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Stratospheric water vapor (H 2 O) is a substantial component of the global radiation budget and therefore important to variability in the climate system. Efforts to understand the distribution, transport, and sources of stratospheric water vapor have increased in recent years, with many studies utilizing long-term satellite observations. Previous work to examine stratospheric H 2 O extrema has typically focused on the stratospheric overworld (pressures ≤ 100 hPa) to ensure the observations used are truly stratospheric. However, this leads to the broad exclusion of the lowermost stratosphere, which can extend over depths of more than 5 km below the 100 hPa level in the midlatitudes and polar regions and has been shown to be the largest contributing layer to the stratospheric H 2 O feedback. Moreover, focusing on the overworld only can lead to a large underestimation of stratospheric H 2 O extrema occurrence. Therefore, we expand on previous work by examining 16 years of Microwave Limb Sounder (MLS) observations of water vapor extrema (≥ 8 ppmv) in both the stratospheric overworld and the lowermost stratosphere to create a new lower-stratosphere climatology. The resulting frequency of H 2 O extrema increases by more than 300 % globally compared to extrema frequencies within stratospheric overworld observations only, though the percentage increase varies substantially by region and season. Additional context is provided for this climatology through a backward isentropic trajectory analysis to identify potential sources of the extrema. We show that, in general, tropopause-overshooting convection presents itself as a likely source of H 2 O extrema in much of the world, while meridional isentropic transport of air from the tropical upper troposphere to the extratropical lower stratosphere is also possible. [ABSTRACT FROM AUTHOR]

The Hunga Tonga Hunga‐Ha'apai (HTHH) volcanic eruption on 15 January 2022 injected water vapor and SO2 into the stratosphere. Several months after the eruption, significantly stronger westerlies, and a weaker Brewer‐Dobson circulation developed in the stratosphere of the Southern Hemisphere and were accompanied by unprecedented temperature anomalies in the stratosphere and mesosphere. In August 2022, the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) satellite instrument observed record‐breaking temperature anomalies in the stratosphere and mesosphere that alternate signs with altitude. Ensemble simulations carried out with the Whole Atmosphere Community Climate Model (WACCM6) indicate that the strengthening of the stratospheric westerlies explains the mesospheric temperature changes. The stronger westerlies cause stronger westward gravity wave drag in the mesosphere. Although the enhanced gravity wave drag is partly balanced by a weakening of planetary wave forcing, the net result is an acceleration of the mesospheric mean meridional circulation. The stronger mesospheric circulation, in turn, plays a dominant role in driving the changes in mesospheric temperatures. This study highlights the impact of large volcanic eruptions on middle atmospheric dynamics and provides insight into their long‐term effects in the mesosphere. On the other hand, we could not discern a clear mechanism for the observed changes in stratospheric circulation. In fact, an examination of the WACCM ensemble reveals that not every member reproduces the large changes observed by SABER. We conclude that there is a stochastic component to the stratospheric response to the HTHH eruption. Plain Language Summary: This work studies the impact of the Hunga Tonga‐Hunga Ha'apai volcanic eruption, which took place on 15 January 2022, on the earth's mesosphere (55–80 km). The eruption injected water vapor and SO2 into the stratosphere, which was followed by changes in the wind patterns in the stratosphere (16–55 km). Concurrent with these changes, we observed unprecedented temperature changes in the mesosphere, with record high and low temperature anomalies in August that alternate signs with altitude. We used climate model simulations to show that the changes in stratospheric winds were ultimately responsible for these record‐breaking mesospheric temperatures. We found that the stronger winds in the stratosphere enhanced gravity wave breaking in the mesosphere, which led to changes in the circulation and thus the temperature. However, we could not find a clear mechanism for the changes observed in the stratosphere. Key Points: Sounding of the Atmosphere using Broadband Emission Radiometry observed unprecedented mesospheric temperature variations in the Southern Hemisphere in August 2022 after the Hunga Tonga Hunga‐Ha'apai eruptionWhole Atmosphere Community Climate Model simulations indicate that changes in the mesospheric temperature are due to a stronger mesospheric meridional circulationStronger stratospheric westerlies after eruption enhance westward gravity wave drag in the mesosphere, thus a stronger circulation [ABSTRACT FROM AUTHOR]

The explosive eruption of the Hunga Tonga-Hunga Ha'apai (HTHH) volcano on 15 January 2022 injected more water vapor into the stratosphere and to higher altitudes than ever observed in the satellite era. Here, the evolution of the stratospherically injected water vapor is examined as a function of latitude, altitude, and time in the year following the eruption (February to December 2022), and perturbations to stratospheric chemical composition resulting from the increased sulfate aerosols and water vapor are identified and analyzed. The average calculated mass distribution of elevated water vapor between hemispheres is approximately 78% Southern Hemisphere (SH) and 22% Northern Hemisphere in 2022. Significant changes in stratospheric composition following the HTHH eruption are identified using observations from the Aura Microwave Limb Sounder satellite instrument. The dominant features in the monthly mean vertical profiles averaged over 15° latitude ranges are decreases in O3 (-14%) and HCl (-22%) at SH midlatitudes and increases in ClO (>100%) and HNO3 (43%) in the tropics, with peak pressure-level perturbations listed. Anomalies in column ozone from 1.2-100 hPa due to the HTHH eruption include widespread O3 reductions in SH midlatitudes and O3 increases in the tropics, with peak anomalies in 15° latitude-binned, monthly averages of approximately -7% and +5%, respectively, occurring in austral spring. Using a 3-dimensional chemistry-climate-aerosol model and observational tracer correlations, changes in stratospheric composition are found to be due to both dynamical and chemical factors. [ABSTRACT FROM AUTHOR]

The Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS) is currently providing the only measurements of vertically resolved chlorodifluoromethane (HCFC-22) from space. This study assesses the ACE-FTS HCFC-22 v5.2 product in the upper troposphere – lower stratosphere, as well as the simulated concentrations of HCFC-22 from a 39-year specified dynamics run of the Canadian Middle Atmosphere Model (CMAM39) in the same region. In general, ACE-FTS HCFC-22 observations tend to agree with subsampled CMAM39 data to within ±5 %, except for between ~15 and 25 km in the extratropical regions where ACE-FTS exhibits a negative bias of 5–30 %, and near 6 km in the tropics where ACE FTS exhibits a bias of 15 %. When comparing against correlative satellite, aircraft, and balloon data, ACE-FTS typically exhibits a low bias on the order of 0–10 % between ~5–15 km and is within ±15 % between ~15–25 km. ACE-FTS, CMAM39, and surface flask measurements from the NOAA Global Monitoring Laboratory's surface air-sampling network, all exhibit consistent tropospheric HCFC-22 trends ranging between 6.8 and 7.8 pptv/year (within 95 % confidence) for 2004–2012, and between 3.1 and 4.7 pptv/year (within 95 % confidence) for 2012–2018. Interhemispheric differences (IHD) of HCFC-22 concentrations were also derived using ACE-FTS, NOAA, and CMAM39 data, and all three yielded consistent and correlated (r≥0.42) IHD timeseries, with the results indicating that surface IHD values decreased at a rate of 2.2±1.1 pptv/decade between 2004 and 2018. [ABSTRACT FROM AUTHOR]

Bromine is a reactive trace element in the atmosphere, that destroys ozone, oxidizes mercury, modifies oxidative capacity and affects the lifetime of climate-active gases (e.g., methane). About 75% of tropospheric ozone and methane is destroyed in the tropics, primarily in the lower free troposphere, where bromine monoxide (BrO) radical measurements are generally scarce. The few available aircraft observations find BrO is variable, and measurements in different compartments of the atmosphere are not easily reconciled. While zenith-sky DOAS measurements provide long-term records of the stratospheric 20 O3 and NO2 abundances, autonomous MAX-DOAS placed at remote mountaintop observatories (MT-DOAS) provides cost effective and maximally sensitive access to probe the lower free troposphere, a climate-relevant yet understudied region of the atmosphere. Here we describe and evaluate an innovative full-atmosphere BrO and formaldehyde (HCHO) profile retrieval algorithm using MT-DOAS measurements at Mauna Loa Observatory (19.536°N; 155.577°W; 3401m asl) during two case study days, 25 characterized by the absence (26 Apr 2017, base case) and presence of a Rossby Wave breaking double tropopause (29 Apr 2017, RW-DT case) above Big Island, Hawaii. The full atmosphere retrieval is based on time-dependent optimal estimation, and simultaneously inverts 190+ individual BrO (and formaldehyde, HCHO) SCDs (slant column densities, SCD = dSCD + SCDRef) from solar stray light spectra measured in the zenith and off-axis geometries at high and low solar zenith angle (92° > SZA > 30°) to derive BrO concentration profiles with 7.5 degrees of freedom (DoF) from 1.9 to 35 km altitude. Stratospheric BrO vertical columns are near identical on both days (VCD = (1.5 ± 0.2) ×1013 molec cm-2), and the stratospheric BrO profile peaks at a lower altitude during the Rossby wave breaking event (1.6 - 2.0 DoFs). Tropospheric BrO VCDs increase from (0.70 ± 0.14) ×1013 molec cm-2 (base case) to (1.00 ± 0.14) ×1013 molec cm-2 (RW-DT), owing to a tropospheric BrO profile re-distribution characterized by a three-fold increase in BrO located in the upper troposphere (1.7 - 1.9 DoF). BrO is found to be more variable in the lower free troposphere (0.2 pptv < BrO < 0.9 pptv) and characterized in three altitude layers (near, above, below) MLO with added time resolution (~3.8 DoF). The BrO mixing ratio at MLO increases from (0.23 ± 0.03) pptv (base case) to (0.46 ± 0.03) pptv BrO (RW-DT); while the maximum of (0.9 ± 0.1) pptv BrO is observed above MLO in the lower free troposphere in absence of the double tropopause. We validate the retrieval using aircraft BrO profiles and in-situ HCHO measurements aboard the NSF/NCAR GV aircraft above MLO (11 Jan 2014) that establish BrO peaks around 2.4 pptv above 13 km in the UTLS during a similar RW-DT event (0.83 ×1013 molec cm-2 tropospheric BrO VCD above 2 km). The tropospheric BrO profile measured from MT-DOAS (RWDT case) and the aircraft agree well (after averaging kernel smoothing). Furthermore, these tropospheric BrO profiles over the Central Pacific are found to closely resemble those over the Eastern Pacific Ocean (2-14 km); and contrast with the Western Pacific Ocean, where a C-shaped tropospheric BrO profile shape had been observed. [ABSTRACT FROM AUTHOR]

