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The impact of transient tropospheric forcing on the deep vertical mountain-wave propagation is investigated by a unique combination of in situ and remote sensing observations and numerical modeling. The temporal evolution of the upstream low-level wind follows approximately a [Formula: see text] shape and was controlled by a migrating trough and connected fronts. Our case study reveals the importance of the time-varying propagation conditions in the upper troposphere and lower stratosphere (UTLS). Upper-tropospheric stability, the wind profile, and the tropopause strength affected the observed and simulated wave response in the UTLS. Leg-integrated along-track momentum fluxes ([Formula: see text]) and amplitudes of vertical displacements of air parcels in the UTLS reached up to 130 kN m−1 and 1500 m, respectively. Their maxima were phase shifted to the maximum low-level forcing by ≈8 h. Small-scale waves ([Formula: see text] km) were continuously forced, and their flux values depended on wave attenuation by breaking and reflection in the UTLS region. Only maximum flow over the envelope of the mountain range favored the excitation of longer waves that propagated deeply into the mesosphere. Their long propagation time caused a retarded enhancement of observed mesospheric gravity wave activity about 12–15 h after their observation in the UTLS. For the UTLS, we further compared observed and simulated [Formula: see text] with fluxes of 2D quasi-steady runs. UTLS momentum fluxes seem to be reproducible by individual quasi-steady 2D runs, except for the flux enhancement during the early decelerating forcing phase.
7Aerosol characteristics in the UTLS region: A satellite-based study over north India
Aerosol characteristics in the UTLS region: A satellite-based study over north India
2Influences of atmospheric ventilation on the composition of the upper troposphere and lower stratosphere during the two primary modes of the South Asia high
There are two key modes of the South Asia high (SAH) during the boreal summer: the Iranian Plateau (IP) and Tibetan Plateau (TP) modes. The anomalies of chemical constituents in the upper troposphere and lower stratosphere (UTLS) region within the SAH area largely depend on this bimodality. To better understand the underlying mechanisms of this dependence, the ensemble of 30-day backward trajectories, initialized in the UTLS region within the SAH, was simulated by a Lagrangian model FLEXPART. The comparative diagnostic was performed from the perspective of atmospheric ventilation. The results show that vertical transport from the lower troposphere to the UTLS during the TP mode was very efficient, resulting in tropospheric air mass transported into the UTLS within a shorter timescale than during the IP mode. Furthermore, the effect of SAH isolation during the TP mode was stronger than during the IP mode. This stronger trapping is likely to force the tropospheric air mass to reside in the SAH area for a longer period of time. In addition, compared to the IP mode, near-surface air mass sources during the TP mode overlapped more with areas of severe air pollution (CO emissions). The above three factors associated with the processes of atmospheric ventilation, i.e., the efficiency of vertical transport, the strength of the SAH isolation, and the boundary layer sources, provide potential explanations as to why the anomalies of atmospheric constituents in the UTLS are different between the TP and the IP mode.
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9Tropopause folds over the Tibetan Plateau and their impact on water vapor in the upper troposphere-lower stratosphere
As one of the most important greenhouse gases, water vapor in the upper troposphere and lower stratosphere (UTLS) has a significant impact on the global earth-atmosphere system. The Tibetan Plateau (TP) is an important high terrain which exerts a profound impact on the change of weather and climate, and mass exchange. Tropopause folds occur frequently over the TP due to the impact of the subtropical westerly jet, which affects water vapor transport between the stratosphere and the troposphere. In this paper, the spatial and temporal distribution characteristics of tropopause folds over the TP are examined by applying an improved three-dimensional (3D) labeling algorithm to the ERA5 reanalysis data (1979 to 2019). The effects of different fold depths in various regions over the TP on the variations of UTLS water vapor are further studied. The results of a case study (25 February 2008) suggest that there is a good continuity in identification of the fold depth for the same fold event using the improved 3D labeling algorithm. The fold depth and height are consistent with the results of radiosonde data and ERA5 reanalysis data. The fold frequency over the TP shows an increasing trend in the last 41 years, with slightly lower frequency of medium folds than that of shallow folds, and lowest frequency of deep folds. There is increasing water vapor in the UTLS over the TP due to tropopause folds. The results indicate that tropopause folds enhance the horizontal divergence of water vapor in the UTLS and increase the vertical water vapor flux in the UTLS region. The folding over the plateau leads to increased moisture in the UTLS. It is argued that vertical velocity anomalies in the vicinity of the fold and subgrid perturbations have a significant impact on the increase of UTLS water vapor over the TP. The results of this work provide a scientific basis for a better understanding of the stratosphere-troposphere exchanges due to tropopause folds over the TP.
