The 2015 fire season and related smoke pollution in Indonesia was more severe than the major 2006 episode, making it themost severe season observed by the NASA Earth Observing System satellites that ...go back to the early 2000s, namely active fire detections from the Terra and Aqua Moderate Resolution Imaging Spectroradiometers (MODIS), MODIS aerosol optical depth, Terra Measurement of Pollution in the Troposphere (MOPITT) carbon monoxide (CO), Aqua Atmospheric Infrared Sounder (AIRS) CO, Aura Ozone Monitoring Instrument (OMI) aerosol index, and Aura Microwave Limb Sounder (MLS) CO. The MLS CO in the upper troposphere showed a plume of pollution stretching from East Africa to the western Pacific Ocean that persisted for 2 mo. Longer-term records of airport visibility in Sumatra and Kalimantan show that 2015 ranked after 1997 and alongside 1991 and 1994 as among the worst episodes on record. Analysis of yearly dry season rainfall from the Tropical Rainfall Measurement Mission (TRMM) and rain gauges shows that, due to the continued use of fire to clear and prepare land on degraded peat, the Indonesian fire environment continues to have nonlinear sensitivity to dry conditions during prolonged periods with less than 4 mm/d of precipitation, and this sensitivity appears to have increased over Kalimantan. Without significant reforms in land use and the adoption of early warning triggers tied to precipitation forecasts, these intense fire episodes will reoccur during future droughts, usually associated with El Niño events.
Aura Microwave Limb Sounder (MLS) measurements show that chemical processing was critical to the observed record‐low Arctic stratospheric ozone in spring 2020. The 16‐year MLS record indicates more ...polar denitrification and dehydration in 2019/2020 than in any Arctic winter except 2015/2016. Chlorine activation and ozone depletion began earlier than in any previously observed winter, with evidence of chemical ozone loss starting in November. Active chlorine then persisted as late into spring as it did in 2011. Empirical estimates suggest maximum chemical ozone losses near 2.8 ppmv by late March in both 2011 and 2020. However, peak chlorine activation, and thus peak ozone loss, occurred at lower altitudes in 2020 than in 2011, leading to the lowest Arctic ozone values ever observed at potential temperature levels from ∼400–480 K, with similar ozone values to those in 2011 at higher levels.
Plain Language Summary
Unlike the Antarctic, the Arctic does not usually experience an ozone hole because temperatures are often too high for the chemistry that destroys ozone. In 2019/2020, satellite measurements show record‐low stratospheric wintertime temperatures and record‐low springtime ozone concentrations in the Arctic lower stratosphere (about 12‐ to 20‐km altitude). Only one other winter/spring season, 2010/2011, in this 16‐year satellite data record comes close. Low temperatures, which result in chlorine being converted from nonreactive forms into forms that destroy ozone, started earlier than in any previous Arctic winter in the record and lingered later than in any year except 2011. The ozone‐destroying chemistry in 2019/2020 occurred at lower altitudes (where more of the ozone that filters out harmful ultraviolet radiation resides) than in 2010/2011. Such extensive ozone loss can have important health and biological impacts because it leads to more ultraviolet radiation reaching the Earths surface. While the success of the Montreal Protocol in limiting human emissions that increase ozone‐destroying gases in the stratosphere has resulted in much less Arctic ozone destruction than we would have otherwise had, future temperature changes could lead to other winters with even more chemical ozone depletion than in 2019/2020.
Key Points
MLS trace gas data show that exceptional polar vortex conditions led to record‐low ozone in the Arctic lower stratosphere in 2019/2020
Early and persistent cold conditions led to the longest period with chlorine in ozone‐destroying forms in the 16‐year MLS data record
Chemical ozone destruction began earlier than in any Arctic winter in the MLS record and ended later than in any year except 2010/2011
Satellite observations of tropospheric chemical constituents (such as carbon monoxide, CO) reveal a persistent maximum in the upper troposphere–lower stratosphere (UTLS) associated with the Asian ...summer monsoon anticyclone. Diagnostic studies suggest that the strong anticyclonic circulation acts to confine air masses, but the sources of pollution and transport pathways to altitudes near the tropopause are the subject of debate. Here we use the Model for Ozone and Related Tracers 4 (MOZART‐4) global chemistry transport model, driven by analyzed meteorological fields, to study the source and transport of CO in the Asian monsoon circulation. A MOZART‐4 simulation for one summer is performed, and results are compared with satellite observations of CO from the Aura Microwave Limb Sounder and the Atmospheric Chemistry Experiment Fourier Transform Spectrometer. Overall, good agreement is found between the modeled and observed CO in the UTLS, promoting confidence in the model simulation. The model results are then analyzed to understand the sources and transport pathways of CO in the Asian monsoon region, and within the anticyclone in particular. The results show that CO is transported upward by monsoon deep convection, with the main surface sources from India and Southeast Asia. The uppermost altitude of the convective transport is ∼12 km, near the level of main deep convective outflow, and much of the CO is then advected in the upper troposphere northeastward across the Pacific Ocean and southwestward with the cross‐equatorial Hadley flow. However, some of the CO is also advected vertically to altitudes near the tropopause (∼16 km) by the large‐scale upward circulation on the eastern side of the anticyclone, and this air then becomes trapped within the anticyclone (to the west of the convection, extending to the Middle East). Within the anticyclone, the modeled CO shows a relative maximum near 15 km, in good agreement with observations.
