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 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 Statistical signature of active D-region HF heating in IRIS riometer data from 1994–2004

2007 ◽  
Vol 25 (2) ◽  
pp. 407-415 ◽  
Author(s):  
A. Kero ◽  
C.-F. Enell ◽  
Th. Ulich ◽  
E. Turunen ◽  
M. T. Rietveld ◽  
...  
Keyword(s):  
Present Theory ◽  
Cosmic Radio ◽  
Radio Noise ◽  
3 Dimensional ◽  
Noise Absorption ◽  
D Region ◽  
Order Of Magnitude ◽  
Representative Model ◽  
Vertical Beam ◽  
Hf Heating

Abstract. In this paper we study the effect of artificial HF heating on cosmic radio noise absorption in the D-region ionosphere. The effect has earlier been studied theoretically in idealised cases and without experimental verification. Here we present a 3-dimensional modelling of the effect, taking into account the directivity patterns of the vertical beam of the EISCAT Heater at Tromsø, Norway, and the intersecting beam of the IRIS imaging riometer at Kilpisjärvi, Finland. The heater-induced enhancement of cosmic radio noise absorption at the IRIS frequency (38.2 MHz) is estimated to be between 0.02 dB and 0.05 dB in the most representative model cases. However, a statistical study of IRIS data from a selected set of heating experiments carried out during the years 1994–2004 shows that the median effect is between 0.002 dB and 0.004 dB, i.e. an order of magnitude less than theoretically predicted. This indicates that the actual HF heating effect at D-region altitudes is substantially overestimated by the present theory.

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 radio noise absorption related to structures in auroral luminosity

1997 ◽  
Vol 102 (A4) ◽  
pp. 7439-7447 ◽  
Author(s):  
P. H. Stoker ◽  
M. J. Mathews ◽  
M. W. J. Scourfield
Keyword(s):  
Cosmic Radio ◽  
Radio Noise ◽  
Noise Absorption ◽  
Auroral Luminosity

scholarly journals Cosmic radio-noise absorption bursts caused by solar wind shocks

2004 ◽  
Vol 22 (8) ◽  
pp. 2973-2987 ◽  
Author(s):  
A. Osepian ◽  
S. Kirkwood
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Geomagnetic Storms ◽  
Quantitative Description ◽  
Threshold Value ◽  
Cosmic Radio ◽  
Radio Noise ◽  
Field Perturbation ◽  
Noise Absorption ◽  
Cyclotron Instability

Abstract. Bursts of cosmic noise absorption observed at times of sudden commencements (SC) of geomagnetic storms are examined. About 300SC events in absorption for the period 1967-1990 have been considered. It is found that the response of cosmic radio-noise absorption to the passage of an interplanetary shock depends on the level of the planetary magnetic activity preceding the SC event and on the magnitude of the magnetic field perturbation associated with the SC (as measured in the equatorial magnetosphere). It is shown that for SC events observed against a quiet background (Kp<2), the effects of the SC on absorption can be seen only if the magnitude of the geomagnetic field perturbation caused by the solar wind shock exceeds a threshold value ΔBth. It is further demonstrated that the existence of this threshold value, ΔBth, deduced from experimental data, can be related to the existence of a threshold for exciting and maintaining the whistler cyclotron instability, as predicted by quasi-linear theory. SC events observed against an active background (Kp<2) are accompanied by absorption bursts for all magnetic field perturbations, however small. A quantitative description of absorption bursts associated with SC events is provided by the whistler cyclotron instability theory.

scholarly journals Cosmic radio noise absorption in the high-latitude ionosphere during solar wind high-speed streams

2017 ◽  
Vol 122 (5) ◽  
pp. 5203-5223 ◽  
Author(s):  
M. Grandin ◽  
A. T. Aikio ◽  
A. Kozlovsky ◽  
T. Ulich ◽  
T. Raita
Keyword(s):  
Solar Wind ◽  
High Latitude ◽  
High Speed ◽  
Cosmic Radio ◽  
Radio Noise ◽  
Noise Absorption ◽  
High Latitude Ionosphere

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.

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