Abstract
Pulsating aurorae (PsA) are caused by the intermittent precipitations of magnetospheric electrons (energies of a few keV to a few tens of keV) through wave-particle interactions, thereby ...depositing most of their energy at altitudes ~ 100 km. However, the maximum energy of precipitated electrons and its impacts on the atmosphere are unknown. Herein, we report unique observations by the European Incoherent Scatter (EISCAT) radar showing electron precipitations ranging from a few hundred keV to a few MeV during a PsA associated with a weak geomagnetic storm. Simultaneously, the Arase spacecraft has observed intense whistler-mode chorus waves at the conjugate location along magnetic field lines. A computer simulation based on the EISCAT observations shows immediate catalytic ozone depletion at the mesospheric altitudes. Since PsA occurs frequently, often in daily basis, and extends its impact over large MLT areas, we anticipate that the PsA possesses a significant forcing to the mesospheric ozone chemistry in high latitudes through high energy electron precipitations. Therefore, the generation of PsA results in the depletion of mesospheric ozone through high-energy electron precipitations caused by whistler-mode chorus waves, which are similar to the well-known effect due to solar energetic protons triggered by solar flares.
The brightness of aurorae in Earth's polar region often beats with periods ranging from sub-second to a few tens of a second. Past observations showed that the beat of the aurora is composed of a ...superposition of two independent periodicities that co-exist hierarchically. However, the origin of such multiple time-scale beats in aurora remains poorly understood due to a lack of measurements with sufficiently high temporal resolution. By coordinating experiments using ultrafast auroral imagers deployed in the Arctic with the newly-launched magnetospheric satellite Arase, we succeeded in identifying an excellent agreement between the beats in aurorae and intensity modulations of natural electromagnetic waves in space called "chorus". In particular, sub-second scintillations of aurorae are precisely controlled by fine-scale chirping rhythms in chorus. The observation of this striking correlation demonstrates that resonant interaction between energetic electrons and chorus waves in magnetospheres orchestrates the complex behavior of aurora on Earth and other magnetized planets.
This paper reports two unique auroral features: postmidnight purple auroral rays and global Pc1 geomagnetic pulsations, observed before the onset of the corotating interaction region (CIR) storm of ...21 March 2017, at the beginning of the first campaign of the new Particles and Waves in the Inner magnetosphere using Ground‐based network observation (PWING) longitudinal ground network with the Arase satellite. The purple auroral rays were observed from ~0315 to 0430 UT (~03–04 magnetic local time) in the northeastern sky at Husafell, Iceland (magnetic latitude: 64.9°N). We newly propose that the entry of high‐density CIR plasma into the magnetotail created purple auroral rays in the sunlit ionosphere. Pc1 geomagnetic pulsations at frequencies of 0–0.5 Hz were observed after ~00 UT over a wide local time range, of 13 hr, from midnight to afternoon sectors at subauroral latitudes associated with CIR arrival. These results indicate preconditioning of the magnetosphere due to crossing of a CIR.
Plain Language Summary
We report auroral ray structures, which show a unique purple color, and global geomagnetic pulsations observed on 17 March 2017. The purple auroral rays were observed in the northeastern sky at Husafell, Iceland. The geomagnetic pulsations at frequencies of below 0.5 Hz were observed over a wide longitudinal range extending from midnight through morning to afternoon sectors at subauroral latitudes. These phenomena took place associated with the arrival of the so‐called corotating interaction region (CIR)” in the interplanetary space, which is characterized by high‐density high‐speed solar wind plasma. The CIR is one of the phenomena frequently occurring during the minimum phase of the 11‐year solar cycle. We suggest that the CIR can cause these unique purple auroras and global geomagnetic pulsations. The present observations also suggest a possible mechanism for dropout of radiation belt electrons due to electromagnetic ion cyclotron waves (=geomagnetic pulsations) associated with the CIR arrival.
Key Points
Unique postmidnight purple auroral rays and global Pc1/EMIC waves were observed during a CIR‐driven solar wind density enhancement
Pc1/EMIC waves were found over a wide longitudinal range extending from midnight through morning to the afternoon due to CIR arrival
Entry of high‐density solar wind plasma into the magnetotail may have created tall purple auroral rays in the sunlit ionosphere
Over‐Darkening of Pulsating Aurora Hosokawa, K.; Miyoshi, Y.; Oyama, S.‐I. ...
