Aura Microwave Limb Sounder Research Articles

The Evolution of the Hunga Hydration in a Moistening Stratosphere

AbstractThe 2022 Hunga eruption caused unprecedented stratospheric hydration. Aura Microwave Limb Sounder (MLS) measurements show that the stratospheric water vapor mass remains essentially unchanged as of early 2024 and that the Hunga hydration occurred atop a robust (possibly accelerating) moistening trend in the stratosphere. Enhanced by the excess Hunga water vapor, dehydration via polar stratospheric cloud sedimentation in the 2023 Antarctic vortex exceeded climatological values by 50%. Simple projections based on modeled exponential decay illustrate that the timing of the return to humidity levels that would have been expected absent the Hunga hydration depends on the ongoing stratospheric water vapor trend. With the Hunga hydration compounding an underlying moistening trend, the stratosphere could remain anomalously humid for an extended period.

Prolonged Quasi‐6‐Day Wave Activities in the Northern Hemisphere MLT Region Due To Antarctic Stratospheric Minor Warming Around September Equinox of 2013 and 2014

AbstractThe geopotential height observations from the Aura Microwave Limb Sounder show that the quasi‐6‐day wave (Q6DW) events with westward zonal wavenumber 1 (W1) in the Northern Hemisphere (NH) mesosphere and lower thermosphere (MLT) during September 2013 and 2014 had a prolonged lifetime of ∼45–50 days and reached their maximum amplitudes after the September equinox, while the climatological Q6DW‐W1 is completely dissipated in the background atmosphere before the equinoxes. The Eliassen‐Palm flux diagnostic results indicate that Q6DW‐W1 during September 2013 and 2014 obtained an additional source at ∼60°‐80°S and ∼40–50 km as the September equinox approached, which is related to the baroclinic/barotropic instability in this region. Further investigation on the background atmosphere reveals that several stratospheric minor warming (SMW) events occurred in the Antarctic region during September 2013 and 2014 due to the enhancement of wavenumber 1 activities, accompanied by the increase in the stratospheric temperature, changes in the shape of the polar vortex and the reversal in the zonal mean circulation. The strong planetary wave breaking during the September 2013 and 2014 Antarctic SMW events significantly weakened the strength of the polar night jet (PNJ) and made its peak height descend below ∼35 km, which generated the baroclinic/barotropic instability at the new upper boundary of the PNJ (∼60°‐80°S and ∼40–50 km) by an anomalous double‐jet configuration in the background winds. This unusual instability provided additional wave source and energy for the trans‐equatorial propagation of Q6DW‐W1, which finally led to prolonged wave activities in the NH MLT region.

The Spread of the Hunga Tonga H2O Plume in the Middle Atmosphere Over the First Two Years Since Eruption

AbstractThe eruption of Hunga in January 2022 injected a large amount of water into the stratosphere. Satellite measurements from Aura Microwave Limb Sounder (MLS) show that this water vapor (H2O) has now spread throughout the stratosphere and into the lower mesosphere, resulting in an increase of >1 ppmv throughout most of this region. Measurements from three ground‐based Water Vapor Millimeter Wave Spectrometer (WVMS) instruments and MLS are in good agreement, and show that in 2023 there was more H2O in the lower mesosphere than at any time since the WVMS measurements began in the 1990's. At Table Mountain, California all WVMS H2O measurements at 54 km since June 2023, and all of the measurements from Mauna Loa, Hawaii, since the resumption of measurements in September 2023, show larger mixing ratios than any previous measurements. At 70 km several recent WVMS retrievals since September 2023 show the largest anomalies ever measured. The MLS measurements show that maximum H2O anomalies over the 2004–2023 record have occurred throughout almost all of the stratosphere and lower mesosphere since the eruption. As of November 2023, almost all of the ∼140 Tg of water originally injected into the stratosphere by the Hunga eruption remains in the middle atmosphere at pressures below 83 hPa (altitudes above ∼17 km). The eruption occurred during a period when stratospheric H2O was already slightly elevated above the 2004–2021 MLS average, and the November 2023 anomaly of ∼160 Tg represents ∼15% of the total mass of H2O in this region.

