scholarly journals Isolated lower mesospheric echoes seen by medium frequency radar at 70° N, 19° E

2006 ◽  
Vol 6 (12) ◽  
pp. 5307-5314 ◽  
Author(s):  
C. M. Hall ◽  
A. H. Manson ◽  
C. E. Meek ◽  
S. Nozawa
Keyword(s):  
Radio Wave ◽  
Solar Proton ◽  
Necessary Condition ◽  
Total Absorption ◽  
Medium Frequency ◽  
Vhf Radar ◽  
Proton Fluxes ◽  
D Region ◽  
Mf Radar

Abstract. We have noted sporadic instances of strong isolated reflections of medium frequency (MF) radar waves from the mesosphere from as low as 50 km altitude and have devised a set of criteria for isolating these apparently anomalous echoes from those normally occurring from progressive partial reflections in the D-region. The object of this study is to map the occurrences of such echoes facilitating comparisons with other observations. For example, the similarity and simultaneity of the echo structure for the 20 January 2005 with VHF radar results presented by Lübken et al. (2006) are particularly striking. In presenting a number of such echo events since 2001 selected from the MF radar dataset (which spans 1997 to present), we find that virtually all echo occurrences coincide with enhanced solar proton fluxes suggesting that substantial ionisation of the mesosphere is a necessary condition. Strong partial reflections of the radio wave in the lower mesosphere combined with seasonally varying total absorption higher up, thus giving false impressions of lower mesospheric layers preferentially in winter, constitute a scenario consistent with our observations.

scholarly journals Isolated lower mesospheric echoes seen by medium frequency radar at 70° N, 19° E

2006 ◽  
Vol 6 (4) ◽  
pp. 7407-7426
Author(s):  
C. M. Hall ◽  
A. H. Manson ◽  
C. E. Meek ◽  
S. Nozawa
Keyword(s):  
Radio Wave ◽  
Solar Proton ◽  
Necessary Condition ◽  
Total Absorption ◽  
Medium Frequency ◽  
Vhf Radar ◽  
Proton Fluxes ◽  
D Region ◽  
Mf Radar

Abstract. We have noted sporadic instances of strong isolated reflections of medium frequency (MF) radar waves from the mesosphere from as low as 50 km altitude and have devised a set of criteria for isolating these apparently anomalous echoes from those normally occurring from progressive partial reflections in the D-region. The object of this study is therefore to map the occurrences of such echoes facilitating comparisons with other observations. For example, the similarity and simultaneity of the echo structure for the 20 January 2005 with VHF radar results presented by Lübken et al. (2006) are particularly striking. In presenting a number of such echo events since 2001 selected from the MF radar dataset (which spans 1997 to present), we find that virtually all echo occurrences coincide with enhanced solar proton fluxes suggesting that substantial ionisation of the mesosphere is a necessary condition. Strong partial reflections of the radio wave in the lower mesosphere combined with seasonally varying total absorption higher up, thus giving false impressions of lower mesospheric layers preferentially in winter, constitute a scenario consistent with our observations.

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.

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.

Detection and Prediction of Absorbed Radiation Doses from Solar Proton Fluxes onboard Orbital Stations

2004 ◽  
Vol 42 (3) ◽  
pp. 203-209 ◽  
Author(s):  
N. V. Kuznetsov ◽  
R. A. Nymmik ◽  
M. I. Panasyuk ◽  
E. N. Sosnovets ◽  
M. V. Teltsov
Keyword(s):  
Solar Proton ◽  
Radiation Doses ◽  
Proton Fluxes

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 Perspective Ground-based Method for Diagnostics of the Lower Ionosphere and the Neutral Atmosphere

2013 ◽  
Vol 22 (1) ◽  
Author(s):  
N. V. Bakhmetieva ◽  
G. I. Grigoriev ◽  
A. V. Tolmacheva
Keyword(s):  
Radio Wave ◽  
High Power ◽  
Relative Concentration ◽  
Spectral Characteristics ◽  
Lower Ionosphere ◽  
Internal Gravity Waves ◽  
Spatial Period ◽  
Neutral Atmosphere ◽  
Radio Waves ◽  
D Region