Journal of geophysical research. Space physics,
April 2021, Letnik:
126, Številka:
4
Journal Article
Recenzirano
Odprti dostop
Recent analyses of high‐time resolution ground‐based optical observations of pulsating aurora (PsA) have reported that the brightness of PsA sometimes decreases below the diffuse background level ...immediately after the ON phase of the main pulsation finishes. To date, however, the generation mechanism of such an “over‐darkening PsA” is still unclarified. In this study, we investigated the characteristics of the over‐darkening PsA by using simultaneous observations of PsA with an electron multiplying charge coupled device all‐sky camera in Sodankylä, Finland and the Arase satellite. During one of the conjunction events in Scandinavia on March 29, 2017, almost all the PsA pulses showed clear over‐darkening characteristics. By analyzing the 2D all‐sky images at the times of over‐darkening we discovered that over‐darkening areas appeared in the trailing edge of PsA patches and moved in tandem with the poleward propagating patches. It was also found that similar over‐decreasing characteristics were not seen in the chorus data from the wave instruments onboard Arase located at the magnetospheric counterpart of PsA. These results indicate that the over‐darkening PsA is not caused by a temporal variation of chorus at a fixed point, but is produced by a propagation of over‐darkening area with PsA patches. That is, the over‐darkening PsA is a result of compounding effects of spatial structure and recurrent propagation of PsA. The mechanism creating the dark area is still unknown, but the existence of over‐darkening PsA suggests that the temporal variation of PsA is not always a perfect copy of the modulation of lower‐band chorus waves in the magnetosphere.
Plain Language Summary
Pulsating auroras (PsAs) are characterized by quasi‐periodic variations in the brightness whose period typically ranges from a few to a few tens of second. Coordinated ground/satellite observations in the last decade demonstrated that the main optical pulsation well correlates with the intensity modulation of electromagnetic wave called “chorus” in the magnetosphere. Recent optical observations of PsA using high‐speed cameras have reported that the brightness of PsA often decreases below the diffuse background level immediately after the ON phase of the optical pulsation. In this study, we investigate the characteristics of such “over‐darkening PsAs” by using simultaneous observations of PsA with an all‐sky camera in Finland and the magnetospheric satellite Arase. By analyzing the 2D all‐sky images of over‐darkening PsA on March 29, 2017, we discovered that over‐darkening areas appeared in the trailing edge of PsA patches and moved in tandem with the poleward propagating patches. Similar over‐decreasing characteristics were not identified in the chorus data from Arase located at the magnetospheric counterpart of PsA. These results indicate that the over‐darkening PsA is not a pure temporal variation of chorus at a fixed point, but a result of compounding effects of spatial structure and dynamical motion of PsA.
Key Points
Over‐darkening of pulsating aurora (PsA) was observed during an interval of conjugate observation with the Arase satellite
Corresponding over‐decreasing of chorus wave intensity was not seen in the wave data from Arase
Over‐darkening is caused by a passage of dark region on the trailing edge of the PsA patch across the sensing area
A specialized ground‐based system has been developed for simultaneous observations of pulsating aurora (PsA) and related magnetospheric phenomena with the Arase satellite. The instrument suite is ...composed of (a) six 100 Hz sampling high‐speed all‐sky imagers (ASIs), (b) two 10 Hz sampling monochromatic ASIs observing 427.8 and 844.6 nm auroral emissions, (c) a 20 Hz sampling fluxgate magnetometer. The 100 Hz ASIs were deployed in four stations in Scandinavia and two stations in Alaska, which have been used for capturing the main pulsations and quasi 3 Hz internal modulations of PsA at the same time. The 10 Hz sampling monochromatic ASIs have been operative in Tromsø, Norway with the 20 Hz sampling magnetometer. Combination of these multiple instruments with the European Incoherent SCATter (EISCAT) radar enables us to detect the low‐altitude ionization due to energetic electron precipitation during PsA and further to reveal the ionospheric electrodynamics behind PsA. Since the launch of the Arase satellite, the data from these instruments have been examined in comparison with the wave and particle data from the satellite in the magnetosphere. In the future, the system can be utilized not only for studies of PsA but also for other classes of aurora in close collaboration with the planned EISCAT_3D project.
