The Wind-Chill Index
2021; Elsevier BV; Volume: 32; Issue: 3 Linguagem: Inglês
10.1016/j.wem.2021.04.005
ISSN1545-1534
AutoresHarvey V. Lankford, Leslie R. Fox,
Tópico(s)Meteorological Phenomena and Simulations
ResumoThis Lessons from History article about the wind-chill index (WCI) explores the historical polar and meteorologic literature relevant to the topic and presents unpublished work from 1939. Geographer Paul Siple (1908–1968) was a 6-time Antarctic explorer and scientist who invented and named the WCI in his doctoral dissertation at Clark University. Siple and Charles Passel (1915–2002) performed studies in Antarctica in 1940 that led to publication in 1945. This paper is often credited as the beginning of the WCI. Through years of critiques and revisions by others, these efforts evolved into the wind-chill equivalent temperatures (WCTs) used today. This essay explores the history, the science, and the overlooked originality, simplicity, and details of Siple’s unpublished work. The remarkable similarity of the original chart to a current chart is shown by adapting and overlaying the 1939 WCI onto a current WCT chart with its times-to-frostbite data. The writings of Siple, Passel, and others provide an evocative supporting narrative to illustrate some of the problems of living in cold environmental conditions. This Lessons from History article about the wind-chill index (WCI) explores the historical polar and meteorologic literature relevant to the topic and presents unpublished work from 1939. Geographer Paul Siple (1908–1968) was a 6-time Antarctic explorer and scientist who invented and named the WCI in his doctoral dissertation at Clark University. Siple and Charles Passel (1915–2002) performed studies in Antarctica in 1940 that led to publication in 1945. This paper is often credited as the beginning of the WCI. Through years of critiques and revisions by others, these efforts evolved into the wind-chill equivalent temperatures (WCTs) used today. This essay explores the history, the science, and the overlooked originality, simplicity, and details of Siple’s unpublished work. The remarkable similarity of the original chart to a current chart is shown by adapting and overlaying the 1939 WCI onto a current WCT chart with its times-to-frostbite data. The writings of Siple, Passel, and others provide an evocative supporting narrative to illustrate some of the problems of living in cold environmental conditions. Wind chill is a phenomenon caused by the effect of wind on heat loss from bare human skin, with a resultant increased rate of cooling and increased sensation of cold. Wind-chill indices and other tools are used in wilderness and nonwilderness weather reporting to warn people of cold weather hazards, particularly frostbite.1US Department of Commerce/National Oceanic and Atmospheric AdministrationOffice of the Federal Coordinator of Meteorological Services and Supporting Research. FCM- R19-2003. Report on wind chill temperature and extreme heat indices: evaluation and improvement projects.http://solberg.snr.missouri.edu/gcc/OFCMWindchillReport.pdfDate accessed: March 12, 2021Google Scholar American geographer Paul Siple (1908–1968) invented the wind-chill index (WCI) in 1939. It was briefly adopted for polar and military purposes and is referred to here as the 1939 WCI. It is an index because it is a scale or chart that correlates clinical manifestations of cold with the environmental parameters of wind and temperature. In 1940, on another trip to Antarctica, Siple and Charles Passel (1915–2002) performed studies of the effects of wind and air temperature on humans. Their study was published in 1945.2Siple P.A. Passel C.F. Measurements of dry atmospheric cooling in subfreezing temperatures.Proc Am Philos Soc. 1945; 89: 177-199Google Scholar This paper is the one usually cited for the creation of the WCI. This Lessons from History article explores the chronicle of the WCIs and related wind-chill equivalent temperatures (WCETs or simply WCTs). It examines the overlooked originality, simplicity, and details of the unpublished 1939 WCI and presents a remarkable comparison of the original and current charts. Wind-chill terminology can be confusing. Wind chill is often used interchangeably with, or as an abbreviation