What does "QNH" stand for in aviation meteorology?

QNH stands for air pressure adjusted to sea level. This measurement is crucial in aviation as it provides pilots with a reference for altimeter settings. When a pilot sets their altimeter to the QNH value, it ensures that the aircraft's altitude reading corresponds to the true height above sea level. This is particularly important for maintaining safe vertical separation between aircraft and for accurate navigation during flight, especially during approach and landing phases.

Understanding QNH is vital for pilots to ensure they are operating at the correct altitude, as variations in atmospheric pressure can affect altimeter readings. The other options do not pertain to QNH: temperature adjustments involve different altitude-specific data, while wind speed and direction are characterized by meteorological terms like "wind shear," and visibility and cloud cover data relate to weather reporting rather than precise altitude altitude measurements. Thus, the definition and usage of QNH is essential for safe and effective flight operations.