| 1. |
- Feldstein, Y. I., et al.
(författare)
-
Structure of the auroral precipitation region in the dawn sector : relationship to convection reversal boundaries and field-aligned currents
- 2001
-
Ingår i: Annales Geophysicae. - : Copernicus GmbH. - 0992-7689 .- 1432-0576. ; 19:5, s. 495-519
-
Tidskriftsartikel (refereegranskat)abstract
- Simultaneous DMSP F7 and Viking satellite measurements of the dawnside high-latitude auroral energy electron and ion precipitation show that the region of the low and middle altitude auroral precipitation consists of three characteristic plasma regimes. The recommendation of the IAGA Working Group IIF/III4 at the IAGA Assembly in Boulder, July 1995 to decouple the nomenclature of ionospheric populations from magnetospheric population is used for their notation. The most equatorial regime is the Diffuse Auroral Zone (DAZ) of diffuse spatially unstructured precipitating electrons. It is generated by the plasma injection to the inner magnetosphere in the nightside and the subsequent drift plasma to the dawnside around the Earth. Precipitating par tides have a hard spectrum with typical energies of electrons and ions of more than 3 keV. In the DAZ, the ion pitch-angle distribution is anisotropic. with the peak near 90 degrees. The next part is the Auroral Oval (AO), a structured electron regime which closely resembles the poleward portion of the nightside auroral oval. The typical electron energy is several keV, and the ion energy is up to 10 keV. Ion distributions are predominantly isotropic. In some cases, this plasma regime may be absent in the prenoon sector. Poleward of the Auroral Oval, there is the Soft Small Scale Luminosity (SSSL) regime. It is caused by structured electron and ion precipitation with typical electron energy of about 0.3 keV and ion energy of about 1 keV. The connection of these low-altitude regimes with plasma domains of the distant magnetosphere is discussed. For mapping of the plasma regimes to the equatorial plane of the magnetosphere, the empirical model by Tsyganenko (1995) and the conceptual model by Alexeev et al. (1996) are used. The DAZ is mapped along the magnetic field lines to the Remnant Layer (RL), which is located in the outer radiation belt region: the zone of structured electrons and isotropic ion precipitation (AO) is mapped to the dawn periphery of the Central Plasma Sheet (CPS); the soft small scale structured precipitation (SSSL) is mapped to the outer magnetosphere close to the magnetopause, i.e. the Low Latitude Boundary Layer (LLBL). In the near-noon sector, earthward fluxes of soft electrons, which cause the Diffuse Red Aurora (DRA), are observed. The ion energies decrease with increasing latitude, The plasma spectra of the DRA regime are analogous to the spectra of the Plasma Mantle (PM). In the dawn sector, the large-scale field-aligned currents flow into the ionosphere at the SSSL latitudes (Region 1) and flow out at the AO or DAZ latitudes (Region 2). In the dawn and dusk sectors, the large-scale Region 1 and Region 2 FAC generation occurs in different plasma domains of the distant magnetosphere. The dawn and dusk FAC connection to the traditional Region 1 and Region 2 has only formal character, as FAC generating in various magnetospheric plasma domains integrate in the same region (Region 1 or Region 2). In the SSSL, there is anti-sunward convection in the DAZ and the AO, there is the sunward convection. At PM latitudes, the convection is controlled by the azimuthal IMF component (By) It is suggested to extend the notation of the plasma pattern boundaries, as proposed by Newell et al. (1996), for the nightside sector of the auroral oval to the dawn sector.
|
|
| 2. |
- Cohen, J., et al.
(författare)
-
Divergent consensuses on Arctic amplification influence on midlatitude severe winter weather
- 2020
-
Ingår i: Nature Climate Change. - : Springer Science and Business Media LLC. - 1758-678X .- 1758-6798. ; 10, s. 20-29
-
Forskningsöversikt (refereegranskat)abstract
- The Arctic has warmed more than twice as fast as the global average since the late twentieth century, a phenomenon known as Arctic amplification (AA). Recently, there have been considerable advances in understanding the physical contributions to AA, and progress has been made in understanding the mechanisms that link it to midlatitude weather variability. Observational studies overwhelmingly support that AA is contributing to winter continental cooling. Although some model experiments support the observational evidence, most modelling results show little connection between AA and severe midlatitude weather or suggest the export of excess heating from the Arctic to lower latitudes. Divergent conclusions between model and observational studies, and even intramodel studies, continue to obfuscate a clear understanding of how AA is influencing midlatitude weather.
|
|
| 3. |
- Feldstein, Y. I., et al.
