[A-AS05] Large-scale moisture and organized cloud systems

[AAS05-06] The Relationship between the Mass Term of Atmospheric Angular Momentum and Water Vapor Mass

*Wirid Birastri^1,2, Tri Wahyu Hadi³, Nining Sari Ningsih⁴ (1.Doctoral Program in Earth Sciences, Faculty of Earth Sciences and Technology, Bandung Institute of Technology, Bandung, Indonesia, 2.Atmospheric Science Research Group, Institut Teknologi Sumatera, South Lampung, Indonesia, 3.Atmospheric Science Research Group, Faculty of Earth Sciences and Technology, Bandung Institute of Technology, Bandung, Indonesia, 4.Oceanography Research Group, Faculty of Earth Sciences and Technology, Bandung Institute of Technology, Bandung, Indonesia)

Keywords:atmospheric angular momentum, mass term, water vapor contribution

In this study, the relationship between water vapor and atmospheric angular momentum's mass term (M_Ω) has been investigated using four reanalysis datasets for the years 1950–2020: ERA5, ERA-20C, JRA55, and NCEP/NCAR. The four reanalysis datasets revealed a consistent positive long-term trend in global M_Ω anomalies, while also identified shifts in the trend from negative to more positive in the period from the early to mid-1970s. Meanwhile, analysis of global water vapor trends shows that there is an additional mass of water vapor, which results in variations in water vapor surface pressure (p_w) of about ~0.3 mbar. The p_w was then used to estimate the contribution of water vapor to M_Ω, which is referred to as M_Ωw. Changes in the contribution of water vapor to M_Ω after the 1970s were calculated based on the anomaly of M_Ωw relative to the climatology value of 1970-1979. It can be shown that the M_Ωw anomalies tend to be positive after the 1970s period. In addition, the ratio of the M_Ωw anomalies relative to the global M_Ω suggests a change in the pattern of the contribution of water vapor to M_Ω, which is indicated from the fluctuation of this percentage every ten years. The highest contribution of water vapor to M_Ω occurred in the equatorial region during 2010-2020, with a ratio of M_Ωw to the increase in global M_Ω at 25-50%. The stability of the relationship between M_Ω and water vapor is examined using the 20 year shifting window correlation. The relationship between water vapor and M_Ω is more consistent on annual and interannual scales, especially in the equatorial region, but there are inconsistencies for longer time scales. Inconsistency between water vapor and M_Ω in the interdecadal scale is characterized by a lower statistical coherence from the mid-1980s to the 2000s, which indicates a decrease in the contribution of water vapor to M_Ω. These results suggest that water vapor alone is insufficient to account for the increase in M_Ω over the period.