BotB

As stated before: I love a challenge T8191…

I just hope we don't put off anyone with descriptions of technical terms...so for the advanced class today:

Lapse rates: as you point out there are two…a dry and a saturated adiabatic lapse rate.. so what are they and why are they of interest?

The adiabatic lapse rates (besides being a brilliant term to use in the pub)…is a way to follow the path any parcel of air would take as it rises in the atmosphere and follow how the physics would apply to that parcel of air.

What? I hear you say…

When you lift a parcel of air up in the atmosphere…it needs to be warmer than the surrounding air or it would not continue to rise @:-) …

So, that particular parcel of air has a known temperature (when it started out), pressure (where we lifted it from) and dew point (moisture content of that parcel of air)….

When we lift this parcel of air (which is warmer than the surrounding air as mentioned) it rises…and because the pressure decreases as it rises the parcel expands…this requires energy…so we use up the energy in the parcel of air and this causes the temperature in the parcel to drop…but the temperature is still higher than the dew point (which remains constant as the amount of moisture in the parcel is still the same and the temperature has not dropped to that dew point level so the air is not saturated yet) so the rate that the parcel rises at is known as the 'dry' adiabatic lapse rate…or according to ICAO we lose about 9.8 degrees C / 1000 meters of ascent in a nice straight forward manner

Obviously, if the air in the parcel is still warmer than the surrounding air, it will continue to rise…once the temperature drops to the dew point, the air becomes saturated…this level where the air becomes saturated is called the convective condensation level (or CCL) and the rate that the parcel then continues to rise is different as the air is saturated and the energy needed to expand and cool now creates heat as well which warms up that parcel a bit at the same time it is cooling so it cools slower as it ascends further…so the rate of temperature lose with height is not as much as when it was dry…this is the saturated adiabatic lapse rate….

We use them to find out where cloud could develop and how thick that convective type cloud could be and what layers of cloud there could be…

This is all a fancy way of knowing how an air parcel will rise in the atmosphere…if it is saturated it rises and loses temperature at a different rate (slower) than when it is not saturated…

The lines of a tephigram show the rates of rise for any given starting temperature / dew point and pressure.

What is a tephigram?

http://en.wikipedia.org/wiki/Tephigram

A great bunch of lines on paper to help decide what is happening in the world according to the laws of physics!

A tephigram is a snap shot of the atmosphere looked at in cross section. (so you see the atmosphere from the ground up to the tropopause in a vertical line and can see where cloud will develop, what the winds are like, if there will be thunderstorms…

This is one of THE most useful tools a meteorologist has to understand what the atmosphere is doing right now…and then looking upstream to understand what is coming towards that location.

I'll have a go at explaining the relevant bits another time but these pages should keep you busy for some time T8191…

Tephigram plots for quite a few locations around the world updated several times a day…

Tephigrams provided by weatheronline

And this page tells you how to read a tephigram…so you can start to disect the atmosphere at any location in the world you choose and know what will happen to that parcel of air you raise up…

How to use a tephigram

Better than any video game I tell you…Here you can create your own world of clouds and thunderstorms, lightning, rain, etc…^

Back in the day...you had to send this weather balloon up and then plot the data by hand and then analyse the chart...nowadays...I tell ya...they have it easy...the bloomin' computer does all this whiz bang stuff...