Response of the incompressible ionosphere to the compression of the magnetosphere during the geomagnetic sudden commencements

Abstract

The ionospheric plasma in midlatitude moves upward/downward during the geomagnetic sudden commencement causing the HF Doppler frequency changes; SCF (+ −) and (− +) on the dayside and nightside, respectively, except for the SCF (+ −) in the evening as found by Kikuchi et al. (1985). Although the preliminary and main frequency deviations (PFD, MFD) of the SCF have been attributed to the dusk‐to‐dawn and dawn‐to‐dusk potential electric fields, there still remain questions if the positive PFD can be caused by the compressional magnetohydrodynamic (MHD) wave and what causes the evening anomaly of the SCF. With the HF Doppler sounder, we show that the dayside ionosphere moves upward toward the Sun during the main impulse (MI) of the SC, when the compressional wave is supposed to push the ionosphere downward. The motion of the ionosphere is shown to be correlated with the equatorial electrojet, matching the potential electric field transmitted with the ionospheric currents from the polar ionosphere. We confirmed that the electric field of the compressional wave is severely suppressed by the conducting ionosphere and reproduced the SC electric fields using the global MHD simulation in which the potential solver is employed. The model calculations well reproduced the preliminary impulse and MI electric fields and their evening anomaly. It is suggested that the electric potential is transmitted from the polar ionosphere to the equator by the zeroth‐order transverse magnetic (TM0) mode waves in the Earth‐ionosphere waveguide. The near‐instantaneous transmission of the electric potential leads to instantaneous global response of the incompressible ionosphere.

Substorm Overshielding Electric Field at Low Latitude on the Nightside as Observed by the HF Doppler Sounder and Magnetometers

“…Using Tanaka's MHD model, Ebihara et al (2014) reproduced the CEJ driven by the intensified R2 FACs similar to the observations reported by Hashimoto et al (2011Hashimoto et al ( ). 1952), leading to that the low-latitude electric field detected by the HF Doppler sounder is well correlated with the EEJ during the SCs (Kikuchi et al, 2016).…”

“…The HF Doppler sounders have been widely used to detect the motion of the reflection height of the HF radio signal, providing the ionospheric electric fields of the geomagnetic sudden commencements (SCs), geomagnetic pulsations (Pc5, Pi2), quasiperiodic DP 2 fluctuations, and substorms (Abdu et al, ; Davies et al, ; Huang et al, ; Jayachandran et al, ; Kikuchi, ; Kikuchi et al, , ; Sastri & Subrahmanyam, ; Tsutsui et al, ).…”

“…We used 1 s sampled magnetometer data from midlatitude (MMB), low latitude (KNY and OKI), and equator (YAP) in the western Pacific zone (Table ) to detect the midlatitude positive bay and equatorial electrojets (EEJs) on the nightside and those from the equator (SLZ) in Brazil (Table ) to detect the equatorial CEJ on the dayside. It is to be noted that the equatorial ionosphere is sensitive to the penetration electric field because the ionospheric currents are intensified by the Cowling effect (Baker & Martyn, ; Hirono, ), leading to that the low‐latitude electric field detected by the HF Doppler sounder is well correlated with the EEJ during the SCs (Kikuchi et al, ).…”

Generation of field‐aligned current (FAC) and convection through the formation of pressure regimes: Correction for the concept of Dungey's convection

“…Since then, the global M‐I coupling simulation has been evolving more and more. In these processes, it has been revealed that the most important element of simulation for the realistic reproduction of magnetospheric and ionospheric observations is to realize a dense grid system that enables high‐resolution calculations in the ionosphere [ Tanaka , , ; Tanaka et al , ; Ebihara et al , ; Kikuchi et al , ]. Recent highly precise global simulations perform the calculation using more than 1000 CPUs through hybrid parallel calculation (60 mpi (message passing interface) and 20 omp open MP (Multi‐Processing) in the present calculation), and achieve the precise reproduction of disturbances in the M‐I coupling system, even a realistic reproduction of the ionospheric substorm [ Tanaka , ; Ebihara and Tanaka , , , ].…”

Prompt GPS TEC response to magnetospheric compression

“…Finally, contrary facts have been found by some studies that a shock can cause ionospheric and plasmaspheric plasmas to move sunward by disturbing magnetospheric convection and related electric field [e.g., Kotova et al , ; Kikuchi et al , ]. Spacecrafts in the outer magnetosphere may observe increased cold plasma density which is in association with sunward motion of plasma that forms plasmaspheric bulge (plume) [ Zhang et al , ; Andréeová et al , ].…”