Work Description

Date: 18 February, 2025

Dataset Title: Dataset for Instantaneous radiative effect of surface long wave spectral emissivity in a Snowball Earth simulation

Dataset Contact: Daniel Zetterberg dzetterb@umich.edu

Dataset Creators:
Name: Daniel S. Zetterberg
Email: dzetterb@umich.edu
Institution: University of Michigan Department of Climate and Space Sciences and Engineering
ORCID: https://orcid.org/0000-0002-5417-2903

Name: Xianglei Huang
Email: xianglei@umich.edu
Institution: University of Michigan Department of Climate and Space Sciences and Engineering
ORCID: https://orcid.org/0000-0002-7129-614X

Name: Johannes Hoerner
Email: johannes.hoerner@univie.ac.at
Institution: University of Vienna Department of Meteorology and Geophysics
ORCID: https://orcid.org/0000-0002-0676-5149

Name: Aiko Voigt
Email: aiko.voigt@univie.ac.at
Institution: University of Vienna Department of Meteorology and Geophysics
ORCID: https://orcid.org/0000-0002-7394-8252

Funding: University of Michigan Dean's Fellowship (DSZ), U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research, Climate and Environmental Science Division under Awards DE-SC0022117 to the University of Michigan (XLH)

Key Points:
- We calculate the instantaneous radiative effect of surface spectral emissivity for conditions in the Neoproterozoic Snowball Earth.
- We find using snow or ice surface conditions can reduce the simulated outgoing longwave radiation (OLR) by 1.1-3.4 Wm^-2.
- This is 1-3% of the radiation budget, which would significantly impact the energy budget of a simulated Snowball climate, more so than the current climate.
- The effect is greater for ice than snow, highlighting the impact of precipitation processes on radiation budgets in Snowball Modelling.

Research Overview:
Spectrally dependent emission by the surface (i.e., surface spectral emissivity) is commonly ignored by current climate models. Surface spectral emissivity matters more in cold and dry environments than in hot and humid environments. Recent modeling studies confirmed that, for current climate simulations, this process affects the polar climate more than the extra-polar climate. As for the Snowball Earth, a period characterized by global polar-like conditions of extreme cold and low humidity, including surface spectral emissivity could alter the simulated global radiation budget. This, in turn, could affect the simulated climate of the Snowball Earth. Here, we use an aqua-planet slab-ocean simulation of Snowball Earth by the ICON model to perform offline radiative transfer calculations to quantify such impact on the outgoing longwave radiation (OLR). The offline radiative transfer model is used to compute the clear-sky OLR for two surfaces that would be present in the extremely cold simulation: ice and snow. Compared to the results with assumed blackbody surface, the global mean OLR decreases by 3.4 and 1.1 W m-2 for ice and snow surfaces, respectively. The impact of surface spectral emissivity on the OLR is strongest at the equator and weakens towards the poles, presenting a noticeable meridional gradient. The seasonal variation of the impact is also obvious. The radiative effects of this often-neglected process warrant further scrutiny for the Snowball Earth simulations, particularly the Jormungand mechanism, as well as simulations of other cold and dry climates.

Methodology:
JH and AV ran the ICON climate model to simulate environmental conditions representative of the formation of a Snowball state. The details of this simulation are in the paper "Sea-ice thermodynamics can determine waterbelt scenarios for Snowball Earth" (https://doi.org/10.5194/esd-15-215-2024). These climate conditions were used as the atmopshere for offline radiative transfer calculations by DSZ and XLH. In these calculations, we took surface spectral emissivity data for three surface types present in Snowball modelling: ocean, ice, and snow surfaces, and calculated the OLR change when these surfaces were used versus a blackbody surface. The surface emissivity data came from the dataset "A global data set of surface spectral emissivity for GCM and NWP use" (https://huang.engin.umich.edu/182-2/). The MODTRAN radiative transfer model (https://doi.org/10.1117/12.606026) was used for the calculations. DSZ then processed the spectral radiance data outputted by MODTRAN into the OLR flux data provided in this dataset. DSZ created the plots, shown in the Jupyter notebook.

Files Contained Here:
- snowball_conditions_plotting_HV2024.nc: A netcdf file that contains the simulation output data from the ICON Snowball model. Data was adapted from the ICON grid to a lat-lon grid, then the zonal averages of several climate variables are presented here for plotting. Also contains averaged atmospheric profiles for the tropical (30S-30N), mid-latitude(+/- 30-60), and polar (+/- 60-90) regions. HV2024 refers to the paper the simulation was run for (https://doi.org/10.5194/esd-15-215-2024).

- emiss_spectral.txt: A text file containing spectral emissivity data for 3 surfaces as a function of wavelength: ocean, ice, and snow. Data comes from the dataset at https://huang.engin.umich.edu/182-2/. Here snow refers to coarse snow in the original dataset.

- sensitivity_results.nc: A netcdf file that presents the results from Section 3.1 of the manuscript. The file contains OLR as a function of atmopsheric total column water vapor (TCWV), surface emissivity, and regional atmospheric temperature/humidity profile. Here the emissivity is modelled as a graybody. The OLR results are used for a sensitivity study that demonstrates how the effect of surface emissivity on OLR changes with TCWV.

- broadband_results.nc: A netcdf file that presents the results from Section 3.2 of the manuscript. The file contains OLR as a function of longitude, latitude, and surface type at 5x4 degree resolution. Broadband refers to radiance being integrated across the entire longwave spectrum.

- RRTMG_band_results.nc: A netcdf file that presents the results from Section 3.3 of the manuscript. Same as "broadband_results.nc" but radiance is integrated over the first 12 longwave RRTMG bands. RRTMG is a popular radiation scheme used in climate models (https://doi.org/10.1029/97JD00237).

- monthly_results.nc: A netcdf file that presents the results from Section 3.4 of the manuscript. Same as "broadband_results.nc" but the OLR is also a function of month of the year, instead of annually averaged.

- figure_creator.ipynb: A Jupyter notebook that contains code for reading and plotting the data. The plots here are formatted as they are in the manuscript. The notebook contains instructions on how to read the data. Additionally, documented code for calculating the sensitivity results from "sensitivity_results.nc" is included. Note that Figure 8 in the manuscript was created using PowerPoint.

Related Publication(s):
Zetterberg, D.S., Huang, X.L., Hoerner, J., & Voigt, A. Instantaneous radiative effect of surface long wave spectral emissivity in a Snowball Earth simulation. Submitted to Journal of Geophysical Research: Atmospheres on 7 February 2025.

Use and Access:
This data set is made available under a Creative Commons Public Domain license (CC0 1.0).

To Cite Data:
Zetterberg, D.S., Huang, X.L., Hoerner, J., & Voigt, A. (2025). Instantaneous radiative effect of surface long wave spectral emissivity in a Snowball Earth simulation [Data set]. University of Michigan - Deep Blue Data. https://doi.org/10.7302/949x-tw78