Asia-Pacific Journal of Atmospheric Sciences最新文献

After making landfall, Typhoon In-Fa (2021) moved slowly, resulting in heavy rainfall and flooding across fourteen provinces in China. This extreme precipitation was primarily linked to the evolution of active mesoscale convective systems. This study analyzes the characteristics and causes of mesoscale rainbands during In-Fa’s slow northward-moving period, aiming to identify the key factors that influence the detailed evolution of typhoon rainbands and to enhance typhoon quantitative precipitation forecasting skill. In-Fa’s mesoscale asymmetric rainbands can be categorized into three types: mesoscale spiral rainbands, a convective rainband to the east of In-Fa, and a rainband to the north of In-Fa. Mesoscale low-level jets are a critical factor in the development of mesoscale spiral rainbands. The wind speed gradient near these jets, along with the convergence of wind directions between two jets, fosters low-level convergence and upward motion, triggering the evolution of several mesoscale rainbands. The convective rainband to the east of In-Fa flourishes under conditions of high humidity and energy, displaying distinct diurnal variations. This is due to the strengthening of low-level jets at night, which enhances both dynamic convergence and water vapor availability. The presence of moderate to strong convective available potential energy (600–1500 J kg⁻¹), substantial whole-layer water vapor (relative humidity exceeding 90–95%), and a high 0 °C-layer favors the development of efficient warm-cloud convective precipitation, leading to intense hourly rainfall. The rainband to the north of In-Fa is primarily associated with cold air intrusion in the lower troposphere, although the interaction between typhoon and mid-latitude systems has not yet occurred. At the interface between cold and warm air, the colder air to the north side sinks while the warmer air to the south side rises, forming a secondary circulation that supports the development and persistence of precipitation on the north side of the typhoon. These findings offer a conceptual model for accurately predicting precipitation associated with typhoons that move slowly northward after landfall.

Over the past few years, sudden high swells (SHSs) have often occurred on the east coast of the Korean Peninsula (KP), especially during the winter season, causing many casualties and considerable property damage. High waves can be generated suddenly even in the absence of strong winds, sweeping away unsuspecting people on breakwaters or causing damage to properties such as ports and fish farms located on coasts. In this study, we developed a detection and warning system for SHSs on the KP’s east coast. First, we developed a method for separating waves into the wind sea and swell components based on one-dimensional wave spectra, wind speed, wind direction, and mean wave direction data obtained from coastal buoys. Using the calculated significant wave height difference between swells and wind seas, as well as wind speed, we developed a SHS alert system with three levels: “Attention,” “Watch,” and “Warning.” This system successfully detected three recent swell events on the east coast of the KP. Applying this system to an operational wave prediction model, it successfully issued an alert 72 h before the SHS reached the coast. The proposed system can provide consistent quantitative forecast information that can greatly contribute to preventing casualties and property damage caused by SHSs.

Soil moisture plays important roles in land surface and hydrological processes, and its changes can greatly affect weather and climate. In this study, we examine how changes in soil moisture impact the urban heat island (UHI) and urban breeze circulation (UBC) through idealized ensemble simulations. As soil moisture increases, the latent heat flux increases considerably in the rural area. Hence, in the rural area, the sensible heat flux and surface temperature decrease, which decreases the rural air temperature. The decrease in rural air temperature leads to increases in UHI intensity and thus UBC intensity. The urban air temperature also decreases with increasing soil moisture since the cooler rural air is advected to the urban area by the enhanced low-level convergent flow of the UBC. However, the decrease in air temperature is smaller in the urban area than in the rural area. As the UBC intensity increases, the sensible heat flux in the urban area increases. The increase in sensible heat flux in the urban area further increases the UHI intensity. The positive feedback between the UHI intensity and the UBC intensity is revealed when soil moisture increases. The decrease in air temperature in both the urban and rural areas leads to the decrease in planetary boundary layer (PBL) height. As a result, the vertical size of the UBC decreases with increasing soil moisture. As the UBC intensity increases with increasing soil moisture, the advection of water vapor from the rural area to the urban area increases. Combined with the decrease in PBL height, this reduces the water vapor deficit or even leads to the water vapor excess in the urban area depending on soil moisture content.

