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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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C. L. Smith
and
A. F. Hasler

Abstract

Low-level, ATS-3 satellite wind estimates are compared with values of wind direction and speed interpolated from analyses based on research aircraft observations of a synoptic tropical wave of moderate intensity on 26 July 1969 during BOMFX. The data were stratified according to whether a satellite estimate was positioned in one of three regions; namely, east or west of the wave trough or north of the disturbance center. When cloud and analysis vector magnitude deviations were computed, regional differences became apparent. These differences are attributed to the physical behavior of the cloud targets tracked under the influence of the surrounding large-scale environment.

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A. Pepler
,
B. Timbal
,
C. Rakich
, and
A. Coutts-Smith

Abstract

The strong relationship between eastern Australian winter–spring rainfall and tropical modes of variability such as the El Niño–Southern Oscillation (ENSO) does not extend to the heavily populated coastal strip east of the Great Dividing Range in southeast Australia, where correlations between rainfall and Niño-3.4 are insignificant during June–October. The Indian Ocean dipole (IOD) is found to have a strong influence on zonal wind flow during the winter and spring months, with positive IOD increasing both onshore winds and rainfall over the coastal strip, while decreasing rainfall elsewhere in southeast Australia. The IOD thus opposes the influence of ENSO over the coastal strip, and this is shown to be the primary cause of the breakdown of the ENSO–rainfall relationship in this region.

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H. Nguyen
,
A. Evans
,
C. Lucas
,
I. Smith
, and
B. Timbal

Abstract

Analysis of the annual cycle of intensity, extent, and width of the Hadley circulation across a 31-yr period (1979–2009) from all existent reanalyses reveals a good agreement among the datasets. All datasets show that intensity is at a maximum in the winter hemisphere and at a minimum in the summer hemisphere. Maximum and minimum values of meridional extent are reached in the respective autumn and spring hemispheres. While considering the horizontal momentum balance, where a weakening of the Hadley cell (HC) is expected in association with a widening, it is shown here that there is no direct relationship between intensity and extent on a monthly time scale.

All reanalyses show an expansion in both hemispheres, most pronounced and statistically significant during summer and autumn at an average rate of expansion of 0.55° decade−1 in each hemisphere. In contrast, intensity trends are inconsistent among the datasets, although there is a tendency toward intensification, particularly in winter and spring.

Correlations between the HC and tropical and extratropical large-scale modes of variability suggest interactions where the extent of the HC is influenced by El Niño–Southern Oscillation (ENSO) and the annular modes. The cells tend to shrink (expand) during the warm (cold) phase of ENSO and during the low (high) phase of the annular modes. Intensity appears to be influenced only by ENSO and only during spring for the southern cell and during winter for the northern cell.

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Steven A. Smith
,
David C. Fritts
, and
Thomas E. Vanzandt

Abstract

The slope and power spectral density of atmospheric velocity fluctuations versus vertical wavenumber at large wavenumber are observed to be nearly independent of altitude. We suggest that such a universality is due to saturation of short vertical-scale fluctuations. A brief review of linear gravity wave saturation theory indicates a physical basis for such spectra. It is demonstrated that observed saturation spectra are not solely due to individually saturated waves but most likely result from amplitude limiting instabilities arising from wave superposition. We also show that while the spectrum is saturated at large wavenumbers, the total kinetic energy per unit mass and the characteristic vertical wavelength increase with altitude. Both of these predictions are consistent with observations.

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C. B. Moore
,
J. R. Smith
, and
A. Gaalswyk

Abstract

In the course of government-sponsored work in the development of the constant-level balloon, the writers supervised many constant-level balloon flights on the standard meteorological surface of 300 millibars. The tracks of these flights are of general meteorological interest, as they are believed to delineate the actual trajectory of an equivalent mass of air travelling on a constant-pressure surface. Some of the original flight data are presented for the information of other investigators of air motion, and to illustrate the application of constant-level balloons to meteorological problems, particularly atmospheric diffusion and the variability of the wind. Suggestions are made regarding the significance of the data presented, and further experiments are proposed which might result in a better understanding of the mechanisms of air motion. Possible applications of constant-level balloons in routine observations, to obtain representative measurements of wind velocity, are set forth.

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M. E. Smith
,
A. P. Hull
, and
C. M. Nagle

Abstract

The continuous release of very small, but detectable amounts of 131I from the Brookhaven Graphite Research Reactor has provided an unusual opportunity for verification of dispersion estimates based on meteorological parameters. Analysis of an entire year's data shows the prediction system to be reliable within a factor of 2, and contains valuable information about such factors as effective stack height, the effectiveness of simplified dispersion models, and the variation of dispersion parameters with season and trajectory.

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S. H. S. Wilson
,
N. C. Atkinson
, and
J. A. Smith

Abstract

The United Kingdom Meteorological Office (UKMO) has developed an airborne interferometer to act as a simulator for future satellite-based infrared meteorological sounders. The Airborne Research Interferometer Evaluation System (ARIES) consists of a modified commercial interferometer mounted on the UKMO C-130 aircraft. The instrument is sensitive to the wavelength range 3.3–18 μm and has a maximum optical path difference of ±1.037 cm. This paper describes the design and performance of ARIES, discusses instrument calibration, and presents some preliminary results. An important problem associated with the use of the new generation of high-spectral resolution infrared meteorological sounders is that improvements need to be made to knowledge of atmospheric spectroscopy and radiative transfer. These improvements are necessary to extract the promised vertical and absolute resolution in temperature and humidity retrievals from these new high-spectral resolution sounders. By virtue of the extensive instrumentation that is available on the C-130 aircraft for observing and measuring the basic meteorological and atmospheric parameters (e.g., in situ temperature, humidity, and ozone), it is hoped that ARIES will be an important tool for use in studying this issue.

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C. B. Moore
,
J. R. Smith
, and
D. A. Church

Abstract

No Abstract Available.

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