Search Results (304)

Upper troposphere (UT) humidity records are crucial for climate studies. To maximize temporal representativeness and enhance the lidar signal, pseudo-monthly averaging—limited to nighttime measurement—is applied, yielding water vapor mixing ratio (WVMR) profiles up to 16 km. This study evaluates 11 years (2013–2023) of WVMR profiles from a UV Raman lidar (Li1200) at Réunion Island, comparing them with MLS-Aura satellite retrievals, ERA5 reanalysis data, and GRUAN-processed M10 radiosondes. The results reveal a systematic dry shift in MLS of up to 30% above 12 km, particularly during the wet season. The lidar exhibits a slight downward shift in WVMR, approximately 5% lower than ERA5 throughout the UT, with the largest deviations occurring above 14 km and greater variability during the wet season. Calibration-related challenges during the dry season result in lidar WVMR profiles that are up to 10% drier than ERA5. Additionally, comparisons with GRUAN-processed radiosondes show a substantial dry shift relative to the lidar, exceeding 30% above 12 km. We investigate the effect of GNSS-based lidar calibration by applying an alternative calibration method, which produces higher WVMR values. This reveals a dry shift in ERA5 relative to the lidar, increasing with altitude in the UT up to 25%. These measurements contribute to the global effort to monitor and validate tropical and subtropical upper tropospheric humidity. Full article

The Madden–Julian Oscillation (MJO) varies seasonally. Both moist and dry dynamical processes would contribute to this seasonality. Previous results have suggested strong dependence of MJO phase speed on planetary-scale upper tropospheric Kelvin waves interacting with the mean flow. Composites and phase speed spectra assess the association between the Indian Basin MJO circulation and convection with variations in equatorial upper tropospheric background wind patterns, including seasonal variability. Results show that the fastest eastward propagation over the Indian Ocean (>10 ms⁻¹) tends to occur during northern spring when background upper tropospheric easterlies are weakest. Northern winter signals typically advance eastward between 4 and 10 ms⁻¹. Strong easterly background wind conditions during northern summer usually prevent propagation eastward along the equator from the Western Indian Ocean. Results also show relative amplitude variations between the MJO’s upper and lower tropospheric zonal wind signals, with the upper tropospheric circulation signals being disproportionately stronger than the lower tropospheric ones over the Western Hemisphere to East Africa. The upper tropospheric easterly wind anomalies grow over the Western Indian Ocean first, as specific humidity increases in lower tropospheric easterly wind to the east. Then, lower tropospheric westerly wind emerges west of the emerging convection, suggesting that lower tropospheric wind change depends more directly on moist processes than the upper tropospheric wind. Full article

This study uses a globally coupled climate framework to examine how regional differences in sulfate emissions, through both direct and indirect aerosol effects, regulate interactions between clouds and radiation and drive nonlinear thermodynamic and hydrological responses in the East Asia and South Asia summer monsoon region. We employ the Community Earth System Model to compare the Shared Socioeconomic Pathways 1–2.6 and 5–8.5 against the historical scenario with perturbations of anthropogenic sulfate. The results reveal regional contrasts in sulfate concentration and aerosol optical depth: direct shortwave radiation increases in East Asia, while South Asia experiences radiation weakening due to higher aerosol optical depth. Indirect aerosol effects induce cloud adjustments, with East Asia developing more low clouds and higher cloud droplet number concentrations and liquid water paths, leading to greater attenuation of surface shortwave radiation and changes in precipitation and convection. Over the Tibetan Plateau, a higher fraction of high clouds and changes in cloud-top heights jointly drive warming, raising net radiation and strengthening both latent-heat and sensible-heat release. South Asia exhibits a north–south oriented precipitation pattern, with intensified warm advection but a distribution shaped by upper and mid-tropospheric circulations. Overall, the coupling of cloud macro-distribution and cloud microphysics emerges as the principal driver, with direct and indirect effects amplifying nonlinear regional responses. To improve predictability, we advocate multi-model comparisons, observational constraints, tighter bounds on cloud-droplet size distributions, liquid water paths, and cloud droplet number concentrations. Full article

