Asia-Pacific Journal of Atmospheric Sciences最新文献

Variations in the wind speed intensity significantly impact evapotranspiration, water cycle processes, air quality and wind utilization. Previous studies have focused primarily on changes in mean wind speed, with little research on variations in different wind speed intensities. In this paper, we defined five wind speed indices to quantify the changes in different wind speed intensities and analyzed their associations with atmospheric circulation based on daily wind speed data collected from 601 meteorological stations across China from 1960 to 2018. The wind speed indices we defined include the annual mean wind speed, the annual maximum daily mean wind speed, the number of heavy wind days, the number of gentle breeze days and the number of light breeze days. The results showed that from 1960 to 2018, the annual mean wind speed, the annual maximum daily mean wind speed, the number of heavy wind days and the number of gentle breeze days exhibited significant decreasing trends (P < 0.05). The number of light breeze days exhibited a significant increasing trend (P < 0.001) in China during the same period. Large-scale atmospheric circulation patterns were one of the main factors affecting the changes in wind speed intensity. The Arctic Oscillation (AO) and the West Pacific Subtropical High Intensity Index (WPSHI) were significantly negatively correlated with the annual mean wind speed, the annual maximum daily mean wind speed, the number of heavy wind days and the number of gentle breeze days (P < 0.01), and the Asian Polar Vortex Intensity Index (APVI) was extremely significantly positively correlated with these four wind speed indices (P < 0.001). This suggests that monitoring and analyzing these atmospheric circulation indices can enable more accurate predictions of wind speed. These findings will provide information for climate change forecast, air pollution risk assessments and wind energy utilization.

Exponential-random vertical overlap of clouds is applied for radiative processes in a research version of the Korean Integrated Model (KIM) to replace the maximum-random vertical overlap of clouds. The cloud radiative effect (CRE) increases overall when the exponential-random overlap is used. This is because vertically continuous clouds, which are assumed to overlap maximally under the maximum-random overlap assumption, can be relaxed to random overlap depending on the vertical distance between cloud layers and the specified decorrelation length of clouds. CRE is more enhanced by considering the latitudinal dependency of cloud decorrelation length based on previous observational studies. This alleviates biases in CRE, which is underestimated overall, except in the low latitudes where the CRE is overestimated in the present simulations. The interaction between radiative and convective processes plays a role in decreasing CRE over the tropical western Pacific region, where strong convections develop, although the direct impact of applying the exponential-random overlap is to decrease the vertical overlap between ice clouds. The simulation of temperature in the lower troposphere is improved owing to the changes in cloud overlap. The warm bias over the Eurasian continent, in particular, is alleviated as more shortwave fluxes are reflected due to increased CRE.

The Weather Research and Forecasting (WRF) model has numerous model parameters that significantly affect rainfall forecasts. However, the multitude of parameters makes it challenging to identify which of these are critical for rainfall forecasting and optimization. This study utilizes the Morris One-At-a-Time (MOAT) Global Sensitivity Analysis (GSA) to ascertain the sensitivity of the simulated rainfall and other key atmospheric variables to 23 tunable model parameters across seven physics schemes in the WRF model. The MOAT mean and standard deviation were used as sensitivity measures and calculated for two Tropical Cyclone (TC)-enhanced southwest monsoon events in August 2012 and 2013 that resulted in catastrophic flooding over Metro Manila, Philippines. Results show that of the 23 model parameters, the ones more critically important to simulating rainfall are parameters that are related to cumulus schemes such as the multiplier for downdraft mass flux rate (P3), multiplier for entrainment mass flux rate (P4), starting height of downdraft over updraft source layer (P4), and mean consumption time of convective available potential energy (P6). To investigate the optimum parameter for the simulation of rainfall for each of the two events, the root mean square error (RMSE) is computed between the simulated rainfall over Metro Manila and observed data from the Global Satellite Mapping of Precipitation (GSMaP). The best performing set of parameters was able to reduce the RMSE of rainfall over Metro Manila by about 42% and 27% for the 2012 and 2013 enhanced monsoon events, respectively, relative to the default runs. For the first time, this study provides insight into which model parameters in the WRF model are critically important to the simulation of enhanced monsoon events. The results of this study may serve as a basis for future optimization studies of extreme weather events over the Philippines.

