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The Indochina biomass burning (BB) season in springtime has a substantial environmental impact on the surrounding areas in Asia. In this study, we evaluated the environmental impact of a major long-range BB transport event on 19 March 2018 (a flight of the High Altitude and Long Range Research Aircraft (HALO; https://www.halo-spp.de , last access: 14 February 2023) research aircraft, flight F0319) preceded by a minor event on 17 March 2018 (flight F0317). Aircraft data obtained during the campaign in Asia of the Effect of Megacities on the transport and transformation of pollutants on the Regional to Global scales (EMeRGe) were available between 12 March and 7 April 2018. In F0319, results of 1 min mean carbon monoxide (CO), ozone (O 3) , acetone (ACE), acetonitrile (ACN), organic aerosol (OA), and black carbon aerosol (BC) concentrations were up to 312.0, 79.0, 3.0, and 0.6 ppb and 6.4 and 2.5 µ g m -3 , respectively, during the flight, which passed through the BB plume transport layer (BPTL) between the elevation of 2000–4000 m over the East China Sea (ECS). During F0319, the CO, O 3 , ACE, ACN, OA, and BC maximum of the 1 min average concentrations were higher in the BPTL by 109.0, 8.0, 1.0, and 0.3 ppb and 3.0 and 1.3 µ g m -3 compared to flight F0317, respectively. Sulfate aerosol, rather than OA, showed the highest concentration at low altitudes (<1000 m) in both flights F0317 and F0319 resulting from the continental outflow in the ECS. The transport of BB aerosols from Indochina and its impacts on the downstream area were evaluated using a Weather Research Forecasting with Chemistry (WRF-Chem) model. The modeling results tended to overestimate the concentration of the species, with examples being CO (64 ppb), OA (0.3 µ g m -3) , BC (0.2 µ g m -3) , and O 3 (12.5 ppb) in the BPTL. Over the ECS, the simulated BB contribution demonstrated an increasing trend from the lowest values on 17 March 2018 to the highest values on 18 and 19 March 2018 for CO, fine particulate matter (PM 2.5) , OA, BC, hydroxyl radicals (OH), nitrogen oxides (NO x) , total reactive nitrogen (NO y) , and O 3 ; by contrast, the variation of J(O1D) decreased as the BB plume's contribution increased over the ECS. In the lower boundary layer (<1000 m), the BB plume's contribution to most species in the remote downstream areas was <20 %. However, at the BPTL, the contribution of the long-range transported BB plume was as high as 30 %–80 % for most of the species (NO y , NO x , PM 2.5 , BC, OH, O 3 , and CO) over southern China (SC), Taiwan, and the ECS. BB aerosols were identified as a potential source of cloud condensation nuclei, and the simulation results indicated that the transported BB plume had an effect on cloud water formation over SC and the ECS on 19 March 2018. The combination of BB aerosol enhancement with cloud water resulted in a reduction of incoming shortwave radiation at the surface in SC and the ECS by 5 %–7 % and 2 %–4 %, respectively, which potentially has significant regional climate implications. [ABSTRACT FROM AUTHOR]

Numerical weather prediction (NWP) systems are crucial tools in atmospheric science education and weather forecasting, and high-performance computing (HPC) is essential for achieving such science. The goals of NWP systems are to simulate different scales of weather systems for educational purposes or to provide future weather information for operational purposes. Supercomputers have traditionally been used for NWP systems; however, supercomputers are expensive, have high power consumption, and are difficult to maintain and operate. In this study, the Raspberry Pi platform was used to develop an easily maintained high-performance NWP system with low cost and power consumption—the Improved Raspberry Pi WRF (IRPW). With 316 cores, the IRPW had a power consumption of 466 W and a performance of 200 Gflops at full load. IRPW successfully simulated a 48-h forecast with a resolution of 1 km and a domain of 32,000 km2 in 1.6 h. Thus, IRPW could be used in atmospheric science education or for local weather forecasting applications. Moreover, due to its small volume and low power consumption, it could be mounted to a portable weather observation system. [ABSTRACT FROM AUTHOR]

