MetOp-IASI to SNPP-CRIS: Concurrence of NUCAPS Operational Sounding Products with Quasi-Continuous ECMWF Forecast/Analysis Fields

The Suomi National Polar-orbiting Partnership satellite (SNPP, 1:30 AM/PM orbit) and the European Meteorological Operational polar-orbiting satellites (MetOp-A and MetOp B, 9:30AM/PM orbit) carry aboard the Cross-track Infrared Sounder (CrIS) and the Infrared Atmospheric Sounding Interferometer (IASI) instruments, respectively. These hyperspectral infrared (IR) sounders are accompanied by microwave (MW) sounding instruments aboard each spacecraft to assist in the generation of high-quality geophysical products in scenes with up to 80% cloud cover. The SNPP CrIS instrument is accompanied by the Advanced Technology Microwave Sounder (ATMS) while MetOp's IASI instruments are accompanied by the Advanced Microwave Sounding Unit (AMSU). As part of NOAA Polar Orbiting Satellite Systems (NPOESS) Data Exploitation (NDE), the National Oceanic and Atmospheric Administration (NOAA) operates a unique sounding product system, viz. the NOAA Unique CrIS/ATMS Product System (NUCAPS), that utilizes the same science and algorithm code to produce sounding products from both the SNPP CrIS/ATMS and MetOP IASI/AMSU observations. The algorithm has heritage from the Aqua-Atmospheric Infrared Sounder (AIRS) science team algorithm (AST) version V5 and uses the first guess retrieval as an initial solution to the final IR retrieval module. The first guess retrieval is based on a fast eigen vector cloudy and clear regression solution using European Center for Medium Range Forecasts (ECMWF) analysis fields as the training data set. The final physical retrieval uses an iterated regularized least squares minimization that mirrors the retrieval process in AST. While NUCAPS continues using the eigen vector regression solution as the first guess, the current AST V6 version replaced the eigenvector cloudy and clear regressions first guess with a two-step stochastic cloud-clearing and neural network solution. The geophysical products generated by the retrieval algorithm include many surface parameters, atmospheric vertical temperature and moisture profiles (AVTP and AVMP), ozone, and other trace gases. The Joint Polar Satellite System (JPSS) satellite (JPSS-1) and follow-on satellites will carry infrared and microwave instruments similar to the CrIS/ATMS instruments currently operating on SNPP. NUCAPS is expected to provide continuity of sounding products for the JPSS series of satellites through NDE operations. This paper presents a global evaluation and characterization of NUCAPS SNPP-CrIS and MetOp IASI AVTP and AVMP sounding products using matched correlated data sets generated for the July 29, 2013 focus day. Space and time collocated ECMWF forecast/analysis fields matching SNPP-CrIS (1:30 AM/PM), and MetOP-IASI (9:30 AM/PM orbit) Field of Regards (FORs) were used as the proxy truth to generate global statistical metrics. In addition, global matches of Aqua AIRS (1:30 AM/PM orbit) version V6 and SNPP NUCAPS AVTP and AVMP retrievals were analyzed to assess the impact of the first guess solution on the final physical retrieval and explore possible improvements and optimizations. The ECMWF model data were further utilized to generate quasi-continuous forecast/analysis fields to study the time evolution of AVTP and AVMP fields between the MetOP-A (9:30 AM/PM) and SNPP/Aqua (1:30 PM/AM) satellite orbits. Global bias and Root Mean Squared (RMS) difference statistics generated for the AVTP and AVMP products with reference to ECMWF analysis reveal that NUCAPS closely meets the JPSS Level-1 requirements. Both SNPP NUCAPS and the AIRS-V6 retrieval products were found to agree well with ECMWF analysis fields with AST-V6 showing slightly better performance due to neural network first guess. Evaluation of quasi-continuous ECMWF fields between MetOp-A and SNPP orbit times show a smooth transition of AVTP and AVMP fields and demonstrate that differences between the MetOP and SNPP AVTP and AVMP soundings are due to the time variation of meteorological fields of the atmosphere between these orbit times.