Key Points
An integrated package of instruments for high‐time resolution measurements of pulsating aurora was deployed in Scandinavia and Alaska
The system has enabled us to capture the fine‐scale spatio‐temporal variations of pulsating aurora in a wide area
Data from those instruments have also been used for simultaneous observations of pulsating aurora with the Arase satellite
A physical mechanism to produce pulsating aurora (PsA) has been considered to be the interaction of the electron and the chorus wave generated near the equatorial plane of the magnetosphere. A recent ...observation of high temporal resolution of chorus waves by the Arase satellite revealed that the presence or absence of the internal modulation of PsA, which is a characteristic sub‐second scintillation at 3 ± 1 Hz within each optical pulsation, is closely related to the discreteness of the element structure of the chorus wave. However, it is still unclear what parameters (or conditions) control the discreteness of the element and the existence of the internal modulation of PsA. In this study, we discuss parameters that determine the presence or absence of the internal modulation of PsA and element structure of chorus by showing a conjugate observation of PsA/chorus by ground‐based cameras and the Arase satellite. During the event, the occurrence of internal modulation increased temporally. The wave data from the satellite show that the repetitive frequency of elements was ∼6 Hz when the internal modulation was indistinct, while the repetitive frequency was ∼3 Hz when the internal modulation was distinct. The particle measurements suggest that this difference was caused by changes in the density and the temperature anisotropy of the hot electron. The internal modulation was clearly observed when the density of hot electrons decreased and the temperature anisotropy relaxed after the injection. Observations of internal modulations from the ground might allow us to estimate the parameters such as energetic electron density and temperature anisotropy in the magnetosphere.
Key Points
We analyzed a pulsating aurora (PsA) event in which the occurrence frequency of internal modulation increased significantly with time
A conjugate observation with Arase suggests that a sudden enhancement of energetic electrons by the injection caused non‐modulated PsAs
The internal modulation may be more often observed after the injection as the density of energetic electrons decreases in the magnetosphere
We present the first and direct comparison between magnetospheric plasma waves and polar mesosphere winter echoes (PMWE) simultaneously observed by the conjugate observation with Arase satellite and ...high‐power atmospheric radars in both hemispheres, namely, the Program of the Antarctic Syowa Mesosphere, Stratosphere, and Troposphere/Incoherent Scatter Radar at Syowa Station (SYO; −69.00°S, 39.58°E), Antarctica, and the Middle Atmosphere Alomar Radar System at Andøya (AND; 69.30°N, 16.04°E), Norway. The PMWE were observed during 03–07 UT on 21 March 2017, just after the arrival of corotating interaction region in front of high‐speed solar wind stream. An isolated substorm occurred at 04 UT during this interval. Electromagnetic ion cyclotron (EMIC) waves and whistler mode chorus waves were simultaneously observed near the magnetic equator and showed similar temporal variations to that of the PMWE. These results indicate that chorus waves as well as EMIC waves are drivers of precipitation of energetic electrons, including relativistic electrons, which make PMWE detectable at 55‐ to 80‐km altitude. Cosmic noise absorption measured with a 38.2‐MHz imaging riometer and low‐altitude echoes at 55–70 km measured with an medium‐frequency radar at SYO also support the relativistic electron precipitation. We suggest a possible scenario in which the various phenomena observed in near‐Earth space, such as magnetospheric plasma waves (EMIC waves and chorus waves), pulsating auroras, cosmic noise absorption, and PMWE, can be explained by the interaction between the high‐speed solar wind containing corotating interaction regions and the magnetosphere.
Key Points
EMIC waves and chorus waves in the magnetosphere and PMWE in the mesosphere were observed simultaneously by the conjugate observation
PMWE were detected by the PANSY and MAARSY radars in both Northern and Southern Hemispheres during the equinox period
The temporal variation of the chorus wave power was quite similar to those of PMWE powers observed in both hemispheres
We performed observations of pulsating aurora (PsA) with an optical spectrograph at Tromsø, Norway, during wintertime in 2016–2017. The data analysis of multiple PsA events revealed the PsA spectra ...for the first time. As the results, the OI 630.0‐nm emissions and the N2 1PG emissions were found in the both spectra during brighter (ON) and darker (OFF) phases in the PsA events. The spectra of pulsations were derived as difference spectra between the ON and OFF spectra. From the obtained spectra of pulsations, it is found that dominant pulsations at 630.0 nm were coming from the N2 1PG (10,7) band, and there were less or minor contributions of the OI 630.0 nm to pulsations at 630.0 nm.