Wind erosion climatic erosivity is a measure of climatic conditions that affect wind erosion. Projecting wind erosion climatic erosivity is curcial for predicting future wind erosion risk. In this study, we employed dynamic downscaling outputs from the MPI-ESM1-2-HR model to project changes in wind erosion climatic erosivity over High Mountain Asia (HMA) from 2041 to 2060 under a middle-emission scenario (an additional radiative forcing of 4.5 W/m² by 2100). From 1995 to 2014, wind erosion climatic erosivity in HMA was high in the southwest, on the Qiangtang Plateau, and in the Qaidam Basin, exceeding 1 kg·m⁻¹ s⁻¹. Compared to the period 1995–2014, wind erosion climatic erosivity is projected to decrease by 0.5 kg·m⁻¹ s⁻¹ over the east of the Qiangtang Plateau and increase by approximately 1 kg·m⁻¹ s⁻¹ in the southwest of the HMA during 2041–2060 under the middle emission scenario. This increase in wind erosion climatic erosivity in the southwest of HMA is attributed to a projected rise in high-wind frequency for 2041–2060 compared to 1995–2014. Conversely, the decrease in wind erosion climatic erosivity in the east of the Qiangtang Plateau results from increased precipitation during 2041–2060, which mitigates the effects of increased high-wind frequencies. Given the growing risk of wind erosion in the southwest of the HMA, it’s essential to implement appropriate mitigation policies for the future.

We present the high and equatorial mesospheric dynamical response to the minor stratospheric warming that occurred in 2014/15 and compared it with the major stratospheric warming events of 2005/06 and 2008/09. Meteor radar observations over Esrange (67.88^oN, 21.07^o E), Mohe (52.97^oN, 122.53^oE) and Kototabang (0.20^oS, 100.32^oE) have been extensively utilized in addition to ERA 5 Reanalysis datasets. Possessing the unique feature of a vortex displacement and split, the minor warming of 2014/15 was observed on 27 December 2014 followed by four subsequent temperature peaks. During the 2014/15 minor SSW, the tropical stratospheric temperature decreased, causing upwelling similar to the major SSW events 2005/06 and 2008/09. The equatorial mesospheric zonal wind in 2014/15 displayed maximum westward wind with a delay of ~ 19 days after the vortex disruption comparable to the major SSW events. Whereas, over Esrange and Mohe, the westward wind maxima occurred about the vortex disruption during all the warming events. During the minor SSW 2014/15, the ~ 16-day planetary wave is observed to be relatively stronger in the equatorial mesosphere than the high latitude mesosphere. The Eliassen Palm flux diagnostics revealed the intrusion of planetary wave energy from high latitudes to the tropical band, suggesting meridional and equatorward propagation of the planetary waves.

The stable isotopes of hydrogen and oxygen in precipitation provide a useful reference for the study of hydrological processes. However, the interpretation of stable isotopes in a monsoon climate zone remains uncertain. To investigate isotopic variations and the controlling factors in the midlatitude monsoon region, continuous observations of precipitation isotopes in Dongying were made. We investigate the controlling factors of precipitation δ¹⁸O by analyzing their relationship with temperature, precipitation amount, relative humidity, surface atmospheric pressure, and outgoing longwave radiation (OLR) data. Back trajectory analysis of the HYSPLIT model based on precipitation events was also used to trace moisture sources. The results show that there is a significant spatial correlation between stable isotopes of precipitation and precipitation amount in both monsoon and non-monsoon periods. The integration of large-scale convection over several days (0–10 days) preceding each event was determined as the main driver of precipitation isotopes in Dongying. The difference is that in the monsoon period, the isotope of precipitation records the convective activity of upstream water vapor in the past 10 days, while in the non-monsoon period, the precipitation isotope reflects the convective activity of upstream water vapor in the past 3 days. These findings improve regional-scale understanding of hydrological cycles in the East Asian mid-latitude monsoon region and have the potential to improve our understanding of isotopic variations in the proxy archives of the East Asian monsoon region.

