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Matt C. Wilbanks
,
Sandra E. Yuter
,
Simon P. de Szoeke
,
W. Alan Brewer
,
Matthew A. Miller
,
Andrew M. Hall
, and
Casey D. Burleyson

Abstract

Density currents (i.e., cold pools or outflows) beneath marine stratocumulus clouds are characterized using 30 days of ship-based observations obtained during the 2008 Variability of American Monsoon Systems (VAMOS) Ocean–Cloud–Atmosphere–Land Study Regional Experiment (VOCALS-REx) in the southeast Pacific. An air density increase criterion applied to the Improved Meteorological (IMET) sensor data identified 71 density current front, core (peak density), and tail (dissipating) zones. The similarity in speeds of the mean density current propagation speed (1.8 m s−1) and the mean cloud-level advection relative to the surface layer wind (1.9 m s−1) allowed drizzle cells to deposit elongated density currents in their wakes. Scanning Doppler lidar captured prefrontal updrafts with a mean intensity of 0.91 m s−1 and an average vertical extent of 800 m. Updrafts were often surmounted by low-lying shelf clouds not connected to the overlying stratocumulus cloud. The observed density currents were 5–10 times thinner and weaker than typical continental thunderstorm cold pools. Nearly 90% of density currents were identified when C-band radar estimated areal average rain rates exceeded 1 mm day−1 over a 30-km diameter. Rather than peaking when rain rates were highest overnight, density current occurrence peaks between 0600 and 0800 local solar time when enhanced local drizzle co-occurred with shallow subcloud dry and stable layers. The dry layers may have contributed to density current formation by enhancing subcloud evaporation of drizzle. Density currents preferentially occurred in a large region of predominantly open cells but also occurred in regions of closed cells.

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Pavlos Kollias
,
Eugene E. Clothiaux
,
Thomas P. Ackerman
,
Bruce A. Albrecht
,
Kevin B. Widener
,
Ken P. Moran
,
Edward P. Luke
,
Karen L. Johnson
,
Nitin Bharadwaj
,
James B. Mead
,
Mark A. Miller
,
Johannes Verlinde
,
Roger T. Marchand
, and
Gerald G. Mace
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Eugene E. Clothiaux
,
Kenneth P. Moran
,
Brooks E. Martner
,
Thomas P. Ackerman
,
Gerald G. Mace
,
Taneil Uttal
,
James H. Mather
,
Kevin B. Widener
,
Mark A. Miller
, and
Daniel J. Rodriguez

Abstract

During the past decade, the U.S. Department of Energy (DOE), through the Atmospheric Radiation Measurement (ARM) Program, has supported the development of several millimeter-wavelength radars for the study of clouds. This effort has culminated in the development and construction of a 35-GHz radar system by the Environmental Technology Laboratory (ETL) of the National Oceanic and Atmospheric Administration (NOAA). Radar systems based on the NOAA ETL design are now operating at the DOE ARM Southern Great Plains central facility in central Oklahoma and the DOE ARM North Slope of Alaska site near Barrow, Alaska. Operational systems are expected to come online within the next year at the DOE ARM tropical western Pacific sites located at Manus, Papua New Guinea, and Nauru. In order for these radars to detect the full range of atmospheric hydrometeors, specific modes of operation must be implemented on them that are tuned to accurately detect the reflectivities of specific types of hydrometeors. The set of four operational modes that are currently in use on these radars are presented and discussed. The characteristics of the data produced by these modes of operation are also presented in order to illustrate the nature of the cloud products that are, and will be, derived from them on a continuous basis.

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Peter R. Oke
,
J. S. Allen
,
R. N. Miller
,
G. D. Egbert
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J. A. Austin
,
J. A. Barth
,
T. J. Boyd
,
P. M. Kosro
, and
M. D. Levine

Abstract

Sixty-day simulations of the subinertial continental shelf circulation off Oregon are performed for a hindcast study of summer 1999. Model results are compared with in situ currents, high-frequency radar–derived surface currents, and hydrographic measurements obtained from an array of moored instruments and field surveys. The correlations between observed and modeled alongshore currents and temperatures in water depths of 50 m are in excess of 0.8. A study designed to test the model's sensitivity to different initial stratification, surface forcing, domain size, and river forcing demonstrates that surface heating is important, and that the model results are sensitive to initial stratification. An objective criterion for assessing the skill of a model simulation relative to a control simulation is outlined, providing an objective means for identifying the best model simulation. The model–data comparisons demonstrate that temperature fluctuations off Newport are primarily in response to surface heating and that subsurface density fluctuations are controlled by the wind-forced circulation through salinity. Experiments with river forcing indicate that, in the vicinity of Newport, the Columbia River plume is typically greater than 15 km from the coast and is confined to the top few meters of the water column. Additionally, the model–data comparisons suggest that the strongest upwelling occurs to the north of Newport where the continental shelf is relatively narrow and uniform in the alongshore direction. Part II of this study investigates the modeled three-dimensional circulation and dynamical balances.

