The nighttime imagery is typically compared to a climatology. In this example, we say that any pixel that differs from climatology by more than 2 degrees C is bad data. This worked well for the cloud in the eastern portion of the above images, but it also removed the upwelling front, which is absolutely necessary to assimilate into the models if we want to have an accurate forecast. This is because the upwelling fronts change temperature so fast, that climatologies are not comparable to the real data.

SO........ we typically do not use night data. But now we must consider the surface skin effect, which is the warming of the skin surface of the ocean by afternoon sun (figure 6). .