AbstractWe present a new perspective ground-based method for diagnostics of the ionosphere and atmosphere parameters. The method uses one of the numerous physical phenomena observed in the ionosphere illuminated by high-power radio waves. It is a generation of the artificial periodic irregularities (APIs) in the ionospheric plasma. The APIs were found while studying the effects of ionospheric high-power HF modification. It was established that the APIs are formed by a standing wave that occurs due to interference between the upwardly radiated radio wave and its reflection off the ionosphere. The API studies are based upon observation of the Bragg backscatter of the pulsed probe radio wave from the artificial periodic structure. Bragg backscatter occurs if the spatial period of the irregularities is equal to half a wavelength of the probe signal. The API techniques makes it possible to obtain the following information: the profiles of electron density from the lower D-region up to the maximum of the F-layer; the irregular structure of the ionosphere including split of the regular E-layer, the sporadic layers; the vertical velocities in the D- and E-regions of the ionosphere; the turbulent velocities, turbulent diffusion coefficients and the turbopause altitude; the neutral temperatures and densities at the E-region altitudes; the parameters of the internal gravity waves and their spectral characteristics; the relative concentration of negative oxygen ions in the D-region. Some new results obtained by the API technique are discussed.

scholarly journals <i>D</i> region ion-neutral coupled chemistry within a whole atmosphere chemistry-climate model

2016 ◽  
Author(s):  
Tamás Kovács ◽  
John M. C. Plane ◽  
Wuhu Feng ◽  
Tibor Nagy ◽  
Martyn P. Chipperfield ◽  
...  
Keyword(s):  
Climate Model ◽  
Negative Ions ◽  
Reaction Scheme ◽  
Solar Proton ◽  
Proton Event ◽  
Test Case ◽  
Neutral Species ◽  
Ion Molecule Reactions ◽  
D Region ◽  
The Impact

Abstract. This study presents a new ion-neutral chemical model coupled into the Whole Atmosphere Community Climate Model (WACCM). The ionospheric D region (altitudes ~ 50–90 km) chemistry is based on the Sodankylä Ion and Neutral Chemistry (SIC) model, a 1-dimensional model containing 306 ion-neutral and ionrecombination reactions of neutral species, positive and negative ions, and electrons. The SIC mechanism was reduced using the Simulation Error Minimization Connectivity Method (SEM-CM) to produce a reaction scheme of 181 ion-molecule reactions. This scheme describes the concentration profiles at altitudes between 20 km and 120 km of a set of major neutral species (HNO3, O3, H2O2, NO, NO2, HO2, OH, N2O5) and ions (O2+, O4+, NO+, NO+(H2O), O2+(H2O), H+(H2O), H+(H2O)2, H+(H2O)3, H+(H2O)4, O3−, NO2−, O−, O2, OH−, O2−(H2O), O2−(H2O)2, O4−, CO3−, CO3−(H2O), CO4−, HCO3−, NO2−, NO3−, NO3−(H2O), NO3(H2O)2, NO3−(HNO3), NO3−(HNO3)2, Cl−, ClO−), which agree with the full SIC mechanism within a 5 % tolerance. Four 3D model simulations were then performed, using the impact of the January 2005 Solar Proton Event (SPE) on D region HOx and NOx chemistry as a test case of four different model versions: the standard WACCM (no negative ions and a very limited set of positive ions); WACCM-SIC (standard WACCM with the full SIC chemistry of positive and negative ions); WACCM-D (standard WACCM with a heuristic reduction of the SIC chemistry, recently used to examine HNO3 formation following an SPE); and WACCM-rSIC (standard WACCM with a reduction of SIC chemistry using the SEM-CM Method). Standard WACCM misses the HNO3 enhancement during the SPE, while the full and reduced model versions predict significant NOx, HOx and HNO3 enhancements in the mesosphere during solar proton events. The SEM-CM reduction also identifies the important ion-molecule reactions that affect the partitioning of odd nitrogen (NOx), odd hydrogen (HOx), and O3 in the stratosphere and mesosphere.

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