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Jefrey D. Hawkins
and
David W. Stuart

Abstract

Temporal and spatial variations in the structure of the lower atmosphere off Oregon's central coast are studied. The response of the wind and thermal fields to a synoptic-scale realignment aloft that causes a rapid shift from surface southerly to northerly winds is detailed. The effects and importance of the infrequent southerlies on the marine inversion, sea breezes and upwelling is also investigated.

A vast array of meteorological and oceanographic observations were measured by aircraft, land stations, buoys and ships during the first Coastal Upwelling Experiment I (CUE-I). The winds, air and water temperature, and currents from the surface ocean layer to 1.5 km are compared during 16–29 August 1972. The period of southerly surface winds created a warm moist lower atmosphere, weak sea breezes, and brought about a cessation to previous upwelling. In contrast, northerlies and ridging aloft produced a distinct marine inversion, strong sea breezes, and an upwelling event. The marked changes reveal the potential effect summer southerlies have on coastal Oregon's air-sea environment.

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Lee W. Eddington
,
J. J. O'brien
, and
D. W. Stuart

Abstract

A simple nonlinear numerical model of a well-mixed marine layer is used to study topographically forced mesoscale variability off coastal California. The model is used to simulate a persistent wind maximum observed near Point Conception during northwesterly winds. The model also demonstrates the development of a coastally trapped Kelvin wave and a marine-layer eddy when the large-scale forcing is suddenly reduced. The model is a one-layer, two-dimensional, gridpoint model with idealized coastal topography. The model assumes that potential temperature and wind are constant with height in the layer and that the layer is capped by an inversion. Effects of diabatic heating, water vapor, entrainment, and spatial variations of potential temperature are neglected in order to focus on topographic effects. The model solves for the two horizontal components of the marine-layer wind and the marine-layer height.

A comparison of the model results with observations taken near Point Conception during the 1983 OPUS (Organization of Persistent Upwelling Structures) project shows that the model simulates the general features of the observed mesoscale wind maximum. The success is due to the very fine grid size of 3.5 km. The model wind perturbation and along-trajectory acceleration show the effect of the prominent Arguello headland on the marine-layer wind. The northwesterly flow is blocked by the headland on the upwind side, and this causes the marine-layer height to rise there. On the downwind side the northwesterly flow removes mass from the region, and the marine-layer height decreases. This perturbation in the marine-layer height creates a local pressure-gradient force that is responsible for the existence of the wind maximum. The model simulation of the marine-layer height is found to be in agreement with observations in the region.

The model also simulates a solitary atmospheric Kelvin wave crest in the marine layer north of the Arguello headland and a marine layer eddy to the south of the headland when the large-scale forcing is sharply reduced. Model simulation of these phenomena supports the hypothesis that they are coastally trapped marine-layer responses to changes in synoptic-scale forcing.

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Patrick C. Caldwell
,
D. W. Stuart
, and
K. H. Brink

Abstract

Wind variability in a mesoscale region near Point Conception, California is studied. The data base is derived from an array of near-surface meteorological recording stations yielding hourly winds during 51 days from 11 April to 31 May 1983, a transitionary period between seasons.

Temporal variability of each record is examined using variance ellipses, rotary spectra, and complex demodulation. The results reveal large differences between the stations in the offshore or exposed areas compared to the sheltered or coastal areas within the Santa Barbara Channel. Considerable variability with 2–5-day periods occurred in the former region, while diurnal variability dominated the latter area. Also, diurnal fluctuations (sea breezes) were highly dependent upon the synoptic scale state.

Spatial and temporal variability of all records were examined simultaneously by use of complex empirical orthogonal function (CEOF) analysis. Almost 85% of the total variance can be explained by the primary CEOF and this characteristic pattern may be identified with synoptic-scale forcing.