for, any of several terms. SP 1945 WCI is used in this article to denote the heat loss rate measurements or the WCI of Siple and Passel. The SP 1945 WCI was employed and criticized for decades until it evolved into the WCTs. WCT may refer to an individual figure but, depending on context, may mean the whole structure of physics, calculations, and charted figures. When “the WCT” is presented on a chart that relates grades of danger, the term WCT index (WCTI) is correct but not always used. The term “old WCT” refers to any WCT or WCTI based on the SP 1945 WCI. The 2001 “new WCT” uses updated biophysical models. It predicts the risk of frostbite, so formally it is the “new WCTI” as described in the official report.1US Department of Commerce/National Oceanic and Atmospheric AdministrationOffice of the Federal Coordinator of Meteorological Services and Supporting Research. FCM- R19-2003. Report on wind chill temperature and extreme heat indices: evaluation and improvement projects.http://solberg.snr.missouri.edu/gcc/OFCMWindchillReport.pdfDate accessed: March 12, 2021Google Scholar Despite this distinction, terms such as “new WCT,” “2001 WCT,” and “current WCT” are commonly used. The convective cooling power of the wind has long been studied. A compilation of 89 early physics-laden references for experiments and calculations between 1912 and 1941 included terms such as comfort index, cooling power, cooling temperature, sensation scales, effective temperature index, and equivalent comfort conditions.3Stone R.G. The practical evaluation and interpretation of the cooling power in bioclimatology.Bull Am Meteorol Soc. 1943; 24: 327-339Crossref Google Scholar These were in the realm of mathematicians and other scientists. The emerging field that studied the interaction of human body temperature with the environment included leaders such as American biophysicist A. Pharo Gagge (1908–1993). In 1941, he proposed new units so that varying specialists could have a common system of communicating about thermal exchanges.4Gagge A.P. Burton A.C. Bazett H.C. A practical system of units for the description of the heat exchange of man with his environment.Science. 1941; 94: 428-430Crossref PubMed Scopus (221) Google Scholar In an individual sitting/resting comfortably indoors at 21°C (70°F) and less than 50% humidity, 1 clo was the insulation value of everyday clothing and 1 metabolic equivalent of task (MET) was the metabolic rate of an average-size person at rest. Today’s related MET is a ratio of the rate at which a person expends energy relative to the mass of that person while performing some specific activity compared to sitting/resting. Gagge et al. produced brief tables suggesting optimal temperatures and clothing requirements for comfort in indoor or outdoor conditions.4Gagge A.P. Burton A.C. Bazett H.C. A practical system of units for the description of the heat exchange of man with his environment.Science. 1941; 94: 428-430Crossref PubMed Scopus (221) Google Scholar Siple and Passel cited the work of Gagge and the other forerunners.2Siple P.A. Passel C.F. Measurements of dry atmospheric cooling in subfreezing temperatures.Proc Am Philos Soc. 1945; 89: 177-199Google Scholar The original MET and clo definitions were restated in 1966 with commonly used engineering terms and other changes at the US Army Research Institute of Environmental Medicine (USARIEM), whose mission statement includes the enhancement of health and performance through medical research.5Fiske D.L. The MET and the CLO. Part 1. Restatement of the original definitions. Technical report 06-21-CM. Advanced projects branch, clothing and organic materials division, US Army Natick Laboratories. 