Weather Systems in a World without Land or Seasons

Aquaplanet simulations—as their name suggests—are idealized representations of Earth where the planet is covered entirely by water. The absence of continents, while unrealistic, provides a clean laboratory where weather systems can develop, evolve, and dissipate as they would do over Earth’s oceans. This kind of simulation is, therefore, useful for learning about the fundamental processes that govern the evolution of weather systems.

Here, the Model for Prediction Across Scales – Atmosphere (MPAS-A) was used to create an aquaplanet simulation with 3-km cell spacing (considered “convection-permitting” resolution) in the tropics transitioning to 15-km cell spacing elsewhere. This simulation develops a climate and weather systems that are very similar to those observed on Earth: a line of intense thunderstorms in the tropics, occasional tropical cyclones that migrate westward and poleward, an area of relatively quiet and dry weather in the subtropics, and a region of very active cyclones in the middle and polar latitudes. NCAR scientists are using this simulation to uncover the processes that favor the formation of powerful tropical cyclones—a very active area of research where our knowledge is very limited.


Weather Systems movie file 1920 x 1080 (262 MB)

Outgoing longwave radiation is used here as a proxy for clouds. The MPAS-A aquaplanet simulation starts from a quiescent state without any weather systems. As the simulation progresses, the combination of a sea-surface temperature condition and model physics lead to the development of weather systems everywhere. By one month, the weather patterns resemble those of real Earth. Of particular interest, tropical cyclones form in the deep tropics, move westward and poleward, and dissipate as they leave the warm tropical oceans.


Weather System

Further Information

Rios‐Berrios, R., Medeiros, B., & Bryan, G. H. (2020). Mean climate and tropical rainfall variability in aquaplanet simulations using the Model for Prediction Across Scales‐Atmosphere. Journal of Advances in Modeling Earth Systems, 12, e2020MS002102.

Computational Modeling

Rosimar Rios-Berrios (NCAR/MMM)

Computational Resources

NCAR Strategic Capability project NASP0010

NCAR/MMM Director’s Reserve project NMMM0042

Visualization and Post-production

Matt Rehme (NCAR/CISL)


Model for Prediction Across Scales-Atmosphere (MPAS-A)

A Multi-scale Nonhydrostatic Atmospheric Model Using Centroidal Voronoi Tesselations and C-Grid Staggering. William C. Skamarock, Joseph B. Klemp, Michael G. Duda, Laura Fowler, Sang-Hun Park, and Todd D. Ringler. 2012 Monthly Weather Review, 240, 3090-3105, doi:10.1175/MWR-D-11-00215.1

Data Source

Post-processed data from this and other MPAS-A aquaplanet simulations are available at

Rios-Berrios, Rosimar, Medeiros, Brian, Bryan, George. (2020). Aquaplanet simulations using the Model for Prediction Across Scales (MPAS) version 6.2. Version 1.0. UCAR/NCAR – DASH Repository. Accessed 22 Feb 2021.

Visualization Software

Imagery produced by VAPOR (, a product of the Computational Information Systems Laboratory at the National Center for Atmospheric Research