The solar wind-magnetosphere coupling and daytime disturbance electric fields in equatorial ionosphere during consecutive recurrent geomagnetic storms

Journal of Atmospheric and Solar-Terrestrial Physics 187 (2019) 40–52

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The solar wind-magnetosphere coupling and daytime disturbance electric fields in equatorial ionosphere during consecutive recurrent geomagnetic storms

T

Thana Yeeram Department of Physics, Faculty of Science, Mahasarakham University, Space Technology and Geoinformatics Section, Maha Sarakham, Thailand

ARTICLE INFO

ABSTRACT

Keywords: Equatorial ionosphere High speed solar wind Disturbance dynamo Ionospheric electrodynamics HILDCAA Geomagnetic storms

This paper investigates evolutions of geomagnetic and equatorial electrodynamic responses during three consecutive 27-day recurrent geomagnetic storms (RGSs) in 2007 by using the solar wind plasma, geomagnetic indices, and magnetometer data. The RGSs are classified as corotating interaction regions (CIR)-induced storms and High Intensity Long Duration Continuous AE Activity (HILDCAA). The RGSs show quasi-stable and diverge variabilities in storm-times that critically control the long-lasting and complex electrodynamic responses in equatorial ionosphere, particularly in CIR-storms. The correlations of Auroral Electrojet (AE)/Polar Cap (PC) indices are moderate for CIRs and HILDCAAs during local summer, which suggest to less effective coupling and/ or different sources of PC and AE. The correlations of reconnection electric field with AE and Fourier analysis of the north-south component of the interplanetary magnetic field with AE reveal that the solar wind-magnetosphere-ionosphere coupling is more effective in the HILDCAAs than in the CIRs. Results indicate that disturbance electric fields are closely related to storm time evolution of the RGSs and are seasonal dependent. Disturbance dynamo electric fields (DDEFs) are related to each group of HSSs during HILDCAA periods. Justification of storm-time effect or seasonal effects is done. The substantial DDEFs are caused by the storm time effects of enhanced thermospheric wind due to the summer-to-winter winds in the late night sector. DDEFs are effective particularly in the morning-to-prenoon time in the summer, while they are less effective in equinoctial months due to the symmetric meridional winds and in winter months due to restriction of the equatorward motion.

1. Introduction At low latitude ionosphere, complex electrodynamics in spatial and temporal variability control various ionospheric phenomena. During daytime of quiet magnetic periods, there are intense eastward ionospheric electric fields flows along the geomagnetic equator (± 3 magnetic dip) called equatorial electrojet (EEJ) created by the E-region ionospheric dynamo process. On the one hand, during periods of enhanced geomagnetic activity, the equatorial ionosphere is highly variable in responses to disturbance electric fields. Two main types of the disturbances are short-lived prompt penetration electric fields (PPEFs) of transient magnetospheric origin and electric fields generated by the longer-lasting ionospheric disturbance dynamo (DD) known as disturbance dynamo electric fields (DDEFs). The PPEF events were at first deduced from their consequent magnetic field observed in the EEJ (Nishida, 1968). PPEFs are generated at high latitudes, when there is a change in Field Aligned Current (FAC) resulting in the electric field enhancement during storm-time

with increasing of magnetospheric convection electric field. PPEFs cause a prompt perturbation in the zonal (dynamo) electric field in the low-latitude ionosphere as a result of the temporary failure of the so called shielding mechanism (Jaggi and Wolf, 1973). The PPEF, driven by the convection electric field in the outer magnetosphere, communicates with the ionosphere through Region1 (R1) FAC in the polar cap, while a shielding electric field communicates with R2 FAC. Under a steady state, the R2 FACs tend to minimize the electric field at low latitudes, producing the shielding electric field due to the charge accumulation in the ring current or the Alfvén layers (Senior and Blanc, 1984; Wolf et al., 2007). Generally, the PPEFs have typical rise and 1 3 h decay shorter than ∼15 min duration, and lifetimes of (Huang et al., 2007). Thermospheric winds produced by enhanced auroral heating during the storm time modify the global circulation generating DDEFs at middle and low latitudes (Blanc and Richmond, 1980; Richmond and Lu, 2000). They cause variations in thermospheric compositions and densities via Joule heating and impulses through the ion-neutral

E-mail address: [email protected]. https://doi.org/10.1016/j.jastp.2019.03.004 Received 28 October 2018; Received in revised form 9 February 2019; Accepted 5 March 2019 Available online 14 March 2019 1364-6826/ © 2019 Elsevier Ltd. All rights reserved.

Journal of Atmospheric and Solar-Terrestrial Physics 187 (2019) 40–52

T. Yeeram

collisions (Rishbeth, 1975). The process sets up gravity waves and equatorward thermospheric meridional winds (Hadley cell) at F-region altitudes (Richmond and Roble, 1979). Under action of Coriolis force due to the Earth's rotation, the equatorward winds cause a westward zonal wind flow which drives a part of the ionized fluid that produces subsequent Pedersen and Hall currents (Zaka et al., 2009). DDEFs have timescales from ∼2 h to 30 h (Fejer and Scherliess, 1997; Scherliess and Fejer, 1997). The quiet-time zonal electric field in ionosphere is eastward (westward) during the day (night), while the DDEF is westward (eastward) in the dayside (nightside). Thus, during the action of DD mechanism the quiet zonal electric field tends to diminish or even reverse that results in suppression of vertical E × B drift and EEJ. Note that at the magnetic equator altitude, there is a substantial amplification of PPEF and DDEF due to the Cowling conductivity effect. Recurrent geomagnetic storms (RGSs) are most prevalent during the declining and rising phases of the solar sunspot cycle (e.g., Sheeley et al., 1976; Tsurutani et al., 2006; Echer et al., 2013). RGSs emerge from repeated interaction of the magnetosphere with quasi-complex stream structures corotating with the Sun of a period 27 days. The corotating structures comprise of preceding corotating interaction regions (CIRs) and following high speed solar wind streams (HSSs) emerging from coronal holes. When the expanding HSSs interact with slow-speed upstreams, CIRs are formed near the ecliptic plane with intense magnetic field and plasma. Typically, CIRs and HSSs are responsible for weak-to-moderate geomagnetic disturbance at the main and recovery phases, respectively. Particularly, significant solar wind energy transfer into the magnetosphere occurs when negative of northsouth (N-S) component of the interplanetary magnetic field, Bz of largeamplitude fluctuating Alfvén waves within some HSSs reconnects to the Earth's magnetic field. This leads to High-Intensity Long-Duration Continuous AE Activity (HILDCAA) that can last for several days to weeks (Tsurutani and Gonzalez, 1987) during a long recovery phase of storms. Effects of RGS on ionospheric-thermosphere have much attention and become a main subject of intense studies (Lei et al., 2008; Tulasi Ram et al., 2010; Pedatella and Forbes, 2011; Verkhoglyadova et al., 2011, 2013; Wang et al., 2011; Burns et al., 2012; Liu et al., 2012b; Dmitriev et al., 2013; Kutiev et al., 2013; Candido et al., 2018). The studies indicated that the ionospheric-thermospheric responses to RGSs are recurrent, prolonged and complicated. The coupling between the magnetosphere and equatorial ionosphere during CIR/HSS has also been studied that found significant coupling processes between the auroral zone and the equatorial ionosphere (Sobral et al., 2006; Wei et al., 2008; Kelley and Dao, 2009; Koga et al., 2011; Silva et al., 2017; Yeeram, 2017). However, the electrodynamic coupling of the solar wind and magnetosphere-ionosphere system in responses to some consecutive RGSs, has not been investigated. In addition, due to the EEJ strength does not exhibit any recurrent signatures at sub-harmonic solar rotational periods, Tulasi Ram et al. (2012) pointed out that a case-bycase basis is vital to understand the impact of RGSs on equatorial electric field and its implication. A lack of this kind are also suggested (Dmitriev et al., 2013). The purpose of this work is to investigate the solar wind coupling and evolution of electrodynamic processes in the Peruvian longitude sector during some selected consecutive RGSs in 2007, a declining phase of solar activity. A pair of magnetometer data in Peru, geomagnetic indices, and the interplanetary data are used. In particular, results indicate that the variabilities are multifaceted, quasiperiodic, and diverse in association with the evolution of the RGSs and seasonal effects.