Wind in the free atmosphere is one of the processes recommended by the World Meteorological Organization for climate monitoring. An analysis of the wind regime on large spatial scales presents specific difficulties, since both the vertical and horizontal distributions of wind speed are highly variable. In order to have an idea about the general characteristics of the wind regime in the main atmospheric layers, the Russian Institute of Hydrometeorological Information, World Data Center (RIHMI-WDC), developed a method for monitoring the wind regime of the free atmosphere over the territory of the Russian Federation. The goal of this article is to further develop these works both in relation to the region and in terms of research fields. The article presents the results of monitoring the wind speed in the free atmosphere not only over the territory of Russia, but also over the entire Northern Hemisphere, compares the results of radio sounding data and the ERA5 fifth-generation reanalysis data, and it also considers trends in variability of the wind regime over the period 1985–2018. An analysis of wind characteristics in the troposphere and lower stratosphere of the Northern Hemisphere has been carried out in accordance with the technique developed earlier for monitoring the wind regime of wind speed in the free atmosphere. The analysis was extended to the entire Northern Hemisphere using two data sources: an array of long-term radiosonde measurements performed at Russian Institute of Hydrometeorological Information, World Data Center (RIHMI-WDC) and fifth-generation ERA5 reanalysis. The monitoring results based on the two data sources are qualitatively and quantitatively consistent with each other in the areas covered by the network of aerological stations, except for individual high-mountain regions. The distribution of long-term averages in general terms coincides with the distribution of wind speed based on earlier studies. At the same time, each year is distinguished by its own characteristics, displacements of zones of weak and strong winds, and their intensity. Variability trends over the period 1985–2018 in different regions of the Northern Hemisphere were oppositely directed. The strongest negative wind speed trends reaching –1.5 m s–1 over 10 years occurred in the lower stratosphere north of 55°–60° N. This may indicate a weakening of the winter west–east transport in this region. In the latitudinal belt 30°–45° N over the Eurasian region, on the contrary, positive trends reaching 1.1 m s–1 over 10 years have been observed. [ABSTRACT FROM AUTHOR]

Estimation of uncertainties (random error statistics) of radio occultation (RO) observations is important for their effective assimilation in numerical weather prediction (NWP) models. Average uncertainties can be estimated for large samples of RO observations and these statistics may be used for specifying the observation errors in NWP data assimilation. However, the uncertainties of individual RO observations vary, and so using average uncertainty estimates will overestimate the uncertainties of some observations and underestimate those of others, reducing their overall effectiveness in the assimilation. Several parameters associated with RO observations or their atmospheric environments have been proposed to estimate individual RO errors. These include the standard deviation of bending angle (BA) departures from either climatology in the upper stratosphere and lower mesosphere (STDV) or the sample mean between 40 and 60 km (STD4060), the local spectral width (LSW), and the magnitude of the horizontal gradient of refractivity (|∇HN|). In this paper we show how the uncertainties of two RO datasets, COSMIC-2 and Spire BA, as well as their combination, vary with these parameters. We find that the uncertainties are highly correlated with STDV and STD4060 in the stratosphere, and with LSW and |∇HN| in the lower troposphere. These results suggest a hybrid error model for individual BA observations that uses an average statistical model of RO errors modified by STDV or STD4060 above 30 km, and LSW or |∇HN| below 8 km. Significance Statement: These results contribute to the understanding of the sources of uncertainties in radio occultation observations. They could be used to improve the effectiveness of these observations in their assimilation into numerical weather prediction and reanalysis models by improving the estimation of their observational errors. [ABSTRACT FROM AUTHOR]

Modulation of tropical convection by the stratospheric quasi-biennial oscillation (QBO) during the austral summer has become evident in recent studies. In this study, we show that the QBO affects the seasonal migration of the tropical convection from the equatorial Indian Ocean to the Western Pacific: large-scale convection over the Maritime Continent (MC) and western Pacific strengthens and moves eastward more effectively during easterly QBO (QBO-E) austral summers than during westerly QBO counterparts. This relationship is consistent with an enhanced Madden-Julian Oscillation (MJO) in the QBO-E. The monsoonal active convection over the Sumatra-Borneo region in December produces Kelvin wave-like low temperature anomalies in the tropical tropopause layer (TTL) over the eastern MC. These temperature anomalies strengthen when the lower stratospheric wind is easterly. We propose a hypothesis that the anomalous cooling associated with Kelvin wave-like response produces a favorable condition for the development of penetrating convection into the TTL over the eastern MC and a more effective seasonal march of deep convection across the MC occurs under the QBO-E. The implication of this process for the QBO modulation of the MJO crossing the MC is also discussed. [ABSTRACT FROM AUTHOR]

Traveling planetary waves surrounding sudden stratospheric warming events can result from direct propagation from below or in situ generation. They can have significant impacts on the circulation in the mesosphere and lower thermosphere. Our study runs a series of ensembles initialized from the Whole Atmosphere Community Climate Model, version 4, nudged up to 50 km by 6-hourly Modern-Era Retrospective Analysis for Research and Application, version 2, reanalysis to compile a library of sudden stratospheric warming events. To our knowledge, we present the first composite or ensemble study that attempts to link direct propagation and in situ generation by evaluating the wave geometries associated with the overreflection perspective, a framework used to describe how planetary waves interact with critical and turning levels. The present study looks at the evolution of these interactions through the onset of sudden stratospheric warmings with an elevated stratopause (ES-SSWs). Robust and unique features of ES-SSWs are determined by employing an ensemble study that compares ES-SSWs with normal winters. Our study evaluates the production and impacts of westward-propagating, quasi-stationary, and eastward-propagating planetary waves surrounding ES-SSWs. Our results show that eastward-propagating planetary waves are generated within the westward stratospheric wind layer after ES-SSW onset which aids in restoring the eastward stratospheric wind. The interaction of quasi-stationary and westward-propagating waves with the westward stratospheric wind is explored from an overreflection perspective and reaffirms that westward-propagating planetary waves are produced from instabilities at the top of the westward stratospheric wind reversal. [ABSTRACT FROM AUTHOR]

The paper describes the development and performance of the Double Extended Stratospheric–Tropospheric (DEST vn1.0) chemistry scheme, which forms a part of the Met Office's Unified Model coupled to the United Kingdom Chemistry and Aerosol (UM–UKCA) chemistry–climate model, which is the atmospheric composition model of the United Kingdom Earth System Model (UKESM). The scheme extends the standard Stratospheric–Tropospheric chemistry scheme (StratTrop) by including a range of important updates to the halogen chemistry. These allow process-oriented studies of stratospheric ozone depletion and recovery, including the impacts from both controlled long-lived ozone-depleting substances (ODSs) and emerging issues around uncontrolled very short-lived substances (VSLS). The main updates in DEST are (i) an explicit treatment of 14 of the most important long-lived ODSs; (ii) an inclusion of brominated VSLS (Br-VSLS) emissions and chemistry; and (iii) an inclusion of chlorinated VSLS (Cl-VSLS) emissions/LBCs (lower boundary conditions) and chemistry. We evaluate the scheme's performance by comparing DEST simulations against analogous runs made with the standard StratTrop scheme and against observational and reanalysis datasets. Overall, our scheme addresses some significant shortcomings in the representation of atmospheric halogens in the standard StratTrop scheme and will thus be particularly relevant for studies of ozone layer recovery and processes affecting it, in support of future World Meteorological Organization (WMO) Ozone Assessment Reports. [ABSTRACT FROM AUTHOR]

A helium‐filled mylar balloon carrying a smartphone and infrasound sensors ascended to a stratospheric height of 35 km over the surface detonation of a chemical explosive, with a total acoustic propagation distance of 127 km. The smartphone was configured to collect multi‐modal data at high rates from internal sensors. Analysis of the data shows successful collection of the explosion signal by both the smartphone's microphone and its accelerometers, the first from an ascending balloon. Comparison of the acoustic signal with that collected by other infrasound sensors, both airborne and ground‐based, provides insight into the possibilities and limitations of collecting acoustic data from the stratosphere. Plain Language Summary: A surface chemical explosion was observed by pressure and acceleration sensors suspended from an ascending free‐floating balloon at a height of 35 km and a total propagation distance of 127 km from the blast. The balloon's sensor package included a smartphone collecting different types of data (including audio, acceleration, and position), as well as more traditional infrasound and location sensors. The explosion signal was observed by the airborne pressure and vertical accelerometer sensors, as well as by surface‐deployed traditional and smartphone pressure and acceleration sensors. The blast signatures recorded by the airborne and ground‐based stations are compared to provide insight into the present capabilities, limitations, and possible improvements to future balloon‐borne collections of seismo‐acoustic signatures on Earth and beyond. Key Points: Explosion signals were captured using acoustic sensors in an ascending balloon at a height of 35 km and a propagation distance of 127 kmThe signal was briefly trapped in the troposphere before escaping into the stratosphereAccelerometers can distinguish acoustic signals from wind noise on ascending balloons [ABSTRACT FROM AUTHOR]

