EGU General Assembly 2022
© Author(s) 2023. This work is distributed under
the Creative Commons Attribution 4.0 License.

Daytime-only-mean data can enhance our understanding of land-atmosphere coupling

Zun Yin1,2, Kirsten Findell2, Paul Dirmeyer3, Elena Shevliakova2, Sergey Malyshev1, Khaled Ghannam1,2, Nina Raoult4, and Zhihong Tan1,2
Zun Yin et al.
  • 1Program in Atmospheric and Oceanic Sciences, Princeton University, Princeton, NJ, USA (
  • 2NOAA/Geophysical Fluid Dynamics Laboratory, Princeton, NJ, USA
  • 3Center for Ocean-Land-Atmosphere Studies, George Mason University, Fairfax, Virginia
  • 4Laboratoire des Sciences du Climat et de l′Environnement, IPSL, CEA-CNRS-UVSQ, Gif-sur-Yvette, France

The major concern of land-atmosphere interactions (L-A) is the evolutionary process between the land surface and the planet boundary layer during the daytime, however many relevant studies had to use entire-day-mean daily time series to perform investigation due to lack of sub-daily data. Yet it is unclear whether the inclusion of nighttime data would alter the results or obscure the L-A interactive processes. To address this question, we generated daytime-only-mean (D) and entire-day-mean (E) daily data based on the ERA5 (5th ECMWF reanalysis) hourly product, and evaluated the strength of L-A coupling through a two-legged metrics, which assessed the coupling strength by the causality as well as the impact magnitude through two segments (land-fluxes and fluxes-atmosphere). The results demonstrated significant differences between the D- and E-based diagnoses as large as 67% (median 20.7%), which strongly depended on the season and the region. More importantly, for the first time, two special L-A coupling mechanisms were revealed. One was the advection-dominant L-A mechanism in tropical hyper-arid regions. The other was the soil moisture and sensible heat flux coupling mechanism during the cooling process over the nighttime. Both processes may play important roles during the night, andweaken the signal of L-A coupling if E was applied. To improve our knowledge of L-A interactions, we call attention to the urgent need for more high frequency data for relevant diagnoses. Meanwhile, we propose two approaches to resolve the dilemma of huge storage for high frequency data: (1) integration of L-A metrics in Earth System Model outputs, and (2) production of daily datasets based on different averaging algorithms.

How to cite: Yin, Z., Findell, K., Dirmeyer, P., Shevliakova, E., Malyshev, S., Ghannam, K., Raoult, N., and Tan, Z.: Daytime-only-mean data can enhance our understanding of land-atmosphere coupling, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6467,, 2022.