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 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 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 Upper-mesospheric temperatures measured during intense substorms in the declining phase of the January 2005 solar proton events

2008 ◽  
Vol 26 (9) ◽  
pp. 2515-2529 ◽  
Author(s):  
H. Nesse Tyssøy ◽  
D. Heinrich ◽  
J. Stadsnes ◽  
M. Sørbø ◽  
U.-P. Hoppe ◽  
...  
Keyword(s):  
Geomagnetic Activity ◽  
Solar Proton ◽  
Temperature Measurements ◽  
Proton Event ◽  
Cosmic Radio ◽  
Measured Temperature ◽  
Radio Noise ◽  
Particle Precipitation ◽  
Particle Measurements ◽  
Noise Absorption

Abstract. Temperature measurements from the ALOMAR Weber Na lidar together with cosmic radio noise absorption measurements from IRIS and particle measurements from NOAA 15, 16 and 17 are used to study effects of geomagnetic activity on the polar winter upper-mesospheric temperature. On 21–22 January 2005 we have 14 h of continuous temperature measurement with the Na lidar coinciding with strong geomagnetic activity in the declining phase of one of the hardest and most energetic Solar Proton Event (SPE) of solar cycle 23. According to measurements by the imaging riometer IRIS in northern Finland, the temperature measurements coincide with two periods of increased cosmic radio noise absorption. Particle measurements from the three satellites, NOAA 15, 16 and 17 that pass through and near our region of interest confirm that the absorption events are probably due to particle precipitation and not due to changes in e.g. the electron recombination coefficient. The measured temperature variation at 85 and 90 km is dominated by a 7.6-h wave with downward phase propagation and a vertical wavelength of approximately 10 km. Assuming that the wave is due to a lower altitude source independent of the particle precipitation, we do not find any temperature modification that seems to be related to the absorption events. The average temperature is larger than expected above 90 km based on MSIS and the monthly mean from falling spheres, which could be due to particle precipitation and Joule heating prior to our measurement period. There is also a possibility that the identified wave phenomenon is an effect of the geomagnetic activity itself. Earlier studies have reported of similar wavelike structures in wind observations made by the EISCAT VHF radar during SPEs, and found it conceivable that the wave could be excited by the effect of energetic particles precipitating into the mesosphere.

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 Poker Flat Incoherent Scatter Radar observations of anomalous electron heating in the E region

2013 ◽  
Vol 31 (7) ◽  
pp. 1163-1176 ◽  
Author(s):  
R. A. Makarevich ◽  
A. V. Koustov ◽  
M. J. Nicolls
Keyword(s):  
Electric Field ◽  
Electron Temperature ◽  
Electric Fields ◽  
Linear Trend ◽  
Incoherent Scatter Radar ◽  
Electron Heating ◽  
Incoherent Scatter ◽  
Convection Electric Field ◽  
Scatter Radar ◽  
E Region

Abstract. A comprehensive 2-year dataset collected with the Poker Flat Incoherent Scatter Radar (PFISR) located near Fairbanks, Alaska (MLAT = 65.4° N) is employed to identify and analyse 22 events of anomalous electron heating (AEH) in the auroral E region. The overall AEH occurrence probability is conservatively estimated to be 0.3% from nearly-continuous observations of the E region by PFISR, although it increases to 0.7–0.9% in the dawn and dusk sectors where all AEH events were observed. The AEH occurrence variation with MLT is broadly consistent with those of events with high convection velocity (>1000 m s−1) or electron temperature (> 800 K), except for much smaller AEH probability and absence of AEH events near magnetic midnight. This suggests that high convection electric field by itself is necessary but not sufficient for measurable electron heating by two-stream plasma waves. The multi-point observations are utilised to investigate the fundamental dependence of the electron temperature on the convection electric field, focusing on the previously-proposed saturation effects at extreme electric fields. The AEH dataset was found to exhibit considerable scatter and, on average, similar rate of the electron temperature increase with the electric field up to 100 mV m−1 as compared with previous studies. At higher (highest) electric fields, the electron temperatures are below the linear trend on average (within uncertainty). By employing a simple fluid model of AEH, it is demonstrated that some of this deviation from the linear trend may be due to a stronger vibrational cooling at very large temperatures and electric fields.

scholarly journals The effects of mesoscale regions of precipitation on the ionospheric dynamics, electrodynamics and electron density in the presence of strong ambient electric fields