1–7. US Army, Natick, MA1966Google Scholar Similarly, in 1966, the first institutional standards for comfortable temperature and airflow in the indoor thermal environment were published by the American Society of Heating, Refrigerating and Air-Conditioning Engineers, last revised in 2020.6ASHRAEThermal Environmental Conditions for Human Occupancy ANSI/ASHRAE Standard 55-2020. ASHRAE, Peachtree Corners, GA2021: 1-75Google Scholar The early studies laid some of the groundwork for a WCI, but a polar venue, a more memorable term, and popularization awaited. Siple was a 6-time Antarctic explorer and scientist. At age 19, he was an American Eagle Scout selected from a national contest to accompany Richard E. Byrd, Jr (1888–1957) on his first expedition to Antarctica in 1928 to 1930.7Siple P.A. A Boy Scout with Byrd. GP Putnam’s Sons, New York1931Google Scholar,8Siple P.A. 90° South. The Story of the American South Pole Conquest. GP Putnam’s Sons, New York1959Google Scholar Siple recorded that “the day we felt the cold most was one when the temperature was down fifty-five degrees [F] below zero [-48°C] and there was a wind of twenty miles an hour [32 km·h-1]. One could remain out of doors for only a few minutes.”7Siple P.A. A Boy Scout with Byrd. GP Putnam’s Sons, New York1931Google Scholar These words were an inkling of his future career. On the second Byrd expedition (1933–1935), a member of the ice party keenly portrayed cold conditions as “the real agony of cold comes from the wind” and, more sharply, “like a knife drawn across the face.”9Murphy C.J.V. The lunatic fringe.Byrd RE. Discovery. The Story of the Second Byrd Antarctic Expedition. GP Putnam’s Sons, New York1935Google Scholar Siple deemed it radically different from his previous trip to now be a supply officer and group leader, participate in biology experiments, head a 77-d exploration studying geology, glaciology, and biology, and have findings published in his name.8Siple P.A. 90° South. The Story of the American South Pole Conquest. GP Putnam’s Sons, New York1959Google Scholar,10South-Pole.comByrd Antarctic Expedition II 1933-35.https://www.south-pole.com/p0000108.htmDate accessed: March 12, 2021Google Scholar,11Siple P.A. The Second Byrd Antarctic Expedition-Botany. I. Ecology and geographical distribution.Ann Missouri Bot Gard. 1938; 25 (Available at:): 467-514https://www.biodiversitylibrary.org/page/16046974#page/477/mode/1upDate accessed: March 12, 2021Crossref Google Scholar Afterward, he earned a doctorate in geography. Siple’s naming of the “wind-chill index” and the rudimentary first formula is found in his unpublished dissertation of 1939.12Siple PA. Adaptation of the explorer to the climate of Antarctica. Parts 1, 2, 3. 1939. pp 1–525. Unpublished dissertation, Clark University Goddard LibraryGoogle Scholar It was only occasionally cited, and few details were published even by Siple himself.2Siple P.A. Passel C.F. Measurements of dry atmospheric cooling in subfreezing temperatures.Proc Am Philos Soc. 1945; 89: 177-199Google Scholar The 1939 WCI was produced by simply multiplying the temperature in degrees below zero Celsius by wind speed (in m·s-1) and correlating the resultant product with the risks of cold outdoor travel. The results were chosen to be unitless, and the formula would never be so plain again. There had not been a known request for the dissertation until the time of this writing, according to the resource sharing librarian of Clark University Goddard Library (K Stebbins, October, 2020; personal communication). More features of Siple’s early work are provided here. Near the conclusion of this paper is an adaptation of Siple’s original work that shows a remarkable comparison of the 1939 WCI to a current WCT chart with its times-to-frostbite data. Charles Passel (1915–2002) was a sedimentary paleontologist on the US Antarctic Expedition of 1939 to 1941, on which Siple was West Base leader. Passel went south to look for fossils in particular during 87 d of exploring by dogsled to map mountains. His contemporaneous diary An Antarctic Journal initially was limited to 200 personal copies and was not published until 1995 as the book Ice.13Ice. The Antarctic diary of Charles F. Passel. Lubbock. Texas Tech Univ Press, Texas1995Google Scholar Siple’s 90° South is not a diary but an autobiographical memoir emphasizing his later trips to Antarctica.8Siple P.A. 90° South. The Story of the American South Pole Conquest. GP Putnam’s Sons, New York1959Google Scholar Passel recalled in an interview that expedition meteorologist Arnold Court was occupied with collecting radiosonde data, so Passel was asked to help with a new experiment.14Passel C. Goerler R. Byrd polar research center archival program, Feb 13–14, 2000.https://kb.osu.edu/bitstream/handle/1811/6040/passelfinaltranscript.pdf?sequence=1&isAllowed=yDate accessed: March 12, 2021Google Scholar Passel attributed to Siple “the wind chill index and the background for his interest in the subject.”13Ice. The Antarctic diary of Charles F. Passel. Lubbock. Texas Tech Univ Press, Texas1995Google Scholar,14Passel C. Goerler R. Byrd polar research center archival program, Feb 13–14, 2000.https://kb.osu.edu/bitstream/handle/1811/6040/passelfinaltranscript.pdf?sequence=1&isAllowed=yDate accessed: March 12, 2021Google Scholar Returning home in 1941, Passel used his own Antarctic material for a master’s degree in geology and served in the US Marine Corps. Siple and Passel’s experiments in Antarctica in 1940 made correlations “between atmospheric cooling rates and states of human comfort.”2Siple P.A. Passel C.F. Measurements of dry atmospheric cooling in subfreezing temperatures.Proc Am Philos Soc. 1945; 89: 177-199Google Scholar Final publication of their landmark 1945 paper was much delayed by the events of December 1941. During World War II, Captain Siple evaluated cold-weather clothing and later joined the US Army Office of Research and Development as a civilian scientist.8Siple P.A. 90° South. The Story of the American South Pole Conquest. GP Putnam’s Sons, New York1959Google Scholar,15Siple P.A. General principles governing selection of clothing for cold climates. In: Reports on scientific results of the United States Antarctic Service Expedition, 1939–1941.Proc Am Philos Soc. 1945; 89: 200-234Google Scholar Siple devoted 26 pages in his dissertation to the Antarctic clothing of his era and in 1945 published an extensive paper on selection of winter clothing and gear that was supplementary to the WCI paper.12Siple PA. Adaptation of the explorer to the climate of Antarctica. Parts 1, 2, 3. 1939. pp 1–525. Unpublished dissertation, Clark University Goddard LibraryGoogle Scholar,15Siple P.A. General principles governing selection of clothing for cold climates. In: Reports on scientific results of the United States Antarctic Service Expedition, 1939–1941.Proc Am Philos Soc. 1945; 89: 200-234Google Scholar Modern materials have solved some of the problems of the older clothing. Siple’s last trip to Antarctica began in 1956 at the US Amundsen-Scott South Pole Station as the inaugural science leader of the International Geophysical Year (IGY) 1957–1958. The history of the WCIs and WCTs continues forward from the 1940s with a return to Siple’s 1939 WCI after that. Leading up to the 1940/1945 study, Siple was aware of thermogenesis, insulation values of subcutaneous tissues, vasoconstriction, individual variability, and more, but early in his career he added a disclaimer that physiology textbooks should be consulted. He recognized that his original qualitative 1939 WCI represented “a real factor of climatic sensible temperatures to a certain extent, although it may not indicate the exact proportion of cooling effect. To calculate or measure the true cooling effect would entail a cumbersome process and would probably not give a much better picture of true wind-chill.”12Siple PA. Adaptation of the explorer to the climate of Antarctica. Parts 1, 2, 3. 1939. pp 1–525. Unpublished dissertation, Clark University Goddard LibraryGoogle Scholar This would prove to be a substantial understatement. He wrote that any scale needed to limit complicating factors such as humidity and solar gain. These were conveniently avoided in the dark and dry dead of Antarctic winter. Siple noted that the effects of insensible losses and clothing could be addressed in later corrections.2Siple P.A. Passel C.F. Measurements of dry atmospheric cooling in subfreezing temperatures.Proc Am Philos Soc. 1945; 89: 177-199Google Scholar With knowledge of chamber experiments by the John B. Pierce Hygiene Laboratories and others, he and Passel proceeded in 1940 to quantitatively perform the carefully described “measurement of dry atmospheric cooling in subfreezing temperatures."2Siple P.A. Passel C.F. Measurements of dry atmospheric cooling in subfreezing temperatures.Proc Am Philos Soc. 1945; 89: 177-199Google Scholar They would opine that, with a limited library in Antarctica, their methodology was not biased by knowledge of all previous studies.2Siple P.A. Passel C.F. Measurements of dry atmospheric cooling in subfreezing