Wind PG Members

	Wind PG Activity Sector
	Ever the wind is in my thoughts and studies! Meterology Rotors Turbulence Thermals Meteorología Basica Thermal visualization Use radio-control UAV coupled with one's flight Using trained birds coupled with one's flight Turbulence visualization instruments Expert programs learn flight/vario reports to produce guide Need much more than average wind speed! • Wind speed probability distribution • Turbulence • Vertical shear • Extreme winds • Extreme coherent gusts • Temperatures • Probability of thunderstorms, hail, icing, tornados, hurricane Artificial lift, artificial thermals, thermal triggers, fences, artificial dunes, windfield helicities near-ground turbulence and effects on various wing types near-ground turbulence and effects on soft-canopy string-formed wings http://www.laboratoridenvol.com/projects/dune/dune.en.html Planetary boundary layer PBL wiki http://en.wikipedia.org/wiki/Geostrophic_wind
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	Tags and notes There is a lot of scattered aerial freak wave knowledge for us to study, but seemingly no definitive compilation of the zoo of effects. Cristina Archer reports new access to better windfield data sets, so freak sky waves should now appear there at the meteorological "micro-scale" (~1000 m). Much of the below is from scattered sources and personal observation. Atmospheric gravity waves are generally surface waves between air layers and easily break as Kelvin-Helmholtz instability. Rising terrain and inversion or convection bubbles commonly trip gravity waves to break. Atmospheric wave peaks break just as whitecaps do, progressively more in storm conditions. It gets really interesting with strong spiral hodographic shear. Freak waveforms occur by many causes, like giant shockwaves caused by major mountains, fronts, or storms. A wave can manifest as a deep isolated trough. Perhaps the freakiest wave is perfectly canceled into momentary nonexistence. Sky waves are easily seen when conditions are right, but one must visualize the large-scale action sped up. Our northern coastal skies spend a lot of time just at dew-point, allowing layers and vortical cores to appear. Often hidden structure reveals as cloud decays, as condensation evaporates or precipitates out. On the edge of the sun's disc, when rising or setting, atmospheric layers are visible, with crossing surface waves. There are endless nature videos showing this effect inadvertently and a few time lapse videos showing large gravity wave crossing stratus cloud layers. Often a convective cell pushes at the windfield around it, revealing layers and waves. One can see breaking wave turbulence faintly across twinkling star fields. Even carefully observed bird flight reveals wave motion. Downburst (and microburst) studies in aviation extensively studied that phenomenon with doppler radar, so airplanes are now rarely at risk. These are vertical down-jets with waves of ring and horseshoe vortices around them. A falling pocket of dry/drying cold air is common, but heats in a pulse as it strikes the surface and can even somewhat bounce. Heavy rain can accelerate a downward jet. Large virga downbursts can occur as breaking waves experienced as white squalls. Willywaws in Tierra del Fuego that Slocum described are extreme versions of the virga catpaws the ordinary sailor sees. A kite signals an ordinary wave by "bobbing" up and down slowly, and a small breaking gravity wave when it is suddenly kicked from above or behind, with a sort of washing machine tumbling--fairly common in gusty conditions. In extreme cases the kite seems to be slapped out of the sky. A vertical vortex as an invisble "gustnado" is a common encounter, seen as a horizontally polarized wave that violently yaws the kite. Breaking waves are so common that Airborne Wind Energy systems must generally be able to cope with several extreme events a year. Altitude is a safety factor, and kites that survive crashes are currently essential. Spanning ordinary turbulence with megascale crosslinked kite structure is very effective in ordinary conditions. Better imaging and prediction, along with better flight automation, will ease the freak sky wave issue. Sailors also will be better prepared, with knock-down warning systems feasible, daveS 29Sept2011