Journal of Geophysical Research: Atmospheres最新文献

This study investigates an ozone intrusion event observed during the Pre-Asian Summer Monsoon Chemical and Climate Impact Project in August 2021, using 26 consecutive daily ozonesonde measurements over South Korea. A pronounced enhancement in total column ozone was observed between 17 and 19 August, which can be largely attributed to an ozone intrusion in the upper troposphere–lower stratosphere (UTLS), accounting for approximately 60% of the increase. The upper tropospheric circulation patterns demonstrate a clear signature of anticyclonic Rossby wave breaking (AWB) on the northeastern edge of the Asian summer monsoon anticyclone, aligned with the summertime jet stream. This AWB, accompanied by a cut-off low and tropopause folding, facilitated downward transport of stratospheric ozone into the upper troposphere. In addition, the ozone variability is investigated in two chemical reanalysis data sets: Modern-Era Retrospective Analysis for Research and Applications, Version 2 (MERRA-2) and European Centre for Medium-Range Weather Forecasts (ECMWF) Atmospheric Composition Reanalysis 4 (EAC4). MERRA-2 and EAC4 capture the ozone intrusion event with relevant synoptic-scale circulation patterns and ozone variability. However, discrepancies of ozone data in the chemical reanalyses were found in vertical ozone structures and persistence in the troposphere. MERRA-2 better represented the secondary ozone peak in the UTLS but underestimated lower-tropospheric ozone. In contrast, EAC4 showed a systematic positive bias particularly in the stratosphere and near the surface. Continued integration of temporally high-resolution ozone measurements is beneficial for understanding synoptic-scale ozone variability and evaluating emerging chemical reanalyses.

Understanding the mechanisms behind heavy precipitation is crucial for predicting those events. Based on hourly ERA5 reanalysis and rain gauge records, this study investigates the spatiotemporal evolution and anomalous upper-level circulation of heavy regional rainfall events (RREs) in summer over the southern Qilian Mountains, a key center of heavy rainfall in the northeastern Tibetan Plateau. Two distinct types of heavy RREs are identified, accounting for 73.6% of the total summer rainfall. Type 1 is confined to a relatively local spatial scale and has a shorter duration, with a diurnal peak occurring at 2200 LST, whereas Type 2 exhibits widespread propagation from the northwest to the southeast, with a longer duration and a diurnal peak occurring at 0600 LST. Distinct upper-level disturbances contribute to the evolution of these two types of events. For Type 1, a positive anomaly in potential vorticity near the tropopause is observed due to the intrusion of high potential vorticity air from the stratosphere, reducing the stability of the lower troposphere. In contrast, Type 2 is characterized by an eastward-moving warm anomaly, centered at 350 hPa. The upper-level warm anomaly contributes to upper tropospheric divergence and lower tropospheric water vapor convergence. The upper-level warm anomaly may result from the northward extension of South Asia High, as well as the warm anomalies in the middle and lower troposphere. The findings of this study enhance the understanding of the impact of upper-level disturbances on heavy precipitation in the complex terrains of arid and semi-arid areas.

This study advances methodologies for retrieving liquid water content (LWC) and effective diameter (De) in Monsoon Frontal Clouds (MFCs) using in situ aircraft observations. Ka-band Precipitation Radar (KPR) reflectivity (dBZ_KPR) and probe-derived reflectivity (dBZ_obs) reveal strong correlation (R = 0.7) but identify deviations linked to particle size characteristics. We leverage this connection by introducing the KPR's reflectivity deviation (ΔdBZ = dBZ_KPR–dBZ_obs) as a key predictor of particle size distribution, establishing novel radar reflectivity (Z)-based empirical relationships for LWC and De within MFCs. Validation against conventional retrieval methods and an independent data set demonstrates significant improvement: LWC retrieval root mean square error (RMSE) decreased by at least 62.5%, and De RMSE reduced by 12.7%–31.5%. However, performance varies across MFC regimes due to coexisting cloud droplets and precipitation particles, which cause non-unique Z–LWC/De relationships. This induces systematic retrieval biases: LWC is overestimated (De underestimated) in precipitation-dominated clouds, while reduced overestimation or underestimation (De overestimation) in weakly/non-precipitating clouds. Optimal conditions for accurate LWC retrieval are weakly precipitating clouds (not limited to MFCs) with moderate vertical extent (3–6.5 km) and low bases (<1 km), where reflectivity remains below 30 dBZ. These clouds typically feature low droplet concentrations (<100 cm⁻³), medium particle sizes (100–500 μm), and low liquid water content (<0.2 g m⁻³). In contrast, optimal De retrieval occurs under Z < 30 dBZ, Nc > 1 cm⁻³, De < 300 μm (especially <100 μm), and LWC between 0.1 and 0.6 g m⁻³. Collectively, the ΔdBZ-incorporated methodology enables more accurate microphysical parameter determination in MFCs and provides deeper insights into cloud processes.

