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Kerstin Ebell
,
Tatiana Nomokonova
,
Marion Maturilli
, and
Christoph Ritter

Abstract

For the first time, the cloud radiative effect (CRE) has been characterized for the Arctic site Ny-Ålesund, Svalbard, Norway, including more than 2 years of data (June 2016–September 2018). The cloud radiative effect, that is, the difference between the all-sky and equivalent clear-sky net radiative fluxes, has been derived based on a combination of ground-based remote sensing observations of cloud properties and the application of broadband radiative transfer simulations. The simulated fluxes have been evaluated in terms of a radiative closure study. Good agreement with observed surface net shortwave (SW) and longwave (LW) fluxes has been found, with small biases for clear-sky (SW: 3.8 W m−2; LW: −4.9 W m−2) and all-sky (SW: −5.4 W m−2; LW: −0.2 W m−2) situations. For monthly averages, uncertainties in the CRE are estimated to be small (~2 W m−2). At Ny-Ålesund, the monthly net surface CRE is positive from September to April/May and negative in summer. The annual surface warming effect by clouds is 11.1 W m−2. The longwave surface CRE of liquid-containing cloud is mainly driven by liquid water path (LWP) with an asymptote value of 75 W m−2 for large LWP values. The shortwave surface CRE can largely be explained by LWP, solar zenith angle, and surface albedo. Liquid-containing clouds (LWP > 5 g m−2) clearly contribute most to the shortwave surface CRE (70%–98%) and, from late spring to autumn, also to the longwave surface CRE (up to 95%). Only in winter are ice clouds (IWP > 0 g m−2; LWP < 5 g m−2) equally important or even dominating the signal in the longwave surface CRE.

Open access
Cathy Hohenegger
,
Felix Ament
,
Frank Beyrich
,
Ulrich Löhnert
,
Henning Rust
,
Jens Bange
,
Tobias Böck
,
Christopher Böttcher
,
Jakob Boventer
,
Finn Burgemeister
,
Marco Clemens
,
Carola Detring
,
Igor Detring
,
Noviana Dewani
,
Ivan Bastak Duran
,
Stephanie Fiedler
,
Martin Göber
,
Chiel van Heerwaarden
,
Bert Heusinkveld
,
Bastian Kirsch
,
Daniel Klocke
,
Christine Knist
,
Ingo Lange
,
Felix Lauermann
,
Volker Lehmann
,
Jonas Lehmke
,
Ronny Leinweber
,
Kristina Lundgren
,
Matthieu Masbou
,
Matthias Mauder
,
Wouter Mol
,
Hannes Nevermann
,
Tatiana Nomokonova
,
Eileen Päschke
,
Andreas Platis
,
Jens Reichardt
,
Luc Rochette
,
Mirjana Sakradzija
,
Linda Schlemmer
,
Jürg Schmidli
,
Nima Shokri
,
Vincent Sobottke
,
Johannes Speidel
,
Julian Steinheuer
,
David D. Turner
,
Hannes Vogelmann
,
Christian Wedemeyer
,
Eduardo Weide-Luiz
,
Sarah Wiesner
,
Norman Wildmann
,
Kevin Wolz
, and
Tamino Wetz

Abstract

Numerical weather prediction models operate on grid spacings of a few kilometers, where deep convection begins to become resolvable. Around this scale, the emergence of coherent structures in the planetary boundary layer, often hypothesized to be caused by cold pools, forces the transition from shallow to deep convection. Yet, the kilometer-scale range is typically not resolved by standard surface operational measurement networks. The measurement campaign Field Experiment on Submesoscale Spatio-Temporal Variability in Lindenberg (FESSTVaL) aimed at addressing this gap by observing atmospheric variability at the hectometer-to-kilometer scale, with a particular emphasis on cold pools, wind gusts, and coherent patterns in the planetary boundary layer during summer. A unique feature was the distribution of 150 self-developed and low-cost instruments. More specifically, FESSTVaL included dense networks of 80 autonomous cold pool loggers, 19 weather stations, and 83 soil sensor systems, all installed in a rural region of 15-km radius in eastern Germany, as well as self-developed weather stations handed out to citizens. Boundary layer and upper-air observations were provided by eight Doppler lidars and four microwave radiometers distributed at three supersites; water vapor and temperature were also measured by advanced lidar systems and an infrared spectrometer; and rain was observed by a X-band radar. An uncrewed aircraft, multicopters, and a small radiometer network carried out additional measurements during a 4-week period. In this paper, we present FESSTVaL’s measurement strategy and show first observational results including unprecedented highly resolved spatiotemporal cold-pool structures, both in the horizontal as well as in the vertical dimension, associated with overpassing convective systems.

Open access
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.

Open access