Prognostic Ozone For ICON: Enabling UV Forecasts

Stratospheric ozone (O3) absorbs biologically harmful solar ultraviolet radiation, mainly in the UV_B and UV_C spectral range. When reaching the surface, such UV radiation poses a well documented hazard to human health. In order to quantify this amount of UV radiation and to make it generally understandable, the World Health Organization has defined an UV Index[1]. It is calculated by weighting the incoming solar irradiance at surface level between 250 and 400 nanometers with their ”harmfulness” to the skin and scaling the results to values that normally range between 1 and 10, surpassing 10 for excessive UV exposure.

Implementing UV Index forecasts in numerical weather prediction (NWP) models allows to alert the public in time if special care for sun protection needs
to be taken. The German Weather Service (DWD) uses its NWP model ICON (ICOsahedral Nonhydrostatic Model)[2] to offer such a forecast for Germany[3]
using external data such as ozone forecasts by the Royal Dutch Weather Service (KNMI) and radiation lookup tables[4].

In our project we extend the capability of ICON to provide a configuration of self-consistent UV Index forecasts that do not require external data. For this, we use ICON-ART[5],[6] with a linearized ozone scheme (LINOZ)[7] and couple the prognostic ozone to the atmospheric radiation scheme Solar-J[8].
Here we present the current state of our UV Index forecast system and compare our results to available reference data.

References:

[1] World Health Organization, World Meteorological Organization, United Nations Environment Programme, and International Commission on Non-
Ionizing Radiation Protection. Global solar uv index : a practical guide,2002.

[2] Günther Zängl et al.. The icon (icosahedral non-hydrostatic) modelling framework of dwd and mpi-m:
Description of the non-hydrostatic dynamical core. Quarterly Journal of the Royal Meteorological Society, 2015.

[3] https://kunden.dwd.de/uvi/index.jsp.

[4] Henning Staiger and Peter Koepke. Uv index forecasting on a global scale. Meteorologische Zeitschrift, 2005.

[5] D. Rieger et al.. Icon–art 1.0 – a new online-coupled model system from the global to regional scale. Geoscientific Model Development, 2015.

[6] J. Schröter et al.. Icon-art 2.1: a flexible tracer framework and its application for composition studies in numerical weather forecasting and climate simulations. Geoscientific Model Development, 2018.

[7] C. A. McLinden et al. Stratospheric ozone in 3-d models: A simple chemistry and the cross-tropopause flux. Journal of Geophysical Research: Atmospheres, 2000

[8] J. Hsu, M. J. Prather et al.. A radiative transfer module for calculating photolysis rates and solar heating in climate models: Solar-j v7.5. Geoscientific Model Development, 2017.