11:30 AM - 11:45 AM
[AOS14-10] Estimation of the eddy diffusivity in the early Martian ocean and its impact on climate
Keywords:Early Mars, General Circulation Model, Ocean circulation, Eddy diffusivity
Background and Objectives
Numerous geological features on early Mars suggest the presence of liquid water flow, and the possibility of ancient oceans existing for a certain period. However, the mechanisms responsible for sustaining a warm and humid climate during that era remain largely unclear. To better understand the climate dynamics of early Mars, simulations using General Circulation Models (GCMs) have been conducted, with comparisons between model outputs and existing topographical features providing insights into past environmental conditions.
Since ocean circulation plays a crucial role in shaping climate, accurately simulating ocean dynamics on early Mars is essential for climate reconstructions. However, due to the limited understanding of ocean circulation on extraterrestrial planets, precise parameterization methods have yet to be established. In particular, mesoscale eddy parameterization significantly influences meridional transport, and improving the estimation of eddy diffusivity could enhance the accuracy of climate simulations. This study aims to determine whether the eddy diffusivity estimation methods used for Earth are applicable to Mars and to investigate the impact of incorporating a novel eddy diffusivity parameterization into a global climate model.
Methods
First, numerical experiments were conducted using a high-resolution model parameter capable of resolving subgrid-scale eddies to estimate eddy diffusivity on Mars. On Earth, eddy diffusivity is known to be proportional to the product of the square root of barotropic kinetic energy and the Rhines scale. However, given the differences in gravity, rotation speed, and planetary size, it remains uncertain whether this relationship holds for Mars, and thus, this parameterization method has not been applied to Martian simulations. To simulate eddy-driven flows in the Martian ocean, the Modular Ocean Model 6 (MOM6) developed by GFDL was employed with a two-layer Phillips model at a resolution of 5 km × 5 km on a beta-plane. Martian parameters for gravity, rotation speed, and planetary size were incorporated into the model to replicate conditions affecting eddy diffusivity. The average values of meridional fluxes over a 10-year simulation period were used to compute eddy diffusivity. The accuracy of the estimation method was assessed by comparing the computed results with theoretical estimates, determining whether the methodology used for Earth could be applied to Mars with comparable accuracy.
Next, the inferred eddy diffusivity was integrated into a global climate model to examine its influence on meridional transport. The global climate model used was ROCKE-3D, developed by NASA’s GISS, with current Martian topography implemented. To account for spatial and temporal variations in eddy diffusivity, the Mesoscale Eddy Kinetic Energy (MEKE) method, originally developed for MOM6, was employed. This method parameterizes eddy diffusivity based on temporally varying barotropic kinetic energy. In this simulation, equilibrium was defined as the point where the planetary net heat balance dropped below a specified threshold. The average meridional tracer transport over 10 Martian years from the equilibrium state was analyzed as the final simulation result.
Results and Discussion
The first simulation using the eddy-resolving model with Martian parameters revealed that eddy diffusivity on Mars is proportional to the Rhines scale, similar to Earth. This result suggests that the Rhines scale can be used to estimate eddy diffusivity on planets with rotation rates comparable to Earth, even if gravity and planetary size differ to some extent.
Further simulations using ROCKE-3D, incorporating the Rhines-scale-based eddy diffusivity parameterization, confirmed that spatially and temporally varying eddy diffusivity could be effectively implemented within the Martian ocean model. Simulations with this new parameterization produced distinct meridional transport patterns compared to those using conventional parameterizations. These findings indicate that by conducting simulations under a range of parameter conditions, this model could provide more accurate reconstructions of early Martian environments and contribute to a deeper understanding of its climatic history.
Numerous geological features on early Mars suggest the presence of liquid water flow, and the possibility of ancient oceans existing for a certain period. However, the mechanisms responsible for sustaining a warm and humid climate during that era remain largely unclear. To better understand the climate dynamics of early Mars, simulations using General Circulation Models (GCMs) have been conducted, with comparisons between model outputs and existing topographical features providing insights into past environmental conditions.
Since ocean circulation plays a crucial role in shaping climate, accurately simulating ocean dynamics on early Mars is essential for climate reconstructions. However, due to the limited understanding of ocean circulation on extraterrestrial planets, precise parameterization methods have yet to be established. In particular, mesoscale eddy parameterization significantly influences meridional transport, and improving the estimation of eddy diffusivity could enhance the accuracy of climate simulations. This study aims to determine whether the eddy diffusivity estimation methods used for Earth are applicable to Mars and to investigate the impact of incorporating a novel eddy diffusivity parameterization into a global climate model.
Methods
First, numerical experiments were conducted using a high-resolution model parameter capable of resolving subgrid-scale eddies to estimate eddy diffusivity on Mars. On Earth, eddy diffusivity is known to be proportional to the product of the square root of barotropic kinetic energy and the Rhines scale. However, given the differences in gravity, rotation speed, and planetary size, it remains uncertain whether this relationship holds for Mars, and thus, this parameterization method has not been applied to Martian simulations. To simulate eddy-driven flows in the Martian ocean, the Modular Ocean Model 6 (MOM6) developed by GFDL was employed with a two-layer Phillips model at a resolution of 5 km × 5 km on a beta-plane. Martian parameters for gravity, rotation speed, and planetary size were incorporated into the model to replicate conditions affecting eddy diffusivity. The average values of meridional fluxes over a 10-year simulation period were used to compute eddy diffusivity. The accuracy of the estimation method was assessed by comparing the computed results with theoretical estimates, determining whether the methodology used for Earth could be applied to Mars with comparable accuracy.
Next, the inferred eddy diffusivity was integrated into a global climate model to examine its influence on meridional transport. The global climate model used was ROCKE-3D, developed by NASA’s GISS, with current Martian topography implemented. To account for spatial and temporal variations in eddy diffusivity, the Mesoscale Eddy Kinetic Energy (MEKE) method, originally developed for MOM6, was employed. This method parameterizes eddy diffusivity based on temporally varying barotropic kinetic energy. In this simulation, equilibrium was defined as the point where the planetary net heat balance dropped below a specified threshold. The average meridional tracer transport over 10 Martian years from the equilibrium state was analyzed as the final simulation result.
Results and Discussion
The first simulation using the eddy-resolving model with Martian parameters revealed that eddy diffusivity on Mars is proportional to the Rhines scale, similar to Earth. This result suggests that the Rhines scale can be used to estimate eddy diffusivity on planets with rotation rates comparable to Earth, even if gravity and planetary size differ to some extent.
Further simulations using ROCKE-3D, incorporating the Rhines-scale-based eddy diffusivity parameterization, confirmed that spatially and temporally varying eddy diffusivity could be effectively implemented within the Martian ocean model. Simulations with this new parameterization produced distinct meridional transport patterns compared to those using conventional parameterizations. These findings indicate that by conducting simulations under a range of parameter conditions, this model could provide more accurate reconstructions of early Martian environments and contribute to a deeper understanding of its climatic history.