• Title/Summary/Keyword: solar wind dynamic pressure

Search Result 15, Processing Time 0.178 seconds

Geosynchronous Magnetic Field Response to Solar Wind Dynamic Pressure

  • Park, Jong-Sun;Kim, Khan-Hyuk;Lee, Dong-Hun;Lee, En-Sang;Jin, Ho
    • Journal of Astronomy and Space Sciences
    • /
    • v.28 no.1
    • /
    • pp.27-36
    • /
    • 2011
  • The present study examines the morning-afternoon asymmetry of the geosynchronous magnetic field strength on the dayside (magnetic local time [MLT] = 06:00~18:00) using observations by the Geostationary Operational Environmental Satellites (GOES) over a period of 9 years from February 1998 to January 2007. During geomagnetically quiet time (Kp < 3), we observed that a peak of the magnetic field strength is skewed toward the earlier local times (11:07~11:37 MLT) with respect to local noon and that the geosynchronous field strength is larger in the morning sector than in the afternoon sector. That is, there is the morning-afternoon asymmetry of the geosynchronous magnetic field strength. Using solar wind data, it is confirmed that the morning-afternoon asymmetry is not associated with the aberration effect due to the orbital motion of the Earth about the Sun. We found that the peak location of the magnetic field strength is shifted toward the earlier local times as the ratio of the magnetic field strength at MLT = 18 (B-dusk) to the magnetic field strength at MLT = 06 (B-dawn) is decreasing. It is also found that the dawn-dusk magnetic field median ratio, B-dusk/B-dawn, is decreasing as the solar wind dynamic pressure is increasing. The morning-afternoon asymmetry of the magnetic field strength appears in Tsyganenko geomagnetic field model (TS-04 model) when the partial ring current is included in TS-04 model. Unlike our observations, however, TS-04 model shows that the peak location of the magnetic field strength is shifted toward local noon as the solar wind dynamic pressure grows in magnitude. This may be due to that the symmetric magnetic field associated with the magnetopause current, strongly affected by the solar wind dynamic pressure, increases. However, the partial ring current is not affected as much as the magnetopause current by the solar wind dynamic pressure in TS-04 model. Thus, our observations suggest that the contribution of the partial ring current at geosynchronous orbit is much larger than that expected from TS-04 model as the solar wind dynamic pressure increases.

Solar Wind Dynamic Pressure during Magnetic Storms and its implications on the Dayside Ring Current Particle Loss

  • Kim, Kyungchan;Lee, Dae-Young
    • Bulletin of the Korean Space Science Society
    • /
    • /
    • pp.39-39
    • /
    • 2004
  • It has been known that ring current particles can be lost through dayside MP(magnetopause). However, details of the loss mechanism of this process has not received much attention. In this study, we show that the solar wind dynamic pressure P$\sub$D/ can play a significant role in the dayside loss. In order to show that, we have first conducted superposed epoch analysis using 95 geomagnetic storm events selected from the period 1997 to 2002. (omitted)

  • PDF

Statistical study of solar wind dynamic pressure enhancements during geomagnetic storms: Preliminary results

  • Baek, Ji-Hye;Lee, Dae-Young
    • Bulletin of the Korean Space Science Society
    • /
    • /
    • pp.93-93
    • /
    • 2004
  • We have examined the solar wind dynamic pressure enhancements during geomagnetic storm main phase. The Dst index has been used to identify more than 100 geomagnetic storms which occurred in the time interval of 1997 to 2001. We have selected only the events having the minimum Dst value less than -50 nT. In order to identify the pressure impact, we have looked at the low latitude ground H data as well as the solar wind pressure data themselves. (omitted)

  • PDF

Response of the Poleward Boundary of the Nightside Auroral Oval to Impacts of Solar Wind Dynamic Pressure Enhancement

  • Cho, Joon-Sik;Lee, Dae-Young;Kim, Kyung-Chan;Lee, Ji-Hee
    • Journal of Astronomy and Space Sciences
    • /
    • v.27 no.3
    • /
    • pp.189-194
    • /
    • 2010
  • In this paper we have investigated latitudinal variations of the poleward boundary of the nightside auroral oval when the magnetosphere is hit by an enhanced solar wind dynamic pressure front. We used precipitating particle data obtained from Defense Meteorological Satellite Program satellites to identify the locations of the boundary before and after enhanced pressure impacts. The boundary locations are represented by a parameter called "b5e". After performing the analysis for a number of events, we found that the basic effect of the solar wind pressure increase impact is often (but not always) to move the poleward boundary of the nightside auroral oval poleward. However, this effect can be often modified by other factors, such as simultaneous variations of the interplanetary magnetic field with a pressure increase, and thus the boundary response is not necessarily a poleward shift in many cases. We demonstrate this with specific examples, and discuss other possible complicating factors.