Large increases in the number of low earth orbit satellites are projected in the coming decades [L. Schulz, K.-H. Glassmeier, Adv. Space Res. 67, 1002–1025 (2021)] with perhaps 50,000 additional satellites in orbit by 2030 [GAO, Large constellations of satellites: Mitigating environmental and other effects (2022)]. When spent rocket bodies and defunct satellites reenter the atmosphere, they produce metal vapors that condense into aerosol particles that descend into the stratosphere. So far, models of spacecraft reentry have focused on understanding the hazard presented by objects that survive to the surface rather than on the fate of the metals that vaporize. Here, we show that metals that vaporized during spacecraft reentries can be clearly measured in stratospheric sulfuric acid particles. Over 20 elements from reentry were detected and were present in ratios consistent with alloys used in spacecraft. The mass of lithium, aluminum, copper, and lead from the reentry of spacecraft was found to exceed the cosmic dust influx of those metals. About 10% of stratospheric sulfuric acid particles larger than 120 nm in diameter contain aluminum and other elements from spacecraft reentry. Planned increases in the number of low earth orbit satellites within the next few decades could cause up to half of stratospheric sulfuric acid particles to contain metals from reentry. The influence of this level of metallic content on the properties of stratospheric aerosol is unknown. [ABSTRACT FROM AUTHOR]

Ozone (O3) in the upper troposphere and lower stratosphere (UTLS) is strongly regulated by upper-level circulation dynamics. Understanding the coupling between UTLS O3 distribution and upper-level circulation dynamics is important not only to understand synoptic processes governing O3 distribution and variability, but also to test the fidelity of chemistry transport models in simulating the stratosphere–troposphere exchange (STE) processes. This study presents the first systematic assessment of observationally constrained UTLS O3 variability associated with upper-level circulation patterns over the Northeast Asia region. By applying the self-organized mapping (SOM) technique to 500, 250, and 100 hPa geopotential height (GPH) data, 12 circulation patterns are quantified and then used to characterize the UTLS O3 distribution in the period 2000–2020 in both four-site (Beijing, Pohang, Tateno, and Sapporo) ozonesonde data and regional-scale satellite products. The underlying dynamic transport mechanism responsible for UTLS O3 responses to different circulation patterns are further explored through correlation analysis between O3 anomalies and transport indicators. The results indicate that although O3 at almost all altitudes shows statistically significant sensitivity to circulation patterns, lower-stratospheric O3 exhibits a far stronger sensitivity when compared with upper-tropospheric O3. Circulation patterns featuring the East Asian Trough (EAT) show clear enhancement of O3 southwest of the trough, and the enhancement zone moves with the eastward propagation of the EAT. Circulation patterns featuring eastward-shedding vortices of the Asia Summer Monsoon Anticyclone (ASMA) show the opposite signal, in which O3 concentrations are decreased, especially at Sapporo, and the negative O3 anomaly zone stretches from South Japan to Sakhalin Island. Each circulation pattern is characterized by distinct transport pathways, which play a determining role in the pattern-specific UTLS O3 response. Positive O3 anomalies are usually associated with post-trough downward and southward transport, whereas negative O3 anomalies are commonly associated with fore-trough upward and northward transport. In the lower stratosphere, the correlation between O3 anomalies and transport indicators is significantly stronger than that in the upper troposphere, and the strongest correlation occurs in the lower stratosphere of Beijing. [ABSTRACT FROM AUTHOR]

Carbonyl sulfide (OCS or COS) is a ubiquitous trace gas and plays a role in forming stratospheric sulfate aerosol particles, thereby influencing climate. In this study, whole‐air samples containing OCS were collected onboard a passenger aircraft (IAGOS‐CARIBIC) from the upper troposphere/lowermost stratosphere (UT/LMS, 10–12 km) region and analyzed with CryoTrap–GC–AED system in the laboratory. Global OCS mixing ratios are presented and by using the OCS measurements in conjunction with other trace gases, an atmospheric OCS lifetime of 2.1 ± 1.3 years, and lowermost stratospheric OCS lifetime of 47 ± 16 years were determined. A total flux of 137 GgS a−1 of OCS from the troposphere into the stratosphere was estimated, and the stratospheric sink estimate yielded 55 ± 23 GgS a−1 of OCS. The 60% smaller sink can be interpreted as 82 GgS a−1 OCS which is transported back from the stratosphere into the troposphere. Plain Language Summary: Carbonyl sulfide (OCS) is the most abundant sulfur compound in the atmosphere. Due to its long atmospheric lifetime, OCS can be transported into the stratosphere where it forms a layer of sulfate aerosol particles at 30 km altitude. By reflecting incoming radiation and through perturbing ozone levels this layer has large impact on the Earth's energy balance and therefore climate. In this study, we have determined OCS mixing ratios in air samples collected in the upper troposphere/lowermost stratosphere (UT/LMS, 10–12 km) region from 2015 to 2018. From these measurements we estimated the total atmospheric lifetime and the stratospheric lifetime of OCS to be 2.1 ± 1.3 years, and 47 ± 16 years, respectively. We also estimated the total flux of OCS transported into the stratosphere from the troposphere to be 137 GgS a−1, of which only 40% 55 GgS a−1 remained in the stratosphere, and the remianing 60% (82 GgS a−1) were transported back into the troposphere. Key Points: Carbonyl sulfide (OCS) atmospheric lifetime of 2.1 ± 1.3 years and lowermost stratospheric lifetime of 47 ± 16 years were determinedTotal flux of OCS into the stratosphere estimated as 137 GgS a−1, of which 60% is estimated to be transported back into the troposphereThe lower back transport estimate might explain the current missing stratospheric sulfate aerosol burden [ABSTRACT FROM AUTHOR]

Water vapour in the upper troposphere and lower stratosphere is a key radiative agent and crucial factor in the Earth's climate system. The largest observed moisture anomaly in the lower stratosphere occurs in boreal summer in the Asian monsoon region, but global climate models face problems with simulating this moisture pattern and show a common regional moist bias above the Pacific. We demonstrate from combination of climate model experiments and atmospheric observations that the enhanced moisture in the Pacific lower stratosphere critically impacts regional circulation systems by inducing local longwave cooling. Related impacts involve a strengthening of isentropic potential vorticity gradients, strengthened westerlies in the Pacific westerly duct region, and a zonally extended anticyclonic monsoon circulation. Hence, improving regional biases in climate model simulated stratospheric water vapour appears to be an important factor for improving simulation of regional circulation systems, in particular in the Asian monsoon and Pacific region. [ABSTRACT FROM AUTHOR]

The mid-infrared lightweight stratospheric hygrometer, "Pico-Light H2O", the successor of Pico-SDLA H2O, is presented and its performances are evaluated during the AsA 2022 balloon-borne intercomparison campaign conducted at CNES Aire-sur-l'Adour (AsA) balloon launch facility and the Aeroclub d'Aire-sur-l'Adour. The Pico-Light instrument primarily been developed for sounding of the upper troposphere and stratosphere. Though, during the AsA 2022 campaign we expand the range of comparison including the lower troposphere additionally. Three different types of hygrometers and two models of radiosonde were flown, operated by the French Space Agency (CNES) and the NOAA Global Monitoring Laboratory (GML) scientific teams: Pico-Light H2O, the NOAA Frost Point Hygrometer (FPH), the micro hygrometer (in an early phase of development), M20 and iMet-4 sondes. In this frame, we intend to validate measurements of Pico-Light H2O through a first intercomparison with the NOAA FPH instrument. The in situ monitoring of water vapour in the UT-LS keeps being very challenging from an instrumental point of view because of the very small amounts of water vapour to be measured in these regions of the atmosphere. Between the lapse rate tropopause (11 to 12.3 km) and 20 km, the mean relative difference between water vapour mixing ratio measurements by Pico-Light H2O and NOAA FPH was (4.2 ± 7.7) %, mean tropospheric difference is was (3.84 ± 23.64)%, with differences depending on the altitude range considered. In the troposphere, relative humidity over water (RH) comparisons leads to an agreement between both Pico-Light and NOAA FPH of -0.2% on average, with excursions of about 30% RH due to moisture variability. Expanding the comparison to meteorological sondes, the iMet-4 sondes agree well with both Pico-Light and FPH between ground and 7.5 km (within ± 3% RH) and so does for M20 sondes, up to 13 km, which are wet biased by 3% RH and dry biased by 20% in case of saturation. [ABSTRACT FROM AUTHOR]

