hoar frost

plural hoar frosts · alternative hoarfrost · alternative hoar-frost

1. countableuncountableOriginally, any frozen dew forming a white deposit on exposed surfaces.

   He [the Lord] geueth ſnowe like woll, & ſcatereth yͤ horefroſt like aſhes.

   1535 October 14 (Gregorian calendar), Myles Coverdale, transl., Biblia: The Byble, […] (Coverdale Bible), [Cologne or Marburg]: [Eucharius Cervicornus and Johannes Soter?], →OCLC, Psalm cxlvij:[16], folio xxxvij, recto, column 2

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   [W]hen vve have, as vve very frequently have, put mixtures of ſnovv and ſalt into vials, and left them in the open Air, vve generally obſerv'd, that the outſide of the Glaſs vvas cas'd vvith ice, or covered vvith hoar froſt, directly over againſt that part of the inſide of the Glaſs, vvherein the frigorifick mixture vvas.

   1663, Robert Boyle, “Title V. Experiments Touching the Tendency of Cold Upwards or Downwards.”, in New Experiments and Observations Touching Cold, or, An Experimental History of Cold, Begun. […], London: […] Richard Davis, […], published 1683, →OCLC, paragraph 4, page 69

   And novv the mounting ſun diſpels the fog; / The rigid hoar-froſt melts before his beam; […]

   a. 1749 (date written), James Thomson, “Autumn”, in The Seasons, London: […] A[ndrew] Millar, and sold by Thomas Cadell, […], published 1768, →OCLC, page 156, lines 1166–1167

   […] It is moſt remarkable on the ſurface of ſnovv, vvhen covered vvith hoarfroſt, and on other bodies vvhere hoarfroſt moſt abounds. In ſuch caſes, I have often found the ſurface to be ſeven degrees colder than the air at the diſtance of tvvo feet; […]

   1785, Patrick Wilson, “[Account of Some Experiments on Cold]”, in Andrew Duncan, compiler, Medical Commentaries, for the Years 1783–84. […], volume IX, London: […] J[ohn] Murray, […], and C[harles] Dilly, […]; Edinburgh: W. Gordon and C. Elliott, →OCLC, section III (Medical News), page 426

   I was informed that the clear spots which are surrounded by woods, are particularly liable to hoar frosts in the spring and autumn; […] When any of our parties pitched their tents near the exits of rivers, they found the nights colder, and observed hoar frosts to occur more frequently, than those whose encampments were differently situated.

   1835 December 19, Henry D. Sewell, “Art. XVII.—Notes upon the Country in the Vicinity of Quebec.”, in Transactions of the Literary and Historical Society of Quebec, volume III, Quebec City, Que.: […] [F]or the Literary and Historical Society [of Quebec], by W. Nielson, […], →OCLC, page 310

   The mean temperature of the day and night at which injurious hoar-frosts may occur, may, relatively to the freezing-point, be very high.

   1857, “HOAR-FROST”, in John M. Wilson, editor, The Rural Cyclopedia, or A General Dictionary of Agriculture. […], volumes II (D–I), Edinburgh; London: A[rchibald] Fullarton and Co. […], →OCLC, page 657, column 1

   Synonyms: white frost

2. countablespecificallyuncountableclimatologyWater vapour which has undergone deposition or desublimation (“transformation directly into ice crystals without first turning into liquid water”) when the air is cold and moist to form a white deposit on exposed surfaces.

   However, high mountains with a long winter and long dry spells, hoarfrosts and infertile soils are not an ideal environment for some annual crops but are well suited for perennial industrial crops and forest species.

   2005, Manh-Cuong Pham, “Conclusions and Policy Implications”, in Land-use Change in the Northwestern Uplands of Vietnam: Empirical Evidence from Spatial Econometric Models and Geo-referenced Analyses and Policy Implications for Sustainable Rural Development, Göttingen: Cuvillier Verlag, →ISBN, page 331

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   On Sunday night, January 23, ſeveral things vvere laid out at the Obſervatory, ſuch as ſheets of brovvn paper, pieces of boards, plates of metal, glaſſes of ſeveral kinds, &c. vvhich all began to contract hoar-froſt ſeemingly as ſoon as each body had time to cool dovvn to the temperature of the air. The ſheets of brovvn paper being ſo thin acquired it ſooneſt, and vvhen beheld in candle-light they became beautifully ſpangled over by innumerable reflections from the ſmall cryſtals of hoar-froſt vvhich had parted from the air.

   1780 April 20, Patrick Wilson, “XXVI. An Account of a Most Extraordinary Degree of Cold at Glasgow in January Last; together with Some New Experiments and Observations on the Comparative Temperature of Hoar-frost and the Air near to It, Made at the Macfarlane Observatory Belonging to the College. […]”, in Philosophical Transactions, of the Royal Society of London, volume LXX, part II, London: […] Lockyer Davis, and Peter Elmsly, printers to the Royal Society, →OCLC, pages 468–469

   This striking fact, of the lower temperature of the surface on which dew and hoarfrost are forming, it was always found difficult to explain; for the transition of a body from the state of vapour to the fluid or solid form is always accompanied with an evolution of heat, […] The surface is not warmer in consequence of the formation of the dew or hoarfrost, but the dew or hoarfrost is deposited because the surface is previously cold; and its low temperature, compared with that of the air above, is owing to the discharge of heat by radiation.

   1817, John Murray, “Of Caloric”, in Elements of Chemistry. […], 4th edition, volume I, Edinburgh: […] Francis Pillans, […]; London: Longman, Hurst, Rees, Orme, & Brown, →OCLC, book II (Of Repulsion, and the Powers by which It is Produced), section III (Of the Communication and Diffusion of Caloric), page 146

   Hoar frost forms when water vapor sublimates^([sic]) onto a surface. It is the frozen equivalent of dew. […] Conditions leading to hoar frost formation include the movement of vapor within the snowpack, the presence of supersaturated air in crevasses, ice caves, and animal burrows, and the occurrence of clear evenings with high levels of outgoing longwave radiation.

   1989, James C. Halfpenny, Roy Douglas Ozanne, “What and Where is Winter?”, in Winter: An Ecological Handbook, Boulder, Colo.: Johnson Books, →ISBN, page 47, column 1

   The samples of hoar frost collected at all the stations contained few NO₃⁻ ions; this may have been because frost forms at night, when the intensity of road traffic is 2–3 times less than during the day. The largest proportion of NO₃⁻ ions was found in the farmland samples of hoar frost; the reason for this may be the application of nitrogen fertilizers in agriculture.

   2013, “Rain Water: Atmospheric Deposition”, in Sven Erik Jørgensen, editor, Encyclopedia of Environmental Management, volume I, Boca Raton, Fla.: CRC Press, →ISBN, page 2257, column 1