optically effective atmosphere

That portion of the atmosphere lying below the altitude (30-36 miles or 50-60 kilometers) from which scattered light at twilight still reaches the observer with sufficient intensity to be discerned. Also known as effective atmosphere.

Related terms:

• effective atmosphere
• effective precipitation
• upper-atmosphere dynamics
• effective rainfall
• effective pressure
• effective radiation
• effective snowmelt
• effective stress
• effective terrestrial radiation
• free atmosphere