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G. L. Stephens
,
R. G. Ellingson
,
J. Vitko Jr.
,
W. Bolton
,
T. P. Tooman
,
F. P. J. Valero
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P. Minnis
,
P. Pilewskie
,
G. S. Phipps
,
S. Sekelsky
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J. R. Carswell
,
S. D. Miller
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A. Benedetti
,
R. B. McCoy
,
R. F. McCoy Jr.
,
A. Lederbuhr
, and
R. Bambha

The U.S. Department of Energy has established an unmanned aerospace vehicle (UAV) measurement program. The purpose of this paper is to describe the evolution of the program since its inception, review the progress of the program, summarize the measurement capabilities developed under the program, illustrate key results from the various UAV campaigns carried out to date, and provide a sense of the future direction of the program. The Atmospheric Radiation Measurement (ARM)–UAV program has demonstrated how measurements from unmanned aircraft platforms operating under the various constraints imposed by different science experiments can contribute to our understanding of cloud and radiative processes. The program was first introduced in 1991 and has evolved in the form of four phases of activity each culminating in one or more flight campaigns. A total of 8 flight campaigns produced over 140 h of science flights using three different UAV platforms. The UAV platforms and their capabilities are described as are the various phases of the program development. Examples of data collected from various campaigns highlight the powerful nature of the observing system developed under the auspices of the ARM–UAV program and confirm the viability of the UAV platform for the kinds of research of interest to ARM and the clouds and radiation community as a whole. The specific examples include applications of the data in the study of radiative transfer through clouds, the evaluation of cloud parameterizations, and the development and evaluation of cloud remote sensing methods. A number of notable and novel achievements of the program are also highlighted.

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J. Teixeira
,
S. Cardoso
,
M. Bonazzola
,
J. Cole
,
A. DelGenio
,
C. DeMott
,
C. Franklin
,
C. Hannay
,
C. Jakob
,
Y. Jiao
,
J. Karlsson
,
H. Kitagawa
,
M. Köhler
,
A. Kuwano-Yoshida
,
C. LeDrian
,
J. Li
,
A. Lock
,
M. J. Miller
,
P. Marquet
,
J. Martins
,
C. R. Mechoso
,
E. v. Meijgaard
,
I. Meinke
,
P. M. A. Miranda
,
D. Mironov
,
R. Neggers
,
H. L. Pan
,
D. A. Randall
,
P. J. Rasch
,
B. Rockel
,
W. B. Rossow
,
B. Ritter
,
A. P. Siebesma
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P. M. M. Soares
,
F. J. Turk
,
P. A. Vaillancourt
,
A. Von Engeln
, and
M. Zhao

Abstract

A model evaluation approach is proposed in which weather and climate prediction models are analyzed along a Pacific Ocean cross section, from the stratocumulus regions off the coast of California, across the shallow convection dominated trade winds, to the deep convection regions of the ITCZ—the Global Energy and Water Cycle Experiment Cloud System Study/Working Group on Numerical Experimentation (GCSS/WGNE) Pacific Cross-Section Intercomparison (GPCI). The main goal of GPCI is to evaluate and help understand and improve the representation of tropical and subtropical cloud processes in weather and climate prediction models. In this paper, a detailed analysis of cloud regime transitions along the cross section from the subtropics to the tropics for the season June–July–August of 1998 is presented. This GPCI study confirms many of the typical weather and climate prediction model problems in the representation of clouds: underestimation of clouds in the stratocumulus regime by most models with the corresponding consequences in terms of shortwave radiation biases; overestimation of clouds by the 40-yr ECMWF Re-Analysis (ERA-40) in the deep tropics (in particular) with the corresponding impact in the outgoing longwave radiation; large spread between the different models in terms of cloud cover, liquid water path and shortwave radiation; significant differences between the models in terms of vertical cross sections of cloud properties (in particular), vertical velocity, and relative humidity. An alternative analysis of cloud cover mean statistics is proposed where sharp gradients in cloud cover along the GPCI transect are taken into account. This analysis shows that the negative cloud bias of some models and ERA-40 in the stratocumulus regions [as compared to the first International Satellite Cloud Climatology Project (ISCCP)] is associated not only with lower values of cloud cover in these regimes, but also with a stratocumulus-to-cumulus transition that occurs too early along the trade wind Lagrangian trajectory. Histograms of cloud cover along the cross section differ significantly between models. Some models exhibit a quasi-bimodal structure with cloud cover being either very large (close to 100%) or very small, while other models show a more continuous transition. The ISCCP observations suggest that reality is in-between these two extreme examples. These different patterns reflect the diverse nature of the cloud, boundary layer, and convection parameterizations in the participating weather and climate prediction models.