A novel infrared imager for studies of hydroxyl and oxygen nightglow emissions in the mesopause above northern Scandinavia

Abstract. The paper describes technical characteristics and presents the first scientific results of a novel infrared imaging system (imager) for studies of nightglow emissions coming from the hydroxyl (OH) and molecular oxygen (O2) layers in the mesopause region (80–100 km) above northern Scandinavia. The OH imager was put into operation in November 2022 at the Swedish Institute of Space Physics in Kiruna (67.86° N, 20.42° E; 400 m altitude). The OH imager records selected emission lines in the OH(3-1) band near 1500 nm to obtain intensity and temperature maps at around 87 km altitude. In addition, the OH imager registers infrared emissions coming from the O2 IR A-band airglow at 1268.7 nm in order to obtain O2 intensity maps at a slightly higher altitude, around 94 km. This technique allows the tracing of wave disturbances in both horizontal and vertical domains in the mesopause region. Validation and comparison of the OH(3-1) rotational temperature with collocated lidar and Aura Microwave Limb Sounder (MLS) satellite temperatures are performed. The first scientific results obtained from the OH imager for the first winter season (2022–2023) are discussed.

How the Hunga Tonga—Hunga Ha'apai Water Vapor Cloud Impacts Its Transport Through the Stratosphere: Dynamical and Radiative Effects

AbstractThe eruption of the Hunga Tonga—Hunga Ha'apai (HTHH) volcano on 15 January 2022 injected about 150 Tg of water vapor (H2O), roughly 10% of the background stratospheric H2O content, to altitudes above 50 km. Simulations of the spatial evolution of the H2O cloud with the ICON‐Seamless model are very close to observations from the Aura Microwave Limb Sounder. The vertical transport of the H2O cloud had three phases: an initial subsidence phase, a stable phase, and a rising phase. Radiative cooling of H2O clearly affects the transport of the H2O cloud, as demonstrated with passive tracers, and is the main driver within the subsidence phase. It also counteracts the large‐scale rising motion in the tropics, leading to the stable phase, and modulates the large‐scale transport of the H2O cloud for about 9 months. This holds for different QBO phases, where the H2O cloud differs mainly in its vertical extent.

Role of Southern Hemisphere sudden stratospheric warming in altering the intensity of Brewer-Dobson circulation and its impact on stratospheric ozone and water vapor

The changes in the intensity of Brewer-Dobson circulation (BDC) in the record-breaking Southern Hemisphere sudden stratospheric warming (SH SSW) event in 2019 are investigated in the present study. Wave driving was observed to be at its highest in 2019 SH SSW, despite the event being classified as a minor warming event. The Eliassen-Palm flux divergence, indicative of wave driving, was observed to be increasing before the SSW, and subsiding afterwards. The stratospheric circulation followed the wave driving and intensified along the warming episode. The resulting stratospheric distribution from Aura Microwave Limb Sounder showed a negative ozone anomaly (∼20%) in the tropical lower stratosphere and a downward propagating positive anomaly in the Southern Hemisphere polar stratosphere around the central dates. The water vapor mixing ratio showed an increase of more than 25% in the polar lower stratosphere and 10% in the tropical upper stratosphere. A cooling of about 5 K was observed in the tropical middle stratosphere. The results indicate that SH SSW can change the intensity of the stratospheric circulation which in turn affects the ozone and water vapor transport from the tropics to the pole.

Impact of the Hunga Tonga volcanic eruption on stratospheric composition.

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.

Stratospheric ozone depletion inside the volcanic plume shortly after the 2022 Hunga Tonga eruption

Abstract. Near-term in-plume ozone depletion was observed for about 10 d by the Aura Microwave Limb Sounder (MLS) right after the January 2022 Hunga Tonga–Hunga Ha'apai (HTHH) eruption. This work analyzes the dynamic and chemical causes of this ozone depletion. The results show that the large water injection (∼ 150 Tg) from the HTHH eruption, with ∼ 0.0013 Tg injection of ClO (or ∼ 0.0009 Tg of HCl), causes ozone loss due to strongly enhanced HOx and ClOx cycles and their interactions. Aside from the gas-phase chemistry, the heterogeneous reaction rate for HOCl + HCl → Cl2 + H2O increases to 104 cm−3 s−1 and is a major cause of chlorine activation, making this event unique compared with the springtime polar ozone depletion where HCl + ClONO2 is more important. The large water injection causes relative humidity over ice to increase to 70 %–100 %, decreases the H2SO4 / H2O binary solution weight percent to 35 % compared with the 70 % ambient value, and decreases the plume temperature by 2–6 K. These changes lead to high heterogeneous reaction rates. Plume lofting of ozone-poor air is evident during the first 2 d after the eruption, but ozone concentrations quickly recover because its chemical lifetime is short at 20 hPa. With such a large seawater injection, we expect that ∼ 5 Tg Cl was lifted into the stratosphere by the HTHH eruption in the form of NaCl, but only ∼ 0.02 % of that remained as active chlorine in the stratosphere. Lightning NOx changes are probably not the reason for the HTHH initial in-plume O3 loss.

