Definition
The assumed rate at which air temperature decreases with an increase in altitude in the International Standard Atmosphere: approximately 2 degrees Celsius (3.5 degrees Fahrenheit) per 1,000 feet of altitude gained, up to the tropopause.
Plain English
On a standard day, the air gets about 2 degrees Celsius colder for every 1,000 feet you climb. It is the average temperature drop with height that aviation calculations are based on.
Context Anchor
Seen in weather, atmosphere, aircraft performance, and instrument flying discussions where temperature change with altitude matters.
Derivation
Lapse comes from the Latin lapsus, meaning a slip or fall. Here it describes how temperature 'falls' as altitude rises. 'Standard' refers to the agreed-upon reference atmosphere used worldwide for aircraft performance and instrument calibration.
Why Pilots Care
Accurate knowledge of the standard lapse rate lets pilots estimate temperature at altitude for density altitude calculations, engine performance, and true airspeed corrections.
Grounding Statement
If the temperature at the surface is 15 °C, the standard lapse rate would estimate about 5 °C at 5,000 feet.
Intuition Check
Do not read “standard” as “what always happens.” It means a reference value used for comparison. Do not read “lapse” as forgetting something. Here it means temperature decreasing as altitude increases.
Example Sentence 1
Climbing from sea level to 10,000 feet on a standard day, the outside air temperature should drop about 20 degrees Celsius based on the standard lapse rate.
Example Sentence 2
Before departure the instructor reminded the student to apply the standard lapse rate when estimating density altitude for takeoff performance.