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Topic: Graupel

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	Graupel
		Graupel is that Styrofoam ball type of snow that stings your face when it falls from the sky.
		Graupel is a common weak layer in maritime climates but more rare in continental climates.
		Graupel tends to become faceted easily when subjected to a strong temperature gradient, in which case, graupel produces avalanches much more persistently.
	www.avalanche.org /~uac/encyclopedia/graupel.htm (227 words)

	Rime and Graupel (Site not responding. Last check: 2007-11-04)
		When this process continues so that the shape of the original snow crystal is no longer identifiable, the resulting crystal is referred to as graupel.
		The frozen droplets on the surface of rimed crystals are hard to resolve and the topography of a graupel particle is not easy to record with a light microscope because of the limited resolution and depth of field in the instrument.
		As the riming process continues, the mass of frozen, accumulated cloud droplets obscures the identity of the original snow crystal thereby giving rise to a graupel particle Fig.5 (17570).
	www.lpsi.barc.usda.gov /emusnow/RimeGraupel/rg.htm (231 words)

	Hard Rains Will Fall
		Graupel, Snow Pellets or Soft Hail are soft, opaque ice particles, irregular in shape and often studded with oblong or branched protrusions.
		With diameters of 1-7 mm, graupel forms in strong updrafts of cold air in blizzards, lake-effect snows and thundersnows, and are often highly electrified.
		Because graupel forms in convective updrafts and may be pushed quickly downward in descending currents, it may fall when the surface temperatures are significantly above freezing.
	www.islandnet.com /~see/weather/elements/hardrain.htm (1043 words)

	Graupel - Glossary Entry (Site not responding. Last check: 2007-11-04)
		A form of precipitation which looks like round pellets.
		Graupel is subject to rolling and can collect in pockets.
		It can also form a layer with a great deal of pore space and poor bonding.
	www.avalanche-center.org /Education/glossary/graupel.php (74 words)

	SPRITES AND BUBBLES
		Upon solidification, the graupel volume contracts and induces a high pressure to force the bubble vapor out of the graupel, the vapor promptly forming positive charged micro-droplets; whereas, the hydroxyl ions tend to remain behind leaving the graupel with a negative charge.
		Bubbles in graupel as a source of atmospheric electricity are therefore consistent with the positive charge in the micro-droplets surrounding a negative charged graupel first measured by Cheng in 1973.
		Thus, hydronium ions from the bubbles in graupel form conductive paths in the stratosphere by which the global circuit discharges the potential difference between the lower ionosphere and the earth during a storm.
	www.angelfire.com /super/cavityqed/sprites.htm (560 words)

	AS 3 Lecture Screens (Site not responding. Last check: 2007-11-04)
		Graupel can look like the hexagonal crystal that first started accreting; or it can look like a somewhat-spherical lump, or it can have a conical shape as shown in the photographs.
		Graupel have been observed to be as large as 1 cm diameter (possibly larger in some situations).
		If the graupel gets much larger than 1 cm, it will usually be falling fast enough to undergo a different type of growth that will result in the production of a hailstone.
	www.atmos.ucla.edu /as3/scrns/precip/Note09.html (200 words)

	Anyone else think Graupel is underated? - Eastern US Weather Forums
		Graupel is a precursor and one of the warning signs that the shaft is imminent.
		Here it's the other way around as graupel is a common occurrence with the convective snow bursts we get with cold frontal passages and it's interesting to hear thunder while it's falling at a heavy rain.
		Yes, graupel is most often associated with convective activity and is frequently observed during thundersnow.
	www.easternuswx.com /bb/index.php?showtopic=10864 (1129 words)

	SignOnSanDiego.com > News > Metro -- Neither rain nor sleet nor snow: 'Graupel' hit area
		Graupel is a form of precipitation consisting of "brittle, white ice particles having a snowlike structure," according to Webster's.
		Meteorologists said snowflakes that melt as they fall, and then collide, are known as graupel.
		Graupel," she said, struggling to pronounce a word she'd never heard before.
	www.signonsandiego.com /news/metro/20020131-9999_6m31weather.html (317 words)

	National Weather Digest: Using WSR-88D reflectivity data for the prediction of cloud-to-ground lightning: a central ... (Site not responding. Last check: 2007-11-04)
		Charge separation most likely occurs during rebounding collisions between ice crystals and large ice hydrometeors (such as graupel and hail) that remain suspended in the mixed phase zone by the updraft of a growing thunderstorm.
		Graupel and hail may also form initially from the freezing of millimeter-sized raindrops.
		Thus, the appearance of a 30-40 dBZ or greater radar echo between -10[degrees]C and -20[degrees]C indicates the possible presence of a sufficient quantity of graupel or hail suspended in an updraft with ice crystals and supercooled water for charging, and ultimately, lightning.
	www.findarticles.com /p/articles/mi_m0QRG/is_27/ai_n11836126 (1228 words)

