The high latitude D-region and mesosphere revealed by the EISCAT incoherent scatter radars during solar proton events

1996 ◽  
Vol 18 (3) ◽  
pp. 83-92 ◽  
Author(s):  
P.N. Collis
Keyword(s):  
High Latitude ◽  
Solar Proton ◽  
Incoherent Scatter ◽  
Incoherent Scatter Radars ◽  
D Region ◽  
Solar Proton Events

Ionization increases associated with the small solar proton events of 5 February 1965 and 16 July 1966

1969 ◽  
Vol 47 (2) ◽  
pp. 131-134 ◽  
Author(s):  
L. W. Hewitt
Keyword(s):  
Lower Ionosphere ◽  
Solar Proton ◽  
Satellite Observations ◽  
Geographic Latitude ◽  
Electron Number ◽  
Partial Reflection ◽  
D Region ◽  
Resolute Bay ◽  
Solar Proton Events

Observations of partial reflections from the ionosphere at vertical incidence at 2.66 MHz have been made at Resolute Bay, geographic latitude 74.7 °N, since September 1963. By measuring the amplitudes of the ordinary and extraordinary backscattered waves information is obtained about electron number densities in the lower ionosphere. The results presented in this paper show that the partial reflection technique is more sensitive than most other ground-based experiments for the detection of D-region ionization increases associated with small solar proton events. Results obtained by the partial reflection experiment during the events of 5 February 1965 and 16 July 1966 are presented and compared with VLF and satellite observations.

scholarly journals Contribution of proton and electron precipitation to the observed electron concentration in October–November 2003 and September 2005

2015 ◽  
Vol 33 (3) ◽  
pp. 381-394 ◽  
Author(s):  
P. T. Verronen ◽  
M. E. Andersson ◽  
A. Kero ◽  
C.-F. Enell ◽  
J. M. Wissing ◽  
...  
Keyword(s):  
Electron Concentration ◽  
Solar Proton ◽  
Electron Ionization ◽  
Climate Impacts ◽  
Electron Precipitation ◽  
Incoherent Scatter ◽  
Solar Proton Events ◽  
Spatio Temporal ◽  
The Difference ◽  
Ionization Rates

Abstract. Understanding the altitude distribution of particle precipitation forcing is vital for the assessment of its atmospheric and climate impacts. However, the proportion of electron and proton forcing around the mesopause region during solar proton events is not always clear due to uncertainties in satellite-based flux observations. Here we use electron concentration observations of the European Incoherent Scatter Scientific Association (EISCAT) incoherent scatter radars located at Tromsø (69.58° N, 19.23° E) to investigate the contribution of proton and electron precipitation to the changes taking place during two solar proton events. The EISCAT measurements are compared to the results from the Sodankylä Ion and Neutral Chemistry Model (SIC). The proton ionization rates are calculated by two different methods – a simple energy deposition calculation and the Atmospheric Ionization Model Osnabrück (AIMOS v1.2), the latter providing also the electron ionization rates. Our results show that in general the combination of AIMOS and SIC is able to reproduce the observed electron concentration within ± 50% when both electron and proton forcing is included. Electron contribution is dominant above 90 km, and can contribute significantly also in the upper mesosphere especially during low or moderate proton forcing. In the case of strong proton forcing, the AIMOS electron ionization rates seem to suffer from proton contamination of satellite-based flux data. This leads to overestimation of modelled electron concentrations by up to 90% between 75–90 km and up to 100–150% at 70–75 km. Above 90 km, the model bias varies significantly between the events. Although we cannot completely rule out EISCAT data issues, the difference is most likely a result of the spatio-temporal fine structure of electron precipitation during individual events that cannot be fully captured by sparse in situ flux (point) measurements, nor by the statistical AIMOS model which is based upon these observations.

scholarly journals D-region electron density and effective recombination coefficients during twilight – experimental data and modelling during solar proton events

2009 ◽  
Vol 27 (10) ◽  
pp. 3713-3724 ◽  
Author(s):  
A. Osepian ◽  
S. Kirkwood ◽  
P. Dalin ◽  
V. Tereschenko
Keyword(s):  
Electron Density ◽  
Zenith Angle ◽  
Solar Zenith Angle ◽  
Solar Proton ◽  
Radio Waves ◽  
Electron Densities ◽  
Partial Reflection ◽  
D Region ◽  
Density Values ◽  
Solar Proton Events

Abstract. Accurate measurements of electron density in the lower D-region (below 70 km altitude) are rarely made. This applies both with regard to measurements by ground-based facilities and by sounding rockets, and during both quiet conditions and conditions of energetic electron precipitation. Deep penetration into the atmosphere of high-energy solar proton fluxes (during solar proton events, SPE) produces extra ionisation in the whole D-region, including the lower altitudes, which gives favourable conditions for accurate measurements using ground-based facilities. In this study we show that electron densities measured with two ground-based facilities at almost the same latitude but slightly different longitudes, provide a valuable tool for validation of model computations. The two techniques used are incoherent scatter of radio waves (by the EISCAT 224 MHz radar in Tromsø, Norway, 69.6° N, 19.3° E), and partial reflection of radio-waves (by the 2.8 MHz radar near Murmansk, Russia, 69.0° N, 35.7° E). Both radars give accurate electron density values during SPE, from heights 57–60 km and upward with the EISCAT radar and between 55–70 km with the partial reflection technique. Near noon, there is little difference in the solar zenith angle between the two locations and both methods give approximately the same values of electron density at the overlapping heights. During twilight, when the difference in solar zenith angles increases, electron density values diverge. When both radars are in night conditions (solar zenith angle >99°) electron densities at the overlapping altitudes again become equal. We use the joint measurements to validate model computations of the ionospheric parameters f+, λ, αeff and their variations during solar proton events. These parameters are important characteristics of the lower ionosphere structure which cannot be determined by other methods.

