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M. Fuchs
and
C. B. Tanner

Abstract

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M. Fuchs
and
C. B. Tanner

Abstract

A combination formula for evaporation that uses the surface temperature measured by infrared thermometers as a boundary condition is successfully tested against the evaporation obtained from a detailed energy balance and Bowen ratio measurements. The transfer coefficients used in the combination formula are obtained from aerodynamic similarity and include the effect of the diabatic turbulence. Two simple resistive models which attempt to account for the reduction of evaporation due to the water vapor desaturation of the soil surface are analyzed, but fail to describe correctly the transfer processes through the dry upper layer of the soil.

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M. Fuchs
and
C. B. Tanner

Abstract

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S. B. Idso
,
M. Fuchs
, and
C. B. Tanner

Abstract

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Z. E. Gillett
,
H. H. Hendon
,
J. M. Arblaster
,
H. Lin
, and
D. Fuchs

Abstract

Stationary Rossby waves, forced by the Indian Ocean dipole (IOD), have an important role in Southern Hemisphere (SH) weather and climate, including promoting Australian drought and driving Antarctic sea ice variations. However, the dynamics of these teleconnections are not fully understood. During winter, the subtropical jet (STJ) should prohibit continuous propagation of a stationary Rossby wave into the SH extratropics due to the negative meridional gradient of absolute vorticity ( β * ) on its poleward flank. The mechanisms that enable this teleconnection are investigated using observational and reanalysis datasets, a hierarchy of atmospheric model experiments and Rossby wave diagnostics. We conduct 90-member simulations using the Community Atmosphere Model, version 5, with an imposed local diabatic heating anomaly over the eastern Indian Ocean. We find an initial zonal propagation along the STJ waveguide, but after about 10 days, a poleward-arcing wave train appears in the extratropics that has the characteristics of the observed IOD teleconnection. Our results suggest that the Rossby wave can overcome the negative β * barrier by (i) propagating directly poleward in the midtroposphere and thus avoiding this evanescent region in the upper troposphere, (ii) partly propagating directly through this barrier, and (iii) propagating around this barrier farther upstream to the west. A transient eddy feedback, previously postulated to be the key mechanism to allow the stationary Rossby wave to appear on the poleward side of the negative β * region, reinforces the response but is not a requisite, which we confirm through comparison with a simplified linear model.

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Susan C. van den Heever
,
Leah D. Grant
,
Sean W. Freeman
,
Peter J. Marinescu
,
Julie Barnum
,
Jennie Bukowski
,
Eleanor Casas
,
Aryeh J. Drager
,
Brody Fuchs
,
Gregory R. Herman
,
Stacey M. Hitchcock
,
Patrick C. Kennedy
,
Erik R. Nielsen
,
J. Minnie Park
,
Kristen Rasmussen
,
Muhammad Naufal Razin
,
Ryan Riesenberg
,
Emily Riley Dellaripa
,
Christopher J. Slocum
,
Benjamin A. Toms
, and
Adrian van den Heever

Abstract

The intensity of deep convective storms is driven in part by the strength of their updrafts and cold pools. In spite of the importance of these storm features, they can be poorly represented within numerical models. This has been attributed to model parameterizations, grid resolution, and the lack of appropriate observations with which to evaluate such simulations. The overarching goal of the Colorado State University Convective CLoud Outflows and UpDrafts Experiment (C3LOUD-Ex) was to enhance our understanding of deep convective storm processes and their representation within numerical models. To address this goal, a field campaign was conducted during July 2016 and May–June 2017 over northeastern Colorado, southeastern Wyoming, and southwestern Nebraska. Pivotal to the experiment was a novel “Flying Curtain” strategy designed around simultaneously employing a fleet of uncrewed aerial systems (UAS; or drones), high-frequency radiosonde launches, and surface observations to obtain detailed measurements of the spatial and temporal heterogeneities of cold pools. Updraft velocities were observed using targeted radiosondes and radars. Extensive datasets were successfully collected for 16 cold pool–focused and seven updraft-focused case studies. The updraft characteristics for all seven supercell updraft cases are compared and provide a useful database for model evaluation. An overview of the 16 cold pools’ characteristics is presented, and an in-depth analysis of one of the cold pool cases suggests that spatial variations in cold pool properties occur on spatial scales from O(100) m through to O(1) km. Processes responsible for the cold pool observations are explored and support recent high-resolution modeling results.

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Yolande L. Serra
,
Jennifer S. Haase
,
David K. Adams
,
Qiang Fu
,
Thomas P. Ackerman
,
M. Joan Alexander
,
Avelino Arellano
,
Larissa Back
,
Shu-Hua Chen
,
Kerry Emanuel
,
Zeljka Fuchs
,
Zhiming Kuang
,
Benjamin R Lintner
,
Brian Mapes
,
David Neelin
,
David Raymond
,
Adam H. Sobel
,
Paul W. Staten
,
Aneesh Subramanian
,
David W. J. Thompson
,
Gabriel Vecchi
,
Robert Wood
, and
Paquita Zuidema
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Susan C. van den Heever
,
Leah D. Grant
,
Sean W. Freeman
,
Peter J. Marinescu
,
Julie Barnum
,
Jennie Bukowski
,
Eleanor Casas
,
Aryeh J. Drager
,
Brody Fuchs
,
Gregory R. Herman
,
Stacey M. Hitchcock
,
Patrick C. Kennedy
,
Erik R. Nielsen
,
J. Minnie Park
,
Kristen Rasmussen
,
Muhammad Naufal Razin
,
Ryan Riesenberg
,
Emily Riley Dellaripa
,
Christopher J. Slocum
,
Benjamin A. Toms
, and
Adrian van den Heever

Capsule Summary

Exploring convective updrafts and cold pools using novel observational strategies, including a “Flying Curtain” of drones, radiosondes, and surface stations, to characterize cold pool heterogeneities, and targeting updrafts using radiosondes.

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