High-latitude crochet (Solar flare effect) as a trigger of pseud-substorm onset

2021 ◽  
Author(s):  
Masatoshi Yamauchi ◽  
Magnar Johnsen ◽  
Shin-Ichi Othani ◽  
Dmitry Sormakov
Keyword(s):  
Solar Flare ◽  
High Latitude ◽  
Current System ◽  
Geomagnetic Latitude ◽  
Geomagnetic Disturbance ◽  
Substorm Onset ◽  
Ionospheric Conductivity ◽  
New Type ◽  
E Region ◽  
Substorm Activity

<p>Solar flares are known to enhance the ionospheric electron density and thus influence the electric currents in the D- and E-region.  The geomagnetic disturbance caused by this current system is called a "crochet" or "SFE (solar flare effect)".  Crochets are observed at dayside low-latitudes with a peak near the subsolar region ("subsolar crochet"), in the nightside high-latitude auroral region with a peak where the geomagnetic disturbance pre-exists during solar illumination ("auroral crochet"), and in the cusp ("cusp crochet").  In addition, we recently found a new type of crochet on the dayside ionospheric current at high latitudes (European sector 70-75 geographic latitude/67-72 geomagnetic latitude) independent from the other crochets.  The new crochet is much more intense and longer in duration than the subsolar crochet and is detected even in AU index for about half the >X2 flares despite the unfavorable latitudinal coverage of the AE stations (~65 geomagnetic latitude) to detect this new crochet (Yamauchi et al., 2020).  </p><p>The signature is sometime s seen in AL, causing the crochet signature convoluting with substorms.  From a theoretical viewpoint, X-flares that enhances the ionospheric conductivity may influence the substorm activity, like the auroral crochet.  To understand the substorm-crochet relation in the dayside, we examined SuperMAG data for cases when the onset of the substorm-like AL (SML) behavior coincides with the crochet.  We commonly found a large counter-clockwise ∆B vortex centered at 13-15 LT, causing an AU peak during late afternoon and an AL peak near noon at higher latitudes than the high-latitude crochet.  In addition, we could recognize a clockwise ∆B vortex in the prenoon sector, causing another poleward ∆B, but this signature is not as clear as the afternoon vortex.  With such strong vortex features, it becomes similar to substorms except for its local time.  In some cases, the vortex expends to the nightside sector, where and when nightside onset starts, suggesting triggering of onset.  Thus, the crochet may behave like pseudo-onset at different latitude than midnight substorms, and may even trigger substorm onset.</p>

scholarly journals Statistical study on the occurrence of ASAID electric fields

2010 ◽  
Vol 28 (2) ◽  
pp. 439-448 ◽  
Author(s):  
S. Liléo ◽  
T. Karlsson ◽  
G. T. Marklund
Keyword(s):  
Electric Fields ◽  
Current System ◽  
Geomagnetic Latitude ◽  
Field Measurements ◽  
Auroral Oval ◽  
Outer Edge ◽  
Ionospheric Conductivity ◽  
Ion Drifts ◽  
Local Current ◽  
Substorm Activity

Abstract. The first statistical results on the occurrence of abnormal subauroral ion drifts (ASAID) are presented based on electric and magnetic field measurements from the low-altitude Astrid-2 satellite. ASAID are narrow regions of rapid eastward ion drifts observed in the subauroral ionosphere. They correspond to equatorward-directed electric fields with peak amplitudes seen to vary between 45 mV/m and 185 mV/m, and with latitudinal extensions between 0.2° and 1.2° Corrected Geomagnetic Latitude (CGLat), reaching in some cases up to 3.0° CGLat. Opposite to subauroral ion drifts (SAID) that are known to be substorm-related, ASAID are seen to occur predominantly during extended periods of low substorm activity. Our results show that ASAID are located in the vicinity of the equatorward edge of the auroral oval, mainly in the postmidnight sector between 23:00 and 03:00 magnetic local time. They are associated with a local current system with the same scale-size as the corresponding ASAID, composed by a region of downward field-aligned currents (FACs) flowing in the ASAID poleward side, and a region of upward flowing FACs in the equatorward side. The FACs have densities between 0.5 and 2.0 μA/m2. The data suggest that ASAID do not contribute significantly to the reduction of the ionospheric conductivity. ASAID are seen to have life times of at least 3.5 h. A discussion on possible mechanisms for the generation of ASAID is presented. We speculate that the proximity of the electron to the ion plasma sheet inner boundaries and of the plasmapause to the ring current outer edge, during extended quiet times, is an important key for the understanding of the generation of ASAID electric fields.

