Lower thermospheric‐enhanced sodium layers observed at low latitude and possible formation: Case studies

Xue, Xianghui; Dou, Xiankang; Lei, Jiuhou; Chen, J. S.; Zhang, Ding; Li, Tao; Gao, Qi; Tang, Weian; Cheng, Xuewu; Wei, Kai

doi:10.1002/jgra.50200

Cited by 56 publications

(56 citation statements)

References 38 publications

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“…With the development of TeSLs over time, RO measurements accordingly show complex E s . Actually, Xue et al (2013) also reported an example showing that the lidar observes TeSLs associated with simultaneous double peaks of SNR made by colocated RO events from TerraSAR-X. According to wind shear theory, at lower (upper) altitudes, the zonal (meridional) wind will dominate the shear due to the altitude variations of the ion-neutral collision frequency regarding the ion gyrofrequency ratio.…”

Section: Multiple E S Layers In One Profilementioning

confidence: 96%

Case study on complex sporadic E layers observed by GPS radio occultations

et al. 2015

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Abstract. The occurrence of sporadic E (E s ) layers has been a hot scientific topic for a long time. The GNSS (global navigation satellite system)-based radio occultation (RO) has proven to be a powerful technique for detecting the global E s layers. In this paper, we focus on some cases of complex E s layers based on the RO data from multiple missions processed in UCAR/CDAAC (University Corporation for Atmospheric Research (UCAR) the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) Data Analysis and Archive Center (CDAAC)). We first show some examples of multiple E s layers occurred in one RO event. Based on the evaluations between colocated simultaneous RO events and between RO and lidar observations, it could be concluded that some of these do manifest the multiple E s layer structures. We then show a case of the occurrence of E s in a broad region during a certain time interval. The result is then validated by independent ionosondes observations. It is possible to explain these complex E s structures using the popular wind shear theory. We could map the global E s occurrence routinely in the near future, given that more RO data will be available. Further statistical studies will enhance our understanding of the E s mechanism. The understanding of E s should benefit both E s -based long-distance communication and accurate neutral RO retrievals.

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Section: Multiple E S Layers In One Profilementioning

confidence: 96%

Case study on complex sporadic E layers observed by GPS radio occultations

et al. 2015

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“…In this context, it is also to be noted that high altitude sporadic metal layers (or high altitude metal layers) have been reported from several observational sites (e.g. Friedman et al 2013, Höffner andFriedman 2004;Chu et al 2011;Xue et al 2013). Gao and Mathews (2014a,b) and references therein report on high altitude radar and optical meteors indicative of sputtering as a source of metal ions above the traditional meteor zone.…”

Section: Introductionmentioning

confidence: 73%

A case study on occurrence of an unusual structure in the sodium layer over Gadanki, India

et al. 2015

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The height-time-concentration map of neutral sodium (Na) atoms measured by a Na lidar during the night of 18 to 19 March 2007 over Gadanki, India (13.5°N, 79.2°E) reveals an unusual structure in the Na layer for around 30 min in the altitude range of 92 to 98 km which is similar to the usual 'C' type structures observed at other locations. In order to understand the physical mechanism behind the generation of this unusual event, an investigation is carried out combining the data from multiple instruments that include the meteor wind radar over Thiruvananthapuram, India (8.5°N, 77°E) and the SABER instrument onboard the TIMED satellite. The temperature and wind profiles from the data set provided by these instruments allow us to infer the Richardson number which is found to be noticeably less than the canonical threshold of 0.25 above 92 km over Thiruvananthapuram suggesting the plausible generation of Kelvin-Helmholtz (KH) billows over southwestern part of the Indian subcontinent. Based on the average wind speed and direction over Thiruvananthapuram, it is proposed that the KH-billow structure was modified due to the background wind and was advected with it in nearly 'frozen-in' condition (without significant decay) in the northeastward direction reaching the Na lidar location (Gadanki). This case study, therefore, presents a scenario wherein the initially deformed KH-billow structure survived for a few hours (instead of a few minutes or tens of minutes as reported in earlier works) in an apparently 'frozen-in' condition under favorable background conditions. In this communication, we suggest a hypothesis where this deformed KH-billow structure plays crucial role in creating the abovementioned unusual structure observed in the Na layer over Gadanki.

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“…Several other studies have also indicated that gravity waves are vulnerable to breaking in the mesopause region (80-105 km) owing to the temperature inversion layer [Hauchecorne et al, 1987;Meriwether et al, 1998;Gardner et al, 2002;Williams et al, 2002]. Clemesha et al, 1999;Friedman et al, 2000;Dou et al, 2010;Xue et al, 2013]. And a less pronounced link, or absence of a link, between Es and SSL is observed below 95 km [Hansen and Von Zahn, 1990].…”

Section: Introductionmentioning

confidence: 94%

“…Several studies Clemesha et al, 1999;Williams et al, 2007;Dou et al, 2010;Xue et al, 2013] have shown that SSLs are associated with sporadic E (Es) layers. Cox and Plane [1998] reported that Na + can …”

Section: Sporadic E Layer Mechanismmentioning

confidence: 99%

Sodium lidar‐observed gravity wave breaking followed by an upward propagation of sporadic sodium layer over Hefei, China

Ban

Fang

et al. 2015

JGR Space Physics

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The University of Science and Technology of China sodium temperature/wind lidar observed a strong zonal wind shear (~60 m/s/km) near 98 km between 1315 and 1330 UT on 29 July 2013 and a cooling near 96–100 km (above a warming near 90–95 km) between 1330 and 1430 UT. This suggests a possible gravity wave (GW) breaking event. Comparison of the lidar results with observations from a nearby meteor radar and with satellite results indicated that the GW likely broke down over a large horizontal area. In addition, the sodium number density suddenly increased 10–12 times (∼13, 000atm/cm3) near 95 km at 1400 UT, immediately following the GW breaking. This sporadic sodium layer (SSL), which is different from most previously observed SSL events (which propagate downward), tended to propagate upward and also appeared ~2 min earlier in the west channel than in the east channel. The horizontal propagation direction of the SSL was aligned with the horizontal wind direction, which was likely due to the propagation of a high‐density sodium layer from the northwest of the lidar site, and was possibly related to the earlier GW breaking event.

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Lower thermospheric‐enhanced sodium layers observed at low latitude and possible formation: Case studies

Cited by 56 publications

References 38 publications

Case study on complex sporadic E layers observed by GPS radio occultations

Case study on complex sporadic E layers observed by GPS radio occultations

A case study on occurrence of an unusual structure in the sodium layer over Gadanki, India

Sodium lidar‐observed gravity wave breaking followed by an upward propagation of sporadic sodium layer over Hefei, China

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