characterized using 1-min-averaged solar wind plasma parameters shifted to the Earth's bow shock nose already together with geomagnetic indices: symH, Auroral Electrojet (AE), and Polar Cap (PC). Note that the symH is essentially the finer resolution of the Dst index. The Auroral Upper (AU) and Auroral Lower (AL) indices express the strongest current intensity of the eastward and westward AE, respectively. The difference, AU minus AL, defines the AE index that describes the global activity of enhanced ionospheric currents flowing below and within the aurora oval in the auroral zone as derived from geomagnetic variations in the H component observed at selected (10 13) observatories along the Northern auroral zone. The Polar Cap North (PCN) index is derived from a magnetometer station at Thule (86.5° invariant geomagnetic latitude). The Polar Cap South (PCS) index is derived from Vostok (83.3° invariant geomagnetic latitude). The PC index is related to the storage of energy in the ring current during magnetic substorms/ storms and is a proxy of the integrated Joule heating rate (Chun et al., 1999). Chun et al. (2002) find that positive PC is consistent with intensification of Joule heating throughout the auroral oval, particularly along the dawn/dusk flanks. It is known that the major contribution to the PC index is the twin-vortice DP2-like current system related to the solar wind electric field (Stauning and Troshichev, 2008; Troshichev et al., 1988). The y component of interplanetary electric field (E y ) is derived from Vx Bz , where Vx is the x component of solar wind velocity. The re1/2 connection electric field is given by ER = Vx (By2 + Bz2) sin( /2) , where θ is the IMF clockwise angle in the y z plane in the GSM coordinate system, with 0° and 180° indicating northward and southward IMF, respectively. This electric field consists of parallel and transverse components to the Earth's magnetic field. The former contributes to the acceleration of charged particles along the magnetic field lines at the magnetopause while the latter becomes the origin of the polar cap potential drops and auroral electrojet. The latter is thus an important parameter for the study of the electrodynamics of the ionosphere. The transverse component of the reconnection electric field is derived from E = ERsin( /2) measured in mV/m (Gonzalez and Mozer, 1974; Kan and Lee, 1979). Hereafter E is just described as ER for the sake of simplicity. We also employed dH data from the difference of horizontal (H) geomagnetic fields measured at pairs of stations in Peru, Jicamarca (11. 9 S, 76. 8 W; magnetic dip 1 N) and Piura (5. 2 S, 80 W; magnetic dip 6. 8 N). The subtraction can eliminate both the global Sq current system and the Dst ring current component in H, that is only related to the EEJ. Note this method is not operative at night due to the absence of the Cowling conductivity. As will be discussed to the seasonal characteristics of EEJ, the data are grouped into three Lloyd's seasons, namely, D months consisting of November, December, January, and February; E months consisting of March, April, September, and October; and J months consisting of May, June, July, and August. 3. Results and interpretation 3.1. Solar wind and geomagnetic conditions The solar wind and geomagnetic conditions during the passages of RGSs show quasi-stable variability in each solar rotation with minor differences as shown in Fig. 1. For convenience, let RGS1, RGS2, and RGS3 represent October, November, and December events, respectively. By defining HSS as the solar wind speed (V) is larger than 450 km s−1, two main groups of HSSs are indicated by numbers 1 and 2 in correspondent to formation of respective CIRs1 and CIRs2 with different sizes at the their leading edges. Second group of long-lasting HSS of RGS1, RGS2, and RGS3 persist about 5.93 days, 7.64 days, and 6.84 days, respectively. They cause more intensive CIR-induced storms and stronger geomagnetic responses, suggesting to higher energy input into the ionosphere. RGS2 is the strongest storm as the minimum value of

2. Observations and data presentation From an investigation of the solar wind plasma data and geomagnetic indices, three properly consecutive quasi-stable RGS events from 9 October to 29 December 2007 are chosen to study their effects on the equatorial ionospheric electrodynamics responses. The RGS events were 41

Journal of Atmospheric and Solar-Terrestrial Physics 187 (2019) 40–52

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Fig. 1. Three selected recurrent geomagnetic storms from 9 October to 29 December 2007 (Day of year 282–363) divided by vertical dashed lines. (a) The solar wind speed. (b) The solar wind dynamic pressure. (c) North-south interplanetary magnetic field. (d) Equatorial electrojet. (e) symH. (f) Polar cap index of the North and South pole with their daily moving averages. (g) AE index. (h) AL (grey) and AU (black)indices. Shaded areas indicate the main phase of the CIR-induced storms. See texts for details.

symH was lowest, while the PC and AE indices were highest. Note that the second HSS group evolved from two sharp peaks in RGS1 to three higher peaks in RGS2 and RGS3 in consistent with morphology and numbers of peak of the AE index. Let I, M, and R indicate the initial, main, and recovery phases of the CIR-induced storms, respectively. The initial phases of the storms were located at the leading edges of the HSSs, where the positive symH indicates the compression of magnetosphere. Concurrently, the solar wind dynamic pressure (SWDP), PC, and AE/AU/AL indices start to increase. The latter indicates a fast rate of reconnection and flux transfer into the magnetosphere as expressed by the cross polar cap potential that is linearly proportional to the PC index (Chun et al., 2002). Note the westward electrojet (AL) was stronger than eastward electrojet (AU). The peaks in the SWDP corresponded to the rising of the symH, which is a storm sudden commencement (SSC) due to a fast shock, particularly seen in the second CIR storms of each RGS. The features indicate that CIRs2 provided larger bulks of pressure that cause stronger compression of the magnetosphere than CIRs1. In the main phase with about one day period, the symH decreased to minimal values due to intensification of the ring current that induces a horizontal magnetic field opposes to the Earth's dipole field, the SWDP dropped but IMF Bz increased. The IMF Bz exhibited large fluctuations in the N-S direction with magnitudes within ± 15 nT. Note that CIRs1

induced only weak storm, while CIRs2 induced abrupt increases in the geomagnetic responses with moderate level in RGS1 and RGS2 and with weak level in RGS3. Finally, in the long recovery phase the symH increased from its minimum, when the SWDP was small and nearly constant. Rapid north-south fluctuations in Bz within ± 10 nT indicate to Alfvén waves in HSS. The recovery phase following CIR2 of each RGS denote HILDCAA periods (HILDCAA1-HILDCAA3) of sustained AE index intensity as empirically defined by Tsurutani and Gonzalez (1987) that AE index should not range below 200 nT, peak is more than 1000 nT, and occur during the recovery phase. In addition, the symH index is not less than 100 nT and there are HSS and high frequency fluctuations of IMF Bz about zero value. Later, Prestes et al. (2017a) modified a HILDCAA criteria by changing the AE values should never drop below 200 nT from 2 h to 4 h at a time and called HILDCAAs*. They suggested that the HILDCAAs × present the same physical characteristic as HILDCAA as observed in 2003. Prestes et al. (2017b) showed that the less strict HILDCAAs × events between the years of 1998 and 2007 contain a larger number of Alfvén waves than the HILDCAA events. As mentioned, the first and second groups of HSSs correspond to non-HILDCAA and sustained HILDCAA × conditions, respectively. Note that EEJ as represented by the dH values tended to be decreased from October to December, which suggests to the seasonal 42

