Physics-based numerical models are essential tools for understanding atmospheric processes from the surface to near-earth space. The mesosphere and lower thermosphere (MLT) as the transition layer between the atmosphere and space is coupled to the underlying atmosphere as well as to space. With our models we can quantify the imprints of tropospheric weather on the MLT from below, and trace the complex chains of radiation-chemistry-dynamics feedbacks triggered by solar-magnetospheric forcing from above. The relevant physical phenomena encompass global scales down to kilometer scales. Our main numerical model, UA-ICON, can cover the entire globe with a fine horizontal and vertical mesh. This enables us to explore atmospheric physics across the relevant spectrum of scales without a need for unphysical scale separation.
Our research encompasses four themes that are strongly interconnected:
- Radiation and chemistry,
- Waves and turbulence,
- Neutral atmosphere-ionosphere coupling, and
- Global circulation and trends.
To capture relevant physical phenomena as accurately as possible we perform continuous model development and validation efforts in coordination with national and international modeling centers. These activities are necessary to conduct our theoretical conceptual studies. We work closely with the other departments of the IAP to produce mutually beneficial synergies between numerical simulations and observations.
Besides our research with the comprehensive UA-ICON model we employ models of different levels of complexity to conduct process studies.
Short-term solar variability in the form of solar flares, solar proton events, and geomagnetic storms disturbs the chemical composition and dynamics of the MLT region due to a complex interplay of physical, chemical and dynamical heating and cooling processes that affect spatial scales of tens to hundreds of kilometers. We investigate these processes and their interactions using UA-ICON. To enable this research, we are enhancing the representation of relevant physical processes in UA-ICON by implementing new radiation schemes to couple solar and geomagnetic forcing, as well as interactive chemistry and new parametrizations for ion drag and Joule heating.
For process studies related to MLT chemistry we are running the chemistry-transport model CTM-IAP. It simulates airglow and the simplified plasma chemistry of the ionospheric D and E regions and can be driven by wind and temperature fields from dynamical models, such as UA-ICON, or from meteorological analyses. Our CTM-IAP experiments allow us to delineate and separate the effects of planetary waves, gravity waves, and anthropogenic forcing on the photochemistry and airglow of the mesopause region. One focus of our research are chemical characteristic times of minor chemical constituents. We identify which sources of atmospheric variability, e.g. planetary waves, gravity waves, tides, result in variations of a given chemical compound and assess the degree to which chemical constituents are in their equilibrium, as this is often an important assumption for theoretical chemical kinetics and reliable interpretations of measurements.
More information
- Project SODY-MLT https://gepris.dfg.de/gepris/projekt/528774615
- Project CLIMATE3D: https://gepris.dfg.de/gepris/projekt/547675919
The impact of the lower and middle atmosphere (troposphere, stratosphere, mesosphere) on the upper atmosphere (thermosphere, ionosphere) is a rapidly advancing topic in solar-terrestrial physics. The multi-scale dynamics of the mesosphere, thermosphere and ionosphere are dominated by tides, gravity waves, and small-scale eddies. Using UA-ICON we study the life cycle of explicitly resolved waves, following them from their sources to their sinks and tracing their wave-wave, wave-mean flow and wave-turbulence interactions.
Gravity waves with large vertical wavelengths and fast vertical phase velocities experience little dissipation and can reach the thermosphere with significant magnitude, creating in-situ patterns in thermospheric variables that are directly related to the thermospheric wave properties. These, in turn, are determined by the initial wave spectrum and its modification whilst propagating. With high-resolution UA-ICON simulations we can achieve a well-resolved gravity wave source spectrum resulting from resolved deep convection, orography, and unbalanced dynamics. The global coverage allows us to investigate how large-scale circulation patterns, such as the polar vortex variability and the quasi-biennial oscillation, affect wave propagation.
Waves and turbulence also pose long-standing theoretical problems. Wave energy has robust spectral slopes but we still lack a complete understanding of the underlying mechanisms. We study spectral energy transfer not only on global domains but also on regional domains to establish links with meteorological regimes, and to allow observational validation of inferred processes. Another focus of theoretical studies is the interaction of waves with turbulence and associated closure procedures. Related simulations use the non-spectral UA-ICON and the spectral KMCM model.
More information:
Atmospheric waves can impact the ionosphere-thermosphere system above 100 km height via several routes. Through electrodynamic processes, waves can generate electric fields and currents via the E-region dynamo around 110 km. Such processes cannot be modeled with standalone UA-ICON, as it does not include an electrodynamics solver. Therefore, we study the effects of neutral dynamics on the ionosphere by forcing additional models with the detailed neutral dynamics computed by UA-ICON.
The additional models can have different levels of complexity. The most comprehensive model is global and has its lower boundary at around 97 km. It solves the equations describing thermosphere-ionosphere physics, including electrodynamics and ion chemistry. Simpler setups can involve chemistry transport models which do not include electrodynamics but let us study how neutral atmospheric variability affects ionization rates and airglow. The advantage of forcing these additional models is that we can apply filtering to the UA-ICON fields before prescribing them. This lets us asses which modes are most relevant for ionospheric variability.
More information:
The middle and upper atmosphere are strongly influenced by climate change due to increasing carbon dioxide and experience rapid cooling. While this process is relatively well understood on a global scale, regional changes have received less attention. We perform multi-decadal UA-ICON simulations with prescribed historical forcing and nudging applied below 50 km. The nudging constrains the lower-atmospheric dynamics to observed meteorological conditions, which can, at least partly, also constrain the dynamics in the mesosphere and thermosphere, as it enforces realistic sources and propagation environments for atmospheric tides, planetary waves and resolved gravity waves. With this approach, we study regional trends in the dynamics of the MLT, their link to the global circulation, as well as feedback mechanisms.
We are also working on better predictions of atmospheric density. Knowledge of the density field in the MLT and above is of particular importance for predicting satellite orbits and re-entry scenarios of space objects. The mesosphere and lower thermosphere are the region where re-entering space objects ablate, which can have impacts on atmospheric chemistry across the whole atmosphere.
More information:
- Project IMPAGT