FAQs
What is GLOMAP?
GLOMAP (Global Model of Aerosol Processes) is a global chemical transport model that simulates the evolution of size and composition resolved aerosols, including their interaction with trace gases and clouds.
There are two GLOMAP flavours. GLOMAP-bin is a comprehensive sectional (bin) model and GLOMAP-mode is a faster modal version. Both models run in the TOMCAT chemical transport model, but GLOMAP-mode will also be used in the UK Chemistry and Aerosol (UKCA) community climate model.
What are the main differences between GLOMAP-bin and GLOMAP-mode?
GLOMAP-bin uses a “bin” scheme to represent the aerosol size distribution while GLOMAP-mode uses a series of “modes”. Bins, or size sections, are computationally expensive because they require at least one model tracer per bin and you need at least 20 bins to represent a typical size distribution. The number of tracers grows rapidly as you introduce more distributions and chemical components. GLOMAP-mode uses log-normal modes defined in terms of particle number and masses of each chemical component. The modes represent the frequently observed nucleation, aitken, accumulation and coarse modes.
How do the processes in GLOMAP-bin and GLOMAP-mode differ?
Not greatly. They both simulate all the relevant aerosol processes: nucleation, growth, coagulation, sedimentation, wet removal etc, except treated in different ways because of their different representations of the size distribution.
What transport models are used to drive GLOMAP?
Both GLOMAP-bin and mode run within the same host chemical transport model, TOMCAT. It’s an offline model that uses analysed meteorological fields (winds, temperature, etc from, e.g., ECMWF). GLOMAP-mode is also being implemented in the UK Unified Model, so will run in ‘climate mode’, interacting with the radiation, clouds and dynamics.
What’s the advantage of having GLOMAP-bin and mode running in one CTM?
This is an important part of our modelling strategy. By implementing both the simple and complex aerosol schemes in the same host CTM (TOMCAT) (see diagram) we can compare both against the same observations and each other. A CTM is an ideal model to compare against observations because it uses “real” meteorology. This can be done using a full climate model nudged towards observations, but it rarely is. Also, the CTM is much faster to run than a climate model, so we can do more comparisons. This approach means that any improvements we make to GLOMAP-mode (e.g., by evaluating against field campaign data) can be passed immediately to the climate model.
What are the advantages and disadvantages of each model?
The main advantage of GLOMAP-bin is that it makes no a priori assumption about the shape of the size distribution, so it’s ideal for studying how the global size distribution is shaped by fundamental processes. The disadvantage is that, for several chemical components, it’s an expensive model. The advantage of GLOMAP-mode is its speed. The main disadvantage is that it assumes a size distribution shape, which may limit the realism in certain environments.
How long can you run GLOMAP-bin and mode?
The run times are always varying as we change the models and as we use new computers. But typically, a global model run with components of sulphate, black carbon and organic carbon will run a factor 10 faster in GLOMAP-mode than bin. We typically run GLOMAP-bin for a few months (plus ~2 months spin up) or a maximum of 1 year. GLOMAP-mode is suitable for running for decades.
What can GLOMAP-bin and mode be used for?
GLOMAP-mode has been designed for long climate runs and GLOMAP-bin for shorter runs for comparison against specific observations. GLOMAP is ideal for comparing against observations where there is detailed information on the size distribution or particle number. Because the GLOMAP-mode aerosol scheme is quite fast, it could be used in combination with a more complete chemistry scheme.
How do things like emissions and chemical scheme differ?
The same chemical scheme is used to drive both bin and mode in the TOMCAT CTM. The emissions are also essentially the same, except in GLOMAP-mode they are prescribed in terms of modes and in GLOMAP-bin in terms of bins.
How do I get to use GLOMAP?
Please contact the principal investigator Ken Carslaw at Leeds. We strongly encourage collaboration, but please read about the obligations of users.
Can I get output fields from GLOMAP?
We are happy to provide ouput fields from the large number of runs that we have done. Please contact us. We have an archive of model output for various periods and for various model set-ups. Standard output consists of montly mean fields of particle number and composition as a function of size on a global 3-D grid. Some output at daily resolution is also available, and at higher tim resolution for several surface observatories. These data may be useful for offline chemistry studies, satellite retrievals etc.
