Meteo
RE: rgbrock1 (#3634) and BOAC (#3631)
Quote:
But, again, do these images tell the entire story?
/Unquote
No they do not. But there is verbal explanation that goes with it. While the meteorologist specialist stuff is at places difficult to follow for a layman like me, they did more than just look at those images. From what I understand, there are two sets of data that permit them to say something about the probability of extreme updrafts at the time of AF447.
The first is the vertical temperature profile of the atmosphere as obtained from radiosonde ascents on that day in the area, combined with the temperature of the seawater. Convective air currents derive their energy from the fact that the rising air is warmer and hence lighter than the surrounding air. The greater this temperature difference, the greater the speeds that upward moving airmasses are likely to attain (probably a gross oversimplification on my part). An analysis by Tim Vasques available on the Web compares these temperatures and concludes from them that extreme updrafts are unlikely.
The second is the apparent "overshoot" in the convective cells as can be seen in the satellite infrared images, as discussed in the BEA report. The rising air, after penetrating the tropopause, will reach an altitude at which its temperature is equal to that of the surrounding atmosphere. At that (equilibrium) level it no longer experiences an upward bouyancy but since it is moving at a certain speed it will not suddenly stop there, but will continue upwards, gradually losing momentum, until it stops. At that point it will be cooler than its surroundings, and that temperature can be seen in the satellite IR images looking at cloud tops. The greater the upward speed, the greater that overshoot beyond the equilibrium level, and hence the lower the temperature where it stops. That analysis, done by Meteofrance in the BEA report, also shows that there is no evidence pointing towards extreme updrafts.
I repeat that this is a layman's account, trying to help fellow-laymen understand the meteo lingo. Hope it helps.
regards,
HN39