Mesospheric Water Vapor in 2022

AbstractThe eruption of the Hunga Tonga undersea volcano in January 2022 injected water vapor to altitudes as high as 53 km, but also an unprecedented and much larger amount of water vapor into the stratosphere. Several months after the eruption, measurements from the Aura Microwave Limb Sounder (MLS) and from three ground‐based Water Vapor Millimeter Wave Spectrometer instruments began to measure record‐high amounts of water vapor in the mesosphere over a wide range of latitudes. While there are indications that some of this mesospheric increase in water vapor was probably caused by the Hunga Tonga eruption, variations in water vapor mixing ratios also depend on dynamical factors. The phase of the QBO in 2015 was similar to that in 2022, and we make use of this similarity in order to better understand what role dynamics played in establishing the unusually large 2022 water vapor mixing ratios, both in the upper and lower mesosphere.

Siege in the Southern Stratosphere: Hunga Tonga‐Hunga Ha'apai Water Vapor Excluded From the 2022 Antarctic Polar Vortex

AbstractWe use Aura Microwave Limb Sounder (MLS) trace gas measurements to investigate whether water vapor (H2O) injected into the stratosphere by the Hunga Tonga‐Hunga Ha'apai (HTHH) eruption affected the 2022 Antarctic stratospheric vortex. Other MLS‐measured long‐lived species are used to distinguish high HTHH H2O from that descending in the vortex from the upper‐stratospheric H2O peak. HTHH H2O reached high southern latitudes in June–July but was effectively excluded from the vortex by the strong transport barrier at its edge. MLS H2O, nitric acid, chlorine species, and ozone within the 2022 Antarctic polar vortex were near average; the vortex was large, strong, and long‐lived, but not exceptionally so. There is thus no clear evidence of HTHH influence on the 2022 Antarctic vortex or its composition. Substantial impacts on the stratospheric polar vortices are expected in succeeding years since the H2O injected by HTHH has spread globally.

Applying machine learning to improve the near-real-time products of the Aura Microwave Limb Sounder

Abstract. A new algorithm to derive near-real-time (NRT) data products for the Aura Microwave Limb Sounder (MLS) is presented. The old approach was based on a simplified optimal estimation retrieval algorithm (OE-NRT) to reduce computational demands and latency. This paper describes the setup, training, and evaluation of a redesigned approach based on artificial neural networks (ANN-NRT), which is trained on >17 years of MLS radiance observations and composition profile retrievals. Comparisons of joint histograms and performance metrics derived between the two NRT results and the operational MLS products demonstrate a noticeable statistical improvement from ANN-NRT. This new approach results in higher correlation coefficients, in addition to lower root-mean-square deviations and biases at almost all retrieval levels compared to OE-NRT. The exceptions are pressure levels with concentrations close to 0 ppbv (parts per billion by volume), where the ANN models fail to establish a functional relationship and tend to predict 0. Depending on the application, this behavior might be advantageous. While the developed models can take advantage of the extended MLS data record, this study demonstrates that training ANN-NRT on just a single year of MLS observations is sufficient to improve upon OE-NRT. This confirms the potential of applying machine learning to the NRT efforts of other current and future mission concepts.

Measurements of Stratospheric Water Vapor at Mauna Loa and the Effect of the Hunga Tonga Eruption

AbstractThe eruption of Hunga Tonga in January 2022 injected an amount of water vapor into the stratosphere that is unprecedented in the satellite era. In the ensuing months Aura Microwave Limb Sounder measurements showed that this plume of water vapor spread from its original injection site at 20.5°S to Mauna Loa, Hawaii at 19.5°N, where an increase was observed in April by the ground‐based Water Vapor Millimeter‐wave Spectrometer instruments. Interannual variations in water vapor occur over Mauna Loa due to both dynamical variations in the tropical stratosphere and variations in the amount of water vapor crossing the tropical tropopause, and we place the observed stratospheric water vapor increase from Hunga Tonga into context of these other variations that have been observed since 2013.