Read more50Climatology of UTLS ozone and the ratio of ozone and potential vorticity over northern Europe
Annual and interannual variations of ozone in the upper troposphere and lower stratosphere (UTLS) region have been studied using ozonesonde data collected between 1994 and 2001 at several northern European stations. The climatology of ozone exhibits a prominent annual cycle in the UTLS region. The observed change in the phase of the annual cycle from late spring‐early summer at 500 hPa to spring at 200 hPa and to winter‐early spring at 100 hPa shows the switching of the ozone control from photochemical to dynamical. Traces of interannual variation in the lower stratosphere are seen not only in the upper troposphere but also in the middle troposphere (not necessarily always) indicating the dynamical influence on tropospheric ozone budget. Further, the correlation between ozone mixing ratio and potential vorticity (PV) is studied at three northern high‐latitude stations. As expected, a good correlation is found in the lower stratosphere, while the correlation is fair in the middle troposphere, except during summer over the European Arctic. This weak correlation at high latitudes indicates the dominance of photochemistry over dynamics in the presence of prolonged hours of solar illumination. The correlation coefficients derived at high latitudes are smaller than those reported at midlatitudes. This could be due to the greater number of tropopause folds at midlatitudes than at high latitudes and this eventually leads to the conclusion that the downward cross‐tropopause flux is greater at midlatitudes than at high latitudes. Absence of a significant north‐south gradient in the ozone/PV ratio in the lower stratosphere suggests that a single ozone/PV ratio (however, the ratio varies with month) can be used to convert global PV fluxes to ozone fluxes. A few cases of tropopause folds (only one case study is reported in the present study) are selected and studied in detail with the help of a very high frequency radar and meteorological analysis. The ratio between ozone and PV for these case studies agrees reasonably well with the climatological ratios.
Read more6Airborne in situ measurements of short-lived chlorocarbons and investigation of their pathways from northern hemispheric source regions into the lowermost stratosphere
Airborne in situ measurements of short-lived chlorocarbons and investigation of their pathways from northern hemispheric source regions into the lowermost stratosphere
Read moreComment on amt-2022-187
Data from ozonesondes launched at ARIES Nainital (29.40° N, 79.50° E, and 1793 m elevation) are used to evaluate the Atmospheric Infrared Sounder (AIRS) version 6 ozone profiles and total column ozone during the period 2011–2017 over the central Himalaya. The AIRS ozone products are analyzed in terms of retrieval sensitivity, retrieval biases/errors, and ability to retrieve the natural variability of columnar ozone, which has not been done so far from the Himalayan region having complex topography. For a direct comparison, averaging kernels information is used to account for the sensitivity difference between the AIRS and ozonesonde data. We show that AIRS can provide quality data of ozone in the lower and middle troposphere and stratosphere with nominal underestimation (<20 %). However, in the upper troposphere and lower stratosphere (UTLS), we observe a considerable overestimation of the magnitude as high as 102 %. The weighted statistical error analysis of AIRS ozone shows higher positive bias, root mean squared error, and standard deviation in the upper troposphere of about 65 %, 65 %, and 25 %, respectively. Similar to AIRS, Infrared Atmospheric Sounding Interferometer (IASI) and Cross-track Infrared Sounder (CrIS) are also able to produce ozone peaks and gradients successfully. However, the statistical errors are again higher in the UTLS region that are likely related to larger variability of ozone, lower ozone partial pressure and inadequate retrieval information on the surface parameters. The monthly variations of columnar ozone (total, UTLS, and tropospheric) are captured well by AIRS, except the total columnar ozone, which shows a strong bimodal variation, unlike unimodal variation seen in ozonesonde and Ozone Monitoring Instrument (OMI). Increases in ozone of 5–20 % (in 2–6 km altitude) after the biomass burning and during events of downward transport (in 2–16 km altitude) are captured well by AIRS. Ozone radiative forcing (RF) derived from total column ozone matches well between ozonesonde (4.86 mW/m2) and OMI (4.04 mW/m2), while significant RF underestimation is seen in AIRS (2.96 mW/m2). The fragile and complex landscapes of the Himalayas are more sensitive to global climate change, and establishing such biases and error analysis of space-borne sensors will help study the long-term trends and estimate accurate radiative budgets.