scholarly journals High-latitude crochet: solar-flare-induced magnetic disturbance independent from low-latitude crochet

2020 ◽  
Vol 38 (6) ◽  
pp. 1159-1170
Author(s):  
Masatoshi Yamauchi ◽  
Magnar G. Johnsen ◽  
Carl-Fredrik Enell ◽  
Anders Tjulin ◽  
Anna Willer ◽  
...  
Keyword(s):  
Solar Flare ◽  
Electron Density ◽  
High Latitude ◽  
Current System ◽  
Density Ratio ◽  
Auroral Electrojet ◽  
Ionospheric Current ◽  
Latitude Range ◽  
Zonal Current ◽  
Ionospheric Current System

Abstract. A solar-flare-induced, high-latitude (peak at 70–75∘ geographic latitude – GGlat) ionospheric current system was studied. Right after the X9.3 flare on 6 September 2017, magnetic stations at 68–77∘ GGlat near local noon detected northward geomagnetic deviations (ΔB) for more than 3 h, with peak amplitudes of >200 nT without any accompanying substorm activities. From its location, this solar flare effect, or crochet, is different from previously studied ones, namely, the subsolar crochet (seen at lower latitudes), auroral crochet (pre-requires auroral electrojet in sunlight), or cusp crochet (seen only in the cusp). The new crochet is much more intense and longer in duration than the subsolar crochet. The long duration matches with the period of high solar X-ray flux (more than M3-class flare level). Unlike the cusp crochet, the interplanetary magnetic field (IMF) BY is not the driver, with the BY values of only 0–1 nT out of a 3 nT total field. The equivalent ionospheric current flows eastward in a limited latitude range but extended at least 8 h in local time (LT), forming a zonal current region equatorward of the polar cap on the geomagnetic closed region. EISCAT radar measurements, which were conducted over the same region as the most intense ΔB, show enhancements of electron density (and hence of ion-neutral density ratio) at these altitudes (∼100 km) at which strong background ion convection (>100 m s−1) pre-existed in the direction of tidal-driven diurnal solar quiet (Sq0) flow. Therefore, this new zonal current can be related to this Sq0-like convection and the electron density enhancement, for example, by descending the E-region height. However, we have not found why the new crochet is found in a limited latitudinal range, and therefore, the mechanism is still unclear compared to the subsolar crochet that is maintained by a transient redistribution of the electron density. The signature is sometimes seen in the auroral electrojet (AE = AU − AL) index. A quick survey for X-class flares during solar cycle 23 and 24 shows clear increases in AU for about half the > X2 flares during non-substorm time, despite the unfavourable latitudinal coverage of the AE stations for detecting this new crochet. Although some of these AU increases could be the auroral crochet signature, the high-latitude crochet can be a rather common feature for X flares. We found a new type of the solar flare effect on the dayside ionospheric current at high latitudes but equatorward of the cusp during quiet periods. The effect is also seen in the AU index for nearly half of the > X2-class solar flares. A case study suggests that the new crochet is related to the Sq0 (tidal-driven part) current.

scholarly journals High-latitude crochet: solar flare-induced magnetic disturbance independent from low-latitude

2020 ◽  
Author(s):  
Masatoshi Yamauchi ◽  
Magnar G. Johnsen ◽  
Carl-Fredrik Enell ◽  
Anders Tjulin ◽  
Anna Willer ◽  
...  
Keyword(s):  
Solar Flare ◽  
Electron Density ◽  
High Latitude ◽  
Current System ◽  
Auroral Electrojet ◽  
Lower Latitude ◽  
Ionospheric Current ◽  
Latitude Range ◽  
Zonal Current ◽  
Local Noon

