Decrease in sodium density observed during auroral particle precipitation over Tromsø, Norway

Tsuda, Takuo T.; Nozawa, Satonori; Kawahara, Takuya; Kawabata, Tetsuya; Saito, Norihito; Wada, Satoshi; Ogawa, Y.; Oyama, Shin‐ichiro; Hall, Chris M.; Tsutsumi, Masaki; Ejiri, Mitsumu K.; Suzuki, Shin; Takahashi, T.; Nakamura, Takuji

doi:10.1002/grl.50897

Cited by 21 publications

(25 citation statements)

References 13 publications

(34 reference statements)

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“…Up to now, three mechanisms have been widely studied: the dust theory (suggesting the release of free sodium atoms from dusty surfaces by the energetic auroral particle bombardment; von Zahn et al, ), the E S theory (supporting the recombination of sodium ions from a series of downward E S ; Collins et al, ; Cox & Plane, ), and the temperature‐controlled theory (suggesting the triggering of sodium atoms by some means through temperature enhancement in a narrow altitude region due to energy damping during gravity wave breaking; Zhou et al, ; Zhou & Mathews, ). However, none of these three viable proposals seems to be able to explain the rather wide variety in specific characteristics of SSLs all over the world: Some SSLs observed at high latitude occurring during the temperature minimum phase (Hansen & von Zahn, ; Østerpart, ), SSLs occurring in a subtropic area were accompanied by no E S (Dou et al, ; Gong et al, ; Miyagawa et al, ), and a decrease in sodium density was also observed during auroral activity (Heinselman et al, ; Tsuda et al, ), all of which indicate a particular mechanism for different SSLs.…”

Section: Introductionmentioning

confidence: 99%

Sudden Sodium Layers: Their Appearance and Disappearance

et al. 2018

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Temperature variation has been proposed to play an important role in the formation of the sporadic sodium layers (SSLs or Na S ) in subtropic area, based on the observed significant correlation between SSLs and high temperatures. The icy-dust particle, which could form in the extremely cold conditions and act as absorbers of sodium species, was proposed to be a possible candidate for the sodium reservoir of the SSLs. In this study, the University of Science and Technology of China temperature/wind lidar and the sodium fluorescence lidar at a subtropic station Hefei (31°N, 117°E), China, were used to observe sodium density, temperature, and wind profiles simultaneously throughout the SSL events. Based on the observations of two SSLs occurring on 12 and 13 May 2013, the possibility of an icy-dust layer existing and acting as the sodium reservoir is tested for the first time in details. Both events experienced an extremely cold temperature (<150 K) several hours before the onset of SSLs, followed by a subsequently fast production of sodium atoms during a large temperature enhancement (>40 K). An empirical model including two main steps is then proposed: first, sodium species are collected by an icy-dust reservoir and stored during the extremely cold phase; second, free sodium atoms could be released from the reservoir by a possible trigger. As a result, this kind of SSLs could possibly be regarded as a quasi-continuous phenomenon caused and modulated by temperature variations with an icy-dust model that can exhibit intermittent time variations related to the water vapor concentration.Plain Language Summary Temperature variation, rather than through the mechanism of cooccurrence of sporadic E layer (ES), has been proposed to play an important role in the formation of the sporadic sodium layers (SSLs or NaS) in subtropic area based on the observed significant correlation between SSLs and high temperatures. But the detailed process and mechanism are still unclear. The icy-dust particle, which could form in the extremely cold temperature conditions and as absorbers of sodium species, was proposed by previous studies to be a possible candidate for the sodium reservoir of the SSLs. However, this most promising scenario has not yet been evaluated in those earlier studies owing to a lack of the relevant observations. In this study, the University of Science and Technology of China temperature/wind lidar and the sodium fluorescence lidar at a subtropic station Hefei (31°N, 117°E), China, were used to observe sodium density, temperature, and wind profiles simultaneously throughout the SSL events and activities. Based on the observations of two SSLs occurring on 12 and 13 May 2013, the possibility of an icy-dust layer existing at the mesopause and acting as the sodium reservoir is tested and verified for the first time in details.