(författare)
-
Auroral electrojets and 3D currents in the ionosphere-magnetosphere system
- 2006
-
Ingår i: “Physics of Auroral Phenomena”, Proc. XXIX Annual Seminar, Apatity. - : Kola Science Centre, Russian Academy of Science. ; , s. 25-30
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- There are shortly described results of the analysis of variations in the location and intensity of the auroral electrojets during magnetic storms and substorms using a numerical method for estimating the equivalent ionospheric currents based on data from meridian chains of magnetic observatories. It is shown that the westward electrojet adjoins to the polar electrojet located at cusp latitudes in the dayside sector. The association of electrojets with the field-aligned currents (FACs), namely Region 1 FAC and Region 2 FAC is considered. During intense disturbances a Region 3 FAC (accompanied with diffuse electron precipitation from the plasma sheet boundary layer) with the downward current was identified. The analysis of observational data is summarized in terms of 2D time-latitude distribution of electrojets at ionospheric altitudes. The magnetic field sawtooth variations generated during the storm main and early recovery phases are also discussed. To follow 3D currents in the magnetosphereionosphere system a clarified view of interrelated 3D currents and magnetospheric plasma domains is presented.
|
|
| 4. |
- Feldstein, Y. I., et al.
(författare)
-
Auroral electrojets and boundaries of plasma domains in the magnetosphere during magnetically disturbed intervals
- 2006
-
Ingår i: Annales Geophysicae. - : Copernicus GmbH. - 0992-7689 .- 1432-0576. ; 24:8, s. 2243-2276
-
Tidskriftsartikel (refereegranskat)abstract
- We investigate variations in the location and intensity of the auroral electrojets during magnetic storms and substorms using a numerical method for estimating the equivalent ionospheric currents based on data from meridian chains of magnetic observatories. Special attention was paid to the complex structure of the electrojets and their interrelationship with diffuse and discrete particle precipitation and field-aligned currents in the dusk sector. During magnetospheric substorms the eastward electrojet (EE) location in the evening sector changes with local time from cusp latitudes (Phi similar to 77 degrees) during early afternoon to latitudes of diffuse auroral precipitation (Phi similar to 65 degrees) equatorward of the auroral oval before midnight. During the main phase of an intense magnetic storm the eastward currents in the noon-early evening sector adjoin to the cusp at Phi similar to 65 degrees and in the pre-midnight sector are located at subauroral latitude Phi similar to 57 degrees. The westward electrojet (WE) is located along the auroral oval from evening through night to the morning sector and adjoins to the polar electrojet (PE) located at cusp latitudes in the day-side sector. The integrated values of the eastward (westward) equivalent ionospheric current during the intense substorm are similar to 0.5 MA (similar to 1.5 MA), whereas they are 0.7 MA (3.0 MA) during the storm main phase maximum. The latitudes of auroral particle precipitation in the dusk sector are identical with those of both electrojets. The EE in the evening sector is accompanied by particle precipitation mainly from the Alfven layer but also from the near-Earth part of the central plasma sheet. In the lower-latitude part of the EE the field-aligned currents (FACs) flow into the ionosphere (Region 2 FAC), and at its higher-latitude part the FACs flow out of the ionosphere (Region 1 FAC). During intense disturbances, in addition to the Region 2 FAC and the Region 1 FAC, a Region 3 FAC with the downward current was identified. This FAC is accompanied by diffuse electron precipitation from the plasma sheet boundary layer. Actually, the triple system of FAC is observed in the evening sector and, as a consequence, the WE and the EE overlap. The WE in the evening sector comprises only the high-latitude periphery of the plasma precipitation region and corresponds to the Hall current between the Region 1 FAC and Region 3 FAC. During the September 1998 magnetic storm, two velocity bursts (similar to 2-4 km/s) in the magnetospheric convection were observed at the latitudes of particle precipitation from the central plasma sheet and at subauroral latitudes near the ionospheric trough. These kind of bursts are known as subauroral polarization streams (SAPS). In the evening sector the Alfven layer equatorial boundary for precipitating ions is located more equatorward than that for electrons. This may favour northward electric field generation between these boundaries and may cause high speed westward ions drift visualized as SAPS. Meanwhile, high speed ion drifts cover a wider range of latitudes than the distance between the equatorward boundaries of ions and electrons precipitation. To summarize the results obtained a new scheme of 3-D currents in the magnetosphere-ionosphere system and a clarified view of interrelated 3-D currents and magnetospheric plasma domains are proposed.
|
|
| 5. |
- Feldstein, Y I, et al.