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Table 1 Correlation coefficients and time lags (in brackets) in hour of the solar wind and geomagnetic parameters of the consecutive RGSs. Event

DOY(UT) (start-stop)

Ey /AE

ER /AE

Bz /AE

AL/symH

AE/AL

AE/AU

PC/AL

AE/PC

CIR1(1) CIR1(2) CIR1(3) CIR2(1) CIR2(2) CIR2(3) HILD-CAA1 HILD-CAA2 HILD-CAA3

291.17–293.79 317.39–321.77 344.88–347.86 298.56–298.85 324.44–324.85 351.32–351.67 298.85–304.67 324.85–332.72 351.67–357.92

0.44 (22) 0.41 (22) 0.50 (16) 0.32 (15) −0.09 (22) 0.03 (29) 0.46 (32) 0.42 (26) 0.36 (20)

0.35 (22) 0.42 (22) 0.40 (16) 0.39 (15) −0.32 (22) 0.06 (29) 0.61 (32) 0.61 (26) 0.48 (20)

−0.46 (46) −0.43 (19) −0.51 (18) −0.37 (17) 0.11 (13) −0.35 (31) −0.47 (31) −0.42 (28) −0.36 (20)

0.56 0.36 0.36 0.28 0.08 0.16 0.24 0.46 0.36

−0.98 −0.95 −0.91 −0.96 −0.93 −0.96 −0.97 −0.97 −0.96

0.52 0.53 0.62 0.69 0.61 0.51 0.55 0.68 0.56

−0.69 −0.66 −0.61 −0.83 −0.61 −0.56 −0.78 −0.71 −0.63

0.71 0.71 0.72 0.88 0.47 0.52 0.80 0.74 0.66

(2.62) (4.38 dd) (2.98 dd) (0.29 dd) (0.41 dd) (0.35 dd) (5.82 dd) (7.87 dd) (6.25 dd)

effects. October is an equinoctial month when large solar dynamo drives the enhanced eastward EEJ due to the great solar illumination. The spectral results showed that the EEJ has maxima around equinoxes in Jicamarca (Shume et al., 2010). As also shown in Fig. 1, the quiet day EEJs (outside the CIR and HILDCAA periods) are substantially smaller (amplitude ∼40 nT) during the summer solstice months than the equinoctial month (amplitude ∼60 nT). However, counter EEJ events are found to be more frequent during winter and summer months during solar minimum (Marriott et al., 1979; Venkatesh et al., 2015). It is found that the electrojet variability during quiet periods is dominated by the zonal wind at 100–120 km altitudes near the magnetic equator (Yamazaki et al., 2014). However, the local summer in the southern hemisphere (November and December) that exhibits noticeably low EEJ can also be interpreted in term of seasonal effects of DDEFs. This point will be discussed more in Sections 3.2 and 4.3.

(18) (15) (23) (35) (38) (0) (3) (19) (1)

The transient fluctuations of storm-time AE/AL index in HILDCAA may not be directly related to the variations of symH because storm-time ring current and AE index develop more or less independently of each other (Grafe and Feldstein, 2000). In addition, the time lags of AL/ symH are 0 38 mins that indicate to time-consuming development of ring current after the AL formation, which is consistent with the nightside sporadic injection of protons into the outer portion of ring current above L > 4 during HSS/HILDCAA events (Søraas et al., 2004). These injections are also associated with continuous substorm activity caused by Alfvénic fluctuations within the HSSs (Tanskanen et al., 2005). The correlations for AE/PC are high (C.C. 0.7) in most cases, except for CIR2(2), CIR2(3), and HILDCAA3 that are moderate. The lower C.C. would suggest less effective couplings and/or different sources of PC and AE during the CIRs and HSSs in the local summer. The result is in agreement with previous work that shows good correlation between PC and AE index, particularly during local winter and equinox with C.C. ranging between 0.7 and 0.9, with lower correlation during summer (Vennerstrom et al., 1991). During summer, the PC index is disturbed by polar cap currents controlled by the northward and east-west components of the IMF (Vennerstrom et al., 1991). As known, the PC indices are mostly due to the FACs flowing at the poleward rim of the aurora oval and to the ionospheric Hall currents in the polar cap. This study covers local summer time in the southern hemisphere (SH) where Hall currents are also important. The high conductivity of the summer ionosphere provides the perfect conditions for closure of the R1 FACs responsible for the cross-polar cap potential and polar cap magnetic activity that can enhance PPEF and DDEF. In addition, high-latitude field-aligned intensities are larger by a factor of 1.5 1.8 in the sunlit (summer) polar cap in comparison with the winter hemisphere (Christiansen et al., 2002). As seen in Fig. 1, the PCN tended to be weaker than PCS only during the summer season, which indicates to higher auroral energy input and high conductivity in the SH. Note during HILDCAA periods the PCN and PCS are quite similar in both the equinox and summer solstice. The above result is also be explained by substantial DD effects during the CIRS/HILDCAA. DD effects are expected to be prevalent due to the equatorward motion of the composition changes (brought in due to geomagnetic storms) in summer (Fuller-Rowell et al., 1996). As a result, the PC and AE would be less correlated at high latitudes during storm times in the summer. This point will be further addressed and discussed.

3.2. Cross correlation between the solar wind and geomagnetic indices The couplings between the solar wind and magnetosphere-ionosphere in the main and recovery phases of the consecutive RGSs are investigated. Table 1 lists the cross correlation coefficients (C.C.s) and time lags of each data pair. Time lags are indicated to compensate for the propagation of effects from the bow shock nose to the polar cap. Note data gaps with no more than three consecutive points (minutes) are linearly interpolated, otherwise they are discarded in the correlation analysis. From Table 1, the correlations of E y /AE and ER /AE are positive and tend to be moderate, except for CIR2(2) and CIR2(3) that exhibit weak correlation. The time lags of these correlations are 15 32 mins. Note that the C.C.s are higher for E y /AE than ER /AE in CIRs1, while they are low and irregular in CIRs2. Remark that the C.C.s are higher for ER /AE than E y /AE in HILDCAA1-HILDCAA3 but still be in the moderate level. This stresses the role of magnetic reconnection in HILDCAA periods. The correlations between AE and Bz are moderate and negative, except for CIR2(2). This suggests complex couplings in the CIR-induced storm and HILDCAA periods. The time lags are in the ranges 13 36 mins. Note that the coupling of penetration of convection electric fields through FACs by Bz with the PC is found to be better than with AE for all RGSs. Typically, correlation of AE/AL is high with C.C.s >0.9 in every CIRs and HILDCAAs, whereas the correlation of AE/AU is generally moderate. Correlations of AL/symH during RGSs are moderate, except for CIR2(1)-CIR2(3) that exhibit weak correlations. The correlation indicates how the ring currents surrounding the Earth during the RGSs are closely associated with the westward auroral electrojet. Sometimes, increases in AE or AL within the HILDCAA event tend to associate with decreases in symH, indicating to temporal ring current intensification. The evidence is that correlations of PC/AL are also moderate but high in CIR2(1) and HILDCAA1-HILDCAA2. Note the PC represents the PCN throughout this paper. The PC is well correlated to ring current intensities (Stauning and Troshichev, 2008) since they both relate to the interplanetary geoeffective electric field (Troshichev et al., 2006) as also observed in CIR-induced storms and HSSs in this work. However,

