Abstract
Long time series of accurate Sea Surface Temperatures (SSTs) are needed to resolve subtle signals that may be indicative of a changing climate. Motivated by the stringent requirements on SST accuracy required for Climate Data Records (CDR) we quantify sampling errors in satellite SSTs. Infrared sensors, including the Moderate Resolution Imaging Spectroradiometer (MODIS), have sampling errors caused by incomplete coverage primarily due to clouds and inter-swath gaps (gaps between successive swaths/orbits). Unlike retrieval errors, the sampling errors are introduced when calculating mean values and in generating gap-free SST fields. We generate MODIS-sampled SST fields by superimposing MODIS cloud masks on top of the Multi-scale Ultrahigh Resolution (MUR) SST field for the same day. Based on the MODIS-sampled fields, we calculate sampling errors at different temporal and spatial resolutions to examine the impacts at different scales. Our results indicate that sampling errors are significant, more so in the high latitudes, especially the Arctic. The 30°N–30°S zonal band is found to have the smallest errors; a notable exception is the persistent negative errors found in the Tropical Instability Wave area, where the mesoscale ocean–atmosphere interaction leads to a more frequently satellite sampling above the cold sections of the wave area. The global mean sampling error is generally positive and increases approximately exponentially with missing data fraction at a fixed averaging interval, while error variability is mainly controlled by SST variability. Areas with persistent cloud cover have large sampling errors in temporally averaged SSTs. We conclude that the sampling error can be an important or even dominant component of the error budget of mean and gap-free SST fields. Climate data generation and interpretation of satellite-derived SST CDRs and their application must be conducted with due regard to the sampling error.
•Sampling errors in MODIS Terra SSTs are quantified.•Large errors are found in the high latitudes.•Small errors are within ±30° latitude, except in the TIW region.•Atmosphere–ocean interactions cause dynamically distributed sampling errors.•MODIS cloud mask for SSTs has imperfections around Antarctica.