Observations of PM₁ nonrefractory species (NRS) were performed for a 12 month period at the high-altitude Helmos Hellenic Atmospheric Aerosol and Climate Change ((HAC)²) station at 2,314 m a.s.l. using real-time online mass spectrometry. Aerosol-cloud interactions were studied as well as influence from the planetary boundary layer (PBL) and air mass origin. Source apportionment was performed on the combined data set of organic species and inorganic ions to track the sources of PM₁. Five factors were identified in all seasons; three factors composed mainly of organic aerosol (OA) (one primary-related and two secondary OA) and two mainly of inorganic species (ammonium nitrate and ammonium sulfate). A 10-fold increase in mass concentration levels was found during the summer compared to winter time, whereas PBL-influenced aerosol mass concentration was up to 6 times higher than free tropospheric (FT). In-cloud aerosol was found to vary between autumn and winter due to different cloud formation pathways between the two seasons. In autumn, in-cloud scavenging resulted in much lower concentration levels compared to clear sky conditions, whereas in winter in-cloud periods resulted in similar or even increased mass concentration for some species. Differentiation of interstitial aerosol from dried cloud droplets, possible by exploiting their variable penetration through the external PM₁₀ inlet during cloud events (in-cloud regimes), showed that during winter time the fraction of the interstitials to dried droplets was much higher compared to autumn time.

The traditional view posits that vertically propagating mixed Rossby-gravity (MRG) waves generated in the troposphere partly contribute to driving the Quasi-Biennial Oscillation (QBO) in the tropical lower stratosphere. However, recent studies suggest that MRG waves may be generated locally within the QBO region, potentially via barotropic instability. This study supports this alternative mechanism by showing that the tropical zonal mean flow at 30 hPa in ERA5 reanalysis satisfies the necessary conditions for barotropic instability approximately in 60% of cases, increasing to about 80% during the westerly QBO phase $��-�$ twice as frequent as during the easterly phase. Additionally, the MRG wave kinetic energy spectra at 30 hPa show increased energy at zonal wavenumbers $��k�>�5�$ in the westerly QBO phase compared to the easterly phase. The linear analysis within the QBO region reveals that MRG waves contribute between 4 and 14 times more to the total energy of the unstable modes during the westerly QBO phase, for zonal wavenumbers $��6�\le �k�\le �12�$. Idealized numerical simulations of the QBO flow demonstrate that the enhanced MRG wave spectral power at synoptic and sub-synoptic scales during the westerly QBO phase results from barotropic instability development. Together, these results suggest that the stronger MRG wave generation observed during the westerly QBO arises from both the greater frequency of unstable flow conditions and the higher MRG wave energy in the unstable modes.

While diurnal pulses (outward propagation) of clouds and precipitation in tropical cyclones (TCs) over the ocean have been well recognized, the diurnal propagation of precipitation (DPP) in landfalling TCs and its impacts on overland precipitation are less known. To fill this gap, this study utilizes the 30-min Integrated Multi-satellite Retrievals for GPM (IMERG) data set to identify overland DPP events in landfalling TCs. Overall, overland DPP events account for approximately 30% of all landfalling TC days globally. In these overland DPP events, a positive precipitation anomaly is observed to propagate radially outward from the inner-core to the outer-rainband region of TCs, with enhanced precipitation occurring along the propagation path. The propagation signal in overland DPP events initiates later (06–09 LST) than open-ocean DPP events, which typically initiate at 03–06 LST. This difference is attributed to the presence of two distinct initiation times for the overland DPP signal: early morning (00–06 LST) and near noon (09–15 LST). The early morning initiation is primarily driven by convection-induced inertial gravity waves, which result from the nocturnal long-wave radiative cooling enhancement of inner-core convection in strong TCs. In contrast, overland DPPs initiated near noon are typically produced by weak TCs where the inner-core convection peaks at noon in response to the short-wave radiative heating. As a result, TCs during overland DPP events tend to produce wider rainfall distribution and more extreme rainfall, even in landfalling weak TCs.