The boreal summer intraseasonal oscillation (BSISO) features more distinctive and complex propagation characteristics than its wintertime counterpart, the Madden–Julian oscillation (MJO). While the relationship between the MJO and the Arctic stratosphere during boreal winter has been widely documented, the linkage between the BSISO and the Antarctic stratosphere during austral winter has not been extensively discussed. Here, after identifying the Southern Hemisphere (SH) stratospheric polar vortex warming (SPVW) events, we reveal the bidirectional connection between BSISO and SPVW. Before onset of the SPVW events, the occurrence frequency and amplitude of BSISO phase 5 (P5) shows a significant increase. The most significant responses of the SH polar stratospheric temperature to the BSISO are found about 10 days after BSISO P5. Thus, to some extent, BSISO P5 can be regarded as a precursor to the SH SPVW event, which is attributed to the enhanced upward propagation and dissipation of planetary waves in the SH stratosphere induced by the BSISO P5. After onset of the SPVW events, a significant increase in the occurrence and amplitude of BSISO P6 is observed, corresponding to the enhanced convection over the South China Sea and southern Philippine Sea. Tropical upwelling associated with the strengthened Brewer–Dobson circulation (BDC) induced by the SPVW tends to result in unstable circumstances in the tropical upper troposphere. Then the high correlation between static stability at 150 hPa and outgoing longwave radiation (OLR) anomalies over the South China Sea and southern Philippine Sea provides robust evidence that the intensity of convective activity in the tropics can indeed be modulated by the variability in SH stratospheric polar vortex. Significance Statement: The relationship between the boreal summer intraseasonal oscillation (BSISO) and the Southern Hemisphere (SH) polar stratosphere remains unclear. After selecting the stratospheric polar vortex warming (SPVW) events, we reveal the two-way connection between BSISO and SPVW. Before the SPVW, the significant increase in occurrence and amplitude of BSISO phase 5 (P5) suggests that BSISO P5 can be regarded as a precursor to the weakened polar vortex. After the SPVW, the significant increase in occurrence and amplitude of BSISO phase 6 (P6) establishes that environmental alteration in tropical upper troposphere induced by the SPVW provides a favorable condition for the growth of ensuing convective activity. The results here help us better understand the potential link between stratospheric polar vortex and tropical intraseasonal oscillation. [ABSTRACT FROM AUTHOR]

The Arctic is warming twice as fast as the global mean, making Arctic research essential for understanding the global climate system. For 50 years, researchers at the NOAA Pacific Marine Environmental Laboratory have sought to detect and understand the numerous changes the Arctic is undergoing, the Arctic's connections with the Earth system, and the impacts of climate change on the people who live in the Arctic. PMEL accomplishments in Arctic research include identifying future states and variability of sea ice, defining the ice-free Arctic threshold and initiating a climate model selection process by applying observational constraints, developing a Bering Sea conveyor belt sea-ice model and a vessel spray-icing index, investigating internal versus forced response of Arctic temperature change, studying the connection between a changing Arctic and midlatitude weather, and rescuing historical data. Through continued study, improved understanding, and communication, PMEL research informs policymakers, managers, and the public to help ensure a sustainable future for the Arctic. [ABSTRACT FROM AUTHOR]

Balloon-borne cryogenic frost-point hygrometer (CFH) observations over two tropical stations Trivandrum (8.53° N, 76.87° E) and Hyderabad (17.47° N, 78.58° E) [2014–2017] along with Microwave Limb Sounder (MLS) observations [2011–2017] are used to examine the signatures of local and regional dynamics in the distribution of lower stratospheric water vapour over the Indian region. The column-integrated water vapour in the lower stratosphere (IWVLS) varies in the range 2.5–5 g/m2 with low values during winter and high values during summer monsoon and post monsoon seasons. About 50–75% of IWVLS lies in the lower regime of the lower stratosphere, the region from cold point tropopause (CPT) to 21 km (LS1). Hygropause is very near to the CPT in winter and pre-monsoon and 2–3 km above the CPT in summer-monsoon and post-monsoon. The CPT and the minimum in saturated mixing ratio (SMRmin) altitudes show a positive correlation, with SMRmin mostly occurring below the CPT. Though water vapour mixing ratio (WVMR) at CPT increases with increase in SMRmin, it is mostly less than the corresponding SMRmin value. CFH observations showed that the tape recorder signal in the LS1 is disturbed by the local/regional dynamics. While the amount of water vapour entering the lower stratosphere is higher over Hyderabad in winter and summer monsoon, it is higher over Trivandrum in the other two seasons. Hydration at the tropopause level is mainly determined by the overshooting/deep convection, monsoon dynamics and horizontal transport and dehydration is determined by temperature variations in the tropical tropopause layer (TTL). [ABSTRACT FROM AUTHOR]

The large-scale extratropical circulation in the Southern Hemisphere is much more zonally symmetric than that of the Northern Hemisphere, but its zonal departures, albeit highly relevant for regional impacts, have been less studied. In this study we analyse the joint variability of the zonally asymmetric springtime stratospheric and tropospheric circulation using Complex Empirical Orthogonal Functions (cEOF) to characterise planetary waves of varying amplitude and phase. The leading cEOF represents variability of a zonal wave 1 in the stratosphere that correlates slightly with the Symmetric Southern Annular Mode (S-SAM). The second cEOF (cEOF2) is an alternative representation of the Pacific-South American modes. One phase of this cEOF is also very highly correlated with the Asymmetric SAM (A-SAM) in the troposphere. Springs with an active ENSO tend to lock the cEOF2 to a specific phase, but have no consistent impact on its magnitude. Furthermore, we find indications that the location of Pacific Sea Surface Temperature anomalies affect the phase of the cEOF2. As a result, the methodology proposed in this study provides a deeper understanding of the zonally asymmetric springtime extratropical SH circulation. [ABSTRACT FROM AUTHOR]

This study explores the abrupt split of the polar vortex in the upper stratosphere prior to a recent sudden stratospheric warming event on 5 January 2021 (SSW21) and the mechanisms of vortex preconditioning by using the Modern-Era Retrospective Analysis for Research and Applications version 2 (MERRA2) global reanalysis data. SSW21 is preceded by the highly distorted polar vortex that was initially displaced from the pole but eventually split at the onset date. Vortex splitting is most significant in the upper stratosphere (1 hPa altitude) accompanied by the anomalous growth of westward-propagating planetary waves (PWs) of zonal wavenumber (ZWN) 2 (WPW2). While previous studies have suggested the East Asian trough as a potential source for the abnormal WPW2 growth, the prominent westward-propagating nature cannot be explained satisfactorily by the upward propagation of the quasi-stationary ZWN2 fluxes in the troposphere. More importantly, WPW2 exhibits an obvious in situ excitation signature within the barotropically and baroclinically destabilized stratosphere, dominated by the easterlies descending from the stratopause containing the WPW2 critical levels. This suggests that the vortex split is attributed to the WPW2 generated in situ within the stratosphere via instability. Vortex destabilization is achieved as the double-jet structure consisting of a subtropical mesospheric core and a polar stratospheric core develops into SSW21 by encouraging the anomalous dissipation of the upward-propagating tropospheric ZWN1 PWs. This double-jet configuration is likely a favorable precursor for SSW onset, not only for the SSW21 but generally for most SSWs, through promoting the anomalous growth of unstable PWs as well as the enhancement of the tropospheric PW dissipation. [ABSTRACT FROM AUTHOR]

The recently developed average latitudinal displacement (ALD) methodology is applied to assess the waviness of the austral-winter subtropical and polar jets using three different reanalysis data sets. As in the wintertime Northern Hemisphere, both jets in the Southern Hemisphere have become systematically wavier over the time series and the waviness of each jet evolves quite independently of the other during most cold seasons. Also, like its Northern Hemisphere equivalent, the Southern Hemisphere polar jet exhibits no trend in speed (though it is notably slower), while its poleward shift is statistically significant. In contrast to its Northern Hemisphere counterpart, the austral subtropical jet has undergone both a systematic increase in speed and a statistically significant poleward migration. Composite differences between the waviest and least wavy seasons for each species suggest that the Southern Hemisphere's lower-stratospheric polar vortex is negatively impacted by unusually wavy tropopause-level jets of either species. These results are considered in the context of trends in the Southern Annular Mode as well as the findings of other related studies. [ABSTRACT FROM AUTHOR]

The winter upper troposphere/lower stratosphere temperature/vertical motion response over the extratropical North Pacific induced by North Atlantic changes is not well understood. Here, using robust diagnostic calculations conducted in a fully coupled high-resolution climate model, we correct the North Atlantic ocean circulation biases and show that during wintertime, the North Atlantic cold surface temperature biases lead to a warmer upper troposphere/lower stratosphere over the extratropical North Pacific. In the upper troposphere/lower stratosphere over the extratropical North Pacific, this winter warming temperature response is linked to the vertical motion response through a simple leading order thermodynamic relationship between changes in the horizontal advection and adiabatic heating. The upper troposphere/lower stratosphere vertical motion response, which is also associated with the North Atlantic induced Walker circulation response over the tropical North Pacific, can provide a rough estimation of the upper troposphere/lower stratosphere warming response over the extratropical North Pacific. [ABSTRACT FROM AUTHOR]