On 4 June 2021, short-duration extreme precipitation occurred in Taipei. Within 2 h, over 200 mm of rainfall accumulated in the Xinyi district. In this study, advanced data assimilation technology (e.g., hybrid data and 3D variations) was incorporated to develop a high-resolution, small-scale (e.g., northern Taiwan) data assimilation forecast system, namely the weather research and forecast-grid statistical interpolation (WRF-GSI) model. The 3D wind field data recorded by the Doppler wind lidar system of Taipei Songshan Airport were assimilated for effective simulation of the extreme precipitation. The results revealed that the extreme rainfall was caused by the interaction between the northeast wind incurred by a front to the north of Taiwan, a humid southerly wind generated by Typhoon Choi-wan, and the regional sea–land breeze circulation. For the Xinyi district, the WRF-GSI_lidar model reported accumulated rainfall 30 mm higher than that in the non-assimilated experiment (WRF-GSI_noDA), indicating that the WRF-GSI model with lidar observation was improved 15% more than the nonassimilated run. [ABSTRACT FROM AUTHOR]

Wind is one of the cleanest renewable energy resources. Through the "Thousand Wind Turbines Project", Taiwan is planning to increase the proportion of power generation from renewable energy and has set a target of 5.7 GW for offshore wind by 2025. The effects of future offshore wind farms (OWFs) over the Taiwan Strait on the atmospheric environment have not been evaluated. This study examined the potential effects of proposed OWFs on the atmospheric environment if the OWFs had existed during Tropical Storm Haitang (2017) by using Weather Research and Forecasting (WRF) model. A small set of ensemble simulations was conducted for studying the sensitivity of the ambient conditions in the region to the wind farm locations, the number and density of the turbines, and the initial time of simulations. Following the landfall and northward movement of Tropical Storm Haitang, a series of complex interactions between the typhoon circulation and the wind farm emerged, including small time slots of wake effect and mountain blocking effect. The combination of these rapidly changing OWFs-related effects contributed to a weak reduction in precipitation (− 1.08 mm) and hub-height wind speed (− 0.25 m s−1), as well as minimal warming near the surface (+ 0.13 °C) over southern Taiwan. [ABSTRACT FROM AUTHOR]

Air pollution is typically at its lowest in Taiwan during summer. The mean concentrations of PM 10 , PM 2.5 , and daytime ozone (08:00–17:00 LST) during summer (June–August) over central Taiwan were 35–40 µ g m -3 , 18–22 µ g m -3 , and 30–42 ppb, respectively, between 2004 and 2019. Sampling analysis revealed that the contribution of organic carbon (OC) to PM 2.5 could have exceeded 30 % in urban and inland mountain sites during July in 2017 and 2018. Frequent episodes of air quality deterioration occur over the western plains of Taiwan when an easterly typhoon circulation interacts with the complex topographic structure of the island. We explored an episode of air quality deterioration that was associated with a typhoon between 15 and 17 July 2018 using the Weather Research Forecasting with Chemistry (WRF-Chem) model. The results indicated that the continual formation of low-pressure systems or typhoons in the area between Taiwan and Luzon island in the Philippines provided a strong easterly ambient flow, which lasted for an extended period between 15 and 17 July. The interaction between the easterly flow and Taiwan's Central Mountain Range (CMR) resulted in stable weather conditions and weak wind speed in western Taiwan during the study period. Numerical modeling also indicated that a lee side vortex easily formed, and the wind direction could have changed from southwesterly to northwesterly over central Taiwan because of the interaction between the typhoon circulation and the CMR. The northwesterly wind coupled with a sea breeze was conducive to the transport of air pollutants from the coastal upstream industrial and urban areas to the inland area. The dynamic process for the wind direction changed given a reasonable explanation for why the observed SO 42- became the major contributor to PM 2.5 during the episode. SO 42- contribution proportions (%) to PM 2.5 at the coastal, urban, and mountain sites were 9.4 µ g m -3 (30.5 %), 12.1 µ g m -3 (29.9 %), and 11.6 µ g m -3 (29.7 %), respectively. Moreover, the variation of the boundary layer height had a strong effect on the concentration level of both PM 2.5 and ozone. The lee vortex and land–sea breeze, as well as the boundary layer development, were the key mechanisms in air pollutant accumulation and transport. As typhoons frequently occur around Taiwan during summer and fall, their effect on the island's air quality merits further research attention. [ABSTRACT FROM AUTHOR]