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Mark A. Donelan
,
Fred W. Dobson
,
Stuart D. Smith
, and
Robert J. Anderson

Abstract

The aerodynamic roughness of the sea surface, z 0, is investigated using data from Lake Ontario, from the North Sea near the Dutch coast, and from an exposed site in the Atlantic Ocean off the coast of Nova Scotia. Scaling z 0 by rms wave height gives consistent results for all three datasets, except where wave heights in the Atlantic Ocean are dominated by swell. The normalized roughness depends strongly on wave age: younger waves (traveling slower than the wind) are rougher than mature waves. Alternatively, the roughness may be normalized using the friction velocity, u *, of the wind stress. Again, young waves are rougher than mature waves. This contradicts some recent deductions in the literature, but the contradiction arises from attempts to describe z 0 in laboratory tanks and in the field with a single simple parameterization. Here, it is demonstrated that laboratory waves are inappropriate for direct comparison with field data, being much smoother than their field equivalents. In the open ocean there is usually a mixture of swell and wind-driven sea, and more work is needed before the scaling of surface roughness in these complex conditions can be understood.

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Mark A. Donelan
,
Fred W. Dobson
,
Stuart D. Smith
, and
Robert J. Anderson

Abstract

No abstract available

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Wiebe A. Oost
,
Christopher W. Fairall
,
James B. Edson
,
Stuart D. Smith
,
Robert J. Anderson
,
John A.B. Wills
,
Kristina B. Katsaros
, and
Janice DeCosmo

Abstract

Several methods are examined for correction of turbulence and eddy fluxes in the atmospheric boundary layer, two of them based on a potential-flow approach initiated by Wyngaard. If the distorting object is cylindrical or if the distance to the sensor is much greater than the size of the body, the undisturbed wind stress can be calculated solely from measurements made by the sensor itself; no auxiliary measurements or lengthy model calculations are needed. A more general potential-flow correction has been developed in which distorting objects of complex shape are represented as a number of ellipsoidal elements.

These models are applied to data from three turbulence anemometers with differing amounts of flow distortion, operated simultaneously in the Humidity Exchange over the Sea (HEXOS) Main Experiment. The results are compared with wind-stress estimates by the inertial-dissipation technique; these are much less sensitive to local flow distortion and are consistent with the corrected eddy correlation results. From these comparisons it is concluded that the commonly used “tilt correction” is not sufficient to correct eddy wind stress for distortion by nearby objects, such as probe supports and neighboring sensors.

Neither potential-flow method is applicable to distortion by larger bodies of a scale comparable to the measuring height, such as the superstructure of the Meetpost Noordwijk (MPN) platform used in HEXOS. Flow distortion has been measured around a model of MPN in a wind tunnel study. The results were used to correct mean winds, but simulation of distortion effects on turbulence levels and wind stress turned out not to be feasible.

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M. Susan Lozier
,
Sheldon Bacon
,
Amy S. Bower
,
Stuart A. Cunningham
,
M. Femke de Jong
,
Laura de Steur
,
Brad deYoung
,
Jürgen Fischer
,
Stefan F. Gary
,
Blair J. W. Greenan
,
Patrick Heimbach
,
Naomi P. Holliday
,
Loïc Houpert
,
Mark E. Inall
,
William E. Johns
,
Helen L. Johnson
,
Johannes Karstensen
,
Feili Li
,
Xiaopei Lin
,
Neill Mackay
,
David P. Marshall
,
Herlé Mercier
,
Paul G. Myers
,
Robert S. Pickart
,
Helen R. Pillar
,
Fiammetta Straneo
,
Virginie Thierry
,
Robert A. Weller
,
Richard G. Williams
,
Chris Wilson
,
Jiayan Yang
,
Jian Zhao
, and
Jan D. Zika

Abstract

For decades oceanographers have understood the Atlantic meridional overturning circulation (AMOC) to be primarily driven by changes in the production of deep-water formation in the subpolar and subarctic North Atlantic. Indeed, current Intergovernmental Panel on Climate Change (IPCC) projections of an AMOC slowdown in the twenty-first century based on climate models are attributed to the inhibition of deep convection in the North Atlantic. However, observational evidence for this linkage has been elusive: there has been no clear demonstration of AMOC variability in response to changes in deep-water formation. The motivation for understanding this linkage is compelling, since the overturning circulation has been shown to sequester heat and anthropogenic carbon in the deep ocean. Furthermore, AMOC variability is expected to impact this sequestration as well as have consequences for regional and global climates through its effect on the poleward transport of warm water. Motivated by the need for a mechanistic understanding of the AMOC, an international community has assembled an observing system, Overturning in the Subpolar North Atlantic Program (OSNAP), to provide a continuous record of the transbasin fluxes of heat, mass, and freshwater, and to link that record to convective activity and water mass transformation at high latitudes. OSNAP, in conjunction with the Rapid Climate Change–Meridional Overturning Circulation and Heatflux Array (RAPID–MOCHA) at 26°N and other observational elements, will provide a comprehensive measure of the three-dimensional AMOC and an understanding of what drives its variability. The OSNAP observing system was fully deployed in the summer of 2014, and the first OSNAP data products are expected in the fall of 2017.