Since early 2023, severe to exceptional drought has developed in southern coastal Australia, with dam levels falling as stream flows plummet. The wet season, April to September, reflects the most equatorward position of the mid-latitude westerly wind regime that brings rain-bearing systems to southern coastal Australia. Climatologically, an upper-level tropospheric split-jet is present in the Australia–New Zealand region. This is evident in the subtropical jet (STJ) location when the 1965 to 1995 u-component of the 250 hPa wind anomaly, relative to 1991 to 2020, is located above northern tropical Australia, and the weaker polar-front jet (PFJ) branch anomaly spans the mid-latitudes south of Australia. Permutation testing revealed a statistically significant decrease in the 2016 to 2025 wet season mean precipitation across southern Australia. Compared with the 1965 to 1995 u-component wind anomaly at 250 hPa, the 2006 to 2015 decadal anomaly still shows the split jet with the STJ branch over northern tropical Australia and the PFJ in the mid-latitudes of the Australia–New Zealand region. However, there is a dramatic change in position and structure of the STJ branch of the split jet, between the 1965 to 2015 and the 2016 to 2025 anomalies. The split jet structure has shifted approximately 10° poleward, causing rain-producing systems to track south of the Australian continent. The reduced precipitation can generate more frequent and intense droughts, with greatly reduced stream flows and dam levels. Historically, the low precipitation warm season follows from October to March when heatwaves, combined with pre-existing dry conditions, often create catastrophic bushfire conditions. Full article

We investigate the multi-layer atmospheric impacts of Typhoon Hagibis (2019), which formed on 6 October, tracked across 12–35° N and 135–155° E, and made landfall on 12 October over the Izu Peninsula, central Honshu, Japan. We present a multi-layer study that involves the troposphere, stratosphere and upper ionosphere to examine the thermodynamic and electromagnetic coupling between these layers due to such extreme weather conditions. Using ERA5 reanalysis, we identify pronounced stratospheric temperature perturbations, elevated atmospheric gravity wave (AGW) potential energy, substantial spatiotemporal variability in the zonal (U) and meridional (V) wind components, relative humidity, and specific rainwater content throughout the cyclone’s evolution. Quantitatively, AGW potential energy increased from background levels of <5 J kg⁻¹ to >40 J kg⁻¹ near the cyclone core, while tropospheric wind anomalies reached $\pm 30$–40 m s⁻¹, accompanied by relative humidity values exceeding 90% and specific rainwater content up to $1.5\times {10}^{-3}$ kg kg⁻¹, indicative of vigorous moist convection and strong vertical energy transport. The ionospheric response, derived from GPS-based Total Electron Content (TEC) at 10 Japanese IGS stations, reveals vertical TEC (VTEC) perturbations whose amplitudes and temporal evolution vary systematically with GPS-station-to-typhoon-eye distance, including clear enhancements and reductions around the closest-approach day. These signatures indicate a measurable ionospheric response to cyclone-driven atmospheric forcing under geomagnetically quiet conditions, confirming that Hagibis produced vertically coupled disturbances linking stratospheric AGW activity with ionospheric electron density variability. Full article

The Mediterranean region has experienced pronounced hydroclimatic variability over recent decades, motivating a closer examination of the physical processes underlying these changes. This study analyzes ERA5 reanalysis data for 1950–2024 to investigate long-term trends and interrelations among temperature, precipitation, evaporation, wind, sensible heat, and column water, distinguishing between land and sea domains and multiple atmospheric layers. Results show a strong warming signal in the lower troposphere, with temperatures increasing by 0.03 °C year⁻¹ over land and 0.015 °C year⁻¹ over sea, and near-stagnancy in the upper troposphere, which indicates a steepening lapse rate. Unlike temperature, evaporation shows no strong long-term increase: over sea, it rises only slightly, and over land, it declines modestly, with both weak tendencies dominated by strong interannual variability and consistent with declining winds. Over land, sensible heat flux increases, while over the sea, it decreases, revealing divergent energy-partition regimes. Precipitation exhibits no significant long-term change, suggesting that the atmosphere has become warmer and slightly moister but less effective in converting vapor into rainfall. Correlation analyses indicate that wind speed exerts a stronger control on evaporation and precipitation than temperature across the whole region. The Hurst–Kolmogorov stochastic framework further reveals persistent long-term variability in Mediterranean hydroclimatic processes, underscoring that the region’s climate behavior is shaped by dynamic and complex interactions rather than by temperature trends alone. Full article

This study investigates the characteristics and causes of a low-level wind shear (LLWS) event induced by downward momentum transport at Xining Airport, China on 5 April 2023. By utilizing Doppler Wind Lidar (DWL), Automated Weather Observing System (AWOS), and ERA5 reanalysis data, the detailed structure and synoptic-scale mechanisms of the event were analyzed. The LLWS manifested as a non-convective, meso-γ scale (2–20 km) directional wind shear, characterized by horizontal variations in wind direction. The system moved from northwest to southeast and persisted for approximately three hours. The shear zone was characterized by westerly flow to the west and easterly flow to the east, with their convergence triggering upward motion. The Range Height Indicator (RHI) and Doppler Beam Swinging (DBS) modes of the DWL clearly revealed the features of westerly downward momentum transport. Diagnostic analysis of the synoptic-scale environment reveals that a developing 300-hPa trough steered the merging of the subtropical and polar front jets. This interaction provided a robust source of momentum. The secondary circulation excited in the jet entrance region promoted active vertical motion, facilitating the exchange of momentum and energy between levels. Simultaneously, the development of the upper-level trough led to the intrusion of high potential vorticity (PV) air from the upper levels (100–300 hPa) into the middle troposphere (approximately 500 hPa), which effectively transported high-momentum air downward and dynamically induced convergence in the low-level wind field. Furthermore, the establishment of a deep dry-adiabatic mixed layer in the afternoon provided a favorable thermodynamic environment for momentum transport. These factors collectively led to the occurrence of the LLWS. This study will further deepen the understanding of the formation mechanism of momentum-driven LLWS at plateau airports, and provide a scientific basis for improving the forecasting and warning of such hazardous aviation weather events. Full article

A kinetic and thermodynamic multi-phase model has been developed to describe the adsorption of gases on ice surfaces and their subsequent diffusional loss into the bulk ice phase. This model comprises a gas phase, a solid surface, a sub-surface layer, and the ice bulk. The processes represented include gas adsorption on the surface, solvation into the sub-surface layer, and diffusion in the ice bulk. It is assumed that the gases dissolve according to Henry’s law, while the surface concentration follows the Langmuir adsorption equilibrium. The flux of molecules from the sub-surface layer into the ice bulk is treated according to Fick’s second law. Kinetic and thermodynamic quantities as applicable to the uptake of small carbonyl compounds on ice surfaces at temperatures around 200 K have been used to perform model calculations and corresponding sensitivity tests. The primary application in this study is acetic acid. The model simulations are applied by fitting the experimental data obtained from coated-wall flow-systems (CWFT) measurements, with the best curve-fit solutions providing reliable estimations of kinetic parameters. Over the temperature range from 190 to 220 K, the estimated desorption coefficient, k_des, varies from 0.02 to 1.35 s⁻¹, while adsorption rate coefficient, k_ads, ranges from 3.92 and 4.17 × 10⁻¹³ cm³ s⁻¹, and the estimated diffusion coefficient, D, changes by more than two orders of magnitude, increasing from 0.03 to 13.0 × 10⁻⁸ cm² s⁻¹. Sensitivity analyses confirm that this parameter estimation approach is robust and consistent with underlying physicochemical processes. It is shown that for shorter exposure times the loss of molecules from the gas phase is caused exclusively by adsorption onto the surface and solvation into the sub-surface layer. Diffusional loss into the bulk, on the other hand, is only important at longer exposure times. The model is a useful tool for elucidating surface and bulk process kinetic parameters, such as adsorption and desorption rate constants, solution and segregation rates, and diffusion coefficients, as well as the estimation of thermodynamic quantities, such as Langmuir and Henry constants and the ice film thickness. Full article

