Studying air – ocean wave interactions using GRNET ARIS high performance computing infrastructure

The importance of studying air – ocean wave interactions

As the global interest in Earth system balance is growing, the accurate prediction of extreme weather phenomena as well as wind and wave power production are becoming more and more crucial. To that end, it is essential to study air – ocean interactions via large scale experiments that require modern network and computing infrastructures. The optimization of atmospheric and ocean parameters forecast, such as wind and wave, affects numerous human activities associated with the sea, such as marine transportation, fishery, tourism, oil extraction and coastal constructions. Air – ocean interactions drive the formation of cyclones, associated with extreme winds, high waves and floods, inflicting human casualties and economic damages. Nevertheless, the understanding of these complex interaction mechanisms is still incomplete.

ARIS High Performance Computing: GRNET’s technological solution used for integrated air – ocean wave simulations

Dr. Petros Katsafados and his Atmosphere and Climate Dynamics research team at Harokopio University of Athens, aimed at implementing an innovative two – way coupled atmosphere – ocean wave modeling system in order to analyze and understand atmosphere – wave interactions. “Obtaining access to computational resources was vital in our effort to produce reliable scientific results and to the overall success of the project”, Dr. Katsafados, adding : “GRNET offered to us a tailor made solution, by providing access to ARIS national supercomputing infrastructure”.

In order to support the synchronous simulation of atmospheric, wave, chemical and hydrological processes, the research group developed CHAOS (Chemical Hydrological Atmospheric Ocean wave System) modeling system (Figure 1). The system was first deployed on ARIS HPC system and consists of the WRF atmospheric model and the WAM wave model. The two models run concurrently, communicate and exchange information through the OASIS3-MCT coupler. For this innovative project, Dr. George Varlas was awarded by the European Meteorological Society with the Young Scientist Award 2018



Figure 1. The components of the two – way coupled modeling system CHAOS.

Scientific findings from cyclone simulations exploiting HPC ARIS capabilities

The coupled modeling system was used to study cyclones at the Mediterranean sea and the Atlantic ocean (hurricane Sandy, 2012). The research showcased, among other findings, that waves attenuate the development of cyclones and are reflected on the vertical structure of atmosphere affecting cloud formation (Figure 2). The study also concluded that rain reduces wave height. Particularly noteworthy is that CHAOS system yields robust improvements compared to traditional modeling approaches. The improvement exceeds 20% under extreme weather conditions.

Figure 2. 3D distribution of water content (cloud, rain, ice, snow and graupel in g kg-1 and horizontal distribution of SWH (m) at 00:00 UTC (approximately the time of landfall of Sandy at eastern United States) on 30 October 2012, based on CHAOS-1way (left) and CHAOS-2way (right) results (Varlas, 2017).

The total number of core hours spent on ARIS HPC system was 1,134,080. The maximum scaling of the research application, namely the maximum number of cores used simultaneously by one process, was 640 cores.


  1. Katsafados, P., Papadopoulos, A., Korres, G., and Varlas, G. (2016). A fully coupled atmosphere-ocean wave modeling system for the Mediterranean Sea: interactions and sensitivity to the resolved scales and mechanisms. Geoscientific Model Development, 9(1), 161-173 (doi: 10.5194/gmd-9-161-2016).
  2. Varlas, G., (2017). Development of an integrated modeling system for simulating the air-ocean wave interactions. PhD Dissertation. Available at:
  3. Varlas, G., Katsafados, P., Papadopoulos, A., and Korres, G. (2018). Implementation of a two-way coupled atmosphere-ocean wave modeling system for assessing air-sea interaction over the Mediterranean Sea. Atmospheric Research, 208, 201-217 (doi: 10.1016/j.atmosres.2017.08.019).
  5. Katsafados, P., Varlas, G., Papadopoulos, A., Spyrou, C., and Korres, G. (2018). Assessing the implicit rain impact on sea state during hurricane Sandy (2012). Geophysical Research Letters, 45, 12.015-12.022 (doi: 10.1029/2018GL078673).
  6. Varlas, G., Anagnostou, M., Spyrou, C., Papadopoulos, A., Kalogiros, J., Mentzafou, A., Michaelides, S., Baltas, E., Karymbalis, E. and Katsafados, P. (2019). A multi-platform hydrometeorological analysis of the flash flood event of 15 November 2017 in Attica, Greece. Remote Sensing, 11(1), 45 (doi: 10.3390/rs11010045).