Modeling the contributions of ring, tail, and magnetopause currents to the corrected Dst index

Abstract

[1] We present a new semiempirical model describing the contributions of the ring, tail, and magnetopause currents to the Dcx index. We use the isotropic boundary (IB) location of energetic particles measured by the NOAA/POES satellites, as a proxy for the tail current strength. Using local linear regression, we derive the model parameters and their functional dependencies on solar wind and interplanetary magnetic field parameters and on IB latitude. The model gives the ring, tail, and magnetopause current contributions for the whole time interval 1999-2007, performing roughly equally well during all activity levels. We find that the coefficient of proportionality between the square root of solar wind pressure and the magnetopause current contribution is larger than in earlier estimates. Ring current decay time is found to decrease with increasing solar wind electric field and dynamic pressure. We estimate the average quiet time level of the combined ring and tail (magnetopause) current contributions to Dcx to be roughly −7 nT (+13 nT). The average tail current contribution is found to be about 34% of the Dcx index, which is somewhat larger than previous estimates based on smaller-intensity storms. For individual storms the tail current contribution can reach up to −160 nT (about 40%-60% of the pressure corrected Dcx). The present model agrees well with earlier results for individual storms based on detailed dynamical models of the magnetosphere. Our work demonstrates that the different current contributions to Dcx during both active and quiet time intervals can be reliably estimated using solar wind observations and isotropic boundary location.Citation: Asikainen, T., V. Maliniemi, and K. Mursula (2010), Modeling the contributions of ring, tail, and magnetopause currents to the corrected Dst index,

The Role of Current Sheet Scattering in the Proton Isotropic Boundary Formation During Geomagnetic Storms

“…To quantify the magnetospheric response to the storm, we use the Sym-H, Kp, and AL indices. The latitude of the IB has been found to be sensitive to all three of Sym-H (e.g., Asikainen et al, 2010;Dubyagin et al, 2013Dubyagin et al, , 2018Ganushkina et al, 2005;Hauge & Söraas, 1975;Lvova et al, 2005;Søraas, 1972;Søraas et al, 2002), Kp (e.g., Søraas, 1972;Sergeev et al, 1993;Yue et al, 2014), and AL (e.g., Dubyagin et al, 2013;Lvova et al, 2005;Søraas, 1972).…”

“…Current sheet scattering (CSS) refers to a process in which particles undergo chaotic motion upon crossing the current sheet, resulting in changes to the particles' pitch angles (Büchner & Zelenyi, 1987;Sergeev et al, 1993;West et al, 1978). This occurs when the radius of curvature, R c , and the effective particle gyroradius, r g , become comparable to each other, resulting in a violation of the first adiabatic invariant (Alfvén & Fälthammar, 1963;Büchner & Zelenyi, 1987;Delcourt et al, 1996;Tsyganenko, 1982). The second mechanism that has been proposed for IB formation is the scattering of particles by electromagnetic ion cyclotron (EMIC) waves, in which plasma waves having oscillations near the particle gyrofrequency result in a violation of the first adiabatic invariant (Kennel & Petschek, 1966;Liang et al, 2014;Sergeev, Chernyaeva, Angelopoulos, et al, 2015;Sergeev, Chernyaeva, Apatenkov, et al 2015).…”

Thermospheric Density and Wind Determination from Satellite Dynamics

“…See, for example, Campbell [1996], Troshichev et al [2006], Asikainen et al [2010] and references therein. These two indices are available at an hourly or higher rate and therefore offer improved temporal resolution compared to the 3-hourly K-derived indices.…”

Influence of the interplanetary driver type on the durations of the main and recovery phases of magnetic storms

“…The Dst index is usually used as a proxy of the dynamics of magnetic storms, and is calculated as an average of the variations of the horizontal magnetic field component measured at four ground low-latitude stations [Sugiura, 1964;Sugiura and Kamei, 1991]. Although the ring current is the main source of Dst variations, the Dst index can contain significant contributions from other magnetospheric currents as well (e.g., magnetopause current and tail current) [see, e.g., Turner et al, 2000;Asikainen et al, 2010]. The contribution of the magnetopause current to the Dst index may be removed by using the so-called solar wind pressure-corrected Dst * index [Burton et al, 1975].…”