Deep Kernel Dictionary Learning for detection of wave breaking features in Atmospheric Gravity Waves

Atmospheric Gravity Waves play a significant role in the Middle Atmosphere Dynamics and breaking of Gravity Waves leads to turbulence. To confirm the breaking of Atmospheric Gravity Waves, we require Wind Velocity profiles with high accuracy and the problem in the existing scenario is the Wind velocity measuring instruments are not accurate at the altitude of interest and are very sparse. We came up with a solution by taking advantage of Dictionary Learning and Deep Learning approach for the detection of the Wave Breaking events from atmospheric temperature perturbations instead of looking for wind velocity profiles.In the present work, we discuss incorporating Kernels into Deep Dictionary Learning. The Deep Dictionary Learning algorithm, introduced recently, shows an improvement in feature detection in comparison to k-means Singular Value Decomposition (KSVD) Dictionary Learning, Convolution Neural Network, and LSTM Auto-Encoders. Incorporating Kernels into Deep Dictionary Learning increases the effectiveness of the detection of the Wave Breaking events. The potential of the proposed method is demonstrated with a case study on the detection of atmospheric Gravity Wave Breaking event leading to turbulence in the atmosphere using satellite data (Aura-Microwave Limb Sounder) and is validated using data available from the ground-based instruments.

M2‐SCREAM: A Stratospheric Composition Reanalysis of Aura MLS Data With MERRA‐2 Transport

AbstractThe MERRA‐2 Stratospheric Composition Reanalysis of Aura Microwave Limb Sounder (M2‐SCREAM) is a new reanalysis of stratospheric ozone, water vapor, hydrogen chloride (HCl), nitric acid (HNO3) and nitrous oxide (N2O) between 2004 and the present (with a latency of several months). The assimilated fields are provided at a 50‐km horizontal resolution and at a three‐hourly frequency. M2‐SCREAM assimilates version 4.2 Microwave Limb Sounder (MLS) profiles of the five constituents alongside total ozone column from the Ozone Monitoring Instrument. Dynamics and tropospheric water vapor are constrained by the MERRA‐2 reanalysis. The assimilated species are in excellent agreement with the MLS observations, except for HNO3 in polar night, where data are not assimilated. Comparisons against independent observations show that the reanalysis realistically captures the spatial and temporal variability of all the assimilated constituents. In particular, the standard deviations of the differences between M2‐SCREAM and constituent mixing ratio data from The Atmospheric Chemistry Experiment Fourier Transform Spectrometer are much smaller than the standard deviations of the measured constituents. Evaluation of the reanalysis against aircraft data and balloon‐borne frost point hygrometers indicates faithful representations of small‐scale structures in the assimilated water vapor, HNO3 and ozone fields near the tropopause. Comparisons with independent observations and a process‐based analysis of the consistency of the assimilated constituent fields with the MERRA‐2 dynamics and with large‐scale stratospheric processes demonstrate the utility of M2‐SCREAM for scientific studies of chemical and transport variability on time scales ranging from hours to decades. Analysis uncertainties and guidelines for data usage are provided.

Observed changes in stratospheric circulation: decreasing lifetime of N2O, 2005–2021

Abstract. Using Aura Microwave Limb Sounder satellite observations of stratospheric nitrous oxide (N2O), ozone, and temperature from 2005 through 2021, we calculate the atmospheric lifetime of N2O to be decreasing at a rate of −2.1 ± 1.2 %/decade. This decrease is occurring because the N2O abundances in the middle tropical stratosphere, where N2O is photochemically destroyed, are increasing at a faster rate than the bulk N2O in the lower atmosphere. The cause appears to be a more vigorous stratospheric circulation, which models predict to be a result of climate change. If the observed trends in lifetime and implied emissions continue, then the change in N2O over the 21st century will be 27 % less than those projected with a fixed lifetime, and the impact on global warming and ozone depletion will be proportionately lessened. Because global warming is caused in part by N2O, this finding is an example of a negative climate–chemistry feedback.

