Radio Occultation Observations as Anchor Observations in Numerical Weather Prediction Models and Associated Reduction of Bias Corrections in Microwave and Infrared Satellite Observations

Abstract

Satellite radiance measurements are used daily at numerical weather prediction (NWP) centers around the world, providing a significant positive impact on weather forecast skill. Owing to the existence of systematic errors, either in the observations, instruments, and/or forward models, which can be larger than the signal, the use of infrared or microwave radiances in data assimilation systems requires significant bias corrections. As most bias-correction schemes do not correct for biases that exist in the model forecasts, the model needs to be grounded by an unbiased observing system. These reference measurements, also known as ''anchor observations,'' prevent a drift of the model to its own climatology and associated biases, thus avoiding a spurious drift of the observation bias corrections. This paper shows that the assimilation of global positioning system (GPS) radio occultation (RO) observations over a 3-month period in an operational NWP system results in smaller, more accurate bias corrections in infrared and microwave observations, resulting in an overall more effective use of satellite radiances and a larger number of radiance observations that pass quality control. A full version of the NCEP data assimilation system is used to evaluate the results on the bias corrections for the High Resolution Infrared Radiation Sounder-3 (HIRS-3) on NOAA-17 and the Advanced Microwave Sounding Unit-A (AMSU-A) on NOAA-15 in an operational environment.

Estimation of the Added Value of the Absolute Calibration of GPS Radio Occultation Data for Numerical Weather Prediction

“…Positive results were confirmed at various meteorological centers (e.g., Healy and Thépaut 2006;Cucurull et al 2007;Aparicio and Deblonde 2008;Rennie 2008). GPSRO probes with high vertical resolution regions that are otherwise poorly sampled, or where most data are of low vertical resolution, most notably over the oceans and polar areas.…”

Impact of Infrared, Microwave, and Radio Occultation Satellite Observations on Operational Numerical Weather Prediction

“…The cold bias in the NCEP stratospheric analyses and forecasts is well known (Yang 2013). The ability of the unbiased RO observations to reduce or eliminate biases in the stratosphere is also well known (Healy et al 2005;Healy and Thépaut 2006;Healy 2008;Poli et al 2010;Cucurull at al. 2014).…”

“…The role of RO observations as ''anchor observations'' in NWP models and the resulting improvements in the bias correction of the satellite radiances has been shown in a number of studies (Healy et al 2005;Healy and Thépaut 2006;Healy 2008;Poli et al 2010;Bauer et al 2014;Cucurull at al. 2014;Bonavita 2014).…”

“…Radio occultation (RO) observations have recently (since late 2006) been shown to have a positive impact on global numerical weather prediction, complementing infrared (IR) and microwave (MW) observations from satellites (Cardinali 2009;Anthes 2011;Bonavita 2014;Healy 2008Healy , 2013Poli et al 2009;Cucurull 2010;Radnóti et al 2010;Rennie 2010;Aparicio and Deblonde 2008;Bauer et al 2014). A radio occultation occurs when a receiver on a low-Earth-orbiting (LEO) satellite tracks a global positioning system (GPS) satellite that is observed to rise or set relative to Earth.…”

On the assimilation of satellite sounder data in cloudy skies in numerical weather prediction models

“…Based on recent studies, contributions from satellite data, especially data from infrared (IR) and microwave (MW) sounders such as Atmospheric Infrared Sounder (AIRS), Infrared Atmospheric Sounding Interferometer (IASI), Crosstrack Infrared Sounder (CrIS), Advanced Microwave Sounding Unit-A (AMSU-A), AMSU-B, Microwave Humidity Sounder (MHS), etc., are becoming the most important observations in operational centers (Le Marshall et al, 2005Marshall et al, , 2006Kelly and Thepaut, 2007;Cardinali, 2009). MW and IR sounders have the most impact on forecast skills in all satellite observations (Garand et al, 2013;Joo et al, 2013;Cucurull et al, 2014). McNally et al (2014) found that the polar-orbiting satellite data play an important role in decreasing the time and location errors of Hurricane Sandy's track forecasts.…”