Nighttime increases in ionosphere electron content (a statistical and experimental study)

The ionospheric electron density generally decreases after sunset under the effect of recombination, but sometimes, it increases, which forms an ionospheric nighttime enhancement (INE). In this research, the observations from two ionosondes in Mohe and Beijing and NASA's Jet Propulsion Laboratory‐Global Ionosphere Maps during the 24th solar cycle were used to explore the feature and mechanism of INE at midlatitudes. It shows that hmF2 always increases when INE occurs in summer, while it either rises or falls in winter. The increase of hmF2 has a significant contribution to INE in summer. For winter INE, however, the hmF2‐rising and the hmF2‐declining type INEs present no significant differences in durations and amplitudes, except that the former occurs slightly earlier than the latter. This suggests that the uplift of the ionosphere induced by equatorward thermospheric wind may not be a dominant factor for controlling the formation of winter INE at midlatitudes. We found that the electron density difference between the summer hemisphere and the winter hemisphere trends increases when the INE occurs in the winter hemisphere. This increased electron density difference between the two hemispheres is beneficial to the summer‐to‐winter interhemispheric plasma transport and the formation of INE in winter. Meanwhile, it is likely that the ionospheric equivalent slab thickness decreases during the winter INE due to downward transport from the topside. These indicate that downward plasma influxes from the topside ionosphere and the conjugate summer hemisphere play dominant roles for the formation of winter INE at middle latitudes.

Section: Methodsmentioning

confidence: 99%

A Statistical Study on the Winter Ionospheric Nighttime Enhancement at Middle Latitudes in the Northern Hemisphere

Chen

Liu

et al. 2020

“…Electron density in the ionospheric F region presents complicated diurnal variations, both at the daytime and nighttime, which still challenges our understanding (e.g., Xu & Liu, 2016). Accumulated investigations have been conducted on the nighttime ionospheric enhancements (Arendt & Soicher, 1964;Balan & Rao, 1987;Chen et al, 2015;Dabas & Kersley, 2003;Davies et al, 1979;Farelo et al, 2002;Gordienko et al, 2001;Jain et al, 2011;Jakowski et al, 1991;Luan et al, 2008;Mikhailov et al, 2000;Pavlov & Pavlova, 2005, 2007Pezzopane et al, 2011;Titheridge, 1968;Trivedi et al, 2013;Tsagouri & Belehaki, 2002;Unnikrishnan et al, 2002;Young et al, 1970). The diurnal peak electron density (NmF2) of the ionospheric F region reaches a peak at nighttime, termed a nighttime enhancement (Titheridge, 1968).…”

Section: Introductionmentioning

confidence: 99%

New Features of the Enhancements in Electron Density at Low Latitudes

Liu

Zhang²,

et al. 2020

In this study, we present some new features of the enhancements of electron density in the ionospheric F region at low latitudes. The peak parameters of the ionosphere were recorded by Sanya (109.6°E, 18.3°N) ionosonde and electron density profiles analyzed were measured by the Qujing (103.8°E, 25.6°N) incoherent scatter radar. The peak electron density of the F2 layer (NmF2) is found to be enhanced in the afternoon and sunset hours. Common features in the cases demonstrate that the NmF2 increases at low latitudes are characterized by a descent of the peak height (hmF2). Meanwhile, the electron density at Qujing shows an increase at the bottom of the ionosphere and a depression at topside altitudes. It is consistent with those of the ionosonde measurements at Sanya, for both the daytime and nighttime enhancements. Cross correlation analyses reveal a lag of NmF2 to hmF2 in the cases. After taking time shifts some events of the enhancements in NmF2 are still associated with a downwelling hmF2, confirming the processes which drive a lower hmF2 and a convergence of plasma flux may possibly bring about a rise in NmF2.

“…Ionospheric plasma density usually embarks on a monotonically decreasing trend during nighttime, due to lack of solar radiation that serves as a decisive factor for atmosphere ionization. Even during these times density can, however, be increased due to nighttime plasma density enhancements (NPDEs), a phenomenon that frequently occurs in the F 2 region of middle geomagnetic latitudes and is characterized by a local nighttime peak of electron density (e.g., Balan et al, 1994; Balan & Rao, 1987; Chen et al, 2015; Farelo et al, 2002; Gordienko et al, 2001; Jakowski et al, 2015; Li et al, 2018; Luan et al, 2008; Mikhailov et al, 2000; Park, 1971; Rajesh et al, 2016; Zhong et al, 2019). Observations of frequently occurring midlatitude NPDEs in the summer hemisphere have been classified as midlatitude summer nighttime anomaly structures (MSNAs) by previous studies (e.g., Burns et al, 2011; Chen et al, 2012; Hsu et al, 2011; Lin et al, 2010; Liu & Watanabe, 2008; Thampi et al, 2009).…”

Section: Introductionmentioning

confidence: 99%

Interaction Between a Southwestward Propagating MSTID and a Poleward Moving WSA‐Like Plasma Patch on a Magnetically Quiet Night at Midlatitude China Region

Sun

Zhu

et al. 2020

In this paper, we first investigate the effects of a postevening Weddell Sea Anomaly (WSA)-like plasma patch on a southwestward propagating medium-scale traveling ionospheric disturbance (MSTID) over Xinglong, China (40.4°N, 117.6°E; Mlat.~30.4°N). We found that some of this kind of WSA-like plasma patches moved northward from the equatorial ionization anomaly (EIA) regions to midlatitudes, as they traveled westward into China. During 2012-2016, these plasma patches frequently occurred during the period of May-August with a monthly occurrence rate of over 20%, causing nighttime plasma density enhancements (NPDEs) in midlatitudes of China. Over 50% of these structures were accompanied by concurrent MSTID and Es. We propose that an intense polarization electric field (PEF) associated with an MSTID/Es from the more northern regions of EIA could frequently drive these plasma patches poleward. On the night of 27 June 2014 (Kp < 2 −), either an MSTID and an intense Es layer (the maximum foEs >12 MHz) occurred at the onset of the poleward motion of a WSA-like plasma patch, lending credence to this possibility. The observed plasma patch was pushed poleward to interact with the observed MSTID, causing some poleward extending C-shaped airglow depletions/enhancements of the MSTID in a transition region where the ionosphere changed from a collapse region to an uplifted one. We attributed those poleward extending airglow depletions to the interaction between the MSTID and the plasma patch because of the secondary gradient drift instability and those of airglow enhancements to the redistribution of plasma. Plain Language Summary This study found that postevening Weddell Sea Anomaly (WSA)-like patchy plasma structures frequently occurred during May-August of 2012-2016 in the East Asian regions. Among these plasma patches, a small portion moved northward from the equatorial ionization anomaly (EIA) regions to midlatitudes, as they moved westward into China. On the magnetically quiet night of 27 June 2014 (Kp < 2 −), such a plasma patch already moved westward and poleward to the midlatitude region of China, affecting the evolution/propagation of a southwestward propagating medium-scale traveling ionospheric disturbance (MSTID). This paper, therefore, investigates the interaction between a midlatitude MSTID and a poleward moving WSA-like plasma patch. We mainly investigate the possible physical mechanisms behind this kind of plasma patches and how they could affect the propagation/evolution of MSTIDs over midlatitudes of China.