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N. L. Miller
,
A. W. King
,
M. A. Miller
,
E. P. Springer
,
M. L. Wesely
,
K. E. Bashford
,
M. E. Conrad
,
K. Costigan
,
P. N. Foster
,
H. K. Gibbs
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J. Jin
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J. Klazura
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B. M. Lesht
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M. V. Machavaram
,
F. Pan
,
J. Song
,
D. Troyan
, and
R. A. Washington-Allen

A Department of Energy (DOE) multilaboratory Water Cycle Pilot Study (WCPS) investigated components of the local water budget at the Walnut River watershed in Kansas to study the relative importance of various processes and to determine the feasibility of observational water budget closure. An extensive database of local meteorological time series and land surface characteristics was compiled. Numerical simulations of water budget components were generated and, to the extent possible, validated for three nested domains within the Southern Great Plains—the Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) Cloud Atmospheric Radiation Testbed (CART), the Walnut River watershed (WRW), and the Whitewater watershed (WW), in Kansas.

A 2-month intensive observation period (IOP) was conducted to gather extensive observations relevant to specific details of the water budget, including finescale precipitation, streamflow, and soil moisture measurements that were not made routinely by other programs. Event and seasonal water isotope (d18O, dD) sampling in rainwater, streams, soils, lakes, and wells provided a means of tracing sources and sinks within and external to the WW, WRW, and the ARM CART domains. The WCPS measured changes in the leaf area index for several vegetation types, deep groundwater variations at two wells, and meteorological variables at a number of sites in the WRW. Additional activities of the WCPS include code development toward a regional climate model that includes water isotope processes, soil moisture transect measurements, and water-level measurements in groundwater wells.

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B. L. Weber
,
D. B. Wuertz
,
R. G. Strauch
,
D. A. Merritt
,
K. P. Moran
,
D. C. Law
,
D. van de Kamp
,
R. B. Chadwick
,
M. H. Ackley
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M. F. Barth
,
N. L. Abshire
,
P. A. Miller
, and
T. W. Schlatter

Abstract

The first wind profiler for a demonstration network of wind profilers recently passed the milestone of 300 h of continuous operation. The horizontal wind component measurements taken during that period are compared with the WPL Platteville wind profiler and the NWS Denver rawinsonde. The differences between the network and WPL wind profilers have standard deviations of 2.30 m s−1 and 2.16 m s−1 for the u- and v-components, respectively. However, the WPL wind profiler ignores vertical velocity, whereas the network radar measures it and removes its effects from the u- and v-component measurements. The differences between the network wind profiler and the NWS rawinsonde (separated spatially by about 50 km) have standard deviations of 3.65 m s−1 and 3.06 m s−1 for the u- and v-components, respectively. These results are similar to those found in earlier comparison studies. Finally, the new network wind profiler demonstrates excellent sensitivity, consistently reporting measurements at all heights msl from 2 to nearly 18 km with very few outages.

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R. E. Carbone
,
F. I. Harris
,
P. H. Hildebrand
,
R. A. Kropfli
,
L. J. Miller
,
W. Moninger
,
R. G. Strauch
,
R. J. Doviak
,
K. W. Johnson
,
S. P. Nelson
,
P. S. Ray
, and
M. Gilet
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Theodore M. McHardy
,
James R. Campbell
,
David A. Peterson
,
Simone Lolli
,
Anne Garnier
,
Arunas P. Kuciauskas
,
Melinda L. Surratt
,
Jared W. Marquis
,
Steven D. Miller
,
Erica K. Dolinar
, and
Xiquan Dong

Abstract

This study develops a new thin cirrus detection algorithm applicable to overland scenes. The methodology builds from a previously developed overwater algorithm, which makes use of the Geostationary Operational Environmental Satellite 16 (GOES-16) Advanced Baseline Imager (ABI) channel 4 radiance (1.378-μm “cirrus” band). Calibration of this algorithm is based on coincident Cloud–Aerosol Lidar with Orthogonal Polarization (CALIOP) cloud profiles. Emphasis is placed on rejection of false detections that are more common in overland scenes. Clear-sky false alarm rates over land are examined as a function of precipitable water vapor (PWV), showing that nearly all pixels having a PWV of <0.4 cm produce false alarms. Enforcing an above-cloud PWV minimum threshold of ∼1 cm ensures that most low-/midlevel clouds are not misclassified as cirrus by the algorithm. Pixel-filtering based on the total column PWV and the PWV for a layer between the top of the atmosphere (TOA) and a predetermined altitude H removes significant land surface and low-/midlevel cloud false alarms from the overall sample while preserving over 80% of valid cirrus pixels. Additionally, the use of an aggressive PWV layer threshold preferentially removes noncirrus pixels such that the remaining sample is composed of nearly 70% cirrus pixels, at the cost of a much-reduced overall sample size. This study shows that lower-tropospheric clouds are a much more significant source of uncertainty in cirrus detection than the land surface.

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