3.3. Fourier analysis Fourier analysis indicates predominant consistent time periods between Bz and AE index during all HILDCAA events not during CIRstorms, particularly CIRs1 and CIRs2 as listed in Table 2. Fig. 2 shows such consistent periods of both parameters (also many inconsistent periods) during HILDCAAs, which suggest that IMF Bz is strongly coupled with the AE. The consistency spans both shorter and longer periods than 1 h. Note that the dominant mode of periods is the >1 h mode as noticed in the spectral magnitudes. The magnitudes are noticeably 43

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Table 2 Dominant oscillatory periods (in h) of Bz and AE index of CIRs and HILDCAAs of each RGS. Consistent periods of both parameters are highlighted in bold only in Bz .

AE

HILD1

HILD2

HILD3

CIR1(1)

CIR1(2)

CIR1(3)

CIR2(1)

CIR2(2)

CIR2(3)

23.27 7.35 8.21 3.03 15.51 2.79 6.35 12.69 23.27 7.35 6.35 8.72 12.69 15.51 5.17

15.73 6.51 5.55 7.62 11.10 4.60 37.36 3.85 30.33 15.73 4.60 5.55 11.10 6.29 3.85

24.99 6.00 149.93 12.49 8.82 16.66 2.88 4.41 74.67 24.99 6.00 8.82 18.74 12.49 5.55

7.87 15.73 3.15 1.37 1.97 2.52 1.53 1.08 15.73 7.62 3.31 4.20 10.49 2.25 3.70

15.03 7.01 35.07 10.52 21.04 3.89 3.51 2.19 15.03 7.5 3.50 26.30 3.09 5.54 3.89

23.87 5.51 11.93 2.10 2.86 71.60 7.96 3.58 17.90 8.95 3.58 5.11 2.75 4.47 1.10

3.45 1.72 0.69

1.23 0.76 3.29 1.97 0.99

4.23 1.69 0.94

1.15 0.86

3.29 1.41

2.82 1.06

However, the consistent periods between Bz and AE are distinct in each HILDCAA, suggesting to independent variability and coupling of the fluctuating Bz and subsequent AE during HSSs. The largest periodicity of Bz found in HILDCAA3 is 149.93 h (6.25 days) that is consistent with the relationship between PPEF and Bz with a 7-day periodicity (Fejer and Scherliess, 1997; Wang et al., 2011). The periodicity of AE index in HILDCAA3 is 74.67 h (3.11 days) which is roughly a subharmonic of 9-day periodicity in auroral energy input and DDEF in the equatorial ionosphere (Deng et al., 2011; Liu et al., 2012b; Sripathi et al., 2016). Prestes et al. (2017b) showed the wavelet coherency scalogram between Bz component and the hly AE index in longertimescales, which reveal strongest correlation between 13 and 30 days, which are the harmonic and sub-harmonic of the solar rotation period. In the same sense, this work reports finer time scale of the correlation between Bz and AE that stresses the role of magnetic reconnection during the RGSs. Moreover, this aspect is also attributed to the Joule and particle heating that caused globally thermal expansion in the thermosphere at all latitudes during RGSs (Thayer et al., 2008; Lei et al., 2008; Tulasi Ram et al., 2012). 3.4. Evolution of daytime disturbance electric fields Superposed temporal evolutions of disturbance electric fields and the solar wind plasma parameters during the three consecutive RGSs of CIRs1 and CIRs2 are shown in Figs. 3 and 4, respectively. In overview, at quiet time the EEJ exhibits similar features during RGS1-RGS3 with positive peaks near noon. For weaker CIRs1 storms and their subsequences as shown in Fig. 3, the storm time onsets of each RGS were different; RGS1 is the last and RGS3 is the first one. Clear PPEFs are indicated by noticeable fluctuations in the daytime dH during the initial and main phases of the CIR storm (in panels (d), (f), and (h)), particularly in RGS2 and RGS3. During RGS3 there are strongest disturbed dH that is almost flat during the first day and more negative during the second day, when the SWDP and AE index (with peak 380 nT and 650 nT in the first day) increased earlier than other RGSs. The feature suggests that DDEF is more slowly varying and sustains in the whole daytime. Negative dH appeared during the early morning of the second day of every RGS and then almost disappeared in later days when AE index was relatively low. Note negative dH appeared in the afternoon time during the third and fourth days of RGS3 when AE index was relatively high during sunrise. The relative high AE index which reaches to the HILDCAA conditions was present during daytime and nighttime of the third day and lasted in the morning of the fourth day of RGS1. This may cause large DDEF during the third day and later. The lowest symH (enhanced westward ring current) in RGS3 in association with the cumulative increases in AE during the first two days may lead to the low dH in the prenoon to afternoon of the second day.

Fig. 2. Spectral magnitudes of Bz and AE index during HILDCAA periods.

small with reducing the time periods, which indicates that the coupling is more efficient during the >1 h mode than during the <1 h mode. It is interesting to note that the AE variability period during HSSs is in the range 1 10 h similar to the ones of interplanetary Alfvénic waves (Diego et al., 2005). By using a wavelet decomposition technique to calculate an AE × time series based on IMF Bz data measured at L1 in the presence of interplanetary Alfvén waves, the calculated AE × was shown to be highly correlated with the observed AE index (Guarnieri et al., 2018). However, they found the lack of a high correlation in some intervals, where they attributed this to non-geoeffective high-frequency turbulence (periods < 8 min) in the solar wind and/or local generation of Alfvén waves in the interplanetary medium (Tsurutani et al., 2018). 44

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Fig. 3. Superposed plots of the solar wind plasma, EEJ, and geomagnetic indices during each RGS for subsequent CIRs1 assigned as non-HILDCAA events. An additional 16 min was added for the solar wind to travel through the magnetosheath to the ionosphere.