	Introduction
		Based on a considerable body of storm observations, numerical modeling studies and laboratory experiments, it is reasonable to expect that variations in the microphysics and kinematics of storms should have a strong effect both on the amount and distribution of charge generated by a storm.
		Most scientists believe that a noninductive mechanism operating during the collisions between ice crystals and riming graupel or hail inside the clouds are the main responsible of the strong storm electrification, enough to produce electric discharges [see e.g.
		Laboratory experiments have been performed in attempts to understand the physical mechanisms that operate as charge separate during ice-ice collisions, as well as to parameterize both the magnitude and sign of the charge transferred when collision occurs in particular environmental conditions.
	www.agu.org /pubs/toc/gl/gl/gl0023/2000GL012302/node1.html (555 words)

	Title (Site not responding. Last check: 2007-11-04)
		Similar to 23 November, the lightning rate appears to be strongly correlated to the graupel mass in the mixed-phase region.
		The results of this study also suggest that graupel is an active participant in thunderstorm electrification and that the lightning flash rate is a strong function of the amount of graupel above the freezing level.
		The 27 November thunderstorms probably did not have updrafts capable of elevating the graupel to extreme heights, possibly allowing their lower layers of positive charge to develop quickly and initiate cloud-to-ground lightning soon after graupel was created.
	olympic.atmos.colostate.edu /~daa/AMMJournal.html (8391 words)

	Rime and Graupel: Description and Characterization as Revealed by Low-Temperature Scanning Electron Microscopy (Site not responding. Last check: 2007-11-04)
		However, the limiting resolution and depth of field associated with the light microscope have prevented detailed descriptions of the microscopic cloud droplets and the three-dimensional topography of the rime and graupel particles.
		This study uses low-temperature scanning electron microscopy to characterize the frozen precipitates that are commonly known as rime and graupel.
		The advanced stages of this process result in graupel, a particle 1 to 3 mm across, composed of hundreds of frozen cloud droplets interspersed with considerable air spaces; the original snow crystal is no longer discernible.
	www.scanning-fams.org /scanabstracts/SCANNING03/25121.html (439 words)

	ARS \| Publication request: Rime and Graupel: Description and Characterization As Revealed by Low Temperature Scanning ...
		In the case of graupel, this study shows clearly the structure of the frozen droplets and internal air spaces.
		In this study, a field emission scanning electron microscope equipped with a cold stage was used to document the structural features, physical associations and atmospheric metamorphosis of rime and graupel snow crystals.
		With the low temperature scanning electron microscopy approach, it is possible to distinguish the original snow crystal types until the accretion of droplets become thick enough to obscure the original crystal and graupel is the result.
	www.ars.usda.gov /research/publications/publications.htm?SEQ_NO_115=142593&pf=1 (460 words)

	[No title]
		Elmo's fire occurs as the graupel clouds that escaped cloud-to-ground lightning descend to the earth's surface, the graupel producing a negative space charge breaking down the nitrogen near positive charged metal protrusions to produce a blue corona.
		Solidification of graupel upon freezing produces a volume contraction that drives the bubble vapor containing hydronium ions into the atmosphere leaving the hydroxyl ions behind in the graupel.
		Cloud-to-cloud lightning is a discharge between graupel and ice crystal clouds, while cloud-to-ground lightning is a discharge between graupel clouds and the positive charged ground.
	www.esdjournal.com /techpapr/sprite.doc (2946 words)

	RES_Paper_SLS20.html
		The 3D modeling study reported herein investigates the impact of graupel on the structure and bulk microphysical characteristics of NCFR convection under conditions closely based on the environment of a notably vigorous winter NCFR in central California (Carbone 1982, Rutledge 1989, Parsons 1992).
		Thus, maximum snow and graupel contents were comparable to those cited by Rutledge (1989) in a 3D kinematic-microphysical simulation of the 5 February 1978 NCFR case using a time-independent flow field derived from dual Doppler radar winds.
		The most abundant hydrometeor is snow rather than graupel, and much more lopsidedly so, contributing an order of magnitude more mass; this is largely because, in the full-physics run, accretion of snow is by far the largest graupel source (and the main reason for the limited snow mass).
	www.meteor.wisc.edu /~schlesin/RES_Paper_SLS20.html (3488 words)