temperatures.Proc Am Philos Soc. 1945; 89: 177-199Google Scholar Siple set aside his elementary 1939 WCI in part because it did not actually measure heat loss.2Siple P.A. Passel C.F. Measurements of dry atmospheric cooling in subfreezing temperatures.Proc Am Philos Soc. 1945; 89: 177-199Google Scholar,8Siple P.A. 90° South. The Story of the American South Pole Conquest. GP Putnam’s Sons, New York1959Google Scholar Instead, in 1940 he constructed a “relative comfort thermometer” on a 10-m pole, stating that “I set up an experiment to try to measure the rate in time it took a small cylinder of water to freeze. Charlie Passel helped me measure accurately the exact length of time that the cylinder remained at the freezing point while it was letting up its heat of crystallization under nearly 100 different combinations of wind velocity and temperature.”8Siple P.A. 90° South. The Story of the American South Pole Conquest. GP Putnam’s Sons, New York1959Google Scholar An anemometer recorded wind speed. Rather than a thermometer, a thermohm measured water and ice temperature by changes in electrical resistance through a platinum wire in the cylinder. A separate naked thermohm measured ambient air temperature. From observational “runs” at different temperatures and wind speeds made in the dark Antarctic winter in the absence of insolation (solar radiation) and ignoring any effects of evaporation or other factors, the data were recorded.2Siple P.A. Passel C.F. Measurements of dry atmospheric cooling in subfreezing temperatures.Proc Am Philos Soc. 1945; 89: 177-199Google Scholar Siple and Passel measured the cooling rate of water freezing into ice in the cylinder, with attention to the time water remained at 0°C while freezing and giving up its heat of fusion. By knowing this property, time, the mass of water, and surface area, they calculated the SP 1945 WCI in units of kcal·m-2·h-1.2Siple P.A. Passel C.F. Measurements of dry atmospheric cooling in subfreezing temperatures.Proc Am Philos Soc. 1945; 89: 177-199Google Scholar The typically 3- or 4-digit WCI figure was neither a temperature nor did it resemble a temperature like the later WCTs. It needed a clinical relationship to have practical use. The inanimate test cylinder had no feelings, so the physics-based values correlated the cold sensations or manifestations of field parties with various wind and temperature combinations. For example, the SP 1945 WCI paper’s Table 5 includes times elapsed to sudden pain and blanching of the cheek, known as frostnip.16McIntosh S.E. Freer L. Grissom C. Auerbach P. Rodway G. Cochran A. et al.Wilderness Medical Society practice guidelines for the prevention and treatment of frostbite: 2019 update.Wilderness Environ Med. 2019; 30: S19-S32Abstract Full Text Full Text PDF PubMed Scopus (18) Google Scholar Table 7 has a column of WCI numbers indexed with clinical descriptors in a second column. Table 7 is not titled as a wind-chill chart but as “stages of relative human comfort and environmental effects of atmospheric cooling.”2Siple P.A. Passel C.F. Measurements of dry atmospheric cooling in subfreezing temperatures.Proc Am Philos Soc. 1945; 89: 177-199Google Scholar The SP 1945 WCI values range from 0 to 100 (“nude sun-bathing possible”) to 2600, including 2300 where “exposed areas of face will freeze within less than 1/2 minute.”2Siple P.A. Passel C.F. Measurements of dry atmospheric cooling in subfreezing temperatures.Proc Am Philos Soc. 1945; 89: 177-199Google Scholar A later reading of 3290 at the South Pole by Siple during the IGY in 1957 indicates “little chance for lengthy survival.”8Siple P.A. 90° South. The Story of the American South Pole Conquest. GP Putnam’s Sons, New York1959Google Scholar Another example from the SP 1945 WCI Table 7 is a reading of 2000, signifying that “travel and living in temporary shelter becomes dangerous.”2Siple P.A. Passel C.F. Measurements of dry atmospheric cooling in subfreezing temperatures.Proc Am Philos Soc. 1945; 89: 177-199Google Scholar That closely echoes the words in Siple’s different scale of 1939, where 500 indicates “conditions dangerous for travel or temporary shelter.” As of 1945, there were 2 indices. One was the uncomplicated practical scale of 1939 still popular with the Antarctic services.2Siple