Abstract. Solar flare-induced High latitude (peak at 70–75° geographic latitude) ionospheric current system was studied. Right after the X9.3 flare on 6 September 2017, magnetic stations at 68–77° geographic latitudes (GGlat) near local noon detected northward geomagnetic deviations (ΔB) for more than 3 hours, with peak amplitudes > 200 nT, without any accompanying substorm activities. From its location, this solar flare effect, or crochet, is different from previously studied ones, namely, subsolar crochet (seen at lower latitude), auroral crochet (pre-requires auroral electrojet in sunlight), or cusp crochet (seen only in the cusp). The new crochet is much more intense and longer in duration than the subsolar crochet. The long duration matches with the period of high solar X-ray flux (more than M3-class flare level). Unlike the cusp crochet, interplanetary magnetic field (IMF) BY is not the driver with BY only 0–1 nT out of 3 nT total field. The equivalent ionospheric current flows eastward in a limited latitude range but extended at least 8 hours in local time (LT), forming a zonal current region equatorward of the polar cap on the geomagnetic closed region. EISCAT radar measurements over the same region as the most intense ΔB near local noon show enhancements of electron density (and hence ion-neutral ratio) at these altitudes (~ 100 km) where the background Sq ion convection (> 100 m/s) pre-existed. Therefore, this new zonal current can be related to the Sq convection and the electron density enhancement, e.g., by descending E-region height. However, we have not found why the new crochet is found in a limited latitudinal range, and therefore the mechanism is still unclear compared to the subsolar crochet that is maintained by transient re-distribution of electron density. The signature is sometimes seen in the Auroral Electrojet (AE) index. A quick eye-survey for X-class flares during solar cycle 23 and 24 shows clear AU increases for about half the > X2 flares during non-substorm time, although the latitudinal coverage of the AE stations is not favorable to detect this new crochet. Although some of them could be due to auroral crochet, this new crochet can be rather common feature for X flares.

scholarly journals The high latitude convection response to an interval of substorm activity

1996 ◽  
Vol 14 (5) ◽  
pp. 518-532 ◽  
Author(s):  
T. K. Yeoman ◽  
M. Pinnock
Keyword(s):  
High Latitude ◽  
Neutral Line ◽  
Substorm Onset ◽  
Hf Radar ◽  
The West ◽  
Expansion Phase ◽  
Incoherent Scatter ◽  
Current Disruption ◽  
Substorm Activity ◽  
Substorm Onsets

Abstract. On 17 March 1991, five clear substorm onsets/intensifications took place within a three hour interval. During this interval ground-based data from the EISCAT incoherent scatter radar, a digital CCD all sky camera, and an extensive array of magnetometers were available, in addition to data from the CRRES and DMSP spacecraft, whose footprints passed over Scandinavia very close to most of the ground-based instrumentation. This interval of substorm activity has been interpreted as being in support of a near-Earth current disruption model of substorm onset. In the present study the ionospheric convection response, observed some four hours to the west in MLT by the Halley HF radar in Antarctica, is related to the growth, expansion and recovery phases of two of the substorm onsets/expansions observed in the Northern Hemisphere. Bursts of ionospheric flow and motion of the convection reversal boundary (CRB) are observed at Halley in response to the substorm activity and changes in the IMF. The delay between the substorm expansion phase onset and the response in the CRB location is dependent on the local time separation from, and latitude of, the initial substorm onset region. These results are interpreted in terms of a synthesis of the very near-Earth current disruption model and the near-Earth neutral line model of substorm onset.

scholarly journals CUTLASS/IMAGE observations of high-latitude convection features during substorms

1997 ◽  
Vol 15 (6) ◽  
pp. 692-702 ◽  
Author(s):  
T. K. Yeoman ◽  
H. Lühr
Keyword(s):  
Time Resolution ◽  
High Latitude ◽  
Geomagnetic Latitude ◽  
Hf Radar ◽  
High Time ◽  
Spatial Extent ◽  
Line Of Sight ◽  
Return Flow ◽  
High Time Resolution ◽  
Substorm Activity

Abstract. The CUTLASS Finland HF radar has been operational since February 1995. The radar frequently observes backscatter during the midnight sector from a latitude range 70–75° geographic, latitudes often associated with the polar cap. These intervals of backscatter occur during intervals of substorm activity, predominantly in periods of relatively quiet magnetospheric activity, with Kp during the interval under study being 2- and ΣKp for the day being only 8-. During August 1995 the radar ran in a high time resolution mode, allowing measurements of line-of-sight convection velocities along a single beam with a temporal resolution of 14 s, and measurement of a full spatial scan of line-of-sight convection velocities every four minutes. Data from such scans reveal the radar to be measuring return flow convection during the interval of substorm activity. For three intervals during the period under study, a reduction in the spatial extent of radar backscatter occurred. This is a consequence of D region HF absorption and its limited extent in the present study is probably a consequence of the high latitude of the substorm activity, with the electrojet centre lying between 67° and 71° geomagnetic latitude. The high time resolution beam of the radar additionally demonstrates that the convection is highly time dependent. Pulses of equatorward flow exceeding ~600 m s–1 are observed with a duration of ~5 min and a repetition period of ~8 min. Their spatial extent in the CUTLASS field of view was 400–500 km in longitude, and 300–400 km in latitude. Each pulse of enhanced equatorward flow was preceded by an interval of suppressed flow and enhanced ionospheric Hall conductance. The transient features are interpreted as being due to ionospheric current vortices associated with field aligned current pairs. The relationship between these observations and substorm phenomena in the magnetotail is discussed.

