According to latitude and time of year
Again you're revealing your ignorance or are purposefully misleading the facts by leaving out important information.
Some of the planes that leave chemtrails in the troposphere are conducting tests using new kinds of smart chaff.
Some of the planes that leave chemtrails in the troposphere are conducting tests for shortwave climate engineering. Cloud modification for increasing cloud reflectivity by adding extra aerosol pollutants.
They are both related to SAG because the data collected in those field tests are used in making climate models.
The top of the stratosphere occurs at 50 km (31 miles) altitude. The boundary between the stratosphere and the mesosphere above is called the stratopause. The altitude of the bottom of the stratosphere varies with latitude and with the seasons, occurring between about 8 and 16 km (5 and 10 miles, or 26,000 to 53,000 feet). The bottom of the stratosphere is around 16 km (10 miles or 53,000 feet) above Earth's surface near the equator, around 10 km (6 miles) at mid-latitudes, and around 8 km (5 miles) near the poles. It is slightly lower in winter at mid- and high-latitudes, and slightly higher in the summer. The boundary between the stratosphere and the troposphere below is called the tropopause.
Aerosols injected into the Troposphere and Tropopause can be lifted by air currents into the Stratosphere.
Some of the Nanotech aerosols are being designed for that purpose. We've covered this before.
edit on 20-4-2011 by MathiasAndrew because: edit