2025-03-06 東京大学
＜関連情報＞
- https://www.s.u-tokyo.ac.jp/ja/press/10683/
- https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2023JE008137
火星大気の残留平均循環の気候学と再解析データセットに基づく分解波と未分解波の寄与 Climatology of the Residual Mean Circulation of the Martian Atmosphere and Contributions of Resolved and Unresolved Waves Based on a Reanalysis Data Set
Anzu Asumi, Kaoru Sato, Masashi Kohma, Yoshi-Yuki Hayashi
Journal of Geophysical Research: Planets Published: 06 March 2025
DOI:https://doi.org/10.1029/2023JE008137
Abstract
The objective of this study is to examine the climatology of the residual mean circulation, and the roles of wave forcings by both resolved waves (RWs) and unresolved waves (UWs). The analysis is performed using data from the Ensemble Mars Atmosphere Reanalysis System (EMARS) over four Mars Years without global dust storms, based on the transformed Eulerian mean equation theory. While the RW forcing is estimated directly as Eliassen-Palm flux divergence, the forcing by UWs, including subgrid-scale gravity waves, is estimated indirectly using the zonal momentum equation. This indirect method, originally devised for studying the Earth’s middle atmosphere, is applicable to latitudinal ranges where angular momentum isopleths are continuous from the surface to the top of the atmosphere, typically mid- and high-latitude regions. In low latitudes of the winter hemisphere, a strong residual mean flow toward the winter pole is observed in a pressure range between ∼20 and ∼0.5 Pa (∼30–60 km), where the latitudinal gradient of the absolute angular momentum is small. The strong poleward flow crosses the isopleths of angular momentum in the regions of its northern and southern ends, indicating the necessity of the wave forcing. Our results suggest that the structure of the residual mean circulation at mid- and high-latitude regions is largely determined by UW forcing, particularly above ∼2 Pa level, whereas the RW contribution is also significant below the ∼2 Pa level.
Key Points
- Climatology of the residual mean circulation of the Martian atmosphere is revealed based on the EMARS reanalysis data set
- The contribution of unresolved waves to the driving of the residual mean circulation was indirectly estimated, along with that of resolved waves
- Results suggest that unresolved waves including gravity waves have more impact on driving the residual mean circulation on Mars than on Earth
Plain Language Summary
The general circulation in a planetary atmosphere is important for determining the distribution of mass, temperature, and minor constituents. However, the Martian general circulation based on observations has not been thoroughly studied. This study examines the annual and seasonal mean climatological features of the Martian general circulation and its driving mechanism by analyzing the interaction between atmospheric waves and mean flows using a reanalysis data set. We found that wave forcings, which drive the circulation, are necessary in mid- and high latitude regions where the Lagrangian mean flow crosses the contours of absolute angular momentum. The wave forcing associated with unresolved small-scale waves is indirectly estimated using a method originally devised for Earth atmosphere studies. The results suggest that the entire structure of the general circulation is largely determined by unresolved small-scale wave forcing, particularly above the ∼2 Pa level, while the contribution of large-scale waves which a reanalysis data can resolve is also present below ∼2 Pa level.
