udder 0 #1 January 30, 2007 2 weekends ago I saw the mother of all dust devils cruising along the runway while walking to the plane. Apart from scaring the shit out of me, it got me thinking. Which is a rare occasion. Does heat create significantly more turbulence over even mostly similarly coloured ground? Landing always seems to be bumpy (temp was 42C or 107F) even though I land in the middle of an extremely large grassed field."In one way or the other, I'm a bad brother. Word to the motherf**ker." Eazy-E Quote Share this post Link to post Share on other sites
jmidgley 0 #2 January 30, 2007 Hi It's the 'cruising along the runway' bit that gives away the answer to your question. You can find thermal-induced turbulence over any surface if there's a breeze blowing, because the trigger for the thermal may have been some distance away. After the initial bubble of hot air 'pops off', the moving air mass will continue to carry it along, merrily sucking air in from below, wherever below happens to be. In the right conditions, and with a reliable thermal source, this can produce those characteristic 'cloud streets' beloved of the other type of free flyer. It may also be responsible for the characteristic gust-lull wind conditions that accompany these kinds of days. The 'right conditions' are usually, but not always, a significant difference between the coldest night-time temp and the warmest day-time temp. I must get one of those little 'beep-only' varios to attach to my helmet... Regards John Quote Share this post Link to post Share on other sites
udder 0 #3 January 30, 2007 so if on a hot day you had to land downwind of a tar road or a red dirt runway, what would be your choice?"In one way or the other, I'm a bad brother. Word to the motherf**ker." Eazy-E Quote Share this post Link to post Share on other sites
tdog 0 #4 January 30, 2007 The difference in temperature, not the overall heat, will make thermals. Thermals are just pockets of different temperature air trying to find equilibrium - with the hot going up and the cool going down. You could have a thermal on a skislope where the temperature is below zero. You could have a very strong one if the difference was great between the white snow and the black parking lot. About the colored ground. The reason why color of ground matters is because of how it absorbs heat relative to the ground near by and overall. Black solid asphalt is going to absorb more heat than light brown tall wet grass. If that asphalt will heat the air right next to it, you will likely get a thermal. Quote Share this post Link to post Share on other sites
billvon 2,384 #5 January 30, 2007 I strongly recommend the book "Understanding the Sky" by Pagen. He devotes entire chapters to the issues of turbulence/thermal creation. Quote Share this post Link to post Share on other sites
skymick 0 #6 January 31, 2007 QuoteI strongly recommend the book "Understanding the Sky" by Pagen. He devotes entire chapters to the issues of turbulence/thermal creation. ditto, it is a great book but tends to focus on paragliders a bit more but apart from the thermal/turbs sections it also explains a lot of macro-meteorology as well which is great for forecasting and very interesting (well for me anyway Quote Share this post Link to post Share on other sites LyraM45 0 #7 January 31, 2007 -- meteorology geek in the house (well, not officially until I get my degree in May, but close enough ) It's differential heating which sometimes causes these unstable pockes of air that we hit. You can see this in the formation of those towering cumulonimbus clouds, especially on any summer day in Florida. The mornings start cloudless, and then after differential heating and radiation absorbtion of the ground, the energy gets released and creates that dynamic forcing upwards of the air-- and, if the conditions are there for cloud development, you can see this in the formation of a big beautiful towering cumulonimbus thats riding that unstable air column right up until it reaches its equilibrium level. That runway that you're talking about has a blackbody temperature much higher than the ground around, so its a much better absorber for that radiational heating from the sun. When it re-emits the radiation, the heat being radiated back in long waves causes the air above the blacktop to be much warmer, less dense, and bouyant; this is the rising which we can feel under canopy if you fly over one of those areas. Sorry if this sounds kinda chopped up, but it's the best I can do without getting too geeky sounding. Apologies for the spelling (and grammar).... I got a B.S, not a B.A. :) Quote Share this post Link to post Share on other sites Squeak 17 #8 January 31, 2007 for Udder hey Pedder remind me about this post when we're at the DZ , I'll talk you through it and show you some interesting places to plqay with you canopy on hot daysWere you there the other week when everyone except one person landed off DZ... The reason only one person landed on was because only one person used the thermals (no it wasn't me, I was watching)You are not now, nor will you ever be, good enough to not die in this sport (Sparky) My Life ROCKS! How's yours doing? Quote Share this post Link to post Share on other sites Join the conversation You can post now and register later. If you have an account, sign in now to post with your account. Note: Your post will require moderator approval before it will be visible. Reply to this topic... × Pasted as rich text. Paste as plain text instead Only 75 emoji are allowed. × Your link has been automatically embedded. Display as a link instead × Your previous content has been restored. Clear editor × You cannot paste images directly. Upload or insert images from URL. Insert image from URL × Desktop Tablet Phone Submit Reply 0
LyraM45 0 #7 January 31, 2007 -- meteorology geek in the house (well, not officially until I get my degree in May, but close enough ) It's differential heating which sometimes causes these unstable pockes of air that we hit. You can see this in the formation of those towering cumulonimbus clouds, especially on any summer day in Florida. The mornings start cloudless, and then after differential heating and radiation absorbtion of the ground, the energy gets released and creates that dynamic forcing upwards of the air-- and, if the conditions are there for cloud development, you can see this in the formation of a big beautiful towering cumulonimbus thats riding that unstable air column right up until it reaches its equilibrium level. That runway that you're talking about has a blackbody temperature much higher than the ground around, so its a much better absorber for that radiational heating from the sun. When it re-emits the radiation, the heat being radiated back in long waves causes the air above the blacktop to be much warmer, less dense, and bouyant; this is the rising which we can feel under canopy if you fly over one of those areas. Sorry if this sounds kinda chopped up, but it's the best I can do without getting too geeky sounding. Apologies for the spelling (and grammar).... I got a B.S, not a B.A. :) Quote Share this post Link to post Share on other sites
Squeak 17 #8 January 31, 2007 for Udder hey Pedder remind me about this post when we're at the DZ , I'll talk you through it and show you some interesting places to plqay with you canopy on hot daysWere you there the other week when everyone except one person landed off DZ... The reason only one person landed on was because only one person used the thermals (no it wasn't me, I was watching)You are not now, nor will you ever be, good enough to not die in this sport (Sparky) My Life ROCKS! How's yours doing? Quote Share this post Link to post Share on other sites
