On the signature of the quasi-3-day wave in the thermosphere during the January 2010 URSI World Day Campaign

Ultra-fast Kelvin waves with periods of 3-5 days are important in the coupling of the lower atmosphere to the thermosphere and ionosphere. Here we focus on the observations and effects of a 3-day wave during January 2010. As this time period coincides with a stratospheric warming event, a coordinated set of observations with incoherent scatter radars are available. While there is no evidence that the occurrence of this 3-day wave is connected with this event, these observations offer an unprecedented glimpse of the thermospheric conditions during this period, including the first-ever detection of a 3-day wave with an incoherent scatter radar. Using a combination of ground-and space-based observations, we identify an eastward moving zonal wave number-one 3-day equatorial wave that is comprised of a Kelvin wave at the lowest latitudes and a Rossby-gravity wave at higher latitudes. In the equatorial region, the vertical wavelength is similar to 40 km and the wave peaks in amplitude around 95-100 km altitude. The wave observed here is only seen to propagate to around 105 km altitude. Evidence of an interaction between this wave and the diurnal tide is seen between 82-88 km. The resultant 3-day periodicity in the diurnal tide is seen to propagate up to altitudes of similar to 150 km. This could have a significant impact on the ionosphere via modulation of the E-region dynamo, thus carrying the 3-day periodicity to higher altitudes.