Read more4The chemical effects on the summertime ozone in the upper troposphere and lower stratosphere over the Tibetan Plateau and the South Asian monsoon region
We use the global three-dimensional Goddard Earth Observing System chemical transport model with the Universal tropospheric–stratospheric Chemistry eXtension mechanism to examine the contributions of the chemical processes to summertime O3 in the upper troposphere and lower stratosphere (UTLS) over the Tibetan Plateau and the South Asian monsoon region (TP/SASM). Simulated UTLS O3 concentrations are evaluated by comparisons with Microwave Limb Sounder products and net chemical production of O3 (NPO3) are evaluated by comparisons with model results in previous studies. Simulations show that the chemical processes lead to an increase in O3 concentration, which is opposite to the effect of O3 transport in the UTLS over the TP/SASM region throughout the boreal summer. NPO3 in UTLS over the TP/SASM region is the largest in summer. Elevated values (0.016–0.020 Tg year−1) of the seasonal mean NPO3 are simulated to locate at 100 hPa in the TP/SASM region, where the mixing ratios of O3 are low and those of O3 precursors (NOx, VOCs, and CO) are high. The high concentrations of O3 precursors (NOx, VOCs, and CO) together with the active photochemical reactions of NO2 in the UTLS over the TP/SASM region during summertime could be important reasons for the enhancement of $${\text{NP}}_{{{\text{O}}_{3} }}$$ over the studied region.
Read moreAerosol perturbation in the UTLS region over the Tibetan Plateau
The Asian tropopause aerosol layer (ATAL) was thicker than other regions at the same latitude due to the strong confinement effect of the Asian summer monsoon anticyclone. The size distribution of the particles remains unknown and requires further investigation. Aerosol&#160;profiles were&#160;measured by balloon-borne sensors (Cobald, POPS) launched from Lhasa&#160;(29.66&#160;&#176;N, 91.14&#160;&#176;E), Golmud (36.48 &#176;N, 94.93 &#176;E), and Kunming (25.01&#160;&#176;N, 102.65&#160;&#176;E) China, from 2019&#160;to 2022&#160;over the Tibetan Plateau&#160;at the part of the SWOP (Sounding Water vapor,&#160;Ozone, and Particle) campaign.&#160;The measurements combined with backward trajectories&#160;show that the volcano Raikoke (48&#176;N, 153&#176;E)&#160;in June 2019 and the dust storm in March 2021 over the Taklamakan desert&#160;have significantly impacted on the aerosol layer in the upper troposphere and lower stratosphere (UTLS). The backscatter ratio at wavelength 455 nm of the volcanic plume and dust storm was higher than the ATAL. The particle number density in the volcanic plume is 30 cm-3, higher than the ATAL and dust storm (10 cm-3) in the lower stratosphere, with particle diameters centered around 0.42-3.4 &#956;m. In contrast, the dust storm has a high density of up to 100 cm-3&#160;in the upper troposphere with particle diameters less than 0.42 &#956;m.
Read more3Study of Lower Tropospheric Ozone over Central and Eastern China: Comparison of Satellite Observation with Model Simulation
The lower tropospheric ozone enhancement over Central and Eastern China (CEC) was reported by Hayashida et al. (Atmos Chem Phys 15(17):9865–9881, 2015) using the Ozone Monitoring Instrument (OMI) multiple-layer product retrieved by Liu et al. (Atmos Chem Phys 10(5):2521–2537, 2010), which first showed the lower tropospheric ozone enhancement from ultraviolet and visible (UV-Vis) spectra measurements from space. However, to clarify the enhancement in the concentration of the lowermost ozone using spaceborne measurements, it is necessary to understand the effect of ozone variation in the upper troposphere and lower stratosphere (UT/LS), because of large smoothing errors in the retrieval scheme. In this study, a scheme was developed to eliminate the artificial effect of UT/LS ozone enhancement on lower tropospheric ozone retrieval using OMI. By applying the UT/LS screening scheme for June 2006, we removed the artificial effect of the UT/LS ozone enhancement on the lower tropospheric ozone. Even after UT/LS screening, we were able to show a clear enhancement in the lower tropospheric ozone over CEC in June 2006 and confirmed the conclusion derived by Hayashida et al. (Atmos Chem Phys 15(17):9865–9881, 2015). To clarify the reason for ozone enhancement in June, the effects of emissions from open crop residue burning (OCRB) in the North China Plain on lower tropospheric ozone were also examined using a comparison with model simulations. On the scale of the vertical resolution of OMI observations, the effect of OCRB on ozone enhancement does not seem to be significant, although it may be more significant when focusing on ozone in the planetary boundary layer.
