Atmospheric Complexity

The Atmospheric Complexity group uses methods from theoretical physics to describe and model atmospheric processes.

The aim is to capture emergent aspects, e.g. self-organization, that originate from small scales but can impact on larger scales. We use high-resolution simulations and observational data and make simplified, conceptual, models of key aspects of atmospheric complexity. Atmospheric Complexity is funded by a Villum Young Investigator Grant and a European Research Council (ERC) Consolidator Grant. Atmospheric Complexity collaborates with Complexity & Climate at the Leibniz Centre for Tropical Marine Research (ZMT), Bremen.

The Atmospheric Complexity group at the Niels Bohr Institute The Atmospheric Complexity group at the Niels Bohr Institute The Atmospheric Complexity group at the Niels Bohr Institute The Atmospheric Complexity group at the Niels Bohr Institute

 

 

 

 

 

 

 

 

 

 

 

 

 

 

How do clouds influence the climate system? How do they form intense precipitation? Such questions have challenged atmospheric science for decades. High-resolution simulations and observations bring us closer to answering them, yet, fundamental processes are not understood.

This is because clouds organize on a range of scales, scales interact and precipitation is a result of abrupt changes of phases, leading to abruptness, e.g. intermittancy, in the moisture dynamics. Furthermore, convective-type cloud has been shown to produce unexpectedly strong precipitation intensity, not explained by equilibrium thermodynamics.

The team uses methods from theoretical physics to describe and model atmospheric processes. The aim is to capture emergent aspects, e.g. self-organization, that originate from small scales but can impact on larger scales. We use high-resolution simulations and observational data and make simplified, conceptual, models to capture key aspects of atmospheric complexity.

What is convection?

Convective precipitation observed over Cuba.

Convection is buoyancy driven

Convection is a consequence of strong heating of moist surface air. Warmer air expands and is therefore subject to buoyancy relative to the surrounding, more dense, air. This buoyancy causes rapid lifting of surface air. In contrast, stratiform cloud is often caused by cyclonic activity, where the collision of fronts causes large-scale lifting of moist air. Such lifting processes are generally slow compared to convective updrafts.

Convective precipitation is local

In general terms, the convective precipitation of a single convective updraft (see the image to the right) falls over relatively short times and covers areas of only few kilometers across. For extreme events, it is not uncommon to measure 50 mm of rain in one hour. Such strong rain can cause flash floods, local floods that arise within hours and can be devastating to human lives and infrastructure.

Convection is hard to simulate in climate models

Because of its local nature and complex dynamics, convection continues to pose basic challenges in coarse-scale models. Standard climate models have horizontal resolutions of roughly 50 km, while typical scales of convective events are far less than that, often around 1-10 km. To simulate single events, or their interaction, properly, models must have resolutions better than 1 km.

Our approach

Stating the problem

Rayleigh-Bénard convection is a classical problem in complex systems science: When a fluid is placed in between two horizontal plates and the lower one is heated relative to the upper, so-called convective rolls will eventually appear. These rolls constitute a form of symmetry breaking, by which some areas see locally rising, others locally sinking fluid parcels.

The dynamics of the atmosphere can be modeled as a fluid for many practical purposes. 

However, in contrast to classical convection, that of the atmosphere arises due to a fluid containing varying phases: The water vapor contained in the air can condense to produce cloud droplets, thereby releasing latent heat. Further, when rain falls to the ground by the action of gravity, latent heat is redistributed vertically. These are processes that can act to break the initially rising motion of moist air parcels, thereby - in a sense - destroying convective rolls. 

Tackling the challenge

State-of-the-art global climate models are still far from capable of resolving scales of convective clouds througout the extended periods needed for climate simulations (at least 100 years). Yet, for short periods and smaller areas, so-called large-eddy simulations (see left column) can resolve turbulent processes down to tens or hundreds of meters. We use such simulations, which also represent simplifications of the real atmosphere, but do allow us to extract processes responsible for the organization of the atmosphere through convection and intensification of precipitation extremes.

While simulations are convenient in accessing processes, the most direct way to study convection is through meteorological observations of the atmosphere. The atmospheric state consists of a large array of variables, e.g. temperature, moisture, wind speed and pressure, just to name a few. Precipitation, however, is the quantity that most directly affects the living environment, e.g. humans. As it plays a crucial role in re-distributing energy and moisture within the climate system, and occurs as an intermittant process, it is particularly important to gather detailed, high-resolution observations on it. Some observations we currently use are those from ground-based stations, radar reflectivity and satellite observations.

Conceptual modeling

Simulations and observations can tell us a whole lot about convective transport of moisture and energy. However, there is always a risk of taking a realistic simulation as meaning that the system is "understood". The more complex the simulation output, and perhaps the more it is visually compatible with observations or intuition, the less we actually grasp the abstract processes behind the formation and organization of clouds in the atmosphere.

We use methods from physics of complex systems to describe the self-organization of convective clouds. Requiring simplified models we can re-enact, at least qualitatively, some of the emergent phenomena seen in observations or simulations. We leave out some of the complexity — leading to better understanding and sometimes inspiring new predictions for future climate change. 

