Magnetosphere

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The focus of this thesis is to identify the role and dynamics of different current systems for storm-time activity at mid-latitude ground level and their relation with other solar, interplanetary and geomagnetic  parameters, in the 2007-2016 time interval. For this purpose, I compared the synthetic series of six magnetospheric current systems computed with the data-based semi-empirical model of Tsyganenko and Sitnov 2005 (TS05), with the measurements of four mid-latitude geomagnetic stations at very near geomagnetic latitudes, but well apart in longitude (Coimbra (COI), Portugal; Panagyurishte (PAG), Bulgary; Novosibirsk (NVS), Russia; Boulder (BOU), USA), and with other ground and satellite-based solar, interplanetary and geomagnetic parameters obtained from the OMNI/NASA database. An evaluation of TS05 model is presented, in order to determine the model ability to reproduce both the total  magnetospheric transient signal and to explain this signal through the contribution of each TS05 magnetospheric current system at ground level, comparing them with hourly data of the four geomagnetic stations selected.

It was found that TS05 model is a useful tool to explain ground-based North-South (or X) component of geomagnetic activity at mid-latitudes, in terms of main current sources. It was verified that TS05 is efficient to reproduce the X component of terrestrial magnetospheric field at mid-latitudes during high geomagnetic activity time, with correlations r ≥ 0.7 in ∼50% of compared data, presenting a lower efficiency during calm time, with correlations r ≥ 0.7 only in ∼30% of data compared. Results
are less favourable for the East-West (or Y ) component, probably due to the fact that TS05 model closes Birkeland (or field-aligned, FAC) currents through the Earth’s centre instead of through the ionosphere. It was found that currents that contribute most to the X component during geomagnetic active periods are the cross-tail (TAIL), the symmetric ring (SRC) and the partial ring (PRC) currents. The currents that contribute
most to Y component are FAC and PRC currents. For all stations the highest correlations among observations and TS05 simulations are obtained for stronger geomagnetic activity. The results in this study indicate that the implementation of TAIL and SRC currents in TS05 model is more successful than that for the FAC current.
The quiet daily (QD) variation has a main contribution from ionospheric currents, which are not considered in TS05 model. For observatories at Northern Hemisphere’s mid-latitudes that are localized close to the ionospheric current vortex center (COI and PAG), it was possible to separate efficiently the QD ionospheric contribution using Principal Component Analysis (PCA). For the other two stations (NVS and BOU) it
was found a relatively higher contribution of magnetospheric signal in the QD variation. After removing the QD variation from data, COI and PAG are better correlated with TS05 series than BOU and NVS. However, BOU and NVS are better correlated with geomagnetic indices Dst (disturbance storm-time) and RC (ring current), with RC showing a slightly less good performance with respect to Dst. Correlations between 33 solar, interplanetary magnetic field (IMF) and geomagnetic activity proxies were analysed for the 2009-2016 time interval. It was found that series of 27-day averages (Bartels’ rotation) give higher correlations than daily or annual series. Parameters that show higher cross-correlations among different groups are the Sun’s northern and southern facular areas (FA-N and FA-S), two geomagnetic indices derived from TS05 model (T-SRC and T-PRC), the total IMF intensity (B), the percentage of IMF southward component (BZS GSM) and the interplanetary coupling Newell’s function. We propose that these parameters are the best candidates to use if we want to relate meaningfully the solar surface events to geomagnetic activity felt on the Earth’s surface. Two new proxies were tested, 1) TI-indices, calculated from the X TS05-derived series of TAIL, SRC, PRC and FAC contributions for the four observatories and 2) BZS GSM, calculated as the daily percentage of IMF southward component along the GSM Z-axis.

Helio-magnetic asymmetries were calculated for the 33 parameters, as the difference between their averaged values in the towards and away magnetic sectors of the interplanetary medium. Improvement in 27-day correlations with respect to annual correlations is the result of an annual oscillation in this asymmetry, which is present in most studied proxies and is probably due to the Russell-McPherron effect. Due to this effect, BZS GSM and BZ GSM have a well-defined annual modulation, and geomagnetic activity indices (GAI) also have annual oscillation and good correlations with BZS GSM and BZ GSM. TI-indices have annual oscillation at declining phase of the cycle, but insignificant oscillation near the minimum. Major percentage of towards days in negative polarity epoch and of away days in positive polarity epoch means that the Earth has been mostly at the northern magnetic hemisphere during the solar cycle 24.

In conclusion, the main part of this Ph.D. thesis was dedicated to the design and implementation of a statistical approach that was applied to test the performance of the TS05 model in explaining geomagnetic activity observed at Earth’s Northern Hemisphere mid-latitudes. This approach can be applied to test any other magnetospheric model. At the end of this work, a prospective study was made using different proxies that describe the Sun surface, the interplanetary medium and geomagnetic activity, to identify those parameters that should be more meaningfully used to relate the Sun to the geomagnetic activity observed on Earth.

Keywords: Sun-Earth interaction, solar activity, solar and geomagnetic data, space weather.

Though the works on geomagnetic storms have many research articles but still the mechanism through which magnetosphere is coupled with low latitude ionosphere during the density pulse events is not comprehensively understood. So the topic is still challenging the present study is of a sudden commencement storm on July 2006 and November 2007 , both the years considered to be in low solar active period was taken into consideration. A detailed comparison of the solar wind parameters with reversal enhancements of IMF Bz and Dst is discussed. Index Terms— Geomagnetic storm, IMF Bz, low solar active period, solar wind parameters and ionospheric parameters.