CIRs2 storms and their subsequences are shown in Fig. 4. Their temporal evolutions are also storm time dependent. The SWDP increased first in RGS2 then in RGS3 and RGS1 (not shown); RGS1 is the last storm, while RGS2 is the first one. For RGS2, the SWDP moderately increased again in daytime of the third day when dH was more positive. For RGS3, the SWDP moderately increased in the afternoon of the fourth day. The signature of PPEFs are found during the initial, main, and recovery phases of the CIR storms. Particularly, substantial PPEFs occurred during the first day that coincided with the main phases in every RGS. Note the large PPEFs occurred at different storm time conditions. For RGS1 they coincide with largely short-lived N-S fluctuating Bz in association with overshielding and undershielding conditions, while for RGS2 they coincide with large southward Bz with a period 14 h. The latter implies that eastward PPEFs can significant reduced DD effects in which the dH is not stronger suppressed than in RGS3, when the PPEFs are less effective under moderately short-lived N-S Bz . Note that remarkable PPEFs and DDEFs occurred also during the afternoon of the fourth day in RGS3, when the AE index is moderate and high; the PPEFs coincide with the 4-h southward Bz of the undershielding conditions. An onset of negative dH in the afternoon of the RGS1 is well consistent with the delay effect of DDEFs in accord to the

AE increase in the morning. It is interesting to note that during afternoon of the third day (DOY 326) of RGS2 reduction of dH is well consistent with the overshielding PPEFs when the Bz turned northward in association with the DD effects due to the auroral heating. From both CIR storms and their subsequences, the results reveal that departures of EEJ from the quiet value are remarkable and critically depend on the storm-times. There are noticeable reductions of EEJ when moderate/high AE was precedent. Therefore, the reduction magnitudes depend upon the size of AE index and the subsequent time delay. The above results are well consistent with the classical shielding theory. Magnetospheric PPEFs are present during RGSs as marked by the short fluctuations of dH as observed in panels (d), (f), and (h) of Figs. 3 and 4. This implies that CIR storms with non-HILDCAA and HILDCAA are basically affected by the PPEFs with undershielding and overshielding conditions. When IMF Bz is southward it corresponds to the undershielding condition; dH (EEJ) was enhanced. The behavior is opposite for the northward Bz , overshielding condition. Combination of eastward PPEF with westward DDEFs leads to negative or small dH during the HILDCAA events. This should cause reduced ionospheric effects in the HILDCAA (Abdu et al., 2013). 45

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Fig. 4. Same as Fig. 3 but for each RGS for subsequent CIRs2 assigned as HILDCAA events.

Remark that EEJ in DOY 324 (20 November 2007) during CIR2 of RGS2 (CIR2(2)) exhibits more complex process and different feature than during the same phase of the RGS1 and RGS3, which are also indicated by the correlation analysis. Wei et al. (2009) suggest that there are two substorms that produce strong westward electric field perturbations that drive westward EEJ on the dayside ionosphere. This westward electric field is closely related to an overshielding-like imbalance state of FACs, which is built up through R2 FAC enhancement rather than R1 FAC reduction due to IMF northward turning.

magnetosphere-ionosphere system during the three consecutive RGSs is quasi-stable and diverse. The result is well consistent with a comprehensive model simulations and data analysis by Solomon et al. (2012). They suggest that even many HSS/CIR events seem similar, the thermosphere-ionosphere response is diverse during three consecutive RGSs in the first half of 2008. Generally, CIR has a greater impact on the ionosphere than HSS/HILDCAA because of the higher auroral energy input (due to most intense AE and largest southward Bz ). However, the solar wind speed (V) can also have an amplifying effect, particularly when it is associated with large amplitude southward Bz of Alfvén waves in HILDCAA events. The picture is well consistent with the solar wind merging rate (Newell et al., 2007) that both IMF Bz and V affect the dayside magnetic reconnection rate in the magnetosphere: V x4/3 BT2/3sin8/3 ( /2) , where BT = (By2 + Bz2)1/2 . More southward IMF Bz values imply a faster rate of reconnection and flux transfer into the magnetosphere. The importance of variations in southward Bz in association with increased V can amplify the magnetosphere-ionosphere/ thermosphere response under the encounters of CIRs and HSSs is demonstrated (Solomon et al., 2012; Luan et al., 2013). This work found that the C.C.s are higher for ER /AE than E y /AE in HILDCAA1-HILDCAA3. Moreover, the C.C.s are lower for ER /AE in the CIRs than in the HILDCAA events, which is in well agreement with the study of Koga et al. (2011). The results suggest that magnetic flux

4. Summary and discussion This study reports the variability of daytime equatorial electrodynamic response to the evolution of three consecutive RGSs including CIR and HSS/HILDCAA. The time periods cover equinoctial and summer solstice months of the southern hemisphere over Peruvian sector. The main results are discussed in light of current theories, simulations, and observations. 4.1. Coupling of the RGS on the magnetosphere-ionosphere This study found that the coupling of the solar wind and 46

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merging is more effective in HILDCAA than in CIR. Guo et al. (2012) also found eastward and westward electrojet currents are better correlated with the merging electric fields (C.C.>0.6 ) by using IMAGE network magnetic measurement. Moreover, the fast Fourier transform indicated that during HILDCAA events the consistent periods of between Bz and AE are clearly seen although the correlation between them is moderate. However, during CIR events the consistent periods between them are rarely found. These results highlight the interesting aspects of the coupling between the solar wind and magnetosphereionosphere system in the CIR and HILDCAA events. During CIR-induced storms, the coupling between Bz and AE index is disturbed by several interplanetary drivers, such as large SWDP and shocks (Pulkkinen et al., 2007; Yeeram, 2017). It is also possible that the frequencies/periods are modified during CIR storms. On the other hand, during HILDCAAs/ HSSs many of the dominant oscillating periods of Bz are well consistent with those of the AE index, implying that the solar wind energy is transferred directly to the magnetosphere by the magnetic reconnection. Therefore, the C.C.s of ER /AE and Fourier analysis provided important data that can separate the CIR storms from HILDCAA events. More cases or statistical studies are needed to confirm this point, however. This study reports high anti-correlation of AE/AL with C.C.s >0.9 in every CIRs and HILDCAAs, but moderate correlation of AE/AU. This suggests that developments of AE during CIRs and HILDCAAs are mainly due to westward electrojet intensifications as found by Tsurutani et al. (2004). The eastward electrojet fluctuation is mainly due to the N-S component of the electric field, while the westward AE fluctuation is attributed to both the electric field and Hall conductance controlled by by dark-side precipitating electrons (Kamide and Kokubun, 1996; Ahn et al., 1999, 2000). There are two types of external energy sources in driving the variations of the auroral activities, solar wind forcing and solar EUV irradiance. However, during the solar minimum, the EUV irradiance does not exhibit any significant spectral peaks at the period of 9 days (Tulasi Ram et al., 2010). Therefore, the recurrent solar wind forcing is the main source of the driving. Previous studies reported that the high latitudes ionospheric convection shows periodic variations in response to the HSSs (Heelis and Sojka, 2011; Pedatella and Forbes, 2011; Guo et al., 2012). During magnetic storms associated with HSSs, the magnetospheric energy input is mainly contributed by Joule heating (>60 %), while it is partially contributed by particle precipitation (∼20%), and ring current (∼10%) in the auroral zones (e.g., Turner et al., 2009; Deng et al., 2011; Hajra et al., 2014). The weak ring current is well consistent with the low and moderate correlations between AL and symH for both CIRs and HILDCAAs.

