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Neeraj Agarwal
,
Armin Köhl
,
Carlos Roberto Mechoso
, and
Detlaf Stammer

Abstract

The early response of the atmosphere–ocean system to meltwater runoff originating from the Greenland ice sheet is studied using a coupled atmosphere–ocean general circulation model (AOGCM). For this purpose, AOGCM ensemble simulations without and with associated ocean freshening around Greenland are compared. For freshwater perturbations initiated in northern winter, the mean response for the first three months shows the emergence of negative sea surface temperature (SST) anomalies in the Denmark Strait, in association with enhanced oceanic advection by the East Greenland Current. The response also shows negative SST anomalies in the North Atlantic associated with enhanced westerlies at the ocean surface. Additionally, the baroclinic atmospheric cyclonic circulation east of Greenland intensifies, and anticyclonic circulations with equivalent barotropic structures develop over western Europe and the North Pacific Ocean. Simulations by the atmospheric component of the AOGCM indicate that atmosphere–ocean interactions contribute significantly to enhance the response. The sensitivity of the coupled system response to the timing of freshwater perturbation is also studied. For freshwater perturbations initialized in northern summer, the response during the following winter is similar, but stronger in magnitude. In the Northern Hemisphere, the atmospheric response resembles the Arctic Oscillation (AO) mode of variability. The association between anomalies in the Denmark Strait SSTs and in the atmosphere east of Greenland is consistent with that observed during previous great salinity anomaly (GSA) events. The results obtained highlight the importance of atmosphere–ocean interaction in the early climate response to Greenland melting, the teleconnections with the North Pacific and the contribution of GSA events to North Atlantic Oscillation (NAO) variability.

Full access
Weisheng Yang
,
Chuanyu Liu
,
Armin Köhl
,
Jin Wang
,
Xin Wang
, and
Fan Wang

Abstract

Central Pacific (CP) El Niño (i.e., CP El Niño) events have occurred more frequently during recent decades. Wind stress patterns are argued to have significant effects on the generation and evolution of CP El Niño. However, the winds differ in different CP El Niño events, making it hard in previous studies to avoid overgeneralizing the timing and location of the winds that indeed matter. In this study, the theoretically favorable wind perturbations (FWPs) that may warm the Niño-4 region, in terms of their directions, horizontal structures, and bounds, in each month before the peak month (December) of CP El Niños are determined, using an adjoint sensitivity method. The mechanisms of the FWPs are interpreted. Primarily, zonal temperature advection via the equatorial wave–associated velocity anomalies is responsible. In particular, easterly FWPs over the central equatorial Pacific with off-equatorial westerly FWPs (constituting a wind structure with a strong north–south gradient) during the first half year can play a positive role in warming the Niño-4 region and so can the westerly FWPs over the western tropical Pacific, while westerly FWPs in the western-central tropical Pacific in the second half year show higher efficiency. Meanwhile, the particular wind structure of the first half year (i.e., the easterly anomaly over the central equatorial Pacific with strong wind stress curl off the equator) has also been verified to be able to produce a CP-type warming in an intermediate coupled model (ICM); similar wind stress anomalies had been observed in some CP El Niño events. Thus, the FWPs provide helpful guidance in analyzing the generation and evolving processes of the wind-driven CP El Niño.

Restricted access
Chuanyu Liu
,
Xiaowei Wang
,
Zhiyu Liu
,
Armin Köhl
,
William D. Smyth
, and
Fan Wang