In this paper, a simple method of estimating reference optical turbulence profiles at the Huairou Solar Observing Station (HSOS) from a large meteorological dataset is used. These reference profiles can be used in simulations of atmospheric variability above the station and the impact of climate change on image quality. By analyzing the statistics of measured optical turbulence and using the ERA-5 reanalysis data, vertical distributions of optical turbulence above HSOS were obtained for different time periods (1940–1969, 1970–1999, 1989–2010, 2000–2025). It has been shown that the intensity of optical turbulence in the surface layer has been decreasing in recent decades, while the intensity in the upper troposphere has a tendency to increase. Trends are also assessed in total cloud cover and atmospheric boundary layer height at the HSOS site. Observed changes are associated with global warming. Full article

The influence of tropical oscillations on the thermodynamics of the middle and upper atmosphere at high latitudes was studied using a nonlinear model of the general circulation of the middle and upper atmosphere (MUAM). The observed oscillations include the quasi-biennial oscillation of the zonal wind in the equatorial stratosphere (QBO) and the El Niño–Southern Oscillation (ENSO). The main focus of this work is to study the influence of these oscillations on the strength and persistence of the stratospheric polar vortex. Four ensemble calculations were carried out (10 runs for each QBO and ENSO phase combination) for January–February. It was shown that the polar vortex and Eliassen–Palm (EP) flux divergence were especially strong under La Niña and the westerly QBO phase (wQBO). This was accompanied by a strengthening of the residual mean circulation (RMC) from the summer to the winter hemisphere, causing positive temperature anomalies in the polar mesosphere and negative anomalies in the stratosphere. The greatest RMC weakening and the weakest and warmest polar vortex occurred during El Niño and eQBO conditions in January and during El Niño and wQBO conditions in February. Such diverse manifestations of tropical oscillations via teleconnections can provide valuable information for predicting the frequency and intensity of sudden stratospheric warmings (SSWs) and subsequent extreme cold wave events in the troposphere. Specifically, SSWs are the least probable during La Niña and wQBO conditions in both January and February. The QBO phase most significantly influences the polar vortex during El Niño events in both months. We conclude that SSW development is more favorable during eQBO in January and wQBO in February under El Niño conditions. Full article

On the morning of 4 April 2025, a rare formation of Cirrostratus undulatus homomutatus was observed over Barcelona. This variety of the homomutatus form of the Cirrostratus cloud genus—originating from the transformation of persistent aircraft contrails—has not previously been documented in the International Cloud Atlas or in any scientific publication, making this observation unique within the current literature. The event was visually recorded and meteorologically analyzed using upper-air data from the Barcelona radiosonde and the ECMWF ERA5 reanalysis at 300 and 500 hPa geopotential heights. Synoptic and thermodynamic analyses revealed a localized region of enhanced wind shear activity coinciding with a thin, moist layer near the tropopause. These conditions likely facilitated the transformation of persistent contrails into cirriform layers exhibiting undulated patterns characteristic of the undulatus variety. This case provides new insight into the microphysical and dynamic mechanisms underlying the evolution of anthropogenic cirriform clouds, contributing to the growing body of knowledge on homomutatus phenomena and their interaction with upper-tropospheric processes. It thus represents the first formal documentation and meteorological interpretation of Cirrostratus undulatus homomutatus, offering a valuable reference for future observational and classification efforts within the WMO framework. Full article

