Wyniki wyszukiwania - BazTech

1

Does the interstellar bow shock exist around the heliosphere?

Ratkiewicz R., Kotlarz J.

Prace Instytutu Lotnictwa

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2016

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Nr 4 (245)

178--188

EN

The paper discusses results of global modeling of the heliosphere regarding the existence of the interstellar bow shock (BS) in front of the heliosphere. The Local Interstellar Medium (LISM) velocity vector (VIS) and temperature (TIS) originally determined through the velocity and temperature of the interstellar helium (He) flowing in the inner heliosphere and measured by the GAS instrument on Ulysses, recently have been challenged by new measurements of the He flow by the Interstellar Boundary Explorer (IBEX). These measurements have initiated discussions on the existence of the BS. The purpose of this paper is a brief overview of studies focusing on in situ measurements of the He flow by the instruments on Ulysses and IBEX missions and indication of the reasons for discrepancies created in the past few years and associated with the existence of the BS.

PL

W pracy przedyskutowano wyniki globalnego modelowania heliosfery dotyczące istnienia czołowej fali uderzeniowej (BS) przed heliosferą. Wektor prędkości (VIS) i temperatura (TIS) lokalnej materii międzygwiazdowej (LISM) oryginalnie wyznaczone przez prędkość i temperaturę międzygwiazdowego helu (He) wpływającego do heliosfery i mierzonego przez przyrząd GAS na sondzie Ulysses, ostatnio zostały zakwestionowane przez nowe pomiary przepływu He wykonane przez sondę Interstellar Boundary Explorer (IBEX). Pomiary te zainicjowały dyskusję na temat istnienia BS. Celem niniejszego artykułu jest krótki przegląd badań poświęconych pomiarom in situ strumienia helu przez instrumenty na sondach Ulysses i IBEX oraz wskazanie przyczyn rozbieżności związanych z istnieniem czołowej fali uderzeniowej powstałych wciągu kilku ostatnich lat [51].

2

Low ram pressure of the solar wind and the heliosphere: comparison of global modeling results with Voyager and IBEX observations

Ratkiewicz R., Strumik M.

Prace Instytutu Lotnictwa

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2015

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Nr 2 (239)

42--52

EN

We discuss results of global modeling of the heliosphere for low ram pressure of the solar wind. A quasi-stationary approach is used to simulate interaction of the solar wind and the interstellar medium for exceptionally deep recent solar minimum. It is shown that the global model may potentially explain the heliopause position strongly shifted towards the Sun. A comparison of the model results with available observations of the Voyager and IBEX spacecraft is presented.

PL

Dyskutujemy wyniki globalnego modelowania heliosfery dla przypadku niskiego ciśnienia dynamicznego wiatru słonecznego. W celu przeprowadzenia symulacji oddziaływania wiatru słonecznego z materią miedzygwiazdową dla wyjątkowo głębokiego ostatniego minimum słonecznego stosujemy quasi-stacjonarne podejście. Pokazujemy, że model globalny może potencjalnie wyjaśnić mocno przesuniętą w stronę Słońca heliopauzę. Wyniki modelu są porównane z dostępnymi obserwacjami misji Voyager i IBEX.

3

On ionospheric phenomena during pre-storm and main phase of a very intense geomagnetic storm

Chukwuma V.U.

Acta Geophysica

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2010

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Vol. 58, no. 6

1164-1192

EN

An investigation to elucidate the mechanisms responsible for the pre-storm and main phase ionospheric phenomena during November 20- 21, 2003, is presented using heliophysical, interplanetary, geomagnetic, and global ionospheric data. The results show that the ionospheric responses in the main phase do not indicate prompt penetration electric fields as the main ionospheric driver. The results also show that the prestorm phenomena do not originate from a local time effect. The simultaneous occurrence of foF2 enhancements at two widely separated longitudinal zones appeared to suggest a role played by the magnetospheric electric field. However, the analysis of hmF2 at the stations could not confirm the notion that these fields are the main drivers of pre-storm phenomena. An investigation of flare effects on the pre-storm phenomena also revealed that solar flares are not the main drivers. The present results appear to suggest that the pre-storm ionospheric phenomena could be a result of some underlying mechanisms that are working together with varying degree of importance.