	Lightning
		When small graupel falls into a region of supercooled water droplets and strike the droplets, the water freezes on the outside of the graupel.
		As long as the graupel is gathering supercooled water droplets, the graupel remains slightly warm.
		The striking of cooler ice crystals by warmer graupel results in electrons moving from the ice crystals to the graupel.
	www.met.tamu.edu /class/Metr304/Severedir/LightningDir/lightning-stu.html (1414 words)

	Graupel trajectories and charging: a new numerical approach for cloud electrification studies (Site not responding. Last check: 2007-11-04)
		The electricity enters both in the charging of the particles through their interactions with other particles and in the motion itself, since in the equation of motion the electrical force is included.
		This kind of approach appears to be a powerful tool to study the electric charging of the graupel in greater detail, since a very high spatial resolution (about 1m) is easily achieved.
		For the sake of comparison, trajectories without the electrical interaction are also computed, and it is shown that in some cases, the final radius with and without E-force can differ by a factor of 2-3 in either direction depending on the initial position.
	exa.unne.edu.ar /investigacion/gica/pulido/articles/qj98.html (239 words)

	Graupel - Wikipedia, the free encyclopedia
		Graupel can be any of the following types of solid-ice precipitation:
		Graupel does not include other frozen precipitation such as snow or ice crystals.
		This page was last modified 06:05, 12 August 2005.
	en.wikipedia.org /wiki/Graupel (101 words)

	Lightning Strikes, Hurricanes, and Dr. John Hallett
		In this region, upward-moving graupel changes to a combination of ice crystals and graupel and then to downward-moving snow.
		Ice crystals are produced from the growing graupel (by the Hallett-Mossop process discovered in a laboratory study during Hallett's sabbatical leave in Australia in 1973) and produce separation of charge.
		The region of graupel, liquid water, and ice in a typical hurricane turns out to be "at the wrong place at the wrong temperature and in insufficient volume to produce a lightning discharge," according to Hallett and Black.
	newsletter.dri.edu /1999/spring/Lightning.html (1425 words)

	COMAP Quiz 2004
		Lighter flakes tend to positively charge the upper portions of the cloud while graupel tend to negatively charge the low portions of the cloud.
		The temperature range where most charge separation occurs is from -10 to -16 C. Both graupel and ice particles are needed for this kind of charging mechanism, which generally takes place around the -10 C to -20 C level.
		As the graupel forms and is pushed upward, it carries with it a general negative charge.
	www.comet.ucar.edu /class/online_surveys/COMAP/comap-qzwk504.html (1255 words)

	2. SIMULATION MODEL
		The numerical cloud model (Straka and Anderson, 1993) used for the simulations is three dimensional and includes detailed bulk microphysics, with separate categories for cloud water, rain, cloud ice (columns, plates, and rimed), snow aggregates, frozen drops, three graupel densities, and two size ranges of hail.
		Graupel gains negative charge at temperatures lower than the reversal temperature and gains positive charge for collisions occurring at higher temperature.
		In the riming rate scheme, the sign of charge gained by graupel depends on both the ambient temperature and the rime accretion rate of the graupel.
	www.cimms.ou.edu /~mansell/slschtml/node2.html (479 words)

	[No title] (Site not responding. Last check: 2007-11-04)
		Graupel particles Plates 1924 Snowfall is increasing in intensity 1930 Snow sample #5: Large dendritic branch 1946 Filter sample #1 ends.
		Snow sample #8: Stellar-like branch not rimed Rimed dendrite Very heavily rimed branch, nearly graupel Heavily rimed crystal or graupel particle - can see light through it 2100 Leaving the site 8.5 km NE of Briggsdale and are heading towards the K-band site for a few samples.
		Dendrite has small graupel or heavily rimed particle in a branch 2309 Finish from the K-band site and are heading back to NCAR.
	www.rap.ucar.edu /projects/wisp/logs/24feb.log (604 words)

	Crater Lake National Park: Nature Notes (1933)
		The graupel which falls at Crater Lake is mixed with soft snow.
		As the masses come on down through cooler layers of atmosphere they freeze and they crumbly graupel aggregates result.
		The Klamath Basin with its upper and lower Klamath Lakes and Agency Lake presents a very interesting phenomenon concerning fog conditions.
	www.nps.gov /crla/notes/vol6-1f.htm (614 words)

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