Chen, Yi-Hsuan陳毅軒

Assistant Research Fellow

Research Interests

My research interests are to understand cloud and radiation processes and their roles in the Earth’s climate system, with a particular focus on parameterizing these processes in climate models. I have extensively worked on cloud and radiation parameterization schemes in climate models, including modifications of existing schemes, implementation of new schemes, and evaluation of simulation results. For instance, during my PhD study, I modified the longwave radiation scheme in NCAR CESM to include surface spectral emissivity and ice-cloud longwave scattering, and then investigated to what extent these modifications influence the simulated climate over the regions of interest, such as the Sahara and Sahel regions and the high latitudes. I also did similar implementations for the DoE E3SM model. During my postdoc, I explored two different coupling strategies for the boundary layer and convection schemes in GFDL AM4. In addition, I implemented a new boundary layer/convection scheme, Mellor-Yamada-Nakanishi-Niino Eddy-Diffusivity/Mass-Flux (MYNN-EDMF), into AM4 and evaluated its performance on marine stratocumulus regions.

Representative Publications

Chen, Y.-H.*, X. L. Huang, P. Yang, C.-P. Kuo, and X. H. Chen, 2020: Seasonal Dependent Impact of Ice-Cloud Longwave Scattering on the Polar Climate, Geophys. Res. Lett., 47, 1-10,

Shiu, C.-J., Y.-C. Wang, H.-H. Hsu, W.-T. Chen, H.-L. Pan, R. Sun, Y.-H. Chen, and C.-A. Chen, 2021: GTS v1.0: A Macrophysics Scheme for Climate Models Based on a Probability Density Function, Geosci. Model Dev., 14, 177-204,

Kuo, C.-P., P. Yang, X. L. Huang, Y.-H. Chen, and G. Liu, 2020: Assessing the accuracy and efficiency of longwave radiative transfer models involving scattering effect with cloud optical property parameterizations. J. Quant. Spectrosc. Radiat. Transf., 240, 106683,

Chen, Y.-H., X. L. Huang, X. H. Chen, and M. Flanner, 2019: The Effects of Surface Longwave Spectral Emissivity on Atmospheric Circulation and Convection over the Sahara and Sahel, J. Climate, 32, 4873-4890,


1. Influence of ice-cloud longwave scattering on the polar climate

Most climate models neglect cloud longwave (LW) scattering because scattering is considered negligible compared to strong LW absorption by clouds and greenhouse gases. While this rationale is valid for simulating extrapolar regions, it is questionable for the polar regions, where the atmosphere is dry and hence has weak absorption, and ice clouds that have strong scattering capability frequently occur. Using the slab-ocean Community Earth System Model, we show that ice cloud LW scattering can warm winter surface air temperature by 0.8–1.8 K in the Arctic and by 1.3–1.9 K in the Antarctic, while this warming becomes much weaker in polar summer. Such scattering effect cannot be correctly assessed when sea surface temperature and sea ice are prescribed as this effect is manifested through a surface-atmosphere coupling. For further details, please check out our 2020 GRL paper (

2. Exploring two coupling strategies of the boundary layer and convection schemes

Planet boundary layer (PBL) and moist convection (Conv) closely couple with each other. Turbulence in the PBL effectively transports heat and moisture from the surface to the atmosphere, helping convective clouds to form. These convective clouds can in turn affect the PBL turbulence and structure. Here we explore two coupling strategies of PBL and convection schemes in GFDL AM4, namely, (1) PBL_then_Conv, in which the convection scheme sees the state updated by the PBL scheme, and (2) PBL_and_Conv, in which both PBL and convection schemes see the same state. The AMIP simulation results show that these coupling strategies have the strongest impact on the marine shallow cumulus regime. PBL_and_Conv has weaker convection, stronger PBL activities, and more low cloud than those in the PBL_then_Conv. We hypothesize that these are because the convection scheme in PBL_and_Conv “sees” a less unstable state, leading to weaker convection.

3. Implementation and evaluation of the MYNN-EDMF scheme in GFDL AM4

GFDL AM4 underestimates marine stratocumulus amount on the west coasts of North and South America and of South Africa, leading to excessive shortwave absorption in these regions. To address this issue, we implement the Mellor-Yamada-Nakanishi-Niino Eddy-Diffusivity/Mass-Flux (MYNN-EDMF) scheme into the AM4. The major implementation challenges include (1) incompatibility of the MYNN-EDMF cloud scheme and AM4 cloud scheme, and (2) coupling the MYNN-EDMF with the other AM4 schemes. The performance of the MYNN-EDMF in AM4 is evaluated using AMIP simulation. AM4 with MYNN ED shows moderate improvements in marine stratocumulus biases. However, AM4 with MYNN-EDMF worsens the already large marine stratocumulus biases, partly due to coupling with the AM4 stratiform cloud scheme.

  • Postdoctoral Research Associate,
    Program in Atmospheric and Oceanic Sciences,
    Princeton University, United States (2020-2023)
  • Ph.D.
    Department of Climate and Space Sciences and Engineering,
    University of Michigan - Ann Arbor, United States (2019)
  • M.S.
    Department of the Atmospheric Sciences,
    National Taiwan University, Taipei, Taiwan (2012)
  • B.S.
    Department of the Atmospheric Sciences,
    INational Central University, Zhongli, Taiwan(2009)