The response of ionospheric currents to different types of magnetospheric fast ﬂow bursts using THEMIS observations

. The magnetotail earthward fast ﬂow bursts can transport most of the magnetic ﬂux and energy into the inner magnetosphere. These fast ﬂow bursts are generally an order of magnitude higher than the typical convection speeds, that are azimuthally localized (1-3RE) and are ﬂanked by plasma vortices which map to ionospheric plasma vortices of the same sense of rotation. This 5 study uses multipoint analysis of conjugate magnetospheric and ionospheric observations to investigate the magnetospheric and ionospheric responses to the fast ﬂow bursts that are associated with both substorms and pseudobreakups. We study in detail what properties control the differences in the magnetosphere-ionosphere responses between substorm and pseudobreakup conditions, and how such differences lead to the different ionospheric responses. The fast ﬂow bursts and pseudobreakup events were observed by the Time History of Events and Macroscale Interaction during Substorms (THEMIS), when the satellites 10 were at least 6RE from the Earth in radial distance, and a magnetic local time (MLT) region of ± 5 hours from local midnight. The results show that the magnetosphere and ionosphere response to substorm fast ﬂow bursts are much stronger and more structured compared to pseudobreakups, which is more likely to be localized, transient, and weak in the magnetosphere. The magnetic ﬂux in the tail is much stronger for strong substorms and much weaker for pseudobreakup events. The B lobe decreases signiﬁcantly for substorm fast ﬂow bursts compared to pseudobreakup events. The curvature force density for pseudobreakups 15 are much smaller than substorm fast ﬂow events, indicating that the pseudobreakups may not be able to penetrate deep into the inner magnetosphere. This association can help us study the properties and activity of the magnetospheric earthward ﬂow vortices from ground data. The magnetosphere-ionosphere responses between substorm and non-substorm (pseudobreakups) conditions have been studied in the past (e.g., Ohtani et al. (1993); Koskinen et al. (1993); Nakamura et al. (1994); Baumjohann et al. (1989); Baumjohann et al. (2010)). They have concluded that substorms and pseudobreakups have common responses (e.g., fast ﬂows, dipolariza- 60 tions, injections, electrojet and current wedge) without phenomenological differences. The differences between substorms and pseudobreakups are thought to be the strength, scale size and duration of activity; substorms have stronger and global activity but non-substorm conditions have weaker and localised activity. It has been shown that the substorm-time ionospheric currents have clockwise and counter-clockwise vortices Keiling et al. (2009) that are connected to plasma ﬂow vortices in the magnetosphere Akasofu (1976); Borovsky and Bonnell (2001). However, there are limited direct observational evidence of this 65 connection largely due to the difﬁculty of ﬁnding conjunctions. Keiling2009 performed a multipoint analysis of conjugate magnetospheric and ionospheric ﬂow vortices for a single substorm related fast ﬂow bursts to show that the equivalent ionospheric currents (EIC) vortices were directly driven by the vortices observed in the magnetosphere. This study uses multipoint analysis of conjugate magnetospheric and ionospheric observations to investigate the magnetospheric and ionospheric responses to fast ﬂow bursts that are associated to both substorms and pseudobreakups. 70 In this study, we look into what properties control the differences in the magnetosphere-ionosphere responses between substorm and pseudobreakup conditions, and how such differences lead to the different ionospheric responses. We analyze the Time History of Events and Macroscale Interaction during Substorms (THEMIS) observations and select 3 pairs of fast ﬂow and pseudobreakup events that were observed by all 3 inner THEMIS satellites (THEMIS A, D, and E) the This analyzes the EICs during conjunctions with satellites for the selected fast ﬂow cases. ﬂux The 75 keV, 150 keV, 275 keV, and 475 keV and has nine telescopes pointing in different directions. This study how electron ﬂux data to different fast ﬂow bursts. observations were used to investigate the magnetospheric and ionospheric responses to substorm fast ﬂow bursts and pseudobreakup events. The 3 inner THEMIS spacecraft (THEMIS A, D, and E) in situ measurements of THEMIS observations were used to select 3 pairs of fast ﬂow bursts associated with substorm and pseudobreakup events. These fast ﬂow bursts were observed during close separations on the night 235 side, beyond 6RE from the Earth in radial distance, and a magnetic local time (MLT) region of ± 5 hours from local midnight. We studied in detail the magnetospheric and ionospheric response to each substorm fast ﬂow burst and pseudobreakup event to understand what properties control the differences in the magnetosphere-ionosphere responses between substorm and pseudobreakup conditions, and how such differences lead to the different ionospheric responses. The results show that ionospheric currents respond to both substorm fast ﬂow bursts and pseudobreakup events, indicating 240 that the ionosphere currents are created by plasma ﬂow vortices in the magnetosphere for fast ﬂow bursts that are associated with substorms and pseudobreakup events. The magnetic ﬂux in the tail is much stronger for strong substorms and much weaker for pseudobreakup events. The B lobe decreases signiﬁcantly (by up to 40 % ) for substorm fast ﬂow bursts, but much smaller decrease in B lobe for pseudobreakup events. The curvature force density for pseudobreakups are much smaller than substorm fast ﬂow events, indicating that the pseudobreakups may not be able to penetrate deep into the inner magnetosphere. 245