Key Points
Pulsating aurora events were observed by an optical spectrograph
ON and OFF spectra showed OI 630.0‐nm and N2 1PG emissions
Dominant pulsations around 630.0 nm were due to N2 1PG (10,7) emissions
Ginkgo biloba extract (GbE) has been indicated as an efficient medicine for the treatment of diabetes mellitus type 2. It remains unclear if its effects are due to an improvement of the insulin ...signaling cascade, especially in obese subjects. The aim of the present study was to evaluate the effect of GbE on insulin tolerance, food intake, body adiposity, lipid profile, fasting insulin, and muscle levels of insulin receptor substrate 1 (IRS-1), protein tyrosine phosphatase 1B (PTP-1B), and protein kinase B (Akt), as well as Akt phosphorylation, in diet-induced obese rats. Rats were fed with a high-fat diet (HFD) or a normal fat diet (NFD) for 8 weeks. After that, the HFD group was divided into two groups: rats gavaged with a saline vehicle (HFD+V), and rats gavaged with 500 mg/kg of GbE diluted in the saline vehicle (HFD+Gb). NFD rats were gavaged with the saline vehicle only. At the end of the treatment, the rats were anesthetized, insulin was injected into the portal vein, and after 90s, the gastrocnemius muscle was removed. The quantification of IRS-1, Akt, and Akt phosphorylation was performed using Western blotting. Serum levels of fasting insulin and glucose, triacylglycerols and total cholesterol, and LDL and HDL fractions were measured. An insulin tolerance test was also performed. Ingestion of a hyperlipidic diet promoted loss of insulin sensitivity and also resulted in a significant increase in body adiposity, plasma triacylglycerol, and glucose levels. In addition, GbE treatment significantly reduced food intake and body adiposity while it protected against hyperglycemia and dyslipidemia in diet-induced obesity rats. It also enhanced insulin sensitivity in comparison to HFD+V rats, while it restored insulin-induced Akt phosphorylation, increased IRS-1, and reduced PTP-1B levels in gastrocnemius muscle. The present findings suggest that G. biloba might be efficient in preventing and treating obesity-induced insulin signaling impairment.
Recent simulation studies have provided evidence that a pulsating aurora (PsA) associated with high-energy electron precipitation is having a clear local impact on ozone chemistry in the polar middle ...mesosphere. However, it is not clear if the PsA is frequent enough to cause longer-term effects of measurable magnitude. There is also an open question of the relative contribution of PsA-related energetic electron precipitation (PsA EEP) to the total atmospheric forcing by solar energetic particle precipitation (EPP).
Here we investigate the PsA-EEP impact on stratospheric and mesospheric odd hydrogen, odd nitrogen, and ozone concentrations. We make use of the Whole Atmosphere Community Climate Model and recent understanding on PsA frequency, latitudinal and magnetic local time extent, and energy-flux spectra. Analysing an 18-month time period covering all seasons, we particularly look at PsA-EEP impacts at two polar observation stations located at opposite hemispheres: Tromsø in the Northern Hemisphere (NH) and Halley Research Station in the Southern Hemisphere (SH). We find that PsA EEP can have a measurable impact on ozone concentration above 30 km altitude, with ozone depletion by up to 8 % seen in winter periods due to PsA-EEP-driven NOx enhancement. We also find that direct mesospheric NOx production by high-energy electrons (E> 100 keV) accounts for about half of the PsA-EEP-driven upper stratospheric ozone depletion. A larger PsA-EEP impact is seen in the SH where the background dynamical variability is weaker than in the NH. Clearly indicated from our results, consideration of polar vortex dynamics is required to understand PsA-EEP impacts seen at ground observation stations, especially in the NH. We conclude that PsA-EEP has the potential to make an important contribution to the total EPP forcing; thus, it should be considered in atmospheric and climate simulations.
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