Direct influence of solar spectral irradiance on the high-latitude surface climate

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  • 1 Department of Climate and Space Sciences and Engineering, University of Michigan, Ann Arbor, Michigan, USA
  • 2 NASA Goddard Space Flight Center, Greenbelt, Maryland, USA
  • 3 Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, Colorado, USA.
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Abstract

Not only total solar irradiance (TSI) but spectral solar irradiance (SSI) matter for our climate. Different surfaces can have different reflectivity for the visible (VIS) and near-infrared (NIR). The recent NASA TSIS-1 mission has provided more accurate SSI observations than before. The TSI observed by TSIS-1 differs from the counterpart used by climate models by no more than 1 W m–2. However, the SSI difference in a given VIS (e.g., 0.44–0.63 μm) and NIR (e.g., 0.78–1.24 μm) band can be as large as 4 W m–2 with opposite signs. Using the NCAR CESM2, we study to what extent such different VIS and NIR SSI partitions can affect the simulated climate. Two sets of simulations with identical TSI are carried out, one with SSI partitioning as observed by the TSIS-1 mission and the other with what has been used in the current climate models. Due to different VIS-NIR spectral reflectance contrasts between icy (or snowy) surfaces and open water, the simulation with more SSI in the VIS has less solar absorption by the high-latitude surfaces, ending up with colder polar surface temperature and larger sea ice coverage. The difference is more prominent over the Antarctic than over the Arctic. Our results suggest that, even for the identical TSI, the surface albedo feedback can be triggered by different SSI partition between the VIS and NIR. The results underscore the importance of continuously monitoring SSI and the use of correct SSI in climate simulations.

Corresponding author, Dr. Xianwen Jing, 2455 Hayward St., the University of Michigan, Ann Arbor, MI 48109-2143. Email: xianwen@umich.edu

Abstract

Not only total solar irradiance (TSI) but spectral solar irradiance (SSI) matter for our climate. Different surfaces can have different reflectivity for the visible (VIS) and near-infrared (NIR). The recent NASA TSIS-1 mission has provided more accurate SSI observations than before. The TSI observed by TSIS-1 differs from the counterpart used by climate models by no more than 1 W m–2. However, the SSI difference in a given VIS (e.g., 0.44–0.63 μm) and NIR (e.g., 0.78–1.24 μm) band can be as large as 4 W m–2 with opposite signs. Using the NCAR CESM2, we study to what extent such different VIS and NIR SSI partitions can affect the simulated climate. Two sets of simulations with identical TSI are carried out, one with SSI partitioning as observed by the TSIS-1 mission and the other with what has been used in the current climate models. Due to different VIS-NIR spectral reflectance contrasts between icy (or snowy) surfaces and open water, the simulation with more SSI in the VIS has less solar absorption by the high-latitude surfaces, ending up with colder polar surface temperature and larger sea ice coverage. The difference is more prominent over the Antarctic than over the Arctic. Our results suggest that, even for the identical TSI, the surface albedo feedback can be triggered by different SSI partition between the VIS and NIR. The results underscore the importance of continuously monitoring SSI and the use of correct SSI in climate simulations.

Corresponding author, Dr. Xianwen Jing, 2455 Hayward St., the University of Michigan, Ann Arbor, MI 48109-2143. Email: xianwen@umich.edu
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