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Section: Introductionmentioning

confidence: 99%

Sudden Sodium Layers: Their Appearance and Disappearance

et al. 2018

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“…One is the direct ionization of Na atoms by auroral precipitation, and the other is chemical reactions involving auroral ionization products (NO + and

{normalO}_{2}^{+}

). Since auroral precipitation is able to ionize only a small fraction (on the order of millionth parts) of neutral particles, direct ionization of Na atoms cannot explain the significant depletion reported in Tsuda et al [], which showed that Na density decreased from about 10% to 30% of the nightly mean Na density during electron density enhancement due to auroral precipitations. Therefore, in this paper, we hypothesize that chemical reactions involving auroral ionization products (NO + and

{normalO}_{2}^{+}

) are the leading mechanism of the Na density depletion and quantitatively evaluate this process.…”

Section: Introductionmentioning

confidence: 99%

Depletion of mesospheric sodium during extended period of pulsating aurora

et al. 2017

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We quantitatively evaluated the Na density depletion due to charge transfer reactions between Na atoms and molecular ions produced by high‐energy electron precipitation during a pulsating aurora (PsA). An extended period of PsA was captured by an all‐sky camera at the European Incoherent Scatter (EISCAT) radar Tromsø site (69.6°N, 19.2°E) during a 2 h interval from 00:00 to 02:00 UT on 25 January 2012. During this period, using the EISCAT very high frequency (VHF) radar, we detected three intervals of intense ionization below 100 km that were probably caused by precipitation of high‐energy electrons during the PsA. In these intervals, the sodium lidar at Tromsø observed characteristic depletion of Na density at altitudes between 97 and 100 km. These Na density depletions lasted for 8 min and represented 5–8% of the background Na layer. To examine the cause of this depletion, we modeled the depletion rate based on charge transfer reactions with NO+ and normalO2+ while changing the R value which is defined as the ratio of NO+ to normalO2+ densities, from 1 to 10. The correlation coefficients between observed and modeled Na density depletion calculated with typical value R = 3 for time intervals T1, T2, and T3 were 0.66, 0.80, and 0.67, respectively. The observed Na density depletion rates fall within the range of modeled depletion rate calculated with R from 1 to 10. This suggests that the charge transfer reactions triggered by the auroral impact ionization at low altitudes are the predominant process responsible for Na density depletion during PsA intervals.

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“…For example, Chu et al (2011) observed temperature enhancements caused by Joule heating and fast gravity waves propagating from the lower atmosphere in the neutral Fe layers (110 to 155 km) in Antarctica. Tsuda et al (2013) showed decreases in sodium density in association with auroral particle precipitation from Figure 19 Temporal variations in the vertical wind speed and the fringe peak count at the zenith. Top and middle panels show the temporal variations in the vertical wind speed and the fringe peak count at the zenith, respectively, measured with the FPI (557.7 nm) from 00:30 to 02:00 UT on 26 January 2009.…”

Section: Mlt Regionmentioning

confidence: 95%

The geospace response to variable inputs from the lower atmosphere: a review of the progress made by Task Group 4 of CAWSES-II

Oberheide

Shiokawa

Gurubaran

et al. 2015

Prog. in Earth and Planet. Sci.

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The advent of new satellite missions, ground-based instrumentation networks, and the development of whole atmosphere models over the past decade resulted in a paradigm shift in understanding the variability of geospace, that is, the region of the atmosphere between the stratosphere and several thousand kilometers above ground where atmosphere-ionosphere-magnetosphere interactions occur. It has now been realized that conditions in geospace are linked strongly to terrestrial weather and climate below, contradicting previous textbook knowledge that the space weather of Earth's near space environment is driven by energy injections at high latitudes connected with magnetosphere-ionosphere coupling and solar radiation variation at extreme ultraviolet wavelengths alone. The primary mechanism through which energy and momentum are transferred from the lower atmosphere is through the generation, propagation, and dissipation of atmospheric waves over a wide range of spatial and temporal scales including electrodynamic coupling through dynamo processes and plasma bubble seeding. The main task of Task Group 4 of SCOSTEP's CAWSES-II program, 2009 to 2013, was to study the geospace response to waves generated by meteorological events, their interaction with the mean flow, and their impact on the ionosphere and their relation to competing thermospheric disturbances generated by energy inputs from above, such as auroral processes at high latitudes. This paper reviews the progress made during the CAWSES-II time period, emphasizing the role of gravity waves, planetary waves and tides, and their ionospheric impacts. Specific campaign contributions from Task Group 4 are highlighted, and future research directions are discussed.

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Decrease in sodium density observed during auroral particle precipitation over Tromsø, Norway

Cited by 21 publications

References 13 publications

Sudden Sodium Layers: Their Appearance and Disappearance

Sudden Sodium Layers: Their Appearance and Disappearance

Depletion of mesospheric sodium during extended period of pulsating aurora

The geospace response to variable inputs from the lower atmosphere: a review of the progress made by Task Group 4 of CAWSES-II

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