Accuracy assessment of MERRA-2 temperature and humidity profiles over the tropical ocean using AEROSE observations and ECMWF analysis Bingkun Luo1, Peter J Minnett1, Goshka Szczodrak1, Nicholas R. Nalli2 •Reanalysis model output is extensively used in atmospheric research to complement the satellite and in situ data. NASA's Goddard Earth Sciences Modern-Era Retrospective analysis for Research and Applications v 2 (MERRA-2) assimilates measurements from different sources to minimize bias errors. The model data must be rigorously evaluated to assess their suitability to study a variety of questions. Here, Sea Surface Temperature (SST) and profiles of temperature and humidity through the marine atmosphere from MERRA-2 are compared to independent ship-based measurements of radiosondes, and retrievals from the ship-based Marine-Atmosphere Emitted Radiance Interferometer (M-AERI), and also the analyses fields of the European Center for Medium - Range Weather Forecasting (ECMWF). The ship measurements include those from Aerosol and Ocean Science Expedition (AEROSE) cruises of the NOAA Ship Ronald H. Brown in the tropical North Atlantic Ocean, focusing on the representation of the spatial and temporal variability. The results reveal that temperature and water vapor profiles from the MERRA-2 are in good agreement with the in situ measurements. For part of the cruises, the atmosphere included a mid-level dry layer emanating from North Africa, the Saharan Air Layer (SAL). With respect to difference, MERRA-2 humidity profiles shows a big difference (40%) with RAOBs at high altitude (pressure level < 300 hPa). These results support the use of MERRA-2 fields in a variety of research applications, including those directed at improving the accuracies of satellite-derived SSTskin retrievals. Abstract The MERRA-2 SST agrees well with M-AERI, and it has a mean bias of 0.125 K and have the potential to provide a satisfactory contribution to studies involving SST. The SST difference distribution between them shows there is negative bias near equatorial region, effort is still required to provide better data especially some water vapor-contaminated data. Table: Statistics of errors of MERRA-2 SST vs M-AERI 2. SST Validation MERRA-2 datasets: The NASA MERRA-2 reanalysis data were generated using the Goddard Earth Observing System data assimilation system by NASA's Global Modeling and Assimilation Office Data Assimilation System V5.12.4. Covering the earth observation data from 1980 to present. MERRA-2 analysis data are computed on a latitude– longitude-altitude cubed sphere grid at the same spatial resolution as the 3DVAR algorithm atmospheric model based on the Grid-point Statistical Interpolation. AEROSE: • A series of intensive field campaigns on the NOAA ship Ronald H. Brown in the Atlantic Ocean. • AEROSE data include complementary measurements to study the transport of aerosols from the African continent across the Atlantic Ocean, including: –Microphysical evolution and regional impacts –Regional atmospheric chemistry and marine meteorology AEROSE tracks, color indicates the days since departure. Independent Validation data: •Radiosonde (RAOB): Balloon-based instrument to make direct in situ measurements of air temperature, humidity, and pressure to about 30 km height. • ECMWF: Contains a set of atmospheric variables on a spatial horizontal grid of 0.5ox 0.5 o at 60 vertical levels. The ECMWF analysis is produced daily for 00, 06, 12 and 18 UTC. The four analyses per day are obtained by four- dimensional variational analysis (4DVAR) schemes. • M-AERI: An accurate, self- calibrating, Fourier transform IR spectroradiometer that measures emission spectra from the sea and atmosphere. (Minnett et al. 2001). 1. Data 19th International GHRSST Science Team Meeting 4th-8th June 2018, EUMETSAT, Darmstadt, Germany Relative Humidity and temperature layer properties of RAOB, MERRA-2 and ECMWF during 2015 AEROSE cruise, color indicates RH and temperat