requires weeks and months of laborious operator work on the same task, while both methods are comparable in accuracy. The automatic geomagnetic method has been tested for diagnostics of AO boundaries during the isolated substorm of August 27, 2001, for which the expected synchronous dynamics of polar caps in two hemispheres has been confirmed. We also show the AO boundaries identified are in qualitative agreement with simultaneous AO images from the IMAGE satellite, as well as with the results of the OVATION and APM models; the boundary of ionospheric convection reversal, determined by the geomagnetic method in two hemispheres, is consistent with the maps of the electric potential of the ionosphere according to the SuperDARN-RG96 model.

Geomagnetic method for automatic diagnostics of auroral oval boundaries in two hemispheres of Earth

The ground-based automatic method for determining auroral oval (AO) boundaries developed by the authors [Lunyushkin, Penskikh, 2019] has been modified and expanded to the Southern Hemisphere. Input data of the method contains large-scale distributions of the equivalent current function and field-aligned current density calculated in the polar ionospheres of two hemispheres in a uniform ionospheric conductance approximation based on the magnetogram inversion technique and the geomagnetic database of the world network of stations of the SuperMAG project. The software implementation of the method processes large volumes of time series of input data and produces coordinates of the main boundaries of AO in both hemi- spheres: the boundaries of the ionospheric convection reversal, the AO polar and equatorial boundaries, the lines of maximum density of field-aligned currents and auroral electrojets. The automatic method reduces the processing time for a given amount of data by 2–3 orders of magnitude (up to minutes and hours) compared to the manual method, which requires weeks and months of laborious operator work on the same task, while both methods are comparable in accuracy. The automatic geomagnetic method has been tested for diagnostics of AO boundaries during the isolated substorm of August 27, 2001, for which the expected synchronous dynamics of polar caps in two hemispheres has been confirmed. We also show the AO boundaries identified are in qualitative agreement with simultaneous AO images from the IMAGE satellite, as well as with the results of the OVATION and APM models; the boundary of ionospheric convection reversal, determined by the geomagnetic method in two hemispheres, is consistent with the maps of the electric potential of the ionosphere according to the SuperDARN-RG96 model.

Dual-lobe reconnection and horse-collar auroras

<p>We propose a mechanism for the formation of the horse-collar auroral configuration common during periods of strongly northwards interplanetary magnetic field, invoking the action of dual-lobe reconnection (DLR).  Auroral observations are provided by the Imager for Magnetopause-to-Auroras Global Exploration (IMAGE) satellite and spacecraft of the Defense Meteorological Satellite Program (DMSP).  We also use ionospheric flow measurements from DMSP and polar maps of field-aligned currents (FACs) derived from the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE).  Sunward convection is observed within the dark polar cap, with antisunwards flows within the horse-collar auroral region, together with the NBZ FAC distribution expected to be associated with DLR.  We suggest that newly-closed flux is transported antisunwards and to dawn and dusk within the reverse lobe cell convection pattern associated with DLR, causing the polar cap to acquire a teardrop shape and weak auroras to form at high latitudes.  Horse-collar auroras are a common feature of the quiet magnetosphere, and this model provides a first understanding of their formation, resolving several outstanding questions regarding the nature of DLR and the magnetospheric structure and dynamics during northwards IMF.  The model can also provide insights into the trapping of solar wind plasma by the magnetosphere and the formation of a low-latitude boundary layer and cold, dense plasma sheet.  We speculate that prolonged DLR could lead to a fully closed magnetosphere, with the formation of horse-collar auroras being an intermediate step.</p>

Formation and decay of a transpolar arc during a major magnetic storm onset

<p>We examine a transpolar arc that formed at the onset of a geomagnetic storm on 15 May 2005 just prior to the arrival of a magnetic cloud. The theta aurora was recorded over the southern hemisphere by the FUV-WIC camera onboard IMAGE satellite. While in most cases transpolar arcs decay as the IMF turns southward, this arc persisted for almost an hour into the cloud, with peak AL-activity below -1500 nT and Dst at the level of -100 nT.  We use the University of Michigan Space Weather Modeling Framework (SWMF) global geospace simulation to study the magnetotail, inner magnetosphere, and ionospheric conditions during the theta aurora to resolve the origin of the polar cap precipitation. At the time of formation of the theta aurora, the SWMF simulation results indicate a single-cell potential pattern, very low Region 2 currents, and slow inner magnetotail convection. A substorm onset took place as a result of IMF turning, re-creating and enhancing the two-cell convection pattern while the theta aurora persisted. The tail flows were a complex mixture of Earthward flows along the plasma sheet boundary layer and tailward flows at the tail center created by the substorm-associated near-tail reconnection. We analyze the ionospheric mapping of the Earthward flows and the effects of the global current systems on the large-scale auroral precipitation pattern.</p>

A New Perspective and Explanation to the Formation of Plasmaspheric Shoulder Structure

Over the hours of 5–9 UT on June 8 2001, the extreme ultraviolet (EUV) instrument onboard IMAGE satellite observed a Shoulder-like formation in the morning sector and a Plume-like structure straddling in the between noon and dusk region. Simulation results of the plasmapause formation based on mechanism of drift motion called Test Particle Model (TPM) and have reproduced various plasmapause structures and subsequent evolution of the Shoulder. The analysis indicated that the Shoulder is created by a dawn-dusk convection electric field intensity, sharp reduction and spatial nonuniform manifested. As, combination of the plasmaspheric rotation rate speed up with L-shell increase and plasma flux do radial outflow in the predawn sector to interact, and produce an asymmetric bulge that rotates eastward. The Shoulder-like structure rotates sunward and develops to the single or double Plume structure during active times.

FORET D'ARBRES ALEATOIRES ET CLASSIFICATION D'IMAGES SATELLITES : RELATION ENTRE LA PRECISION DU MODELE D'ENTRAINEMENT ET LA PRECISION GLOBALE DE LA CLASSIFICATION

Résumé: En télédétection, il existe un grand nombre d'algorithmes permettant de classifier une image satellite. Parmi ces algorithmes de classification, la Forêt d'Arbres Aléatoires apparait comme particulièrement performant. Cette étude a pour objectifs d'évaluer (1) l'importance de la sélection des images pour le niveau de précision du modèle d'entrainement et (2) la nature de la relation qui existe entre le niveau de précision du modèle et celui de la précision globale de la carte thématique résultant de la classification de l'image satellite avec cet algorithme de classification. A partir d'une image Landsat 8 OLI prise au-dessus d'une zone de montagne tropicale : la région de l'Ouest Cameroun, 35 modèles ont été construits et testés. Les résultats montrent que le niveau de la précision globale des résultats de la Forêts d'Arbres Aléatoires est étroitement dépendant d'une part de la précision du modèle d'entrainement utilisé pour classifier l'image satellite, et d'autre part du choix des images utilisées pour entrainer ce modèle. De plus, la sélection de ces images est elle-même dépendante de la qualité des zones d'entrainement qui serviront à la construction du modèle. Il est donc important de mettre en accent particulier sur la qualité des données d'entrée afin de garantir des résultats satisfaisants avec cet algorithme. Mots clés : Forêt d’Arbres Aléatoires ; précision ; modèle d’entrainement ; télédétection ; Cameroun