What does ACSL stand for in a METAR report?

In the context of a METAR report, the abbreviation ACSL actually stands for "Automated Cloud Sensor Log." METAR reports are aviation routine weather reports that provide critical information about current weather conditions for pilots and dispatchers, and they may include observations of cloud types and altitudes. Understanding the specific terms used in these reports is essential for interpreting weather conditions accurately.

The choice indicating "Automated Cloud Sensor Log" is correct because it refers to a system that provides quantitative cloud observations, which can be key in understanding weather patterns and potential flying conditions. This sensor log is especially relevant in the context of automated weather observing systems that streamline and enhance the reliability of weather reporting.

The other options, while they contain aviation-related terminology, do not reflect existing terminology or definitions used in METAR reports. Altocumulus clouds, airborne layers, and altitude change signaling are not standardized references or terms recognized in METAR reporting standards.