The dayside magnetosphere contains a region where the field strength has a local maximum. This region, located just inside the magnetopause around the equatorial plane and between the cusps, has a width of 2-3Re. When a drift shell with a sufficiently small mirror field intersects this region, it will bifurcate into two branches near local noon, each branch going across one cusp and joining together at the symmetrical local time. The particle then drifts around the Earth over a single branch until it comes back to local noon.

In the neighborhood of the bifurcation points, the bounce period tends to infinity, and thus the adiabaticity of the bounce motion is broken there, but not elsewhere. This breaking causes a small but finite jump ∆I in the second invariant. Repeated crossings lead to a random walk in second invariant space, and thus to radial diffusion.
We use theory and simulations to determine the magnitude of ∆I. Our study is limited to static magnetic fields, but it can be extended to general fields.

Our results indicate that ∆I is sensitively dependent on bounce phase at bifurcation, and it can grow significantly for some initial conditions. When the initial second invariant I_0 is much larger than the mirror gyroradius ρ_m , we use separatrix crossing
theory. The average of ∆I over bounce phases is zero, and the rms ∆I is of the order of ρ_m . When I_0 is comparable to ρ_m , the equation of bounce motion is approximated as the second Painlevé equation, whose asymptotic solutions are used to determine ∆I. In this limit, the rms ∆I is still O(ρ_m); however, the average is nonzero, in the form exp(−I 0 /ρ m ).

Drift-shell bifurcation leads to significant radial diffusion. For MeV electrons, the diffusion coefficient can be several R_e per day. Also, because of bifurcation, some quasitrapped particles can remain in the magnetosphere for a finite number of drifts before they leave permanently. Such behavior leads to metastable particles, a new
kind of trapping. These results can be useful for radiation-belt modeling efforts.

VERY MUCH A PRECURSOR TO THE 3 DAYS OF DARKNESS EVENT – LETTING US KNOW THAT IT IS A GOOD THING THAT WE DESIGNED FOR THIS TIME.  A CLEANSING PULSE – THE EVENT IS MEANT TO CLEAR ALL OF THE PLASTIC OUT OF THE OCEANS, RETURN THE ENTIRE PLANET TO PRISTINE, RETURN ALL PEOPLE TO THEIR 20 YEAR OLD PRISTINE BODIES AND CAUSE MOST FEARFUL BEINGS TO PERISH OF THEIR OWN ACCORD, WHICH HAPPENS AROUND THE ORGANMIC BUBBLE NOW.

Abstract Unshielded magnetic tunnel junction (MTJ) sensors stabilized by insulating hard magnetic tails have been fabricated. Testing results showed that the control of oxidation condition was important for obtaining MTJ with low junction resistances and high TMR ...

Episodes of southward (Bz<0) interplanetary magnetic field (IMF) which lead to disturbed geomagnetic conditions are associated either with coronal mass ejections (CMEs) and possess long and continuous negative IMF Bz excursions, or with high speed solar wind streams (HSS) whose geoeffectiveness is due to IMF Bz profiles fluctuating about zero with various amplitudes and duration. We simulate ring current evolution during a HSS-driven storm that occurred during 24-26 October 2002 and compare its dynamics with a CME-driven storm of similar strength during 22-23 April 2001. We use our kinetic ring current-atmosphere interactions model (RAM), and investigate the mechanisms responsible for trapping particles and for causing their loss. Ring current evolution depends on the interplay of time-dependent inflow of plasma from the magnetotail, particle acceleration and loss (mainly due to charge exchange) along adiabatic drift paths, and outflow of plasma from the dayside magnetopause; all of these processes are incorporated in our model. We compare results from simulations using a newly developed, Cluster data based, University of New Hampshire inner magnetospheric electric field (UNH-IMEF) convection model with simulations using a Volland-Stern (V-S) type convection model. We find that, first, periods of increased magnetospheric convection coinciding with enhancements of plasma sheet density are needed for strong ring current buildup. Second, during the HSS-driven storm the convection potential from UNH-IMEF model is highly variable and causes sporadic shallow injections resulting in a weak ring current. The long period of enhanced convection during the CME-driven storm causes a continuous ion injection penetrating to lower L shells and stronger ring current buildup. V-S model predicts larger ring current injection during both storms. Third, the RAM driven by either convection model underestimates the total ring current energy during the recovery phase of the HSS storm, thus indicating that additional injections from substorm-induced electric fields and/or radial diffusion are needed to better reproduce its several-day long geomagnetic activity.

Thumbnail link to Figure 1 Figure 1.(a) RPI plasmagram showing signal amplitude (dBnV/m) as a function of frequency and time delay expressed in terms of virtual range in units of Earth radius (RE). The local plasma and gyro resonances appear as vertical line segments, and ...

... Twisted magnet wire transmission lines using the wire size range from 4 to 44 can be realized with characteristic impedances ranging from 10 to 85 R. More practical examples would be a 50-a line made with a pair of number 40 wires and a 25,a line made with a pair of number ...

We have used a global model of the solar wind magnetosphere interaction to model the high latitude part of the external contributions to the geomagnetic field near the Earth. The model also provides corresponding values for the electric field. Geomagnetic quiet conditions were modeled to provide simulated external contributions relevant for internal field modeling. These have proven very valuable for