Jupiter’s atmosphere is the largest in the solar system, consisting of mostly hydrogen and helium, which are the two lightest elements. There are trace amounts of methane, ammonia, hydrogen sulfide, and water as well. Being one of the gas giants, Jupiter has no solid surface aside from its relatively small rocky core, which is surrounded by a deep layer of liquid metallic hydrogen. Hydrogen exists in this phase because of the extreme atmospheric pressure that it is under.
The planet’s Great Red Spot is a massive anticyclonic storm with a diameter that is equivalent to two or three Earths on average (24-40000 km E-W, 12-14000 km N-S). Experimental observations have shown that the Great Red Spot is colder than most of the rest of the planet. Although the inner section of the storm is nearly stagnant, the outer edge has wind speeds of up to 432 km/h (120 m/s).
(image sources: www.astronomy.ohio-state.edu, http://nssdc.gsfc.nasa.gov/photo_gallery/photogallery-jupiter.htmwww.astronomy.ohio-state.edu, http://nssdc.gsfc.nasa.gov/photo_gallery/photogallery-jupiter.htm)