P.A. Passel C.F. Measurements of dry atmospheric cooling in subfreezing temperatures.Proc Am Philos Soc. 1945; 89: 177-199Google Scholar,8Siple P.A. 90° South. The Story of the American South Pole Conquest. GP Putnam’s Sons, New York1959Google Scholar The other was the physics-based SP 1945 WCI.2Siple P.A. Passel C.F. Measurements of dry atmospheric cooling in subfreezing temperatures.Proc Am Philos Soc. 1945; 89: 177-199Google Scholar The preliminary 1940 table of results made its way into polar, military, and climatology usage and publications.14Passel C. Goerler R. Byrd polar research center archival program, Feb 13–14, 2000.https://kb.osu.edu/bitstream/handle/1811/6040/passelfinaltranscript.pdf?sequence=1&isAllowed=yDate accessed: March 12, 2021Google Scholar,17Court A. Wind chill.Bull Am Meteorol Soc. 1948; 29: 487-493Crossref Google Scholar The final form was published in 1945 and used for decades. Pragmatic rules of thumb were also commonplace. For example, military personnel in Alaska in 1964 were taught the “rule of 30s.” At -30°F (-34°C) with a wind speed of 30 mph (13 m·s-1), there was risk of frostbite in 30 s according to a former US Army Specialist 4 (I. Coddington, December, 2020; personal communication). In 1948, the aforementioned meteorologist Court focused on wind chill, stating that “no precise explanation or critical discussion of it and its method of computation has heretofore appeared.”17Court A. Wind chill.Bull Am Meteorol Soc. 1948; 29: 487-493Crossref Google Scholar Despite working with Siple in Antarctica in 1940, Court cited only the 1939 WCI but did not mention the graphs and tables. Instead, he focused on the physics-based SP 1945 WCI work, disagreed with the units, and rightly noted that the method did not consider the complex ways the human body exchanged heat with its surroundings. Court did compliment the study as the first performed at such low temperatures.17Court A. Wind chill.Bull Am Meteorol Soc. 1948; 29: 487-493Crossref Google Scholar In a discussion section accompanying a 1951 report of 35 indoor workers’ subjective sensations of the outdoors of Saskatchewan, Court audaciously declared that an objective numerical indicator would someday make such subjectivity unnecessary.18Currie B.W. Sensations isopleths on a wind-temperature diagram for winter weather on the Canadian prairies.Bull Am Meteorol Soc. 1951; 32: 371-374Crossref Google Scholar In 1960, as displeasure with the SP 1945 WCI units continued, Siple recommended that the index be used “just as numbers,” perhaps harkening back to what his 1939 WCI plainly did.19Siple P. An evaluation of windchill - conference discussion. Molnar G.in: Horvath S.M. Cold injury. Transactions of the Sixth Conference. Josiah Macy Jr. Foundation, New York1960: 216-218Google Scholar,20Osczevski R. The basis of wind chill.Arctic. 1995; 48: 372-382Crossref Google Scholar He continued defensively: “looking back, we perhaps made a rather too naive approach, and we may have made assumptions which were a little careless. From the practical standpoint, I think we evolved a schema that has been of some use.”19Siple P. An evaluation of windchill - conference discussion. Molnar G.in: Horvath S.M. Cold injury. Transactions of the Sixth Conference. Josiah Macy Jr. Foundation, New York1960: 216-218Google Scholar It was useful, but modifications would come. The portrayal of the cooling effect of the wind would eventually be changed from the WCI to a different type of index that was more intuitively understood by regular users as a “feels like” temperature. Equivalent temperatures have been used for years to express various environmental conditions, but in the context here, WCTs are mathematically computed colder temperature-like figures at which the cooling effect of the wind and cold on the exposed dry face is the same as if wind is not present.1US Department of Commerce/National Oceanic and Atmospheric AdministrationOffice of the Federal Coordinator of Meteorological Services and Supporting Research. FCM- R19-2003. Report on wind chill temperature and extreme heat indices: evaluation and improvement projects.http://solberg.snr.missouri.edu/gcc/OFCMWindchillReport.pdfDate accessed: March 12, 2021Google Scholar,20Osczevski R. The basis of wind chill.Arctic. 