disturbance electric fields are weak, but long lasting. PPEFs typically 1 3 h in HILDCAAs due to the sporadic oscillate with periods coupling by the Alfvén waves in HSSs, while the effect of DD can persist for more than a day (Scherliess and Fejer, 1997). In addition, when transient negative drift decays, the DD drift remains because of the persistence of the disturbance winds that take many hs to relax back to the quiet state (e.g., Richmond and Lu, 2000). Means of self-consistent model of the Earth's upper atmosphere are performed to separate PPEF and DDEF at the geomagnetic equator during storm-time (Maruyama et al., 2005; Zaka et al., 2010). Maruyama et al. (2005) found that PPEF is dominant in the equatorial disturbed electric field during the daytime at the early stage of the storm, while DDEF is initiated later. The PPEF and DDEF effects are comparable at nighttime. The result suggests that when the PPEF is negligible or absent at daytime, DDEF is the main disturbance field in the F-region and vice versa. During HILDCAA periods, it is important to point that there are interplays of the undershielding/overshielding electric fields, and DDEFs. DDEFs are expected to be continuously present and delayed during long HILDCAA periods due to the continuity of high AE index. When the overshielding PPEFs associated with the northward turning of Bz superpose on the long-lasting westward DDEFs at daytime the westward electric field must be enhanced. On the other hand, when the DDEFs merge on the undershielding PPEFs at daytime the westward electric fields must be suppressed. Therefore, during daytime of the HILDCAA periods one would expect to observe alternating enhanced and suppressed westward electric fields with the oscillatory periods about 1 3 hs during overshielding and undershielding conditions, respectively. Rodríguez-Zuluaga et al. (2016) also concluded that the response of the low latitude ionosphere geomagnetic storm is largely determined through the oscillation frequency of the IMF Bz by affecting the generation of the PPEF and DDEF differently. Previous studies on the magnetic data have found that the reduction of the H component amplitude at the magnetic equator is a result of the DD opposing the regular eastward EEJ (Sastri, 1988; Fambitakoye et al., 1990; Le Huy and Amory-Mazaudier, 2005). The DDEF has westward polarity at daytime as can be seen in the response of EEJ current intensity. The DDEF can compress remarkably the H component of the geomagnetic field in the equatorial ionosphere and last for more than 30 hs during the July 2012 storm and the evolution of the disturbance winds changes the local time morphology of the DDEF in the low latitudes as observed by (Zhang et al., 2017). In the long recovery phase of moderate storm when the auroral activity is weak, only the DD process is active in the ionosphere (Le Huy and Amory-Mazaudier, 2005; Zaka et al., 2009). However, when the AE is high such as in CIR/HILDCAA periods the PPEFs must be present as well. Recently, Fejer et al. (2017) reviewed the DD mechanism extending to post-storm periods and its effects on the electrodynamics of middle and low latitude ionosphere. Liu et al. (2012b) found an appearance of DDEF in daytime on 5 7 January 2008 after the RGS3 with time scales of 10 h at Jicamarca. Fathy et al. (2014) also found ionospheric DD in association with HSSs in 2010. The DD reduces the amplitude of the daytime H component at low latitudes during four consecutive days and the amplitude of DDEF decreases with time. The latter is also observed in this work and is interpreted by reduction of the Joule heating during post-HILDCAA periods. Characteristics of the disturbance electric fields during CIR storms tend to be different from that of HILDCAA events. As shown in Figs. 3 and 4, PPEFs critically depend on the direction and magnitude of the IMF Bz and on magnitude of SWDP during CIR-storms. They exhibited multiple short-lived feature and the prefer conditions of undershielding PPEFs are large southward Bz and high SWDP as typically observed in CIRs (Yeeram, 2017). As known, the DD drifts disappear a few hs after the end of main phase of geomagnetic activity, but reappear with relatively large nighttime values about a day later (Scherliess and Fejer, 1997). However, during HILDCAA DDEFs may not have enough time to

4.2. Disturbance electric fields The most important contributors to the storm time effects of the equatorial F region are the electric field disturbances, PPEFs and DDEFs. These disturbance electric fields during CIRs and HSSs are observed when the auroral activities are intensified by R1 FACs. Intermittence magnetic reconnection between southward components of Alfvén waves fluctuations and magnetopause magnetic fields cause penetration of the convection electric field. The magnetospheric penetration electric fields from high latitude are rapidly transmitted to the equatorial ionosphere. The meridional neutral winds, set-up by Joule heating of the thermosphere in the auroral region travel to the equatorial region and cause the DDEF. The propagation of the disturbance from high to low latitudes is controlled mainly by meridional wind circulation (Blanc and Richmond, 1980; Liu and Lühr, 2005). With a speed of about 600 m/s, these disturbances reach low-latitudes about 4 5 h after the onset of a storm (Fuller-Rowell et al., 1997). Since the storm time of CIR is frequently longer than this time delay, PPEFs and DDEFs can simultaneously present in the CIR. For case of long duration AE activity such as HILDCAAs, Abdu et al. (2013) suggest that the 47

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4.3. Seasonal dependence of disturbance electric fields As pointed out in Section 3.1 and 3.4, disturbance electric fields are also dependent on seasons. EEJ (dH) is smaller in D months than E months, which is also observed in Fig. 3. On the first day, under the low AE activity, the EEJ of RGS1 was larger than RGS2 about 38 nT. On the fourth day, EEJ in RGS2 was clearly larger than in RGS3 even they were under similar low AE conditions. These strongly suggest the season dependence of EEJ. However, EEJ can be suppressed by effects of DDEF that also be seasonal dependent. Remark from Fig. 4 that the strongest DD effects are observed during RGS3 (December) when dH was 110 nT around 0800 LT of the first day. The stronger suppression of dH in the morning of RGS3 than of RGS2 is more dependent on the preceding equally large AE rather than the weak decreased symH. This justify the seasonal effects of the enhanced AE that generated the largest DDEFs at equatorial ionosphere in December (RGS3). Subsequently, the DDEFs were still present in the next day with smaller amplitudes when the AE decreased. In addition, during day 4 around 10 16 LT dH was reduced more in RGS3 than in RGS1, when AE was about 800 nT in RGS3 and was 400 nT in RGS1. There is no clear reduction of dH even the AE was large in RGS1, while there is noticeable reduction in the dH of RGS3. Moreover, a small reduction of dH at the same time was apparent in RGS2 even the AE was lower than the RGS1. The features also justify the seasonal effects of DDEFs, which are stronger during the summer months than the equinoctial months. Results indicate that DDEFs possibly play a more dominant role in the local summer in the Peruvian region. The aspect can be explained in terms of seasonal effects of thermospheric neutral winds propagating from high-to low latitudes. Variabilities of dH and geomagnetic responses during winter solstice (J months) are also shown in Figs. 5 and 6 for comparison. Note there are no data available during storms in June. Mark that no obvious reductions of dH in the whole day were observed during these months as found in D months. There was only a shortly large reduction in the morning of DOY 201 when the AE was almost 1000 nT even though there are three multiple events of increased AE and decreased symH shown in Fig. 6. The behavior suggests that DDEFs are less effective during this winter in the southern hemisphere. The Joule heating rate at auroral zone is generally larger in the summer hemisphere than in the winter hemisphere because of higher electrical conductivity in the summer high latitudes (Fuller-Rowell et al., 1996; Forbes et al., 1996; Rodger et al., 2001). Asymmetric currents due to different ionospheric conductivities in the dark and sunlit conjugated hemispheres have been established (Benkevich et al.,

Fig. 5. The solar wind conditions, geomagnetic activity, and EEJ during DOY 141–145 (21–25 May), winter solstice in 2007.

