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Daniel J. Cziczo
,
Luis Ladino
,
Yvonne Boose
,
Zamin A. Kanji
,
Piotr Kupiszewski
,
Sara Lance
,
Stephan Mertes
, and
Heike Wex

Abstract

It has been known that aerosol particles act as nuclei for ice formation for over a century and a half (see Dufour). Initial attempts to understand the nature of these ice nucleating particles were optical and electron microscope inspection of inclusions at the center of a crystal (see Isono; Kumai). Only within the last few decades has instrumentation to extract ice crystals from clouds and analyze the residual material after sublimation of condensed-phase water been available (see Cziczo and Froyd). Techniques to ascertain the ice nucleating potential of atmospheric aerosols have only been in place for a similar amount of time (see DeMott et al.). In this chapter the history of measurements of ice nucleating particles, both in the field and complementary studies in the laboratory, are reviewed. Remaining uncertainties and artifacts associated with measurements are described and suggestions for future areas of improvement are made.

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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.

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Manfred Wendisch
,
Andreas Macke
,
André Ehrlich
,
Christof Lüpkes
,
Mario Mech
,
Dmitry Chechin
,
Klaus Dethloff
,
Carola Barrientos Velasco
,
Heiko Bozem
,
Marlen Brückner
,
Hans-Christian Clemen
,
Susanne Crewell
,
Tobias Donth
,
Regis Dupuy
,
Kerstin Ebell
,
Ulrike Egerer
,
Ronny Engelmann
,
Christa Engler
,
Oliver Eppers
,
Martin Gehrmann
,
Xianda Gong
,
Matthias Gottschalk
,
Christophe Gourbeyre
,
Hannes Griesche
,
Jörg Hartmann
,
Markus Hartmann
,
Bernd Heinold
,
Andreas Herber
,
Hartmut Herrmann
,
Georg Heygster
,
Peter Hoor
,
Soheila Jafariserajehlou
,
Evelyn Jäkel
,
Emma Järvinen
,
Olivier Jourdan
,
Udo Kästner
,
Simonas Kecorius
,
Erlend M. Knudsen
,
Franziska Köllner
,
Jan Kretzschmar
,
Luca Lelli
,
Delphine Leroy
,
Marion Maturilli
,
Linlu Mei
,
Stephan Mertes
,
Guillaume Mioche
,
Roland Neuber
,
Marcel Nicolaus
,
Tatiana Nomokonova
,
Justus Notholt
,
Mathias Palm
,
Manuela van Pinxteren
,
Johannes Quaas
,
Philipp Richter
,
Elena Ruiz-Donoso
,
Michael Schäfer
,
Katja Schmieder
,
Martin Schnaiter
,
Johannes Schneider
,
Alfons Schwarzenböck
,
Patric Seifert
,
Matthew D. Shupe
,
Holger Siebert
,
Gunnar Spreen
,
Johannes Stapf
,
Frank Stratmann
,
Teresa Vogl
,
André Welti
,
Heike Wex
,
Alfred Wiedensohler
,
Marco Zanatta
, and
Sebastian Zeppenfeld

Abstract

Clouds play an important role in Arctic amplification. This term represents the recently observed enhanced warming of the Arctic relative to the global increase of near-surface air temperature. However, there are still important knowledge gaps regarding the interplay between Arctic clouds and aerosol particles, and surface properties, as well as turbulent and radiative fluxes that inhibit accurate model simulations of clouds in the Arctic climate system. In an attempt to resolve this so-called Arctic cloud puzzle, two comprehensive and closely coordinated field studies were conducted: the Arctic Cloud Observations Using Airborne Measurements during Polar Day (ACLOUD) aircraft campaign and the Physical Feedbacks of Arctic Boundary Layer, Sea Ice, Cloud and Aerosol (PASCAL) ice breaker expedition. Both observational studies were performed in the framework of the German Arctic Amplification: Climate Relevant Atmospheric and Surface Processes, and Feedback Mechanisms (AC) project. They took place in the vicinity of Svalbard, Norway, in May and June 2017. ACLOUD and PASCAL explored four pieces of the Arctic cloud puzzle: cloud properties, aerosol impact on clouds, atmospheric radiation, and turbulent dynamical processes. The two instrumented Polar 5 and Polar 6 aircraft; the icebreaker Research Vessel (R/V) Polarstern; an ice floe camp including an instrumented tethered balloon; and the permanent ground-based measurement station at Ny-Ålesund, Svalbard, were employed to observe Arctic low- and mid-level mixed-phase clouds and to investigate related atmospheric and surface processes. The Polar 5 aircraft served as a remote sensing observatory examining the clouds from above by downward-looking sensors; the Polar 6 aircraft operated as a flying in situ measurement laboratory sampling inside and below the clouds. Most of the collocated Polar 5/6 flights were conducted either above the R/V Polarstern or over the Ny-Ålesund station, both of which monitored the clouds from below using similar but upward-looking remote sensing techniques as the Polar 5 aircraft. Several of the flights were carried out underneath collocated satellite tracks. The paper motivates the scientific objectives of the ACLOUD/PASCAL observations and describes the measured quantities, retrieved parameters, and the applied complementary instrumentation. Furthermore, it discusses selected measurement results and poses critical research questions to be answered in future papers analyzing the data from the two field campaigns.

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