Search Results (22)

Aviation is widely recognised to have global-scale climate impacts through the formation of ozone (O₃) in the upper troposphere and lower stratosphere (UTLS), driven by emissions of nitrogen oxides (NO_X). Ozone is known to be one of the most potent greenhouse gases formed from the interaction of aircraft emission plumes with atmospheric species. This paper follows up on previous research, where a Photochemical Trajectory Model was shown to be a robust measure of ozone formation along flight trajectories post-flight. We use a combination of a global Lagrangian chemistry-transport model and a box model to quantify the impacts of aircraft NO_X on UTLS ozone over a five-day timescale. This work expands on the spatial and temporal range, as well as the chemical accuracy reported previously, with a greater range of NO_X chemistry relevant chemical species. Based on these models, route optimisation has been investigated, through the use of network theory and algorithms. This is to show the potential inclusion of an understanding of climate-sensitive regions of the atmosphere on route planning can have on aviation’s impact on Earth’s Thermal Radiation balance with existing resources and technology. Optimised flight trajectories indicated reductions in O₃ formation per unit NO_X are in the range 1–40% depending on the spatial aspect of the flight. Temporally, local winter times and equatorial regions are generally found to have the most significant O₃ formation per unit NO_X; moreover, hotspots were found over the Pacific and Indian Ocean. Full article

This study explores how the variation of Gravity Waves (GWs) is modified and intensified during tropical cyclones using high-resolution ERA5 reanalysis data. GWs play a vital role in understanding tropical cyclone dynamics due to their connection with energy and momentum transfer in the atmosphere. Different issues related to six tropical cyclones in the Bay of Bengal from 2019 to 2022, spanning different intensities and seasonal conditions, are analyzed. Using temperature and pressure data across 37 vertical levels, several variables like perturbation temperature and potential energy $E_p$ profiles associated with GWs are computed. Spatial temperature distributions and $E_p$ exhibit spiral formations resembling cyclone structures with significant altitude-dependent variations. Temperature signatures are observed at altitudes between 1.4 km and 5.8 km, with Pressure Levels (PLs) of 850 hPa and 500 hPa, respectively, varying by season and intensity, while $E_p$ signatures are prominent between 15.25 km and and 20.77 km, with PLs of 125 hPa and PL 50 hPa, respectively, peaking at 16.58 km and PL 100 hPa for most cyclones, except Cyclone Fani, which peaked at 18.72 km with a PL of 70 hPa. $E_p$ values range from 10 to 25 J/kg, reflecting strong GW–cyclone interactions. These findings highlight the influence of cyclone intensity, seasonality, and atmospheric dynamics on GW behavior, enhancing the understanding of energy transfer processes in the upper troposphere and lower stratosphere. Full article

The impact of the quasi-biennial oscillation (QBO) and Madden–Julian oscillation (MJO) on the dynamics of major sudden stratospheric warmings (SSWs) observed in the winters of 2018, 2019, and 2021 is investigated. Using data from the MERRA-2 reanalysis, we analyze the daily mean variability of critical atmospheric parameters at the 10 hPa level, including zonal mean polar cap temperature, zonal mean zonal wind, and the amplitudes of planetary waves 1 and 2. The results reveal dramatic increases in polar cap temperature and significant wind reversals during the SSW events, particularly in 2018. The analysis of planetary wave (PW) amplitudes demonstrates intensified wave activity coinciding with the onset of SSWs, underscoring the pivotal role of PWs in these stratospheric disruptions. Further examination of outgoing long-wave radiation (OLR) anomalies highlights the influence of QBO phases on tropical convection patterns. During westerly QBO (w-QBO) phases, enhanced convective activity is observed in the western Pacific, whereas the easterly QBO (e-QBO) phase shifts convection patterns to the maritime continent and central Pacific. This modulation by QBO phases influences the MJO’s role during SSWs, affecting tropical and extra-tropical weather patterns. The day-altitude variability of upward heat flux reveals distinct spatiotemporal patterns, with pronounced warming in the polar regions and mixed heat flux patterns in low latitudes. The differences observed between the SSWs of 2017–2018 and 2018–2019 are likely related to the varying QBO phases, emphasizing the complexity of heat flux dynamics during these events. The northern annular mode (NAM) index analysis shows varied responses to SSWs, with stronger negative anomalies observed during the e-QBO phase compared to the w-QBO phases. This variability highlights the significant role of the QBO in shaping the stratospheric and tropospheric responses to SSWs, impacting surface weather patterns and the persistence of stratospheric anomalies. Overall, the study demonstrates the intricate interactions between stratospheric dynamics, QBO, and MJO during major SSW events, providing insights into the broader implications of these atmospheric phenomena on global weather patterns. Full article