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Sarah A. Tessendorf
,
Roelof T. Bruintjes
,
Courtney Weeks
,
James W. Wilson
,
Charles A. Knight
,
Rita D. Roberts
,
Justin R. Peter
,
Scott Collis
,
Peter R. Buseck
,
Evelyn Freney
,
Michael Dixon
,
Matthew Pocernich
,
Kyoko Ikeda
,
Duncan Axisa
,
Eric Nelson
,
Peter T. May
,
Harald Richter
,
Stuart Piketh
,
Roelof P. Burger
,
Louise Wilson
,
Steven T. Siems
,
Michael Manton
,
Roger C. Stone
,
Acacia Pepler
,
Don R. Collins
,
V. N. Bringi
,
M. Thurai
,
Lynne Turner
, and
David McRae

As a response to extreme water shortages in southeast Queensland, Australia, brought about by reduced rainfall and increasing population, the Queensland government decided to explore the potential for cloud seeding to enhance rainfall. The Queensland Cloud Seeding Research Program (QCSRP) was conducted in the southeast Queensland region near Brisbane during the 2008/09 wet seasons. In addition to conducting an initial exploratory, randomized (statistical) cloud seeding study, multiparameter radar measurements and in situ aircraft microphysical data were collected. This comprehensive set of observational platforms was designed to improve the physical understanding of the effects of both ambient aerosols and seeding material on precipitation formation in southeast Queensland clouds. This focus on gaining physical understanding, along with the unique combination of modern observational platforms utilized in the program, set it apart from previous cloud seeding research programs. The overarching goals of the QCSRP were to 1) determine the characteristics of local cloud systems (i.e., weather and climate), 2) document the properties of atmospheric aerosol and their microphysical effects on precipitation formation, and 3) assess the impact of cloud seeding on cloud microphysical and dynamical processes to enhance rainfall. During the course of the program, it became clear that there is great variability in the natural cloud systems in the southeast Queensland region, and understanding that variability would be necessary before any conclusions could be made regarding the impact of cloud seeding. This article presents research highlights and progress toward achieving the goals of the program, along with the challenges associated with conducting cloud seeding research experiments

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Britton B. Stephens
,
Matthew C. Long
,
Ralph F. Keeling
,
Eric A. Kort
,
Colm Sweeney
,
Eric C. Apel
,
Elliot L. Atlas
,
Stuart Beaton
,
Jonathan D. Bent
,
Nicola J. Blake
,
James F. Bresch
,
Joanna Casey
,
Bruce C. Daube
,
Minghui Diao
,
Ernesto Diaz
,
Heidi Dierssen
,
Valeria Donets
,
Bo-Cai Gao
,
Michelle Gierach
,
Robert Green
,
Justin Haag
,
Matthew Hayman
,
Alan J. Hills
,
Martín S. Hoecker-Martínez
,
Shawn B. Honomichl
,
Rebecca S. Hornbrook
,
Jorgen B. Jensen
,
Rong-Rong Li
,
Ian McCubbin
,
Kathryn McKain
,
Eric J. Morgan
,
Scott Nolte
,
Jordan G. Powers
,
Bryan Rainwater
,
Kaylan Randolph
,
Mike Reeves
,
Sue M. Schauffler
,
Katherine Smith
,
Mackenzie Smith
,
Jeff Stith
,
Gregory Stossmeister
,
Darin W. Toohey
, and
Andrew S. Watt