The magnetosphere-ionosphere responses between substorm and non-substorm (pseudobreakups) conditions have been studied in the past (e.g., Ohtani et al. (1993); Koskinen et al. (1993); Nakamura et al. (1994); Baumjohann et al. (1989);Baumjohann et al. (2010)). They have concluded that substorms and pseudobreakups have common responses (e.g., fast flows, dipolariza-60 tions, injections, electrojet and current wedge) without phenomenological differences. The differences between substorms and pseudobreakups are thought to be the strength, scale size and duration of activity; substorms have stronger and global activity but non-substorm conditions have weaker and localised activity. It has been shown that the substorm-time ionospheric currents have clockwise and counter-clockwise vortices Keiling et al. (2009) that are connected to plasma flow vortices in the magnetosphere Akasofu (1976); Borovsky and Bonnell (2001). However, there are limited direct observational evidence of this 65 connection largely due to the difficulty of finding conjunctions. Keiling2009 performed a multipoint analysis of conjugate magnetospheric and ionospheric flow vortices for a single substorm related fast flow bursts to show that the equivalent ionospheric currents (EIC) vortices were directly driven by the vortices observed in the magnetosphere. This study uses multipoint analysis of conjugate magnetospheric and ionospheric observations to investigate the magnetospheric and ionospheric responses to fast flow bursts that are associated to both substorms and pseudobreakups.

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In this study, we look into what properties control the differences in the magnetosphere-ionosphere responses between substorm and pseudobreakup conditions, and how such differences lead to the different ionospheric responses. We analyze the Time History of Events and Macroscale Interaction during Substorms (THEMIS) observations and select 3 pairs of fast flow and pseudobreakup events that were observed by all 3 inner THEMIS satellites (THEMIS A, D, and E) on the night side.  Angelopoulos et al. (2008). In this study, 11 years (2008-2019) of observations from the 3 inner probes (A, D and E) are analyzed to identify fast flow bursts that were observed when the 3 satellites were closely separated on the night side, located at least 6RE away from the Earth in radial distance, and within a magnetic local time (MLT) region of ±5 hours from local midnight.
The all sky imager (ASI) data on the ground is analyzed to complement the response of ionosphere to fast flow bursts. The 85 ground data provides contextual information on the processes observed in space by providing a two-dimensional view of the injection's formation and propagation, as well as its connection to the substorm evolution. A series of ground magnetometer arrays are used to generate the equivalent ionospheric currents (EICs) and current amplitudes at 10s resolution using the spherical elementary current systems (SECS) technique Amm and Viljanen (1999); Weygand et al. (2011Weygand et al. ( , 2012; Weygand and Wing (2016). They consist of a curl-free system whose divergences represent the FACs. It also consists of a divergence-free

Selection Criteria
In this study, we analyzed the THEMIS observations to identify fast flow burst events that were observed by all 3 inner THEMIS satellites (THEMIS A, D, and E) during close separation on the night side, located at least 6RE away from the Earth in radial 105 distance, and within a magnetic local time (MLT) region of ±5 hours from local midnight. The MPB index and the Auroral Electrojet Indices were used to distinguish between pseudobreakups (quiet conditions) and substorm (active conditions) fast flow bursts, where a MPB substorm is defined as the MPB index larger than 25nT 2 . This study specifically searched for events that were observed at the end of 2015 when the THEMIS configuration was identical to that considered by Sergeev2012 was recreated by the THEMIS mission operations team. This unique configuration lasted around 3 months (October,November,110 and December) and allowed us to derive the time varying parameters such as the current density, lobe magnetic field, and plasma pressure. Three pairs of fast flow bursts, where one event represented pseudobreakups and another event represented substorm fast flow bursts. Also the fast flow burst pair were selected to occur within a few hours of each other on the same orbit, so that the background conditions were as similar as possible.
In addition, the fast flow bursts were selected based on at least one sample of the perpendicular velocity projected to the  All 3 spacecraft observed fluctuations in magnetic field and ion perpendicular velocity. The peak ion perpendicular velocity of around 290km/s was observed by THEMIS A while all 3 spacecraft observed an increase in the Bz magnetic field component.