In light of the rapid Arctic warming and continuous reduction in Arctic Sea ice, the complex two-way Arctic–midlatitudes connection has become a focal point in recent climate research. In this paper, we review the current understanding of the interactive influence between midlatitude atmospheric variability and Arctic Sea ice or thermal conditions on interannual timescales. As sea ice diminishes, in contrast to the Arctic warming (cooling) in boreal winter (summer), Eurasia and North America have experienced anomalously cold (warm) conditions and record snowfall (rainfall), forming an opposite oscillation between the Arctic and midlatitudes. Both statistical analyses and modeling studies have demonstrated the significant impacts of autumn–winter Arctic variations on winter midlatitude cooling, cold surges, and snowfall, as well as the potential contributions of spring–summer Arctic variations to midlatitude warming, heatwaves and rainfall, particularly focusing on the role of distinct regional sea ice. The possible physical processes can be categorized into tropospheric and stratospheric pathways, with the former encompassing the swirling jet stream, horizontally propagated Rossby waves, and transient eddy–mean flow interaction, and the latter manifested as anomalous vertical propagation of quasi-stationary planetary waves and associated downward control of stratospheric anomalies. In turn, atmospheric prevailing patterns in the midlatitudes also contribute to Arctic Sea ice or thermal condition anomalies by meridional energy transport. The Arctic–midlatitudes connection fluctuates over time and is influenced by multiple factors (e.g., continuous melting of climatological sea ice, different locations and magnitudes of sea ice anomalies, internal variability, and other external forcings), undoubtedly increasing the difficulty of mechanism studies and the uncertainty surrounding predictions of midlatitude weather and climate. In conclusion, we provide a succinct summary and offer suggestions for future research. Full article

Gravity wave (GW) momentum flux spectra help to uncover the mechanisms through which GWs influence momentum transfer in the atmosphere and provide crucial insights into accurately characterizing atmospheric wave processes. This study examines the momentum flux spectra of GWs in the troposphere (2–14 km) and stratosphere (18–28 km) over Koror Island (7.2°N, 134.3°W) using radiosonde data from 2013–2018. Utilizing hodograph analysis and spectral methods, the characteristics of momentum flux spectra are discussed. Given that the zonal momentum flux spectra of low-level atmospheric GWs generally follow a Gaussian distribution, Gaussian fitting was applied to the spectral structures. This fitting further explores the seasonal variations of the zonal momentum flux spectra and the average spectral parameters for each month. Additionally, the GW energy is analyzed using SABER (Sounding of the Atmosphere using Broadband Emission Radiometry) satellite data and compared with the results of the momentum flux spectra from radiosonde data, revealing the close negative correlation between wave energy and wave momentum for stratospheric GW changing with time. The findings indicate that the Gaussian peak shifts more eastward in both the troposphere and stratosphere, primarily due to the absorption of eastward-propagating GWs by the winter tropospheric westerly jet and critical layer filtering. The full width at half maximum (FWHM) in the stratosphere is larger than in the troposphere, especially in June and July, as the spectrum broadens due to propagation effects, filtering, and interactions among waves. The central phase speed in the stratosphere exceeds that in the troposphere, reflecting the influences of Doppler effects and background wind absorption. The momentum flux in the stratosphere is lower than in the troposphere, which is attributed to jet absorption, partial reflection, or the dissipation of GWs. Full article