Southern Hemisphere Response to the Secondary Planetary Waves Generated During the Arctic Sudden Stratospheric Final Warmings: Influence of the Quasi‐Biennial Oscillation

AbstractBased on the Modern‐Era Retrospective analysis for Research and Applications version 2 reanalysis and Aura Microwave Limb Sounder geopotential height observations, the anomalously strong secondary planetary waves (PWs) with westward zonal wavenumber 1 and periods of 10–16 days are unexpectedly captured in the Southern (summer) Hemisphere (SH) during the Arctic sudden stratospheric final warmings (SSFWs) in 2015 and 2022, while no distinct secondary PW signal occurs in the SH during the 2005, 2014, and 2016 Arctic SSFWs. The Eliassen‐Palm (EP) flux diagnostics show that the secondary PWs during the 2015 and 2022 SSFWs have strong trans‐equatorial components at ∼35–60 km, but the southward EP flux from the Northern Hemisphere during the other three SSFWs decays dramatically around the equator. Further diagnostic results on the background conditions indicate that the phase of the quasi‐biennial oscillation (QBO) in the middle stratosphere plays a crucial role in the SH response to the secondary PW during SSFW. The strong equatorial westward winds at ∼32–42 km result in the critical layers and negative waveguides for the secondary W1 PW during the 2005, 2014, and 2016 SSFWs, which significantly block the trans‐equatorial propagation of PW. Such PW suppression is not observed during the 2015 and 2022 SSFWs since the middle stratospheric QBO is in the eastward phase. Moreover, the strong secondary PW in the SH during the 2015 and 2022 SSFWs can additionally induce the poleward residual circulation to facilitate the mesospheric total residual circulation transition from summer pattern to winter pattern in the SH.

Dynamical linear modeling estimates of long-term ozone trends from homogenized Dobson Umkehr profiles at Arosa/Davos, Switzerland

Abstract. Six collocated spectrophotometers based in Arosa/Davos, Switzerland, have been measuring ozone profiles continuously since 1956 for the oldest Dobson instrument and since 2005 for the Brewer instruments. The datasets of these two ground-based triads (three Dobsons and three Brewers) allow for continuous intercomparisons and derivation of long-term trend estimates. Mainly, two periods in the post-2000 Dobson D051 dataset show anomalies when compared to the Brewer triad time series: in 2011–2013, an offset has been attributed to technical interventions during the renewal of the spectrophotometer acquisition system, and in 2018, an offset with respect to the Brewer triad has been detected following an instrumental change on the spectrophotometer wedge. In this study, the worldwide longest Umkehr dataset (1956–2020) is carefully homogenized using collocated and simultaneous Dobson and Brewer measurements. A recently published report (Garane et al., 2022) described results of an independent homogenization of the same dataset performed by comparison to the Modern-Era Retrospective analysis for Research and Applications version 2 (MERRA-2) Global Modeling Initiative (M2GMI) model simulations. In this paper, the two versions of homogenized Dobson D051 records are intercompared to analyze residual differences found during the correction periods. The Aura Microwave Limb Sounder (MLS) station overpass record (2005–2020) is used as an independent reference for the comparisons. The two homogenized data records show common correction periods, except for the 2017–2018 period, and the corrections are similar in magnitude. In addition, the post-2000 ozone profile trends are estimated from the two homogenized Dobson D051 time series by dynamical linear modeling (DLM), and results are compared with the DLM trends derived from the collocated Brewer Umkehr time series. By first investigating the long-term Dobson ozone record for trends using the well-established multilinear regression (MLR) method, we find that the trends obtained by both MLR and DLM techniques are similar within their uncertainty ranges in the upper and middle stratosphere but that the trend's significances differ in the lower stratosphere. Post-2000 DLM trend estimates show a positive trend of 0.2 to 0.5 % yr−1 above 35 km, significant for Dobson D051 but lower and therefore nonsignificantly different from zero at the 95 % level of confidence for Brewer B040. As shown for the Dobson D051 data record, the trend only seems to become significantly positive in 2004. Moreover, a persistent negative trend is estimated in the middle stratosphere between 25 and 30 km. In the lower stratosphere, the trend is negative at 20 km, with different levels of significance depending on the period and on the dataset.

