Asia-Pacific Journal of Atmospheric Sciences最新文献

From 31 July to 2 August 2022, a successive three-day gust front (GF) event occurred over southeastern coastal China, as clearly observed in satellite and radar data. Such successive GF events were uncommon in this region of complex hilly terrain. This study employed multi-source observations and reanalysis data to conduct observational and mechanistic analyses of these events. The GFs originated primarily from multicellular storms, with surface stations recording characteristic abrupt temperature drops and relative humidity increases. Results showed that the GF event was closely linked to specific synoptic conditions during the northward movement of Typhoon “Trases”, which established an environment conducive to parent storm and GF development. Composite analysis of non-GF days preceding and following the event indicated that GF occurrence was inhibited regardless of whether the typhoon was positioned south or north of the region. Conversely, the typhoon’s remote enhancement of land–sea circulation played an essential role in GF formation by moistening the boundary layer—an effect notably absent on non-GF days. Objective classification of mid-to-low-level circulation patterns from 2018 to 2022 (July–August) using T-mode principal component analysis with oblique rotation and self-organizing map showed that GF days corresponded to a circulation pattern occurring on only 2.9% of the total days, confirming the rarity of such synoptic configurations.

Cold surges over South Korea are among the most extreme winter weather events, typically triggered by wave-train propagation or subarctic blocking in the upper troposphere. A widely used classification framework categorizes cold surges based on the upper-tropospheric circulation pattern on the day of onset. To overcome the limitation of this framework, cold surge indices are newly developed by considering the spatiotemporal evolution of circulation features characteristic of each cold surge type. During the pre-onset period (Day − 3 to 0), the daily geopotential height anomalies at 300 hPa are projected onto wave-train and blocking features in the dynamically defined domains, and new wave-train index (WI_n) and blocking index (BI_n) are developed based on this projection. Compared to the original scheme, the newly developed indices more accurately represent the dynamical evolution of upper-tropospheric circulation patterns, significantly reducing the number of Mixed-type cold surges (MT) from 115 to 77 and Unclassified cold surges from 64 to 18. Furthermore, thermodynamic analysis reveals that blocking-type cold surges (BT) exhibit longer duration, colder temperature anomalies, and greater intensity than wave-train-type cold surges (WT), consistent with their quasi-stationary blocking structure. By incorporating the evolution of circulation features before onset, the new indices offer clearer dynamical distinctions between cold surge types and provide a robust, physically interpretable foundation for their improved diagnosis and prediction.

The research reveals the origins and persistence of the extremely heavy rainstorm in North China in July 2023 (known as the “23.7” rainstorm). Unlike previous research, it applies scale separation and an advanced energy diagnostic equation to analyze energy transformations among multi-scale weather systems, highlighting their collective impact. Utilizing hourly rainfall data from over 70,000 national stations, along with daily global Final Analysis Data (FNL 1 º × 1 º) from NCEP/NCAR, the study employs Barnes bandpass filtering for atmospheric field separation and an energy equation to diagnose energy conversions. It finds that the “23.7” rainstorm is a complex, multi-scale phenomenon, with the synoptic to meso-α scales scales playing a pivotal role. The storm’s sustenance mechanism resembles the conditional instability of second kind (named R-CISK), focusing on upper tropospheric westerly jet divergence that triggers mid-tropospheric ascent, diverging from CISK’s emphasis on boundary layer friction. This initiates cumulus convection, followed by lower tropospheric jet convergence and typhoon-induced low-pressure trough interaction, uplifting lower layer air and coupling with mid-to-upper level convection. The energy diagnosis shows that large scale and synoptic scale systems are the primary energy sources. The kinetic energy interplay and conversion of buoyancy work and baroclinic energy are the main drivers of energy transformation, essential for storm development. These insights and methods enhance traditional rainstorm models and diagnostic techniques, offering valuable references for future regional heavy rainstorm forecasting and analysis.

The Korean Integrated Model (KIM) is a global numerical weather prediction model that uses the spectral element method on a (quasi-) uniform-resolution cubed-sphere grid. However, to investigate high-resolution prediction performance in the domain of interest, global high-resolution experiments must be considered. These experiments incur a significant computational burden owing to the increased number of grid points and the need for temporal integration at finer time steps. To address this issue, we implemented a stretched variable-resolution grid in the KIM, based on the Schmidt transformation. This approach allows for high-resolution effects in the region of interest while using a coarser grid elsewhere. With the stretched global grid, grid sizes are seamlessly scaled between high and low resolutions.

