Simulations and observations of cloud contributions to RO refractivity biases
Presenter:
Pawel Hordyniec (1,2)
(1) RMIT University, SPACE Research Centre, Melbourne, Australia, (2) Wroclaw University of Environmental and Life Sciences, Institute of Geodesy and Geoinformatics, Wroclaw, Poland
(3) Bureau of Meteorology, Science and Innovation Group, Melbourne, Australia, (4) National Space Organization, HsinChu, Taiwan
Talk
The upper troposphere and lower stratosphere (UTLS) is recognized as a core region for radio occultation (RO) retrievals in terms of error magnitudes. In contrary, the lowermost troposphere, namely the planetary boundary layer (PBL), often results in systematic errors of refractivity due to ill-conditioned inversions. The quality control based on observed minus background statistics is crucial for the error assessment of RO measurements. However, referencing to background models can be questioned under certain weather conditions. In addition to retrieval errors, simplifications in modeling of background fields imposed by gaseous state of the atmosphere can contribute to refractivity biases. Clouds are amongst factors that induce propagation delays to RO signals. We show that the cloud water is distributed within an extensive altitude range that varies with respect to the latitude as well as between land and water bodies. The most pronounced contributions occur around the altitude of 4 km for the liquid water and at 10 – 12 km for the ice water. The refractivity components are modeled from the corresponding water contents and their impact is converted to RO observables by means of end-to-end simulations. The induced fractional refractivity errors can exceed 0.5% in the UTLS and 2% in the middle troposphere when clouds are modeled as spherically symmetrical structures. The liquid clouds over marine PBL are found to be collocated with super-refractions and negative refractivity errors. Altitudes of critical refractivity gradients agree well with those corresponding to spikes in liquid water profiles. The most significant cloud fractions are expected over Atlantic and Pacific Oceans at Tropical Circles.
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