Read moreComment on acp-2022-274
Sulfur compounds in the upper troposphere and lower stratosphere (UTLS) impact the atmosphere radiation budget, either directly as particles or indirectly as precursor gas for new particle formation. In situ measurements in the UTLS are rare, but are important to better understand the impact of the sulfur budget on climate. The BLUESKY mission in May/June 2020 explored an unprecedented situation. 1) The UTLS experienced extraordinary dry conditions in spring 2020 over Europe, in comparison to previous years and 2) the first lockdown of the COVID-19 pandemic caused major emission reductions from industry, ground, and airborne transportation. With the two research aircraft HALO and Falcon, 20 flights were conducted over Central Europe and the North Atlantic to investigate the atmospheric composition with respect to trace gases, aerosol, and clouds. Here, we focus on measurements of sulfur dioxide (SO2) and particulate sulfate (SO42-) in the altitude range of 8 to 14.5 km which show unexpectedly enhanced mixing ratios of SO2 in the upper troposphere and of SO42- in the lowermost stratosphere. In the UT, we find SO2 mixing ratios of (0.07 ± 0.01) ppb, caused by the remaining air traffic, reduced SO2 sinks due to low OH and low cloud fractions, and to a minor extend by uplift from boundary layer sources. Particulate sulfate showed elevated mixing ratios of up to 0.33 ppb in the LS. We suggest that the eruption of the volcano Raikoke in June 2019, which emitted about 1 Tg SO2 into the stratosphere in northern midlatitudes caused these enhancements, in addition to Siberian and Canadian wildfires and other minor volcanic eruptions. Our measurements can help to test models and lead to new insights in the distribution of sulfur compounds in the UTLS, their sources and sinks. Moreover, these results can contribute to improve simulations of the radiation budget in the UTLS with respect to sulfur effects.
Read moreHigh-Alitutde Aircraft Measurements of NO and NO2 in the Upper Troposphere and Lower Stratosphere over South-East Asia
Nitric oxide (NO) and nitrogen dioxide (NO2) are important trace gases in the upper troposphere and lower stratosphere (UTLS).&#160; In the upper troposphere, NO is primarily formed by lightning and can react with other radicals to form a suite of reactive nitrogen (NOy) species and produce ozone.&#160; In the lower stratosphere, NOx can be responsible for catalytic ozone destruction and can form halogen reservoirs such as ClNO2 and ClONO2.&#160; Accurate measurements of NOx species are therefore important for understanding and diagnosing UTLS chemical regimes.&#160; Further, understanding NO2 concentrations in the stratosphere and upper troposphere is critical for accurate satellite retrievals of tropospheric NO2.&#160;In-situ measurements of NOx species above 12-15 km are infrequent and challenging.&#160; Where there are measurements of NOx species up to about 12 km, NO mixing ratios tend to be reasonably well-reproduced using global models.&#160; However, NO2 measurements frequently agree well with models and photostationary state calculations up to about 8 km, but at higher altitudes routinely are significantly higher than expected relative to the measured NO.&#160; Proposed sources of this discrepancy include measurement artifacts affecting the in-situ measurements, inaccuracies in rate constants at low temperatures, and missing chemistry.&#160; The net result is significant uncertainty in the NO2 concentrations in the UTLS.Here we present results from the recent high-altitude aircraft campaign Asian Summer Monsoon Chemistry and CLimate Impact Project (ACCLIP) over southeast Asia in summer 2022.&#160; We show measurements from the recently-developed NOAA NO laser-induced fluorescence instrument up to altitudes of almost 20 km.&#160; This instrument makes direct NO measurements with precision and accuracy sufficient for measurements below one ppt with one second of integration, making it ideal for aircraft campaigns.&#160; In order to measure NO2 with this instrument, we have developed a photolysis inlet which converts NO2 to NO using an LED centered at 395 nm.&#160; What is novel about this NO2 conversion is that it is done in an unpressurized pylon of the aircraft and thus the sample remains at the UTLS ambient temperatures until after photolysis.&#160; This thus significantly reduces the potential interferences from NOy species that can thermally decompose to NO2 at room temperature, eliminating a potential source of major artifact.&#160; Our data show good agreement with photostationary state calculations performed for these flights.&#160;
Read more1Anomalous temperature changes in the UTLS region prior to the 2008 Nura Earthquake
The paper presents results of retrospective analysis of satellite temperature time series above the epicentral area of the destructive Nura earthquake of M=6.7, occurred in a seismically active Tien-Shan region on October 5, 2008. An algorithm based on the use of a modified STA/LTA criterion has been developed for the purpose of selection and identification of perturbations associated with seismic activity. It has been established that an explicit mesoscale temperature anomaly in the upper troposphere and lower stratosphere (UTLS) was observed during the period from October 1 to 3, 2008. Temporal and spatial distributions of the temperature perturbations consistently appeared at various UTLS levels suggest probable association with seismic event preparation.
