User talk:DDilworth

Thermals
Before I re-instate my edit of the article that I took to featured status, may I ask you to state your qualifications as a glider pilot? There are places where the thermals will last for hours. May I suggest "flows"? My image of a bubble is a spherical object created by soap. JMcC (talk) 10:17, 11 April 2017 (UTC)

David writes: Thank you for asking. However, my qualifications as a pilot should be relatively irrelevant as I thought Wikipedia relied upon referenced materials like the related wikipedia article I referenced. In any case, I have nearly 1,500 hours of soaring in a dozen or so countries with hang gliders and gliders where thermals are a significant part of our flying phenomena. I teach advanced hang glider pilots how to soar thermals and in 1977 was the first pilot to teach leading Japanese pilots how to fly long distance, including their first formal use of thermals. I've even observed butterflies soaring a thermal bubble - not a stream (not yet published).

I can understand your concern when thinking of a spherical bubble shape as made by soap. Thermals are actually shaped much like a doughnut; a torus. However, pilots and aviation writers most commonly call them "bubbles."

The wikipedia Thermals article says it fairly well "Generally, when the air is cold, bubbles of warm air are formed by the ground heating the air above it and can rise like a hot air balloon." "Flows" can be accurate as can "streams" for well-developed specific (some would say excellent) conditions; and they can indeed last for hours. However, both terms ignore the majority of thermals which are bubbles that form, then pop off the ground and are fairly discrete and coherent - with no connection to subsequent bubbles formed from the same place.

An atomic bomb explosion is a weak example, but it it is useful by providing a dynamic visual depiction of how a thermal forms. The initial heat on the ground soon rises to make a mushroom cloud. Soon after the cloud becomes coherent and disconnects from its ground heated source. Even when normal solar-generated thermals are making streams or flows, they typically generate enough clouds that they cut off the solar radiation causing the thermals, until the clouds adequately dissipate and the cycle restarts.

JMcc: I understand your point of view. I am not going to trade experience but I can say that that I have flown in the Alps as well as the UK for over thirty years. There are definitely thermals that last all day coming up the sides of mountains. Although flat-land thermals do start with a bubble, even they are fed from quite long periods by inrushing air long after the initial bubble has created the cumulus. Can we agree on "Thermals start with bubbles of rising air that are formed on the ground through the warming of the surface by sunlight. The rising air often draws in more warm air from the surrounding land and so can set up a continuing vertical flow."? PS Minor edits are generally typos and punctuation. JMcC (talk) 19:30, 11 April 2017 (UTC)

David: Here's my suggestion: "Thermals start with bubbles of heated air formed by sunlight unevenly warming Earth’s surface. The heated bubbles begin rising, and normally form a doughnut shape, that can rise for thousands of meters. In some cases the solar heating can form a localized stream of rising air that lasts for hours.”

Thank you for your clarification of "minor edit." I'm pretty new to this process.

Thermals, Inrushing Cooler Air
Regarding the "inrushing air" idea: Sorry, but besides never having heard this concept before, at best, it doesn't make sense to me. At worst it could confuse readers with several complex dynamics that are likely beyond the bounds of detail for the article.

Let me try to illuminate one. Thermals require uneven heating of the surface. If all the heating were roughly uniform, like the ocean surface, there would not be any aircraft sized thermals popping off. This means the only air that could rush in would be inherently cooler than the air in the already formed and rising thermal. Cooler air does not normally add to a thermal, it tends to make it dissipate, evaporate or at least stop rising.


 * If you think of a thermal as a cylinder of air, more ground area is needed to keep it going than just the patch from which it launched. As the warm air rises from its original site, it will inevitably draw in more warm air (not cooler) from the surrounding surface for the thermal to continue even for a few minutes. If thermals were just bubbles fuelled by a single patch of warm ground they would only last a few seconds. If you are familiar with cloud streets which can run for tens of miles and which can last for long periods, the description of them as a bubble does not work. JMcC (talk) 09:46, 13 April 2017 (UTC)

David: Yes, air is drawn in to the heated ground patch, but it is inherently cooler - otherwise it would have risen by itself in its original location. That new air is heated by the original thermal's ground patch and then rises to support your stream idea. It is vital to understand that uneven heating by adjacent ground patches is required for thermal activity. Think asphalt parking lot surrounded by a grassy field. On a clear sunny day the asphalt parking lot will often indeed act as your stream and the stream does pull in air from the surrounding areas, but the new air simply cannot be as warm as the heated bubble or parcel of air that just ascended.

Missing Signatures
You are continuing to not sign your responses in the Talkpages. Unsigning them caused others problems in reading communications between Users. The guidelines for this can be found here WP:Signatures. Be aware, "Persistent failure to sign may become disruptive, and if it is persistent, despite the problems being pointed out to the user, doing so may be subject to sanctions." Please in future do so, or further actions will be taken. Arianewiki1 (talk) 03:18, 11 February 2018 (UTC)