Journal of Geophysical Research: Atmospheres最新文献

In lightning research, there is a growing interest in measuring the extremely low frequency (ELF, 3 Hz–3 kHz) electromagnetic (EM) radiation of lightning, as this frequency band can be used to infer various characteristics of lightning discharges that are currently not available from state-of-the-art lightning detection networks. One of these characteristics is the presence of a continuing current (CC), which can last for hundreds of milliseconds and therefore poses an increased risk of physical lightning damage. In this paper, we investigate the modeling capability of the global EM resonance field excited by lightning with a CC using a modified version of a well-known analytical model describing Schumann resonances (SRs) and a full FDTD model. Since analytical models are much faster and require significantly less memory than full numerical models, they are widely used to interpret ELF data. On the other hand, the flexibility of a full numerical model allows the simulation of model configurations that cannot be described by analytical models. To use the two models confidently, it is important to check their consistency for similar configurations. Here, we demonstrate that, for a uniform Earth-ionosphere cavity, the theoretical ELF spectra provided by the analytical and full numerical models show good agreement ∼7(±5) % for both the impulse-like (describing SRs) and exponentially decaying (describing the presence of a CC) current sources. Our results confirm that the analytical model is well suited to interpret ELF measurements for the purpose of studying global lightning activity or individual lightning discharges.

The middle atmosphere circulation in the Korean Integrated Model (KIM) was evaluated at various horizontal resolutions and integration timescales. It was found that the intensities of the polar night jet and summer hemisphere easterly jet are underestimated. Consistent with the zonal wind, a warm (cold) bias in the mesosphere was found in the winter (summer) hemisphere high latitudes. This suggests that the gravity wave drag (GWD) is generally overestimated in KIM. The GWD in the mesosphere is dominated by the frontal GWD in the present simulations. In the frontal GWD parameterization, it was found that waves are launched more frequently and over a wider area at higher horizontal resolutions. To prevent the excessive generation of frontal gravity waves in the parameterization, the frontogenesis threshold used to diagnose the wave-launching region was revised. Instead of a constant threshold across different resolutions, the threshold value was modified to depend on the horizontal grid size so that wave regions are diagnosed similarly regardless of the horizontal resolution. Using a modified threshold decreases the GWD, which induces mesospheric cooling (warming) in the winter (summer) hemisphere high latitudes. As a result, the biases are alleviated in the mesosphere. The responses are extended to the lower stratosphere over an extended medium-range timescale. Lower stratospheric biases are reduced overall, but increase slightly in winter. Since the GWD is reduced to a greater degree at higher resolutions, biases are less reduced at lower resolutions, suggesting that the parameters for scale awareness in the GWD parameterization require further revisions.

Thunderstorm-related activities in the lower atmosphere are usually observed and investigated based on atmospheric weather radars. In this study, the occurrence of thunderstorms has been observed and investigated for the first time by all-sky meteor radars, which are primarily employed in mesospheric/ionospheric observations. By applying the radar interferometry technique to a bi-static all-sky radar system installed on Hainan Island, China, the thunderstorm activities on 5 June 2024 were captured and tracked. The thunderstorm echoes occurred at the altitudes ∼5–20 km along the southern coast of Hainan Island, lasted for ∼2 hr, and migrated northeastward at a speed of ∼15 m/s. The occurrence time, spatial locations in both the horizontal and vertical planes, and evolution of the echoes all corresponded well with the thunderstorm development process confirmed by multiple other kinds of lower-atmospheric observations. The study highlights the extended capability of all-sky radars in investigating lower-atmospheric activities, i.e., thunderstorms, which may favor the investigation on tropospheric-ionospheric coupling process during extreme convective activities in the future.

This study analyzes the thermodynamic effects of atmospheric vertical motion recorded in satellite observations to investigate the processes behind the evolution of tropical convection. These processes, difficult to observe directly, are diagnosed from satellite retrievals of precipitation (P) and atmospheric cloud radiative effect (ACRE) with the aid of a simple theory. It is found that hourly changes of P and ACRE projected onto the P-ACRE plane have a tendency of pointing toward a settling point at LP $��\sim �$ 700 W $��m^{�-�2�}�$ and ACRE $��\sim �$ 75 W $��m^{�-�2�}�$, corresponding to a state of midheavy ascent. These physically driven transitions are counteracted largely by inverse transitions ascribed mainly to the stochastic effects due to a sample density gradient, except where samples are very few. The net effect of these mutually competing transitions is an evolutionary path qualitatively reminiscent of the known Lagrangian life cycle of a traveling convective system, whereas the P-ACRE trajectory stays in the close vicinity of the settling point when spatially averaged over the system.

Vertical air motion is a key factor in many meteorological phenomena, yet measuring it remains challenging. VHF Stratosphere-Troposphere radars, however, provide methods to measure vertical air velocities ($��W�)�$ in the tropo-stratosphere. From Middle and Upper (MU) atmosphere radar data spanning 38 years (1987–2024), we found that the well-known reversal in mean $��W�$ profiles at the height of the jet stream maximum, with negative $��W�$ below 12 km and positive $��W�$ above occurs almost every month, not just in winter as previously reported. We developed a refined model, complementary to the ad-hoc model by Muschinski (1996), https://doi.org/10.1175/1520-0450(1996)035%3C2210:PEOKHI%3E2.0.CO;2, which accounts for power imbalance between symmetric oblique beams. This model confirms that the monthly mean $��W�$ profiles above ∼4.0 km are primarily influenced by contamination from a slight tilt in the scatter diagram, induced by horizontal wind shear. Additionally, our analysis of 30 years of ERA5 reanalysis data indicates that adiabatic ascent/descent along potential temperature surfaces can also cause a $��W�$ reversal in winter, consistent with earlier studies. However, the climatological mean vertical velocities are much weaker than those observed by the MU radar, suggesting that wind shear-induced layer tilt dominates the long-term effect.