Simulations and predictions of evapotranspiration (ET) over the Tibetan Plateau (TP) are typically affected by both model uncertainties and the accuracy of the initial conditions. In this study, a minimization technique and a data assimilation method are first applied to reduce the impact of initial errors on the uncertainties in the ET simulation over the TP. Second, the conditional nonlinear optimal parameter perturbation ensemble prediction (CNOP-PEP) method is employed to evaluate the simulation and forecast performances with imperfect model physical parameters based on the reduction of impact of initial errors. The main features are the combined contribution for ensemble prediction of ET over the TP through the perturbed parameter and the optimization and assimilation of the initial conditions. The numerical results show that the minimization technique and the data assimilation method are useful for reducing uncertainties in ET over the TP due to errors of initial values. Moreover, the ensemble prediction of ET over the TP with assimilated initial conditions is better than that without assimilated initial conditions using the CNOP-PEP method. Moreover, the ensemble prediction of ET over the TP using the CNOP-PEP method (17.3%) is better than that using traditional methods, such as the one-at-a-time (OAT) method (2.0%) and the stochastically perturbed parametrization (SPP) method (10.6%) with and without assimilated initial conditions. And, the absolute errors using anomaly-based metrics by removing the climatological mean are 71.80, 101.06, and 105.52 mm/year using the CNOP-PEP, OAT and SPP methods.

This study presents a climatological analysis of cold air intrusions over the Maritime Continent using atmospheric reanalysis data. We consider the Asian-Australian monsoon as a cold air intrusion from the winter hemisphere into the Maritime Continent and quantify the amount and flux of cold air by an isentropic analysis method. This approach enables a systematic assessment of the cold air transport along the monsoon routes and a consistent analysis of cold air intrusions associated with seasonally reversing monsoons. During the East Asian winter monsoon, cold air covers the western Maritime Continent and flows from the South China Sea throughout the Java Sea to the north of the Australian continent with high flux of cold air. Cold air enters the Maritime Continent partly from the southeast of the Philippine Islands and from the Timor Sea. During the Australian winter monsoon, cold air inflows from the Coral Sea through the sea between the Australian continent and New Guinea Island and accumulates in the southern Maritime Continent due to the topographic barriers of the islands. Cold air outflowing through the islands to the Java Sea and the Pacific Ocean induces cross-equatorial flows. Cold air transport over the Coral Sea in August is approximately 1.7 times higher than that over the South China Sea in January. The duration period of cold air inflow associated with the Australian winter monsoon is 1.5 times longer than that associated with the East Asian winter monsoon.

Oceans are the primary source of atmospheric bromoform (CHBr₃) and dibromomethane (CH₂Br₂), with implications for tropospheric chemistry and the ozone layer. Nevertheless, socio-economic developments are changing the oceans' biological characteristics, which could impact the magnitude and distribution of oceanic emissions in the future. In this work, we couple a machine learning (ML) framework to the Community Earth System Model (CESM) data of the Coupled Model Intercomparison Project (CMIP) and estimate the monthly sea surface concentrations of CHBr₃ and CH₂Br₂ between 2015 and 2100, under different climate change scenarios. We use these estimates to run CESM version 2 (CESM2), with comprehensive halogen chemistry, and calculate present-day global emissions of 269–271 Gg Br and 61–65 Gg Br for CHBr₃ and CH₂Br₂, respectively, based on different scenarios. Furthermore, we project 14%–40% and 8%–23% increases for global mean emissions of CHBr₃ and CH₂Br₂, respectively, by 2100; where more stringent scenarios lead to smaller enhancements. Regionally, there are uncertainties within the magnitudes and signs of the changes that depend on the climate scenarios considered. Nevertheless, the largest enhancements, under all scenarios, were predicted over the western tropical Pacific Ocean, tropical Atlantic Ocean, and Indian Ocean. We attribute these changes primarily to biological parameters rather than physical parameters. These changes project a 0.47–1.13 ppt Br increase from the combined source gases (CHBr₃ and CH₂Br₂) in the upper troposphere by 2100, which could impact the stratospheric ozone budget. Overall, this study highlights the far-reaching influence of human activities on natural oceanic emissions and atmospheric chemistry.