We use Aura Microwave Limb Sounder (MLS) trace gas measurements to investigate whether water vapor (H2O) injected into the stratosphere by the Hunga Tonga‐Hunga Ha'apai (HTHH) eruption affected the ...2022 Antarctic stratospheric vortex. Other MLS‐measured long‐lived species are used to distinguish high HTHH H2O from that descending in the vortex from the upper‐stratospheric H2O peak. HTHH H2O reached high southern latitudes in June–July but was effectively excluded from the vortex by the strong transport barrier at its edge. MLS H2O, nitric acid, chlorine species, and ozone within the 2022 Antarctic polar vortex were near average; the vortex was large, strong, and long‐lived, but not exceptionally so. There is thus no clear evidence of HTHH influence on the 2022 Antarctic vortex or its composition. Substantial impacts on the stratospheric polar vortices are expected in succeeding years since the H2O injected by HTHH has spread globally.
Plain Language Summary
The 2022 Hunga Tonga‐Hunga Ha'apai eruption injected vast amounts of water vapor into the stratosphere. Concern arose that this excess water vapor could affect the 2022 Antarctic stratospheric polar vortex and ozone hole: Water vapor plays a crucial role in forming polar stratospheric clouds, which provide surfaces upon which chemical reactions that destroy ozone take place. Enhanced water vapor also affects temperatures, which in turn affect the powerful winds defining the polar vortex boundary. Antarctic polar vortex development began in April–May; by June the intense vortex‐edge winds presented a formidable obstacle to transport. Satellite trace‐gas measurements show that when water vapor from the Hunga Tonga eruption reached the vortex edge in June, it faced an impenetrable barrier and “besieged” the vortex, building up exceptionally strong water vapor gradients across the vortex edge. Water vapor, ozone, and chemicals involved in ozone destruction remained near historical average levels within the vortex through spring 2022. Because excess water vapor spread throughout the south polar regions after vortex breakup, much larger effects on the Antarctic vortex and chemical processing within it are expected in 2023 and beyond, when high water vapor will be entrained into the vortex as it develops.
Key Points
Microwave Limb Sounder (MLS) trace gas data show that the Hunga Tonga‐Hunga Ha'apai H2O plume was effectively excluded from the 2022 Antarctic polar vortex
Antarctic lower stratospheric vortex strength, size, and longevity were among the largest on record, but within the range of previous years
Antarctic chemical ozone loss in 2022 was unexceptional, with MLS ozone and related trace gases observed to be near average
A major stratospheric sudden warming (SSW) in January 2009 was the strongest and most prolonged on record. Aura Microwave Limb Sounder (MLS) observations are used to provide an overview of dynamics ...and transport during the 2009 SSW, and to compare with the intense, long‐lasting SSW in January 2006. The Arctic polar vortex split during the 2009 SSW, whereas the 2006 SSW was a vortex displacement event. Winds reversed to easterly more rapidly and reverted to westerly more slowly in 2009 than in 2006. More mixing of trace gases out of the vortex during the decay of the vortex fragments, and less before the fulfillment of major SSW criteria, was seen in 2009 than in 2006; persistent well‐defined fragments of vortex and anticyclone air were more prevalent in 2009. The 2009 SSW had a more profound impact on the lower stratosphere than any previously observed SSW, with no significant recovery of the vortex in that region. The stratopause breakdown and subsequent reformation at very high altitude, accompanied by enhanced descent into a rapidly strengthening upper stratospheric vortex, were similar in 2009 and 2006. Many differences between 2006 and 2009 appear to be related to the different character of the SSWs in the two years.