In July 2018, Super Typhoon Maria moved in the northwestward direction, passed by the northern tip of Taiwan Island, and severely impacted the coasts along Fujian and Zhejiang Provinces, China. In this paper, the storm surge and wind waves induced by Typhoon Maria are numerically simulated using a weather research and forecasting (WRF) model and the wind–surge–wave modeling suite [semi-implicit cross-scale hydroscience integrated system model (SCHISM)—wind wave model III (WWMIII)]. Numerical results are compared against available field measurements, including winds, atmospheric pressures, storm tides, and wave parameters. Using the model results, the significance of waves on modulating storm surges during Typhoon Maria is examined. Wind waves contribute significantly to surge heights in the Taiwan Strait and in nearshore waters. The models are then employed to conduct numerical experiments by reducing the topographic heights of Taiwan to 25% of their original values so as to investigate their effects on wind fields, surges, and currents. From these results, we observe that reduced topography weakens the wind intensity on the eastern side of the island while intensifying the wind on the other side of the island by up to 10 m/s, which is due to the terrain-induced blocking and channeling effects. The scenario with reduced topography also shows elevated surge heights on the right-hand side of typhoon landfalling coasts but slightly attenuated surge in the Taiwan Strait. Storm surge tends to increase the southwestwardly flux via the Taiwan Strait with maximum current velocities increased by approximately 0.5 m/s, compared with the case induced by astronomical tides only. The reduced island topography slightly weakens the southwestwardly current, decreasing maximum flux by approximately 16%, relative to the hindcast simulation using the original island topography. The results in this study indicate that the presence of island influences the propagation of surge wave with elevated surge height and storm-induced flux in the Taiwan Strait, this blocking effect weakens with reduced island topographic heights; meanwhile, the terrain-induced channeling effect, which alters the typhoon circulation and further impacts the surge pattern, is prone to forming in the case of high island topography. [ABSTRACT FROM AUTHOR]

This study compares the performance of 12 regional chemical transport models (CTMs) from the third phase of the Model Inter-Comparison Study for Asia (MICS-Asia III) on simulating the particulate matter (PM) over East Asia (EA) in 2010. The participating models include the Weather Research and Forecasting model coupled with Community Multiscale Air Quality (WRF-CMAQ; v4.7.1 and v5.0.2), the Regional Atmospheric Modeling System coupled with CMAQ (RAMS-CMAQ; v4.7.1 and v5.0.2), the Weather Research and Forecasting model coupled with chemistry (WRF-Chem; v3.6.1 and v3.7.1), Goddard Earth Observing System coupled with chemistry (GEOS-Chem), a non-hydrostatic model coupled with chemistry (NHM-Chem), the Nested Air Quality Prediction Modeling System (NAQPMS) and the NASA-Unified WRF (NU-WRF). This study investigates three model processes as the possible reasons for different model performances on PM. (1) Models perform very differently in the gas–particle conversion of sulfur (S) and oxidized nitrogen (N). The model differences in sulfur oxidation ratio (50 %) are of the same magnitude as that in SO42- concentrations. The gas–particle conversion is one of the main reasons for different model performances on fine mode PM. (2) Models without dust emission modules can perform well on PM 10 at non-dust-affected sites but largely underestimate (up to 50 %) the PM 10 concentrations at dust sites. The implementation of dust emission modules in the models has largely improved the model accuracies at dust sites (reduce model bias to -20 %). However, both the magnitude and distribution of dust pollution are not fully captured. (3) The amounts of modeled depositions vary among models by 75 %, 39 %, 21 % and 38 % for S wet, S dry, N wet and N dry depositions, respectively. Large inter-model differences are found in the washout ratios of wet deposition (at most 170 % in India) and dry deposition velocities (generally 0.3–2 cm s -1 differences over inland regions). [ABSTRACT FROM AUTHOR]

