Abstract

Radio occultation (RO) is widely considered to be an observation technique that is particularly well suited for establishing a long-term stable global climate record of density, temperature and bending angle profiles in the 8-30 km height range of the atmosphere. To measure profiles in this heigh... Show moreRadio occultation (RO) is widely considered to be an observation technique that is particularly well suited for establishing a long-term stable global climate record of density, temperature and bending angle profiles in the 8-30 km height range of the atmosphere. To measure profiles in this height range the ionospheric effect on the RO signals must be eliminated. This ionospheric correction is not perfect and is the most challenging noise source affecting GPS radio occultation temperature profiles in the upper stratosphere. The ionosphere introduces random noise on individual temperature profiles that can affect weather forecasting applications. More serious for climate monitoring are systematic bending angle and resulting temperature biases that change with the solar cycle. We have found a strong correlation between these bending angle biases and F10.7 solar flux values. We have also found a diurnal signal which shows stronger bending angle biases during the day than at night. While the ionosphere is expected to be the main source of these diurnal effects, additional neutral atmospheric influence due to tides cannot be ruled out and needs further investigation. With different GNSS signals and improving receiver technology ionospheric correction in RO processing will evolve in the future. We will also investigate if tracking of the stronger L2C GPS signal could introduce a bias between past and future GNSS observations. This presentation will discuss ways to quantify and limit the ionospheric effect on the RO climate record. Show less