what drives the high-speed winds in venus's atmosphere
Atmosphere of Venus All winds on Venus are ultimately driven by convection.[4] Hot air rises in the equatorial zone, where solar heating is concentrated, and flows to the poles. Such an almost-planetwide overturning of the troposphere is called Hadley circulation.[4] However, the meridional air motions are much slower than zonal winds. The poleward limit of the planet wide Hadley cell on Venus is near ±60° latitudes.[4] Here air starts to descend and returns to the equator below the clouds. This interpretation is supported by the distribution of the carbon monoxide, which is also concentrated in the vicinity of ±60° latitudes.[4] Poleward of the Hadley cell a different pattern of circulation is observed. In the latitude range 60°–70° cold polar collars exist.[4][7] They are characterised by temperatures about 30–40 K lower than in the upper troposphere at nearby latitudes.[7] The lower temperature is probably caused by the upwelling of the air in them and by the resulting adiabatic cooling.[7] Such an interpretation is supported by the denser and higher clouds in the collars. The clouds lie at 70–72 km altitude in the collars—about 5 km higher than at the poles and low latitudes.[4] A connection may exist between the cold collars and high speed midlatitude jets in which winds blow as fast as 140 m/s. Such jets are a natural consequence of the Hadley–type circulation and should exist on Venus between 55–60° latitude.[24]