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1

Peculiar features of some high-latitude magnetic impulse events

Kraiński W.

Acta Geophysica Polonica

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2003

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Vol. 51, nr 2

227-241

EN

Similarities and dissimilarities of magnetic impuels (MIE) recorded at the chain of six northernmost stations of IMAGE magnetometer array and visualized in forms of (a) stacked magnetograms, (b) sequences of equivalent overhead currents (OC) for these stations, and (c) sequences of elements of time-dependent covariance matrics (TCM) are analysed. Ad hoc MIE types - one "ordinary", and three "strange" - are discerned as a result of this analysis. The existence of these types, as well as of the MIE features not utilized to separate the types, leads to the conclusion that three is a great, hitherto depreciated influence of horizontal irregularities in ionospheric Hall (sigma)H and Pedersen (sigma)P integrated conductivities in the behaviour of geomagnetic phenomena of small and middle scale. One of these "strange" MIE types, for which a minimum in magnetic variations amplitude is visible at the station under the MIE's center trace, gets a simple explanation using the assumption of a small-scale irregularity of (sigma)H over this station and nearby area, when compared with other stations. Somewhat more complicated explanations will probably be needed for two other "strange" types. It seems, however, that they will also be possible using proper assumptions on distributions of (sigma)H and/or (sigma)P over the array of magnetometer stations. An additional substantial conclusion resulting from the evident great role of (sigma)H- irregularities is that the localization of MIE's (centers)according to maximum amplitude of magnetic variations, as done in some paper, may result in large errors.

2

Dependence of latitudes of high-latitude, forenoon, westward moving, isolated magnetic impulse events centres on season and Kp

Kraiński W.

Acta Geophysica Polonica

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2000

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Vol. 48, nr 4

479-488

EN

Data from meridional magnetometer chain of six northernmost stations of IMAGE magnetometer array are used to determine the dependence of magnetic latitudes of a subclass of magnetic impulse events (MIE) centres on season and magnetic activity. The events centres are defined, and their motion directions (east-or westward) are determined, using elements of covariance matrices of magnetic variations recorded on all magnetometers. The latitudes of centres of high-latitude, forenoon, westward moving, isolated MIEs are found to be contained in the range of latitudes of dayside area of central plasma sheet (CPS) and of boundary plasma sheet (BPS) and to decrease with increasing magnetic activity. In summer and for Kp = 0, these latitudes are the highest and their decreasing rate with increasing Kp is minimal, while in winter they are the lowest and the rate is maximal. For all seasons, this decreasing rate is less than the decreasing rate of the cusp latitude. In summer (on "summer-side" of the magnetosphere in solstices seasons), the loci of appearing MIEs are deep, well below the magnetopause layer for the activity interval 0 =< Kp =< 5. On the "winter-side" of the magnetosphere, MIEs can emerge near the magnetopause. Same relations are proposed for CPS' and BPS' dayside areas.

3

Small scale dayside magnetospheric convection observed from image magnetometer network data

Kraiński W.

Acta Geophysica Polonica

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1999

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Vol. 47, nr 2

215-222

EN

An exemplary analysis of a simple, modeled moving ionospheric current structure (ICS) is presented. Computed time series of magnetic field variations for several 'magnetometer stations' beneath the path of moving 'structure' are used to display and interpret the sequences of variation vectors and elements of time-dependent covariance matrices (TCM). Analogical analysis is performed for two cases of real magnetic pulsations recorded on 6 northen magnetometer stations from IMAGE network. The first of these cases reveals quite simple ICS related to a regular dual magnetospheric convection cell passing westward over the network. The other case, however, reveals some elements of more complicated ICS, where the motion of ICS (its part) was eastward over 3 northernmost stations, and ot was westward over 3 southern stations. This case is interpreted as the overlapping and carrying of a transient local disturbance in the magnetosphere with a greater scale and quasi-permanent convection structure in which the plasma moved eastward over northen stations, and westward over southern ones.