Beyond this, simplified models can be more universal, describing similarities of disparate fields, such as atmospheric science and biology or even social science, fields that are also explored at Niels Bohr Institute.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Complex Physics (MSc level course, Block 1)

In Fall 2018, 2019, and 2020, Jan O. Haerter was teaching the first part of the Master's course "Complex Physics". 

Topics in Complex Systems (MSc level course, Block 1)

In Fall 2017, Jan was teaching part of the NBI graduate course "Topics in Complex Systems", which is aimed at MSc students of physics and related disciplines. The topics I teach include critical phenomena and various techniques to explore them. As a model system, we use the classical Ising model.

download the lecture notes

Topics include:

Mean field theory, 1D transfer matrix method, Low and high temperature series expansion, Monte Carlo (Metropolis) method, 1D renormalization group method.

This course also includes lectures on complex networks, interfaces, agent-based models, and self organization, etc. (instructor: Kim Sneppen).

 

 

PhD position on tropical climate extremes (deadline: Mar 31, 2021)


Jannik Hoeller and Irene Kruse have joined the team as PhD students

Welcome!


Congrats to Herman!

For a very successful thesis defense. Best wishes for the future.


Herman Fuglestvedt

Feb 20th, 2019

Thesis defense by Herman Fuglestvedt

Niels Bohr Institute, Blegdamsvej 17, Aud D

Feb 20th, 2019, 10 a.m.

Title: A Conceptual Model for Self-Organisation of Precipitating Convection


Jan 24th, 2019

Paper accepted in the Journal of Advances in Earth System Modeling (JAMES)

C. Moseley, O. Henneberg, J. O. Haerter: A statistical model for isolated convective precipitation events


Jan 10th, 2019

Marielle successfully defended her M.Sc. thesis, congratulations and all the best for the future!Marielle 

Thesis title: Tracking Convective Cold Pools - A study of cloud interactions   

   

   


Dec 10th, 2018

Marielle will hand in her MSc thesis on Dec 18th, and her thesis defense will be on Jan 10th, 10 a.m. in Auditorium D.

Thesis title: Tracking Convective Cold Pools - A study of cloud interactions                       Marielle 

                    

       

     

   


Nov 1st, 2018

Enrico Maria Fenoaltea start a MSc project on human decision making under complex circumstances, using the example system chess.

Big welcome! Enrico Maria Fenoaltea

>> read more

               

               

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Sept 1st, 2018

Christian starts a MSc project in Atmospheric Complexity.

Welcome to the team! Christian

>> read more


Sept 1st, 2018

Christian starts a MSc project in Atmospheric Complexity

Welcome to the team! Christian

>> read more

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May 31, 2018: New paper published in Geophysical Research Letters:

Jan O. Haerter & Linda Schlemmer: Intensified cold-pool dynamics under stronger surface heating

key result: A new feedback between precipitation and cold pool dynamics, which could explain the super-Clausius-Clapeyron increase of convective precipitation extremes.

Broadening of temperature histograms during precipitation.

Histograms of near-surface temperature. Note the broadening in the course of precipitation (details: GRL)

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Bettina Meyer

May 28, 2018: Bettina Meyer will join the Atmospheric Complexity group as a postdoc on June 15th, welcome!

 

Bettina has recently completed her Ph.D. at ETH Zürich in collaboration with Caltech. 

» read more

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May 4, 2018: Experimental Economics meets Statistical Physics

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Apr 26, 2018: A warm welcome to Kai Lochbihler from TU Delft/KNMI, who will be visitingKai Lochbihler our group for several weeks. We will be collaborating on convective organization in a range of systems.  

Kai is currently a Ph.D. student with Geert Lenderink (KNMI) and Pier Siebesma (TU Delft). 

He has worked on extreme convective precipitation and the possible exceedance of the Clausius-Clapeyron relation.

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Apr 25, 2018: Olga Henneberg will be giving a talk at the AMS meeting in Vancouver in July: "From Cold Pool Interaction to Extreme Precipitation"

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Apr 25, 2018: Thanks to all for the great workshop on convective self-organization! 

Cloud self-organization over the Western Pacific (NASA)

 

We hope that this event has helped bring about new ideas and get people together.

Check back for slides and photos of this event on the webpage below.

 

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Dec 15, 2017Jan receives ERC Consolidator Grant 

We are thankful for this generous grant offered by the European Commission!

European Research Council

» read more

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Researchers

Name Title Image
Search in Name Search in Title
Fiévet, Romain Frédéric Sébastien Postdoc Billede af Fiévet, Romain Frédéric Sébastien
Härter, Jan Olaf Mirko Associate Professor Billede af Härter, Jan Olaf Mirko
Höller, Jannik External, Ph.d Student Billede af Höller, Jannik
Jensen, Gorm Gruner Postdoc Billede af Jensen, Gorm Gruner
Kruse, Irene Livia External, Ph.d Student Billede af Kruse, Irene Livia

Jan Olaf Mirko HärterGroup leader

Jan O. Haerter, Associate Professor
Tel: (+45) 93 56 57 36
Email: haerter [at] nbi.ku.dk

Funded by

European Research CouncilVillum Foundation

Eksterne forskere

Faranak Tootoonchi
Ph.D. Student (co-supervised) faranak.tootoonchi@geu.uu.se
Reyk Börner M.Sc. Student
Johan Fridrik Kjølbro M.Sc. Student sfk351@alumni.ku.dk