Gustfronts

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Asterix
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Gustfronts

Postby Asterix » Sun Mar 04, 2012 12:24 pm

Nice! I'll kick of by re-posting my last post on another topic:

From Wikipedia:

"A gust front is the leading edge of cool air rushing down and out from a thunderstorm. There are two main reasons why the air flows out of some thunderstoms so rapidly. The primary reason is the presence of relatively dry (low humidity) air in the lower atmosphere. This dry air causes some of the rain falling through it to evaporate, which cools the air. Since cool air sinks (just as warm air rises), this causes a down-rush of air that spreads out at the ground. The edge of this rapidly spreading cool pool of air is the gust front. The second reason is that the falling precipitation produces a drag on the air, forcing it downward. If the wind following the gust front is intense and damaging, the windstorm is known as a downburst."

GO READ THIS:

http://www.aviationweek.com/aw/generic/ ... t%20Fronts

If you look at the pic below it shows the stages of a gustfront. Stage 1 formative, in the main picture, is basically underneath the storm - not what happened. But if you look at the thumbnails - I was probably caught in stage 3, with the storm behind me, towards my 07 o'clock. The spreading cold air from the Thunderstorm's out pour caught up with me from behind. Stage 3 and 4 can occur MILES away from the actual storm itself. (Sometimes known as an OLD Gust Front)

This would make sense in terms of my experience, since those red arrows whirling up, caught up with me from behind, inducing the sudden increase in airspeed and vertical velocity, followed by the purple arrows as it moved pass me and made my airspeed drop like a stone, leaving me stalled. In quite a high nose-up attitude, I may ad, as I was pushing bar to bleed airspeed.. )

From my link above - the following seems relevant to what I encountered:

"Old gust fronts can be found in clear air more than 20 miles away from the generating thunderstorm(s). These gust fronts can still produce a strong shear zone and cause the surface wind to change rapidly." (This is probably what happened - I was in stable air at the time, and the thunderstorm was towards Bethal, at my back, miles away)

"Turbulence Threat: Definition: Encounter with man-made or atmospheric scales of motion that cause intense, short-lived, random accelerations on the aircraft." (Thus the sudden uncontrollable increase in speed and vertical speed)

"Wind-Shear Threat:Definition: Encounter with atmospheric events that cause critical reduction in airspeed or altitude, such as to threaten the ability of an aircraft to remain airborne." (Thus the stall. Although I might have induced it whilst pushing on the bar trying to keep down airspeed) :oops:

Bottom line: Dis nie lekker nie - voel soos doodgaan! So pasop om te gaan vlieg as daar groot Cumulonimbus aan die bou is - al dink jy hulle is ver. The minute that bugger starts to collapse on itself and produces a thunderstorm, you are screwed. , even if you are miles away.

You are gonna join the (-) (-) , physically and spiritually.!
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Bundy
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Re: Gustfronts

Postby Bundy » Mon Mar 05, 2012 6:03 am

Hi James,

From this diagram (and those posted on your other topic) it's clear that these large CB's are definately something to avoid at all costs. Even "behind" the storm, there seems to be quite a bit of bad air. These bad boys will just suck you in and spit you out...in pieces. :(

Scary stuff....best witnessed from the safety of the ground. :)
Alan "Bundy" Hussey
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nicow
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Re: Gustfronts

Postby nicow » Mon Mar 05, 2012 7:17 am

Thanks for the info.
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Bundy
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Re: Gustfronts

Postby Bundy » Mon Mar 05, 2012 7:29 am

Not really "related" but interesting nonetheless.... Have you ever asked yourself how much a cloud actually weighs?

Found this...

"According to a meteorology text I have, the water content (density) of clouds varies quite a bit, from about 1/10 gram per cubic meter to over 5 grams per cubic meter. It is even harder to come up with an "average" cloud volume, as this varies even more widely than water content. Nonetheless, let us use Dr. Topper's formula (see response #1 to this question) to get at least a rough order-of-magnitude estimate. We can model the cloud as a sphere of, say, 1 kilometer radius. This gives a volume of about 4 billion cubic meters. Then if we use 1 gram per cubic meter as a "representative" water content, we get an estimate for the mass of the cloud of 4 billion grams, or 4 million kilograms."

Ronald Winther

Holy crap! :shock:
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