A large part of the population living in cities is exposed to ozone levels above the EU air quality target value. The CityChem extension of the urban air quality model EPISODE enables a detailed treatment of the atmospheric chemistry in urban areas and near-field dispersion close to industrial stacks and in street canyons. The application of the model in the city of Hamburg (Germany) shows good performance for ozone, nitrogen dioxide and particulate matter at air quality monitoring stations.

Highly resolved forecasts of precipitation fields are difficult to evaluate since individual rain features are typically not placed precisely at the right location. Instead of comparing forecasts and observations pixel by pixel, we base our verification on the fields' wavelet transforms which compactly summarize the overall structure. The methodology is rigorously tested using randomly generated rain fields for which that structure can be determined at will.

Given the large number of available data sets and products currently produced for climate impact studies, it is challenging to distil the most accurate and useful information for climate services. This work presents a comparison of methods widely used to generate climate projections, from different sources and at different spatial resolutions, in order to assess the role of downscaling and statistical post-processing (bias correction).

GEOS-Chem 12.0.0 has been recognized to significantly overestimate the concentrations of gaseous nitric acid, aerosol nitrate, and aerosol ammonium over the United States. In this study, we show that most or all of the overestimation issue appears to be associated with wet scavenging processes. With the updated wet scavenging scheme in this work, we successfully improve the skill of the model in predicting the three species concentrations, which are important for air quality and climate studies.

The VISIR ship-routing model is updated in order to deal with ocean currents. The optimal tracks we computed through VISIR in the Atlantic ocean show great seasonal and regional variability, following a variable influence of surface gravity waves and currents. We assess how these tracks contribute to voyage energy-efficiency gains through a standard indicator (EEOI) of the International Maritime Organization. Also, the new model features are validated against an exact analytical benchmark.

We evaluated the skill of the road weather model RoadSurf to reproduce present-day road weather conditions in Finland when driven by a high-resolution regional climate model. Simulated road surface temperatures and conditions were compared to observations between 2002 and 2014 at 25 Finnish road weather stations. RoadSurf accurately captured the main characteristics of road weather conditions. Thus, this model can be used to study the future scenarios of road weather in the study area.

Few Earth system models represent permafrost soil biogeochemistry, contributing to uncertainty in estimating its response and that of the planet to warming. Because the permafrost contains over double the carbon in the present atmosphere, its fate as it is unlocked by warming is globally significant. One way it can be mobilised is into rivers, the sea, or the atmosphere: a vector previously ignored in climate modelling. We present a model scheme for resolving this vector at a global scale.

WRF-Hydro needs to be calibrated to optimize its output with respect to observations. However, when applied to a relatively large domain, both WRF-Hydro simulations and calibrations require intensive computing resources and are best performed in parallel. This study ported an independent calibration tool (parameter estimation tool – PEST) to high-performance computing clusters and adapted it to work with WRF-Hydro. The results show significant speedup for model calibration.

We present an upper-atmosphere extension of the ICOsahedral Non-hydrostatic (ICON) model. This includes an extension of the model dynamics from a shallow to a deep atmosphere and the implementation of upper-atmosphere physics parameterizations. Idealized test cases and climate simulations are performed in order to evaluate this new configuration, named UA-ICON.

Parcels is a framework to compute how ocean currents transport stuff such as plankton and plastic around. In the latest version 2.0 of Parcels, we focus on more accurate interpolation schemes and implement methods to seamlessly combine data from different sources (such as winds and currents, possibly in different regions). We show that this framework is very efficient for tracking how microplastic is transported through the North Sea into the Arctic.

This work presents a submodel description for the atmospheric cycling and air–surface exchange processes of semivolatile organic compounds. The submodel is meant to be applied within a global atmospheric chemistry–climate model. The simulation results for polycyclic aromatic hydrocarbons confirm progress in modelling semivolatile species, verified by comparison with surface monitoring data. The significance of new modelling features for tracer distributions was quantified in a sensitivity study.