Fifty years of daily ERA5 reanalysis data are employed to investigate the linkages between the strength of the stratospheric polar vortex and the tropospheric polar vortex during the boreal winter. The strong coupling events, anomalies in both the stratospheric and tropospheric polar vortices, can be classified into four configurations, each representing the distinct characteristics of planetary wave vertical propagation and tropospheric circulation anomalies. The findings reveal the following patterns: (1) Strong stratospheric polar vortex and weak tropospheric polar vortex periods are associated with anomalous downward E-P flux from the stratosphere to the troposphere, predominantly induced by planetary waves 1 and 2. Warm anomalies occur along the North Atlantic coasts, while cold anomalies are evident over Eastern Europe and East Asia at the surface. (2) Weak stratospheric polar vortex and strong tropospheric polar vortex periods exhibit anomalous upward E-P flux in high latitudes, with dominant wave 1, and anomalous downward E-P flux in the middle latitudes, dominated by wave 2. Warm anomalies are observed over North America, Western Europe, and the northern side of the Gulf of Oman at the surface. (3) Strong stratospheric polar vortex and strong tropospheric polar vortex periods feature anomalous downward E-P flux in high latitudes, dominated by wave 1, and anomalous upward E-P flux in middle latitudes, with a wave 2 predominance. Warm anomalies prevail over Northeast Asia, Southern Europe, and North America at the surface. (4) Weak stratospheric polar vortex and weak tropospheric polar vortex periods display anomalous upward E-P flux in mid-to-high latitudes, predominantly with wave 1. In contrast to the tropospheric circulation anomalies observed in the third category, this pattern results in the presence of cold anomalies over Northeast Asia, Southern Europe, and North America. [ABSTRACT FROM AUTHOR]

Sudden stratospheric warming (SSW) events can form a window of forecast opportunity for polar vortex predictions on subseasonal‐to‐seasonal time scales. Analyzing numerical ensemble simulations, we quantify the associated enhanced predictability due to reduced upward planetary wave fluxes during the mostly radiatively driven recovery phase following SSWs. Ensembles that predict an SSW show reduced ensemble spread in terms of polar vortex strength for several weeks to follow, as well as a corresponding reduction in forecast errors. This increased predictability is particularly pronounced for strong SSWs and even occurs if not all ensemble members predict a major SSW. Furthermore, we found a direct impact of the occurrence of SSWs on the date of the final warming (FW): the decrease in upward wave fluxes delays the FW significantly. The reduced spread after SSWs and the delay in FW date have potentially further implications for (subseasonal) predictions of the tropospheric and mesospheric circulations. Plain Language Summary: The polar vortex is a large scale circulation active during winter in the higher levels of the polar atmosphere. Changes in the strength of the polar vortex can have an impact on the weather over mid‐latitude regions like Europe. This is the case especially for the period after so‐called sudden stratospheric warming (SSW) events, where the polar vortex breaks down very abruptly and then slowly recovers over several weeks. Such a break‐down of the polar vortex tends to suppress wave activity and hence reduces the dynamical variability in the polar stratosphere, leading to a more predictable evolution of the circulation. We quantify the strength and timescale of this increase in predictability of the polar vortex after an SSW using a large set of winter time model forecasts. Key Points: Sudden stratospheric warmings (SSWs) lead to reduced forecast spread in the polar stratosphere for several weeks after the eventReduced forecast spread after SSWs is driven by suppressed vertical planetary wave propagation due to persistent negative wind anomaliesFinal warmings are delayed for winters with SSW, consistent with reduced upward wave fluxes following the SSW [ABSTRACT FROM AUTHOR]

Tropical waves play an important role in driving the quasi‐biennial oscillation of zonal winds in the tropical stratosphere. In our study we analyze these waves based on temperature observations from the 2021–2022 Strateole‐2 campaign when the Reel‐down Atmospheric Temperature Sensor (RATS) was successfully deployed for the first time. RATS provides long‐duration, continuous and simultaneous high‐resolution temperature observations at two altitudes (balloon float level and 200 m below) allowing for an analysis of vertical wavelengths. This separation distance was chosen to focus on waves near the resolution limit of reanalyses. Here, we found tropical waves with periods between about 6 hr and 2 days, with vertical wavelengths between 1.5 and 5 km, respectively. Comparing our results to Fifth generation European Centre for Medium‐Range Weather Forecasts (ERA5) reanalyses we found good agreement for waves with a period longer than 1 day. However, the ERA5 amplitudes of higher‐frequency waves are under‐estimated, and the temporal evolution of most wave packets differs from the observations. Plain Language Summary: We present measurements from the maiden flight of the Reel‐down Atmospheric Temperature Sensor (RATS) in November/December 2021. The instrument lowered a temperature sensor down to about 200 m from a balloon floating at about 18 km. By combining the temperature measurements at balloon floating level and RATS we analyze tropical waves with relatively small vertical wavelengths (<6 km). These waves are important as they drive the quasi‐biennial oscillation in the east‐west winds in the tropical stratosphere. This oscillation is acknowledged as an important process for seasonal forecasts, but it is currently not well resolved in weather or seasonal forecast models. In our study we compare the observed waves with waves in one weather model system (European Centre for Medium‐Range Weather Forecasts Reanalysis (ERA5)) and find that the spectral energies are similar for long‐period waves (>1 day). However, the higher‐frequency gravity waves (that are necessary for quasi‐biennial oscillation forcing) are under‐estimated by ERA5, which may in part be related to the limited vertical resolution. Key Points: High‐resolution observations in the lowermost stratosphere from a new instrument (Reel‐down Atmospheric Temperature Sensor (RATS))The RATS instrument detected tropical waves at resolution limit of reanalysesFifth generation European Centre for Medium‐Range Weather Forecasts Reanalysis reproduces long‐period waves, but temporal evolution differs from observations [ABSTRACT FROM AUTHOR]

Stratospheric ozone is important for both stratospheric and surface climate. In the lower stratosphere during winter, its variability is governed primarily by transport dynamics induced by wave–mean flow interactions. In this work, we analyze interannual co-variations between the distribution of zonal-mean ozone and the strength of the polar vortex as a measure of dynamical activity during northern hemispheric winter. Specifically, we study co-variability between the seasonal means of the ozone field from modern reanalyses and polar-cap-averaged temperature at 100 hPa, which represents a robust and well-defined index for polar vortex strength. We focus on the vertically resolved structure of the associated extratropical ozone anomalies relative to the winter climatology and shed light on the transport mechanisms that are responsible for this response pattern. In particular, regression analysis in pressure coordinates shows that anomalously weak polar vortex years are associated with three pronounced local ozone maxima just above the polar tropopause, in the lower to mid-stratosphere and near the stratopause. In contrast, in isentropic coordinates, using ERA-Interim reanalysis data, only the mid- to lower stratosphere shows increased ozone, while a small negative ozone anomaly appears in the lowermost stratosphere. These differences are related to contributions due to anomalous adiabatic vertical motion, which are implicit in potential temperature coordinates. Our analyses of the ozone budget in the extratropical middle stratosphere show that the polar ozone response maximum around 600 K and the negative anomalies around 450 K beneath both reflect the combined effects of anomalous diabatic downwelling and quasi-isentropic eddy mixing, which are associated with consecutive counteracting anomalous ozone tendencies on daily timescales. We find that approx. 71 % of the total variability in polar column ozone in the stratosphere is associated with year-by-year variations in polar vortex strength based on ERA5 reanalyses for the winter seasons 1980–2022. MLS observations for 2005–2020 show that around 86 % can be explained by these co-variations with the polar vortex. [ABSTRACT FROM AUTHOR]

NO and NO 2 (NOx) play major roles in both tropospheric and stratospheric chemistry. This paper provides a novel method to obtain a global and accurate photolysis rate for NO 2 based on satellite data. The photolysis rate J(NO2) dominates the daytime diurnal variation of NOx photochemistry. Here the spatial variation of J(NO2) at 50–90 ∘ S in December from 20–40 km is obtained using data from the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) experiment. Because NO and NO 2 rapidly exchange with one another in the daytime, J(NO2) can be attained assuming steady state, and the results are shown to be consistent with model results. The J(NO2) value decreases as the solar zenith angle increases and has a weak altitude dependence. A key finding is that satellite-derived J(NO2) increases in the polar regions, in good agreement with model predictions, due to the effects of ice and snow on surface albedo. Thus, the method presented here provides an observation-based check on the role of albedo in driving polar photochemistry. [ABSTRACT FROM AUTHOR]

Using a common analysis approach for data sets produced by the Stratospheric Aerosol and Gas Experiment instruments SAGE II and SAGE III/ISS, we identify 13 likely smoke events based on enhancements in the aerosol extinction coefficient. Nine of these are sufficiently large compared to ambient aerosol levels to compute mean mid-latitude 1020 nm optical depth enhancements that range from 0.0005 to 0.011. We also note that, for large events, the 525 to 1020 nm aerosol extinction coefficient ratio asymptotes at a high extinction coefficient to values between 2 and 3, suggesting that the aerosol radius is relatively small (< 0.3 µm) and relatively consistent from event to event. Most of these events are primarily confined to the lower stratosphere and rarely can be observed above 20 km. We also infer an increase in the frequency of smoke events between the SAGE II (1984–1991, 1996–2005) and SAGE III/ISS (2017-present) periods by almost a factor of 2 and also note that the two largest events occur in the latter data set. However, given the low frequencies overall, we are not confident that the differences can be attributed to changes between the two periods. We also attempt to disentangle the mixing of aerosol in the Northern Hemisphere summer of 1991 from a pyrocumulus event (Baie-Comeau, Quebec) and Mt. Pinatubo and conclude that, while there is evidence for smoke in the lower stratosphere, virtually all of the enhanced aerosol observations in the northern mid-latitudes in the summer of 1991 are associated with the Mt. Pinatubo eruption. [ABSTRACT FROM AUTHOR]

