Polar mesosphere summer echoes during the July 2000 solar protonevent

A Kutepov,V Barabash,S Kirkwood,A Feofilov

doi:10.5194/angeo-22-759-2004

A Kutepov, V Barabash + Show 2 more

Open Access

https://doi.org/10.5194/angeo-22-759-2004

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Journal: Annales Geophysicae	Publication Date: Mar 19, 2004
Citations: 31	License type: CC BY 3.0

Affiliation: Swedish Institute of Space Physics

Abstract

Abstract. The influence of the solar proton event (SPE) 14–16 July 2000 on Polar Mesosphere Summer Echoes (PMSE) is examined. PMSE were observed by the Esrange VHF MST Radar (ESRAD) at 67°53'N, 21°06'E. The 30MHz Imaging Riometer for Ionospheric Studies IRIS in Kilpisjärvi (69°30'N, 20°47'E) registered cosmic radio noise absorption caused by ionisation changes in response to the energetic particle precipitation. An energy deposition/ion-chemical model was used to estimate the density of free electrons and ions in the upper atmosphere. Particle collision frequencies were calculated from the MSISE-90 model. Electric fields were calculated using conductivities from the model and measured magnetic disturbances. The electric field reached a maximum of 91mV/m during the most intensive period of the geomagnetic storm accompanying the SPE. The temperature increase due to Joule and particle heating was calculated, taking into account radiative cooling. The temperature increase at PMSE heights was found to be very small. The observed PMSE were rather intensive and extended over the 80–90km height interval. PMSE almost disappeared above 86km at the time of greatest Joule heating on 15 July 2000. Neither ionisation changes, nor Joule/particle heating can explain the PMSE reduction. Transport effects due to the strong electric field are a more likely explanation. Key words. Meteorology and atmospheric dynamics (middle atmospheric dynamics), ionosphere (ionospheric disturbances; solar radiation and cosmic ray effects)

Highlights

Solar proton events (SPE) are characterized by intensive particle precipitation, mostly protons of energies from 10– 300 MeV (Brasseur and Solomon, 1986)
This study presents Polar Mesospheric Summer Echoes (PMSE) measurements made by the 52 MHz MST radar (ESRAD) located at Esrange (67◦53 N, 21◦06 E) in Northern Sweden during the SPE on 14–16 July 2000
The PMSE observed by Esrange VHF MST Radar (ESRAD) during the solar proton event on 14–16 July 2000 reveal a substantial decrease in the radar echoes above 86 km at the time of the greatest ionospheric disturbances on 15 July

Summary

Introduction

Solar proton events (SPE) are characterized by intensive particle precipitation, mostly protons of energies from 10– 300 MeV (Brasseur and Solomon, 1986). Comparison of the radar signal height profiles with the total electron number density demonstrates their strong altitude dependence (Fig. 4) and reveals a decrease in the radar signal above 86 km during the strong ionospheric disturbances on 15 July. The ion-neutral and electron-neutral collision frequencies have been calculated from the MSISE-90 thermospheric model, which provides estimates of the temperature of the atmosphere and of the number density of several prevalent species. It uses the 10.7 cm solar radio flux and the Ap geomagnetic indices as input. Since radiative relaxation times are of the order of several days (Fig. 10) those temperature changes are expected to be rather stable and last several days after the event

Findings

Discussion

Conclusion