![]() An important question is whether the ring current also exhibits an explicit B y‐dependence. As the above recent studies indicate, understanding how IMF B y modulates the magnetospheric energetic particles and their precipitation into ionosphere are of key importance. The physical mechanism of the explicit B y‐effect is still not fully understood. Recent studies (Holappa et al., 2021 Weimer & Edwards, 2021) have indeed found a similar IMF B y‐dependence of ionospheric conductance, maximizing in the dawn sector. The B y‐dependence of electron precipitation implies a similar B y‐dependence of ionospheric conductance. This so‐called explicit B y‐dependence is especially strong in the AL index (measuring the westward electrojet), which is about 40% stronger for B y > 0 than for B y 30 keV) precipitating electrons in the dawn sector (measured by the National Oceanic and Atmospheric Administration (NOAA) Polar Operational Environmental satellites, POES) are modulated by IMF B y similarly as the westward electrojet (greater precipitation for B y 0 in NH winter). On dayside, the postnoon auroral bright spot is brighter for negative IMF B y than for positive IMF B y and the effect is reversed in the southern hemisphere (Liou & Mitchell, 2019) Also several studies (Friis‐Christensen et al., 1972, 2017 Holappa & Mursula, 2018 Murayama et al., 1980 Smith et al., 2017 Workayehu et al., 2021 Holappa et al., 2021) have shown that there is a strong IMF B y‐dependence in auroral currents which is not symmetric with the B y sign. For example, a negative IMF B y component results in larger nightside auroral intensity in the Northern Hemisphere (NH Liou et al., 1998 Shue et al., 2001) while the effect is reversed in the southern hemisphere (Liou & Mitchell, 2019). However, several magnetospheric and ionospheric phenomena are known to respond differently to positive and negative IMF B y. For example, all empirical solar wind coupling functions assume a symmetric dependence on IMF B y (Kan & Lee, 1979 Newell et al., 2007 Perreault & Akasofu, 1978). It is also known that IMF B y modulates the dayside reconnection rate by affecting, for example, the geometry of the merging line (Laitinen et al., 2007 Sonnerup, 1974 Trattner et al., 2012), its effect on the magnetospheric response is usually assumed to be symmetric with respect to its sign. The dawn‐dusk ( B y) component of IMF is also known play an important role, leading, for example, to a B y‐dependence of the ionospheric convection patterns (Cowley et al., 1991 Heppner & Maynard, 1987 Ruohoniemi & Greenwald, 2005 Thomas & Shepherd, 2018). ![]() The interaction between solar wind, interplanetary magnetic field (IMF) and the Earth's magnetic field is dominated by the north‐south ( B z) component of IMF, which is the most important driver of dayside reconnection (Dungey, 1961), and thus the energy input into the magnetosphere. Using satellite observations and a global magnetohydrodynamic model coupled with a ring current model, we show that for a fixed level of solar wind driving the flux of energetic magnetospheric protons and the growth-rate of the ring current are greater for B y B y > 0) than for B y > 0 (B y B y -effect is not yet fully understood, our results suggest that IMF B y modulates magnetospheric convection and plasma transport in the inner magnetosphere. Here we demonstrate for the first time a seasonally varying, explicit IMF B y -dependence of the ring current and Dst index. While the dawn-dusk (B y ) component of the IMF is also known to play an important role, its effects are usually assumed to be independent of its sign. The most important parameter driving the solar wind-magnetosphere interaction is the southward (B z ) component of the interplanetary magnetic field (IMF).
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |