Assessment of Extreme Diurnal Warming in Operational Geosynchronous Satellite Sea Surface Temperature Products

Gary A Wick,Sandra L Castro

doi:10.3390/rs12223771

Abstract

We evaluate the reliability and basic characteristics of observations of extreme DW events from current operational geostationary satellite sea surface temperature (SST) products through examination of three months of diurnal warming (DW) estimates derived by different methodologies from the Spinning Enhanced Visible and Infrared Imager on Meteosat-11, Advanced Himawari Imager on Himawari-8, and Advanced Baseline Imager on the Geostationary Operational Environmental Satellite (GOES)-16. This work primarily focuses on the following research questions: (1) Can these operational SST products accurately characterize extreme DW events? (2) What are the amplitudes and frequencies of these events? To answer these, we compute distributions of DW and DW exceedance and compare them amongst the different methods and geostationary sensors. Examination of the DW estimates demonstrates several challenges in accurately deriving distributions of the DW amplitude, particularly associated with estimating the “foundation” temperature and uncertainties in cloud screening. Overall, the results suggest that current geostationary sensors can reliably assess extreme DW, but the estimates are sensitive to the computational methods applied. We thus suggest careful processing/screening of the SST retrievals. We find a value of 3 K, corresponding to the 99th percentile, provides a potential practical threshold for extreme warming, but events of at least 6 K were reliably observed. Warming in excess of 6 K occurred somewhere an average of 47% of the time, and its probability at a given location was of O(10−6).

Highlights

The daily cycle of solar radiation leads to periodic heating of the near-surface layer of the ocean
The results consistently suggest the occurrence of large diurnal warming (DW) events in excess of 6 K but demonstrate uncertainty as to the frequency of these events as well as the absolute peak values depending on the method utilized
While there seems to be little doubt that such large DW events occur and are detectable, the results are sensitive to the method employed, and some level of screening/filtering is required in addition to the operational sea surface temperature (SST) processing

Summary

Introduction

The daily cycle of solar radiation leads to periodic heating of the near-surface layer of the ocean. Turbulent mixing is reduced and a warm layer and diurnal thermocline can form near the ocean surface during the day. While the amplitude of diurnal warming is relatively small on average (O(0.5 K), e.g., [1,2]), under conditions of very low wind speed and sufficient insolation, the warming at the surface sensed by satellites can be highly significant (e.g., [3,4]). Satellite observations from multiple sensors have observed extreme warming events up to 7 K in magnitude at the surface, and it has been suggested that events exceeding 5 K are not infrequent [3,4]

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Discussion

Conclusion