scholarly journals Case study of the mesospheric and lower thermospheric effects of solar X-ray flares: coupled ion-neutral modelling and comparison with EISCAT and riometer measurements

2008 ◽  
Vol 26 (8) ◽  
pp. 2311-2321 ◽  
Author(s):  
C.-F. Enell ◽  
P. T. Verronen ◽  
M. J. Beharrell ◽  
J. P. Vierinen ◽  
A. Kero ◽  
...  
Keyword(s):  
Solar Proton ◽  
Spectral Irradiance ◽  
Cluster Ions ◽  
Ion Chemistry ◽  
Density Profiles ◽  
X Ray ◽  
Noise Absorption ◽  
D Region ◽  
Electron Density Profiles ◽  
Cosmic Noise

Abstract. Two case studies of upper mesospheric and lower thermospheric (UMLT) high-latitude effects of solar X-ray flares are presented. Sodankylä Ion-neutral Chemistry Model (SIC) electron density profiles agree with D-region EISCAT and riometer observations, provided that the profiles of the most variable ionisable component, nitric oxide, are adjusted to compensate for NOx production during preceding geomagnetically active periods. For the M6-class flare of 27 April 2006, following a quiet period, the agreement with cosmic noise absorption observed by the Sodankylä riometers was within reasonable limits without adjustment of the [NO] profile. For the major (X17-class) event of 28 October 2003, following high auroral activity and solar proton events, the NO concentration had to be increased up to on the order of 108 cm−3 at the D-region minimum. Thus [NO] can in principle be measured by combining SIC with observations, if the solar spectral irradiance and particle precipitation are adequately known. As the two case events were short and modelled for high latitudes, the resulting neutral chemical changes are insignificant. However, changes in the model ion chemistry occur, including enhancements of water cluster ions.

scholarly journals The influence of ozone concentration on the lower ionosphere – modelling and measurements during the 29–30 October 2003 solar proton event

2009 ◽  
Vol 27 (2) ◽  
pp. 577-589 ◽  
Author(s):  
A. Osepian ◽  
S. Kirkwood ◽  
P. Dalin
Keyword(s):  
Electron Density ◽  
Ozone Concentration ◽  
Negative Ions ◽  
Solar Proton ◽  
Proton Event ◽  
Ion Chemistry ◽  
Density Profiles ◽  
Proton Fluxes ◽  
D Region ◽  
Electron Density Profiles

Abstract. A numerical model of D-region ion chemistry is used to study the influence of the ozone concentration in the mesosphere on ion-composition and electron density during solar proton events (SPE). We find a strong sensitivity in the lower part of the D-region, where negative ions play a major role in the ionization balance. We have chosen the strong SPE on 29–30 October 2003 when very intense proton fluxes with a hard energetic spectrum were observed. Deep penetration into the atmosphere by the proton fluxes and strong ionisation allows us to use measurements of electron density, made by the EISCAT 224 MHz radar, starting from as low as 55 km. We compare the electron density profiles with model results to determine which ozone concentration profiles are the most appropriate for mesospheric altitudes under SPE conditions. We show that, during daytime, an ozone profile corresponding to depletion by a factor of 2 compared to minimum model concentrations for quiet conditions (Rodrigo et al., 1986), is needed to give model electron density profiles consistent with observations. Simple incorporation of minor neutral constituent profiles (NO, O and O3) appropriate for SPE conditions into ion-chemistry models will allow more accurate modeling of electron and ion densities during such events, without the need to apply a complete chemical model calculating all neutral species.

scholarly journals Effects of D-region RF heating studied with the Sodankylä Ion Chemistry model

2005 ◽  
Vol 23 (5) ◽  
pp. 1575-1583 ◽  
Author(s):  
C.-F. Enell ◽  
A. Kero ◽  
E. Turunen ◽  
Th. Ulich ◽  
P. T. Verronen ◽  
...  
Keyword(s):  
Lower Thermosphere ◽  
Negative Ions ◽  
Solar Proton ◽  
Proton Event ◽  
High Electron ◽  
Ion Chemistry ◽  
Auroral Electron ◽  
D Region ◽  
Radio Transmitters ◽  
Cosmic Noise

Abstract. The upper mesosphere and lower thermosphere, or ionospheric D region, is an atmospheric layer which is difficult to access experimentally. A useful method that also has a large potential for further studies is artificial heating of electrons by means of powerful radio transmitters. Here we estimate the effect of D-region heating for a few typical cases of high electron density – daylight, typical auroral electron precipitation, and a solar proton event – by coupling a model of RF electron heating to the Sodankylä Ion Chemistry (SIC) model. The predicted effects are among others an increase in the ratio of the concentration of negative ions to that of free electrons, and an increase in the absorption of cosmic noise as measured by riometers. For the model runs presented in this paper we have calculated the absorption for the frequency (38.2MHz) of the IRIS imaging riometer in Kilpisjärvi, Finland, as observing the ionosphere above the EISCAT Heater in Tromsø, Norway. The predicted enhancements of the absorption are 0.2–0.8dB, an effect which is clearly detectable. Keywords. Ionosphere (Active experiments; Ion chemistry and composition; Wave propagation)

scholarly journals Electron density profiles in the quiet lower ionosphere based on the results of modeling and experimental data