We investigated the microphysical characteristics of low-level Arctic clouds using four cloud microphysics parameterization schemes (Morrison, WDM6, NSSL, and P3) implemented in the Polar-optimized Weather Research and Forecasting (PWRF) model. Our assessment was based on a comparison with data collected during the Arctic Cloud Observations Using Airborne Measurements during the Polar Day (ACLOUD) experiment, which occurred near Svalbard between May and June 2017. During the ACLOUD campaign, a substantial number of clouds were observed, primarily influenced by adiabatic motions and sensible/latent heat fluxes that led to air masses warming up by 4 °C as they traversed over the sea ice and ocean transition zone. Among the parameterization schemes tested, the Morrison and WDM6 schemes demonstrated superior performance overall, showing frequency bias (FB) values closer to 1 (1.07 and 1.13) and high log-odds ratios (0.50 and 0.48) in cloud occurrence predictions, indicating good agreement with observed data. In contrast, the NSSL and P3 schemes exhibited higher FB values (1.30 and 1.56) with lower log-odds ratios (0.17 and 0.16), indicating an overestimation of cloud occurrence. The WDM6 scheme produced higher ice-mixing ratios compared to Morrison and NSSL schemes, while the latter two tended to generate more snow and graupel. The NSSL scheme showed the least bias in simulating ice water content (IWC) in mixed-phase clouds; however, all schemes generally underestimated both liquid water content (LWC) and IWC. Notably, significant deviations in IWC were observed at an altitude of 1.2 km compared to observations, attributed to differences in temperature thresholds for ice formation. This study emphasizes the importance of developing cloud parameterization in the Arctic based on observations to improve the accuracy of estimating cloud impacts on Arctic climate under rapid Arctic warming trends.

For climate risk assessments accurate gridded data sets are needed. An important aspect of such data sets is that they reliably represent the spatial and temporal characteristics of extreme events. This is particularly important for precipitation extreme events which are still not well represented in climate models. Here, we compare South Korean station data with two observation-based gridded data sets (APHRODITE and ERA5-Land) and data from global high-resolution Community Earth System Model (CESM) simulations with an atmospheric resolution of about 25km. We find that the two observation-based data sets have a lower level of the 99th percentile than the station data, but that CESM reproduces extreme events better. Our study provides evidence for an overall historical decrease in very large extreme events in the station data, which is not the case in the two gridded data sets. However, changes in extremes are locally dependent as shown by local quantile regression analysis; where local historical increases in precipitation extremes are statistically significant. The spatial dependence of extreme precipitation events is not well reproduced by the two gridded data sets but well by CESM. The temporal clustering of precipitation extremes is well reproduced by all data sets. Compared to the present day simulation, the CESM simulation of a warmer climate state shows an overall increase in mean precipitation and precipitation extremes and regionally dependent changes in temporal clustering. The model results also provide evidence for a change in spatial dependence in a warmer climate with spatially larger extreme precipitation systems possible. Our results highlight the need to produce better observation-based gridded data sets and also the need to adapt to more intense and frequent extreme precipitation events in the future in South Korea.

We developed a rice paddy model based on Noah land surface model (LSM) considering the standing water layer during the irrigation periods. In the model, we adopted a consistent subcanopy process from thin to thick canopy conditions and considered a small scalar roughness length of the water surface in the rice paddy fields. We evaluated the performance of the model using observations from three rice paddy sites with different leaf area index and water depth in Japan during the growing season. Two simulations were performed in an offline mode: a Noah LSM simulation with saturated soil moisture in the top two soil layers (IRRI) and a rice paddy model simulation (RICE). The average root mean squared errors of ground, sensible, and latent heat fluxes, and first soil layer temperature decreased by 20%, 16%, 17%, and 31%, respectively in the RICE simulation, compared to the IRRI simulation. The better performance of the RICE simulation was attributed to the consideration of the heat storage of the standing water layer during the irrigation periods and the realistic energy partitioning by the single-canopy model during the non-irrigation periods. Two sensitivity tests were performed related to the roughness length of the water and the constant mean water depth. When the small roughness length of the water surface during the irrigation periods was not considered, the subcanopy resistance decreased, which resulted in a cold bias in the daily mean ground and soil temperature and an overestimation of the daily mean latent heat flux under low leaf area index conditions. The use of constant mean water depth in the model did not significantly change simulated surface fluxes and ground and first soil layer temperature, implying that detailed information on temporally changing water depth is less important in the simulation.