4

ULF wave indices to characterize the solar wind-magnetosphere interaction and relativistic electron dynamics

Romanova N., Pilipenko V.

Acta Geophysica

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2009

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Vol. 57, no. 1

158-170

EN

To quantify the level of low-frequency wave activity of the magnetosphere and IMF, a set of the ULF wave power indices has been introduced. We demonstrate that the ULF activity global level can be very useful in space weather related problems. The application of the interplanetary index to an analysis of auroral activity driving has shown that a turbulent IMF drives auroral activity more strongly than the laminar solar wind does. The enhancements of relativistic electrons at the geosynchronous orbit are known not to be directly related to the intensity of magnetic storms. We found that the electron dynamics correlated well with long-lasting intervals of elevated ground ULF wave index. This fact confirms the importance of magnetospheric ULF turbulence in energizing electrons up to relativistic energies. The time-integrated ULF index demonstrates a significantly higher correlation with electron fluxes, which implies the occurrence of a cumulative effect in the electron energization.

5

Investigating dynamic coupling in geospace through the combined use of modeling, simulations and data analysis

Daglis I., Balasis G., Ganushkina N., Metallinou F-A., Palmroth M., Pirjola R., Tsagouri I.

Acta Geophysica

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2009

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Vol. 57, no. 1

141-157

EN

Comprehensive understanding of the dynamics of the coupled solar wind-magnetosphere-ionosphere system is of utmost interest, both from the perspective of solar system astrophysics and geophysics research and from the perspective of space applications. The physical processes involved in the dynamical evolution of this complex coupled system are pertinent not only for the Sun-Earth connection, but also for major phenomena in other astrophysical systems. Furthermore, the conditions in geospace collectively termed space weather affect the ever increasing technological assets of mankind in space and therefore need to be understood, quantified and efficiently forecasted. The present collaborative paper communicates recent advances in geospace dynamic coupling research through modeling, simulations and data analysis and discusses future directions.

6

ANN forecast of hourly averaged AE index based on L1 IMF and plasma measurements

Amata E., Consolini G., Pallocchia G., Mercucci M.

Acta Geophysica

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2009

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Vol. 57, no. 1

185-196

EN

The AE index has two components: one driven by the solar wind and one related to the magnetotail unloading process. We recall some past findings on this issue and present a new ANN algorithm for the AE forecasting at 5 and 60 min time scales, built by adding to a previous algorithm a further layer with a hyperbolic tangent transfer function and two more inputs, the output at time t and the difference between the input at time t and the output at time t - 1. We show that, at the 60 min time scale and for AE > 400 nT, the new algorithm performs better than the former one, while no improvement is obtained at the 5 min time scale. This result confirms that the AE component driven by the solar wind can be forecast, at least partially, while the unloading component may not be reproduced from solar wind inputs.

7

On the geomagnetic and ionospheric responses to an intense storm associated with weak IMF Bz and high solar wind dynamic pressure

Chukwuma V.U.

