No, they're not. Otherwise they would always be seen. Troposphere temp is fairly stable...
According to the ICAO . . .
The International Standard Atmosphere at mean sea level is a temperature of +15ºC (59ºF) at a Pressure of 1013.2mb (29.92 InHg) decreasing by 1.98ºC (35.564ºF) per 1000 feet of increased altitude.
However, at the tropopause, the temperature remains constant at -56.5ºC (-69.7ºF). The height of the tropopause varies all the time but it is USUALLY around the 36,000 ft mark - depending on time of year and the latitude (higher near the equator than the poles).
No, they're not. Otherwise they would always be seen.
According to the ICAO . . .
The International Standard Atmosphere at mean sea level is a temperature of +15ºC (59ºF) at a Pressure of 1013.2mb (29.92 InHg) decreasing by 1.98ºC (35.564ºF) per 1000 feet of increased altitude.
However, at the tropopause, the temperature remains constant at -56.5ºC (-69.7ºF). The height of the tropopause varies all the time but it is USUALLY around the 36,000 ft mark - depending on time of year and the latitude (higher near the equator than the poles).
No, they're not. Otherwise they would always be seen.