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Temperature measurements from the ALOMAR Weber Na lidar together with cosmicradio noise absorption measurements from IRIS and particle measurements fromNOAA 15, 16 and 17 are used to study effects of geomagnetic activity on thepolar winter upper-mesospheric temperature. On 21–22 January 2005 we have 14 hof continuous temperature measurement with the Na lidar coincidingwith strong geomagnetic activity in the declining phase of one of thehardest and most energetic Solar Proton Event (SPE) of solar cycle 23.According to measurements by the imaging riometer IRIS in northern Finland,the temperature measurements coincide with two periods of increased cosmicradio noise absorption. Particle measurements from the three satellites,NOAA 15, 16 and 17 that pass through and near our region of interest confirmthat the absorption events are probably due to particle precipitation andnot due to changes in e.g. the electron recombination coefficient.  The measured temperature variation at 85 and 90 km is dominated by a 7.6-hwave with downward phase propagation and a vertical wavelength ofapproximately 10 km. Assuming that the wave is due to a lower altitudesource independent of the particle precipitation, we do not find anytemperature modification that seems to be related to the absorption events.The average temperature is larger than expected above 90 km based on MSISand the monthly mean from falling spheres, which could be due to particleprecipitation and Joule heating prior to our measurement period. There isalso a possibility that the identified wave phenomenon is an effect of thegeomagnetic activity itself. Earlier studies have reported of similarwavelike structures in wind observations made by the EISCAT VHF radar duringSPEs, and found it conceivable that the wave could be excited by the effectof energetic particles precipitating into the mesosphere

Upper-mesospheric temperatures measured during intense substorms in the declining phase of the January 2005 solar proton events