Stratospheric dynamics are strongly affected by the absorption/emission of radiation in the Earth’s atmosphere and Rossby waves that propagate upward from the troposphere, perturbing the zonal flow. Reduced order models of stratospheric wave–zonal interactions, which parameterize these effects, have been used to study interannual variability in stratospheric zonal winds and sudden stratospheric warming (SSW) events. These models are most sensitive to two main parameters: $\Lambda$, forcing the mean radiative zonal wind gradient, and h, a perturbation parameter representing the effect of Rossby waves. We take one such reduced order model with 20 years of ECMWF atmospheric reanalysis data and estimate $\Lambda$ and h using both a particle filter and an ensemble smoother to investigate if the highly-simplified model can accurately reproduce the averaged reanalysis data and which parameter properties may be required to do so. We find that by allowing additional complexity via an unparameterized $\Lambda \left(t\right)$, the model output can closely match the reanalysis data while maintaining behavior consistent with the dynamical properties of the reduced-order model. Furthermore, our analysis shows physical signatures in the parameter estimates around known SSW events. This work provides a data-driven examination of these important parameters representing fundamental stratospheric processes through the lens and tractability of a reduced order model, shown to be physically representative of the relevant atmospheric dynamics. Full article

Sudden Stratospheric Warming (SSW) events have a strong impact on the tropospheric weather and climate. Past researchers have carried out extensive studies investigating the theories of interactions between the stratosphere and the troposphere. However, detailed studies on the influences of the global tropopause are rarely shown. This study uses Global Navigation Satellite System (GNSS) Radio Occultation (RO) data from the years 2007 to 2013 to investigate the influences of different types of SSW events on the tropopause over latitude bands from 30° S to 90° N. It was found that SSW events have strong influences on the tropopause over 60° N–90° N and over 20° N–30° N regions. In 60° N–90° N, SSW events cause a tropopause temperature increase and, therefore, a tropopause height decrease. The increment in the tropopause temperature are more than 10 K and the decrement in the tropopause height is about to 2 km during strong events. Such influences last for about 1.5 months for strong split events and about 10 days for weaker and/or displacement type events. The influences of SSW events on 20° N–30° N are weaker. Only the January 2009 SSW event shows a visible influence on the tropopause layer with a tropopause temperature decrease of about 4 K and a tropopause height increase of about 1 km. Other SSW events share no common characteristics on the tropical tropopause. This is mainly because SSW events are not strong enough to dominate the tropopause variations and other factors, especially the planetary waves in the troposphere, have stronger impacts on the tropopause layer. Full article

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. Full article

Every year, cut-off low (COL) pressure systems produce severe weather conditions and heavy rainfall, often leading to flooding, devastation and disruption of socio-economic activities in South Africa. COLs are defined as cold-cored synoptic-scale mid-tropospheric low-pressure systems which occur in the mid-latitudes and cause persistent heavy rainfall. As they occur throughout the year, these weather systems are important rainfall producing systems that are also associated with extreme cold conditions and snowfalls. An in-depth review of COLs is critical due to their high impacts which affect some parts of the country regularly, affecting lives and livelihoods. Here, we provide a comprehensive review of the literature on COLs over the South African domain, whilst also comparing them with their Southern Hemisphere counterparts occurring in South America and Australia. We focus on the occurrence, development, propagation, dynamical processes and impacts of COLs on society and the environment. We also seek to understand stratospheric–tropospheric exchanges resulting from tropopause folding during the occurrence of COLs. Sometimes, COLs may extend to the surface, creating conditions conducive to extreme rainfall and high floods over South Africa, especially when impinged on the coastal escarpment. The slow propagation of COLs appears to be largely modulated by a quasi-stationary high-pressure system downstream acting as a blocking system. We also reviewed two severe COL events that occurred over the south and east coasts and found that in both cases, interactions of the low-level flow with the escarpment enhanced lifting and deep convection. It was also determined from the literature that several numerical weather prediction models struggle with placement and amounts of rainfall associated with COLs, both near the coast and on the interior plateau. Our study provides the single most comprehensive treatise that deals with COL characteristics affecting the South African domain. Full article

