Search the RAMMB website
A publication in ESS details the unexpected finding of false low cloud fields in conventional nighttime cloud masks, which are produced under special circumstances of a cool/uniform lower surface and a warmer/moist lower atmospheric layer. These conditions can happen in regions of tidal mixing, river outflows, coastal upwelling, and radiative cooling over lake bodies, as well as over some land surfaces. This study, which used Day/Night Band moonlight imagery as a definitive statement on the presence/absence of clouds-over-ocean, suggests that some areas are predisposed to the false cloud artifact. Discarding valid clear-sky information in these areas as cloud-contaminated may impart local biases to the sea-surface temperature record, which is compiled at night.
S-NPP VIIRS observations and derived products on 30 July 2018 at 0630 UTC. (a) SST retrievals, (b) the conventional “low cloud at night test” (NLCT; 10.7–3.7 μm BTD), (c) ASCPO Clear Sky Mask (only “Confidently Clear” pixels are used for SST), and (d) the NOAA Enterprise Cloud Mask. Magenta lines encompass the regions of main low-cloud false alarm around Georges Bank/Nantucket Shoals and coastal Gulf of Maine.
Miller S. D., Y.-J. Noh, L. D. Grasso, C. J. Seaman, A. Ignatov, A. K. Heidinger, S.H. Nam, W. E. Line, and B. Petrenko, 2022: A Physical Basis for the Overstatement of Low Clouds at Night by Conventional Satellite Infrared-Based Imaging Radiometer Bi-Spectral Techniques. Earth and Space Science. 9 (2), e2021EA002137, https://doi.org/10.1029/2021EA002137
(POCs S. Miller, CIRA, Steven.Miller@colostate.edu; Y.-J. Noh, L. D. Grasso, C. J. Seaman, A. Ignatov, A. K. Heidinger, S.H. Nam, W. E. Line, and B. Petrenko, Funding: JPSS Program Office)