Abstract

The origins of an observed weakly sheared nonturbulent (laminar) layer (WSL), and a strongly sheared turbulent layer above the Equatorial Undercurrent core (UCL) in the eastern equatorial Pacific are studied, based mainly on the data from the Tropical Atmosphere and Ocean mooring array. Multiple-time-scale (from 3 to 25 days) equatorial waves were manifested primarily as zonal velocity oscillations with the maximum amplitudes (from 10 to 30 cm s−1) occurring at different depths (from the surface to 85-m depths) above the seasonal thermocline. The subsurface-intensified waves led to vertically out-of-phase shear variations in the upper thermocline via destructive interference with the seasonal zonal flow, opposing the tendency for shear instability. These waves were also associated with depth-dependent, multiple-vertical-scale stratification variations, with phase lags of π/2 or π, further altering stability of the zonal current system to vertical shear. The WSL and UCL were consequently formed by coupling of multiple equatorial waves with differing phases, particularly of the previously identified equatorial mode and subsurface mode tropical instability waves (with central period of 17 and 20 days, respectively, in this study), and subsurface-intensified waves with central periods of 6, 5, and 12 days and velocity maxima at 45-, 87-, and 40-m depths, respectively. In addition, a wave-like feature with periods of 50–90 days enhanced the shear throughout the entire UCL. WSLs and UCLs seem to emerge without a preference for particular tropical instability wave phases. The generation mechanisms of the equatorial waves and their joint impacts on thermocline mixing remain to be elucidated.

Open access
Jochem Marotzke
,
Wolfgang A. Müller
,
Freja S. E. Vamborg
,
Paul Becker
,
Ulrich Cubasch
,
Hendrik Feldmann
,
Frank Kaspar
,
Christoph Kottmeier
,
Camille Marini
,
Iuliia Polkova
,
Kerstin Prömmel
,
Henning W. Rust
,
Detlef Stammer
,
Uwe Ulbrich
,
Christopher Kadow
,
Armin Köhl
,
Jürgen Kröger
,
Tim Kruschke
,
Joaquim G. Pinto
,
Holger Pohlmann
,
Mark Reyers
,
Marc Schröder
,
Frank Sienz
,
Claudia Timmreck
, and
Markus Ziese

Abstract

Mittelfristige Klimaprognose (MiKlip), an 8-yr German national research project on decadal climate prediction, is organized around a global prediction system comprising the Max Planck Institute Earth System Model (MPI-ESM) together with an initialization procedure and a model evaluation system. This paper summarizes the lessons learned from MiKlip so far; some are purely scientific, others concern strategies and structures of research that target future operational use.

Three prediction system generations have been constructed, characterized by alternative initialization strategies; the later generations show a marked improvement in hindcast skill for surface temperature. Hindcast skill is also identified for multiyear-mean European summer surface temperatures, extratropical cyclone tracks, the quasi-biennial oscillation, and ocean carbon uptake, among others. Regionalization maintains or slightly enhances the skill in European surface temperature inherited from the global model and also displays hindcast skill for wind energy output. A new volcano code package permits rapid modification of the predictions in response to a future eruption.

MiKlip has demonstrated the efficacy of subjecting a single global prediction system to a major research effort. The benefits of this strategy include the rapid cycling through the prediction system generations, the development of a sophisticated evaluation package usable by all MiKlip researchers, and regional applications of the global predictions. Open research questions include the optimal balance between model resolution and ensemble size, the appropriate method for constructing a prediction ensemble, and the decision between full-field and anomaly initialization.

Operational use of the MiKlip system is targeted for the end of the current decade, with a recommended generational cycle of 2–3 years.

Full access
Christiane Voigt
,
Ulrich Schumann
,
Andreas Minikin
,
Ahmed Abdelmonem
,
Armin Afchine
,
Stephan Borrmann
,
Maxi Boettcher
,
Bernhard Buchholz
,
Luca Bugliaro
,
Anja Costa
,
Joachim Curtius
,
Maximilian Dollner
,
Andreas Dörnbrack
,
Volker Dreiling
,
Volker Ebert
,
Andre Ehrlich
,
Andreas Fix
,
Linda Forster
,
Fabian Frank
,
Daniel Fütterer
,
Andreas Giez
,
Kaspar Graf
,
Jens-Uwe Grooß
,
Silke Groß
,
Katharina Heimerl
,
Bernd Heinold
,
Tilman Hüneke
,
Emma Järvinen
,
Tina Jurkat
,
Stefan Kaufmann
,
Mareike Kenntner
,
Marcus Klingebiel
,
Thomas Klimach
,
Rebecca Kohl
,
Martina Krämer
,
Trismono Candra Krisna
,
Anna Luebke
,
Bernhard Mayer
,
Stephan Mertes
,
Sergej Molleker
,
Andreas Petzold
,
Klaus Pfeilsticker
,
Max Port
,
Markus Rapp
,
Philipp Reutter
,
Christian Rolf
,
Diana Rose
,
Daniel Sauer
,
Andreas Schäfler
,
Romy Schlage
,
Martin Schnaiter
,
Johannes Schneider
,
Nicole Spelten
,
Peter Spichtinger
,
Paul Stock
,
Adrian Walser
,
Ralf Weigel
,
Bernadett Weinzierl
,
Manfred Wendisch
,
Frank Werner
,
Heini Wernli
,
Martin Wirth
,
Andreas Zahn
,
Helmut Ziereis
, and
Martin Zöger