In this study, we evaluated the forecasting accuracy and computational efficiency of the variable-resolution KIM and compared these metrics with those of the corresponding uniform-resolution KIM. In the higher-resolution target region, the forecast skill of the variable-resolution grid was similar to that of the 8-km high-resolution uniform grid and even outperformed the 25-km reference-resolution uniform grid in the KIM. Furthermore, the variable-resolution configuration offers a significant improvement in computational efficiency, reducing the total 3-day forecast run time by approximately 88% compared with that of the high-resolution configuration with a uniform grid.

This study investigates observation error adjustment strategies for three recent Global Navigation Satellite System Radio Occultation (GNSS RO) datasets (GRACE-D, Sentinel-6 A, and SPIRE) within the Korean Integrated Model (KIM), aiming to mitigate forecast degradation of mid-tropospheric geopotential height. Experiments were conducted using a low-resolution KIM (July-August 2022), with verification against European Centre for Medium-Range Weather Forecasts (ECMWF) Integrated Forecasting System (IFS) analyses. The standard GNSS RO error model (20% observation error at the surface and 1% at 10 km) was used as the control (EXP_ctl). Two adjustment strategies were tested: EXP_zfrac, which increased the lowest-level error to 40%, thereby reducing the influence below 10 km; and EXP_obserr, which applied a uniform inflation factor (√2, from 2.2 to 3.1) across all levels to account for doubled observation counts. Relative to the Baseline, EXP_ctl degraded the global 500 hPa geopotential height analysis by 4.01%, while EXP_zfrac and EXP_obserr improved performance by 2.01% and 2.28%, respectively. For 5-day forecasts of Northern Hemisphere 500 hPa geopotential height, EXP_ctl degraded performance by 0.11%, while EXP_zfrac and EXP_obserr demonstrated improvements of 0.74% and 0.99%, respectively. These findings demonstrate that uniform observation error inflation, which reflects increased data density, is more effective for KIM than selective layer-specific error adjustments.

Severe convective storms provide a significant weather threat in Northern Thailand, especially during the pre-monsoon season (March–May), however a comprehensive storm database has been unavailable. The absence of comprehensive records complicates the research of storm features, the validation of numerical weather models, and the enhancement of radar-based detection methods. To address this deficiency, we established a spatial-temporal database that integrates official report records with crowdsourced social media data, documenting 259 distinct storm days at the regional level and 478 documented instances at the province level across a decade (2015–2024). Temporal study indicated a distinct seasonal pattern, characterized by an escalation in storm frequency from early March to late April, followed by a reduction in late May. Interannual variability was apparent, with 2018 exhibiting anomalously low activity (6 storm days) in contrast to peak years in 2020–2021 (33–35 days). Statistical analysis revealed substantial disparities in storm occurrences between early and late March (p = 0.0073), while Mann-Whitney U tests demonstrated that 2018 had significantly less storms than the following years (p < 0.05). The majority of storms impacted individual provinces (141 occurrences), with a diminishing frequency as the spatial expanse expanded. GIS-generated spatial anomaly maps indicated provincial variations in storm frequency compared to the decadal average. An investigation of atmospheric sounding from ten exceptional multi-province occurrences revealed elevated CAPE values (1215–1876 J/kg) and negative Lifted Index values, indicating conditions favorable to severe convective development. The database differentiates between hail-producing and non-hail-producing storms, facilitating the detection of unique meteorological variables linked to each category. This research establishes a systematic framework for storm recording in areas with limited observational networks, hence enhancing early warning systems, disaster preparedness, and the validation of radar-based storm detection. Future applications encompass comparative research of hail and non-hail storm situations, as well as integration with Thailand’s national radar mosaic to improve severe storm identification.

KMA has launched a project to produce global ocean reanalysis dataset from 1993 to 2020 by using KMA operational system– Global Ocean Data Assimilation and Prediction System2-ReAnalysis (GODAPS2-RA). We test-run GODAPS2-RA for recent five years (2016-2020) before the project formally initiated. The reason for prioritizing this period is that the year of Global Seasonal Forecasting System (GloSea6) hindcast is only available until 2016, highlighting the immediate necessity to extend to more recent years. In this study, we analyzed this preliminary experiment and examined whether GODAPS2-RA is properly implemented. It is found that the differences of GODAPS2-RA against the other validation dataset are within acceptable range. Compared with KMA operation system, GODAPS2-RA shows the reduction of observation innovation for most variables, signifying an improvement. However, the number of sub-surface temperature and salinity profile observations assimilated in the GODAPS2-RA is less than that in the operational run, consequently it turns out that further examination on the collection and processing procedure of profile data is necessary. In addition, the experimental GloSea6 hindcast using initial conditions produced by GODAPS2-RA is further tested. The results reveal that there is little difference between this experiment and existing operational GloSea6 hindcast, which indicating that GODAPS2-RA can be applied to the operational GloSea6 hindcast as oceanic initial conditions. By supplementing and preprocessing observations more appropriately and by further investigating the preliminary results, we will improve GODAPS2-RA to make it perform better, and finally official production will begin for releasing to publics.

