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Kevin Raeder
,
Jeffrey L. Anderson
,
Nancy Collins
,
Timothy J. Hoar
,
Jennifer E. Kay
,
Peter H. Lauritzen
, and
Robert Pincus

Abstract

The Community Atmosphere Model (CAM) has been interfaced to the Data Assimilation Research Testbed (DART), a community facility for ensemble data assimilation. This provides a large set of data assimilation tools for climate model research and development. Aspects of the interface to the Community Earth System Model (CESM) software are discussed and a variety of applications are illustrated, ranging from model development to the production of long series of analyses. CAM output is compared directly to real observations from platforms ranging from radiosondes to global positioning system satellites. Such comparisons use the temporally and spatially heterogeneous analysis error estimates available from the ensemble to provide very specific forecast quality evaluations. The ability to start forecasts from analyses, which were generated by CAM on its native grid and have no foreign model bias, contributed to the detection of a code error involving Arctic sea ice and cloud cover. The potential of parameter estimation is discussed. A CAM ensemble reanalysis has been generated for more than 15 yr. Atmospheric forcings from the reanalysis were required as input to generate an ocean ensemble reanalysis that provided initial conditions for decadal prediction experiments. The software enables rapid experimentation with differing sets of observations and state variables, and the comparison of different models against identical real observations, as illustrated by a comparison of forecasts initialized by interpolated ECMWF analyses and by DART/CAM analyses.

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Jason A. Otkin
,
Mark Svoboda
,
Eric D. Hunt
,
Trent W. Ford
,
Martha C. Anderson
,
Christopher Hain
, and
Jeffrey B. Basara

Abstract

Given the increasing use of the term “flash drought” by the media and scientific community, it is prudent to develop a consistent definition that can be used to identify these events and to understand their salient characteristics. It is generally accepted that flash droughts occur more often during the summer owing to increased evaporative demand; however, two distinct approaches have been used to identify them. The first approach focuses on their rate of intensification, whereas the second approach implicitly focuses on their duration. These conflicting notions for what constitutes a flash drought (i.e., unusually fast intensification vs short duration) introduce ambiguity that affects our ability to detect their onset, monitor their development, and understand the mechanisms that control their evolution. Here, we propose that the definition for “flash drought” should explicitly focus on its rate of intensification rather than its duration, with droughts that develop much more rapidly than normal identified as flash droughts. There are two primary reasons for favoring the intensification approach over the duration approach. First, longevity and impact are fundamental characteristics of drought. Thus, short-term events lasting only a few days and having minimal impacts are inconsistent with the general understanding of drought and therefore should not be considered flash droughts. Second, by focusing on their rapid rate of intensification, the proposed “flash drought” definition highlights the unique challenges faced by vulnerable stakeholders who have less time to prepare for its adverse effects.

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Hsi-Yen Ma
,
A. Cheska Siongco
,
Stephen A. Klein
,
Shaocheng Xie
,
Alicia R. Karspeck
,
Kevin Raeder
,
Jeffrey L. Anderson
,
Jiwoo Lee
,
Ben P. Kirtman
,
William J. Merryfield
,
Hiroyuki Murakami
, and
Joseph J. Tribbia

Abstract

The correspondence between mean sea surface temperature (SST) biases in retrospective seasonal forecasts (hindcasts) and long-term climate simulations from five global climate models is examined to diagnose the degree to which systematic SST biases develop on seasonal time scales. The hindcasts are from the North American Multimodel Ensemble, and the climate simulations are from the Coupled Model Intercomparison Project. The analysis suggests that most robust climatological SST biases begin to form within 6 months of a realistically initialized integration, although the growth rate varies with location, time, and model. In regions with large biases, interannual variability and ensemble spread is much smaller than the climatological bias. Additional ensemble hindcasts of the Community Earth System Model with a different initialization method suggest that initial conditions do matter for the initial bias growth, but the overall global bias patterns are similar after 6 months. A hindcast approach is more suitable to study biases over the tropics and subtropics than over the extratropics because of smaller initial biases and faster bias growth. The rapid emergence of SST biases makes it likely that fast processes with time scales shorter than the seasonal time scales in the atmosphere and upper ocean are responsible for a substantial part of the climatological SST biases. Studying the growth of biases may provide important clues to the causes and ultimately the amelioration of these biases. Further, initialized seasonal hindcasts can profitably be used in the development of high-resolution coupled ocean–atmosphere models.