Following the Australian New Year's pyrocumulonimbus complex between 29 December 2019 and 4 January 2020, the Aura Microwave Limb Sounder (MLS) observed a plume with unprecedented enhancements of H2O ...and biomass‐burning products (CO, HCN, CH3Cl, CH3CN, and CH3OH) in the lower/middle stratosphere, accompanied by depressions in stratospheric species (O3 and HNO3). The plume persisted for ∼110 days, circling the globe twice while ascending to 5.62 hPa (∼35 km). Air masses drawn off the main plume moved toward the developing Antarctic polar vortex but do not appear to have penetrated it. Comparison of species in the plume requires consideration of their measurements' spatial resolutions and background abundances. The apparent decay of some long‐lived plume constituents is largely attributable to their coarsening spatial resolution with height, which reduces observed peak values. Differing HCN/H2O signatures indicate that multiple early plumes originated from different stratospheric injection events.
Plain Language Summary
Severe wildfires can trigger vigorous smoke‐infused thunderstorms called pyrocumulonimbuses (pyroCbs) that rapidly loft polluted air from the surface, in the most extreme cases depositing it in the lower stratosphere (
≳ 14 km altitude). Three times in the past 16 years, long‐lived stratospheric plumes from major pyroCbs have been observed in a suite of biomass‐burning products measured by the Microwave Limb Sounder on NASA's Aura satellite. Dark smoke in these plumes absorbs sunlight; the plumes rise because they are warmer than the surrounding air. The third, and by far the largest, of these plumes was produced by an extraordinary set of pyroCbs in Australia between 29 December 2019 and 4 January 2020, collectively known as the Australian New Year's event (ANY). The ANY plume core remained remarkably compact, circling the globe twice while rising from ∼14 km to ∼35 km altitude over a period of 4 months. Record‐setting concentrations of five biomass‐burning products were measured by MLS throughout the lower stratosphere. Plume fragments tended to move south but do not seem to have influenced ozone‐hole chemistry. Differing gas mixtures suggest that several plumes in the first month originated in different pyroCbs. Careful comparison of plume gases requires consideration of the blurriness of the measurements.
Key Points
MLS observed record‐high stratospheric trace gas abundances from the 2019–2020 Australian New Year's fires rising to 5.6 hPa over 110 days
Plume fragments moved poleward but do not appear to have entered the developing Antarctic winter vortex
Analysis of correlations between constituent measurements requires consideration of their spatial resolutions
The Tropospheric Emission Spectrometer (TES) on the A-Train Aura satellite was designed to profile tropospheric ozone and its precursors, taking measurements from 2004 to 2018. Starting in 2008, TES ...global sampling of tropospheric ozone was gradually reduced in latitude, with global coverage stopping in 2011. To extend the record of TES, this work presents a multispectral approach that will provide O3 data products with vertical resolution and measurement error similar to TES by combining the single-footprint thermal infrared (TIR) hyperspectral radiances from the Aqua Atmospheric Infrared Sounder (AIRS) instrument and the ultraviolet (UV) channels from the Aura Ozone Monitoring Instrument (OMI). The joint AIRS+OMI O3 retrievals are processed through the MUlti-SpEctra, MUlti-SpEcies, MUlti-SEnsors (MUSES) retrieval algorithm. Comparisons of collocated joint AIRS+OMI and TES to ozonesonde measurements show that both systems have similar errors, with mean and standard deviation of the differences well within the estimated measurement error. AIRS+OMI and TES have slightly different biases (within 5 parts per billion) vs. the sondes. Both AIRS and OMI have wide swath widths (∼1650 km for AIRS; ∼2600 km for OMI) across satellite ground tracks. Consequently, the joint AIRS+OMI measurements have the potential to maintain TES vertical sensitivity while increasing coverage by 2 orders of magnitude, thus providing an unprecedented new data set with which to quantify the evolution of tropospheric ozone.
Remote sensing of atmospheric state variables typically relies on the inverse solution of the radiative transfer equation. An adequately characterized retrieval provides information on the ...uncertainties of the estimated state variables as well as on how any constraint or a priori assumption affects the estimate. Reported characterization data should be intercomparable between different instruments, empirically validatable, grid-independent, usable without detailed knowledge of the instrument or retrieval technique, traceable and still have reasonable data volume. The latter may force one to work with representative rather than individual characterization data. Many errors derive from approximations and simplifications used in real-world retrieval schemes, which are reviewed in this paper, along with related error estimation schemes. The main sources of uncertainty are measurement noise, calibration errors, simplifications and idealizations in the radiative transfer model and retrieval scheme, auxiliary data errors, and uncertainties in atmospheric or instrumental parameters. Some of these errors affect the result in a random way, while others chiefly cause a bias or are of mixed character. Beyond this, it is of utmost importance to know the influence of any constraint and prior information on the solution. While different instruments or retrieval schemes may require different error estimation schemes, we provide a list of recommendations which should help to unify retrieval error reporting.
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