1. Scientific challenges in GPS RO assimilation for weather forecasting
Lidia Cucurull
COSMIC retreat, October 2011

2. Principle: the ‘rawer’ the product to assimilate the better
Use of bending angles instead of refractivities
No super-refraction negative bias in lower troposphere
Less correlated errors within a profile
No use of climatology
NCEP’s Bending angle FO is under current pre-operational testing for Q3FY12 implementation
The updated code in bending angle uses compressibility factors, updated refractivity coefficients, and extends top to 50 km

3. Challenges in the lower troposphere
Assimilation of RO under super-refraction conditions - still a problem with bending angle?
Moisture – why don’t we get more improvement?
quality control?
Observation/model error characterization?
Model limitations?
Verification?
Forward operator not accurate enough?
Challenges in the stratosphere
Ionospheric correction noise - use of a non-linear quality control?
Stratospheric water vapor - better understanding of interaction with radiances

4. Use of more accurate forward operators
Account for horizontal gradients of refractivity
Explore cost/benefits of a 2D forward operator versus local operator, and versus full ray-tracing