Guest Program

International highly regarded scientists will be invited as Guest Scientists, which will facilitate the progress of (AC)³ through:

  • Constructive discussions,
  • Scientific Colloquia,
  • Lectures,
  • Participation in field campaigns, and
  • Exchange of theoretical expertise with regard to modelling and data assimilation.

Dr. Linette Boisvert (NASA Goddard Space Flight Center, Cryospheric Sciences Lab, Greenbelt MD, USA) May 28-31, 2018

NASA scientist Linette Boisvert from NASA GSFC visited the Alfred Wegener Institute, Helmholtz Centre for Polar and marine Research in Potsdam (AWI-P). Her research interests, which cover Arctic sea ice, moisture flux and Arctic precipitation establish a strong link to our (AC)³ project-related work, particularly in the projects E04 and D03. She introduced her submitted paper on Arctic Ocean precipitation in reanalyses. We discussed this in context of Benjamin Seggers complementary work on  characteristics and variability of Arctic precipitation and snowfall from a reanalysis ensemble. We exchange our findings of the widely different results in the magnitude and phase of precipitation across the reanalyses, which highlights in particular the differences in model’s cloud microphysical parameterization. Although there are discrepancies between the different reanalyses, they agree that the amount of snowfall is decreasing over recent decade. We discussed potential feedbacks on sea ice, which is a joint interest in our future research.


Prof. Xiangdong Zhang (IARC/UAF): August 21-25, 2017 at AWI-Potsdam

Xiangdong Zhang from the International Arctic Research Center (IARC) / University of Alaska Fairbanks (UAF) visited the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI-P), and gave a seminar on “Modeling Studies on Linkage Between Arctic Change and Mid-latitude Climate and Weather”.
As a co-chair of the US CLIVAR Working Group on Arctic Change and Possible Influence on Mid-latitude Climate and Weather, he presented an overview of current existing knowledge on such links including weather extremes. Xiangdong’s associated research includes Arctic climate variability and change, storm track dynamics, and air-ice-sea interaction.
Additionally to Xiangdong Zhang, we welcomed his two PhD students Yang Yang and Liran Peng. During their visit, they all had extensive discussions with several (AC)³ members about their work. In particular, we discussed the continuation of our collaboration on storm-sea ice interaction, which is part of the D03 project. We compiled a first joint paper draft on “Arctic regional modeling investigation of summer storm – sea ice – ocean interactions”. We discussed results of the analysis of ensemble simulations of our regional coupled atmosphere-ice-ocean model HIRHAM-NAOSIM with respect to cyclone characteristics and how it might be affected by the underlying surface (e.g. sea ice extent). We also discussed specific details of the set up of our planned new model simulations when we plan to store additional oceanic model output for future analyses.


Dr. Robert M. Graham (Norwegian Polar Institute): July 24-28, 2017 at AWI-Potsdam

Robert Graham from the Norwegian Polar Institute (NPI) in Tromsø visited the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI-P), and gave a seminar on “The role of winter storms in the Arctic Ocean”. The recent Norwegian young sea ice campaign (N-ICE2015) provides a valuable multi-disciplinary dataset from the pack ice north of Svalbard, covering the period from January – June 2015. During N-ICE2015, multiple winter storms were observed. Detailed observations show how the strong winds associated with these storms acted to deform the sea ice, enhance ocean mixing, and in certain cases generate large ocean surface heat fluxes that contributed to bottom melt of the sea ice. These storms were also associated with heavy snowfall and snow redistribution. Two recent studies performed in collaboration with (AC)³ members at AWI-P and Robert have shown that there has been an increased number of Arctic winter storms in recent years, particularly in the region around Svalbard. Robert visited AWI-P for five days and held extensive discussions with several (AC)³ members about their ongoing work and continued links with the research at NPI, particularly with the N-ICE2015 project. We discussed the potential application of a 1-D ice model with satellite-derived sea-ice back trajectories and atmospheric reanalyses to predict snow depth on sea ice. The multi-disciplinary N-ICE2015 dataset can also help to evaluate the performance of our regional climate model, remote sensing products, and atmospheric reanalyses in this region of ongoing climate change in the Arctic.


Prof. Rodrigo Caballero (MISU): February 6-7, 2017 at AWI-Potsdam

Rodrigo Caballero from the Department of Meteorology in Stockholm University (MISU) visited for two days the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI-P). He gave a seminar talk on “The role of moist intrusions in winter Arctic warming and sea ice decline”. There is increasing observational evidence that the Arctic winter climate is strongly controlled by filamentary intrusions of moist, warm air which cross the entire Arctic basin. He discussed how the distribution of these intrusions is affected by large-scale atmospheric circulation, particularly mid-latitude storm track activity, blocking events, and possibly by interaction with the stratosphere. All AWI-P (AC)³ members working in clusters D and E had very extensive and fruitful discussions with Rodrigo about this topic in general and specific links with our projects, particularly with D03, E02, and E04. For the latter also our (AC)³ colleagues from University of Cologne took part in the discussion via telecon. We discussed future topics of collaboration within our (AC)³ projects. The application of his intrusion algorithm can help us to better understand the spatial patterns of temperature, precipitation and storminess trends from reanalyses and our regional climate model simulations. Also, this will help us to discuss the peculiarity of climate change at Ny-Ålesund/Svalbard, which is strongly affected by moisture intrusions, compared to observational sites in other Arctic regions.


Dr. Jussi Leinonen (UCLA): November 7 – 18, 2016 at University of Cologne

Ideal single ice particles as we can buy them on Christmas Markets are quite rare in natural clouds. In the atmosphere, single crystals often build aggregates (snowflakes) or become rimed, i.e. liquid droplets freeze onto them which leads to much denser particles (graupel). While these ice processes are known to be of key importance for climate and weather forcast models, they are still very poorly understood.

Dr. Jussi Leinonen from the Joint Institute for Regional Earth Science and Engineering, University of California (UCLA) developed a comprehensive numerical model for ice particle aggregation and riming and is also an expert in the field of how these particles interact with microwave radiation used by ground-based and satellite remote sensors. During his two-week visit of the University of Cologne (UoC), he introduced the (AC)³ members in his aggregation and riming model and future topics of collaboration within (AC)³ were discussed. This exchange will help to further improve the microwave forward models needed to generate synthetic observations based on model simulations performed in (AC)³. Members of the UoC also visited with Dr. Leinonen the German Weather Service (DWD) and discussed with Dr. Axel Seifert how his aggregation and riming model could help to improve ice microphysical parametrizations which are currently under devlopment at DWD. In future such novel parametrizations will also be tested with the long-term and campaign data collected within (AC)³.

Illustration of modeled snow particles with a numerical aggregation and riming model.
Illustration of modeled snow particles with a numerical aggregation and riming model.