1995; 48: 372-382Crossref Google Scholar,21Kessler E. Wind chill errors.Bull Am Meteorol Soc. 1993; 74: 1743-1744Crossref Google Scholar The US Department of Defense has long been interested in developing operational thermal indices.1US Department of Commerce/National Oceanic and Atmospheric AdministrationOffice of the Federal Coordinator of Meteorological Services and Supporting Research. FCM- R19-2003. Report on wind chill temperature and extreme heat indices: evaluation and improvement projects.http://solberg.snr.missouri.edu/gcc/OFCMWindchillReport.pdfDate accessed: March 12, 2021Google Scholar In 1961, the US Army Armored Medical Research Laboratory (AMRL) at Fort Knox, Kentucky, consolidated with other laboratories into what is now USARIEM at Natick, Massachusetts. The AMRL’s WCT chart of 1961 was based on the SP 1945 WCI and, despite its unrealistically cold results and awkward design, the AMRL chart was included in a 1963 textbook.22Meteorological measurements.in: Consolazio C.F. Johnson R.E. Pecora L.J. Physiological Measurements of Metabolic Functions in Man. McGraw-Hill, New York1963: 413Google Scholar In 1967, the site of the US Air Force Arctic Aeromedical Laboratory at Ladd AFB, Alaska, became the Arctic Medical Research Lab, a subsidiary of USARIEM, at US Army Garrison Alaska, Fort Wainwright. A 1965 US Air Force Arctic Aeromedical Laboratory paper by Canadian biophysicist Charles Eagan identified problems with the AMRL WCT chart.23Eagan C. Effect of air movement on atmospheric cooling power.in: Kolb C. Holstrom F. Review of research on military problems in cold regions. Technical documentary report No. AAL-TDR-64-28. US Army Garrison, Alaska, Fort Wainwright: Arctic Aeromedical Laboratory Aerospace, Medical Division, Air Force Systems Command and Arctic Test Center, Test and Evaluation Command. Army Materiel Command, 1964: 147-156Google Scholar His WCT chart, while still based on SP 1945 WCI, had warmer WCTs than the AMRL version. It was much easier to use and, being indexed to degrees of danger, it was a WCTI. The source or formula of the chart in Eagan’s paper was not stated. The US Army printed WCT charts on pocket cards.23Eagan C. Effect of air movement on atmospheric cooling power.in: Kolb C. Holstrom F. Review of research on military problems in cold regions. Technical documentary report No. AAL-TDR-64-28. US Army Garrison, Alaska, Fort Wainwright: Arctic Aeromedical Laboratory Aerospace, Medical Division, Air Force Systems Command and Arctic Test Center, Test and Evaluation Command. Army Materiel Command, 1964: 147-156Google Scholar Eagan would be recognized for his explanation that natural convection around the body produces a “wind” of 0.9 m·s-1 (2 mi·h-1) and that people in the cold outdoors do not stand still but move themselves or their limbs at about 1.8 m·s-1 (4 mi·h-1). Baseline wind velocity necessitated Eagan’s correction of earlier WCTs.23Eagan C. Effect of air movement on atmospheric cooling power.in: Kolb C. Holstrom F. Review of research on military problems in cold regions. Technical documentary report No. AAL-TDR-64-28. US Army Garrison, Alaska, Fort Wainwright: Arctic Aeromedical Laboratory Aerospace, Medical Division, Air Force Systems Command and Arctic Test Center, Test and Evaluation Command. Army Materiel Command, 1964: 147-156Google Scholar,24Bluestein M. An evaluation of the wind chill factor: its development and applicability.J Biomech Engin. 1998; 120: 255-258Crossref PubMed Scopus (27) Google Scholar The definition of walking speed was decreased to 1.3 m·s-1 (3 mi·h-1) in the 2001 WCT revision.1US Department of Commerce/National Oceanic and Atmospheric AdministrationOffice of the Federal Coordinator of Meteorological Services and Supporting Research. FCM- R19-2003. Report on wind chill temperature and extreme heat indices: evaluation and improvement projects.http://solberg.snr.missouri.edu/gcc/OFCMWindchillReport.pdfDate accessed: March 12, 2021Google Scholar In the 1970s, the use of WCTs began to supplant the SP 1945 WCI.1US Department of Commerce/National Oceanic and Atmospheric AdministrationOffice of the Federal Coordinator of Meteorological Services and Supporting Research. FCM- R19-2003. Report on wind chill t
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