Letter to the editor: Electric field fluctuations (25-35 min) in the midnight dip equatorial ionosphere

Abstract

Abstract. Measurements with a HF Doppler sounder at Kodaikanal (10.2°N, 77.5°E, geomagnetic latitude 0.8°N) showed conspicuous quasi-periodic¯uctuations (period 25±35 min) in F region vertical plasma drift, V z in the interval 0047±0210 IST on the night of 23/24 December, 1991 (A p = 14, K p < 4 ) ). The¯uctuations in F region vertical drift are found to be coherent with variations in B z (north-south) component of interplanetary magnetic ®eld (IMF), in geomagnetic H/X components at high-mid latitude locations both in the sunlit and dark hemispheres and near the dayside dip equator, suggestive of DP2 origin. But the polarity of the electric ®eld¯uctuations at the midnight dip equator (eastward) is the same as the dayside equator inferred from magnetic variations, contrary to what is expected of equatorial DP2. The origin of the coherent occurrence of equatorial electric ®eld¯uctuations in the DP2 range of the same sign in the day and night hemispheres is unclear and merits further investigations.

Three different types of electric field disturbances affecting equatorial ionosphere during a long‐duration prompt penetration event

“…As ∼40 min periodicity is observed in the magnetic data simultaneously, the present observation probably provides a clear evidence of DP2 type fluctuations during midnight and postmidnight hours over equatorial region. The present case, similar to the case of Sastri et al [2000] with the periodicity of 25-35 min, provides another evidence for DP2 type (occasionally eastward too) electric field perturbations affecting the dip equatorial ionosphere even during midnight hours. The eastward polarity (similar to daytime polarity) of the DP2 electric field during midnight hours is in contrast [e.g., Sastri et al, 2000] to the expectation [Tsunomura, 1999] and requires further investigation.…”

“…The present case, similar to the case of Sastri et al [2000] with the periodicity of 25-35 min, provides another evidence for DP2 type (occasionally eastward too) electric field perturbations affecting the dip equatorial ionosphere even during midnight hours. The eastward polarity (similar to daytime polarity) of the DP2 electric field during midnight hours is in contrast [e.g., Sastri et al, 2000] to the expectation [Tsunomura, 1999] and requires further investigation. It is interesting to note that during the interval (segment 3) of DP2 type prompt penetration, a substorm onset also took place at 0100 h. This substorm onset conspicuously makes SYM-H less negative (see Figure 2c), causes enhancement in ASY-H (see Figure 2d), and generates clear positive bay in the ΔH variations over both Indian and Japanese sectors (see Figure 3).…”

Solar wind flow angle and geoeffectiveness of corotating interaction regions: First results

“…Therefore, although it is clear that the frequency response around the ring current region decides the prompt penetration frequency, the nature [e.g., Ohtani and Uozumi, 2014] of the processes that controls this response is not comprehensively understood. Nevertheless, the present study (Table 1) shows that on some occasions, DP2 (30 and 60 min periodicities) type [Nishida, 1968;Sastri et al, 2000;Chakrabarty et al, 2008Chakrabarty et al, , 2015 periodic fluctuations can reach up to dip equatorial ionosphere in daytime during the passage of CIRs. Table 1 suggests that the presence of PP electric field during CIR depends on the azimuthal solar wind flow angle (Φ) with the events which do not show causal relationship between EEJ and IMF B z , having | Φ | more than 6 ∘ .…”

The Ionospheric Impact of an ICME‐Driven Sheath Region Over Indian and American Sectors in the Absence of a Typical Geomagnetic Storm

“…It is to be noted that the ionospheric electric field was found to oscillate east and westward corresponding to north and southward fluctuations in IMF Bz and the time scale of quasiperiodic fluctuations can range from half an hour to several hours (Chakrabarty et al, ; Kikuchi et al, ). A wide range of periodicities of 30–40 min (Kikuchi et al, ), 25–35 min (Hanumath Sastri et al, ), and 40 min (Chakrabarty et al, , ) have been reported by earlier investigations by various measurements. Further, a recent investigation of Rout et al () revealed that periodicities of 30 and 60 min in IMF Bz affected the equatorial ionosphere during the corotating interaction region‐driven geomagnetic storms.…”