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On the other hand, the substorm fast flow burst, Case 4, was observed around 2 hours later. The MPB index increased to more than 2500nT 2 , indicating a large substorm. All 3 THEMIS spacecraft observed significant variation in magnetic field and ion perpendicular velocity. The peak ion perpendicular velocity, around 530km/s, was observed by THEMIS E. In addition, Figure 3 shows the pair of fast flow bursts, Cases 5 and 6, that were observed on 10 th December 2015. The pseudobreakups fast flow burst, Case 5, was observed around 06:50 UT when the MPB index was around 10nT 2 . All 3 THEMIS spacecraft 140 observed fluctuations in magnetic field and ion perpendicular velocity. In this case THEMIS E observed the largest peak ion velocity of around 600km/s. The substorm fast flow burst was observed less than an our later, around 07:40 UT, as the MPB index increased to around 570nT 2 . Again the fluctuations in the magnetic field and ion perpendicular velocity was consistently observed by all 3 THEMIS spacecraft. The Bx magnetic field components decreased while THEMIS D observed the maximum ion perpendicular velocity of around 500km/s in the x direction. were very favourable for determining the magnetic field gradients and plasma parameters in the magnetotail, because the y coordinates of the 3 satellites were almost the same, and it could be assumed that all differences between the magnetic field 150 measured at the 3 satellites are caused by satellites separation in the (x, z) plane. In the tail science phase (September to December 2015 ) the apogee of the 3 THEMIS spacecraft were approximately 12 Re. The probes were separated by 1000 km to a few Earth radii at apogee. In addition, during the observation of the selected fast flow bursts, at least, one of the two GOES fast flow bursts. The next section discusses the derived equivalent ionospheric currents and current amplitudes, the ASI data on the ground, and the electron flux data from the MAGED measurements onboard the GOES 13 and 15 satellites associated with each fast flow burst.
The substorm ionospheric currents are typically accompanied with a clockwise and a counter-clockwise vortex associated with corresponding vortices in the magnetosphere. Multipoint analysis of conjugate magnetospheric and ionospheric flow vortices for a single substorm related fast flow burst was performed by Keiling2009 to show that the EIC vortices were directly 160 driven by the flow vortices in the magnetosphere. In this study, we investigate the magnetospheric and ionospheric response to fast flow bursts during both substorm and non-subtorm times. We analyzed in detail the six fast flow burst cases. Figure 5 shows observed an increase in flux across all energy channels a few minutes later, despite being located more than 3h MLT away on 225 the dawn-side. This shows that substorm fast flow bursts are more likely to produce a strong inner magnetosphere response.
The other two substorm fast flow bursts also show strong magnetosphere responses that were similarly observed by the GOES spacecraft. It is worth noting that we studied flux observations for other geosynchronous satellites that were ideally located on the night side to observe such injections at the time of these fast flow bursts, such as the Los Alamos National Laboratory (LANL) satellites, for which similar particle injections were observed. The results show a clear and consistent difference between pseudobreakups and substorm fast flow bursts. For pseudobreakups (Figure 7), the B lobe decreased from ∼42nT before the fast flow burst to ∼34nT after fast flow burst, while there were fluctuations during the fast flow burst. The curvature force density also fluctuated, but was largely similar and relatively small before and after the fast flow burst (∼50 In contrast, for substorm fast flow burst shown in Figure 8, the decrease in B lobe value was much more apparent as B lobe decreased from (∼54nT) to (∼34nT). Also the fluctuations consisted of larger amplitudes and higher frequencies. The curvature force density increased gradually to ∼3400

Conclusion
In this study, multipoint analysis of conjugate magnetospheric and ionospheric observations were used to investigate the magnetospheric and ionospheric responses to substorm fast flow bursts and pseudobreakup events. The 3 inner THEMIS spacecraft (THEMIS A, D, and E) in situ measurements of THEMIS observations were used to select 3 pairs of fast flow bursts associated with substorm and pseudobreakup events. These fast flow bursts were observed during close separations on the night 235 side, beyond 6RE from the Earth in radial distance, and a magnetic local time (MLT) region of ±5 hours from local midnight. We studied in detail the magnetospheric and ionospheric response to each substorm fast flow burst and pseudobreakup event to understand what properties control the differences in the magnetosphere-ionosphere responses between substorm and pseudobreakup conditions, and how such differences lead to the different ionospheric responses.
The results show that ionospheric currents respond to both substorm fast flow bursts and pseudobreakup events, indicating 240 that the ionosphere currents are created by plasma flow vortices in the magnetosphere for fast flow bursts that are associated with substorms and pseudobreakup events. The magnetic flux in the tail is much stronger for strong substorms and much weaker for pseudobreakup events. The B lobe decreases significantly (by up to 40%) for substorm fast flow bursts, but much smaller decrease in B lobe for pseudobreakup events. The curvature force density for pseudobreakups are much smaller than substorm fast flow events, indicating that the pseudobreakups may not be able to penetrate deep into the inner magnetosphere.