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Aerosonde UAV about to fly into a tropical storm...
Flying in sub-zero temperatures
Changes in the maximum coefficient of lift and the critical angle of attack with different degrees of icing (" Rime" ) on the wings, from http://www.icao.int/icao/en/jr/2006/6104_en.pdf.
Results of wind-tunnel studies of the effects of very thin layers of ice on a full scale Russian Yak-40 wing with flaps extended 11 degrees. Also from http://www.icao.int/icao/en/jr/2006/6104_en.pdf.
What is " rime" ?
From http://www.weatheronline.co.uk/feature/cc231002.htm
Rime is a white or milky and opaque granular deposit of ice formed by the rapid freezing of supercooled water drops as they impinge upon an cold exposed object. Rime is denser and harder than hoar frost, but lighter, softer, and less transparent than glaze. Rime might have long 'feathers' and 'tails' of rough ice granules or might even be a fairly compact coating if favorable conditions for rime formation persisted over a longer time.
Generally the 'feathers' and 'tails' point into the wind, but under calm conditions the 'needles' might grow into every direction. This is why they can be mistaken as hoar frost. However, unlike hoar frost rime is formed by freezing fog or cloud droplets. The tiny supercooled water droplets remain liquid until they come in contact with any obstacle, when they freeze almost instantaneously. If the fog persists for some longer time large amounts of ice can be deposited.
Whereas rime usually builds up moderately in lowland areas it may accumulate to an ice cover of several feet in mountaineous regions. In fact rime ice makes up a significant source for valley glaciers as it breaks away falling into the valley below. Rime usually accumulates best on exposed obstacles, such as trees, radio masts or rock pinnacles. It might sometimes cause some structural damage, but generally far less severe than black ice or glaze.
Arctic temperature: from http://igloo.atmos.uiuc.edu/IPCC/arctic.temp.slp.ipcc.lowres.pdf
Temperatures in the Sahara region: from http://lexicorient.com/e.o/sahara.htm
Maximum temperature from the above is 43ºC.
Winds in the Sahara, in m/s: from http://www.iset.uni-kassel.de/abt/w3-w/projekte/Risoe200305.pdf
Multiply wind speeds in m/s by 3.6 to get Kmph.
“The Sahara is the most important source of desert dust on a global scale (Washington et al., 2003). Huge dust outbreaks are frequently observed over the Sahara and the surrounding oceans (see cover image) causing considerable atmospheric turbidity. Lidar measurements (cf. Fig. 1) onboard of a spacecraft (Winker et al., 1996) have revealed that even under non-dust storm conditions the lower troposphere over deserts can be regarded as a reservoir of atmospheric dust. Due to intensified land use, and changes in human practices in and around deserts a contribution of up to 10% of the total globally emitted annual amount of mineral dust has been estimated as anthropogenic (Tegen et al., 2003).”
- from http://www.tropos.de/samum/scopeintro.html
Wednesday, March 12, 2003 satellite image of an exceptional dust storm over Morocco, with strong winds sweeping thick Saharan Desert dust over to the Canary Islands in the Atlantic Ocean.
Image true-color acquired by the Moderate Resolution Imaging Spectroradiometer (MODIS) aboard NASAs Aqua satellite. (AP Photo/MODIS Rapid Response Team at NASA GSFC) – www.saharawind.com
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