This study investigates the statistical and dynamical relationship between the El Niño-Southern Oscillation (ENSO) and winter surface air temperature (SAT) in Korea, using station observations and reanalysis data from 1920 to 2023. Historical SAT records are compiled from 7, 14, and 60 stations for 1920–1959, 1960–1972, and 1973–2023, respectively. Despite the statistically significant correlation (r = 0.28) between the Niño 3.4 index and winter SAT in Korea, ENSO alone explains only a limited amount of interannual variability. Classifying the SAT anomalies according to the ENSO phase (i.e., warm for El Niño and cold for La Niña), the Niño 3.4 index yields binary-classification accuracy of 0.68; however, about half of the correctly classified anomalies fall within ±0.5 standard deviations from the climatological mean. Also, composite circulation patterns based on ENSO phases differ structurally from those associated with actual SAT anomalies. A multiple linear regression analysis reveals that mid- to high-latitude climate variables, such as the East Asian winter monsoon, western North Pacific (WNP) sea surface temperatures (SSTs), and the Arctic Oscillation, exhibit stronger and more stable associations with Korean winter SAT than ENSO. Especially WNP SSTs show the largest standardized regression coefficients (> 5.0) to indicate their dominant role. This study suggests the need for integrated forecasting approaches that consider both the tropical and extratropical influences, rather than relying solely on ENSO signals for improving the accuracy of seasonal climate predictions and supporting adaptive risk management strategies for wintertime extremes in the Korean Peninsula.

The atmospheric aerosol properties near Iranshahr City in Southwest Baluchestan, Iran, were investigated using handheld Calitoo sunphotometer measurements, space-borne CALIPSO-CALIOP lidar recordings, and synoptic station data. The findings indicate the prevalence of dust aerosols throughout the year, with a pronounced presence during the summer season. The aerosol optical depth (AOD), as determined by Calitoo measurements at 540 nm between April and October 2022, peaked in July with a monthly-mean value of 0.61 ± 0.14. During this month, the Angstrom exponent reached 0.43 ± 0.19, providing further evidence of severe dust storm activities in the region. An analysis of the level 2 aerosol profile data obtained from CALIOP measurements during 2006-2023 has been presented. The monthly-averaged AOD at 532 nm obtained from CALIOP data has a bell-shaped distribution with a peak in July (0.92 ± 0.39). These results are in agreement with those measured by Calitoo. The vertical profile of the particulate depolarization ratio (PDR) at 532 nm confirms the dominance of dust at all altitudes. Moreover, the extinction coefficient spike near the surface explains why horizontal visibility decreases during dust events. Consistent with previous studies, our findings identify the dry bed of Hamun Lakes as the primary dust source for the Baluchestan region. Additionally, the dry bed of the Jazmurian ephemeral lake and parts of the Lut Desert appear to be other major dust sources, particularly affecting the western parts of Baluchestan, Iran. These latter sources should be studied in more detail.

Tropical cyclones (TCs) in the tropical western North Pacific and the east Asia subtropical westerly jet (EASWJ) are important circulation systems in the east Asia–western north Pacific region, and interactions exist between them. Through statistical analysis and numerical experiments, this study delved into the influence of thermal remote disturbances induced by TC on the EASWJ, and the mechanism has also been analyzed. Statistical results show that TC activities in the tropical western North Pacific can cause anomalous westerlies near Japan, and the EASWJ axis in the corresponding area shifts significantly toward the high-value area of anomalous westerlies caused by TCs. Results of numerical experiments with TC Maria verified the results of the statistical analysis, and further revealed that TC Maria, locating in the tropical western North Pacific, induced anomalous cold advection in the vicinity of mid-latitude Japan. This, in turn, caused anomalous descent, ultimately leading to both anomalous adiabatic heating and anomalous latent heat absorption. Consequently, these changes altered the temperature distribution in the East Asian mid-latitudes and resulted in anomalous meridional temperature gradients. Under the constraint of thermal wind balance, the zonal wind over East Asian mid-latitudes changed accordingly, causing a shift in the location of the high-value westerly, which corresponds to the anomalous meridional movement of the EASWJ axis. The findings of this study indicate that TCs can affect EASWJ by exciting remote thermal disturbances.