scholarly journals EISCAT and ESRAD radars observations of polar mesosphere winter echoes during solar proton events on 11–12 November 2004

2013 ◽  
Vol 31 (7) ◽  
pp. 1177-1190 ◽  
Author(s):  
E. Belova ◽  
S. Kirkwood ◽  
T. Sergienko
Keyword(s):  
Power Spectrum ◽  
Electron Gas ◽  
Spectral Width ◽  
Solar Proton ◽  
Solar Proton Event ◽  
Complete Theory ◽  
Proton Event ◽  
Maximum Volume ◽  
Incoherent Scatter ◽  
Solar Proton Events

Abstract. Polar mesosphere winter echoes (PMWE) were detected by two radars, ESRAD at 52 MHz located near Kiruna, Sweden, and EISCAT at 224 MHz located near Tromsø, Norway, during the strong solar proton event on 11–12 November 2004. PMWE maximum volume reflectivity was estimated to be 3 × 10−15 m−1 for ESRAD and 2 × 10−18 m−1 for EISCAT. It was found that the shape of the echo power spectrum is close to Gaussian inside the PMWE layers, and outside of them it is close to Lorentzian, as for the standard ion line of incoherent scatter (IS). The EISCAT PMWE spectral width is about 5–7 m s−1 at 64–67 km and 7–10 m s−1 at 68–70 km. At the lower altitudes the PMWE spectral widths are close to those for the IS ion line derived from the EISCAT data outside the layers. At the higher altitudes the PMWE spectra are broader by 2–4 m s−1 than those for the ion line. The ESRAD PMWE spectral widths at 67–72 km altitude are 3–5 m s−1, that is, 2–4 m s−1 larger than ion line spectral widths modelled for the ESRAD radar. The PMWE spectral widths for both EISCAT and ESRAD showed no dependence on the echo strength. It was found that all these facts cannot be explained by turbulent origin of the echoes. We suggested that evanescent perturbations in the electron gas generated by the incident infrasound waves may explain the observed PMWE spectral widths. However, a complete theory of radar scatter from this kind of disturbance needs to be developed before a full conclusion can be made.

Reaction of the high-latitude lower ionosphere to solar proton events from observations in the ELF range

2017 ◽  
Vol 57 (1) ◽  
pp. 51-57 ◽  
Author(s):  
O. M. Lebed’ ◽  
A. V. Larchenko ◽  
S. V. Pil’gaev ◽  
Yu. V. Fedorenko
Keyword(s):  
High Latitude ◽  
Lower Ionosphere ◽  
Solar Proton ◽  
Solar Proton Events

scholarly journals Statistical response of middle atmosphere composition to solar proton events in WACCM-D simulations: importance of lower ionospheric chemistry

2020 ◽  
Author(s):  
Niilo Kalakoski ◽  
Pekka T. Verronen ◽  
Annika Seppälä ◽  
Monika E. Szeląg ◽  
Antti Kero ◽  
...  
Keyword(s):  
Climate Model ◽  
Middle Atmosphere ◽  
Lower Ionosphere ◽  
Solar Proton ◽  
Atmospheric Effects ◽  
Ion Chemistry ◽  
Global Models ◽  
Superposed Epoch Analysis ◽  
D Region ◽  
Solar Proton Events

Abstract. Atmospheric effects of solar proton events (SPE) have been studied for decades, because their drastic impact can be used to test our understanding of upper stratospheric and mesospheric chemistry in the polar cap regions. For example, SPEs cause production of odd hydrogen and odd nitrogen, which leads to depletion of ozone in catalytic reactions, such that the effects are easily observed from satellites during the largest events. Until recently, the complexity of the ion chemistry in the lower ionosphere (i.e. in the D region) has restricted global models to simplified parameterizations of chemical impacts induced by energetic particle precipitation (EPP). Because of this restriction, global models have been unable to correctly reproduce some important effects, such as the increase of mesospheric HNO3 or the changes in chlorine species. Here we use simulations from the WACCM-D model, a variant of the Whole Atmosphere Community Climate Model, to study the statistical response of the atmosphere to the 66 largest SPEs that occurred in years 1989–2012. Our model includes a set of D-region ion chemistry, designed for a detailed representation of the atmospheric effects of SPEs and EPP in general. We use superposed epoch analysis to study changes in O3, HOx (OH + HO2), Clx (Cl + ClO), HNO3, NOx (NO + NO2) and H2O. Compared to the standard WACCM which uses an ion chemistry parameterization, WACCM-D produces a larger response in O3 and NOx, weaker response in HOx and introduces changes in HNO3 and Clx. These differences between WACCM and WACCM-D highlight the importance of including ion chemistry reactions in models used to study EPP.

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