Browsing by Author "Wan, Weixing"
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Item Restricted Comparative study of the equatorial ionosphere over Jicamarca during recent two solar minima(American Geophysical Union, 2012-01-21) Liu, Libo; Yang, Jun; Le, Huijun; Chen, Yiding; Wan, Weixing; Lee, C. C.It is a critical issue that whether or not the extremely deep solar minimum of solar cycle 23/24 brought serious influences on the Earth's space environment. In this study, we collected and manually scaled the ionograms recorded by a DPS ionosonde at Jicamarca (12.0°S, 283.2°E) to retrieve F layer parameters and electron density (Ne) profiles. A comparative study is performed to evaluate the equatorial ionosphere in solar minima of cycle 22/23 (1996–1997) and 23/24 (2008–2009). The seasonal median values of the critical frequency of F2 layer (foF2) were remarkably reduced in four seasons during the deep solar minimum, compared to those in 1996–1997. It is the first time to find that lower values prevail at most times in 2008–2009 in the F2 layer peak height (hmF2) and Chapman scale height (Hm). The bottomside profile thickness (B0) shows higher values in 2008–2009 than that in 1996–1997 at some daytime intervals, although it also becomes smaller during the rest times. Furthermore, the ionosphere in 2008–2009 is contracted strongly at altitudes above hmF2 and more perceptible in the afternoon hours. The decrease in Ne is strongest in September equinox and weakest in June solstice. The ionospheric responses from solar minimum to minimum are mainly caused by the reduction in solar extreme ultraviolet intensity, and the contribution from dynamical processes competes and is variable. Analysis reveals that semiannual and longer‐scale components are certainly reduced during the deep solar minimum, while shorter scale (e.g., 4 month) components may disrupt the decline picture at some times.Item Restricted Modeling the relationship between E × B vertical drift and the time rate of change of hmF2 (ΔhmF2/Δt) over the magnetic equator(American Geophysical Union, 2008-03-13) Yue, Xinan; Wan, Weixing; Lei, Jiuhou; Liu, L.A middle and low latitude ionospheric model is used to model the relationship between E × B vertical drift velocity and time rate of change of hmF2 (ΔhmF2/Δt) over the magnetic equator. F107 (10.7 cm solar radiation flux) is chosen to be equal to 100, 150, and 200 to represent low, middle, and high solar activities, respectively, and Ap is equal to 1 to represent quiet geomagnetic activity. Our simulations show that hmF2 derived vertical drifts over the magnetic equator are in good agreement with the E × B vertical drift imposed in the model during 0600–0730 and 1700–2100 LT. This is consistent with previous comparisons between vertical drift velocities derived from ionosonde, Jicamarca incoherent scatter radar, and AE‐E observations well. However, the amplitudes of hmF2 derived drift are smaller than the given drift velocities during other local times. During disturbed conditions, the variations of hmF2 can be used to determine the occurrence of intense electric field disturbance.Item Restricted Response of the American equatorial and low‐latitude ionosphere to the X1.5 solar flare on 13 September 2005(American Geophysical Union, 2014-11-25) Xiong, Bo; Wan, Weixing; Zhao, Biqiang; Yu, You; Wei, Yong; Ren, Zhipeng; Liu, JingBased on the coordinated observations by the incoherent scatter radar (ISR), ionosonde, magnetometers, and GPS receivers, the electrodynamic effects on the equatorial and low‐latitude ionosphere have been investigated during the intense solar flare (X1.5/2B) on 13 September 2005. In the initial stage of the flare, the ISR and ionosonde measurements at Jicamarca show the decreases of 10.14 m/s and 20 km in the upward vertical E × B drift velocity and the F2 region peak height, respectively, while equatorial electrojet (EEJ) strength over American sector indicates a sudden increase of 53.7 nT. The decrease of the upward vertical E × B drift velocity reveals the weakening of eastward electric field during the flare, which is firstly and directly observed by instrument. It is well known that the variation of equatorial electric field is mainly attributed to the ionospheric dynamo electric field and partially affected by the penetration of interplanetary electric field. The observations during this flare suggest that the flare‐induced increase of Cowling conductivity changes the ionospheric dynamo electric field and further results in the weakening of eastward electric field and the decrease of the upward vertical E × B drift velocity. Meanwhile, the upward vertical E × B drift velocity and the EEJ strength during the flare are negatively correlated, which is contrary to the knowledge established by Anderson et al. (2002) based on 10 days of observations in the Peruvian longitude sector. The difference may be caused by the flare‐induced enhancement of Cowling conductivity. In addition, GPS total electron content (TEC) observations from six stations in the American equator and low latitudes show an enhancement of 1.47–3.09 TEC units. The measurements of GPS and ISR indicate that the contribution of the enhanced photoionization to the increase of TEC is more than that of electrodynamic effect during the initial stage of the intense flare.Item Restricted The long‐duration positive storm effects in the equatorial ionosphere over Jicamarca(American Geophysical Union, 2015-01-06) Kuai, Jiawei; Liu, Libo; Liu, Jing; Zhao, Biqiang; Chen, Yiding; Le, Huijun; Wan, WeixingThe long‐duration positive storm (LPS) in the equatorial regions is relatively poorly understood. In this report, we conducted a statistical analysis of the LPS effects in the equatorial ionosphere over Jicamarca (12.0°S, 283.2°E) in 1998–2010. There are 250 geomagnetic storms (minimum Dst < −50 nT) in 1998–2010, but the ionosonde observations at Jicamarca are available only for 204 storms. A total of 46 LPSs are identified in terms of the criterion that the storm time relative deviation of peak density of F2 layer (NmF2) exceeds 25% for more than 6 h. A salient feature is that the occurrence of LPSs tends to decay approximately exponentially on the following days after the main phase of geomagnetic storms. The ratios of the number of equatorial LPSs to that of geomagnetic storms have no obvious dependence on season and solar activity. During the daytime LPSs, the disturbed zonal electric field is mostly westward, as indicated from the geomagnetic field changes in the equatorial American region. For the nighttime LPSs, the significant uplifting of F2 layer caused by an eastward electric field is the most important feature. Therefore, the disturbed electric field should play an essential role in forming the equatorial LPSs.Item Restricted Unusually long lasting multiple penetration of interplanetary electric field to equatorial ionosphere under oscillating IMF Bz(American Geophysical Union, 2008-01-17) Wei, Yong; Hong, Minghua; Wan, Weixing; Du, Aimin; Lei, Jiuhou; Zhao, Biqiang; Wang, Wenbin; Ren, Zhipeng; Yue, XinanDuring November 11–16, 2003, the interplanetary magnetic field (IMF) Bz oscillated between northward and southward directions, which suggests discontinuous magnetic reconnection associated with the multiple pulses‐like reconnection electric field. The Jicamarca incoherent scatter radar (ISR) measurements of ionospheric zonal electric field showed similar fluctuations during this period. The high correlation coefficient of 0.71 between the reconnection electric field and equatorial zonal electric field during 125 hours suggests that the interplanetary electric field (IEF) pulsively penetrated into the equatorial ionosphere due to the discontinuous magnetic reconnection. It is implied that the short lifetime (<3 hours) dawn‐dusk IEF pulses can penetrate into ionosphere without shielding, in other words, they may exhibit the “shielding immunity”. The averaged penetration efficiency is about 0.136 and highly local time‐dependent. Furthermore, the intense AU and AL indices imply that the multiple electric field penetration is associated with a “High‐Intensity Long‐Duration Continuous AE Activity (HILDCAA).