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Donald A. Haines

Abstract

Observational evidence from nine crown fires suggests that horizontal roll vortices are a major mechanism in crown-fire spread. Post-burn aerial photography indicates that unburned tree-crown streets are common with crown fire. Investigation of the understory of these crown streets after two fires showed uncharred tree trunks along a center line. This evidence supports a hypothesis of vortex action causing strong downward motion of air along the streets. Additionally, photographs of two ongoing crown fires show apparent horizontal roll vortices. Discussion also includes laboratory and numerical studies in fluid dynamics that may apply to crown fires.

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EARL L. KUEHNAST and DONALD A. HAINES

Abstract

A 1969 Minnesota tornado was photographed by a number of observers at various points along its track. The pictures show an unusual combination of features that might possibly lend visual evidence to theoretical tornado models and such related phenomena as fire whirlwinds.

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DONALD A. HAINES and JAY S. WINSTON

Abstract

Monthly mean values of meridional transport of sensible heat by the atmosphere in the layer 850-500 mb. over the Northern Hemisphere poleward from the subtropics are analyzed for a period of 3½ years. The latitudinal values of this transport exhibit an annual cycle which is characterized by a rapid buildup from August to November and a slightly less rapid decline from February to June. Dissimilarities among the transport patterns for the same calendar months in different years are generally small; however, the month of December has marked variability. The longitudinal makeup of heat transport across latitude 45° N. in the cold season is dominated by three contributing regions which are associated with two of the three major waves observed in monthly mean flow patterns. The most sharply defined region of contribution to the heat transport across latitude 45° N. is associated with cold air moving southward to the rear of the trough line along the east coast of Asia. At 60° N., however, pronounced heat transport zones are generally absent except for the occasional appearance of a maximum over the eastern Atlantic and western Europe.

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Donald A. Haines and Mahlon C. Smith

Abstract

Observation shows that three types of horizontal vortices may form during intense wildland fires. Two of these vortices are longitudinal relative to the ambient wind and the third is transverse. One of the longitudinal types, a vortex pair, occurs with extreme heat and low to moderate wind speeds. It may be a somewhat common structure on the flanks of intense crown firm when burning is concentrated along the fire's perimeter. The second longitudinal type, a single vortex, occurs with high winds and can dominate the entire fire. The third type, the transverse vortex, occurs on the upstream side of the convection column during intense burning and relatively low winds. These vortices are important because they contribute to fire fighter and are a threat to fire fighter safety.

This paper documents field observations of the vortices and supplies supportive meteorological and fuel data. The discussion includes applicable laboratory and conceptual studies in fluid flow and heat transfer that may apply to vortex formation.

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Donald A. Haines and Mahlon C. Smith

Abstract

No abstract available.

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ARTHUR F. KRUEGER, JAY S. WINSTON, and DONALD A. HAINES

Abstract

Computations of atmospheric energy and several of its transformation terms from data extending back to October 1958 have been carried out using the National Meteorological Center's ADP analyses. From these calculations the annual variation of the atmosphere's energy cycle has been estimated. In addition, some yearly differences for the colder half of the year are described.

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