The deterministic forecast of the stratospheric polar vortex intensity (iSPV) is limited by 2 weeks, but it can be probabilistically predicted for a longer period due to low-frequency components of the climate system, such as large-scale sea surface temperature anomalies (SSTAs) (e.g., El Niño Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO)). For a qualitative and quantitative assessment of the effect of the large-scale Pacific SSTAs on the iSPV anomalies formation, idealized model experiments were carried out using the Isca platform. There is no statistically significant response of the SPV dynamics to the SSTAs corresponding to PDO phases, but they noticeably correct the effect of ENSO modes when added to it. The effect of the El Niño (EN) and La Niña (LN) events with neutral PDO phases on the iSPV is asymmetric; in the “single” EN experiment the vortex is 40% weaker relative to the control values, and, in the “single” LN, the SPV is weakened by no more than 20%. When EN accompanied with the positive PDO phase, iSPV is reduced by 58%. When the negative PDO phase is added, the EN effect is significantly weakened. The LN effect is weakened by both positive and negative PDO phases. Full article

An analysis of the relationship between changes in Arctic stratospheric ozone (ASO) and precipitation in eastern North America (38°–54°N, 65°–87°W; PENA) was performed using observational and reanalysis data coupled with the Whole Atmosphere Community Climate Model version 4 (WACCM4). We found that March ASO exhibits a strong correlation with PENA in April, indicating that the one-month leading ASO exerts a potentially strong impact on April PENA. Changes in tropospheric circulation over the North Pacific and North America can be influenced by ASO anomalies via stratosphere–troposphere interactions. Increased ASO typically results in the transport of drier, colder air from northwest to eastern North America and suppresses local convective activity by enhancing regional downwelling. These conditions lead to a decrease in regional atmospheric water vapor content (1000–600 hPa). Abnormally high ASO may therefore suppress precipitation, whereas abnormally low ASO serves to enhance precipitation, and the finding is supported by WACCM4 simulations incorporating these ASO anomaly signals. We also present an ASO-based statistical linear model for predicting April PENA. Results confirm that the linear model reproduces April PENA for both training and testing periods, based on March ASO, demonstrating the reliability and stability of this linear model. This study verifies that ASO is a viable predictor for projecting April PENA and thus improving forecasts of regional seasonal precipitation. Full article

Using global ocean vertical temperature anomaly data, we identified that a significant response of the sea temperature anomaly (STA) to the solar radio flux (SRF) exists. We found that the STA exhibited a significant correlation with Asian summer and winter precipitation, among which the response from the Qinghai–Tibet Plateau (the QTP) was particularly noticeable. Based on NCEP/NCAR reanalysis data, the latent heat flux (LHF) anomaly, which plays a key role in winter precipitation in China, especially over the QTP, showed a significant response to the SRF in the Pacific. The results demonstrated the bottom-up mechanism of impact of solar activity (SA) on the plateau snow through sea–air interaction. Meanwhile, a top-down mechanism was also present. When the SRF was high, the stratospheric temperature in the low and mid-latitudes increased and the temperature gradient pointed to the pole to strengthen the westerly wind in the mid-latitudes. The EP flux showed that atmospheric long waves in the high altitudes propagated downward from the stratosphere to the troposphere. A westerly (easterly) wind anomaly occurred in the south (north) of the QTP at 500 hPa and the snowfall rate over the QTP tended to increase. When the SRF was low, the situation was the opposite, and the snowfall rate tended to decrease. The model results confirmed that when total solar irradiance (TSI) became stronger (weaker), both of the solar radiation fluxes at the top of the atmosphere and the surface temperature over the QTP increased (decreased), the vertical updraft intensified (weakened), and the snowfall rate tended to increase (decrease) accordingly. These conclusions are helpful to deepen the understanding of SA’s influence on the snow cover over the QTP. Full article

