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  • Author or Editor: Erland Källén x
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Nedjeljka Žagar
,
John Boyd
,
Akira Kasahara
,
Joseph Tribbia
,
Erland Källén
,
Hiroshi Tanaka
, and
Jun-ichi Yano
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Ad Stoffelen
,
Jean Pailleux
,
Erland Källén
,
J. Michael Vaughan
,
Lars Isaksen
,
Pierre Flamant
,
Werner Wergen
,
Erik Andersson
,
Harald Schyberg
,
Alain Culoma
,
Roland Meynart
,
Martin Endemann
, and
Paul Ingmann

The prime aim of the Atmospheric Dynamics Mission is to demonstrate measurements of vertical wind profiles from space. Extensive studies conducted by the European Space Agency over the past 15 years have culminated in the selection of a high-performance Doppler wind lidar based on direct-detection interferometric techniques. Such a system, with a pulsed laser operating at 355-nm wavelength, would utilize both Rayleigh scattering from molecules and Mie scattering from thin cloud and aerosol particles; measurement of the residual Doppler shift from successive levels in the atmosphere provides the vertical wind profiles. The lidar would be accommodated on a satellite flying in a sun-synchronous orbit, at an altitude of ~400 km, providing near-global coverage; target date for launch is in 2007. Processing of the backscatter signals will provide about 3000 globally distributed wind profiles per day, above thick clouds or down to the surface in clear air, at typically 200-km separation along the satellite track. Such improved knowledge of the global wind field is crucial to many aspects of climate research and weather prediction. Knowledge over large parts of the Tropics and major oceans is presently quite incomplete—leading to major difficulties in studying key processes in the climate system and in improving numerical simulations and predictions; progress in climate modeling is indeed intimately linked to progress in numerical weather prediction. The background studies, potential impact on climate and weather prediction, choice of measurement specifications, and the lidar technology are discussed.

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Ad Stoffelen
,
Angela Benedetti
,
Régis Borde
,
Alain Dabas
,
Pierre Flamant
,
Mary Forsythe
,
R. Michael Hardesty
,
Lars Isaksen
,
Erland Källén
,
Heiner Körnich
,
Tsengdar Lee
,
Oliver Reitebuch
,
Michael Rennie
,
Lars-Peter Riishøjgaard
,
Harald Schyberg
,
Anne Grete Straume
, and
Michael Vaughan
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Ghassem Asrar
,
Sandrine Bony
,
Olivier Boucher
,
Antonio Busalacchi
,
Anny Cazenave
,
Mark Dowell
,
Greg Flato
,
Gabi Hegerl
,
Erland Källén
,
Teruyuki Nakajima
,
Alain Ratier
,
Roger Saunders
,
Julia Slingo
,
Byung-Ju Sohn
,
Johannes Schmetz
,
Bjorn Stevens
,
Peiqun Zhang
, and
Francis Zwiers
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Mark J Rodwell
,
Linus Magnusson
,
Peter Bauer
,
Peter Bechtold
,
Massimo Bonavita
,
Carla Cardinali
,
Michail Diamantakis
,
Paul Earnshaw
,
Antonio Garcia-Mendez
,
Lars Isaksen
,
Erland Källén
,
Daniel Klocke
,
Philippe Lopez
,
Tony McNally
,
Anders Persson
,
Fernando Prates
, and
Nils Wedi

Medium-range weather prediction has become more skillful over recent decades, but forecast centers still suffer from occasional very poor forecasts, which are often referred to as “dropouts” or “busts.” This study focuses on European Centre for Medium-Range Weather Forecasts (ECMWF) day-6 forecasts for Europe. Although busts are defined by gross scores, bust composites reveal a coherent “Rex type” blocking situation, with a high over northern Europe and a low over the Mediterranean. Initial conditions for these busts also reveal a coherent flow, but this is located over North America and involves a trough over the Rockies, with high convective available potential energy (CAPE) to its east. This flow type occurs in spring and is often associated with a Rossby wave train that has crossed the Pacific. A composite on this initial flow type displays enhanced day-6 random forecast errors and some-what enhanced ensemble forecast spread, indicating reduced inherent predictability.

Mesoscale convective systems, associated with the high levels of CAPE, act to slow the motion of the trough. Hence, convection errors play an active role in the busts. The subgrid-scale nature of convection highlights the importance of the representation of model uncertainty in probabilistic forecasts. The cloud and extreme conditions associated with mesoscale convective systems also reduce the availability and utility of observations provided to the data assimilation.