decay because they are combined with a following new DDEF that is generated by the DD effects in association with a new high AE index. In addition, AE index tends to decrease with time in HILDCAA as seen in Fig. 1, therefore the DDEFs must be suppressed with time as found by Fathy et al. (2014). Yamazaki and Kosch (2015) investigated substorm and storm-driven equatorial electrojet perturbations that found a semidiurnal variation with a westward disturbance in the morning and eastward disturbance in the afternoon in agreement with the empirical model of Scherliess and Fejer (1997). They found that not only the DDEF in the morning but also the PPEF in the afternoon increases with increasing storm intensity. For HILDCAA, Sobral et al. (2006) studied less strict HILDCAA events in 2000 and 2001 over three equatorial–low-latitude stations in Brazil. Their results indicated evidence of the DD and disturbed thermospheric winds not PPEFs. Wei et al. (2008) found that multiple electric field penetration to equatorial ionosphere is associated with HILDCAAs, however. Koga et al. (2011) studied electrodynamic coupling processes between the magnetosphere and the equatorial ionosphere over Sao Luis-SL, Brazil during a 5-day-long HILDCAA event in 2003. They found that the PP drifts are not clear. The result is attributed to the presence of DD drift and other effects as they found a good relationship between the disturbed height and DD drift calculated from the model of Fejer and Scherliess (1997). However, short-period correlation of the PPEF is present many time of the pre-HILDCAA (CIR) and HILDCAA periods. Zaourar et al. (2017) study geomagnetic and ionospheric responses to a HSS impacting the magnetosphere on 24 August 2010. From the magnetic disturbance, they observed the presence of short time fluctuations (15 min–1.5 h) simultaneously at all latitudes related to the PPEF and also long time fluctuations (19 24 h) associated with the DDEF. Huang (2012) studied equatorial electrodynamics in association with HSSs during January–April 2007. They found anti-correlation between the solar wind velocity and the equatorial vertical ion drift measured by the Defense Meteorological Satellite Program (DMSP) satellites. The result is consistent with the consecutive evolution of HSSs during HILDCAA events. Several peaks of HSSs as seen in Fig. 1 induced enhanced magnetic flux merging on the dayside magnetopause and resulted in large ionospheric Joule heating as indicated by their correspondent high AE index. Each group of HSSs is therefore expected to induce each of the equatorial DDEF. This indicates also that strong storms (high AE) can produce major thermospheric perturbations that extend to middle and low latitudes as suggested by Fejer et al. (1983).

Fig. 6. Same as Fig. 5 but for DOY 191–202 (10–21 July 2007). 48

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2000). Roble et al. (1983) suggested that for moderate levels of geomagnetic activity, there is about three times more Joule heating in the summer hemisphere as compared to winter hemisphere. During solstices, the seasonal winds are directed from the hotter summer to the cooler winter hemisphere (i.e., the neutral winds are equatorwards in the summer and polewards in the winter hemisphere). Therefore, these ambient winds restrict the equatorward motion of the composition changes (brought in due to geomagnetic storms) in winter while allowing them to reach lower-latitudes in the summer (Fuller-Rowell et al., 1996; Yadav and Pallamraju, 2015). Burns et al. (2004) found that horizontal advection is more important during solar minimum than solar maximum since equatorward winds are stronger, and the high-latitude air is relatively more enhanced in molecular specie. They suggested that stronger equatorward winds are results from weaker pressure gradients driven by solar EUV heating. Neutral density is generally larger in the summer hemisphere than in the winter hemisphere and density increases with increasing geomagnetic activity (Emmert, 2015). Mayr and Volland (1972) explained the compositional variations as resulting from a net summer-towinter meridional circulation that preferentially transports the lighter species (He and O) relative to the heavier species (N2 and O2). Therefore, the large-scale downward thermospheric circulation carries atomic oxygen-rich air to low latitude across pressure levels thereby enhancing O/N2 ratio at these latitudes, while reduction of O/N2 ratio at high latitudes. The picture is in agreement with the study of CIR storms in 2001–2008 conducted by Liu et al. (2012a). They found that at the daytime, O/N2 at high latitudes suffers more reduction in the summer hemisphere than in the winter hemisphere. This signifies that DDEF is generated by the meridional wind flowing to equatorial region, which is more prevalent in the summer hemisphere. In addition, over Jicamarca, Results from Liu et al. (2012b) suggest that during D months increases in electron density spans from 0 30 S, while during J months the increases spans from 0 20 N. This suggests to N-S asymmetry in the electron density that depends on seasons. As daytime DDEF is associated with downward vertical drift that drives more electrons into the equatorial ionosphere, stronger DD effect is expected during local summer (D months) in the southern hemisphere. Plasmas are transported into this hemisphere and downward diffusions are speeded up by the summer-to-winter transequatorial winds. Convergence of neutral atmosphere at low-equatorial latitudes results in increments in the O/N2 ratio and electron density (e.g., Zhao et al., 2007). Fang et al. (2012) suggested that the N-S asymmetric input energy and the composition changes can induce the N-S asymmetric of ionospheric electron density during the intense geomagnetic storms. This study reports effects of this mechanism that also plays a role during moderate storms induced by CIRs and HILDCAA. Zaourar et al. (2017) found that time duration and amplitude of the prolonged DDEFs reveal hemispheric asymmetry in geomagnetic response to HSS event during J month, displaying the amplitude of DDEF is notably highest in NH than in SH observatories. This remarks the seasonal dependence when the conductivities of solar origin are enhanced in summer (NH) and diminished in winter (SH) during J month. Remark that the delayed DD effects are particularly important in the morning/before noon as clearly observed in RGS2 shown in Fig. 4. Equatorial longitudinally averaged ROCSAT-1 satellite ion drift measurements at an ∼600 km altitude showed the daytime DD drifts are small at all seasons and the nighttime drifts are upward with the largest magnitudes in the postmidnight sector during December solstice (Fejer et al., 2008). The latter obviously remarks the signature of DDEF as observed in this study. Moreover, DDEFs are westward during the day and larger eastward at night with peak near sunrise and they occur most frequently in the postmidnight-to-prenoon time at Jicamarca with time delays of about 1–12 hs (Scherliess and Fejer, 1997). Signatures of DDEF over Jicamarca are also observed in the recovery phase of strong geomagnetic storms at 10 16 LT and eastward at postmidnight and early morning sectors (Zhang et al.., 2019). These features suggest that

the enhanced equatorial DDEF generated by the meridional wind flowing from high-to equatorial latitudes at the postmidnight to prenoon is effective in the summer hemisphere. With CHAMP observations, Liu and Lühr (2005) found that the propagation of the meridional winds during the November storm is faster in summer (southern) than in the winter (northern) hemisphere on both dayside and nightside. The propagation of the meridional winds was investigated by applying a cross correlation analysis to the average thermospheric density (from CHAMP) in the polar and equatorial regions (geomagnetic) to determine the time lags between these regions for both hemispheres. It is important to mention that the DDs are hemispheric asymmetric and vary dramatically due to a combination of various effects such as seasons, solar cycle, local time, and storm conditions (see Liu and Lühr (2005); Huang (2013)). With the NACR/TIEGCM simulations, Huang and Chen (2008) found that normal quiet time electrodynamics, at different seasons with different solar activities, significantly affect the distribution of perturbed electric field associated with geomagnetic activity. In addition, significant DDEFs tend to build up six hs after the onset of geomagnetic activity, except at regions close to sunset and sunrise. The strong DDEFs are present at around sunrise after the onset of geomagnetic activity ∼18 h and almost maintain the same magnitude after 24 h. 5. Concluding remarks This work investigated the solar wind-magnetosphere coupling and electrodynamic responses in the equatorial ionospheric F-region to 27day RGSs during October–December in 2007 over Jicamarca, by using the solar wind plasma, geomagnetic indices, and magnetometer data. The main results of this study are as follows.

