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>

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 Quasi-periodic precipitation with periods between 40 and 60 minutes

1996 ◽  
Vol 14 (7) ◽  
pp. 707-715 ◽  
Author(s):  
K. Rinnert
Keyword(s):  
Electric Field ◽  
Electron Density ◽  
Electron Precipitation ◽  
Statistical Characteristics ◽  
Geomagnetic Disturbances ◽  
Maximum Probability ◽  
Dst Index ◽  
Incoherent Scatter ◽  
Magnetospheric Tail ◽  
E Region

Abstract. Intervals of periodic enhancements of E-region electron density have been found in EISCAT (European Incoherent SCATter) data. The periods are typically between 40 and 60 min. The phenomenon is observed during relatively quiet times, though after geomagnetic disturbances; it may last up to 6 h. The events can occur at all times of day with a maximum probability in the MLT morning sector. Using the EISCAT database from recent years, the statistical characteristics of these events, and their relation to magnetospheric conditions defined by the Dst index and the d.c. electric field perpendicular to B\\= have been derived. The latitudinal extent is found to be several degrees, but the longitudinal extent is not known. It is concluded that these events are due to the periodically modulated flux of electron precipitation controlled by oscillations in the magnetospheric tail.

Solar quiet daily (Sq) geomagnetic variation during minimum of solar cycle 23/24

2020 ◽  
Author(s):  
Anatoly Soloviev ◽  
Artem Smirnov
Keyword(s):  
Solar Activity ◽  
Current System ◽  
Geomagnetic Variation ◽  
Solar Cycles ◽  
Middle Latitudes ◽  
Observatory Data ◽  
Summer Hemisphere ◽  
Orthogonal Components ◽  
E Region ◽  
Good Agreement

<p class="Textbody"><span lang="EN-US">The most regular of all daily geomagnetic field variations is the so-called solar quiet, or Sq, variation. It is attributed to the two current vortices flowing in the E-region of the dayside ionosphere. We present an investigation of the time-dependent parameters of Sq variation for the historical minimum of solar activity in 2008. We apply "Measure of Anomalousness" algorithm to detection of magnetically quiet days. The global maps of seasonal Sq amplitudes of the three orthogonal components are derived using 75 INTERMAGNET and 46 SuperMAG stations at low and middle latitudes. The global Sq amplitudes are compared to the previous Coupled Magnetosphere-Ionosphere-Thermosphere (CMIT) model simulations and show good agreement. Significant variability was found in Sq(X) and Sq(Y) based on the solar activity and latitude, while almost no difference is observed in Sq(Z) for across all latitudes and seasons. We analyze equivalent Sq current system using observatory data from the Australian mainland and narrow European-African latitudinal segment. Sq current system also strongly depends on solar activity, as current vortices are strongest in the local summer-hemisphere and disintegrate during local winter. The dynamics of Sq variation along the solar cycles 23 and 24 is also discussed and compared to Swarm-based spherical harmonic Sq model.</span></p>

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.

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 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)

White-Light Coronal Structures: Streamers and CMEs

1994 ◽  
Vol 144 ◽  
pp. 82
Author(s):  
E. Hildner
Keyword(s):  
Emission Line ◽  
Electron Density ◽  
White Light ◽  
Coronal Mass Ejections ◽  
X Rays ◽  
Solar Cycles ◽  
Temperature Function ◽  
X Ray ◽  
Eclipse Observations ◽  
Coronal Structures

AbstractOver the last twenty years, orbiting coronagraphs have vastly increased the amount of observational material for the whitelight corona. Spanning almost two solar cycles, and augmented by ground-based K-coronameter, emission-line, and eclipse observations, these data allow us to assess,inter alia: the typical and atypical behavior of the corona; how the corona evolves on time scales from minutes to a decade; and (in some respects) the relation between photospheric, coronal, and interplanetary features. This talk will review recent results on these three topics. A remark or two will attempt to relate the whitelight corona between 1.5 and 6 R⊙to the corona seen at lower altitudes in soft X-rays (e.g., with Yohkoh). The whitelight emission depends only on integrated electron density independent of temperature, whereas the soft X-ray emission depends upon the integral of electron density squared times a temperature function. The properties of coronal mass ejections (CMEs) will be reviewed briefly and their relationships to other solar and interplanetary phenomena will be noted.

scholarly journals Measurement of geomagnetically induced current (GIC) around Tokyo, Japan

2021 ◽  
Vol 73 (1) ◽  
Author(s):  
Shinichi Watari ◽  
Satoko Nakamura ◽  
Yusuke Ebihara
Keyword(s):  
Solar Flare ◽  
Geomagnetic Storms ◽  
Power Grids ◽  
Geomagnetic Variation ◽  
Induced Current ◽  
Interplanetary Shocks ◽  
Geomagnetic Disturbances ◽  
Geomagnetically Induced Current ◽  
Middle Latitudes ◽  
Sudden Commencements

AbstractWe need a typical method of directly measuring geomagnetically induced current (GIC) to compare data for estimating a potential risk of power grids caused by GIC. Here, we overview GIC measurement systems that have appeared in published papers, note necessary requirements, report on our equipment, and show several examples of our measurements in substations around Tokyo, Japan. Although they are located at middle latitudes, GICs associated with various geomagnetic disturbances are observed, such as storm sudden commencements (SSCs) or sudden impulses (SIs) caused by interplanetary shocks, geomagnetic storms including a storm caused by abrupt southward turning of strong interplanetary magnetic field (IMF) associated with a magnetic cloud, bay disturbances caused by high-latitude aurora activities, and geomagnetic variation caused by a solar flare called the solar flare effect (SFE). All these results suggest that GIC at middle latitudes is sensitive to the magnetospheric current (the magnetopause current, the ring current, and the field-aligned current) and also the ionospheric current.

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