Statistical Characteristics of Solar Wind Dynamic Pressure Enhancements During Geomagnetic Storms

  • Choi, C.R.;Kim, K.C.;Lee, D.Y.;Kim, J.H.;Lee, E.
    • Journal of Astronomy and Space Sciences
    • /
    • v.25 no.2
    • /
    • pp.113-128
    • /
    • 2008
  • Solar wind dynamic pressure enhancements are known to cause various types of disturbances to the magnetosphere. In particular, dynamic pressure enhancements may affect the evolution of magnetic storms when they occur during storm times. In this paper, we have investigated the statistical significance and features of dynamic pressure enhancements during magnetic storm times. For the investigation, we have used a total of 91 geomagnetic storms for 2001-2003, for which the Dst minimum $(Dst_{min})$ is below -50 nT. Also, we have imposed a set of selection criteria for a pressure enhancement to be considered an event: The main selection criterion is that the pressure increases by ${\geq}50%\;or\;{\geq}3nPa$ within 30 min and remains to be elevated for 10 min or longer. For our statistical analysis, we define the storm time to be the interval from the main Dst decrease, through $Dst_{min}$, to the point where the Dst index recovers by 50%. Our main results are summarized as follows. $(i){\sim}$ 81% of the studied storms indicate at least one event of pressure enhancements. When averaged over all the 91 storms, the occurrence rate is ${\sim}$ 4.5 pressure enhancement events per storm and ${\sim}$ 0.15 pressure enhancement events per hour. (ii) The occurrence rate of the pressure enhancements is about three times higher for CME-driven storm times than for CIR-driven storm times. (iii) Only 21.1% of the pressure enhancements show a clear association with an interplanetary shock. (iv) A large number of the pressure enhancement events are accompanied with a simultaneous change of IMF $B_y$ and/or $B_z$: For example, 73.5% of the pressure enhancement events are associated with an IMF change of either $|{\Delta}B_z|>2nT\;or\;|{\Delta}B_y|>2nT$. This last finding suggests that one should consider possible interplay effects between the simultaneous pressure and IMF changes in many situations.

VARIABILITY OF BOW SHOCK LOCATION AT MARS

  • Yi, Yu;Kim, Eo-Jin;Kim, Yong-Ha;Kim, Jhoon
    • Journal of Astronomy and Space Sciences
    • /
    • v.16 no.2
    • /
    • pp.139-148
    • /
    • 1999
  • Bow shock formation, in case the supersonic solar wind flow is hindered by the atmosphere of Mars, is investigated. The atoms newly ionized from the extensive neutral atmosphere of Mars are loaded to the solar wind. By the conservation of momentum, the solar wind velocity is decreased. Then the supersonic flow velocity drops to the subsonic flow velocity in front of Mars at certain region, which is called the bow shock. The location of Mars subsolar bow shock is highly varying in the range of 1.3 to 2.5 Rm. Martian bow shock location is estimated by one-dimensional flux tube equations reduced from full three-dimensional MHD equations. The variability of Mars bow shock location effected by the solar wind conditions is studied. It is evident that the solar wind dynamic pressure change is able to make the Mars bow shock location variable.

  • PDF

Pc1/EMIC waves observed at subauroral latitude during sudden magnetospheric compressions

  • Kim, Khan-Hyuk;Shiokawa, Kazuo;Lee, Dong-Hun;Kwon, Hyuck-Jin;Lee, Ensang
    • The Bulletin of The Korean Astronomical Society
    • /
    • v.37 no.2
    • /
    • pp.117.2-117.2
    • /
    • 2012
  • It is generally accepted that sudden compressions of the magnetosphere cause electromagnetic ion cyclotron (EMIC) wave growth by increasing the proton temperature anisotropy. These compression-associated EMIC waves are expected to be on higher latitudes (i.e., higher-L regions close to the magnetopause). In this study we examine Pc1 pulsations, which are believed to be generated by the EMIC instability, observed at subauroral latitude near the nominal plasmapause when the magnetosphere is suddenly compressed by solar wind dynamic pressure variations, using induction magnetometer data obtained from Athabasca, Canada (geomagnetic latitude = 61.7 N, L ~ 4.5). We identified 9 compression-associated Pc1 waves with frequencies of ~0.5-2.0 Hz. The wave activity appears in the horizontal H (positive north) and D (positive eastward) components. All of events show low coherence between H and D components. This indicates that the Pc1 pulsations in H and D oscillate with a different frequency. Thus, we cannot determine the polarization state of the waves. We will discuss the occurrence location of compression-associated Pc1 pulsations, their spectral structure, and wave properties.

  • PDF