The need to reduce data center operational costs has necessitated siting cloud computing platforms in cold locations such as the stratosphere. The stratosphere has also been found to play an important role in understanding life origins as it hosts life forms. The use of stratosphere based computing platforms however requires the hosting of multiple server payloads (requiring high energy consumption) at a higher altitude. In addition, smaller server payloads lead to smaller sized stratospheric computing platforms (SCPs) which limit interaction with stratospheric organisms. However, these challenges are not considered when designing SCPs. Hence, there is a risk of wrongly evaluating the power usage effectiveness (PUE) associated with SCPs. In addition, there is a risk of installing and deploying large sized SCPs thereby leading to contamination and limiting research potential on studying life forms. The research being presented proposes an intelligent architecture enabling the identification, selection and use of only light weight servers aboard SCPs. The incorporation of the intelligent architecture is observed to enhance the PUE by 43.9%. In addition, the use of the intelligent architecture is noted to enhance the overall PUE by 59.6% for hosting altitudes spanning the low to mid stratosphere regions. In addition, the reduction in server weight by an amount exceeding 92% is noted by simulations to enable the realization of a PUE that is close to the ideal value of unity. [ABSTRACT FROM AUTHOR]

The observed stratospheric quasi‐biennial oscillation (QBO) and the tropospheric Madden‐Julian oscillation (MJO) are strongly connected in boreal winter, with stronger MJO activity when lower‐stratospheric winds are easterly. However, the current generation of climate models with internally generated representations of the QBO and MJO do not simulate the observed QBO‐MJO connection, for reasons that remain unclear. This study builds on prior work exploring the QBO‐MJO link in climate models whose stratospheric winds are relaxed toward reanalysis, reducing stratospheric biases in the model and imposing a realistic QBO. A series of ensemble experiments are performed using four state‐of‐the‐art climate models capable of representing the MJO over the period 1980–2015, each with similar nudging in the stratosphere. In these four models, nudging leads to a good representation of QBO wind and temperature signals, however no model simulates the observed QBO‐MJO relationship. Biases in MJO vertical structure and cloud‐radiative feedbacks are investigated, but no conclusive model bias or mechanism is identified that explains the lack of a QBO‐MJO connection. Plain Language Summary: Observations show a strong link between the stratospheric quasi‐biennial oscillation (QBO)—the alternation of tropical stratospheric zonal winds between easterly and westerly phases—and the Madden‐Julian oscillation (MJO), an eastward propagating phenomenon in the tropical troposphere in which the circulation and convection are coupled. Stronger MJO activity is observed when lower‐stratospheric winds are easterly. This coupling is intriguing for many reasons, but most practically because it suggests that the stratosphere can potentially enhance surface weather and inform subseasonal climate prediction. However, current climate models do not show this observed connection. One reason may be related to biases in how models simulate stratospheric winds, which can be corrected for in an artificial way by relaxing the model simulated winds to better match observationally constrained data sets. One recent study, however, showed that correcting for this bias using this approach in one climate model still fails to produce credible QBO‐MJO coupling. Here we expand that analysis to include four climate models and find that no model produces a robust QBO‐MJO relationship like that seen in observations. Our results show that properly representing the QBO winds and temperatures via nudging is therefore not sufficient for reproducing the observed relationship. Furthermore, while biases in how models represent cloud processes may still be a likely culprit, any definitive model bias or missing mechanism remains elusive. Key Points: The link between the quasi‐biennial oscillation (QBO) and Madden‐Julian oscillation (MJO) is explored in four climate models with nudged stratospheric winds and free‐evolving tropospheresNo model shows as strong of a QBO‐MJO connection as in observationsModel biases in cloud‐radiative feedbacks and MJO vertical velocity are diagnosed, but neither conclusively explains the lack of a QBO‐MJO connection [ABSTRACT FROM AUTHOR]

In this study we provide a systematic characterization of Rossby wave activity during the 25 sudden stratospheric warming (SSW) and 31 strong polar vortex (SPV) events that occurred in the period 1979–2021, identifying the specific tropospheric and stratospheric waves displaying anomalous behaviour during such events. Space-time spectral analysis is applied to ERA5 data for this purpose, so that both the wavenumber and the zonal phase speed of the waves can be assessed. We find that SSW events are associated with a reduction in the phase speed of Rossby waves, first in the stratosphere and then in the troposphere; SPV events are tied to a concomitant increase of phase speed across vertical levels. Phase speed anomalies become significant around the event and persist for 2–3 weeks afterwards. Changes of Rossby wave properties in the stratosphere during SSW and SPV events are dominated by changes in the background flow, with a systematic reduction or increase, respectively, in eastward propagation of the waves across most wavenumbers. In the troposphere, on the other hand, the effect of the background flow is also complemented by changes in wave properties, with a shift towards higher wavenumbers during SSW events and towards lower wavenumbers for SPV events. The opposite response between SSW and SPV events is also visible in the meridional heat and momentum flux co-spectra, which highlight from a novel perspective the connection between stratospheric Rossby waves and upward propagation of waves. [ABSTRACT FROM AUTHOR]

As of now, direct measurements of middle and upper atmospheric wind are still scarce, and the observation method is limited, especially for the upper stratosphere and lower mesosphere. This paper presents a study of band selection to derive line-of-sight wind from 30 km to more than 120 km using a high-spectral-resolution terahertz (THz) radiometer, which can fill the measurement gap between lidar and interferometer data. Simulations from 0.1–5 THz for evaluating the feasibility of the spaceborne THz limb sounder are described in this study. The results show that high-precision wind (better than 5 ms-1) can be obtained from 40 to 70 km by covering a cluster of strong O3 lines. By choosing strong O2 or H2O lines, the high-quality measurement can be extended to 105 km. The O atom (OI) lines can provide wind signals in the higher atmosphere. In addition, performance of different instrument parameters, including spectral resolution, bandwidth, and measurement noise, was analyzed, and, lastly, four different band combinations are suggested. [ABSTRACT FROM AUTHOR]

Sudden stratospheric warmings (SSWs) are extreme disruptions of the wintertime polar vortex that can alter the tropospheric weather for over 2 months. However, the reasons why only some SSWs have a tropospheric impact are not yet clear. This study analyses the tropospheric impact of SSWs over the Atlantic region as measured by the latitudinal displacement of the North Atlantic eddy-driven jet following SSWs. We use reanalysis data for the period 1950–2020 to examine differences in the stratospheric and tropospheric circulation for SSWs with an equatorward (EQ) or a poleward (POLE) shift. Our results show a stronger and more persistent Northern Annular Mode (NAM) signal in the lower stratosphere for EQ than for POLE, beginning 2 weeks before the onset date. In the troposphere, we find precursory signals of the Atlantic jet behavior over Siberia, consistent with previous studies, and also over the central North Pacific and central Europe. In particular, our results suggest that the noncanonical poleward jet shift response to SSWs is in part modulated by circulation anomalies over the central North Pacific, and that these are in turn connected to the cold phase of El Niño–Southern Oscillation. Further analysis of the enhanced predictability given by these precursors suggests that the sign of the lower-stratospheric NAM and the geopotential anomalies over the central North Pacific significantly affect the probability of having an EQ or POLE response of the Atlantic jet. [ABSTRACT FROM AUTHOR]

Simulating whole atmosphere dynamics, chemistry, and physics is computationally expensive. It can require high vertical resolution throughout the middle and upper atmosphere, as well as a comprehensive chemistry and aerosol scheme coupled to radiation physics. An unintentional outcome of the development of one of the most sophisticated and hence computationally expensive model configurations is that it often excludes a broad community of users with limited computational resources. Here, we analyze two configurations of the Community Earth System Model Version 2, Whole Atmosphere Community Climate Model Version 6 (CESM2(WACCM6)) with simplified "middle atmosphere" chemistry at nominal 1 and 2° horizontal resolutions. Using observations, a reanalysis, and direct model comparisons, we find that these configurations generally reproduce the climate, variability, and climate sensitivity of the 1° nominal horizontal resolution configuration with comprehensive chemistry. While the background stratospheric aerosol optical depth is elevated in the middle atmosphere configurations as compared to the comprehensive chemistry configuration, it is comparable among all configurations during volcanic eruptions. For any purposes other than those needing an accurate representation of tropospheric organic chemistry and secondary organic aerosols, these simplified chemistry configurations deliver reliable simulations of the whole atmosphere that require 35% and 86% fewer computational resources at nominal 1 and 2° horizontal resolution, respectively. Plain Language Summary: Modeling the entire atmosphere, or at least from the surface to an altitude of 140 km (87 miles), takes a lot of computer resources. Simulating 1 year can require the equivalent of thousands of personal computers running for 1 day, for example, which is only realistic for researchers with access to a supercomputer. There are many people who would like to simulate the whole atmosphere to study climate change, space weather, and extreme events, but even with access to a supercomputer, it is still computationally expensive to run. We examined a whole atmosphere model with a simpler chemistry scheme, and at a lower horizontal resolution, to see if it still reproduces major features of climate and climate change. The two configurations perform similarly to the high resolution simulation with complex chemistry, with some minor and understandable differences. Anyone looking to simulate the whole atmosphere, using fewer computational resources, can do so confidently using the described model configurations, as long as they are aware of some of the deficiencies. Key Points: There are differences in stratospheric aerosol optical depth between comprehensive and simplified chemistry configurationsSimplifying the chemistry scheme generally has smaller global impacts than coarsening the horizontal resolutionAll configurations have similar climate sensitivities and responses to forcings [ABSTRACT FROM AUTHOR]