Ammonia (NH₃) contributes to fine particle formation and nitrogen deposition. Observations of NH₃ are limited compared to other major anthropogenic pollutants. Here, we explore the relationships between NH₃ and other urban pollutants using measurements collected from the NASA DC-8 aircraft during the Atmospheric Emissions and Reactions Observed from Megacities to Marine Areas (AEROMMA) field campaign in summer 2023. We report on NH₃ abundance, NH_x (NH₃ + NH₄⁺) phase partitioning, enhancement ratios of NH₃ to carbon monoxide (CO), ethyne (C₂H₂), and nitrogen oxides (NO_x/y), and comparisons of enhancement ratios to previous studies. NH₃ abundance and NH_x phase partitioning varied based on city. Between Los Angeles (LA), Chicago, and New York City (NYC), LA had the highest average NH₃ concentration (4.3 ± 4.0 ppb) whereas NYC had the lowest average NH₃ concentration (0.8 ± 0.4 ppb). ΔNH₃:ΔCO ratios ranged from 0.014 ± 0.002 ppb ppb⁻¹ in NYC to 0.037 ± 0.004 in LA. The strong correlations with CO, C₂H₂, and NO_x/y suggest that vehicles are the dominant source of NH₃ during the summer months in these locations. The ΔNH₃:ΔCO ratio over NYC observed during the AEROMMA campaign is consistent with National Emissions Inventory (NEI) emissions for on-road vehicles, whereas the ΔNH₃:ΔCO ratios observed over LA and Chicago during AEROMMA are significantly higher than expected from the NEI on-road emissions.

In the context of global warming, the frequency, intensity, and duration of heatwaves (HWs) are significantly increasing, threatening both human society and natural environment. However, the underlying mechanism of the evolutions of spatiotemporally contiguous summer HWs remains unclear hindering the forecasting of HWs. Therefore, a 3D perspective of HWs was introduced in the present work (i.e., latitude × longitude × time), which can track the horizontal evolution of HWs continuously. Here, our work objectively followed the 3D evolutions of regional summer HWs in China during 1979–2022, and investigated their characteristics, including intensity, duration, and affected area. Among them, the dynamic evolutions of 29 HWs are influenced by compound typhoons and high-pressure systems. Specifically, the high-pressure system affects the triggering and maintenance of regional HWs by enhancing the surface heating and subsidence warming, whereas typhoon tracks can modulate the retreat of regional HWs. Westward-moving typhoons that are influenced by easterly airflows on the southern edge of strong inland high-pressure systems can force the high-pressure system to slowly retreat eastward. This interaction results in a long duration and a large affected area of regional HWs. In contrast, northeastward-moving typhoons quickly cut the weak inland high-pressure system, and then the fragmented high-pressure systems in turn promote the northeastward movement of typhoons, leading to the low intensity, short duration, and small affected area of the regional HWs. These findings systematically reveal the interactions between inland high-pressure systems and typhoon tracks and provide new insights for improving the warning and forecasting skills for the 3D evolution of spatiotemporally contiguous HWs.

Fog is a vital component of montane climates, providing essential moisture for cloud forests and supporting the productivity of high-value crops. This life-sustaining feature, however, is increasingly vulnerable to disruption from rapid urbanization and climate change. To investigate the individual and combined impacts of these two drivers on fog dynamics, we employed a high-resolution weather model and a full factorial design, excluding the effect of aerosols. Our results reveal that urbanization shifts the fog belt upward, reducing fog occurrence in lowlands while enhancing it at mid-elevations. In contrast, warming-induced circulation changes reduce fog in the west of the Central Mountain Range (CMR) but promote fog formation in the east. The complex interplay among local terrain, urbanization, and climate warming resulted in asymmetric changes in mountain fog, which can worsen the water stress differential between the western and eastern flanks of the CMR in Taiwan.

Shallow cumulus (ShCu) influences regional atmospheric circulation and suppresses summer precipitation by modulating surface radiation and energy budgets, yet its macrophysical characteristics and environmental controls remain unclear over the Tibetan Plateau (TP). This study defines ShCu as cumulus with depth ≤2 km and analyzes its properties and environmental drivers using 15 years (2006–2020) of CloudSat and CALIPSO satellite observations, complemented by ERA5 reanalysis and high-resolution topography. ShCu occurs most frequently in summer and during the daytime, with the highest cloud fractions over the western and southeastern TP. It dominates cumulus across all seasons, accounting for approximately three-quarters of the cumulus over the TP annually. Among the environmental drivers, near-surface relative humidity (RH2m) emerges as the primary control, regulating both ShCu occurrence and dominance. Specifically, moderate RH2m levels tend to favor frequent and dominant ShCu by promoting condensation while limiting deep convection, as seen in the western TP year-round. In contrast, highly moist conditions combined with strong updrafts at 500 hPa in the southeastern TP during summer promote cloud deepening into cumulus congestus, yielding lower ShCu cloud fraction (∼8.8%) and dominance (∼0.62) than in the west (∼14.4%, ∼0.80). Furthermore, ShCu over the TP exhibits a lower average cloud base (∼0.83 km) than in surrounding regions, with the lowest values observed over the western TP during winter and nighttime, closely linked to reduced lifting condensation levels. These findings highlight a distinct ShCu regime over the TP and offer insights for improving its parameterization by incorporating terrain complexity and realistic near-surface humidity.