Springtime is the biomass burning (BB) season in Indochina. BB emissions are transported to East Asia and Taiwan at elevations of between 2000 and 4000 m and then transported downward to the near-surface layer when weather conditions are favorable. In this study, a numerical model, the Weather Research Forecast with Chemistry (WRF–Chem) model with tracer simulation was employed to explore the downward transport mechanisms and evaluate their potential effects on the planetary boundary layer (PBL) and near-surface layer during the springtime (Feb.–April) in 2018. Ambient backscatter was measured through LiDAR, aerosol optical depth was measured by MODIS and Himawari-8 satellites and by ground observations from the stations of AERONET. The data were applied to identify the transport mechanisms and evaluate the performance of the model. We summarized the downward transport mechanisms surrounding Taiwan, including the thermal effects of mountain downslope circulations (MDC), frontal secondary circulation (FSC) downward transport, and the mixing of MDC and FSC (MMF). Over Taiwan, the contributions of BB emissions for the MDC to the near-surface layer (<500 m), PBL (<1500 m), and free atmosphere (1500–6000 m) were 0.4%, 4.7%, and >95%, respectively, during springtime in 2018. For the FSC (MMF) mechanisms, the BB contributions to the near-surface layer, PBL, and free atmosphere were 2.5% (3.3%), 15.7% (17.1%), and 84.3% (82.9%), respectively. MMF occurred the most frequently among these three mechanisms and had the largest effect on the near-surface layer and PBL. The downward contributions of BB in different regions, including Taiwan, southern China, and the East China Sea (ECS), were also evaluated. Southern China had the highest value (11.0% [2.1%]) in the PBL (near-surface layer), followed by Taiwan and the ECS (8.2% [1.2%] and 4.5% [0.4%]). Overall, this research fills a gap in our understanding of the mechanisms by which BB emissions are transported to the surface and how they affect air quality in East Asia in general and Taiwan in particular. • We analyzed the BB emissions transport from Indochina to East Asia in general. • The downward transport mechanisms of aloft BB emissions have been explored. • The Impacts of BB emission on the PBL over the study regions were discussed. [ABSTRACT FROM AUTHOR]

This study investigates the effects of horizontal resolution and surface flux formulas on typhoon intensity and structure simulations through the case study of the Super Typhoon Haiyan (2013). Three sets of surface flux formulas in the Weather Research and Forecasting Model were tested using grid spacings of 1, 3, and 6 km. Increased resolution and more reasonable surface flux formulas can both improve typhoon intensity simulation, but their effects on storm structures differ. A combination of a decrease in momentum transfer coefficient and an increase in enthalpy transfer coefficients has greater potential to yield a stronger storm. This positive effect of more reasonable surface flux formulas can be efficiently enhanced when the grid spacing is appropriately reduced to yield an intense and contracted eyewall structure. As the resolution increases, the eyewall becomes more upright and contracts inward. The size of updraft cores in the eyewall shrinks, and the region of downdraft increases; both updraft and downdraft become more intense. As a result, the enhanced convective cores within the eyewall are driven by more intense updrafts within a rather small fraction of the spatial area. This contraction of the eyewall is associated with an upper-level warming process, which may be partly attributed to air detrained from the intense convective cores. This resolution dependence of spatial scale of updrafts is related to the model effective resolution as determined by grid spacing. [ABSTRACT FROM AUTHOR]

ABSTRACT It is difficult and inadequate to use a global model alone for projecting future climate changes in areas such as Taiwan, a complex geographic nature island, due to its coarse resolution. In this study, we have performed dynamic downscaling of Taiwan's climate in the recent past (1979-2003) and climate change projection for the near and distant future (2015-2039 and 2075-2099, respectively) by using the Weather Research Forecasting (WRF) model. The simulation is forced by the Max Plank Institute Hamburg, global model, ECHAM5/MPIOM. Simulation results showed close correlation between fine-resolution downscaling by WRF nested with ECHAM5/MPIOM and the actual observation data for the period 1979-2003. Projection of future climate changes revealed both altitudinal and latitudinal variations in warming trend, with more significant temperature increase in mountain areas than in plain areas towards the end of the 21st century and more obvious warming in the north than in the south of Taiwan. The results obtained in this study can be applied to other regions of similar latitudes and with comparable relief. [ABSTRACT FROM AUTHOR]

In the winter and spring times, the cold continental airs not only often outflow to Taiwan, but also bring air pollutants and dusts. Moreover, springtime happens to be the biomass burning season in Indochina. Under favor weather conditions, the products of biomass burning pollutants could be transported easily to Taiwan and even East Asia. Due to the unique geographic location of Taiwan, that allows us to receive more than just one source in spring. Actually, the complex interactions of these air pollutants and aerosols features in the boundary layer and aloft have resulted in complex characteristics of air pollutants and aerosols distributions in the lower troposphere over Taiwan and East Asia. The impacts are also essential and complex. The project "Effect of Megacities on the transport and transformation of pollutants on the Regional and Global scales (EMeRGe)" aims to improve our knowledge and prediction of the transport and transformation patterns of European and Asian megacities pollutant outflows. In EMeRGe Asia, the composition of the plumes of pollution entering and leaving Asia measured by the new High Altitude and LOng Range (HALO) aircraft research platform. The HALO aircraft performing optimized transects and vertical profiling in Asia during 12 March and 7 April in 2018. To design the measurement of aircraft flight paths and elevations, a high resolution, 9 km, numerical prediction by Weather Research Forecast (WRF) and WRF-Chem models were joined and performed during the campaigns. The EMeRGe Asia has successfully finished more than 10 missions during study period. Model performances and preliminary results will discuss in this meeting. Overall, this series of studies significantly fill the gap of our understanding on air pollutants transformation and transport to Taiwan and East Asia, and show the potential directions of future studies. [ABSTRACT FROM AUTHOR]