Measurements of Mesospheric Water Vapor From 1992 to 2021 at Three Stations From the Network for the Detection of Atmospheric Composition Change

AbstractWe present ground‐based microwave measurements of mesospheric water vapor made by the Water Vapor Millimeter‐wave Spectrometer (WVMS) instruments since the early 1990s from sites in California, Hawaii, and New Zealand. These measurements are compared with coincident measurements from the Halogen Occultation Experiment, the Aura Microwave Limb Sounder, and Sounding of the Atmosphere using Broadband Emission Radiometry; all of which combine to cover the entire time period of the ground‐based measurements. Comparisons are presented both on ∼weekly timescales in order to better identify discontinuities in the relative differences and on annual timescales in order to better study geophysical variations. The WVMS retrievals shown here are available on the Network for the Detection of Atmospheric Composition Change database. The range of WVMS trends and the differences from the satellite trends, with the latter varying over a range of ∼3%/decade, provide an estimate of how accurately it would be possible to determine multidecadal trends using ground‐based microwave instruments in a postsatellite era. This uncertainty is comparable to the trend in mesospheric water vapor that is expected to have occurred since the early 1990s.

An Examination of the Recent Stability of Ozonesonde Global Network Data

AbstractThe recent Assessment of Standard Operating Procedures for Ozonesondes 2.0 (WMO/GAW Report #268) addressed questions of homogeneity and long‐term stability in global electrochemical concentration cell (ECC) ozone sounding network time series. Among its recommendations was adoption of a standard for evaluating data quality in ozonesonde time series. Total column ozone (TCO) derived from the sondes compared to TCO from Aura's Ozone Monitoring Instrument (OMI) is a primary quality indicator. Comparisons of sonde ozone with Aura's Microwave Limb Sounder (MLS) are used to assess the stability of stratospheric ozone. This paper provides a comprehensive examination of global ozonesonde network data stability and accuracy since 2004 in light of the sudden post‐2013 TCO “dropoff” of ∼3%–4% that was reported previously at select stations (Stauffer et al., 2020, https://doi.org/10.1029/2019GL086791). Comparisons with Aura OMI TCO averaged across the network of 60 stations are stable within about ±2% over the past 18 years. Sonde TCO has similar stability compared to three other TCO satellite instruments, and the stratospheric ozone measurements average to within ±5% of MLS from 50 to 10 hPa. Thus, sonde data are reliable for trends, but with a caveat applied for a subset of dropoff stations in the tropics and subtropics. The dropoff is associated with only one of two major ECC instrument types. A detailed examination of ECC serial numbers pinpoints the timing of the dropoff. However, we find that overall, ozonesonde data are stable and accurate compared to independent measurements over the past two decades.

A severe weather system accompanied by a stratospheric intrusion during unusual warm winter in 2015 over the South Africa: An initial synoptic analysis

This study aims to highlight the abnormally warm winter experienced in South Africa during 2015. This work also investigates the synoptic and dynamic aspects of the specific severe weather system (late July 2015) which affected the western, southern, and eastern provinces including some parts in the Northern Cape, Western Cape, Lesotho, KwaZulu-Natal, and Eastern Cape. This is followed by an investigation of the stratospheric-tropospheric transport of the high-level ozone associated with a deep cut-off low weather system over the southern and central regions of South Africa which occurred on 24–25 July 2015. The case characteristics of the dynamical analysis of the weather system associated with a stratospheric-tropospheric intrusion was also determined. This research illustrated that this system was accompanied by deep upper and mid-tropospheric troughs which developed over the eastern part of the country. This resulted in tropopause folding controlled by the upper meandered tropospheric jet stream axis in the east of the upper and mid-tropospheric troughs. This caused the strong downward injection of stratospheric ozone-rich air with a maximum ozone value of 320 ppb at a level of 300 hPa observed using MERRA reanalysis data in the north of the North Cape province together with very dry higher tropospheric air at 300 hPa. In the lower troposphere, ozone levels as high as 61 ppb at 850 hPa were found within these intrusions in the northern-central region during the active cut-off low weather system. Using the Aura-Microwave Limb Sounder (MLS) to determine the vertical ozone profile at different pressure levels over South Africa indicated that a maximum value of approximately 270 ppb ozone was recorded on 24 July 2015. The observational measurements from this study show good agreement with the findings from the reanalysis models together with the results taken from the MERRA database for the specific day of peak ozone activity.