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

<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>

Analysis of the Geomagnetic Component Z Daily Variation Amplitude Based on the China Geomagnetic Network

The daily variation amplitude of geomagnetic component Z is one of the important data products in Geomagnetic Network of China (GNC). It comes from the difference between maximum and minimum of the component Z recorded by the geomagnetic instrument in a day. Based on this data product, the daily variation amplitude of Z is analyzed in the past twelve years (2008–2019), including variation for each month in high and low solar activity years, seasonal variations and comparisons between the stations in Yunnan Province and in southeast China. The study indicates that the ionospheric conductivity mainly contributes to the Z daily variations amplitude in the same month or season changing along with solar activity. But the neutral wind in ionosphere could make the Z daily variations amplitude in equinox months equal to or greater than it in summer solstice months during some solar high activity years. Due to the complicated underground electrical structures in Yunnan province, the conductivity underground acts as an amplifier to make the Z daily variations amplitude increase by about 12 % ~ 41 % in Yunnan Province during equinox and summer solstice months.

Modeling particle precipitation and effects on the ionospheric conductivity

<p>Particle precipitation originated from the magnetosphere provides important energy source to the upper atmosphere, leading to ionization and enhancement of conductivity, which in turn changes the electric potential in the MI system to influence the plasma convection in the magnetosphere. In this study, we simulate ring current particle precipitation caused by several important loss mechanisms, including electron precipitation due to whistler wave scattering, ion precipitation due to EMIC wave diffusion and field line curvature scattering. These physical mechanisms are implemented in the kinetic ring current model via diffusion equation with associated pitch angle diffusion coefficients. The precipitation is subsequently input to a two-stream transport model at the top of ionosphere in order to examine its impact on the ionsopheric conductivity. It is found that during intense storm time, electron precipitation of tens of keV dominates in the dawn sector and leads to significant enhancement of conductivity at low altitudes. On the other hand, proton precipitation on the nightside mostly occurs for energy below 10 keV, and contributes to ionization above 100 km, resulting in enhancement of conductivity there. Consequently, the height profile of both Pedersen and Hall conductivity exhibits two layers, potentially complicating the current closure in the ionosphere system.</p>

Explicit IMF By-dependence in geomagnetic activity

<p>The interaction of the solar wind with the Earth’s magnetic field produces geomagnetic activity, which is critically dependent on the orientation of the interplanetary magnetic field (IMF). Most solar wind coupling functions quantify this dependence on the IMF orientation with the so-called IMF clock angle in a way, which is symmetric with respect to the sign of the By component. However, recent studies have shown that IMF By is an additional, independent driver of high-latitude geomagnetic activity, leading to higher (weaker) geomagnetic activity in Northern Hemisphere (NH) winter for By > 0 (By < 0). For NH summer the dependence on the By sign is reversed. We quantify the size of this explicit By-effect with respect to the solar wind coupling function, both for northern and southern high-latitude geomagnetic activity. We show that for a given value of solar wind coupling function, geomagnetic activity is about 40% stronger for By > 0 than for By < 0 in NH winter. The physical mechanism of the By-effect is not yet fully understood. Here we show that IMF By modulates the flux of energetic electrons precipitating into the ionosphere which likely modulates the ionospheric conductivity and, thus, geomagnetic activity. Our results highlight the importance of the IMF By-component for space weather and must be taken into account in future space weather modeling.</p>

Charging Thunderclouds Affect Ionospheric Conductivity

As thunderstorm updrafts strengthen, electrification of clouds can heat the lower ionosphere, explaining prolonged disturbances to radio waves in the rarefied atmospheric layer.

Solar quiet variation of the horizontal and vertical components of geomagnetic field using wavelet analysis

The solar quiet (Sq) variations of horizontal and vertical (SqH and SqZ) components of the geomagnetic field obtained from both the Northern Hemisphere and Southern Hemisphere of the International Real-Time Magnetic Observatory Network (INTERMAGNET) during solar maximum year 2001 were investigated. The results show enlargement of the SqH component of the geomagnetic field during the daytime, attributed to equatorial electrojet (EEJ) current closer to the geomagnetic equator at the electrojet stations (BNG and MBO), which are produced from large eastward flow of the current. It was observed that SqZ is positive at the southward and negative at the northward hemispheres. SqZ is amplified at HER and HBK around the daytime. Wavelet power spectrum based approach was employed to analyse the SqH, SqZ, and rate of induction (SqZ/SqH) time series in a sequence of time scaling from January to December. The higher energy of SqH and SqZ of the wavelet coefficients is noticeable at high frequency. The monthly variation rate of induction (SqZ/SqH) analyses during the Sq variations are associated with the influence of equatorwards penetration of electric fields from the field-aligned current, Earth conductivity, effect of the ocean, and ionospheric conductivity.