scholarly journals Meridional equatorial electrojet current in the American sector

1999 ◽  
Vol 17 (2) ◽  
pp. 220-230 ◽  
Author(s):  
R. G. Rastogi
Keyword(s):  
Solar Flare ◽  
Geomagnetic Field ◽  
Current System ◽  
Equatorial Electrojet ◽  
Simultaneous Increase ◽  
Equatorial Station ◽  
Counter Electrojet ◽  
Negative Impulse ◽  
Electrojet Current ◽  
E Region

Abstract. Huancayo is the only equatorial electrojet station where the daytime increase of horizontal geomagnetic field (H) is associated with a simultaneous increase of eastward geomagnetic field (Y). It is shown that during the counter electrojet period when ∆H is negative, ∆Y also becomes negative. Thus, the diurnal variation of ∆Y at equatorial latitudes is suggested to be a constituent part of the equatorial electrojet current system. Solar flares are known to increase the H field at an equatorial station during normal electrojet conditions (nej). At Huancayo, situated north of the magnetic equator, the solar flare effect, during nej, consists of positive impulses in H and Y and negative impulse in Z field. During counter electrojet periods (cej), a solar flare produces a negative impulse in H and Y and a positive impulse in Z at Huancayo. It is concluded that both the zonal and meridional components of the equatorial electrojet in American longitudes, as in Indian longitudes, flows in the same, E region of the ionosphere.Key words. Geomagnetism and paleomagnetism (dynamo theories) · Ionosphere (equatorial ionosphere; ionosphere disturbances)

Solar flare effect on the ionospheric current in the polar region: a new phenomena

2020 ◽  
Author(s):  
Masatoshi Yamauchi ◽  
Magnar Johnsen ◽  
Carl-Fredrik Enell
Keyword(s):  
Solar Flare ◽  
Electron Density ◽  
Current System ◽  
Radar Data ◽  
Oscillation Period ◽  
Lower Latitude ◽  
Solar Cycles ◽  
Geomagnetic Disturbances ◽  
Density Enhancement ◽  
E Region

<p>Solar flares are known to enhance the ionospheric electron density in the D- and E-region, enhancing twin vortex pattern in the dayside (e.g., Curto et al., 1994).  The geomagnetic deviation due to this current system is called as "crochet" or "SFE (solar flare effect)".  For X-flares, the crochet is easily detected as an enhancement in ASY-D index (Sing et al., 2012).  Since the effect is expected stronger at low solar zenith angles where solar radiation is high, high-latitude behavior (> 70° geographic latitudes: GGlat) has not been well studied and simply assumed as minor (such as weak return current).</p><p>However, the X flares on 6 September 2017 (X2.2 at 9 UT and X9.3 at 12 UT), caused large non-substorm geomagnetic disturbances at high latitudes, lasting much longer than the burst of electron density enhancement in the the D- and E-region (Yamauchi et al., 2018).  Both the polarity and duration turned out to be different from mid-latitude crochet which is characterized by short-lived (< 30 min) dH<0: dH is positive for over 5 hours with much higher amplitude than the crochet although the event took place near equator.  In addition, this dH showed oscillations on the order of 30 minute.  Since the X-ray intensity during 12-17 UT was higher than X-flare criterion until 17 UT, this long-lasting dH>0 with peak at 74-75 GGLat must also be caused by the X-flare.  The EISCAT radar data showed strong enhancement of convection lasting hours after the flare onset and relevant bursty (< 10 min) enhancement of the electron density.  This is consistent with long-lasting positive dH.  On the other hand, density oscillation period is about 15 min and different from the oscillation period of dH.   </p><p>Using Norwegian geomagnetic chain and EISCAT data, we examined X flares (> X2.0) for past two solar cycles, and found that (1) dH>0 at > 70 GGLAT with dH<0 (and positive ASY-D change is quite common) at lower latitude, (2) duration of crochet (dH<0) is shorter at higher latitude as the start timing and amplitude of dH>0 becomes earlier and larger at higher latitude, (3) at some latitude, crochet (dH<0) disappears and dH>0 dominates the entire period much longer than the crochet, and (4) electron density enhancement is spike-like no matter the duration of X-flare.  We interpret this long-lasting dH>0 is caused by independent mechanism from crochet.</p><p>Reference<br>Curto et al. (1994): doi:10.1029/93JA02270<br>Singh et al. (2012): doi:10.1016/j.jastp.2011.12.010<br>Yamauchi et al. (2018): doi:10.1029/2018SW00193</p>