Abstract

The Midlatitude Cirrus experiment (ML-CIRRUS) deployed the High Altitude and Long Range Research Aircraft (HALO) to obtain new insights into nucleation, life cycle, and climate impact of natural cirrus and aircraft-induced contrail cirrus. Direct observations of cirrus properties and their variability are still incomplete, currently limiting our understanding of the clouds’ impact on climate. Also, dynamical effects on clouds and feedbacks are not adequately represented in today’s weather prediction models.

Here, we present the rationale, objectives, and selected scientific highlights of ML-CIRRUS using the G-550 aircraft of the German atmospheric science community. The first combined in situ–remote sensing cloud mission with HALO united state-of-the-art cloud probes, a lidar and novel ice residual, aerosol, trace gas, and radiation instrumentation. The aircraft observations were accompanied by remote sensing from satellite and ground and by numerical simulations.

In spring 2014, HALO performed 16 flights above Europe with a focus on anthropogenic contrail cirrus and midlatitude cirrus induced by frontal systems including warm conveyor belts and other dynamical regimes (jet streams, mountain waves, and convection). Highlights from ML-CIRRUS include 1) new observations of microphysical and radiative cirrus properties and their variability in meteorological regimes typical for midlatitudes, 2) insights into occurrence of in situ–formed and lifted liquid-origin cirrus, 3) validation of cloud forecasts and satellite products, 4) assessment of contrail predictability, and 5) direct observations of contrail cirrus and their distinction from natural cirrus. Hence, ML-CIRRUS provides a comprehensive dataset on cirrus in the densely populated European midlatitudes with the scope to enhance our understanding of cirrus clouds and their role for climate and weather.

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Manfred Wendisch
,
Ulrich Pöschl
,
Meinrat O. Andreae
,
Luiz A. T. Machado
,
Rachel Albrecht
,
Hans Schlager
,
Daniel Rosenfeld
,
Scot T. Martin
,
Ahmed Abdelmonem
,
Armin Afchine
,
Alessandro C. Araùjo
,
Paulo Artaxo
,
Heinfried Aufmhoff
,
Henrique M. J. Barbosa
,
Stephan Borrmann
,
Ramon Braga
,
Bernhard Buchholz
,
Micael Amore Cecchini
,
Anja Costa
,
Joachim Curtius
,
Maximilian Dollner
,
Marcel Dorf
,
Volker Dreiling
,
Volker Ebert
,
André Ehrlich
,
Florian Ewald
,
Gilberto Fisch
,
Andreas Fix
,
Fabian Frank
,
Daniel Fütterer
,
Christopher Heckl
,
Fabian Heidelberg
,
Tilman Hüneke
,
Evelyn Jäkel
,
Emma Järvinen
,
Tina Jurkat
,
Sandra Kanter
,
Udo Kästner
,
Mareike Kenntner
,
Jürgen Kesselmeier
,
Thomas Klimach
,
Matthias Knecht
,
Rebecca Kohl
,
Tobias Kölling
,
Martina Krämer
,
Mira Krüger
,
Trismono Candra Krisna
,
Jost V. Lavric
,
Karla Longo
,
Christoph Mahnke
,
Antonio O. Manzi
,
Bernhard Mayer
,
Stephan Mertes
,
Andreas Minikin
,
Sergej Molleker
,
Steffen Münch
,
Björn Nillius
,
Klaus Pfeilsticker
,
Christopher Pöhlker
,
Anke Roiger
,
Diana Rose
,
Dagmar Rosenow
,
Daniel Sauer
,
Martin Schnaiter
,
Johannes Schneider
,
Christiane Schulz
,
Rodrigo A. F. de Souza
,
Antonio Spanu
,
Paul Stock
,
Daniel Vila
,
Christiane Voigt
,
Adrian Walser
,
David Walter
,
Ralf Weigel
,
Bernadett Weinzierl
,
Frank Werner
,
Marcia A. Yamasoe
,
Helmut Ziereis
,
Tobias Zinner
, and
Martin Zöger

