[1] Analysis of global meteorological assimilations between midJuly and late-August 2000 shows strong 5-day planetary waves in the middle atmosphere. Observations of temperature, zonal wind, noctilucent clouds and polar mesosphere summer echoes (PMSE) near Kiruna, Sweden, all at heights between 80 and 95 km, show variations correlating with the passage of the 5-day waves. Temperature variations correlated with the 5-day wave reach 15 K peak-to-peak and correspond to modulation of PMSE occurrence by up to 50%. These observations appear to be the first experimental evidence of amplification of 5-day waves at the summer mesosphere which was predicted theoretically in 1976. A close linear relation is found between mean daily temperature and mean daily occurrence of PMSE. This can be explained if temperature is the primary factor controlling PMSE occurrence and time and height variations within each day between 80 and 90 km altitude reach 30 -50 K. INDEX TERMS: 0305 Atmospheric

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 F 10.7 have been incorporated into the model. Influence of minor neutral species (NO, H 2 O, O, O 3 ) 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.

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.

No abstract

Abstract.The correlation between variations in Polar Mesosphere Summer Echoes (PMSE) and variations in energetic particle precipitation is examined. PMSE were observed by the Esrange VHF MST Radar (ESRAD) at 67 • 53 N, 21 • 06 E. The 30 MHz riometer in Abisko (68 • 24 N, 18 • 54 E) registered radio wave absorption caused by ionization changes in response to energetic particle precipitation. The relationship between the linear PMSE intensity and the square of absorption has been estimated using the Pearson linear correlation and the Spearman rank correlation. The mean diurnal variation of the square of absorption and the linear PMSE intensity are highly correlated. However, their day-to-day variations show significant correlation only during the late evening hours. The correlation in late evening does not exceed 0.6. This indicates that varying ionization cannot be considered as a primary source of varying PMSE, and the high correlation found when mean diurnal variations are compared is likely a by-product of daily variations caused by other factors.