The calculation of the tropopause height is crucial to the investigation of fundamental interactions between the troposphere and stratosphere, playing an essential role in areas such as climatology, geodesy, geophysics, ecology, and aeronautics. Since the troposphere and stratosphere have many distinct features, it is possible to define the boundary between them using different variables, such as temperature lapse rate, potential vorticity and chemical concentrations. However, according to the chosen variable, different tropopause definitions are created, each one with some limitations. Using 41 years of European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis (ERA5) data, we examined the variability of the tropopause for the north and south hemispheres and developed two models, both based on blending the potential vorticity and thermal tropopauses. One model (based on a sigmoid function, named STH) depends only on latitude and day of the year, while the other model (based on bilinear interpolation, named BTH) requires an additional look-up table. In order to account for the different behaviors of the tropopauses in the north and south hemispheres, we estimated two sets of model coefficients (one for each hemisphere). When compared against a benchmark of estimated tropopause heights during three years of radiosonde data, we obtained an average RMSE for the differences of 0.88 km for the STH model and 0.67 km for the BTH model. A similar comparison for alternative models available in the literature shows that the new models have superior performance and represent a significant improvement in tropopause height determination. Full article

The Quasi-Biennal Oscillation (QBO) and the El Niño-Southern Oscillation (ENSO) largely modulate the zonal wind in the tropics. Previous studies showed that QBO phases produce changes in deep convection through an increase/decrease in the tropopause height over the tropics and subtropics. This study investigates the combined effects of QBO and ENSO on tropical cyclone activity by modulating tropopause height. We found that tropopause height increases over the Gulf of Mexico, the Caribbean region, and the Western North Atlantic Ocean during La Niña + QBOW, allowing deeper tropical convection to develop over those regions. As a consequence, TC activity over those regions is not only increased in number but also enhanced in intensity. Conversely, during El Niño + QBOE, most deep tropical convection is inhibited over those same regions due to the decrease in tropopause height over the subtropics. We conclude that QBO effects on TCs and deep convection should be studied in combination with ENSO. Additional comparative studies using long record data at high vertical resolution are needed to fully understand to what extent QBO interacts with ENSO in the lower tropical stratosphere and upper tropical troposphere. Full article

A better understanding of the water and energy cycles at climate scale in the Third Pole Environment is essential for assessing and understanding the causes of changes in the cryosphere and hydrosphere in relation to changes of plateau atmosphere in the Asian monsoon system and for predicting the possible changes in water resources in South and East Asia. This paper reports the following results: (1) A platform of in situ observation stations is briefly described for quantifying the interactions in hydrosphere-pedosphere-atmosphere-cryosphere-biosphere over the Tibetan Plateau. (2) A multiyear in situ L-Band microwave radiometry of land surface processes is used to develop a new microwave radiative transfer modeling system. This new system improves the modeling of brightness temperature in both horizontal and vertical polarization. (3) A multiyear (2001–2018) monthly terrestrial actual evapotranspiration and its spatial distribution on the Tibetan Plateau is generated using the surface energy balance system (SEBS) forced by a combination of meteorological and satellite data. (4) A comparison of four large scale soil moisture products to in situ measurements is presented. (5) The trajectory of water vapor transport in the canyon area of Southeast Tibet in different seasons is analyzed, and (6) the vertical water vapor exchange between the upper troposphere and the lower stratosphere in different seasons is presented. Full article