Where is the LX S80?

As should have been clear from what I wrote, in the bottom third of the
thermal the air is still warmer, but steadily mixing in surrounding air.
Once properly formed the momentum of the tons of air moving is presumed to
keep the circulation active. Air close to the ground is also more humid
which increases the buoyancy. We did not fully model the mechanism, just
took measurements that illustrated the scale and characteristics of
meso-scale air motion in a range of situations, including convective
weather.


At 13:33 03 November 2014, Andy Blackburn wrote:
On Monday, November 3, 2014 3:15:06 AM UTC-8, pete purdie wrote:
...An important finding is that above about
one-third of the distance to the inversion, there is no significant
temperature difference between the thermal and surrounding air; near
the
inversion the temperature is actually lower since the warmer air above
the
inversion is being mixed down around the rising air. Humidity is a
significant indicator, H2O molecules being lighter than O2 or N2.

So thermals rise, not because of the sun heating the ground and making a
bubble of warm air that breaks free, but because somehow a more humid
bubble of air is created. What mechanism creates the bubble of humidity?

9B

On Monday, November 3, 2014 6:15:05 AM UTC-8, pete purdie wrote:
Once properly formed the momentum of the tons of air moving is presumed to
keep the circulation active.

Not entirely sure I buy momentum as a first-order effect since blue thermals don't typically overrun the top of the invasion level by very much, so I can't imagine the top 2/3 of the thermal is simply momentum. Also, if it's thoroughly mixed from a temperature perspective wouldn't it also be mixed from a humidity perspective as well so it wouldn't be rising from having higher humidity either?

Curious.

9B

On Monday, 3 November 2014 16:15:05 UTC+2, pete purdie wrote:
As should have been clear from what I wrote, in the bottom third of the
thermal the air is still warmer, but steadily mixing in surrounding air.
Once properly formed the momentum of the tons of air moving is presumed to
keep the circulation active. Air close to the ground is also more humid
which increases the buoyancy. We did not fully model the mechanism, just
took measurements that illustrated the scale and characteristics of
meso-scale air motion in a range of situations, including convective
weather.


At 13:33 03 November 2014, Andy Blackburn wrote:
On Monday, November 3, 2014 3:15:06 AM UTC-8, pete purdie wrote:
...An important finding is that above about
one-third of the distance to the inversion, there is no significant
temperature difference between the thermal and surrounding air; near
the
inversion the temperature is actually lower since the warmer air above
the
inversion is being mixed down around the rising air. Humidity is a
significant indicator, H2O molecules being lighter than O2 or N2.

So thermals rise, not because of the sun heating the ground and making a
bubble of warm air that breaks free, but because somehow a more humid
bubble of air is created. What mechanism creates the bubble of humidity?

9B



Interesting study:

http://journals.ametsoc.org/doi/abs/...B%3E2.0.CO%3B2

Figure 6 gives quite good overview of temperature and humidity variability during (weakish) convective activity. Temp. differences are appr. 0,5 deg and humidity 1 g/kg close to ground.

Other Weckwerth papers are worth reading too, IMHO.