scholarly journals Energetic electron precipitation during sawtooth injections

2007 ◽  
Vol 25 (5) ◽  
pp. 1199-1214 ◽  
Author(s):  
A. J. Kavanagh ◽  
G. Lu ◽  
E. F. Donovan ◽  
G. D. Reeves ◽  
F. Honary ◽  
...  
Keyword(s):  
National Laboratory ◽  
Energetic Electron ◽  
Electron Precipitation ◽  
Optical Observations ◽  
Cosmic Radio ◽  
Magnetospheric Substorms ◽  
Los Alamos National Laboratory ◽  
Sustained Activity ◽  
Noise Absorption ◽  
Cosmic Noise

Abstract. We present simultaneous riometer observations of cosmic noise absorption in the nightside and dawn-noon sectors during sawtooth particle injections during 18 April 2002. Energetic electron precipitation (>30 keV) is a feature of magnetospheric substorms and cosmic radio noise absorption acts as a proxy for qualitatively measuring this precipitation. This event provides an opportunity to compare the absorption that accompanies periodic electron injections with the accepted paradigm of substorm-related absorption. We consider whether the absorption is consistent with the premise that these injections are quasi-periodic substorms and study the effects of sustained activity on the level of precipitation. Four consecutive electron injection events have been identified from the LANL (Los Alamos National Laboratory) geosynchronous data; the first two showing that additional activity can occur within the 2–4 h sawtooth periodicity. The first three events have accompanying absorption on the nightside that demonstrate good agreement with the expected pattern of substorm-absorption: discrete spike events with poleward motion at the onset followed by equatorward moving structures and more diffuse absorption, correlated with optical observations. Dayside absorption is linked to gradient-curvature drifting electrons observed at geostationary orbit and it is shown that low fluxes can lead to a lack of absorption as precipitation is suppressed; precipitation begins when the drifting electron flux surpasses some critical level following continuous injections of electrons from the magnetotail. In addition it is shown that the apparent motion of absorption determined from an azimuthal chain of riometers exhibits an acceleration that may be indicative of an energisation of the drifting electron population.

scholarly journals The enhancement of cosmic radio noise absorption due to hiss-driven energetic electron precipitation during substorms

2015 ◽  
Vol 120 (7) ◽  
pp. 5393-5407 ◽  
Author(s):  
Haimeng Li ◽  
Zhigang Yuan ◽  
Xiongdong Yu ◽  
Shiyong Huang ◽  
Dedong Wang ◽  
...  
Keyword(s):  
Energetic Electron ◽  
Electron Precipitation ◽  
Cosmic Radio ◽  
Radio Noise ◽  
Noise Absorption

scholarly journals Cosmic radio noise absorption events associated with equatorward drifting arcs during a substorm growth phase

2004 ◽  
Vol 22 (5) ◽  
pp. 1675-1686 ◽  
Author(s):  
J. R. T. Jussila ◽  
A. T. Aikio ◽  
S. Shalimov ◽  
S. R. Marple
Keyword(s):  
Electron Temperature ◽  
Electric Fields ◽  
Growth Phase ◽  
Energetic Electron ◽  
Cosmic Radio ◽  
Radio Noise ◽  
Particle Precipitation ◽  
Noise Absorption ◽  
D Region ◽  
E Region

Abstract. Cosmic radio noise absorption (CNA) events associated with equatorward drifting arcs during a substorm growth phase are studied by using simultaneous optical auroral, IRIS imaging riometer and EISCAT incoherent scatter radar measurements. The CNA is generally attributed to energetic particle precipitation in the D-region. However, it has been argued that plasma irregularities or enhanced electron temperature (Te) in the E-region could also produce CNA. Both of the latter mechanisms are related to intense electric fields in the ionosphere. We present two events which occur during a substorm growth phase in the evening MLT sector. In both of the events, an auroral arc is drifting equatorward, together with a region of CNA (auroral absorption bay) located on the equatorward side and outside of the arc. Both of the events are associated with enhanced D-region electron density on the equatorward side of the auroral arc, but in the second event, a region of intense electric field and enhanced electron temperature in the E-region is also located on the equatorward side of the arc. We show that in the studied events neither plasma instabilities nor enhanced Te play a significant role in producing the measured CNA, but the CNA in the vicinity of the equatorward drifting arcs is produced by D-region energetic electron precipitation. Key words. Ionosphere (auroral ionosphere; particle precipitation; electric fields and currents)

scholarly journals Multi beam observations of cosmic radio noise using a VHF radar with beam forming by a Butler matrix

