Ultraviolet radiation modelling using output from the Chemistry Climate Model Initiative.

Area of Science:

• Atmospheric Science
• Climate Science
• Ozone Layer Research

Background:

• Clouds are a major uncertainty in climate projections, necessitating clear-sky Ultraviolet Index (UVI) simulations.
• The Tropospheric Ultraviolet Model (TUV) is used to derive UVI values.
• Climate simulations from the Chemistry-Climate Model Initiative (CCMI-1) provide necessary atmospheric data.

Purpose of the Study:

• To model clear-sky UVI evolution throughout the 21st century under various Representative Concentration Pathways (RCPs).
• To compare modeled UVI with satellite and ground-based measurements for validation.
• To analyze the influence of greenhouse gases (GHGs) and ozone-depleting substances (ODSs) on UVI.

Main Methods:

• Utilized the Tropospheric Ultraviolet Model (TUV) driven by CCMI-1 climate simulations.
• Compared modeled UVI climatologies with OMI-Aura and NDACC network data.
• Simulated UVI changes for RCPs 2.6, 4.5, 6.0, and 8.5, and performed sensitivity analyses with fixed GHGs or ODSs.

Main Results:

• Modeled UVI showed regional differences compared to ground-based measurements (-5.9% to 10.6%).
• Projected UVI increases in the tropical belt (2-4%) and mid-latitudes (1.8-3.4% in SH for RCPs 2.6, 4.5, 6.0), with decreases in NH for RCP 8.5.
• Ozone recovery drives UVI normalization at high latitudes; GHGs delay ozone return, impacting UVI.

Conclusions:

• Clear-sky UVI is projected to increase in many regions by 2100, influenced by GHGs and ozone recovery.
• Southern Hemisphere UVI is primarily driven by total ozone, while Northern Hemisphere UVI is influenced by both ozone and aerosols.
• Aerosol optical depth has a significant impact on Northern Hemisphere UVI, twice that of total ozone.