Towards Improved Quality Control of In Situ Sea Surface Temperatures from Drifting and Moored Buoys in the NOAA iQuam System  
[PERSON]  
1 STAR, NOAA Center For Weather and Climate Prediction (NCWCP), College Park, MD 20740, USA;  
[EMAIL_ADDRESS] (V.P. ); [EMAIL_ADDRESS] (O.J. )12 Global Science and Technology, Inc., Greenbelt, MD 2070, USA  
[PERSON]  
1 STAR, NOAA Center For Weather and Climate Prediction (NCWCP), College Park, MD 20740, USA;  
[EMAIL_ADDRESS] (V.P. ); [EMAIL_ADDRESS] (O.J. )12 Global Science and Technology, Inc., Greenbelt, MD 2070, USA  
[PERSON]  
1 STAR, NOAA Center For Weather and Climate Prediction (NCWCP), College Park, MD 20740, USA;  
[EMAIL_ADDRESS] (V.P. ); [EMAIL_ADDRESS] (O.J. )12 Global Science and Technology, Inc., Greenbelt, MD 2070, USA  
[PERSON]  
1 STAR, NOAA Center For Weather and Climate Prediction (NCWCP), College Park, MD 20740, USA;  
[EMAIL_ADDRESS] (V.P. ); [EMAIL_ADDRESS] (O.J. )12 Global Science and Technology, Inc., Greenbelt, MD 2070, USA  
Footnote 1: [[https://www.mdpi.com/journal/applsci](https://www.mdpi.com/journal/applsci)]([https://www.mdpi.com/journal/applsci](https://www.mdpi.com/journal/applsci))  
Footnote 2: [[https://www.mdpi.com/journals/pdf/12/1](https://www.mdpi.com/journals/pdf/12/1)]([https://www.mdpi.com/journals/pdf/12/1](https://www.mdpi.com/journals/pdf/12/1))  
All current L4 analyses are daily gap-free products. They provide continuous coverage of the world ocean with a'reference SST', \(T_{L4}\), which allows examining deviations \(\Delta T_{L4}=T_{IS}-T_{L4}\) at any location. The Reference Check (RC) is a critical part of the current \(i\)Quam QC, which identifies most low-quality \(T_{IS}\)'s [2; 9]. The current RC in the latest \(i\)Quam v2.10 employs a Bayesian approach [10] to transform the \(\Delta T_{L4}\) into posterior probability of 'gross error' (PCE), under certain assumptions on prior distributions of \(\Delta T_{L4}\) and noise in \(T_{IS}\). The quality level (QL) is downgraded for a specific \(T_{IS}\) if its PGE exceeds the predefined threshold [2]. It was recognized, however, that the efficiency of the current RC is limited due to intrinsic features of the available L4 SST analyses [5; 9], which often represent the so-called 'foundation' SST (i.e., corresponding to depths of \(\sim\)10 m, at which the diurnal warming cycle is absent [11]). Such analyses do not capture the diurnal warming at the depths of drifting (\(\sim\)0.2 m) and moored (\(\sim\)1 m) buoys, which causes overscreening in the presence of significant diurnal signal (DS) in \(T_{IS}\). Intensive diurnal SST variations were observed under conditions of prolonged insolation and suppressed mixing in the ocean upper layer (typically associated with clear skies and low winds) in both satellite [12; 13; 14; 15] and in situ [15; 16; 17] SSTs in various oceanic regions, from the Tropics all the way to high latitudes. Furthermore, the gridded daily L4 analyses often fail to track fine-scale spatial and rapid temporal SST variations [9], also causing overscreening, mainly in the dynamic oceanic areas, such as the Gulf Stream, Kuroshio and Agulhas currents, upwellings, downwellings, etc. In this study, we explore the new Diurnal Reference Check (DRC), which largely mitigates the overscreening problems related to both diurnal warming in \(T_{IS}\) and inaccurate \(T_{L4}\) in the dynamic areas. We also explore using the satellite SSTs, \(T_{SAT}\), as an additional source of reference information. The advantage of satellite SSTs is that they are timelier and often more accurate than \(T_{L4}\). However, the comparisons with \(T_{SAT}\) are only possible for \(T_{IS}\) measured at times and locations of satellite overpasses and under clear-sky conditions (for \(T_{SAT}\) obtained from IR radiometer measurements). Ideally, the QC should take advantage of comparisons with both \(T_{L4}\) and \(T_{SAT}\). In [3], the \(i\)Quam data were compared with satellite SSTs from NOAA-17 AVHRR and ENVISAT AATSR. However, the current \(i\)Quam QC does not use satellite SSTs routinely.