2011 ◽  
Vol 9 ◽  
pp. 349-357 ◽  
Author(s):  
T. Renkwitz ◽  
W. Singer ◽  
R. Latteck ◽  
M. Rapp
Keyword(s):  
Middle Atmosphere ◽  
Beam Forming ◽  
Cosmic Radio ◽  
Radio Noise ◽  
Spatiotemporal Resolution ◽  
Vhf Radar ◽  
Butler Matrix ◽  
The North ◽  
Noise Absorption ◽  
Cosmic Noise

Abstract. The Leibniz-Institute of Atmospheric Physics (IAP) in Kühlungsborn started to install a new MST radar on the North-Norwegian island Andøya (69.30° N, 16.04° E) in 2009. The new Middle Atmosphere Alomar Radar System (MAARSY) replaces the previous ALWIN radar which has been successfully operated for more than 10 years. The MAARSY radar provides increased temporal and spatial resolution combined with a flexible sequential point-to-point steering of the radar beam. To increase the spatiotemporal resolution of the observations a 16-port Butler matrix has been built and implemented to the radar. In conjunction with 64 Yagi antennas of the former ALWIN antenna array the Butler matrix simultaneously provides 16 individual beams. The beam forming capability of the Butler matrix arrangement has been verified observing the galactic cosmic radio noise of the supernova remnant Cassiopeia A. Furthermore, this multi beam configuration has been used in passive experiments to estimate the cosmic noise absorption at 53.5 MHz during events of enhanced solar and geomagnetic activity as indicators for enhanced ionization at altitudes below 90 km. These observations are well correlated with simultaneous observations of corresponding beams of the co-located imaging riometer AIRIS (69.14° N, 16.02° E) at 38.2 MHz. In addition, enhanced cosmic noise absorption goes along with enhanced electron densities at altitudes below about 90 km as observed with the co-located Saura MF radar using differential absorption and differential phase measurements.

scholarly journals Cosmic noise absorption signature of particle precipitation during ICME sheaths and ejecta

2019 ◽  
Author(s):  
Emilia Kilpua ◽  
Liisa Juusola ◽  
Maxime Grandin ◽  
Antti Kero ◽  
Stepan Dubyagin ◽  
...  
Keyword(s):  
Radiation Belt ◽  
Geomagnetic Latitude ◽  
Electron Precipitation ◽  
Occurrence Frequency ◽  
Ulf Waves ◽  
Interplanetary Coronal Mass Ejections ◽  
Noise Absorption ◽  
Radiation Belt Electrons ◽  
Cosmic Noise ◽  
Trapped Radiation

Abstract. We study here energetic (E > 30 keV) electron precipitation using cosmic noise absorption (CNA) during the sheath and ejecta structures of 61 interplanetary coronal mass ejections (ICMEs) observed in the near-Earth solar wind between 1997 and 2012. The data comes from the Finnish riometer chain from stations extending from auroral (IVA, 65.2 geomagnetic latitude, MLAT) to subauroral (JYV, 59.0 MLAT) latitudes. We find that sheaths and ejecta lead frequently to enhanced CNA (> 0.5 dB) both at auroral and subauroral latitudes, although the CNA magnitudes stay relatively low (medians around 1 dB). Due to their longer duration, ejecta typically lead to more sustained enhanced CNA periods (on average 6–7 hours), but the sheaths and ejecta were found to be equally effective in inducing enhanced CNA when relative occurrence frequency and CNA magnitude were considered. Only at the lowest MLAT station JYV ejecta were more effective in causing enhanced CNA. Some clear magnetic local time (MLT) trends and differences between the ejecta and sheath were found. The occurrence frequency and magnitude of CNA activity was lowest close to midnight, while it peaked for the sheaths in the morning and afternoon/evening sectors and for the ejecta in the morning and noon sectors. These differences may reflect differences in typical MLT distributions of wave modes that precipitate substorm-injected and trapped radiation belt electrons during the sheath and ejecta. Our study also emphasizes the importance of substorms and magnetospheric ULF waves for enhanced CNA.

Electric Conductivity of Vitreous Silica during Pulsed-Electron-Beam Irradiation

1984 ◽  
Vol 35 ◽  
Author(s):  
Stanley H. Stern ◽  
Ralph B. Fiorito
Keyword(s):  
Electron Beam ◽  
Electric Conductivity ◽  
Electron Beam Irradiation ◽  
National Laboratory ◽  
Energetic Electron ◽  
Vitreous Silica ◽  
High Energy ◽  
X Rays ◽  
Los Alamos National Laboratory ◽  
Pulsed Electron Beam