Many chemical processes depend non‐linearly on temperature. Gravity‐wave‐induced temperature perturbations have been shown to affect atmospheric chemistry, but accounting for this process in chemistry‐climate models has been a challenge because many gravity waves have scales smaller than the typical model resolution. Here, we present a method to account for subgrid‐scale orographic gravity‐wave‐induced temperature perturbations on the global scale for the Whole Atmosphere Community Climate Model. Temperature perturbation amplitudes T^ $\hat{T}$ consistent with the model's subgrid‐scale gravity wave parameterization are derived and then used as a sinusoidal temperature perturbation in the model's chemistry solver. Because of limitations in the parameterization, we explore scaling of T^ $\hat{T}$ between 0.6 and 1 based on comparisons to altitude‐dependent T^ $\hat{T}$ distributions of satellite and reanalysis data, where we discuss uncertainties. We probe the impact on the chemistry from the grid‐point to global scales, and show that the parameterization is able to represent mountain wave events as reported by previous literature. The gravity waves for example, lead to increased surface area densities of stratospheric aerosols. This increases chlorine activation, with impacts on the associated chemical composition. We obtain large local changes in some chemical species (e.g., active chlorine, NOx, N2O5) which are likely to be important for comparisons to airborne or satellite observations, but the changes to ozone loss are more modest. This approach enables the chemistry‐climate modeling community to account for subgrid‐scale gravity wave temperature perturbations interactively, consistent with the internal parameterizations and are expected to yield more realistic interactions and better representation of the chemistry. Plain Language Summary: Sub‐grid scale gravity waves have long been incorporated in the momentum budgets of global chemistry‐climate models using parameterizations, but their associated impacts on temperature dependent chemistry within the models have not been included in a self‐consistent way. Here we present an approach to modeling these chemical impacts in the Whole Atmosphere Community Climate Model. We obtain large local changes in some chemical species (e.g., active chlorine, NOx, N2O5) but smaller impacts on ozone. The approach can be expected to advance the ability of the chemistry‐climate modeling community to examine gravity wave effects on a wide range of chemical problems. Key Points: We present a method for estimating subgrid‐scale orographic gravity wave temperature perturbations on a global scaleThe distributions of these perturbations are compared with Constellation Observing System for Meteorology Ionosphere and Climate/Formosa Satellite 3 and ECMWF Reanalysis version 5 to estimate scaling factorsThese temperature perturbations impact stratospheric aerosols and chemistry particularly near the tropical tropopause and polar regions [ABSTRACT FROM AUTHOR]

Man-made activities can release the ozone depleting substances (ODSs) like chlorofluorocarbons (CFCs) and other halocarbons stable in atmosphere and ultimately, they migrate to the stratosphere where they can destroy the ozone layer through the XOx catalytic cycle (X = Cl, Br). The active forms in this catalytic cycle are X and XO that can be arrested in the inactive forms like XONO2 (halogen nitrate, an additive compound of two odd electron molecules XO and NO2) and HX (produced in the reaction of X with CH4) in the stratosphere to prevent the ozone depletion cycle. The catalytically active forms from these inactive species can be regenerated in the reactions on heterogeneous solid surface like polar stratospheric cloud (specially Type II PSC formed at about −85 °C). Formation of such PSC in the stratosphere is only possible in the supercooled stable Antarctic vortex produced in the prolonged winter. In fact, formation of such PSC in the stratosphere is not possible in the other regions of the earth and not even in the Arctic pole where no stable Arctic vortex is generally formed in the winter. Thus nature confines the ozone depletion reactions mainly in the stratosphere of Antarctica pole which is practically inhabited.

The application of starlight refraction navigation to spacecraft and space weapons is a significant development. However, the irregular stratospheric atmosphere can cause fluctuations in relative light intensity and refraction angles of refracted stars, which need to be analyzed to provide guidance for system design and simulation verification. The internal gravity wave (IGW) is an important component of the irregular atmosphere. Based on the Rytov approximation, closed-form approximations were obtained, which can more intuitively reveal the relationship between the IGW parameters and the star signals’ statistical characteristics. From the GOMOS observations, the influence of the stratosphere from 25 km to 35 km on the fluctuations in relative intensity and refraction angles was analyzed in this study. As the height increased, the fluctuations in starlight signals gradually weakened. Compared with the numerical solution, the error of the closed-form approximations for relative intensity fluctuations was no more than 10%, and the error for refraction angle fluctuations was 1.0%. Compared with the measured data, the error of the closed-form approximations for relative intensity was 6.3%. The proposed approximations better reflect the relationship between IGW parameters and star signal fluctuations compared to the existing approximation. The research in this article can provide a reference for application assessment based on starlight refraction navigation.

This study presents a performance analysis for an Internet-of-Things wildlife radio-tracking mission using drones, satellites and stratospheric platforms for data relay with Spread Spectrum Modulation devices. The performance analysis is presented with link and data budgets, calculations of the area coverage, an estimation of the time resolution and allowable data amount of each collar, a power and energy budget and consequent battery pack and collar weight estimations, cost budgets, and considerations on synergetic approaches to incorporate more mission segments together. The paper results are detailed with example species to target with each collar weight range, and with design drivers and guidelines to implement improved mission segments.

Abstract Simulating whole atmosphere dynamics, chemistry, and physics is computationally expensive. It can require high vertical resolution throughout the middle and upper atmosphere, as well as a comprehensive chemistry and aerosol scheme coupled to radiation physics. An unintentional outcome of the development of one of the most sophisticated and hence computationally expensive model configurations is that it often excludes a broad community of users with limited computational resources. Here, we analyze two configurations of the Community Earth System Model Version 2, Whole Atmosphere Community Climate Model Version 6 (CESM2(WACCM6)) with simplified “middle atmosphere” chemistry at nominal 1 and 2° horizontal resolutions. Using observations, a reanalysis, and direct model comparisons, we find that these configurations generally reproduce the climate, variability, and climate sensitivity of the 1° nominal horizontal resolution configuration with comprehensive chemistry. While the background stratospheric aerosol optical depth is elevated in the middle atmosphere configurations as compared to the comprehensive chemistry configuration, it is comparable among all configurations during volcanic eruptions. For any purposes other than those needing an accurate representation of tropospheric organic chemistry and secondary organic aerosols, these simplified chemistry configurations deliver reliable simulations of the whole atmosphere that require 35% and 86% fewer computational resources at nominal 1 and 2° horizontal resolution, respectively.

Abstract Many chemical processes depend non‐linearly on temperature. Gravity‐wave‐induced temperature perturbations have been shown to affect atmospheric chemistry, but accounting for this process in chemistry‐climate models has been a challenge because many gravity waves have scales smaller than the typical model resolution. Here, we present a method to account for subgrid‐scale orographic gravity‐wave‐induced temperature perturbations on the global scale for the Whole Atmosphere Community Climate Model. Temperature perturbation amplitudes T^ consistent with the model's subgrid‐scale gravity wave parameterization are derived and then used as a sinusoidal temperature perturbation in the model's chemistry solver. Because of limitations in the parameterization, we explore scaling of T^ between 0.6 and 1 based on comparisons to altitude‐dependent T^ distributions of satellite and reanalysis data, where we discuss uncertainties. We probe the impact on the chemistry from the grid‐point to global scales, and show that the parameterization is able to represent mountain wave events as reported by previous literature. The gravity waves for example, lead to increased surface area densities of stratospheric aerosols. This increases chlorine activation, with impacts on the associated chemical composition. We obtain large local changes in some chemical species (e.g., active chlorine, NOx, N2O5) which are likely to be important for comparisons to airborne or satellite observations, but the changes to ozone loss are more modest. This approach enables the chemistry‐climate modeling community to account for subgrid‐scale gravity wave temperature perturbations interactively, consistent with the internal parameterizations and are expected to yield more realistic interactions and better representation of the chemistry.

Observations of nitrogen dioxide (NO2) and nitrogen oxide (NO) in the stratosphere are relevant to understand long-term changes and variabilities in stratospheric nitrogen oxide (NOx) and ozone (O3) concentrations. Due to the versatile role of NO2 and NO in stratospheric O3 photochemistry they are important for recovery and build-up of O3 holes in the stratosphere, and therefore can indirectly affect the human life. Thus, we present in this work the evaluation of NO2 and NO stratospheric partial columns (> 16 km altitude) retrieved from ground-based Fourier-transform infrared (FTIR) measurements from over 25 years at Zugspitze (47.42° N, 10.98° E, 2964 m a.s.l.) and 18 years at Garmisch (47.47° N, 11.06° E, 745 m a.s.l.), Germany. The obtained stratospheric columns are only weakly influenced by tropospheric pollution and show only a very small bias of (2.5±0.2) % when comparing NO2 above Zugspitze and Garmisch. Stratospheric columns of both NO2 and NO show a diurnal increase in dependence of local solar time (LST). We quantified this behavior by calculating diurnal increasing rates. Here, we find mean values for the NO2 diurnal increasing rate of (0.89±0.14)·1014 cm-2 h-1 and (0.94±0.14)·1014 cm-2 h-1 at Zugspitze and Garmisch, respectively. The mean NO a.m. diurnal increasing rate above Zugspitze can be found to be (1.42±0.12)·1014 cm-2 h-1. Regarding the seasonal dependency of these increasing rates, for the first time, we were able to detect a significant seasonal variation of both NO2 diurnal increasing rates and NO a.m. diurnal increasing rates experimentally with a maximum of (1.13±0.04)·1014 cm-1 h-1 for NO2 and (1.76±0.25)·1014 cm-1 h-1 for NO in September and a minimum of (0.71±0.18)·1014 cm-1 h-1 in December for NO2 and a minimum of (1.18±0.41)·1014 cm-1 h-1 in November for NO. This similar behavior may be explained by the interconnection of both species in stratospheric photochemistry. The outcome of this work is a retrieval and analyzation strategy of FTIR data for NOx stratospheric columns, which can help to further validate photochemical models or improve satellite validations. The first use of this data set is shown in a companion paper (Nürnberg et al., 2023) extracting experiment-based NOx scaling factors describing the diurnal increase out of the retrieved partial columns and validating recently published model-based scaling factors. [ABSTRACT FROM AUTHOR]

