The thermal atmospheric region of the atmosphere between the troposphere and the mesosphere. The lower boundary of the stratospheric region is marked by the tropopause and begins at approximately 13 km; however, this altitude of the troposphere depends on latitude. The upper limit of the stratosphere is marked by the stratopause at approximately 50 km. The stratosphere is characterised by relatively stable temperatures (between -80°C and -50°C) in the lower regions, and begins warming near 20 km, reaching its maximum temperature of approximately 0°C at the stratopause. Stratospheric chemistry is of particular interest to scientists because ozone, the principal substance that shields Earth from incoming solar ultraviolet radiation, is found in the stratosphere. It should also be noted that wind currents in the stratosphere are primarily horizontal in nature.