Polar mesosphere summer echoes during the July 2000 solar protonevent

Abstract

Abstract. The influence of the solar proton event (SPE) • 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 91 mV/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 80-90 km height interval. PMSE almost disappeared above 86 km 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.

The influence of geomagnetic activity on mesospheric summer echoes in middle and polar latitudes

“…But also changes of the temperature in the meso-and lower thermosphere are probable. However, it is not quite clear if the temperature always increases as expected from some model calculations (Roble et al, 1987;Barabash et al, 2004) and observations (von Savingny et al, 2007). Recent model results from Jackmann et al (2007) gave decreasing temperatures in most cases of the investigated events.…”

“…Such lowering of the charged aerosol density would reduce their influence on the reduction of the electron diffusivity and should therefore reduce the PMSE signal. A weakening of the radar signals caused by an increasing ionospheric absorption due to markedly enhanced electron densities can be neglected as demonstrated by model calculations of Barabash et al (2004). Signals of the ESRAD radar in Kiruna, Sweden, whose frequency with 52 MHz is very similar to the frequency of the ALWIN radar, are during strongly enhanced electron densities only slightly reduced by less than 0.5 dB.…”

“…However, results of rocket-born measurements show PMSE also at ratios clearly below 1 down to 0.02 (Blix et al, 2003). Another possible reason for the PMSE decay was proposed by Barabash et al (2004). Strong precipitating high energetic particles fluxes induce strong electric fields which can cause a transport of charged aerosols.…”

“…Such investigations have often been made for single events or relatively small data sets (e.g. Bremer et al, 1995;Rapp et al, 2002;Barabash et al, 2004). Analyses Bremer et al (2000Bremer et al ( , 2001 and Barabash et al (2002) concentrating mainly on the diurnal variation of the correlation between PMSE and geomagnetic activities.…”

Polar mesosphere summer echoes with ESRAD, Kiruna, Sweden: Variations and trends over 1997–2008

“…In contrast, Barabash et al (2002) did not find significant correlation between day-to-day variations in PMSE intensity and CNA, comparing the same time on each day using 1-min resolution data (for the summer of 1997). Barabash et al (2004) made a case study of the strong solar proton event (SPE) on July 15, 2000 and its whole effect on the lower thermosphere, mesosphere and PMSE. They found evidence that enhancement of the ionospheric electric field rather than electron density and neutral temperature might explain the observed disappearance of PMSE during part of the SPE.…”