CRRES/Ground-based multi-instrument observations of an interval of substorm activity

1994 ◽  
Vol 12 (12) ◽  
pp. 1158-1173 ◽  
Author(s):  
T. K. Yeoman ◽  
H. Lühr ◽  
R. W. H. Friedel ◽  
S. Coles ◽  
M. Grandé ◽  
...  
Keyword(s):  
Current System ◽  
Expansion Phase ◽  
Magnetic Field Data ◽  
Incoherent Scatter ◽  
Magnetic Signature ◽  
Low Latitudes ◽  
E Region ◽  
Substorm Activity ◽  
Substorm Onsets ◽  
Auroral Luminosity

Abstract. Observations are presented of data taken during a 3-h interval in which five clear substorm onsets/intensifications took place. During this interval ground-based data from the EISCAT incoherent scatter radar, a digital CCD all sky camera, and an extensive array of magnetometers were recorded. In addition data from the CRRES and DMSP spacecraft, whose footprints passed over Scandinavia very close to most of the ground-based instrumentation, are available. The locations and movements of the substorm current system in latitude and longitude, determined from ground and spacecraft magnetic field data, have been correlated with the locations and propagation of increased particle precipitation in the E-region at EISCAT, increased particle fluxes measured by CRRES and DMSP, with auroral luminosity and with ionospheric convection velocities. The onsets and propagation of the injection of magnetospheric particle populations and auroral luminosity have been compared. CRRES was within or very close to the substorm expansion phase onset sector during the interval. The onset region was observed at low latitudes on the ground, and has been confirmed to map back to within L=7 in the magnetotail. The active region was then observed to propagate tailward and poleward. Delays between the magnetic signature of the substorm field aligned currents and field dipolarisation have been measured. The observations support a near-Earth plasma instability mechanism for substorm expansion phase onset.

scholarly journals Decay of the Dst field of geomagnetic disturbance after substorm onset and its implication to storm-substorm relation

1996 ◽  
Vol 14 (6) ◽  
pp. 608-618 ◽  
Author(s):  
T. Iyemori ◽  
D. R. K. Rao
Keyword(s):  
Ring Current ◽  
Geomagnetic Storms ◽  
Sharp Decrease ◽  
Geomagnetic Disturbance ◽  
Substorm Onset ◽  
Significant Development ◽  
H Index ◽  
Magnetospheric Tail ◽  
Storms And Substorms ◽  
Substorm Onsets

Abstract. In order to investigate the causal relationship between magnetic storms and substorms, variations of the mid-latitude geomagnetic indices, ASY (asymmetric part) and SYM (symmetric part), at substorm onsets are examined. Substorm onsets are defined by three different phenomena; (1) a rapid increase in the mid-latitude asymmetric-disturbance indices, ASY-D and ASY-H, with a shape of so-called `mid-latitude positive bay\\'; (2) a sharp decrease in the AL index; (3) an onset of Pi2 geomagnetic pulsation. The positive bays are selected using eye inspection and a pattern-matching technique. The 1-min-resolution SYM-H index, which is essentially the same as the hourly Dst index except in terms of the time resolution, does not show any statistically significant development after the onset of substorms; it tends to decay after the onset rather than to develop. It is suggested by a simple model calculation that the decay of the magnetospheric tail current after substorm onset is responsible for the decay of the Dst field. The relation between the IMF southward turning and the development of the Dst field is re-examined. The results support the idea that the geomagnetic storms and substorms are independent processes; that is, the ring-current development is not the result of the frequent occurrence of substorms, but that of enhanced convection caused by the large southward IMF. A substorm is the process of energy dissipation in the magnetosphere, and its contribution to the storm-time ring-current formation seems to be negligible. The decay of the Dst field after a substorm onset is explained by a magnetospheric energy theorem.

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