Taichung City has become the second largest city in Taiwan, where PM 2.5 and O 3 pollution events occur frequently. The causes of these events urgently need a comprehensive and in-depth study. Therefore, a series of well-planned observation experiments were conducted in the city and its surrounding areas. The first experiment supported the current simulation study of the major causes of air quality deterioration in Central-Western Taiwan. First, we utilized the Weather Research and Forecasting (WRF)/Community Multiscale Air Quality (CMAQ) modeling system to simulate the intensive observation period (IOP) from 31 October 2021 to 22 November 2021. The performance of WRF-CMAQ is well justified by comparison with the observations. Next, we selected the PM 2.5 (particles with aerodynamic diameters equal to or <2.5 μm) pollution event occurring on 3–6 November 2021 for detailed analysis. The results reveal that the meteorological conditions of this event were the prevailing easterly/southeasterly winds blocked by the Central Mountain Range (CMR). Central Taiwan is located on the leeward side of the CMR and embedded in a calm wind area, which is especially favorable for the accumulation of PM 2.5 during the nighttime. At noon, the PM 2.5 concentration increased from the surface to the planetary boundary layer height (PBLH), even though the PBLH was overestimated. In the afternoon, the clean sea breeze would dilute the PM 2.5 in the Taichung Basin and the urban PM 2.5 plume would be transported to the mountains. The current simulation suggests that the aloft return PM 2.5 layer would subside along with the sinking PBLH and deteriorate the PM 2.5 concentration at night. At the downtown site of the IOP (UAPRS), from the trend of radicals and nitrogen oxides, ozone (O 3) is closely involved in the formation of nitrate (NO 3 −) during both daytime and nighttime. If Taichung City is Volatile Organic Compounds (VOC)-limited according to our previous study, then reducing VOC emissions could decrease O 3 and thus the NO 3 − concentration in Taichung City. [Display omitted] • The modeling of an intensive observation campaign is comprehensively evaluated. • The modeling performed well and reproduced meteorological and chemical fields. • Aloft return PM 2.5 layer subsidence could enhance pollution at night. • NO 3 − is a major species during nighttime PM 2.5 pollution events. • Reducing VOCemissions could decrease NO 3 − in the Taichung Basin. [ABSTRACT FROM AUTHOR]

Reliable energy models are required to predict urban-scale air-conditioning (AC) load under extreme outdoor temperatures which is crucial to power security. In this study, we proposed a new landuse/landcover (LULC) scheme for these models by combining the local climate zones (LCZs) from World Urban Database Access Portal Tools (WUDAPT) and building category (BC) map. Apart from evaluating against the conventional LULC of Moderate-resolution Imaging Spectrometer (MODIS) and WUDAPT, the impact of urban canopy parameters and BC on the simulated meteorological conditions and AC load during the 2016 heatwave in Hong Kong was examined by the Weather Research and Forecasting (WRF) model. Incorporating LCZs (BC) reduced the bias of 2-m temperature (T 2), 2-m relative humidity (RH 2), and AC load intensity by 0.4 °C (2.0 °C), 1.98% (0.68%) and 6.78 W m−2 (13.09 W m−2), respectively. It captured the heterogeneous, intra-urban T 2 and turbulence kinetic energy (TKE). Further sub-classifying the BC in LCZs led to WUDAPT/BC which performed even better and significantly improved WRF output. It simulated well the daytime wind speed, mitigated the overprediction (underprediction) of T 2 (RH 2), and rectified the underpredicted AC load in WUDAPT. Its benefit was prominent in daytime as well as in compact high-rise/mid-rise and open high-rise areas. (200 words). • A new LULC scheme is proposed by combining WUDAPT and building category (BC) data. • WUDAPT/BC is unprecedentedly used to improve WRF reliability. • WUDAPT/BC outperforms WUDAPT and MODIS in urban-climate simulation. • WUDAPT/BC outperforms WUDAPT and MODIS representing intra-urban heterogeneity. • Including BC data reduces the bias of urban-scale air-conditioning load by 54.23%. [ABSTRACT FROM AUTHOR]