A question of relevance to the wider community is, do we have observations with sufficient accuracy to better constrain the important error structures in the initial conditions? Meanwhile, improvements to ensemble prediction systems should help us better predict the increase in forecast uncertainty.

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Ad Stoffelen
,
Angela Benedetti
,
Régis Borde
,
Alain Dabas
,
Pierre Flamant
,
Mary Forsythe
,
Mike Hardesty
,
Lars Isaksen
,
Erland Källén
,
Heiner Körnich
,
Tsengdar Lee
,
Oliver Reitebuch
,
Michael Rennie
,
Lars-Peter Riishøjgaard
,
Harald Schyberg
,
Anne Grete Straume
, and
Michael Vaughan

Abstract

The Aeolus mission objectives are to improve numerical weather prediction (NWP) and enhance the understanding and modeling of atmospheric dynamics on global and regional scale. Given the first successes of Aeolus in NWP, it is time to look forward to future vertical wind profiling capability to fulfill the rolling requirements in operational meteorology. Requirements for wind profiles and information on vertical wind shear are constantly evolving. The need for high-quality wind and profile information to capture and initialize small-amplitude, fast-evolving, and mesoscale dynamical structures increases, as the resolution of global NWP improved well into the 3D turbulence regime on horizontal scales smaller than 500 km. In addition, advanced requirements to describe the transport and dispersion of atmospheric constituents and better depict the circulation on climate scales are well recognized. Direct wind profile observations over the oceans, tropics, and Southern Hemisphere are not provided by the current global observing system. Looking to the future, most other wind observation techniques rely on cloud or regions of water vapor and are necessarily restricted in coverage. Therefore, after its full demonstration, an operational Aeolus-like follow-on mission obtaining globally distributed wind profiles in clear air by exploiting molecular scattering remains unique.

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Ad Stoffelen
,
Angela Benedetti
,
Régis Borde
,
Alain Dabas
,
Pierre Flamant
,
Mary Forsythe
,
R. Michael Hardesty
,
Lars Isaksen
,
Erland Källén
,
Heiner Körnich
,
Tsengdar Lee
,
Oliver Reitebuch
,
Michael Rennie
,
Lars-Peter Riishøjgaard
,
Harald Schyberg
,
Anne Grete Straume
, and
Michael Vaughan
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Wayman E. Baker
,
Robert Atlas
,
Carla Cardinali
,
Amy Clement
,
George D. Emmitt
,
Bruce M. Gentry
,
R. Michael Hardesty
,
Erland Källén
,
Michael J. Kavaya
,
Rolf Langland
,
Zaizhong Ma
,
Michiko Masutani
,
Will McCarty
,
R. Bradley Pierce
,
Zhaoxia Pu
,
Lars Peter Riishojgaard
,
James Ryan
,
Sara Tucker
,
Martin Weissmann
, and
James G. Yoe

The three-dimensional global wind field is the most important remaining measurement needed to accurately assess the dynamics of the atmosphere. Wind information in the tropics, high latitudes, and stratosphere is particularly deficient. Furthermore, only a small fraction of the atmosphere is sampled in terms of wind profiles. This limits our ability to optimally specify initial conditions for numerical weather prediction (NWP) models and our understanding of several key climate change issues.

Because of its extensive wind measurement heritage (since 1968) and especially the rapid recent technology advances, Doppler lidar has reached a level of maturity required for a space-based mission. The European Space Agency (ESA)'s Atmospheric Dynamics Mission Aeolus (ADM-Aeolus) Doppler wind lidar (DWL), now scheduled for launch in 2015, will be a major milestone.

This paper reviews the expected impact of DWL measurements on NWP and climate research, measurement concepts, and the recent advances in technology that will set the stage for space-based deployment. Forecast impact experiments with actual airborne DWL measurements collected over the North Atlantic in 2003 and assimilated into the European Centre for Medium-Range Weather Forecasts (ECMWF) operational model are a clear indication of the value of lidar-measured wind profiles. Airborne DWL measurements collected over the western Pacific in 2008 and assimilated into both the ECMWF and U.S. Navy operational models support the earlier findings.

These forecast impact experiments confirm observing system simulation experiments (OSSEs) conducted over the past 25–30 years. The addition of simulated DWL wind observations in recent OSSEs performed at the Joint Center for Satellite Data Assimilation (JCSDA) leads to a statistically significant increase in forecast skill.

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