Abstract

Between 1 September and 4 October 2014, a combined airborne and ground-based measurement campaign was conducted to study tropical deep convective clouds over the Brazilian Amazon rain forest. The new German research aircraft, High Altitude and Long Range Research Aircraft (HALO), a modified Gulfstream G550, and extensive ground-based instrumentation were deployed in and near Manaus (State of Amazonas). The campaign was part of the German–Brazilian Aerosol, Cloud, Precipitation, and Radiation Interactions and Dynamics of Convective Cloud Systems–Cloud Processes of the Main Precipitation Systems in Brazil: A Contribution to Cloud Resolving Modeling and to the GPM (Global Precipitation Measurement) (ACRIDICON– CHUVA) venture to quantify aerosol–cloud–precipitation interactions and their thermodynamic, dynamic, and radiative effects by in situ and remote sensing measurements over Amazonia. The ACRIDICON–CHUVA field observations were carried out in cooperation with the second intensive operating period of Green Ocean Amazon 2014/15 (GoAmazon2014/5). In this paper we focus on the airborne data measured on HALO, which was equipped with about 30 in situ and remote sensing instruments for meteorological, trace gas, aerosol, cloud, precipitation, and spectral solar radiation measurements. Fourteen research flights with a total duration of 96 flight hours were performed. Five scientific topics were pursued: 1) cloud vertical evolution and life cycle (cloud profiling), 2) cloud processing of aerosol particles and trace gases (inflow and outflow), 3) satellite and radar validation (cloud products), 4) vertical transport and mixing (tracer experiment), and 5) cloud formation over forested/deforested areas. Data were collected in near-pristine atmospheric conditions and in environments polluted by biomass burning and urban emissions. The paper presents a general introduction of the ACRIDICON– CHUVA campaign (motivation and addressed research topics) and of HALO with its extensive instrument package, as well as a presentation of a few selected measurement results acquired during the flights for some selected scientific topics.

Full access
Ibrahim Hoteit
,
Yasser Abualnaja
,
Shehzad Afzal
,
Boujemaa Ait-El-Fquih
,
Triantaphyllos Akylas
,
Charls Antony
,
Clint Dawson
,
Khaled Asfahani
,
Robert J. Brewin
,
Luigi Cavaleri
,
Ivana Cerovecki
,
Bruce Cornuelle
,
Srinivas Desamsetti
,
Raju Attada
,
Hari Dasari
,
Jose Sanchez-Garrido
,
Lily Genevier
,
Mohamad El Gharamti
,
John A. Gittings
,
Elamurugu Gokul
,
Ganesh Gopalakrishnan
,
Daquan Guo
,
Bilel Hadri
,
Markus Hadwiger
,
Mohammed Abed Hammoud
,
Myrl Hendershott
,
Mohamad Hittawe
,
Ashok Karumuri
,
Omar Knio
,
Armin Köhl
,
Samuel Kortas
,
George Krokos
,
Ravi Kunchala
,
Leila Issa
,
Issam Lakkis
,
Sabique Langodan
,
Pierre Lermusiaux
,
Thang Luong
,
Jingyi Ma
,
Olivier Le Maitre
,
Matthew Mazloff
,
Samah El Mohtar
,
Vassilis P. Papadopoulos
,
Trevor Platt
,
Larry Pratt
,
Naila Raboudi
,
Marie-Fanny Racault
,
Dionysios E. Raitsos
,
Shanas Razak
,
Sivareddy Sanikommu
,
Shubha Sathyendranath
,
Sarantis Sofianos
,
Aneesh Subramanian
,
Rui Sun
,
Edriss Titi
,
Habib Toye
,
George Triantafyllou
,
Kostas Tsiaras
,
Panagiotis Vasou
,
Yesubabu Viswanadhapalli
,
Yixin Wang
,
Fengchao Yao
,
Peng Zhan
, and
George Zodiatis

