Asia-Pacific Journal of Atmospheric Sciences最新文献

Convective boundary layer height (CBLH) is an essential parameter of the boundary layer climatology, which is associated with the intensity of turbulence mixing. Radiosonde data derived from the "Sino-Japanese Center for Cooperation on Meteorological Disasters" (JICA) during three intensive observation periods in 2008 in Gerze (32.17°N, 84.03°E) were used to verify the applicability of ERA5 reanalysis data in the Tibetan Plateau (TP). Thus, the spatiotemporal variations in the CBLH (boundary layer height from 08:00 to 20:00) and the contributions of the influencing factors during different monsoon seasons in various regions of the TP were investigated using the ERA5 data (1983–2022). The results indicate that variable characteristics in the CBLH derived from radiosonde data are basically consistent with that from ERA5 during the three observation periods. The monthly-averaged CBLH showed only one peak in the eastern region during the full development of the CBL (14:00–18:00), while two peaks were shown in the western region. The CBLH over the TP exhibited a decreasing trend during the monsoon period while the CBLH in the eastern region showed an increasing trend during the post-monsoon period. Wind speed at 10 m height was a key factor influencing the CBLH during the non-monsoon period, while surface sensible heat flux considerably influenced variations in the CBLH during the monsoon period.

September is widely considered to be the final month of the monsoon season on the Indian subcontinent. Precipitation levels during this month exert a pivotal influence on the duration of monsoon rainfall, with the potential to substantially impact subsequent dry spells in the region. Consequently, further investigation into the variations in September rainfall is imperative for ensuring social and agricultural security. This study, therefore, examined the possible role of the South Asian high (SAH) modulating Indian rainfall in September. The study found that the SAH was generally stable around South Asia in September, prior to its retreat over the ocean. The SAH was found to be weaker and shifted in a southeastward direction in September compared to its summer mean. A strong SAH in September was often concomitant with a delayed withdrawal of Indian summer monsoon (ISM) rainfall and vice versa, with positive rainfall anomalies primarily manifesting over central-northeastern, west-central, and peninsular India. The enhanced SAH was accompanied by stronger westerly and easterly jet streams, respectively, over the southern Caspian Sea and northwest India in the upper troposphere. A notable upper-tropospheric anticyclonic circulation has been observed over the western Tibetan Plateau. Additionally, a significant lower-tropospheric cyclonic circulation has been observed over India, accompanied by an enhanced Somali cross-equatorial flow. The associated anomalous westerly anomaly over southern India and southeasterly anomaly over northern India can transport abundant moisture over most of India. Consequently, there is a tendency for substantial rainfall tends to occur in conjunction with an enhanced SAH.

Convectively induced turbulence (CIT) is a severe aviation hazard. It is challenging to forecast CIT because low-resolution models cannot explicitly resolve convective motions at kilometer scales. In this study, we used the Model for Prediction Across Scales (MPAS) to simulate CIT cases with convection-permitting resolution ((sim )1 km) in the region of the CIT events and coarse resolution in other parts of the globe. We developed a method to estimate the eddy dissipation rate (EDR) using the resolved wind field of the MPAS simulations. The method is based on explicit filtering and reconstruction in the turbulence modeling for large-eddy simulations (LES). It estimates turbulence kinetic energy (TKE), which is then used to derive EDR. The new method produces different turbulence distribution and intensity than previous methods based on second-order structure functions and convective gravity wave drag, with higher accuracy and better correlation with observations for CIT cases tested in this study. The 1-km resolution simulation generates more accurate EDR and improves spatial patterns, but it is computationally demanding. The 3-km resolution can get benefits from reasonable accuracy and affordable computational cost. Because convection-permitting resolutions are in the gray zone for simulating convection, we evaluated the sensitivity of the prediction to the variations in physical and numerical schemes. Varying cumulus convection parameterization and monotonicity of numerical schemes are identified as practical approaches to generate beneficial ensemble spread. However, the physical perturbation-based ensemble has limitations, and initial condition perturbations are still necessary to encompass uncertainties in the development of convection.