Abstract

The Southern Ocean plays a critical role in the global climate system by mediating atmosphere–ocean partitioning of heat and carbon dioxide. However, Earth system models are demonstrably deficient in the Southern Ocean, leading to large uncertainties in future air–sea CO2 flux projections under climate warming and incomplete interpretations of natural variability on interannual to geologic time scales. Here, we describe a recent aircraft observational campaign, the O2/N2 Ratio and CO2 Airborne Southern Ocean (ORCAS) study, which collected measurements over the Southern Ocean during January and February 2016. The primary research objective of the ORCAS campaign was to improve observational constraints on the seasonal exchange of atmospheric carbon dioxide and oxygen with the Southern Ocean. The campaign also included measurements of anthropogenic and marine biogenic reactive gases; high-resolution, hyperspectral ocean color imaging of the ocean surface; and microphysical data relevant for understanding and modeling cloud processes. In each of these components of the ORCAS project, the campaign has significantly expanded the amount of observational data available for this remote region. Ongoing research based on these observations will contribute to advancing our understanding of this climatically important system across a range of topics including carbon cycling, atmospheric chemistry and transport, and cloud physics. This article presents an overview of the scientific and methodological aspects of the ORCAS project and highlights early findings.

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Leo J. Donner
,
Bruce L. Wyman
,
Richard S. Hemler
,
Larry W. Horowitz
,
Yi Ming
,
Ming Zhao
,
Jean-Christophe Golaz
,
Paul Ginoux
,
S.-J. Lin
,
M. Daniel Schwarzkopf
,
John Austin
,
Ghassan Alaka
,
William F. Cooke
,
Thomas L. Delworth
,
Stuart M. Freidenreich
,
C. T. Gordon
,
Stephen M. Griffies
,
Isaac M. Held
,
William J. Hurlin
,
Stephen A. Klein
,
Thomas R. Knutson
,
Amy R. Langenhorst
,
Hyun-Chul Lee
,
Yanluan Lin
,
Brian I. Magi
,
Sergey L. Malyshev
,
P. C. D. Milly
,
Vaishali Naik
,
Mary J. Nath
,
Robert Pincus
,
Jeffrey J. Ploshay
,
V. Ramaswamy
,
Charles J. Seman
,
Elena Shevliakova
,
Joseph J. Sirutis
,
William F. Stern
,
Ronald J. Stouffer
,
R. John Wilson
,
Michael Winton
,
Andrew T. Wittenberg
, and
Fanrong Zeng

Abstract

The Geophysical Fluid Dynamics Laboratory (GFDL) has developed a coupled general circulation model (CM3) for the atmosphere, oceans, land, and sea ice. The goal of CM3 is to address emerging issues in climate change, including aerosol–cloud interactions, chemistry–climate interactions, and coupling between the troposphere and stratosphere. The model is also designed to serve as the physical system component of earth system models and models for decadal prediction in the near-term future—for example, through improved simulations in tropical land precipitation relative to earlier-generation GFDL models. This paper describes the dynamical core, physical parameterizations, and basic simulation characteristics of the atmospheric component (AM3) of this model. Relative to GFDL AM2, AM3 includes new treatments of deep and shallow cumulus convection, cloud droplet activation by aerosols, subgrid variability of stratiform vertical velocities for droplet activation, and atmospheric chemistry driven by emissions with advective, convective, and turbulent transport. AM3 employs a cubed-sphere implementation of a finite-volume dynamical core and is coupled to LM3, a new land model with ecosystem dynamics and hydrology. Its horizontal resolution is approximately 200 km, and its vertical resolution ranges approximately from 70 m near the earth’s surface to 1 to 1.5 km near the tropopause and 3 to 4 km in much of the stratosphere. Most basic circulation features in AM3 are simulated as realistically, or more so, as in AM2. In particular, dry biases have been reduced over South America. In coupled mode, the simulation of Arctic sea ice concentration has improved. AM3 aerosol optical depths, scattering properties, and surface clear-sky downward shortwave radiation are more realistic than in AM2. The simulation of marine stratocumulus decks remains problematic, as in AM2. The most intense 0.2% of precipitation rates occur less frequently in AM3 than observed. The last two decades of the twentieth century warm in CM3 by 0.32°C relative to 1881–1920. The Climate Research Unit (CRU) and Goddard Institute for Space Studies analyses of observations show warming of 0.56° and 0.52°C, respectively, over this period. CM3 includes anthropogenic cooling by aerosol–cloud interactions, and its warming by the late twentieth century is somewhat less realistic than in CM2.1, which warmed 0.66°C but did not include aerosol–cloud interactions. The improved simulation of the direct aerosol effect (apparent in surface clear-sky downward radiation) in CM3 evidently acts in concert with its simulation of cloud–aerosol interactions to limit greenhouse gas warming.

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