Thermospheric and geomagnetic responses to interplanetary coronal mass ejections observed by ACE and GRACE: Statistical results

Abstract

For the period July 2003 to August 2010, the interplanetary coronal mass ejection (ICME) catalogue maintained by Richardson and Cane lists 106 Earth‐directed events, which have been measured in situ by plasma and field instruments on board the ACE satellite. We present a statistical investigation of the Earth's thermospheric neutral density response by means of accelerometer measurements collected by the Gravity Recovery And Climate Experiment (GRACE) satellites, which are available for 104 ICMEs in the data set, and its relation to various geomagnetic indices and characteristic ICME parameters such as the impact speed ( vmax), southward magnetic field strength (Bz). The majority of ICMEs causes a distinct density enhancement in the thermosphere, with up to a factor of 8 compared to the preevent level. We find high correlations between ICME Bz and thermospheric density enhancements (≈0.9), while the correlation with the ICME impact speed is somewhat smaller (≈0.7). The geomagnetic indices revealing the highest correlations are Dst and SYM‐H(≈0.9); the lowest correlations are obtained for Kp and AE (≈0.7), which show a nonlinear relation with the thermospheric density enhancements. Separating the response for the shock‐sheath region and the magnetic structure of the ICME, we find that the Dst and SYM‐H reveal a tighter relation to the Bz minimum in the magnetic structure of the ICME, whereas the polar cap indices show higher correlations with the Bz minimum in the shock‐sheath region. Since the strength of the Bz component—either in the sheath or in the magnetic structure of the ICME—is highly correlated (≈0.9) with the neutral density enhancement, we discuss the possibility of satellite orbital decay estimates based on magnetic field measurements at L1, i.e., before the ICME hits the Earth magnetosphere. These results are expected to further stimulate progress in space weather understanding and applications regarding satellite operations.

Coronal mass ejections and their sheath regions in interplanetary space

“…For example, CHAMP observations have shown significant changes in response of atmospheric densities to ICMEs (Forbes et al 2005). Recently, Krauss et al (2015) made a statistical analysis of the thermospheric neutral density content during ICME impacts. The authors found significant density enhancements, up to a factor of eight, as a response to ICMEs and a strong correlation with the magnitude of the enhancement and the magnitude of the southward magnetic field in the ICME.…”

Reação da termosfera a tempestades geomagnéticas

“…plo, os efeitos causados por interações de estruturas magnéticas de CMEs com a magnetosfera (início da fase principal de tempestade) são mais intensos do que os efeitos causados pelo impacto de CMEs com a magnetosfera (compressão) [51,52].…”

“…Por exemplo, como mostra a equação (1), a densidade de partículas neutraś e proporcionalà aceleração de arrasto do satélite. Utilizando equações para o eixo maior de trajetórias elípticas de satélitesé possível se estimar suas acelerações de arrasto e seu decaimento orbital através da densidade de partículas neutras [52]. Fig.…”

Kinematical properties of coronal mass ejections

“…Together with their embedded magnetic field (magnetized plasma clouds) and shocks ahead, CMEs propagate into interplanetary (IP) space with velocities of a few hundred to a few thousand km/s (e.g., Yashiro et al 2004) and may cause severe space weather effects when interacting with the Earth's magnetic field (see e.g., Pulkkinen 2007;Schwenn 2006, and references therein). Even thermospheric responses in terms of a neutral density increase are observed due to CME-Earth interactions (e.g., Guo et al 2010;Krauss et al 2015). The transit times to reach a distance of 1 AU is of about one to five days, and depends on the CME's initial velocity, size, and mass, as well as on the Corresponding author: manuela.temmer@uni-graz.at conditions of the ambient solar wind flow in IP space (see e.g., Bothmer & Daglis 2007).…”