This image shows the Nowcasting Satellite Application Facility (NWCSAF) Cloud Liquid Water Path (LWP) product for 2020-01-08T12:00:00Z:

Cloud Liquid Water Path from NWCSAF
Cloud LWP from NWCSAF. Source: NWCSAF.

The Algorithm Theoretical Baseline Document (ATBD; PDF, 5.9 MB) divides the full disc into the illumination regimes night, twilight, and daytime by their solar elevation, defining daylight as a solar elevation of larger than 10° (ATBD, Table 3 on Page 14). In the same document, § describes products only calculated in daytime conditions, including the LWP pictured above. But in the image, the retrieval appears to only include elevation angles larger than around 20° (at noon UTC, near the prime meridian, it reaches about 48°N).

Why do the data appear not to extend to solar elevation angles down to 10° such as documented, but rather truncate at around 20°?

  • 1
    $\begingroup$ I have asked this question to the NWCSAF helpdesk (and meanwhile found the relevant configuration/input files in the source code configuration). $\endgroup$
    – gerrit
    Jan 10, 2020 at 13:49


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