Abstract

The Red Sea, home to the second-longest coral reef system in the world, is a vital resource for the Kingdom of Saudi Arabia. The Red Sea provides 90% of the Kingdom’s potable water by desalinization, supporting tourism, shipping, aquaculture, and fishing industries, which together contribute about 10%–20% of the country’s GDP. All these activities, and those elsewhere in the Red Sea region, critically depend on oceanic and atmospheric conditions. At a time of mega-development projects along the Red Sea coast, and global warming, authorities are working on optimizing the harnessing of environmental resources, including renewable energy and rainwater harvesting. All these require high-resolution weather and climate information. Toward this end, we have undertaken a multipronged research and development activity in which we are developing an integrated data-driven regional coupled modeling system. The telescopically nested components include 5-km- to 600-m-resolution atmospheric models to address weather and climate challenges, 4-km- to 50-m-resolution ocean models with regional and coastal configurations to simulate and predict the general and mesoscale circulation, 4-km- to 100-m-resolution ecosystem models to simulate the biogeochemistry, and 1-km- to 50-m-resolution wave models. In addition, a complementary probabilistic transport modeling system predicts dispersion of contaminant plumes, oil spill, and marine ecosystem connectivity. Advanced ensemble data assimilation capabilities have also been implemented for accurate forecasting. Resulting achievements include significant advancement in our understanding of the regional circulation and its connection to the global climate, development, and validation of long-term Red Sea regional atmospheric–oceanic–wave reanalyses and forecasting capacities. These products are being extensively used by academia, government, and industry in various weather and marine studies and operations, environmental policies, renewable energy applications, impact assessment, flood forecasting, and more.

Full access
Ibrahim Hoteit
,
Yasser Abualnaja
,
Shehzad Afzal
,
Boujemaa Ait-El-Fquih
,
Triantaphyllos Akylas
,
Charls Antony
,
Clint Dawson
,
Khaled Asfahani
,
Robert J. Brewin
,
Luigi Cavaleri
,
Ivana Cerovecki
,
Bruce Cornuelle
,
Srinivas Desamsetti
,
Raju Attada
,
Hari Dasari
,
Jose Sanchez-Garrido
,
Lily Genevier
,
Mohamad El Gharamti
,
John A. Gittings
,
Elamurugu Gokul
,
Ganesh Gopalakrishnan
,
Daquan Guo
,
Bilel Hadri
,
Markus Hadwiger
,
Mohammed Abed Hammoud
,
Myrl Hendershott
,
Mohamad Hittawe
,
Ashok Karumuri
,
Omar Knio
,
Armin Köhl
,
Samuel Kortas
,
George Krokos
,
Ravi Kunchala
,
Leila Issa
,
Issam Lakkis
,
Sabique Langodan
,
Pierre Lermusiaux
,
Thang Luong
,
Jingyi Ma
,
Olivier Le Maitre
,
Matthew Mazloff
,
Samah El Mohtar
,
Vassilis P. Papadopoulos
,
Trevor Platt
,
Larry Pratt
,
Naila Raboudi
,
Marie-Fanny Racault
,
Dionysios E. Raitsos
,
Shanas Razak
,
Sivareddy Sanikommu
,
Shubha Sathyendranath
,
Sarantis Sofianos
,
Aneesh Subramanian
,
Rui Sun
,
Edriss Titi
,
Habib Toye
,
George Triantafyllou
,
Kostas Tsiaras
,
Panagiotis Vasou
,
Yesubabu Viswanadhapalli
,
Yixin Wang
,
Fengchao Yao
,
Peng Zhan
, and
George Zodiatis
Full access