Stratosphere The stratosphere is the middle layer of the Uranian atmosphere, in which temperature generally increases with altitude from 53 K in the tropopause to between 800 and 850 K at in the thermosphere .  The heating of the stratosphere is caused by the downward heat conduction from the hot thermosphere,   as well as by absorption of solar UV and IR radiation by methane and the complex hydrocarbons formed from methane photolysis .   The methane enters the stratosphere through the cold tropopause, where its mixing ratio relative to molecular hydrogen is about 3 × 10 –5 , three times below saturation.  The mixing ratio decreases to about 10 −7 at an altitude corresponding to the pressure of 0.1 mbar.  Hydrocarbons other than methane are present in a relatively narrow layer between 160 and 320 km in altitude, corresponding to a pressure range of 10 to 0.1 mbar and temperatures of between 100 and 130 K. 
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This note was uploaded on 12/15/2011 for the course AST AST1002 taught by Professor Emilyhoward during the Fall '10 term at Broward College.