The global aerosol–climate model ECHAM6.3–HAM2.3 as well as the previous model versions ECHAM5.5–HAM2.0 and ECHAM6.1–HAM2.2 are evaluated. The simulation of clouds has improved in ECHAM6.3–HAM2.3. This has an impact on effective radiative forcing due to aerosol–radiation and aerosol–cloud interactions and equilibrium climate sensitivity, which are weaker in ECHAM6.3–HAM2.3 than in the previous model versions.

Models of ozone air pollution are often evaluated with the policy metric set by the EPA of the maximum daily 8 h average ozone concentration. These models may be used in policy settings to evaluate air quality regulations. However, most models have difficulty simulating how ozone varies over the course of the day, and thus the use of this metric in model evaluation is problematic. Improved representation of mixed layer dynamics and ozone loss to the surface is needed to resolve this issue.

As part of the Past Global Changes (PAGES) working group on Quaternary Interglacials, we propose a protocol to perform transient simulations of the penultimate deglaciation for the Paleoclimate Modelling Intercomparison Project (PMIP4). This design includes time-varying changes in orbital forcing, greenhouse gas concentrations, continental ice sheets as well as freshwater input from the disintegration of continental ice sheets. Key paleo-records for model-data comparison are also included.

The retrieval of a hazardous source (from a leak, terrorist attack, etc.) is an important operational issue for local authorities and health professionals in terms of security and defense. The estimation of the source parameters must therefore be precise. To ensure this, an established monitoring network must be optimal. This study presents a methodology for the optimization of a monitoring network of sensors in an urban-like environment with a view to estimating an unknown emission source.

Numerical weather prediction model HIRLAM includes prognostic treatment of lake surface state since 2012. Forecast is based on the Freshwater Lake model (Flake). We compared the predicted lake water temperature, freeze-up and break-up dates as well as the ice thickness and snow depth during six years over 45 lakes in Finland against observations by Finnish Environment Institute. Water surface temperatures and freezing of lakes were well predicted but the ice tended to melt too early in spring.

We present a novel set of atmospheric simulations designed to address changes in high-impact weather events. We simulate 10 years under current and projected late 21st century climate conditions. Our model reasonably replicates present-day climate features, reproduces features of climate change that are expected from global climate models, and captures smaller-scale, high-impact weather events. We anticipate these simulations will have great value in understanding changes in extreme weather.

Sea ice thickness varies considerably on spatial scales of several meters. However, contemporary climate models cannot resolve such scales yet. This is why sea ice models used in climate models include an ice thickness distribution (ITD) to account for this unresolved variability. Here, we explore with the ocean–sea ice model NEMO3.6-LIM3 the sensitivity of simulated mean Arctic and Antarctic sea ice states to the way the ITD is discretized.

Snow cover significantly influences the surface albedo and radiation budget. Therefore, a realistic representation of snowfall in climate models is important. Here, using decade-long estimates of snowfall derived from the satellite sensor, four climate models are evaluated to assess how well they simulate snowfall in the Arctic. It is found that light and median snowfall is overestimated by the models in comparison to the satellite observations, and extreme snowfall is underestimated.

Here we evaluate the performance of the Community Atmosphere Model version 6 (CAM6) released in 2018, with the default 1º horizontal resolution and a higher-resolution simulation (approximately 0.25º), against various precipitation observational datasets over Asia. With the prognostic treatment of precipitation processes (which is missing in CAM5) and the new microphysics module, CAM6 is able to better simulate climatological mean and extreme precipitation over Asia.

The pygeodyn package is a geomagnetic data assimilation tool written in Python. It gives access to the Earth's core flow dynamics, controlled by geomagnetic observations, by means of a reduced numerical model anchored to geodynamo simulation statistics. It aims to provide the community with a user-friendly and tunable data assimilation algorithm. It can be used for education, geomagnetic model production or tests in conjunction with webgeodyn, a set of visualization tools for geomagnetic models.

The Thermodynamic Diagnostic Tool (TheDiaTo v1.0) is a collection of diagnostics for the study of the thermodynamics of the climate system in climate models. This is fundamental in order to understand where the imbalances affecting climate projections come from and also to allow for easy comparison of different scenarios and atmospheric regimes. The tool is currently being developed for the assessment of models that are part of the next phase of the Coupled Model Intercomparison Project (CMIP).