Lets Twist Again...Added : Friday at 13:05 Most of our working days, meteorologists use two dimensional modelling. After all, when we have forecast charts like this :-
We can see the geographic location and how heavy the model expects any rainfall to be. But for convection, we need to use three dimensions to get a decent idea as to what is going on in the atmosphere. Granted, the model already does this and can then calculate things like the K Index etc which we use to ascertain the risk of thunderstorms becoming supercellular.
To look at the atmosphere in a 3d way, you'll be surprised to know that we don't use 3d glasses or anything like that, but instead we look at charts like SKEW-T :-
This enables us to look at a cross section of the atmosphere at any given location and look how buoyant the air is and what happens to it as it rises.
The profile above for East Anglia later this afternoon shows a moist and unstable lower atmosphere, you can also see how the yellow line bends quicker than the red line which shows low level instability and that any air near the surface will have little reason not to start rising.
We then look at the winds on the right hand side of the image. You can see how they twist as you go up through the atmosphere, this is called vorticity and also become much stronger, this is wind shear. The two combined we refer to as Helicity (a cork screw effect).
In a nutshell, it tells us that the air is unstable and that any parcel of warmed air near the surface will rise to around 35,000ft and always be warmer than its surroundings, not just that, but the air will drift off to the North thanks to the stronger Southerly upper level winds.
Thankfully, the numerical models already convert this for us, so the CAPE value of 2000J/kg shows an unstable atmosphere, the CIN or Convective Inhibition is negative and you can see on the chart that there is little stopping the air rising near the surface.
Of course, the forecast profile could be wrong and surface temperatures don't reach what the model suggested, but if it's right, then the model equates this to the development of thunderstorms and heavy rain which it does here :-
But, when we want to look at the risk of hail, lightning, supercell structures, storm lifespan and risk of tornadoes, then we need to look at the atmosphere in a three dimensional way.
So, 3D is the future, but not with the silly glasses...
METEOROLOGIST : MARSH |