A new COllaborative Carbon Column Observing Network (COCCON) site has been established in South Korea to monitor greenhouse gases (GHGs) effectively. This study focuses on the calibration of the COCCON observing instrument through precise measurements of the instrumental line shape (ILS) parameters and comparison with TCCON measurements. The COCCON network employs Bruker's EM27/SUN mobile Fourier transform infrared spectrometer (mFTIR), requiring validation against data from high-resolution (HR-FTIR) instruments. To achieve this, we compared data from the mFTIR with Bruker's IFS 125HR HR-FTIR to derive an instrument-specific calibration factor. Two ILS values were obtained by analyzing the water vapor spectrum using the open path (OP) method and the C₂H₂ Gas-filled cell (GFC) spectrum. The ILS measurements indicated a modulation efficiency amplitude (MEA) difference of 0.712% between the GFC and OP methods, with values of (0.982 ± 0.005) and (0.975 ± 0.008), respectively. Notably, a comparison of the XGas values derived from both sets of ILS parameters revealed a high degree of consistency, as indicated by slopes close to 1, suggesting that the choice of ILS parameters had minimal impact on the accuracy of XGas retrieval. In this study, a 0.82% increase in the MEA value led to increases of 0.17% in XCO₂, 0.09% in XCH₄, 0.13% in XCH₄_S5P, and 0.14% in XCO concentrations. Furthermore, seasonal variations were observed in the mFTIR measurements for XCO₂, XCH₄, and XCO. The highest XCO₂ value recorded was 427.82 ± 0.56 ppmv in April 2024, while the lowest monthly average of 415.23 ± 0.58 ppmv was observed in September 2023. The highest XCH₄ concentration was recorded in September 2024 at 1.966 ± 0.021 ppmv, while the lowest occurred in March 2024, with a value of 1.917 ± 0.016 ppmv. The highest XCO concentration was observed in spring, reaching 0.114 ± 0.014 ppmv in March 2024, while the lowest was recorded in fall at 0.102 ± 0.011 ppmv in September 2024. Additionally, the mFTIR measurements were compared to those obtained from HR-FTIR to evaluate the compatibility between the COCCON and TCCON measurement methods. Results indicated a strong correlation between the two measurement techniques, with instrument-specific calibration factors ranging from 0.9884 for XCO to 1.0017 for XH₂O. These results demonstrate that the mFTIR is ready for use in measurements at the COCCON site and for measurement campaigns in South Korea.

Typical snowfall structure over the coastal mountainous region of the Korean Peninsula is investigated. East coast-type snowfall (ET) due to the lake-effect over the East Sea of Korea is dominant for snowfall intensity and duration. The ET can be divided by the high-pressure system over the Gaema Plateau (GH) and the extratropical low-pressure system passing southern part of the Korean Peninsula in addition to the GH pattern (GHSL). Composite analysis showed that the GHSL can allow a greater inflow of the snowfall from the sea into the land than the GH. The key factors for snowfall structure are 1) the wind-turning layer (WTL), which is the transition level from the lower-level easterly to the upper-level westerly; 2) vertical wind shear suppressing updrafts near the WTL and 3) the Froude number (Fr), which determines the snowfall penetration beyond the mountain. A higher WTL height indicates a deeper easterly layer, indicating favorable conditions for inland snowfall penetration. The strong vertical wind shear plays a role of suppressed updrafts near the WTL via downward momentum transport. It is presented that updraft limitation is mostly exerted by the wind shear. Fr indicates whether the weather system is blocked or unblocked by the mountains. It is shown that the larger Fr generally increases with height, which means that snow systems or flows near the mountain tops can easily to overcome the topography. It is shown that both dynamic and thermodynamic factors are important for understanding and predicting the structure and regions of snowfall.

This case study presents a thorough investigation of the environmental setup that led to the hail-producing severe storm that impacted the municipality of Norzagaray and City of San Jose Del Monte, including other nearby areas, in the province of Bulacan on the afternoon of August 13, 2021. During this period, 2–5 cm and potentially as large as ~8 cm diameter hail was reported over these locations of Bulacan. For this purpose, the combination of HIMAWARI-8 AHI, PLDN and its flash counts, and meteorological indices; synoptic, thermodynamic, and kinematic indices, calculated from the ERA5 reanalysis are utilized to understand the nature of the hail event. In the morning, the pre-convective environment was comprised by a warm inversion layer that inhibited storm initiation, until the arrival of ample moisture and convective heating in the afternoon. By the afternoon, model sounding analysis revealed that the environment transitioned into uncapped profile with steep low-level lapse rate owing to warm, moist south-westerly wind flow from the Manila Bay in the lower troposphere and north-easterlies aloft crossing the SMMR induced by a weak low-pressure system located in the eastern Philippine Sea, with minimal turning on the wind profile. This promoted low-level convergence within the area of interest and build up of instability. The updraft associated with convectively unstable atmosphere, sufficient cloud-layer bulk shear, and storm nudging at its maturing phase countered entrainment-driven dilution and aided the growth of ice crystals by rapid collection of supercooled cloud liquid particles, which ultimately led to formation of hailstones.

Atmospheric fine particulate matter (PM_2.5) is one of the most significant air pollutants posing a threat to human health and the environment. Investigating its water-soluble ions is both essential and urgent. From January to December 2022, continuous monitoring of PM_2.5and its components was conducted using the Urumqi Atmospheric Environment Super Station. Nine water-soluble ions in PM_2.5 were analyzed using ion chromatography (IC) and other instruments, and their sources were identified through principal component analysis and the PMF model.The results revealed that the annual average PM_2.5 concentration in 2022 was 60.40 μg m⁻³. During both the heating period and the Spring Festival, PM_2.5 levels exceeded 75 μg/m³, while the non-heating period exhibited relatively lower concentrations, averaging 16.88 μg m⁻³. The primary water-soluble ions in PM_2.5 were SO₄²⁻, NH₄⁺, and NO₃⁻, accounting for 24%–55%, 11%–38%, and 10%–25%, respectively. These three ions constituted 90.5% of the total mass concentration of water-soluble anions and cations. The strongest correlations were observed between NH₄⁺ and SO₄²⁻ (r = 0.948) and NH₄⁺ and NO₃⁻ (r = 0.937).The concentrations of secondary inorganic aerosols (SNAs) during the non-heating and heating periods were (31.31 ± 4.95) μg m⁻³ and (79.31 ± 46.31) μg/m³, representing 68.17% and 80.53% of the total water-soluble ions, respectively. Additionally, the metal elements Sb, As, Cd, Pb, and Ti were found to be highly enriched. In summary, the primary sources of water-soluble ions in PM_2.5 originate from secondary aerosol formation, combustion processes, and fugitive dust emissions. Meanwhile, the concentration of PM2.5 components continues to exceed the national secondary air quality standards, necessitating intensified regional environmental governance measures.