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Eugene S. Takle
,
Christopher J. Anderson
,
Jeffrey Andresen
,
James Angel
,
Roger W. Elmore
,
Benjamin M. Gramig
,
Patrick Guinan
,
Steven Hilberg
,
Doug Kluck
,
Raymond Massey
,
Dev Niyogi
,
Jeanne M. Schneider
,
Martha D. Shulski
,
Dennis Todey
, and
Melissa Widhalm

Abstract

Corn is the most widely grown crop in the Americas, with annual production in the United States of approximately 332 million metric tons. Improved climate forecasts, together with climate-related decision tools for corn producers based on these improved forecasts, could substantially reduce uncertainty and increase profitability for corn producers. The purpose of this paper is to acquaint climate information developers, climate information users, and climate researchers with an overview of weather conditions throughout the year that affect corn production as well as forecast content and timing needed by producers. The authors provide a graphic depicting the climate-informed decision cycle, which they call the climate forecast–decision cycle calendar for corn.

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Robert E. Dickinson
,
Stephen E. Zebiak
,
Jeffrey L. Anderson
,
Maurice L. Blackmon
,
Cecelia De Luca
,
Timothy F. Hogan
,
Mark Iredell
,
Ming Ji
,
Ricky B. Rood
,
Max J. Suarez
, and
Karl E. Taylor

A common modeling infrastructure ad hoc working group evolved from an NSF/NCEP workshop in 1998, in recognition of the need for the climate and weather modeling communities to develop a more organized approach to building the software that underlies modeling and data analyses. With its significant investment of pro bono time, the working group made the first steps in this direction. It suggested standards for model data and model physics and explored the concept of a modeling software framework. An overall software infrastructure would facilitate separation of the scientific and computational aspects of comprehensive models. Consequently, it would allow otherwise isolated scientists to effectively contribute to core U.S. modeling activities, and would provide a larger market to computational scientists and computer vendors, hence encouraging their support.

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David M. Schultz
,
Altuğ Aksoy
,
Jeffrey Anderson
,
Tommaso Benacchio
,
Kristen L. Corbosiero
,
Matthew D. Eastin
,
Clark Evans
,
Jidong Gao
,
Almut Gassman
,
Joshua P. Hacker
,
Daniel Hodyss
,
Matthew R. Kumjian
,
Ron McTaggart-Cowan
,
Glen Romine
,
Paul Roundy
,
Angela Rowe
,
Elizabeth Satterfield
,
Russ S. Schumacher
,
Stan Trier
,
Christopher Weiss
,
Henry P. Huntington
, and
Gary M. Lackmann
Open access
David M. Schultz
,
Jeffrey Anderson
,
Tommaso Benacchio
,
Kristen L. Corbosiero
,
Matthew D. Eastin
,
Clark Evans
,
Jidong Gao
,
Joshua P. Hacker
,
Daniel Hodyss
,
Daryl Kleist
,
Matthew R. Kumjian
,
Ron McTaggart-Cowan
,
Zhiyong Meng
,
Justin R. Minder
,
Derek Posselt
,
Paul Roundy
,
Angela Rowe
,
Michael Scheuerer
,
Russ S. Schumacher
,
Stan Trier
, and
Christopher Weiss
Free access
Edward J. Zipser
,
Cynthia H. Twohy
,
Si-Chee Tsay
,
K. Lee Thornhill
,
Simone Tanelli
,
Robert Ross
,
T. N. Krishnamurti
,
Q. Ji
,
Gregory Jenkins
,
Syed Ismail
,
N. Christina Hsu
,
Robbie Hood
,
Gerald M. Heymsfield
,
Andrew Heymsfield
,
Jeffrey Halverson
,
H. Michael Goodman
,
Richard Ferrare
,
Jason P. Dunion
,
Michael Douglas
,
Robert Cifelli
,
Gao Chen
,
Edward V. Browell
, and
Bruce Anderson

In 2006, NASA led a field campaign to investigate the factors that control the fate of African easterly waves (AEWs) moving westward into the tropical Atlantic Ocean. Aircraft and surface-based equipment were based on Cape Verde's islands, helping to fill some of the data void between Africa and the Caribbean. Taking advantage of the international African Monsoon Multidisciplinary Analysis (AMMA) program over the continent, the NASA-AMMA (NAMMA) program used enhanced upstream data, whereas NOAA aircraft farther west in the Atlantic studied several of the storms downstream. Seven AEWs were studied during AMMA, with at least two becoming tropical cyclones. Some of the waves that did not develop while being sampled near Cape Verde likely intensified in the central Atlantic instead. NAMMA observations were able to distinguish between the large-scale wave structure and the smaller-scale vorticity maxima that often form within the waves. A special complication of the east Atlantic environment is the Saharan air layer (SAL), which frequently accompanies the AEWs and may introduce dry air and heavy aerosol loading into the convective storm systems in the AEWs. One of the main achievements of NAMMA was the acquisition of a database of remote sensing and in situ observations of the properties of the SAL, enabling dynamic models and satellite retrieval algorithms to be evaluated against high-quality real data. Ongoing research with this database will help determine how the SAL influences cloud microphysics and perhaps also tropical cyclogenesis, as well as the more general question of recognizing the properties of small-scale vorticity maxima within tropical waves that are more likely to become tropical cyclones.

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