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Both the scientific and operational communities are increasingly interested in subseasonal to seasonal variations of weather and climate. The Semi-Annual Oscillation (SAO) has been studied extensively at the surface as well as in the middle atmosphere (upper stratosphere and the lower mesosphere). However, the SAO in the upper troposphere and lower stratosphere (UTLS) has been less discussed. Here we find evident SAO of temperature in the UTLS (250–175 hPa) from the subtropics to mid-latitudes (22.5–42.5º) using high-quality satellite measurements, reanalysis data, and model simulations. We show the mechanism of its formation by an energy budget analysis. The temperature in the Northern Hemisphere (NH) UTLS shows the first peak in February according to the dynamical heating and shows the second peak in July due to the dynamical heating and moist processes. Similar to the NH, the winter time maximum of temperature in the SH is related to dynamical heating and the summer time maximum is related to both moist and dynamical heating in the UTLS. Model simulations indicate that the SAO in the UTLS is partly modified by the SAO of sea surface temperatures (SSTs).
Read more21The quasi-biennial oscillation (QBO) and global-scale tropical waves in Aeolus wind observations, radiosonde data, and reanalyses
Abstract. The quasi-biennial oscillation (QBO) of the stratospheric tropical winds influences the global circulation over a wide range of latitudes and altitudes. Although it has strong effects on surface weather and climate, climate models have great difficulties in simulating a realistic QBO, especially in the lower stratosphere. Therefore, global wind observations in the tropical upper troposphere and lower stratosphere (UTLS) are of particular interest for investigating the QBO and the tropical waves that contribute significantly to its driving. In our work, we focus on the years 2018–2022 and investigate the QBO and different tropical wave modes in the UTLS region using global wind observations made by the Aeolus satellite instrument and three meteorological reanalyses: the fifth generation European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis (ERA-5), the Japanese 55-year Reanalysis (JRA-55) of the Japan Meteorological Agency (JMA), and the Modern-Era Retrospective Analysis for Research and Applications, version 2 (MERRA-2). Further, we compare these data with observations of selected radiosonde stations. By comparison with Aeolus observations, we find that, on zonal average, the QBO in the lower stratosphere is well represented in all three reanalyses, with ERA-5 performing best. Averaged over the years 2018–2022, agreement between Aeolus and the reanalyses is better than 1 to 2 m s−1, with somewhat larger differences during some periods. Differently from zonal averages, radiosonde stations provide only local observations and are therefore biased by global-scale tropical waves, which limits their use as a QBO standard. While reanalyses perform well on zonal average, there can be considerable local biases between reanalyses and radiosondes. We also find that, in the tropical UTLS, zonal wind variances of stationary waves and the most prominent global-scale traveling equatorial wave modes, such as Kelvin waves, Rossby-gravity waves, and equatorial Rossby waves, are in good agreement between Aeolus and all three reanalyses (in most cases better than 20 % of the peak values in the UTLS). On zonal average, this supports the use of reanalyses as a reference for comparison with free-running climate models, while locally, certain biases exist, particularly in the QBO wind shear zones and around the 2019–2020 QBO disruption.
Read more34Ozone Profile Retrieval from an Advanced Infrared Sounder: Experiments with Tropopause-Based Climatology and Optimal Estimation Approach
Motivated by a significant potential for retrieving atmospheric ozone profile information from advanced satellite infrared sounders, this study investigates various methods to optimize ozone retrievals. A set of retrieval experiments has been performed to assess the impact of different background states (or the a priori states) and retrieval algorithms on the retrieved ozone profiles in the upper troposphere and lower stratosphere (UTLS) using Atmospheric Infrared Sounder (AIRS) measurements. A new tropopause-based ozone climatology, using publicly available global ozonesonde data to construct the a priori state, is described. Comparisons are made with the AIRS version 5 (v5) ozone climatology. The authors also present the result of a newly implemented optimal estimation (OE) algorithm and compare it to the current AIRS science team (AST) algorithm used in version 5. The ozone climatology using tropopause-referenced coordinates better preserves the shape and the magnitude of the ozone gradient across the tropopause, especially in the extratropical region. The results of the retrieval experiments indicate that the tropopause-referenced climatology not only helps to optimize the use of instrument sensitivity in the UTLS region, but it also provides better constraints to the OE algorithm.
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