2012 ◽  
Vol 30 (9) ◽  
pp. 1345-1360 ◽  
Author(s):  
V. Barabash ◽  
A. Osepian ◽  
P. Dalin ◽  
S. Kirkwood
Keyword(s):  
Solar Activity ◽  
Electron Density ◽  
Lower Ionosphere ◽  
Ionization Rate ◽  
Number Density ◽  
Density Profiles ◽  
Oxide Concentration ◽  
D Region ◽  
Nitric Oxide Concentration ◽  
Electron Density Profiles

Abstract. The theoretical PGI (Polar Geophysical Institute) model for the quiet lower ionosphere has been applied for computing the ionization rate and electron density profiles in the summer and winter D-region at solar zenith angles less than 80° and larger than 99° under steady state conditions. In order to minimize possible errors in estimation of ionization rates provided by solar electromagnetic radiation and to obtain the most exact values of electron density, each wavelength range of the solar spectrum has been divided into several intervals and the relations between the solar radiation intensity at these wavelengths and the solar activity index F10.7 have been incorporated into the model. Influence of minor neutral species (NO, H2O, O, O3) concentrations on the electron number density at different altitudes of the sunlit quiet D-region has been examined. The results demonstrate that at altitudes above 70 km, the modeled electron density is most sensitive to variations of nitric oxide concentration. Changes of water vapor concentration in the whole altitude range of the mesosphere influence the electron density only in the narrow height interval 73–85 km. The effect of the change of atomic oxygen and ozone concentration is the least significant and takes place only below 70 km. Model responses to changes of the solar zenith angle, solar activity (low–high) and season (summer–winter) have been considered. Modeled electron density profiles have been evaluated by comparison with experimental profiles available from the rocket measurements for the same conditions. It is demonstrated that the theoretical model for the quiet lower ionosphere is quite effective in describing variations in ionization rate, electron number density and effective recombination coefficient as functions of solar zenith angle, solar activity and season. The model may be used for solving inverse tasks, in particular, for estimations of nitric oxide concentration in the mesosphere.

Multifrequency Observations of Sudden Cosmic Noise Absorption and X-Ray Flares

Radio Science ◽  
1966 ◽  
Vol 1 (10) ◽  
pp. 1188-1195 ◽  
Author(s):  
A. P. Mitra ◽  
C. V. Subrahmaniyam ◽  
V. C. Jain
Keyword(s):  
X Ray ◽  
Noise Absorption ◽  
Cosmic Noise

scholarly journals Spectral characteristics of high latitude raw 40 MHz cosmic noise signals

2015 ◽  
Vol 2 (4) ◽  
pp. 969-987
Author(s):  
C. M. Hall
Keyword(s):  
Brownian Motion ◽  
Fractional Brownian Motion ◽  
Hurst Exponent ◽  
Spectral Characteristics ◽  
Noise Signal ◽  
Density Profiles ◽  
Generalized Hurst Exponent ◽  
Electron Density Profiles ◽  
Cosmic Noise ◽  
Non Gaussian

Abstract. Cosmic noise at 40 MHz is measured at Ny-Ålesund (79° N, 12° E) using a relative ionospheric opacity meter ("riometer"). A riometer is normally used to determine the degree to which cosmic noise is absorbed by the intervening ionosphere, giving an indication of ionization of the atmosphere at altitudes lower than generally monitored by other instruments. The usual course is to determine a "quiet-day" variation, this representing the galactic noise signal itself in the absence of absorption; the current signal is then subtracted from this to arrive at absorption expressed in dB. By a variety of means and assumptions, it is thereafter possible to estimate electron density profiles in the very lowest reaches of the ionosphere. Here however, the entire signal, i.e. including the cosmic noise itself will be examined and spectral characteristics identified. It will be seen that distinct spectral subranges are evident which can, in turn be identified with non-Gaussian processes characterized by generalized Hurst exponents, α. Considering all periods greater than 1 h, α ≈ 1.24 – an indication of fractional Brownian motion, whereas for periods greater than 1 day α ≈ 0.9 – approximately pink noise and just in the domain of fractional Gaussian noise. The results are compared with other physical processes suggesting that absorption of cosmic noise is characterized by a generalized Hurst exponent ≈ 1.24 and thus non-persistent fractional Brownian motion, whereas generation of cosmic noise is characterized by a generalized Hurst exponent ≈ 1.

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