Anomalies and Changes in Mass Meridional Circulation during a Positive Trend of Mass Term in the Atmospheric Angular Momentum Budget 1970-2020.
Wirid Birastri, Tri Wahyu Hadi, Nining Sari Ningsih

Doctoral Program of Earth Sciences, Faculty of Earth Sciences and Technology, Bandung Institute of Technology/Atmospheric and Earth System Sciences Research Group, Faculty of Science, Institut Teknologi Sumatera
Atmospheric Science Research Group, Faculty of Earth Sciences and Technology, Bandung Institute of Technology
Oceanography Research Group, Faculty of Earth Sciences and Technology, Bandung Institute of Technology

Abstract

In this research, mass flux and meridional budget analyses were conducted during the positive trend of the mass part of the Atmospheric Angular Momentum (AAM) Budget 1970-2020 using the ERA5 dataset. It is shown that after the 1970s, the equatorial belt experienced an increase in mass flux (I), primarily due to the addition of dry air (D) and water vapor flux (Q) from the Southern Hemisphere. The analysis of meridional wind and mass flux anomalies shows an increase in equatorward transport due to the strengthening of the SH-EQ circulation, which coincides with the weakening of the NH-EQ circulation. The latter contributes to a decrease in the amount of air mass that is transported leaving the equator.

Furthermore, the annual climatology of mean mass meridional circulation calculated using the conventional Eulerian mean method over the 1970-1979 baseline period provides an overview of the meridional atmospheric circulation which is dominated by the Hadley Cell (HC) around the equator to 30 degree and the Ferrel Cell (FC) around 30 to 60 degree latitude in the NH and SH. The meridional cell intensity analysis reveals that after the 1970s, HC and HC in SH are strengthening, whereas weakening predominates in the NH. Hereafter, the Mass-Weighted Isentropic Zonal Mean (MIM) analysis was performed to examine for seasonality discrepancies in the patterns and interaction between tropical and extratropical circulation using residual zonal mean stream function. The strengthening of the SH HC and FC was persistent throughout the year. In contrast, in the NH, weaker circulation was observed throughout the season except for DJF. During this season, the extratropical direct (ETD) feature was observed, connecting the descending branch of the HC with the extratropical circulation in the NH. Meanwhile, the strengthening of SH-HC escalates to the 20N connecting the NH and extratropical SH circulation.

Keywords: atmospheric angular momentum, mass term, trend, water vapor, dry atmosphere, mean meridional circulation

Topic: Atmospheric Sciences