Following the 15 January 2022 Hunga Tonga-Hunga Ha’apai eruption, several trace gases measured by the Aura Microwave Limb Sounder displayed anomalous stratospheric values. Trajectories and radiance simulations confirm that the H2O, SO2, and HCl enhancements were injected by the eruption. In comparison with those from previous eruptions, the SO2 and HCl injections were unexceptional, although they reached higher altitudes. In contrast, the H2O injection was unprecedented in both magnitude (far exceeding any previous values in the 17-year MLS record) and altitude (penetrating into the mesosphere). We estimate the mass of H2O injected into the stratosphere to be 146+-5 Tg - ~10% of the stratospheric burden. It may take several years for the H2O plume to dissipate. This eruption could impact climate not through surface cooling due to sulfate aerosols, but rather through surface warming due to the radiative forcing from the excess stratospheric H2O.

The exceptionally strong and long-lived Arctic stratospheric polar vortex in 2019/2020 resulted in large transport anomalies throughout the fall-winter-spring period from vortex development to breakup. These anomalies are studied using Aura MLS long-lived trace gas data for N2O, H2O,and CO, ACE-FTS CH4 , and meteorological and trace gas fields from reanalyses. Strongest anomalies are seen throughout the winter in the lower through middle stratosphere (from about 500K through 700K), with record low (high) departures from climatology in N2O and CH4 (H2O). CO also shows extreme high anomalies in midwinter through spring down to about 550K. Examination of descent rates, vortex confinement, and trace gas distributions in the preceding months indicates that the early-winter anomalies in N2O and H2O arose primarily from entrainment of air with already-anomalous values (which likely resulted from transport linked to an early January sudden stratospheric warming the previous winter during a favorable quasi-biennial oscillation phase) into the vortex as it developed in fall 2019 followed by descent of those anomalies to lower levels within the vortex. Trace gas anomalies in midwinter through the late vortex breakup in spring 2020 arose primarily from inhibition of mixing between vortex and extravortex air because of the exceptionally strong and persistent vortex. Persistent strong N2O and H2O gradients across the vortex edge demonstrate that air within the vortex and its remnants remained very strongly confined through late April (mid-May) in the middle (lower) stratosphere.

Regionally and seasonally resolved relationships of upper tropospheric jet variability to El Niño / Southern Oscillation (ENSO) in multiple reanalyses are presented, with subtropical and polar jets analyzed separately. Previously reported results confirmed herein include strengthening of tropical jets associated with monsoons and Walker circulation during La Niña and a statistically significant subtropical jet latitude decrease (increase) during El Niño (La Niña) in the zonal mean view in both hemispheres. However, subtropical jet latitudes increase significantly during El Niño over the NH eastern Pacific in DJF, and in different limited SH regions in MAM and SON. Subtropical jet altitudes increase significantly during El Niño in the zonal mean in all seasons (DJF / MAM) in the NH (SH). Subtropical jet windspeed correlations with ENSO vary, showing increasing windspeed during El Niño in both hemispheres in DJF and MAM. Polar jet correlations with ENSO are typically not significant in the zonal mean, but there are a few regions/seasons with significant correlations with ENSO, particularly in the SH, where polar jet latitudes decrease over Asia and the western Pacific in DJF, and increase over the eastern Pacific in JJA and SON, during El Niño. Typically, significantly weaker (stronger) polar jet windspeeds are associated with El Niño (La Niña) in the western than in the eastern hemisphere in both NH and SH. All reanalyses analyzed agree well. This work highlights the importance of regional and seasonal variations in the upper tropospheric jet response to ENSO and provides new information for model evaluation.

A moments/area study of meteorological reanalyses (focusing on MERRA-2, ERA-Interim, and JRA-55) allows a novel investigation of the climatology of and interannual variability and trends in the Asian summer monsoon anticyclone (ASMA). The climatological ASMA is nearly elliptical, with its major axis aligned along its centroid latitude and an aspect ratio of ∼5–8. The ASMA centroid shifts northward with height, northward and westward during development, and in the opposite direction as it weakens. ASMA position and seasonal evolution generally agree among the reanalyses, except that MERRA-2 shows over 40% larger area at 350 K. No evidence of climatological bimodality is seen in the ASMA, consistent with previous studies using modern reanalyses. ASMA moments trends are mostly neither statistically significant nor consistent among reanalyses, but area and duration increase significantly over 1979–2018, and over 1958–2018 in JRA-55; JRA-55 trends are largest for 1979–2018, suggesting that reanalysis trends may have accelerated in recent decades. ASMA centroid latitude is significantly negatively (positively) correlated with subtropical jet core latitude (altitude), and significantly negatively correlated with concurrent ENSO. Other ASMA moments and area are not strongly correlated with concurrent ENSO, but ASMA area is significantly positively correlated with ENSO two months previously. Significant (negative) correlations of ASMA area with QBO are seen only during June at 370, 390, and 410 K. These results provide a unique and comprehensive view of the structure and evolution of the ASMA and introduce new tools that can be used to further explore ASMA characteristics and impacts.

In the Antarctic ozone hole, ozone mixing ratios have been decreasing to extremely low values of 0.01-0.1 ppm in nearly all spring seasons since the late 1980s, corresponding to 95-99 % local chemical loss. In contrast, Arctic ozone loss has been much more limited and mixing ratios have never before fallen below 0.5 ppm. In Arctic spring 2020, however, ozone sonde measurements in the most depleted parts of the polar vortex show a highly depleted layer, with ozone loss averaged over sondes peaking at 93 % at 18 km. Typical minimum mixing ratios of 0.2 ppm were observed, with individual profiles showing values as low as 0.13 ppm (96 % loss). The reason for the unprecedented chemical loss was an unusually strong, long-lasting and cold polar vortex, showing that for individual winters the effect of the slow decline of ozone-depleting substances on ozone depletion may be counteracted by low temperatures.

Measurements of solar ultraviolet radiation (UVR) performed between January and June 2020 at 10 Arctic and subarctic locations are compared with historical observations. Differences between 2020 and prior years are also assessed with total ozone column and UVR data from satellites. Erythemal (sunburning) UVR is quantified with the UV Index (UVI) derived from these measurements. UVI data show unprecedently large anomalies, occurring mostly between early March and mid-April 2020. For several days, UVIs observed in 2020 exceeded measurements of previous years by up to 140%. Historical means were surpassed by more than six standard deviations at several locations. In northern Canada, the average UVI for March was about 75% larger than usual. UVIs in April 2020 were elevated on average by about 25% at all sites. However, absolute anomalies remained below 3.0 UVI units because the enhancements occurred during times when the solar elevation was still low.