RimeTan

= Rime = Julian Burns & Christian Freniere Tan Class

Introduction Rime is a white or milky and opaque granular deposit of ice formed by the rapid freezing of supercooled cloud droplets as they condense on exposed objects (1). Rime is often referred to as hoarfrost, however this is a common misconception as rime is denser,harder, and more severe than hoarfrost (1). Rime, though potentially severe, is lighter, softer, less tra nsparent, and less drastic than glaze (1). Rime has a general density of 0.2 - 0.3g/cm*-3 (2). Rime is one of the many severe weather phenomena that influence and effect the world we live in. Dangers  Rime, though not as dangerous as glaze, can be potentially lethal and causes a notable amount of structural damage (1). Rime buildup on aircraft is extremely dangerous and often occurs when aircraft fly through supercooled clouds (3). The rapid progression of ice buildup on the wings and propellers soon weigh down the aircraft and add prohibitive drag (3). Rime also changes the shape of the wings, which could cause drastic consequences (3). Potentially, rime can have serious consequences if an aircraft is not properly equipped to handle it.

Conditions of Formation Rime, like most other extreme weather phenomena, have favorable conditions that support formation. The factors that support the formation of rime are: small drop size, slow accretion, a high degree of supercooling, and a rapid dissipation of latent heat of fusion (2). Rime may also form on snow crystals, droxtals (tiny ice particles measuring 10-20um in diameter), and other ice particles in the atmosphere. Higher up in the atmosphere or on a cold day, when the relative humidity is high water vapor becomes supercooled and suspended in the atmosphere. When this supercooled water vapor comes in contact with an object, the supercooled water droplets freeze instantaneously, creating rime (1). Rime may also be formed by freezing fog or cloud droplets (1). These tiny supercooled droplets will also freeze instantly when condensed onto an exposed object (1). If a fog persists over an extended duration, great amounts of ice may be deposited (1). In order for this fog to stick around it must become trapped in a valley, there must not be a significant amount of wind to push it away, or the fog is forming to fast. Rime generally accumulates in lowland areas in slight to moderate amounts (1). However, given enough moisture rime can accumulate in huge amounts in mountainous regions with several feet of ice cover spawning from the high relative humidity (1). This could be because of the high altitude of the mountains and the adiabatic cooling process along with the sparseness of the atmosphere which disperses heat over a wide space. Once clouds form because of the said processes, the cloud droplets then become supercooled due to -3*C temperatures and then accumulate on exposed surfaces in great amounts because of the moisture content and high relative humidity.

Safety Most people in the lower levels of the troposphere don't have to prepare for rime (1). It is usually harmless to the majority of people on earth(1). However, airplanes have to account for rime when flying through supercooled clouds (3). Rime may build up on the wings of the aircraft and cause damage to the structure of the airplane (3). This can cause the affected airplane's structure to fail. Pilots usually try to avoid supercooled clouds, by flying around, or over them (3). If a pilot did not take the necessary precautions and prepared for a possible encounter with rime, lives could be lost; and this only reminds us just how EXTREME rime is and the seriousness required to handle such a demanding weather phenomena.



Sources

1) ////Weather Online////. Weather UK, n.d. Web. 1 Dec. 2010.   . @http://www.weatheronline.co.uk/reports/wxfacts/Rime.htm

2) RIme." ////Glossary of Meteorology////. American Meteorological Society, n.d. Web. 1  Dec. 2010.  search?id=rime1>. @http://amsglossary.allenpress.com/glossary/search?id=rime1

3) Collins, Donald F. "Rime Ice in the Craggies." ////Warren-Wilson////. Warren-Wilson  College, 2 Dec. 2005. Web. 1 Dec. 2010.  ~physics/PhysPhotOfWeek/20051202RimeIce/>. @http://www.warren-wilson.edu/~physics/PhysPhotOfWeek/20051202RimeIce/

4) @http://thundafunda.com/5/Winter-Scenes/photos-of-Hoar-Frost-Purcell-Mountains-Br-pictures.php

5) @http://www.treknature.com/gallery/photo194191.htm

6) @http://lh4.ggpht.com/_hVOW2U7K4-M/S3kO_ABqjXI/AAAAAAABP68/nAjwcb0XVWQ/s640/3w54ywe54tyr.jpg

7) @http://www2.tech.purdue.edu/at/courses/aeml/airframeimages/wing%20ice%20alb.JPG

8) @http://vulcan.wr.usgs.gov/Imgs/Jpg/MSH/MSH08/MSH08_sugarbowl_camera_housing_rime_ice_01-16-08.jpg