ABSTRACTWe describe a measurement of the transient conductivity induced in amorphous SiO2 during irradiation by an intense and energetic electron beam. Preliminary results of an experiment [1] we performed at the Pulsed High - Energy Radiographic Machine Emitting X Rays (PHERMEX) facility of Los Alamos National Laboratory indicate that a beam of electrons of energy 17.5 MeV, of current density 1 kA/cm2, and of micropulse duration 3 nsec induce in a-SiO2 an electric conductivity 007E 6 × 10-3 (03A9-cm)-1. This value is 15 orders of magnitude larger than the ordinary (ionic) conductivity of the material [2].

scholarly journals Observations of precipitation energies during different types of pulsating aurora

2020 ◽  
Vol 38 (6) ◽  
pp. 1191-1202
Author(s):  
Fasil Tesema ◽  
Noora Partamies ◽  
Hilde Nesse Tyssøy ◽  
Derek McKay
Keyword(s):  
Electron Density ◽  
Electromagnetic Waves ◽  
Energetic Electron ◽  
Noise Absorption ◽  
Receiver Array ◽  
Maximum Electron Density ◽  
Different Types ◽  
Imaging Receiver ◽  
Cosmic Noise ◽  
Uhf Radar

Abstract. Pulsating aurora (PsA) is a diffuse type of aurora with different structures switching on and off with a period of a few seconds. It is often associated with energetic electron precipitation (>10 keV) resulting in the interaction between magnetospheric electrons and electromagnetic waves in the magnetosphere. Recent studies categorize pulsating aurora into three different types – amorphous pulsating aurora (APA), patchy pulsating aurora (PPA), and patchy aurora (PA) – based on the spatial extent of pulsations and structural stability. Differences in precipitation energies of electrons associated with these types of pulsating aurora have been suggested. In this study, we further examine these three types of pulsating aurora using electron density measurements from the European Incoherent Scatter (EISCAT) VHF/UHF radar experiments and Kilpisjärvi Atmospheric Imaging Receiver Array (KAIRA) cosmic noise absorption (CNA) measurements. Based on ground-based all-sky camera images over the Fennoscandian region, we identified a total of 92 PsA events in the years between 2010 and 2020 with simultaneous EISCAT experiments. Among these events, 39, 35, and 18 were APA, PPA, and PA types with a collective duration of 58, 43, and 21 h, respectively. We found that, below 100 km, electron density enhancements during PPAs and PAs are significantly higher than during APA. However, there are no appreciable electron density differences between PPA and APA above 100 km, while PA showed weaker ionization. The altitude of the maximum electron density also showed considerable differences among the three types, centered around 110, 105, and 105 km for APA, PPA, and PA, respectively. The KAIRA CNA values also showed higher values on average during PPA (0.33 dB) compared to PA (0.23 dB) and especially APA (0.17 dB). In general, this suggests that the precipitating electrons responsible for APA have a lower energy range compared to PPA and PA types. Among the three categories, the magnitude of the maximum electron density shows higher values at lower altitudes and in the late magnetic local time (MLT) sector (after 5 MLT) during PPA than during PA or APA. We also found significant ionization down to 70 km during PPA and PA, which corresponds to ∼200 keV of precipitating electrons.

GEOMAGNETIC AND IONOSPHERIC OBSERVATIONS ASSOCIATED WITH AURORAL ACTIVITY DURING THE TOTAL SOLAR ECLIPSE OF JULY 20, 1963

1965 ◽  
Vol 43 (3) ◽  
pp. 457-462
Author(s):  
T. A. Clark ◽  
C. D. Anger
Keyword(s):  
Solar Eclipse ◽  
Noise Level ◽  
Total Solar Eclipse ◽  
Electron Precipitation ◽  
Moderate Degree ◽  
X Rays ◽  
Auroral Activity ◽  
Noise Absorption ◽  
Cosmic Noise ◽  
Auroral Luminosity

Data obtained at Fort Providence, N.W.T., Canada, during the total solar eclipse of July 20, 1963, indicate that during most of the partial eclipse there was a moderate degree of auroral activity. This activity became slight during the period of totality and no auroral luminosity was detected. Electron precipitation was indicated by an enhancement of the intensity of X rays of energy greater than 9 keV at balloon altitudes and by small amounts of cosmic-noise absorption. A small but irregular increase in cosmic-noise level at 30 Mc/s, which was greater than 0.2 dB at totality, was recorded. It was concluded that the irregularity was caused by small amounts of superimposed auroral absorption.

scholarly journals Comparison of methods to determine auroral ionospheric conductances using ground-based optical and riometer data

2008 ◽  
Vol 26 (12) ◽  
pp. 3831-3840 ◽  
Author(s):  
A. Senior ◽  
M. J. Kosch ◽  
F. Honary
Keyword(s):  
Cosmic Radio ◽  
Hall Conductance ◽  
Incoherent Scatter ◽  
Noise Absorption ◽  
Radar Measurements ◽  
Conductance Ratio ◽  
Cosmic Noise ◽  
Auroral Arcs ◽  
Current Systems ◽  
Magnetic Zenith