2010 ◽  
Vol 28 (6) ◽  
pp. 1345-1360 ◽  
Author(s):  
J. D. de Boer ◽  
J.-M. A. Noël ◽  
J.-P. St.-Maurice
Keyword(s):  
Electron Density ◽  
Electric Fields ◽  
Current Density Distribution ◽  
Electron Density Profile ◽  
Particle Precipitation ◽  
Advection Term ◽  
Nonlinear Advection ◽  
High Latitude Ionosphere ◽  
E Region ◽  
Current Densities

Abstract. We have developed a new high resolution two-dimensional model of the high latitude ionosphere in which nonlinear advection terms are closely coupled with the electrodynamics. The model provides a self-consistent description of the ionospheric feedback on the electrodynamical perturbations produced by auroral arc-related particle precipitation in regions with strong ambient electric fields. We find in particular that a heretofore neglected ion Pedersen advection term can introduce considerable changes in the electron density profile, the current density distribution, the conductivities and the electron temperatures. We find that the convective effects can carry the ionisation more than 150 km outside the precipitation region in a few minutes, with attendant large changes in the current distribution and E-region densities that become enhanced outside the region of particle precipitation. The production of a tongue of ionisation that slowly decays outside the auroral boundaries contrasts with the sharp geometric cut-off and associated stronger current densities found in previous studies.

The role of energetic electron precipitation and background dynamics on the seasonal NO variability in the MLT region

2021 ◽  
Author(s):  
Christine Smith-Johnsen ◽  
Hilde Nesse Tyssøy ◽  
Daniel Robert Marsh ◽  
Anne Smith ◽  
Ville Maliniemi
Keyword(s):  
Climate Model ◽  
Lower Thermosphere ◽  
Energetic Electron ◽  
Sensitivity Study ◽  
Electron Precipitation ◽  
Ion Chemistry ◽  
Wave Forcing ◽  
D Region ◽  
E Region ◽  
Cluster Ion

<p><span>Energetic electron precipitation (EEP) ionizes the Earth's atmosphere and leads to production of nitric oxide (NO) throughout the polar Mesosphere and Lower Thermosphere (MLT). In this study we investigate the direct and indirect NO response to the EEP using the Whole Atmosphere Community Climate Model (WACCM) version 6. In comparison to observations from SOFIE / AIM (Solar Occultation For Ice Experiment / Aeronomy of Ice in the Mesosphere), we find that EEP production of NO in the D-region is well simulated when both medium energy electron precipitation and negative and cluster ion chemistry are included in the model. However, the main EEP production of NO occurs in the E-region, and there the observed and modeled production differ. This discrepancy impacts also the D-region due to downward transport of long lived NO. The transport across the mesopause is seasonally dependent, and WACCM’s underestimate of D-region NO is highest during winter when downwelling from above is strong. The drivers of this transport are further investigated by a sensitivity study of WACCM’s gravity wave forcing.</span></p>

The role of EEP forcing and background dynamics on the seasonal NO variability in the MLT region

2020 ◽  
Author(s):  
Christine Smith-Johnsen ◽  
Hilde Nesse Tyssøy ◽  
Daniel Marsh ◽  
Anne Smith
Keyword(s):  
Climate Model ◽  
Energetic Electron ◽  
Eddy Diffusion ◽  
Electron Precipitation ◽  
Ion Chemistry ◽  
D Region ◽  
E Region ◽  
Cluster Ion ◽  
Mlt Region

<p><a name="docs-internal-guid-803d1a38-7fff-fefe-52f7-d0a055a4547b"></a><a name="docs-internal-guid-b8d76d48-7fff-149a-6440-413c0de833ae"></a> <span>Energetic electron precipitation (EEP) ionizes the Earth's atmosphere and leads to production of nitric oxide (NO) from 50 to 150 km altitude. In this study we investigate the direct and indirect NO response to EEP using the Whole Atmosphere Community Climate Model (WACCM). In comparison to observations from SOFIE / AIM (Solar Occultation For Ice Experiment / Aeronomy of Ice in the Mesosphere), we find that EEP production of NO in the D-region is well simulated when both medium energy electron precipitation and negative and cluster ion chemistry is included in the model. However, the main EEP production of NO occurs in the E-region, and there the observed and modeled production differ. This discrepancy impacts also the D-region, and is seasonally dependent with the highest underestimate of D-region NO occuring during winter. The modeled transport across the mesopause during winter is generally weak, but strengthens with increased gravity wave activity. Increased eddy diffusion, increases NO at all altitudes through the polar MLT region</span></p>

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