This paper presents the results of the recent development of the all-sky radiance assimilation system in the Korean Integrated Model (KIM). In the cycled analysis and forecast experiments, the increased coverage of radiance data in cloudy regions improved the quality of initial fields for mass variables, temperature and humidity. The experimental period covered the record-breaking heavy rainfall event on August 9, 2022. We examined the simulation accuracy of the western North Pacific subtropical high (WNPSH) in both clear- and all-sky experiments. In the clear-sky experiment, northward propagation of the WNPSH was restricted. A humid bias exists with clear-sky radiance assimilation over the WNPSH region. Since humid air is lighter than dry air, in this situation, the geopotential height (GPH) should be lower to achieve the same pressure, and a low-pressure bias occurs. All-sky radiance assimilation dries the moisture field, which helps elevate the GPH over the WNPSH region. The expansion of the WNPSH yielded a steeper confrontation in the air between the land and ocean around the southeastern sea of the Korean Peninsula to predict the strength of rainfall events more accurately. A more accurate simulation of the jet stream outlet was also demonstrated in an all-sky experiment. This study shows that the all-sky radiance assimilation can help to more accurately predict extreme rainfall events via proper simulations of large-scale fields.

This study examines the characteristics of the urban heat island (UHI) in Dhaka, the densely populated capital city of Bangladesh under the influence of the South Asian monsoon, and its interaction with heat waves. For this, meteorological data at Dhaka (urban) and Madaripur (rural) stations and reanalysis data for the period of 1995–2019 are used for analysis. Here, the UHI intensity is defined as the urban-rural difference in 2-m temperature, and a heat wave is defined as the phenomenon which persists for two or more consecutive days with the daily maximum 2-m temperature exceeding its 90th percentile. The UHI intensity in Dhaka is in an increasing trend over the past 25 years (0.21 °C per decade). The average UHI intensity in Dhaka is 0.48 °C. The UHI is strongest in winter (0.95 °C) and weakest in the monsoon season (0.23 °C). In all seasons, the UHI is strongest at 2100 LST. The average daily maximum UHI intensity in Dhaka is 2.15 °C. Through the multiple linear regression analysis, the relative importance of previous-day daily maximum UHI intensity (PER), wind speed, relative humidity (RH), and cloud fraction which affect the daily maximum UHI intensity is examined. In the pre-monsoon season, RH is the most important variable followed by PER. In the monsoon season, RH is the predominantly important variable. In the post-monsoon season and winter, PER is the most important variable followed by RH. The occurrence frequency of heat waves in Dhaka shows a statistically significant increasing trend in the monsoon season (5.8 days per decade). It is found that heat waves in Bangladesh are associated with mid-to-upper tropospheric anticyclonic-flow and high-pressure anomalies in the pre-monsoon season and low-to-mid tropospheric anticyclonic-flow and high-pressure anomalies in the monsoon season. Under heat waves, the UHI intensity is synergistically intensified in both daytime and nighttime (nighttime only) in the pre-monsoon (monsoon) season. The decreases in relative humidity and cloud fraction are favorable for the synergistic UHI-heat wave interaction.

The moisture sources, transport paths and the quantitative moisture contribution of each source region and path of the South-West, West, North-East and South-East heavy rainfall types in the Three-River-Headwater region (TRHR) of Tibetan Plateau (TP) in summer are tracked, calculated and compared using the FLEXPART model. The results show that: the southern TP and the local target region of TRHR contribute the most moisture to the four types of precipitation. In addition, the northern TP is the third predominant moisture source region to the South-West and West rainfall types, which are distributed in the west of TRHR. Nevertheless, the third critical source region of the North-East and South-East rainfall types, which occur in the east of TRHR, is the eastern areas outside the TP. Four kinds of rainfall events have four identical moisture transport paths: Southern short-distance path, Southern long-distance path, Southwest path and Northwest path. The Southern short-distance path contributes the most moisture to the South-West (24.2%), West (19.8%) and South-East (15.9%) rainfall types, the second most moisture of which respectively comes from the Northwest path, Southwest path and Southeast path. In addition, the Southern short-distance path and Southwest path are the most active moisture transport channels of the three types of precipitation (more moisture trajectories are transported through these two paths). The moisture of North-East rainfall type is primarily contributed by the East path (26.0%) and the Northwest path (18.2%), and the most active moisture transport channels are the East path (21.9%) and the Southern long-distance path (19.9%).