Abstract. Ground-based images of auroral optical emissions and cosmic radio noise absorption provide information on particle precipitation which enhances ionospheric conductances. Knowledge of this conductance field is important to understand the current systems associated with auroral features. Three methods of using ground-based optical and riometer data to estimate ionospheric conductances in the aurora are compared to conductances derived from incoherent scatter radar measurements. It is shown that a method using the 557.7 nm emission intensity alone gives the best results for the Pedersen conductance whilst a method using both this intensity and cosmic noise absorption is best for the Hall conductance. A method using cosmic noise absorption alone gives reasonable performance for the Hall conductance and the Hall/Pedersen conductance ratio, but performs poorly for the Pedersen conductance. It also appears to underestimate the Hall conductance significantly during times when softer precipitation is present, for example in discrete auroral arcs. There is some indication that the methods do not degrade noticeably for angles up to ~20° off magnetic zenith.

scholarly journals Sudden Cosmic Noise Absorption at 29 Mc/s

1962 ◽  
Vol 15 (1) ◽  
pp. 20 ◽  
Author(s):  
M Krishnamurthi ◽  
G Sivarama Sastry ◽  
T Seshagiri Rao
Keyword(s):  
Solar Flare ◽  
Radio Emission ◽  
Solar Flares ◽  
Initial Conditions ◽  
Cosmic Radio ◽  
Radio Noise ◽  
Terrestrial Atmosphere ◽  
Noise Absorption ◽  
Cosmic Noise

Cosmic radio noise observations at 29 Mc/s made at Hyderabad, India (17� 26' N., 78� 27' E.), have been compared with solar flare data for the year 1958. For flares of importance 3 or 3�, there is a correlation of 84% with regard to related effects observed in the cosmic noise records. These effects are either enhanced radio emission or SCNA's. Particular study of the 9 SCNA's observed during the year and comparison with results of Bhonsle working at Ahmedabad, India (23� 02' N., 72� 38' E.), reveal that (a) even in the case of intense flares initial conditions in the terrestrial atmosphere govern the production and maintenance of an SCNA, and (b) therefore, at least at frequencies above 25 Mc/s, SCNA's cannot be used for patrolling even intense solar flares.

scholarly journals Cosmic noise absorption signature of particle precipitation during interplanetary coronal mass ejection sheaths and ejecta

2020 ◽  
Vol 38 (2) ◽  
pp. 557-574
Author(s):  
Emilia Kilpua ◽  
Liisa Juusola ◽  
Maxime Grandin ◽  
Antti Kero ◽  
Stepan Dubyagin ◽  
...  
Keyword(s):  
Energetic Electron ◽  
Geomagnetic Latitude ◽  
Low Frequency ◽  
Occurrence Frequency ◽  
Interplanetary Coronal Mass Ejections ◽  
Interplanetary Coronal Mass Ejection ◽  
Noise Absorption ◽  
Cosmic Noise ◽  
Trapped Radiation ◽  
Mass Ejection

Abstract. We study here energetic-electron (E>30 keV) precipitation using cosmic noise absorption (CNA) during the sheath and ejecta structures of 61 interplanetary coronal mass ejections (ICMEs) observed in the near-Earth solar wind between 1997 and 2012. The data come from the Finnish riometer (relative ionospheric opacity meter) chain from stations extending from auroral (IVA, 65.2∘ N geomagnetic latitude; MLAT) to subauroral (JYV, 59.0∘ N MLAT) latitudes. We find that sheaths and ejecta lead frequently to enhanced CNA (>0.5 dB) both at auroral and subauroral latitudes, although the CNA magnitudes stay relatively low (medians around 1 dB). Due to their longer duration, ejecta typically lead to more sustained enhanced CNA periods (on average 6–7 h), but the sheaths and ejecta were found to be equally effective in inducing enhanced CNA when relative-occurrence frequency and CNA magnitude were considered. Only at the lowest-MLAT station, JYV, ejecta were more effective in causing enhanced CNA. Some clear trends of magnetic local time (MLT) and differences between the ejecta and sheaths were found. The occurrence frequency and magnitude of CNA activity was lowest close to midnight, while it peaked for the sheaths in the morning and afternoon/evening sectors and for the ejecta in the morning and noon sectors. These differences may reflect differences in typical MLT distributions of wave modes that precipitate substorm-injected and trapped radiation belt electrons during the sheaths and ejecta. Our study also emphasizes the importance of substorms and magnetospheric ultra-low-frequency (ULF) waves for enhanced CNA.

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