Quality Control of Temperature and Humidity Profile Retrievals from Ground-based Microwave Radiometer

Ground-based microwave radiometer profiler (MWR) can continuously retrieve thermodynamic profiles of the atmosphere on a minute time scale. These profiles are important supplements to radiosonde observations. Since the presence of liquid water on the profiling radiometer, radio frequency interference and other events can cause errors, quality control procedures that can detect data-quality problems are of critical importance. QC procedures are proposed for ground-based MWR-retrieved atmospheric profiles of temperature and humidity using 10-year radiosonde soundings (January 2004 to December 2014) at Baoshan Station in Shanghai and observations from MP-3000A MWR (January 2012 to May 2014) at Shanghai Expo Station. QC procedures include three types of checks:Climatological test, time consistency test, and vertical consistency test. Climatological check aims to verify if the values of instantaneous data are within climatology range limits. Thresholds are set based on the seasonally varying statistics of 10-year radiosonde soundings. The time consistency check focus on the change rate of instantaneous data. If the difference between the current instantaneous value with the previous one exceeds a specific limit, the current value will be flagged as doubtful. The test is applied level by level, and the profile with suspected data at more than one level is flagged as doubtful. Vertical consistency checks operate on dT_h and contain two tests: A test for the plausible value check of dT_hand a test for the standard deviation of dT_h (σ (dT_h)). dT_h (unti:℃· (100 m)^-1) is defined as the ratio of temperature difference to height difference at consecutive levels. The plausible value check of dT_h is proposed to verify if there are spikes in a profile. The test for (σ (dT_h)) is used to sort profiles with excessive level-to-level fluctuations throughout a sounding. Results show that QC methods can effectively identify various suspected observations, such as climatological outliers, temporal inconsistency and excessive vertical fluctuations in profiles. The frequency of suspected temperature and humidity profiles detected in rainy days is much higher than that in other weather conditions. The accuracy of MWR retrieved temperature and vapor density profiles is improved after applying these QC procedures. Correlation coefficients of both temperature and humidity observations between the MWR and radiosonde increase and corresponding root mean square error (RMSE) decrease after QC, especially those in rainy days. QC procedures for MWR-retrieved thermodynamic profiles are also proposed, through which various suspected profiles can be flagged. The accuracy of MWR retrievals is improved significantly after applying QC procedures.