Acta Geophysica

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2007

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Vol. 55, no. 4

469-489

EN

A study of the geomagnetic storm of July 13-14, 1982, and its ionospheric response is presented using the low-latitude magnetic index, Dst, and interpreted using solar wind interplanetary data: proton number density, solar wind flow speed, interplanetary magnetic field southward component BZ, and solar wind dynamic pressure. The F2 region structure response to the geomagnetic storm was studied using foF2 data obtained during the storm from a network of various ionosonde stations. Our results appear to show simultaneous abrupt depletion of foF2 that occurred at all latitudes in both the East Asian and African/European longitudinal zone during the period: 18:00–19:00 UT on July 13 and is as result of an abrupt in-crease in the dynamic pressure between 16:00 and 17:00 UT. The dynamic pressure increased from 3.21 to 28.07 nPa within an hour. The aforementioned abrupt depletion of foF2 simultaneously resulted in an intense negative storm with peak depletion of foF2 at about 19:00 at all the stations in the East Asian longitudinal zone. In the African/European longitudinal zone, this simultaneous abrupt depletion of foF2 resulted in intense negative storm that occurred simultaneously at the low latitude stations with peak depletion at about 20:00 UT on July 13, while the resulting negative storm at the mid latitude stations recorded peak depletion of foF2 simultaneously at about 2:00 UT on July 14. The present results indicate that most of the stations in the three longitudinal zones showed some level of simultaneity in the depletion of foF2 between 18:00 UT on July 13 and 2:00 UT on July 14. The depletion of foF2 during the main phase of the storm was especially strongly dependent on the solar wind dynamic pressure.

8

Interplanetary phenomenon, geomagnetic and ionospheric response associated with the storm of October 20-21, 1989

Chukwuma V.

Acta Geophysica Polonica

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2003

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Vol. 51, nr 4

549-472

EN

Recent results of the study of March 13-14, 1989, geomagnetic (Dst=-600nT) show that the depletion of foF2 was simultaneously worldwide and extended to very low latitudes. These results appear to indicate that during intense storms there are no distinct local time variations of ionospheric storm effects. Presently, the F2 region global structure response to another intense storm was studies as to confirm the earlier results. The investigation used measured parameters of solar wind plasma and imbedded IMF, and foF2 data obtained from a global network ionosondes. The results obtained from the analysis of the measured parameters of solar wind plasma, Dst and Ap data show that arrival of the shock in the interplanetary medium is indicated by increases in plasma density and velocity , and a large southward turning of Bz. In addition, Ap peak accompanies the beginning of a high-speed stream. The event of October 20-21, 1989, is a triple step storm. The analysis of the foF2 data shows that during the October 20-21 storm the depletion of foF2 was restricted to the high and middle latitudes. Although the depletion diminished in amplitude towards the lower latitude, the F2 region global structure response lacked simultaneity unlike the storm of March 13-14 in which the depletion of foF2 was extended to a latitude as low as 12.4N, and at the same time globally. The present results appear to confirm the suggestion of Chukwuma (2003) that the F2 region global structure response during the storm of March 13-14 may be due to the very intensive nature of that particular storm.

9

Two-Dimensional MHD Simulations of the Solar Wind Interaction with Comet Halley

Murawski K., Boice D. C., Huebner W. F., DeVore C. R.

Acta Astronomica

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1998

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Vol. 48, No. 4

803--817

EN

Numerical simulations are performed in the framework of nonlinear two-dimensional magnetohydrodynamics to investigate the solar wind interaction with Comet Halley at 0.83 a.u. corresponding to the Vega 2 encounter. The governing equations are solved by a flux corrected transport method. For a gas (water) production rate of 1030 molecules/sec, it was found that a weak bow shock is formed at about 0.5 million km upstream the comet nucleus while a contact surface and an inner shock are located at about 20 000 km in the subsolar direction from the nucleus. We also found an enhancement of the ion-mass density just inside the contact surface, at the position of the inner shock. The model reasonably reproduced the locations of the bow shock and the diamagnetic cavity that were observed by recent missions to Comet Halley.

10

Reflection Coefficient and Non-WKB Effects for Alfvén Waves Propagating in the Solar Wind

Krogulec M., Musielak Z. E.

Acta Astronomica

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1998

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Vol. 48, No. 1

77--90

EN

The propagation of Alfvén waves in spherically symmetric, isothermal solar wind models with two different temperatures T0=2.85×106 K and T0=8.2×105 K is considered. The steady-state Alfvén wave equations are solved numerically and the resulting reflection coefficient and non-WKB effects are calculated. The obtained results show that the reflection coefficient is practically zero in the high-temperature wind model, where wave reflection and non-WKB effects are essentially absent, and that it can also be zero in the low-temperature model, where wave reflection and non-WKB effects are present. A physical explanation of these results is given.