2. Data sets
As discussed in S22, we use MLS v5 for ozone, N2O, temperature and H2O. The data quality for the HT anomaly is detailed in M22 and MLS data is described in Livesey et al. (2021). The MLS V5 algorithm quality flags and convergence alerts were set for some plume profiles in the week or so after the eruption. However, even with the quality flag and convergence filters set, the data look reasonable and generally agree with sonde and other validation data. We restrict our constituent analysis to below 35 km. The MLS and OMPS data sets are averaged over 3 days and then averaged onto a 5°x10° latitude-longitude grid. For aerosols, we use OMPS-LP level-2 V2.1 997 nm extinction-to-molecular ratio data (AE) from all three OMPS-LP slits (see Taha et al., 2021). Taha et al. (2022) indicated that the standard V2.1 released data (used in this study) provided the most accurate aerosol retrieval up to 36 km.
The Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA2) reanalysis winds, temperatures, and heating rates used in this study are described in Gelaro et al., (2017). The residual circulation is computed using the formulas in Andrews et al. (1987), specifically Eq 3.5.5b for computing the residual vertical velocity (w*) from the heating rate. The upward residual circulation velocity magnitude from our computation agrees with analysis of the water vapor tape recorder (Schoeberl et al., 2009). The continuity equation is then used to compute the residual meridional velocity (v*). MERRA2 data assimilation system does not include the water vapor measurements from MLS and thus does not account for the additional cooling from the water vapor anomaly (Coy et. al., 2022). To include that anomalous water vapor cooling we compute the total IR heating rate using 2022 MLS observed trace gases and temperatures using the radiative transfer model (RTM) described by Mlawer et al. (1997). We then we rerun the heating rate calculation assuming pre-eruption concentration of water vapor (~ 4 ppm). We compute the difference in radiative heating between the two computations and add that difference to the MERRA2 net heating rate, then recompute w*. At 15°S, 26.8 km the MERRA2 residual circulation is upward with ~ 0.1 cm/s in January, decreasing to 0.03 cm/s in October. With the addition of the water vapor cooling the residual circulation is slower by 5% in January. The circulation is further reduced by ~20% by mid-February through March then the water vapor cooling effect fades through July. Over the equator the reduction in w* is only a few percent over this period.