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J. W. Deardorff
and
E. W. Peterson

Abstract

A local interfacial boundary condition between a turbulent and non-turbulent layer is constructed in a manner that allows local entrainment. The Reynolds average of this equation produces a mean boundary-layer growth rate that contains additional terms not heretofore included in boundary-layer growth models. One of these terms represents the net effect of fluctuating horizontal entrainment and can be absorbed into the usual net entrainment term. The other two terms may become important in horizontally inhomogeneous boundary layers: one represents mean horizontal entrainment across an interface which slopes in the mean, and the other is a divergence of a small-scale horizontal flux of boundary-layer height which presumably acts to smooth variations in the mean boundary-layer height.

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E. W. Peterson
and
L. Hasse

Abstract

Possible long-term variations of the Beaufort scale of wind speeds are investigated from frequency distributions of about 300 000 ship observations. Records from the western entrance to the English Channel are taken as representative for observing and coding practices of voluntary weather observing ships. There is some indication that a change of either the Beaufort scale or of the wind climate occurred at the turn of the century. There is also a significant bias of the Beaufort estimates from those ships that carry anemometers.

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Anita D. Rapp
,
Alexander G. Peterson
,
Oliver W. Frauenfeld
,
Steven M. Quiring
, and
E. Brendan Roark

Abstract

Tropical Rainfall Measuring Mission Precipitation Radar precipitation features are analyzed to understand the role of storm characteristics on the seasonal and diurnal cycles of precipitation in four distinct regions in Costa Rica. The distribution of annual rainfall is highly dependent on the stratiform precipitation, driven largely by seasonal increases in stratiform area. The monthly distribution of stratiform rain is bimodal in most regions, but the timing varies regionally and is related to several important large-scale features: the Caribbean low-level jet, the ITCZ, and the Chorro del Occidente Colombiano (CHOCO) jet. The relative importance of convective precipitation increases on the Caribbean side during wintertime cold air surges. Except for the coastal Caribbean domain, most regions show a strong diurnal cycle with an afternoon peak in convection followed by an evening increase in stratiform rain. Along the Caribbean coast, the diurnal cycle is weaker, with evidence of convection associated with the sea breeze, as well as a nocturnal increase in storms. The behavior of extreme precipitation features with rain volume in the 99th percentile is also analyzed. They are most frequent from May to November, with notable differences between features at the beginning/end of the rainy season versus those in the middle, as well as between wet and dry seasons. Convective rain exceeds stratiform in winter and midsummer extreme features, while stratiform rain is larger at the beginning and end of the wet season. Given projected changes in precipitation and extreme events in Costa Rica for future climate change scenarios, the results indicate the importance of understanding both changes in total precipitation and in the storm characteristics.

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David A. Peterson
,
Laura H. Thapa
,
Pablo E. Saide
,
Amber J. Soja
,
Emily M. Gargulinski
,
Edward J. Hyer
,
Bernadett Weinzierl
,
Maximilian Dollner
,
Manuel Schöberl
,
Philippe P. Papin
,
Shobha Kondragunta
,
Christopher P. Camacho
,
Charles Ichoku
,
Richard H. Moore
,
Johnathan W. Hair
,
James H. Crawford
,
Philip E. Dennison
,
Olga V. Kalashnikova
,
Christel E. Bennese
,
Thaopaul P. Bui
,
Joshua P. DiGangi
,
Glenn S. Diskin
,
Marta A. Fenn
,
Hannah S. Halliday
,
Jose Jimenez
,
John B. Nowak
,
Claire Robinson
,
Kevin Sanchez
,
Taylor J. Shingler
,
Lee Thornhill
,
Elizabeth B. Wiggins
,
Edward Winstead
, and
Chuanyu Xu

Abstract

The 2019 Fire Influence on Regional to Global Environments and Air Quality (FIREX-AQ) field experiment obtained a diverse set of in situ and remotely sensed measurements before and during a pyrocumulonimbus (pyroCb) event over the Williams Flats fire in Washington State. This unique dataset confirms that pyroCb activity is an efficient vertical smoke transport pathway into the upper troposphere and lower stratosphere (UTLS). The magnitude of smoke plumes observed in the UTLS has increased significantly in recent years, following unprecedented wildfire and pyroCb activity observed worldwide. The FIREX-AQ pyroCb dataset is therefore extremely relevant to a broad community, providing the first measurements of fresh smoke exhaust in the upper troposphere, including from within active pyroCb cloud tops. High-resolution remote sensing reveals that three plume cores linked to localized fire fronts, burning primarily in dense forest fuels, contributed to four total pyroCb “pulses.” Rapid changes in fire geometry and spatial extent dramatically influenced the magnitude, behavior, and duration of pyroCb activity. Cloud probe measurements and weather radar identify the presence of large ice particles within the pyroCb and hydrometers below cloud base, indicating precipitation development. The resulting feedbacks suggest that vertical smoke transport efficiency was reduced slightly when compared with intense pyroCb events reaching the lower stratosphere. Physical and optical aerosol property measurements in pyroCb exhaust are compared with previous assumptions. A large suite of aerosol and gas-phase chemistry measurements sets a foundation for future studies aimed at understanding the composition of smoke plumes lifted by pyroconvection into the UTLS and their role in the climate system.

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D. J. McNaughton
,
N. E. Bowne
,
R. L. Dennis
,
R. R. Draxler
,
S. R. Hanna
,
T. Palma
,
S. L. Marsh
,
W. T. Pennell
,
R. L. Peterson
,
J. V. Ramsdell
,
S. T. Rao
, and
R. J. Yamartino

The Eighth Joint Conference on Applications of Air Pollution Meteorology with the Air and Waste Management Association was held in conjunction with the AMS 74th Annual Meeting in Nashville, Tennessee, on 23–28 January 1994. Sessions at the meeting covered a broad range of topics including the dispersion environment, meteorology in emissions determination, long-range and mesoscale pollutant transport and fate, meteorology and photochemistry, advanced dispersion models and modeling systems, model evaluation, complex flows affecting dispersion near structures, and coastal and complex terrain issues. Papers followed some recurrent themes but many reported applications of new technology that provide new opportunities to see atmospheric characteristics and complexities for the first time. Innovative techniques were described in data analysis and presentation and modeling.

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