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.

Satellite image by the Global Precipitation Measurement mission (NASA).

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.

M.Sc. project idea

In simulations, cold pools are found to produce near circular shapes as they spread. In a recent paper, we described this spreading in a simple mathematical model, where circles collide in space to produce new rain cells. A possible MSc project would take this idea further, to allow for a depletion effect, where circles that have spread will make it less likely for new events to occur in the same location.

	What is convection? Convection is buoyancy driven motion of moist air. When air near the surface is heated, e.g. by solar irradiation, vertical air motion and cloud formation can be induced. Read more >>
	Our Approach We use a combination of methods to address convective processes: High-resolution observations, idealized simulations and conceptual modeling.  Read more >>
Full publication list here >>	Research highlights Find a number of selected publications, which highlight, why convection is exciting both observationally, as well as in terms of numerical modeling. Demanding new ways of thinking about self-organizaiton. Read more >>

• Center for Ice and Climate, Niels Bohr Institute
• Danish Meteorological Institute
• Max Planck Institute for Meteorology, Hamburg, Germany
• Swedish Hydrological and Meteorological Institute, Norrköping, Sweden
• University of Adelaide, Australia (Prof. Seth Westra)
• TU Delft and KNMI Netherlands (Kai Lochbihler)

List of relevant publications (chronological order)

“Complex Fluids” brings together the complex systems and geophysical fluid dynamics fields. The focus is on talks with a conceptual modeling view on complexity, e.g. as arising in earth's atmosphere and ocean, in biology, or within the solid earth. 

Sign up for the mailing list
We encourage subscription to the Complex Fluids mailing list, to receive information about upcoming seminars.

For suggested speakers and queries please contactJan O. Haerter, Peter Ditlevsen, Markus Jochum, Joachim Mathiesen, Eigil Kaas, or Mogens H. Jensen.

Scope
The scope of this seminar is to encourage models that describe complex processes in fluids, e.g. those involving some type of emergent aspect, self-organization, bistability, oscillations, scale interactions, long-ranged order, you name it ;) Examples are bistability in the climate system, convective processes, extreme events, self-similarity and pattern formation in geology or atmospheric processes, interactions and feedbacks between atmosphere and biosphere, etc.

Conceptual models
We are interested in conceptual (but not necessarily complicated) models that are able to capture the core dynamical processes and (some of) the feedbacks in a fluid dynamical system, without getting lost in comprehensive models and many parameters. The sacrifice may sometimes be, that not all processes are considered, and that quantitative detail is missing.

The gain however lies in the theoretical understanding of the model and thereby at least some aspects of reality. We therefore encourage talks that offer a speculate, provocative view on crucial processes, e.g. in the climate system, that are currently not well understood or uncertain.

When and where
Wednesdays at noon (communal informal lunch). Presentations start around 12:30 and normally take around 45 minutes. Initially, the seminar will be approximately twice per month.

Where? Kc7, C-floor of K-building, Blegdamsvej 17, 2100 København Ø.

This workshop aims to provide a platform to present ongoing work and open questions about organised and self-organised phenomena in cloud fields. We want to bring together the communities working on climate physics, statistical mechanics and meso-scale meteorology. The workshop will be organised around 3 topics, mentioned below with some examples of the type of questions we would like to address. 

Some of the presentations will be on convection, but we are keen to also involve scientists working on related topics, such as soil-moisture and ocean (e.g. ocean mixed-layer) feedbacks. 
 

A) Detecting and understanding regimes of organisation

• How can we quantify organisation? 
• How can we detect the existence of specific regimes of organisation? 
• What ingredients are required to model the emergence and evolution of organisation? 
• What can we learn from simplified models? 
• What is the role of feedbacks through, for example, the soil-moisture and the ocean mixed-layer? 
• Is machine learning a suitable tool to address these questions? 

B) Organisation as a tool for model evaluation

• What are suitable diagnostics for evaluating organisation in models (examples could be potential vorticity and its spatial structure, and measures of instability in the presence of shear)? 
• What diagnostics are currently used for meso-scale meteorology? 
• Can diagnostics of organisation be used to constrain climate sensitivity and extreme events? 

C) Introducing organisation in climate models

• At what resolution is there a need for a below grid-scale representation of organised structures, including gravity waves, unresolved updraughts, cold pools and meso-scale circulations? 
• Can we represent subgrid organisation in climate models in a crude manner, or do the details matter? 
• How can we ensure such a representation is scale-adaptive and does not deteriorate simulations as resolution continues to increase? 

Date: May 27-29 2020

Venue: Niels Bohr Institute, Blegdamsvej 17, 2100 Copenhagen, Denmark

Contact: Jan Härter, haerter@nbi.ku.dk

Submission of abstracts and posters is open until January 15, 2019 

Registration fee: 150€