In this study, the effects of cloud seeding experiments were analyzed using ensemble numerical modeling. This study focuses on an aircraft seeding experiment conducted over the East Sea near the Yeongdong region of Gangwon Province on October 4, 2022. The weather research and forecasting (WRF) model was applied with parameterization to reflect the effects of hygroscopic seeding materials. The particle size distribution of domestically produced sodium chloride (NaCl) powder was measured and incorporated into the model. Fifty ensemble members (seeding start time legs) were constructed to calculate the probability of seeding-induced precipitation, which was then used to analyze the precipitation efficiency. The results showed that seeding materials were primarily dispersed to the Yeongdong and Yeongseo regions of Gangwon Province due to northeasterly winds. The 6-h (14:00–20:00 KST) cumulative simulated precipitation enhancement was 2.7, 4.4, and 0.9 mm at Bukgangneung (BGN), Gangneungseongsan (GNSS), and Daegwallyeong (DGY), respectively. Analysis of the precipitation ion components confirmed a distinct increase in seeding material-related ions at the BGN site, corresponding to 98% probability of seeding-induced precipitation, as per ensemble-based analysis. Areas with a high probability of seeding-induced precipitation exhibited increased precipitation, with an efficiency of 19.63% (median) and 23.50% (mean) in the 100% probability zones. The highest precipitation efficiency occurred at altitudes of 1000–1200 m above sea level, aligning with the seeding altitude (approximately 1.5 km above sea level) and cloud formation height.

Accurate seasonal climate forecasts are vital for regions like Cambodia's Northern Tonle Sap Basin (NTSB), where agriculture is closely tied to rainfall patterns. While most studies have focused on the TSB, the northern areas, crucial contributors to Cambodia's national food basket, have remained largely unstudied. Here, this gap is addressed by evaluating the performance of 8 state-of-the-art seasonal forecast models from the Copernicus Climate Change Service (C3S) over a 24-year hindcast period (1993–2016). The evaluation is bolstered by ground-based data from 38 agrometeorological stations. Among the models, the Ensemble, the Japan Meteorological Agency (JMA) model, and the European Centre for Medium-Range Weather Forecasts (ECMWF) model emerged as top performers, with the Ensemble particularly excelling in replicating both temporal and spatial precipitation patterns, making it invaluable for agrometeorological applications. The Ensemble demonstrates particularly strong performance in regions such as western Oddar Meanchey and eastern Preah Vihear, where biases are less than 5%. To tailor the Ensemble to the specific climatic and geographic context of the NTSB, we refined it using the Delta Change technique, and this reduced biases even further to < 1%. Our study not only contributes to improving the precision of agrometeorological advisories in a key, but under-researched region, but also sets a precedent for how regional climate forecasting can be enhanced through context-specific model evaluations and corrections. These findings provide a practical framework for supporting resilient agricultural strategies in areas vulnerable to climate change, bridging a critical gap between climate science and agricultural practice.

Using long-term rawinsonde observation data collected from nine stations, we obtained the climatology of low-level jets (LLJs) over Korea, including occurrence frequency, altitude, wind direction, and wind speed. The characteristics (frequency, altitude, speed, direction) of LLJ occurrence on the Korean Peninsula show unique spatiotemporal variations. At stations located on the west coast (Baengnyeongdo and Heuksando), LLJ frequency was high from April to May (approximately 40%) and low in winter (approximately 15%). The station on the northeastern coast (Sokcho) displayed a double-peak pattern in LLJ frequency (approximately 30%), with peaks occurring from April to May and July to August. The inland areas (Gwangju and Osan) showed significantly lower LLJ occurrence frequencies than the coastal stations. In contrast, the southeastern coast (Pohang) and Jeju Island exhibited high occurrence frequencies (30–50%) throughout the year, unlike other stations where LLJs rarely occur even in winter. The altitude at which LLJs primarily occur is low (concentrated below 500 m) at the west coast stations and higher (evenly distributed up to 3 km) at the east coast stations. The wind directions of LLJs at the west coast and inland stations exhibited seasonal changes, being southerly in summer and northerly in winter, which were attributed to monsoon. In contrast, the east coast (Sokcho and Gangneung) consistently showed westerly wind LLJs throughout the year. LLJ wind speeds ranged from 13 to 20 m/s, with the strongest winds occurring in the northern part of the east coast (Sokcho and Gangneung).