The Korean Peninsula frequently experiences localized torrential rainfall (LTR) in the summer. However, on August 8, 2022, a peculiar LTR occurred by the continuous generation of convective clouds within a few hours, numerical weather prediction model was hard to forecast such a high intensity of LTR. This study explores the possibility of uncovering potential precursory signals using remote sensing techniques in both Geostationary Korea Multi-Purpose Satellite 2A (GK2A) and the operational RKSG (Camp Humphreys) Weather Surveillance Radar 88 Doppler (WSR-88D). Using cloud properties from GK2A, cloud top temperature showed a decrease and maintained low values below 220 K 1–1.5 h before the LTR events. However, discerning the exact onset of LTR in already mature stage clouds using only GK2A variables proved challenging. Instead, liquid water content from RKSG sharply increased before the LTR started. Our calculation of the LTR potential from a combination of GK2A and RKSG cloud properties shows a more accurate precursory signal of LTR than from GK2A cloud properties solely or RKSG either. This study highlights the synergistic benefits of combining geostationary satellite and radar observations to understand and predict early precursors of LTR events.

The zonal gradients in sea surface temperature and convective heating across the tropical Pacific play a pivotal role in setting the weather and climate patterns globally. Under global warming, the current generation of climate models predict that the zonal gradients will decrease, but the trajectory of the observed trends is the opposite. Theories supporting either of the two projections exist, but there are many relevant processes whose net effect is unclear. In this study, a global constraint – the maximum material entropy production (maxMEP) hypothesis—is considered to help close the gap. The climate system considered here is comprised of a one-layer atmosphere and surface in six regions that represent the western tropical Pacific, eastern tropical Pacific, northern and southern midlatitudes, and northern and southern polar regions. The model conserves energy but does not explicitly include dynamics. The model input is observation-based radiative parameters. The radiative effect of greenhouse gas (GHG) loading is mimicked by prescribing increases in the longwave absorptivity (epsilon). The model solutions predict that zonal contrasts in surface temperature, convective heat flux, and surface pressure increase with increasing (epsilon). While maxMEP solutions in general cannot provide a definite answer to the problem, these model results strengthen the possibility that the trajectory of the observed trend reflects the response to increasing GHG loading in the atmosphere.

High concentration Asian Dust Storms (ADSs) significantly impact health and economic activities by increasing atmospheric particulate matter. This study aims to understand the mechanisms, migration paths, and activity patterns of ADSs, which are essential for issuing timely warnings and aiding in atmospheric environment research. Using unsupervised learning methods, including the principal component analysis (PCA) and K-means clustering, we analyzed the mega ADS events from 2002 to 2022 based on the ECMWF reanalysis (ERA5) data. We identified key meteorological factors, including geopotential height and temperature at lower levels (800–1000 hPa), and classified synoptic patterns associated to the mega ADSs during the origination stages in the source regions and the peak concentration stages in Korea. Findings highlight that, during the origination stage, enhanced troughs and high temperature at low levels are primary factors affecting atmospheric instability and consequently strong updrafts that lift dust particles, combined with high planetary boundary layer heights, ranging 1400─2950 m, and strong pressure gradients at the source regions. It is further noted that low-level temperature and specific humidity are critical during the peak stages in Korea, with contributions from higher atmospheric levels. Variability in atmospheric conditions among different patterns affects dust concentrations, with certain patterns experiencing sharp declines in humidity leading to peak dust events. Noting also that the mega ADSs occur under specific synoptic patterns classified at both the origination stages and the peak concentration stages in Korea, this comprehensive analysis provides crucial insights into the dynamics and prediction of mega ADSs in Korea.