The dominant pattern of Northern Hemisphere extratropical climate variability is the Northern Annular Mode (NAM), which in wintertime represents the coupling of the stratospheric and tropospheric circulations. The internal variability associated with the NAM has been shown to give rise to substantial uncertainty in climate projections of regional surface air temperatures (SATs), but it's unclear how much of this variability arises from stratosphere‐troposphere coupling processes. Here, using three large‐ensemble coupled climate model simulations from 1850 to 2100 with varying fidelity of stratosphere‐troposphere coupling processes, we demonstrate that regional SAT variability across timescales is amplified when the tropospheric NAM is coupled to the stratospheric NAM. Moreover, models that lack adequate simulation of stratosphere‐troposphere coupling processes may not capture the magnitude of uncertainty in near‐term SAT projections associated with this coupling. Plain Language Summary: Large‐scale atmospheric circulation variability drives substantial variation in regional surface air temperatures (SATs), so that even on 30–40 year timescales local cooling trends are possible even as global‐mean temperatures increase. We provide evidence that when the stratospheric mean flow is coupled to the tropospheric mean flow, the decadal variability of SATs is amplified in some regions. Some models do not represent well the observed coupling of the stratosphere to the troposphere, and these models may underestimate decadal variability associated with this coupling. Key Points: The Northern Annular Mode (NAM) exhibits decadal variability that can accelerate or slow the rate of anthropogenic regional surface warmingAmplified decadal variability of extratropical surface temperatures occurs when the NAM is coupled from the stratosphere to the troposphereModels that fail to adequately capture vertical coupling may underestimate the magnitude of decadal variations in surface air temperatures [ABSTRACT FROM AUTHOR]

The year when total column ozone (TCO) returns to 1980 levels is commonly used to quantify recovery from disturbance caused by ozone‐depleting substances. This date is reasonable but somewhat arbitrary. Here we borrow an indicator from climate change research, the signal‐to‐noise (S/N) metric to investigate how TCO might return to statistically similar levels to those of the pre‐ozone hole era (1960–1970). We calculate S/N for ozone projections from the Chemistry‐Climate Model Initiative. In most regions, a return to 1980 levels doesn't represent TCO recovery to pre‐disturbance conditions because it does not account for internal variability or reflect when statistically significant TCO losses occurred. Future projections show that, in most regions, TCO "de‐emerges" (i.e., S/N becomes less than one standard deviation from the pre‐disturbance mean) before it returns to its 1980 value. We conclude that S/N is an appropriate, perhaps complementary metric for determining when TCO returns to a pre‐disturbance state. Plain Language Summary: The stratospheric ozone layer is expected to recover from the damaging effects of chlorofluorocarbons (CFCs) and other halogen‐containing source gases this century. Ozone recovery is traditionally but somewhat arbitrarily defined as the year when total column ozone (TCO) abundances return to 1980 levels. Here, we use a metric commonly used in the climate change emergence literature—signal‐to‐noise (S/N)—to quantify statistically significant changes in TCO in models and observations relative to a period before CFC‐induced ozone depletion began. The S/N framing ties recovery to unperturbed environmental conditions, rather than to the environment in a specific year. We argue that tying recovery to unperturbed local environmental conditions is at least as reasonable as tying it to the same global date. Our calculations, which account for natural variability, show that 1980 does not reflect the onset of statistically significant ozone loss. Using a return of TCO to 1980 levels underestimates the time of recovery in Antarctica, where losses have been most significant, and overestimates the time to recovery in other regions. We conclude that signal‐to‐noise is a useful metric to assess the return of TCO to its baseline state and evaluate the effectiveness of the Montreal Protocol. Key Points: We present signal‐to‐noise calculations of stratospheric ozone depletion in chemistry‐climate models relative to 1960–1970Statistically significant ozone depletion does not emerge in 1980, which is traditionally used as a benchmark for ozone recoveryIn most regions de‐emergence occurs before ozone returns to 1980 levels except in Antarctica where de‐emergence occurs 25 years later [ABSTRACT FROM AUTHOR]

Stratospheric Aerosol Injection (SAI) aims to offset some climate hazards by injecting aerosols into the stratosphere to reflect solar radiation. The lifetime of injected particles influences SAI's radiative efficacy—the ratio of radiative forcing to particle mass flux. We employ a Lagrangian trajectory model with particle sedimentation to simulate how background circulations influence the transport of passive particles (without microphysical growth) in the stratosphere and quantify sensitivities of particle lifetime to injection locations. At 20 km, optimizing injection locations can increase particle lifetime by >40%. Injection strategies can be constrained to maintain an interhemispheric balance of particle lifetime without significantly decreasing total lifetime. Generally, increasing injection altitude increases particle lifetime while also increasing costs and environmental impacts of deployment aircraft. Optimizing injection latitude and longitude can relax this altitude‐lifetime trade‐off by increasing lifetime without needing to increase altitude, which warrants further testing in global climate models with aerosol microphysics. Plain Language Summary: Stratospheric Aerosol Injection (SAI) aims to reduce climate change by increasing the amount of aerosols in the stratosphere. These additional aerosols can reflect additional sunlight to partially offset the energy imbalance caused by greenhouse gases. The lifetime of injected particles in the stratosphere is one of the important factors that can influence the cooling effects of SAI, as particles that stay longer in the stratosphere can reflect more sunlight over their lifetime. We use observed stratospheric winds to simulate the transport of injected particles and then calculate the particle's lifetime in the stratosphere, aiming to understand how lifetime is related to the location and season at which the particles are injected. For particles injected at 20 km altitude, we can increase particle lifetime by >40% by optimally choosing injection locations. Increasing injection altitude can increase particle lifetime while also increasing the costs and environmental impacts of deployment aircraft. Our results suggest that optimizing injection latitude and longitude to increase lifetime can relax the trade‐off between altitude and lifetime by increasing particle lifetime without needing to increase injection altitude. Key Points: Injection longitudes influence particle lifetime because of zonal asymmetry of poleward winds, especially in the lower stratosphereOptimizing injection latitude and longitude can increase stratospheric lifetime of injected particles without increasing injection altitudeInjection strategies can be developed to maintain an interhemispheric balance of particle lifetime without compromising total lifetime [ABSTRACT FROM AUTHOR]

Previous studies have found that Madden‐Julian Oscillation (MJO) amplitude depends on the Quasi‐Biennial Oscillation (QBO) during boreal winter. This MJO‐QBO relationship is important to realizing subseasonal‐to‐seasonal prediction skills, but the underlying mechanism remains unclear. It is often thought that this relationship arises through the modulation of the upper‐troposphere and lower‐stratosphere lapse rate by the QBO, but this mechanism assumes the one‐way impact of the QBO onto the MJO. Alternatively, the MJO can be hypothesized to influence the QBO by modulating stratospheric wave activity that is known to be critical to QBO dynamics. Therefore, using satellite and reanalysis data, this study examines whether MJO monthly activity can impact stratospheric wave activity and QBO downward propagation speed. The results depicted a lack of such impacts, suggesting this observed MJO‐QBO relationship cannot be driven by the MJO modulation of stratospheric wave forcing. Plain Language Summary: The intraseasonal fluctuation in cloudiness and rainfall in the troposphere around Indonesia and nearby oceans is higher when the lower‐stratospheric winds become easterly during December, January, and February. It is important to understand why this troposphere‐stratosphere coupling occurs to extend the range of prediction skills. The changes in the lower‐stratospheric winds are associated with changes in the upper‐tropospheric temperature, which is often claimed responsible for enhancing or suppressing the development of cumulonimbus clouds and driving the documented troposphere‐stratosphere coupling. However, this previously hypothesized mechanism assumes a one‐way impact where the stratosphere impacts the troposphere. Instead, this study analyzes the potential influence of tropospheric cloudiness on the stratospheric winds. Cumulonimbus clouds can generate stratospheric waves, which are known to regulate the direction of stratospheric winds. However, our results show that the intraseasonal fluctuation of cloudiness cannot affect the stratospheric waves. It displays a lack of evidence that the intraseasonal fluctuation in cloudiness can drive its observed connection with the stratosphere. Key Points: The Madden‐Julian Oscillation (MJO) convective activities have no significant impact on Quasi‐Biennial Oscillation (QBO) downward propagation speedThere is also no evidence that monthly MJO activities impact stratospheric wave activity that could potentially influence QBO dynamicsThe documented relationship between the QBO and the MJO is not driven by MJO modifications to the stratospheric wave spectrum [ABSTRACT FROM AUTHOR]