Geosynchronous magnetic field response to solar wind dynamic pressure pulse

Abstract

We present a study of the response of the geosynchronous magnetic field to abrupt enhancements of the solar wind dynamic pressure. Results are obtained separately for cases of northward and southward interplanetary magnetic field (IMF) prior to and after the solar wind pressure jump. For pressure enhancements with southward IMF we find that the response of the geosynchronous magnetic field on the dayside is mostly compression. However, on the nightside it can be a dipolarization‐like change that is similar to that which occurs during substorms. We report four events showing the dipolarization‐like response on the nightside. Analysis using low‐latitude geomagnetic data as well as the geosynchronous energetic particle flux data leads us to argue that this dipolarization is part of the global disturbance directly driven by the solar wind pressure enhancement. We also find that the nightside magnetosphere is remarkably sensitive to small solar wind dynamic pressure enhancements when the IMF is strongly southward (i.e., Bz is below ∼−10 nT). For northward IMF, solar wind pressure enhancements generally lead to magnetic compression, with a few cases of depression on the nightside, neither of which is a dipolarization‐like response. The compression is strongest near noon, decreases toward dawn and dusk, and increases with the amount of increase in dynamic pressure.

Effect of solar wind pressure enhancements on storm time ring current asymmetry

“…In recent years, much work has been done on how pressure enhancements influence aurora activity Kamide, 1998, 2001;Zhou and Tsurutani, 1999;Lyons et al, 2000;Zesta et al, 2000;Chua et al, 2001;Boudouridis et al, 2003]. Also, some authors investigated its effect on the geosynchronous magnetic field [Wing et al, 2002;Lee and Lyons, 2004]. However, the effect of the solar wind dynamic pressure on the development of the storm time ring current has received almost no attention until the recent work by Wang et al [2003].…”

Sudden Impulses in the Magnetosphere and at Ground

“…Consistently, Wang et al (2007) concluded that the IMF orientation does not affect the geosynchronous response significantly (see also Figure 2a). Kuwashima and Fukunishi (1985) and, more recently, Lee and Lyons (2004) suggested that midnight events associated with southward IMF orientations were often characterized by a dipolarization-like change similar to that one occurring during substorms, while the dayside response was mostly compressional; for northward IMF, a compression of the entire magnetosphere was generally observed, with few cases of depression near midnight. Lee and Lyons (2004) suggested that the magnetosphere is very sensitive to small SW pressure enhancements when the IMF is strongly southward for a long period of time.…”

“…Kuwashima and Fukunishi (1985) and, more recently, Lee and Lyons (2004) suggested that midnight events associated with southward IMF orientations were often characterized by a dipolarization-like change similar to that one occurring during substorms, while the dayside response was mostly compressional; for northward IMF, a compression of the entire magnetosphere was generally observed, with few cases of depression near midnight. Lee and Lyons (2004) suggested that the magnetosphere is very sensitive to small SW pressure enhancements when the IMF is strongly southward for a long period of time. Focusing attention on the midnight sector, Wang et al (2009) concluded that ≈75% of the negative responses were associated with southward IMF orientations.…”

“…Kokubun (1983) and Kuwashima and Fukunishi (1985) found that the magnetospheric change had highest values at local noon and very small values, or even negative, near midnight. More recently, Lee and Lyons (2004) concluded that SW pressure enhancements generally lead to a magnetospheric compression at all time sectors (with few exceptions in the nightside): it is strongest near noon and decreases toward dawn and dusk. Borodkova et al (2005Borodkova et al ( , 2006 found that, in general, the changes of the SW pressure (positive and negative) were associated with corresponding variations of the magnetospheric field; they also remarked that all the events without an explicit response were located either before 7:30 LT or after 16:30 LT. Wang et al (2007) confirmed that the field variation peaked near local noon and decreased toward dawn and dusk.…”

Geosynchronous magnetic field responses to fast solar wind dynamic pressure enhancements: MHD field model

“…It is noted that although PE serves as a good metric when the magnetic field has large variations, such as the ground and geosynchronous magnetic field variations during storms (e.g., Pulkkinen et al, 2010), it tends to exaggerate a small inconsistency if the field responses (the denominator) are weak. Usually, B responds more apparently near noon (typically tens of nT) than in the nightside (usually several nT) (Lee and Lyons, 2004), and the variations of the smaller components (B x and B y ) are weaker. Therefore, PE might have some limitations in validating the model responses around the mid-night and for the minor components.…”