• The three consecutive RGSs show quasi-stable variabilities in storm• • • • • •

times that concurrently control the electrodynamic responses in equatorial ionosphere. The responses also vary dramatically with local time from event to event depending on the geomagnetic conditions, particularly in CIR-storms. Correlations analysis indicates that HILDCAA shows more effective magnetic flux merging on the dayside magnetopause than CIR storm. Fourier analysis indicates that consistent periods between AE and Bz are consistent with Alfvén waves and are more dominant in HILDCAA than in CIR-storms. This suggests that both types of the storms are controlled by different interplanetary drivers and are independently established. Not only PPEFs but also DDEFs are present during the long main phase of CIR-induced storms. By investigating the AE and dH data, DDEFs are predominant for many hours in the morning to prenoon. Moreover, the more intense storm is, the stronger the DDEF becomes. During HILDCAA periods, PPEFs and DDEFs are weaker than during CIRs, but they are simultaneously present and combined over several days. Each subgroup of HSSs is correspondent to each increased AE that enhances DDEF at the equatorial region through the high latitude Joule heating. The season effects play a dominant role in affecting the electrodynamic processes in the equatorial latitude. Storm-time DDEFs are less effective in equinoctial months due to the symmetric meridional winds and in winter months due to restriction of the equatorward motion, but enhanced in the summer months according to the asymmetric meridional winds.

These findings may improve our understanding about the effects of RGSs on the ionospheric electrodynamic processes. The processes are closely related to prominent ionospheric effects such as equatorial spread-F that affect the satellite based communication and navigation 49

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applications. In addition, further analysis in more different conditions are needed for improving model and prediction.

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Acknowledgement This work was financially supported by Mahasarakham University 2017 and the National Research Council of Thailand, Thailand. The author is grateful to the Jicamarca Radio Observatory which is a facility of the Instituto Geofisico del Peru operated with support from the NSF AGS-0905448 through Cornell University, United States. The OMNI data were obtained from the GSFC/SPDF OMNIWeb interface. Geomagnetic indices are provided by the World Data Center for Geomagnetisms, Kyoto (http://wdc.kugi.kyoto-u.ac.jp). The staffs at the observatories in Qaanaaq (Thule), Vostok, Resolute Bay and DomeC, and their supporting institutes are gratefully acknowledged for providing high-quality geomagnetic data for this study. The author also wish to thank the reviewer for constructive comments that have led to notable improvement in the manuscript. Appendix A. Supplementary data Supplementary data to this article can be found online at https:// doi.org/10.1016/j.jastp.2019.03.004. References Abdu, M.A., De Souza, J.R., Sobral, J.H.A., Batista, I.S., 2013. Magnetic Storm Associated Disturbance Dynamo Effects in the Low and Equatorial Latitude Ionosphere. American Geophysical Union (AGU), pp. 283–304. https://doi.org/10.1029/ 167GM22. https://agupubs.onlinelibrary.wiley.com/doi/10.1029/167GM22. Ahn, B.H., Emery, B.A., Kroehl, H.W., Kamide, Y., 1999. Climatological characteristics of the auroral ionosphere in terms of electric field and ionospheric conductance. J. Geophys. Res. 104, 10031–10040. https://doi.org/10.1029/1999JA900043. Ahn, B.H., Kroehl, H.W., Kamide, Y., Kihn, E.A., 2000. Seasonal and solar cycle variations of the auroral electrojet indices. J. Atmos. Sol. Terr. Phys. 62, 1301–1310. https:// doi.org/10.1016/S1364-6826(00)00073-0. Benkevich, L., Lyatsky, W., Cogger, L.L., 2000. Field-aligned currents between conjugate hemispheres. J. Geophys. Res.: Space Physics 105 (A12), 27727–27737. https://doi. org/10.1029/2000JA900095. https://agupubs.onlinelibrary.wiley.com/doi/abs/10. 1029/2000JA900095. Blanc, M., Richmond, A.D., 1980. The ionospheric disturbance dynamo. J. Geophys. Res. 85, 1669–1686. https://doi.org/10.1029/JA085iA04p01669. Burns, A.G., Killeen, T.L., Wang, W., Roble, R.G., 2004. The solar-cycle-dependent response of the thermosphere to geomagnetic storms. J. Atmos. Sol. Terr. Phys. 66, 1–14. https://doi.org/10.1016/j.jastp.2003.09.015. Burns, A.G., Solomon, S.C., Qian, L., Wang, W., Emery, B.A., Wiltberger, M., Weimer, D.R., 2012. The effects of Corotating interaction region/High speed stream storms on the thermosphere and ionosphere during the last solar minimum. J. Atmos. Sol. Terr. Phys. 83, 79–87. https://doi.org/10.1016/j.jastp.2012.02.006. Candido, C.M.N., Batista, I.S., Klausner, V., de Siqueira Negreti, P.M., Becker-Guedes, F., de Paula, E.R., Shi, J., Correia, E.S., 2018. Response of the total electron content at Brazilian low latitudes to corotating interaction region and high-speed streams during solar minimum 2008. Earth Planets Space 70, 104. https://doi.org/10.1186/s40623018-0875-8. Christiansen, F., Papitashvili, V.O., Neubert, T., 2002. Seasonal variations of high-latitude field-aligned currents inferred from Ørsted and Magsat observations. J. Geophys. Res. 107, 1029. https://doi.org/10.1029/2001JA900104. Chun, F.K., Knipp, D.J., McHarg, M.G., Lu, G., Emery, B.A., Vennerstrøm, S., Troshichev, O.A., 1999. Polar cap index as a proxy for hemispheric Joule heating. Geophys. Res. Lett. 26, 1101–1104. https://doi.org/10.1029/1999GL900196. Chun, F.K., Knipp, D.J., McHarg, M.G., Lacey, J.R., Lu, G., Emery, B.A., 2002. Joule heating patterns as a function of polar cap index. J. Geophys. Res. 107, 1119. https:// doi.org/10.1029/2001JA000246. Deng, Y., Huang, Y., Lei, J., Ridley, A.J., Lopez, R., Thayer, J., 2011. Energy input into the upper atmosphere associated with high-speed solar wind streams in 2005. J. Geophys. Res. 116, A05303. https://doi.org/10.1029/2010JA016201. Diego, P., Storini, M., Parisi, M., Cordaro, E.G., 2005. AE index variability during corotating fast solar wind streams. J. Geophys. Res. 110, A06105. https://doi.org/10. 1029/2004JA010715. Dmitriev, A.V., Huang, C.M., Brahmanandam, P.S., Chang, L.C., Chen, K.T., Tsai, L.C., 2013. Longitudinal variations of positive dayside ionospheric storms related to recurrent geomagnetic storms. J. Geophys. Res. 118, 6806–6822. https://doi.org/10. 1002/jgra.50575. arXiv:1312.5390. Echer, E., Tsurutani, B.T., Gonzalez, W.D., 2013. Interplanetary origins of moderate (-100 nT ＜Dst -≤50 nT) geomagnetic storms during solar cycle 23 (1996-2008). J. Geophys. Res. 118, 385–392. https://doi.org/10.1029/2012JA018086. Emmert, J.T., 2015. Thermospheric mass density: a review. Adv. Space Res. 56, 773–824. https://doi.org/10.1016/j.asr.2015.05.038.

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