[1] GPS radio occultation measurements from CHAMP, GRACE-A and FORMOSAT-3/COSMIC are used to derive global information on small-scale ionospheric irregularities such as sporadic E layers between January 2002 and December 2007. The investigations are based on the analysis of amplitude variations of the GPS radio occultation signals. The global distribution of ionospheric irregularities shows strong seasonal variations with highest occurrence rates during summer in the middle latitudes. The long-term data set of CHAMP allows for first climatological studies, while the data coverage increases significantly with the combination of CHAMP, GRACE and FORMOSAT-3/ COSMIC measurements. This allows for global maps of sporadic E occurrence rates of very high spatial resolution where the influence of the Earth's magnetic field becomes visible in global sporadic E maps for the first time.

We present a study of horizontal winds in the mesosphere and lower thermosphere (MLT) during the boreal winters of 2009-2010 and 2012-2013 produced with a new high-altitude numerical weather prediction (NWP) system. This system is based on a modified version of the Navy Global Environmental Model (NAVGEM) with an extended vertical domain up to ∼116 km altitude coupled with a hybrid four-dimensional variational (4DVAR) data assimilation system that assimilates both standard operational meteorological observations in the troposphere and satellite-based observations of temperature, ozone and water vapor in the stratosphere and mesosphere.

Abstract. GPS (Global Positioning System) Radio occultation (RO) measurements from CHAMP, GRACE and FORMOSAT-3/COSMIC satellites at Northern Hemisphere midlatitides (50 • -55 • N) are analysed to obtain the diurnal variation of sporadic E layer occurrence frequency in 2006 and 2007. Interconnections with zonal wind shears measured by meteor radar at Collm (51.3 • N, 13 • E), Germany, are investigated. According to theory, maximum E s occurrence is expected when the zonal wind shear, which is mainly produced by the semidiurnal tide in midlatitudes, is negative. This is confirmed by the present measurements and analysis.

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