The Ozone Monitoring Suite–Limb (OMS-L) carried by the Fengyun-3F (FY-3F) satellite, as China’s first effective payload using the limb observation mode to conduct hyperspectral atmospheric detection in the ultraviolet (UV) and visible (Vis) bands, was successfully launched on 3 August 2023. It mainly serves the research in the fields of climate change, atmospheric chemistry, and atmospheric environment. This study is the first to conduct the retrieval of the ozone profiles from OMS-L data. The retrieval scheme utilizes the radiances within the UV band, normalizing them to the radiance at the upper tangent height. To minimize the impact of aerosol scattering, the pair method is implemented, with seven carefully selected wavelength pairs fully exploiting ozone’s UV absorption characteristics. The weighted multiplicative algebraic reconstruction technique (WMART) is then applied to effectively integrate multi-wavelength information, in tandem with an iterative retrieval process using the radiative transfer model. This approach yields ozone concentration profiles in the altitude range of approximately 18–55 km. The retrieval errors resulting from the parameters are estimated to be 5–13% above 25 km, increasing to 10–30% in the upper troposphere. Comparison of OMS-L retrieved ozone profiles with the OMPS/LP v2.6 product reveals good consistency, with differences generally within 10% in the 20–50 km altitude range. However, biases are more pronounced at lower altitudes, particularly in tropical regions. This work conclusively demonstrates that OMS-L can accurately measure stratospheric ozone profiles with high vertical resolution, thereby contributing significantly to the field of atmospheric science. Full article

As climate change intensifies, enhancing numerical weather prediction (NWP) accuracy has been increasingly critical. While data assimilation optimizes NWP initial conditions, its effectiveness over complex terrain requires further systematic evaluation. This study implemented a high-resolution WRF/4D-Var data assimilation framework, overcoming its inherent limitation of not supporting two-layer nested assimilation across domains by designing a two-layer nested “assimilation-forecast” workflow. Representative winter and summer cases from February and June 2019 were selected to evaluate improvements in near-surface and upper-air meteorological parameters. The results indicated that the 4D-Var data assimilation significantly improved the correlation coefficients of near-surface variables during winter by 2.9% (temperature), 14.5% (relative humidity), 6.6% (wind speed), and 10.4% (wind direction), with even greater improvements observed in summer reaching 13.3%, 5.8%, 35.3%, and 42.3%, respectively. Meanwhile, 4D-Var considerably enhanced the atmospheric vertical profiling, with the middle troposphere (300–700 hPa) exhibiting the most pronounced improvement. Among different surface types, water bodies exhibited the strongest assimilation response. Results also revealed systematic corrections to the background fields, with February exhibiting more uniform adjustments in contrast to June’s complex spatiotemporal patterns. Positive effects persisted throughout the 24-h forecasts, with the maximum benefit occurring within the first 12 h. These results demonstrate the effectiveness of 4D-Var in regional meteorological forecasting, highlighting its value for constructing high-precision multidimensional meteorological fields to support both weather and air quality simulations. Full article

On 7 September 2024, a trough, situated over the Black Sea, in combination with a northeasterly outflow of a surface anticyclone over Russia, increased moisture and established an instability environment in Greece. Veering winds with height, in combination with high CAPE values in the middle and upper troposphere, produced a violent supercell. Cloud base updrafts, intense lightning activity and severe precipitation in the form of large hail were the main characteristics of this case. Egg-sized hail was reported, contributing to the highest observed CDC index (+4) in Thessaly. Weather RADAR data were recorded and processed by TITAN, revealing an extensive WER in the RHI. Full article

The monthly variability of Upper Tropospheric Humidity with respect to ice (UTHi) is examined during the forty-year period 1979–2020. Trends per decade are calculated for every month separately and for 10° latitude bands. Statistical significance is estimated with the Mann–Kendall test. Results show significant positive UTHi trends in northern and southern midlatitude regions. In the northern midlatitudes, the strongest trends are observed in November, December and February and in the southern midlatitudes in April, May and June. These trends range between 0.5 and 1.2% per decade. In contrast, tropical regions display weak or negative trends. These patterns highlight regional and seasonal differences in upper tropospheric moisture changes, which are critical for understanding water vapour feedback and its role in climate variability and long-term atmospheric moisture behaviour. Full article