(författare)
-
Electromagnetic characteristics of the high-latitude ionosphere during the various phases of magnetic substorms
- 1996
-
Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 101:A9, s. 19921-19936
-
Tidskriftsartikel (refereegranskat)abstract
- Model calculations of the electrodynamics of the high-latitude ionosphere are compared to measurements made by the Viking satellite during July-August 1986. The model calculations are based on the IZMEM procedure, where the electric field and currents in the ionosphere are given as functions of the interplanetary magnetic field. The events chosen correspond to the growth, the expansion, and the recovery phases of substorms. During the growth and expansion phases the correlation between the model results and the satellite data is rather good. During recovery phase the correlation is not as good. The correlation between modeled and observed quantities suggest that during growth and expansion phase the magnetosphere is mainly directly driven by the solar wind, whereas during recovery phase it is mainly driven by internal processes, i.e., loading-unloading. Best fit is obtained when averaging the measured quantities over a few minutes, which means adjusting the spatial resolution of the measurements to the resolution of the model. Different time delays between the interplanetary magnetic field observations and those of Viking were examined. Best agreement was obtained, not surprisingly, for time delays corresponding to the estimated information transit time from the solar wind spacecraft to the ionosphere.
|
|
| 6. |
- Feldstein, Y. I., et al.
(författare)
-
Electromagnetic weather at 100 km altitude on 3 August 1986
- 1994
-
Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 21, s. 2095-2098
-
Tidskriftsartikel (refereegranskat)abstract
- The electromagnetic weather at high altitudes above the Earth’s surface is determined by the transport of ionospheric plasma, which in turn is governed by the magnitude as well as the direction of the electric and magnetic fields. Different models [Levitin et al., 1984; Friis-Christensen et al., 1985; Mishin, 1990] have been proposed that allow an estimation of the electromagnetic parameters of the upper atmosphere, given a knowledge of the magnitude and orientation of the interplanetary magnetic field. Here we use one such model to estimate the global convection pattern and its temporal evolution during a pass of the Swedish satellite Viking over the northern polar cap. The model predictions are shown to agree well with the electric and magnetic fields measured along the satellite trajectory. The good agreement implies that the model can be used to reconstruct, with reasonable confidence, the large-scale distribution of electric and magnetic fields and their time-variation in the entire auroral ionosphere.
|
|
| 7. |
|
|
| 8. |
|
|
| 9. |
- Feldstein, Y. I., et al.
(författare)
-
High-latitude electrojets and auroral luminosity and auroral particle precipitations
- 2007
-
Ingår i: “Physics of Auroral Phenomena”, Proc. XXX Annual Seminar, Apatity. - : Kola Science Centre, Russian Academy of Science. ; , s. 55-59
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The mutual location of high-latitude electrojets, typical regions of the auroral luminosity and regions of auroral energy particle participations into the upper atmosphere under substorm conditions are considered. Three electrojets exist at high latitudes during substorm intervals: WE - westward electrojet, EE - eastward electrojet and PE – polar electrojet. Geomagnetic latitudes of the WE/EE and PE location vary depend on local time and magnetic activity level, respectively. It is shown that the WE is located within the limits of the auroral oval precipitation (AOP), the EE in the evening sector is located within the diffuse auroral zone (DAZ) and the PE near noon is located at the poleward AOP boundary shifting poleward with decreasing the magnetic activity level. The relationship of electrojets with different plasma domains in the magnetosphere is discussed.
|
|
| 10. |
- Gromova, L. I., et al.
(författare)
-
High-Latitude Ionospheric Convection Patterns Dependent on the IMF Orientation
- 2007
-
Ingår i: <em>“</em>Physics of Auroral Phenomena”, Proc. XXX Annual Seminar, Apatity. - : Kola Science Centre, Russian Academy of Science. ; , s. 64-68
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The IZMEM model provides high-latitude ionospheric plasma convection patterns in both hemispheres as a function of the IMF orientation. Model electric potentials are compared with electric field measurements from the DE2, FAST and DMSP satellites along high-latitude passes of the Northern and Southern hemispheres during IMF Bz < 0 and By < 0 (By >0). It has been shown that the IZMEM model electric potentials are in good agreement with measurements along the satellite passes, which makes the IZMEM global spatial convection patterns for these plausible. For small IMF magnitude ionospheric convection patterns generally consist of two cells with a positive potential cell on the dawn-side and a negative potential cell on the dusk-side. For IMF By<0 (By>0) a positive (negative) potential cell becomes dominant in the northern hemisphere, and oppositely in the southern hemisphere. During Bz > 0 the convection pattern changes from the standard two-cell pattern to a more complicated one. IZMEM shows two additional convection cells in the dayside polar cap, positive (negative) potential cell is present duskward (dawnward) of the noon-midnight meridian, and may cause three-cell or four-cell convection pattern depending on By/Bz ratio.
|
|
