<P> High - altitude clouds on Neptune have been observed casting shadows on the opaque cloud deck below . There are also high - altitude cloud bands that wrap around the planet at constant latitude . These circumferential bands have widths of 50--150 km and lie about 50--110 km above the cloud deck . These altitudes are in the layer where weather occurs, the troposphere . Weather does not occur in the higher stratosphere or thermosphere . Unlike Uranus, Neptune's composition has a higher volume of ocean, whereas Uranus has a smaller mantle . </P> <P> Neptune's spectra suggest that its lower stratosphere is hazy due to condensation of products of ultraviolet photolysis of methane, such as ethane and ethyne . The stratosphere is also home to trace amounts of carbon monoxide and hydrogen cyanide . The stratosphere of Neptune is warmer than that of Uranus due to the elevated concentration of hydrocarbons . </P> <P> For reasons that remain obscure, the planet's thermosphere is at an anomalously high temperature of about 750 K . The planet is too far from the Sun for this heat to be generated by ultraviolet radiation . One candidate for a heating mechanism is atmospheric interaction with ions in the planet's magnetic field . Other candidates are gravity waves from the interior that dissipate in the atmosphere . The thermosphere contains traces of carbon dioxide and water, which may have been deposited from external sources such as meteorites and dust . </P> <P> Neptune resembles Uranus in its magnetosphere, with a magnetic field strongly tilted relative to its rotational axis at 47 ° and offset at least 0.55 radii, or about 13,500 km from the planet's physical centre . Before Voyager 2's arrival at Neptune, it was hypothesised that Uranus's tilted magnetosphere was the result of its sideways rotation . In comparing the magnetic fields of the two planets, scientists now think the extreme orientation may be characteristic of flows in the planets' interiors . This field may be generated by convective fluid motions in a thin spherical shell of electrically conducting liquids (probably a combination of ammonia, methane and water) resulting in a dynamo action . </P>

Which is a unique characteristic of neptune’s atmosphere